Patent Application
20080217563
1. Field of the Invention
The present invention relates to manufacturing methods of semiconductor devices such as thin film transistors (hereinafter referred to as TFTs) and the like. In particular, the present invention relates to semiconductor manufacturing apparatuses by which doping processes are performed.
2. Description of the Related Art
In techniques for formation of high performance circuits over conventional substrates using semiconductor films, in order to control the threshold voltage of the semiconductor elements such as TFTs and the like that act as basic structural elements of the high performance circuits, doping is performed. Doping is a process by which an impurity (a dopant) such as arsenic (As), boron (B), phosphorus (P), or the like is introduced into a semiconductor film. For example, a toxic gas such as diborane (B2H6) or the like is made to be a plasma in an ion doping apparatus to form boron ions, and the boron ions are accelerated by an electric field and doped into a semiconductor film formed over a substrate. Subsequently, by activation of the impurity that has been introduced, the threshold voltage of a semiconductor element formed using the semiconductor film is controlled.
Moreover, for doping techniques, in addition to the ion doping technique given above, there is a technique that is referred to as laser doping (for an example of this technique, refer to Patent Document 1). In laser doping, in a laser chamber, a dopant gas is made to flow over the surface of a semiconductor film formed over a substrate, and the surface of the semiconductor film is irradiated with a laser beam that has a wavelength in the ultraviolet light region of the electromagnetic spectrum. By this process, the dopant gas over the surface of the semiconductor film is decomposed by a photochemical reaction, the irradiated part of the semiconductor film is locally melted and solidified, and doping with the impurity can be performed.
The laser doping apparatus used in laser doping is different from an ion doping apparatus in that, with a laser doping apparatus, the formation of cracks in the semiconductor film at the time of doping is suppressed, and furthermore, no annealing process is required in order to activate the introduced impurity. It is to be noted that, for a laser oscillator, for example, an excimer laser with a short wavelength is used.
Aside from the doping performed to control the threshold voltage as described above, there is a technique in which impurities are introduced into a source region and a drain region of a semiconductor element and the resistance of the semiconductor element is reduced. For example, by exposure of the source region and drain region of a semiconductor film to a substance that has dopant atoms, the dopant atoms are attached to the semiconductor film, the source region and the drain region are irradiated with a laser beam, and the dopant atoms are introduced into the semiconductor film (Patent Document 2).
To control the amount of variation in threshold voltage, extremely strict control of the amount of impurity implanted is being demanded. However, with doping performed using an ion doping apparatus, because control of the amount of impurity introduced is difficult due to fluctuations in the ratio of types of ion of the dopant and the like, there is a large amount of variation in the threshold voltage of fabricated semiconductor elements. Furthermore, ion doping apparatuses are extremely expensive devices. Moreover, because ion doping apparatuses are sheet-fed apparatuses, operating efficiency is extremely poor, as well.
Furthermore, damage is incurred by an activation layer because of doping, and this damage comes to be a reason that the crystallinity of the semiconductor is reduced. There is a method that is used to restore the damage incurred at the time of doping by recrystallization of the semiconductor film with a laser after the semiconductor film is doped. However, because the concentration of impurities needs to be lowered at the time of doping due to the rate of activation of impurities within the semiconductor film by a laser irradiation process being high, controlling the threshold voltage becomes difficult.
Meanwhile, with a semiconductor manufacturing apparatus that uses a laser doping apparatus, the amount of impurity introduced into the semiconductor film fluctuates if the laser irradiation conditions change, and there is a need to keep the laser irradiation conditions constant in order to obtain threshold voltages with little variation, which is caused by fluctuations in the rate of activation within the semiconductor film.
However, keeping laser irradiation conditions constant is difficult, and, in particular, excimer laser apparatuses that are generally used at wavelengths in the ultraviolet light region of the electromagnetic spectrum are extremely unstable devices.
In addition, with laser doping apparatuses, because the impurity gas is decomposed by a photochemical reaction, the coating on the inside of a laser chamber of a quartz window used to introduce the laser beam into the laser chamber might receive damage. Because of this damage, the optical transmission rate of the laser beam declines dramatically, and keeping laser conditions constant becomes difficult.
Furthermore, in recent years, the design rule for TFTs used to form high performance circuits over glass substrates has been shrinking. In order to control short channel effects caused by shortening of the channel length, it is desirable that the surface of the activation layer be evened out and the gate insulating film be made to be thin, that the concentration of impurities in the activation layer be reduced, and that the activation layer be made extremely thin (for example, the film thickness of the activation layer be made to be less than 50 nm). However, keeping the concentration of the impurity in the depth-wise direction of the activation layer uniform has been difficult with conventional ion doping apparatuses, and keeping conditions for laser irradiation of the activation layer stable has been difficult with conventional laser doping apparatuses.
Moreover, when dopant atoms are attached to a source region or a drain region and introduced by laser irradiation, there is no need to accurately control the number of dopant atoms that are attached as long as the number of dopant atoms that are to be introduced at a high concentration can be introduced into the semiconductor film at a concentration above a certain level. For this reason, the number of dopant atoms that are to be attached at a low concentration cannot be controlled, and the amount of variation in the threshold voltage of semiconductor elements fabricated using conventional doping methods cannot be suppressed.
The present invention is formed in consideration of the aforementioned problems, and an object of the present invention is to introduce impurities into an activation layer at low concentration and high precision, in order to provide semiconductor elements that have little variation in threshold voltage.
An object of the semiconductor manufacturing apparatus of the present invention is to provide a crystalline semiconductor film by which a high performance semiconductor element can be fabricated, by control of the amount of the impurity attached to the semiconductor film based on a linear, correlative relationship between the length of time of exposure to an impurity concentration atmosphere and the threshold voltage, and then formation of a crystalline semiconductor film that contains an impurity at a low concentration corresponding to that of channel doping simultaneous with crystallization of the semiconductor film by laser crystallization.
One semiconductor manufacturing apparatus of the present invention is a semiconductor manufacturing apparatus by which impurities are introduced into a semiconductor film provided over an insulating substrate, and the semiconductor manufacturing apparatus has a washing unit used to wash a surface of the semiconductor film; an impurity introduction unit used to attach impurities to the surface of the semiconductor film; and a laser crystallization unit used to irradiate the surface of the semiconductor film to which the impurities have been attached with a laser beam to crystallize the semiconductor film; where transfer robots are connected to each of the washing unit, the impurity introduction unit, and the laser crystallization unit. Furthermore, an impurity atmosphere chamber and an impurity generator used to supply an impurity gas in the impurity atmosphere chamber are provided in the impurity introduction unit.
Moreover, in the semiconductor manufacturing apparatus of the present invention, the insulating substrate that has a semiconductor film is exposed to an impurity atmosphere in the impurity introduction unit, and the amount of impurity that is attached to the semiconductor film is controlled by the length of time of exposure to the impurity atmosphere in the impurity introduction unit.
Another semiconductor manufacturing apparatus of the present invention is a semiconductor manufacturing apparatus that has a washing unit used to wash a surface of a semiconductor film; a film formation unit used to form an oxide film over the semiconductor film; an impurity introduction unit used to attach impurities to the surface of the oxide film; and a laser crystallization unit used to irradiate the oxide film and the semiconductor film to which the impurities have been attached with a laser beam to crystallize the semiconductor film; where transfer robots are connected to each of the washing unit, the film formation unit, the impurity introduction unit, and the laser crystallization unit. Furthermore, an impurity atmosphere chamber and an impurity generator used to supply an impurity gas in the impurity atmosphere chamber are provided in the impurity introduction unit.
A semiconductor manufacturing apparatus of the present invention is a semiconductor manufacturing apparatus that has a washing unit used to wash a surface of the semiconductor film; an impurity introduction unit used to attach impurities to the surface of the semiconductor film; and a laser crystallization unit used to irradiate the semiconductor film to which the impurities have been attached with a laser beam to crystallize the semiconductor film; where transfer robots are connected to each of the washing unit, the impurity introduction unit, and the laser crystallization unit. Furthermore, an impurity atmosphere chamber and an impurity generator used to supply an impurity gas in the impurity atmosphere chamber are provided in the impurity introduction unit. In addition, the impurity atmosphere chamber has wires used to support the insulating substrate; wire holders used to hold the wires in place; support mechanisms used to grasp onto the wire holders in the impurity atmosphere; and drivers used to move the support mechanisms inside the impurity atmosphere chamber up and down. The insulating substrates that are introduced into the impurity introduction unit are transferred to the laser crystallization unit in the order in which they are received.
A method of manufacturing a semiconductor device of the present invention includes the steps of forming a semiconductor film over an insulating substrate; washing the semiconductor film and then transporting the insulating substrate into an impurity atmosphere and attaching an impurity to the surface of the semiconductor film; transporting and mounting the insulating substrate to which the impurity is attached to a stage; irradiating the insulating substrate on the stage with a laser beam that is projected from a laser oscillator; crystallizing the semiconductor film to which the impurity is attached; and forming a crystalline semiconductor film that contains an impurity.
Furthermore, another method of manufacturing a semiconductor device of the present invention includes the steps of forming a semiconductor film over an insulating substrate; washing the semiconductor film and then forming an oxide film over the semiconductor film; transporting the insulating substrate to an impurity atmosphere and attaching an impurity to the semiconductor film through the oxide film; transporting and mounting the insulating substrate to which the impurity is attached to a stage; irradiating the insulating substrate on the stage with a laser beam that is projected from a laser oscillator; crystallizing the semiconductor film to which the impurity is attached; and forming a crystalline semiconductor film that contains an impurity.
With the semiconductor manufacturing apparatus of the present invention, introduction of an impurity into an active layer of a semiconductor element at low concentration and a high level of accuracy can be realized. As a result, the ability to control threshold voltage can be improved, and an even more high performance semiconductor device can be fabricated. Furthermore, because an impurity can be introduced into an active layer of a semiconductor element at low concentration and at a high level of accuracy within a surface of a substrate and between substrates, a high performance semiconductor device can be manufactured at high yield.
Hereinafter, Embodiment Modes and Embodiments of the present invention will be described based on drawings. However, the present invention can be implemented in a lot of different modes, and it is to be easily understood by those skilled in the art that various changes and modifications can be made without any departure from the spirit and scope of the present invention. Accordingly, the present invention is not to be taken as being limited to the described content of the embodiment modes included herein. It is to be noted that identical portions or portions having similar functions in all figures used to describe embodiment modes are denoted by the same reference numerals, and repetitive description thereof is omitted.
In the present embodiment mode, steps for fabrication of a crystalline semiconductor film that contains an impurity at low concentration over an insulating substrate using a semiconductor manufacturing apparatus of the present invention will be described.
First, using
A substrate that is introduced into the semiconductor manufacturing apparatus of the present invention is first washed in the prewashing unit 1001 that is used to eliminate impurities. At this time, impurities which are not needed for doping, for example, an oxide film or the like formed by natural oxidation at the time that the semiconductor film is formed, are removed. It is to be noted that a sheet-fed spin washing machine 1030 is used for a washing machine in
The impurity introduction unit in the present embodiment mode has an impurity generator 1003, an introduction chamber 1004, a discharge chamber 1005, an impurity atmosphere chamber 1006, and exhaust vents 1007. However, the exhaust vents 1007 need not necessarily be formed. Alternatively, the exhaust vents 1007 may be supply and exhaust vents, as well. After a substrate washed in the prewashing unit 1001 that is used to eliminate impurities is introduced into the introduction chamber 1004 by one of the transfer robots 1002, the substrate is transported to the impurity atmosphere chamber 1006. Then, the substrate is exposed to the impurity atmosphere for only the amount of time needed for the impurity to be attached to the surface at the desired concentration and then transported to the laser irradiation unit 1018 by one of the transfer robots 1002 via the discharge chamber 1005.
It is to be noted that, in the impurity atmosphere chamber 1006, while the substrate is being exposed to the impurity atmosphere, other substrates are being transferred into the impurity atmosphere chamber 1006; by the interval between starting times for exposure of each substrate being made to be roughly equal to the length of operating time for the laser crystallization unit, the transport timing for each substrate may be adjusted so that the production efficiency of the impurity introduction unit is not rate-limited. For example, with the operating time of the prewashing unit that is used to eliminate impurities set to t0, the exposure starting time of the first substrate set to t1, and the exposure starting time of the second and subsequent substrate set to tn(n≧2), the interval Δt between the exposure starting times of each substrate is represented by Formula 1: Δt=tn+1−tn(n≧2).
In addition, if the operating time for the laser crystallization process is set to be T, the transport timing should be controlled so that Δt comes to be T, or Δt=T. However, because the minimum value of Δt is equal to the operating time t0 in the prewashing unit 1001 that is used to eliminate impurities, when T≦t0, the operating time of the semiconductor manufacturing apparatus of the present invention is rate-limited by the prewashing unit 1001 that is used to eliminate impurities. In this case, if more of the prewashing units 1001 that are used to eliminate impurities are added, productivity can be increased.
Furthermore, productivity can be increased if more laser crystallization apparatuses are added in the case where the length of the time that a substrate is exposed to the impurity atmosphere is short enough compared to the operating time of the laser crystallization unit. In addition, productivity may also be increased by lowering the impurity concentration of the atmosphere so that the exposure time becomes longer. It is to be noted that, when the length of the exposure time is increased, in order to maintain productivity, because there is a need to increase the number of substrates that are exposed at one time, space used to stock a plurality of substrates in the impurity introduction chamber becomes necessary. By reducing the size of the stock space to a minimum, equipment costs can be reduced.
Next, the laser crystallization unit 1018 will be described. In the present embodiment mode, the laser crystallization unit 1018 has a laser oscillator 1013, an incident light mirror 1014, a slit 1015, a major axis cylindrical lens 1016, a minor axis cylindrical lens 1017, and stages 1010 and 1012. In addition, the substrate that is transported from the impurity introduction unit is placed onto the stage 1010. However, the present invention is not to be taken as being limited to this structure; for example, the slit 1015 and the incident light mirror 1014 need not necessarily be provided. Furthermore, in exchange for the major axis cylindrical lens 1016 and the minor axis cylindrical lens 1017, an optical element such as a spherical lens, an aspherical lens, an aspherical cylindrical lens, an exposure lens, a diffractive optical element, a light pipe, a homogenizer, a fly's eye lens, a cylindrical lens array, or the like or a combination of any of these may be used, as well. Moreover, in order to increase the size of the laser beam projected from the laser oscillator 1013, a beam expander can be used. In order to change the intensity of the laser beam, an attenuator can be used.
The laser beam projected from the laser oscillator 1013 is bent in a direction perpendicular to the substrate on the stage 1010 by the incident light mirror 1014 and passes through the slit 1015, and the part of the laser beam that has weak energy density is blocked. Subsequently, the laser beam passes through the major axis cylindrical lens 1016, and an image is passed through the slit 1015 to the surface that is to be irradiated. Furthermore, the laser beam passes through the minor axis cylindrical lens 1017 and is focused along the minor axis and formed into a linear laser beam, the substrate placed on the stage 1010 is scanned, and laser crystallization is performed.
It is to be noted that, when the width of the major axis of the laser beam is short, the laser beam may be used to scan along a direction perpendicular to the surface that is scanned. Alternatively, the stage 1010 may be used to scan in a direction perpendicular to the surface that is scanned. In addition, a θ-axis system and an alignment camera may be provided in the stage 1010 to obtain the alignment of the laser beam scanning direction and the substrate on the stage 1010. Furthermore, a Z-axis system may be provided in the stage 1010 and a mechanism put into place so that the surface that is irradiated is not shifted from the depth of focus in the surface that is to be irradiated by the laser beam. Moreover, a plurality of laser oscillators may be prepared and laser crystallization may be performed by use of a plurality of laser beams at the same time, or a plurality of laser beams each with a different wavelength may be combined together to form a single laser beam and laser crystallization may be performed by use of the one laser beam. Additionally, laser crystallization may also be performed using a combination of any of these laser beams.
It is to be noted that a linear laser beam is a laser beam by which the shape of the surface that is irradiated is linear. Here, “linear” does not refer to the strict meaning of “having the shape of a line” but rather to the case where the aspect ratio forms a large rectangular shape (for example, a case where the aspect ratio is 10 or more (preferably, 100 or more)). It is to be noted that setting the laser beam to be linear is done in order to maintain a high enough energy density for adequate performance of laser treatment on the object that is to be irradiated, but the laser beam may also be set to be rectangular or elliptical, as well, as long as an adequate amount of laser treatment can be performed on the object that is to be irradiated using the rectangular or elliptical laser beam.
It is to be noted that, in
Next, steps for fabrication of a crystalline semiconductor film that contains an impurity at low concentration using the semiconductor manufacturing apparatus shown in
First, a step will be described in which a semiconductor film is formed over an insulating substrate. As illustrated in
The base insulating film may be set to have a single-layer structure using any of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a silicon nitride oxide film or a structure in which any of these films are stacked together as appropriate. It is to be noted that, in the present specification, “silicon oxynitride” refers to a substance in which the composition ratio of oxygen is higher than that of nitrogen and can also be used to refer to a silicon oxide that contains nitrogen. In addition, in the present specification, “silicon nitride oxide” refers to a substance in which the composition ratio of nitrogen is higher than that of oxygen and can also be used to refer to a silicon nitride that contains oxygen. In the present embodiment mode, the base insulating film is set to have a stacked-layer structure of a silicon nitride film 101 that has a film thickness of from 30 nm to 150 nm and a silicon oxide film 102 that has a film thickness of from 20 nm to 150 nm which are stacked together in the order given.
Next, over the base insulating film, an amorphous semiconductor film, formed at a film thickness of from 2 nm to 100 nm, preferably, at a film thickness of from 20 nm to 70 nm, is formed as a semiconductor film 103. For a method of formation of the semiconductor film 103, as with the base insulating film, a method such as a CVD method, a sputtering method, or the like may be used.
It is to be noted that the base insulating film, which is used to function as a blocking film in order to prevent the diffusion of impurities, may be provided according to need. When the substrate 100 is a glass substrate that contains impurities, in particular, mobile ions that easily move around, the base insulating layer is used to prevent the diffusion of impurities from the glass into the semiconductor film 103. However, in the case where a quartz substrate is used for the substrate 100, there is no need to provide a base insulating layer that is used to function as a blocking layer.
It is to be noted that a silicon nitride film has more blocking capability for the prevention of impurity diffusion from glass than a silicon oxide film. On the other hand, fewer interface states are generated in the interface of a base insulating film formed in contact with the semiconductor film 103 with a silicon oxide film than with a silicon nitride film. As a consequence, for the structure of the base insulating film, it is preferable that the base insulating film formed in contact with the substrate side be a silicon nitride film and the base insulating film formed in contact with the semiconductor film 103 be a silicon oxide film. The reason for this is that, when a TFT in which a silicon nitride film is formed in contact with the semiconductor film and an interface state is generated therebetween is fabricated, charge is trapped in the interface between the base insulating film and the semiconductor film, and there are wide fluctuations in threshold voltage due to the effects on electric field by the trapped charge.
Furthermore, the structure may be one in which a separation layer is provided between the base insulating film and the substrate 100 and the semiconductor element is separated from the substrate 100 after completion of the semiconductor element fabrication steps. It is to be noted that, for a separation layer, for example, a silicon oxynitride film with a thickness of from 50 nm to 200 nm is formed over the substrate 100 as the base insulating film by a plasma CVD method. Then, a tungsten film with a thickness of from 10 nm to 100 nm is formed over the base insulating film as a metal film by a sputtering method. Moreover, a silicon oxide film with a thickness of from 50 nm to 400 nm is formed over the metal film as an insulating film by a sputtering method. A film of a plurality of layers formed in this way is used for the separation layer. It is to be noted that the interface at which separation occurs is the interface between the metal film and the insulating film.
It is to be noted that amorphous silicon is used for the semiconductor film 103 in the present embodiment mode; however, polycrystalline silicon may also be used. For example, after formation of the amorphous silicon film, a polycrystalline silicon film can be formed by the addition of trace amounts of an element such as nickel, palladium, germanium, iron, aluminum, tin, zinc, cobalt, platinum, copper, gold, or the like to the amorphous silicon film and the performance of heat treatment at 650° C. for 6 minutes thereafter. Alternatively, silicon germanium or the like may be used instead of the amorphous silicon; furthermore, single-crystal silicon carbide (SiC), which has a diamond structure, can be used. In addition, any of these films may be stacked together as appropriate, as well.
Moreover, after the amorphous silicon film is formed for the semiconductor film 103, the semiconductor film 103 may be heated in an electric furnace at 500° C. for one hour in order to remove hydrogen from the amorphous silicon film. It is to be noted that the removal of hydrogen is performed in order to prevent bumping of hydrogen gas in the semiconductor film 103 at the time that the semiconductor film 103 is irradiated with a laser beam and ablation of the semiconductor film 103. However, if the amount of hydrogen contained in the semiconductor film 103 is low, this step may be omitted.
It is to be noted that a silicon oxide film is formed on the surface of the semiconductor film 103 by natural oxidation at the time that the semiconductor film 103 is formed; at the time that hydrogen is removed from the semiconductor film 103, by heat treatment; or during the time that the substrate is transported after the semiconductor film 103 is formed, by exposure to a clean room (hereinafter, CR) atmosphere. Furthermore, an oxidized film layer 104 is formed over the silicon oxide film by attachment of an organic substance, an impurity, or the like at the time of exposure to the CR atmosphere (
Next, a step for introduction of an impurity into the semiconductor film 103 at a desired concentration, in order to control threshold voltage, using the semiconductor manufacturing apparatus of the present invention will be described.
First, by the steps described above, the substrate 100 over which is provided the semiconductor film 103 is transported to the prewashing unit 1001 that is used to eliminate impurities of the semiconductor fabrication apparatus shown in
The substrate 100 from which impurities not needed for doping are removed is transported to the impurity atmosphere chamber 1006 and exposed to the impurity atmosphere of low concentration for only the length of time required for the impurity to be attached at the desired concentration. Accordingly, as shown in
Next, in the laser crystallization unit, as shown in
In
It is to be noted that, for the scanning direction of the laser beam, for example, the laser beam may be used to scan in one direction, or the scanning direction may differ by 180° alternatingly in adjacent laser crystallized regions 303. Furthermore, the repetition rate of the quasi-continuous wave laser is not limited to being 80 MHz, and a laser oscillator that oscillates at a repetition rate of 10 MHz or more, for example, may be used.
In addition, in the present embodiment mode, a quasi-continuous wave laser is used for the laser oscillator. However, the laser oscillator is not limited to being a quasi-continuous wave laser, and a pulsed laser may be used or a continuous wave laser may be used. Here, for a laser beam that can be pulse-oscillated, an Ar laser, a Kr laser, an excimer laser, a CO2 laser, a YAG laser, a Y2O3 laser, a YVO4 laser, a GdVO4 laser, a YLF laser, a YAlO3 laser, a glass laser, a ruby laser, an alexandrite laser, a Ti:sapphire laser, a copper vapor laser, a gold vapor laser, or the like can be used. Furthermore, for a laser beam that can be oscillated continuously, a gas laser or a solid-state laser can be used. For a gas laser, there is an Ar laser, a Kr laser, and the like. In addition, for a solid-state laser, a laser that uses a crystal such as YAG, YVO4, YLF, YAlO3, Y2O3, GdVO4, or the like, which is doped with Cr, Nd, Er, Ho, Ce, Co, Ti, Yb, or Tm, or the like can be used. The fundamental waves of solid-state lasers differ depending on the material with which the laser is doped, and a laser beam with a fundamental wave of about 1 μm can be obtained. The harmonics of the fundamental wave can be obtained by use of a non-linear optical element.
Moreover, in the present embodiment mode, a linear laser beam with a width of approximately 500 μm in the direction of the major axis is formed with the output of the laser oscillator being 20 W; however, the beam width in the direction of the major axis is not to be limited to being 500 μm. For example, if a laser of a laser oscillator that has a greater output is used, a linear laser beam with a width greater than or equal to 500 μm can be formed. Furthermore, the same is true in the case where the light use efficiency in an optical system is increased. In addition, in the present embodiment mode, the optimal value of the substrate scanning speed is set to be 350 mm/s. However, because the optimal value is determined by the rate of change of optical constants, thermal conductivity of a bottom layer of the semiconductor film, laser oscillation output, laser repetition rate, transmittance of an optical system, shape of the beam on the irradiated surface, stability of constant velocity of the stage, device operating efficiency, and the like along with film thickness of the amorphous semiconductor film, absorptivity of the amorphous semiconductor film, and phase change of the semiconductor film, the substrate scanning speed is not limited to being 350 mm/s, and the optimal value may be set in each condition.
It is to be noted that both edges of the laser crystallized regions 303 have regions 304 that have poor crystallinity. If a semiconductor element pattern 305 is formed in one of the regions 304, because variations in the electrical characteristics of the semiconductor elements occur due to differences in crystallinity, it is preferable that the semiconductor element pattern 305 be placed inside the laser crystallized region 303.
It is to be noted that, in the steps described above for fabrication of the crystalline semiconductor film that contains an impurity, after the silicon nitride film 101, the silicon oxide film 102, and the semiconductor film 103 are formed over the substrate 100 as shown in
Next, a resist is applied over the crystalline semiconductor film 107, and the resist is exposed to light and developed, whereby a resist pattern of a desired shape is formed. Furthermore, etching is performed using the resist pattern formed here as a mask, and the crystalline semiconductor film 107 that is exposed by development is removed as selected. By this step, island-shaped semiconductor films are formed, and a semiconductor device that has a semiconductor element such as a thin film transistor, a diode, a resistive element, a capacitive element, a CCD, a nonvolatile memory element, or the like can be fabricated using these island-shaped semiconductor films.
In
Furthermore, in addition to the structure given in the present embodiment mode, a structure that includes a unit that has other functions may be used, as well. For example, a structure that includes an inspection unit 1022 as shown in
By use of the semiconductor manufacturing apparatus of the present invention, an impurity can be introduced into a semiconductor film at low concentration and at a high level of accuracy. Furthermore, because no expensive doping apparatus is used in the introduction of the impurity into the semiconductor film, it becomes possible to provide semiconductor devices at low cost. In addition, by separation of functions into that of the laser crystallization unit and that of the impurity introduction unit, the length of time for exposure of the surface of the substrate to the impurity atmosphere can be set to be constant. For this reason, while process conditions for the laser crystallization process are held stable, there is no reduction in productivity, and the amount of variation in the amount of impurity introduced into a surface of a substrate and between substrates can be greatly decreased. As a result, variations in threshold voltage of semiconductor devices formed by use of these semiconductor films can be suppressed, and high performance semiconductor devices can be fabricated at high productivity and high yield.
Moreover, because the semiconductor manufacturing apparatus of the present invention is a low-cost, simple device in which the impurity introduction unit is simplified structurally and because initial costs can be decreased substantially and running costs can also be decreased substantially due to dramatic improvements in maintenance, semiconductor devices can be manufactured at low cost. In addition, by separation of each unit of the semiconductor manufacturing apparatus of the present invention on a unit-to-unit basis, productivity can easily be optimized.
In the present embodiment mode, an example of a structure of an impurity introduction unit of a semiconductor manufacturing apparatus of the present invention will be described using
The impurity introduction unit shown in
The wire 1411 is held in place by a wire holder 1410 on each side. Furthermore, in the introduction chamber 1401, the wire holder 1410 is supported by support mechanisms 1409. Consequently, the substrate 100 is indirectly supported by the support mechanism 1409 in the introduction chamber 1401.
In transfer of the substrate 100 that is supported by the support mechanisms 1409 from the introduction chamber 1401 to the impurity atmosphere chamber 1404, after the wire holders 1410 are grasped onto by gripper arms 1408, the wire holders 1410 are disconnected from the support mechanisms 1409. This allows the wire holders 1410 to be supported by the gripper arms 1408. Then, the gripper arms 1408 are made to move downward, and the substrate 100 is introduced into the impurity atmosphere chamber 1404 through a part 1403 that opens and closes.
In the impurity atmosphere chamber 1404, each wire holder 1410 is supported by any one of a plurality of support mechanisms 1412 that are provided in the impurity atmosphere chamber 1404 and separated from the gripper arm 1408. Here, the substrate 100 is indirectly supported by the support mechanisms 1412 that are provided in the impurity atmosphere chamber 1404, and the substrate 100 comes to be transported along to the impurity atmosphere chamber 1404. It is to be noted that the support mechanism 1412 is rotated within the impurity atmosphere chamber 1404 in an up and down direction by a driver 1413. In addition, the gripper arms 1208 are removed to the introduction chamber 1401 after being separated from the substrate 100. By the driver 1413 rotating in an up and down direction, the substrate that is transported along moves down in the impurity atmosphere chamber 1404. Moreover, the support mechanisms 1412 that are not supporting a substrate are prepared in sequence for acceptance of a substrate that is transferred from the introduction chamber 1401.
By being made to move down within the impurity atmosphere chamber 1404, the substrate 100 is exposed to the impurity atmosphere for a given length of time, and an impurity is attached to the surface of the semiconductor film at a desired concentration. It is to be noted that, in the present embodiment mode, an element belonging to group 13 or group 15 of the periodic table of the elements or a compound thereof may be used for the impurity; for example, an element such as boron (B), phosphorus (P), arsenic (As), or the like or a compound thereof may be used.
After the impurity is attached to the surface of the semiconductor film, the substrate 100 is moved from the impurity atmosphere chamber 1404 to the discharge chamber 1405 through a part 1406 that opens and closes. Here, for a specific movement method, first, support arms 1414 that are provided in the discharge chamber 1405 are moved upward to the impurity atmosphere chamber 1404 through the part 1406 that opens and closes. Then, after the wire holders 1410 are supported by the support arms 1414, the wire holders 1410 are disconnected from the support mechanisms 1412. Accordingly, the wire holders 1410 can be supported by the support arms 1414. Next, by the support arms being made to move down, the substrate is transferred to the discharge chamber 1405 through the part 1406 that opens and closes.
The substrate that is transported to the discharge chamber 1405 in this way is transported through a part 1407 that opens and closes to the laser crystallization unit of the semiconductor manufacturing apparatus of the present invention by a transfer robot. With the impurity introduction unit of the present embodiment mode, first-in first-out is realized in which the substrates 100 are transported in order starting with the first to enter the introduction chamber 1401 so as to be transported from the discharge chamber 1405 to the laser crystallization unit after being exposed to the impurity atmosphere, and the length of time of exposure for each substrate to the impurity atmosphere can be controlled.
It is to be noted that the wire 1411 and wire holders 1410 that are being supported by the support arms 1414 are moved to the transport driving bay 1416 through a part 1419 that opens and closes after the substrate is discharged to the laser crystallization unit. In the transport driving bay 1416, the wire holders 1410 are supported by support mechanisms 1417 and released from the support arms 1414. It is to be noted that the support mechanisms 1417 are rotated within the transport driving bay 1416 in an up and down direction by a driver 1418. Furthermore, the support arms 1414 from which the wire holders 1410 have been released are removed to the discharge chamber 1405. The wire holders 1410 that are gripped by the support mechanisms 1417 are moved upward by the driver 1418. Next, the wire holders 1410 are again grasped onto by the gripper arms 1408 that have moved from the introduction chamber 1401 through a part 1420 that opens and closes, released from the support mechanisms 1417, and moved to the introduction chamber 1401 through the part 1420 that opens and closes.
It is to be noted that, because each side of the wire 1411 is held in place by one of a pair of the wire holders 1410, there are cases where one of the gripper arms 1408 physically interferes with another gripper arm 1408 when being moved from the transport driver bay 1416 to the introduction chamber 1401. In order to avoid this physical interference, after the gripper arm 1408 grasps the wire holder 1410, the gripper arm 1408 is moved in the direction (inner side) in which the wire is slack so as not to interfere with another gripper arm 1408. Furthermore, this set up is preferable because, if the gripper arm 1408 is moved backward only by as much as it has been moved in the opposite direction after the gripper arm 1408 is moved back to the introduction chamber 1401, there is no interference between one of the gripper arms 1408 and a different one of the gripper arms 1408 and the wire holders 1410 can be transported in order.
In the same way, when the gripper arm 1408 is moved from the discharge chamber 1405 to the transport driver bay 1416, this set up is preferable because, when the gripper arm 1408 is moved along the outer side after being separated from the wire holder 1410 and returned to the discharge chamber 1405, there is no physical interference and the wire holders 1410 can be transported from the support arm 1414 in order.
Here, a structure used to support the substrate 100 in the introduction chamber will be described using
In this way, the substrate 100 is directly supported by the wire 1411, but the substrate 100 cannot be supported in the introduction chamber unless the wire holder 1410 is supported. Consequently, a support mechanism used to support the wire holder 1410 in the introduction chamber will be described using enlarged top-view diagrams shown in
As shown in
Furthermore, as shown in
It is to be noted that the support mechanism 1412 in the impurity introduction chamber 1404 shown in
Next, a structure of the impurity generator 1415 will be described using
It is to be noted that, for the impurity gas, a gas, such as diborane (B2H6), phosphine (PH3), or the like, that contains an element belonging to group 13 or group 15 of the periodic table may be diluted and used. In addition, for a dilution gas, hydrogen, argon, helium, neon, or the like can be used. However, because diffusion of impurities occurs if the amount of the element of the dilution gas absorbed into the semiconductor film increases, resulting in deterioration of electrical characteristics, preferably, hydrogen is used as the dilution gas. Furthermore, in the case where the impurity gas has a high level of toxicity, the structure may be one in which exhaust vents provided in the introduction chamber, the impurity atmosphere chamber, and the discharge chamber are each connected to an abatement system.
It is to be noted that the structure of the impurity introduction chamber in the semiconductor manufacturing apparatus of the present invention is not limited to that of the present embodiment mode. For example, a supply and exhaust vent used for adjustment of the impurity concentration may be provided in the impurity introduction unit. By provision of the supply and exhaust vent, simplification of maintenance and optimization of process conditions can be achieved. In addition, retention of a substrate in the impurity introduction unit is not limited to being done using a wire; for example, a cassette in which a plurality of substrates can be loaded may be also used. In this case, by a cassette being set in a stocker of the impurity introduction unit, a plurality of substrates can be retained in the impurity atmosphere. For the cassette, an object commonly used in the semiconductor industry that is formed of a macromolecular material by injection molding or the like can be used. For the macromolecular material, a fluoroplastic PFA, a fluoroplastic PVDF, a flouroplastic ECTFE, a fluoroplastic ETFE, polycarbonate, polypropylene, polyethylene, and the like can be given.
Furthermore, in the present embodiment mode, an example is given in which an impurity gas is generated using the gas canister 1100 that contains an impurity in the impurity generator 1415; however, the embodiment of the present invention is not limited to being the embodiment given as the example here. For example, the impurity gas may be generated using a chemical solution or a fan filter unit, as well. A case in which a chemical solution and a fan filter unit (hereinafter referred to as an FFU) shown in
The impurity generator shown in
In addition, when a solution that contains an impurity is used for the chemical solution 1200, the filter of the FFU 1206 may or may not contain an impurity. For a chemical solution that contains an impurity, an inorganic acid that contains boron such as boric acid or the like, for example, a borate such as trimethyl borate, triethyl borate, triisopropyl borate, tripropyl borate, tri-n-octyl borate, an aqueous solution of ammonium borate, or the like; a phosphate, for example, trimethyl phosphate, triethyl phosphate, tri-n-amyl phosphate, 2-ethythexyl diphenyl phosphate, an aqueous solution of ammonium phosphate, or the like; or the like may be used.
It is to be noted that the filter of the FFU also has an objective of removing particles, and a combination of a chemical filter, a HEPA filter, and a ULPA filter may be used, depending on the objective.
Moreover, the impurity generator 1415 may have a structure in which a plurality of FFUs is provided, as shown in
For the chemical solution, an ester compound that contains an impurity is used, an ester compound 1305 that is volatilized by the chemical solution temperature adjustment mechanism 1302 is extracted by the first FFU 1306, the amount of humidity is adjusted by moisture by the humidity control mechanism 1308 and the ester compound 1305 is hydrolyzed, and a mixed vapor 1307 that is decomposed into alcohol and an acid that contains an impurity is formed. Then, the alcohol constituent is removed by a filter in the second FFU 1309, and a vapor 1310 that contains the acid, which contains an impurity, as its main component is formed. It is to be noted that, for the ester compound that contains an impurity, for example, trimethyl borate, triethyl borate, triisopropyl borate, tripropyl borate, tri-n-octyl borate, trimethyl phosphate, triethyl phosphate, tri-n-amyl phosphate, 2-ethylhexyl diphenyl phosphate, or the like may be used.
It is to be noted that the filter of the first FFU 1306 or that of the second FFU 1309 also has an objective of removing particles, and any of a chemical filter, a HEPA filter, and a ULPA filter may be combined together, depending on the objective, and used, or a fan only may be used.
In the structure of the impurity introduction unit given in the present embodiment mode, by use of a wire as a substrate support, flexure of a substrate holding mechanism caused by the weight of the substrate itself can be suppressed. As a result, the amount of space between substrates within the unit can be decreased, and the weight of parts used in the substrate support can be reduced. Furthermore, because each structural component of the unit is made up of a simple structure, the number of different types of parts used can be reduced by the number of parts that can be used in common being increased, maintenance can be improved, and equipment costs can be dramatically reduced.
By use of the semiconductor manufacturing apparatus that is equipped with the impurity introduction unity that is presented in the present embodiment mode, an impurity can be introduced into a semiconductor film at low concentration and at a high level of accuracy. As a result, variations in threshold voltage of semiconductor devices formed by use of these semiconductor films can be suppressed, and high performance semiconductor devices can be fabricated at high productivity and high yield. Furthermore, because no expensive doping apparatus is used in the introduction of the impurity into the semiconductor film, it becomes possible to provide semiconductor devices at low cost.
In addition, by use of the semiconductor manufacturing apparatus that is equipped with the impurity introduction unit that is presented in the present embodiment mode, because an impurity can be attached to a plurality of substrates over which a semiconductor film has been formed all at the same time and the amount of the impurity attached to the semiconductor film of each substrate can be controlled efficiently, productivity can be increased dramatically.
In the present embodiment mode, steps by which a thin film transistor (a TFT) is fabricated by use of the semiconductor manufacturing apparatus of the present invention and by use of a crystalline semiconductor film, which contains an impurity at low concentration, fabricated according to the fabrication steps given in Embodiment Mode 1 will be described. It is to be noted that a fabrication method of a top gate (forward staggered) TFT is described in the present embodiment mode; however, the present invention can be used for a bottom gate (reverse staggered) TFT or the like in the same way. However, the present invention can be implemented in a lot of different modes, and it is to be easily understood by those skilled in the art that various changes and modifications can be made without any departure from the spirit and scope of the present invention. Accordingly, the present invention is not to be taken as being limited to the described content of the embodiment mode included herein.
First, as shown in
Next, as shown in
Next, gate electrodes are formed by etching of conductive layers formed over the gate insulating film 708. Then, using the gate electrodes or a resist that is formed and etched as a mask, impurities imparting n-type or p-type conductivity are added to the island-shaped semiconductor films 704 to 707 as selected, and source regions, drain regions, LDD regions, and the like are formed. By the steps described above, n-type transistors 710 and 712 and p-type transistors 711 and 713 can be formed over the same substrate (
Subsequently, an organic insulating film 715 is formed over the insulating film 714. For the organic insulating film 715, an organic insulating film of polyimide, polyamide, BCB, acrylic, or the like that is applied by an SOG method is used. Because the organic insulating film 715 reduces the amount of unevenness due to a TFT formed over the substrate 100, with a strong implication being that the organic insulating film 715 is used to planarize the substrate 100, it is preferable that a film that has an excellent level of flatness be used for the organic insulating film 715. Moreover, using a photolithography method, the insulating film 714 and the organic insulating film 715 are processed into patterns, and contact holes that reach the impurity regions are formed therein.
Next, a conductive film is formed using a conductive material and processed into a pattern, whereby wirings 716 to 723 are formed. Then, with formation of an insulating film 724 that is used as a protective film, a semiconductor device like that illustrated in
It is to be noted that a fabrication method of a semiconductor device manufactured using the semiconductor manufacturing apparatus of the present invention is not limited to having the steps described above for fabrication of a TFT. In the present invention, a crystalline semiconductor film, which contains an impurity at low concentration and is obtained by exposure of a semiconductor film to an impurity atmosphere and irradiation thereafter of the semiconductor film with a laser beam, is used as an active layer of a TFT. As a result thereof, the amount of variation in the threshold voltage of semiconductor elements formed using the semiconductor films can be suppressed.
Furthermore, in the semiconductor manufacturing apparatus of the present invention, a crystallization step that uses a catalytic element may be performed before crystallization by laser beam is performed. For the catalytic element, an element such as nickel (Ni), germanium (Ge), iron (Fe), palladium (Pd), tin (Sn), lead (Pb), cobalt (Co), platinum (Pt), copper (Cu), or gold (Au) can be used. If a crystallization step of crystallization by laser beam is performed after the crystallization step that uses a catalytic element is performed, crystals formed when crystallization is performed by use of the catalytic element are left remaining without being melted by irradiation with a laser beam, and crystallization proceeds with these crystals used as crystal nuclei.
For this reason, compared to a case in which only a step for crystallization by laser beam is performed, crystallinity of the semiconductor film can be improved even more, and the amount of roughness on the surface of the semiconductor film after crystallization by laser beam has been performed can be suppressed. Consequently, the amount of variation in the characteristics of semiconductor elements (for example, TFTs) that are to be formed later can be suppressed even more. It is to be noted that crystallinity by irradiation with a laser beam may be increased even more with promotion of crystallization by performance of heat treatment after the addition of a catalytic element, or the heat treatment step may be omitted. Specifically, crystallinity may be set to be increased by irradiation with a laser beam instead of by heat treatment, after the catalytic element has been added.
In the present invention, an example is given in which the semiconductor manufacturing apparatus of the present invention is used in the introduction of an impurity into a channel formation region, but the semiconductor manufacturing apparatus of the present invention may be used in the introduction of an impurity into an LDD region or into a source region or a drain region, as well. In addition, a fabrication method of a semiconductor device formed by use of the present invention can be used for the fabrication method of an integrated circuit or a semiconductor display device, as well. For transistors applied to functional circuits of drivers, CPUs, and the like, an LDD structure or a structure in which an LDD is overlapped with a gate electrode would be the preferred structure, and for an increase in speed, it is preferable that miniaturization of the transistor be achieved. Because the transistors 710 to 713 completed by use of the present embodiment mode have LDD structures, use in a driver circuit that requires a low Ioff is preferable.
By use of the semiconductor manufacturing apparatus of the present invention, an impurity can be introduced into a semiconductor film at low concentration and at a high level of accuracy. As a result, variations in threshold voltage of semiconductor devices formed by use of these semiconductor films can be suppressed, and high performance semiconductor devices can be fabricated at high productivity and high yield. Furthermore, because no expensive doping apparatus is used in the introduction of the impurity into the semiconductor film, it becomes possible to provide semiconductor devices at low cost.
In the present embodiment mode, a process by which a thin film integrated circuit or a contactless thin film integrated circuit device (also referred to as a wireless chip, a wireless IC tag, and radio frequency identification (RFID, wireless identification) is fabricated using the semiconductor manufacturing apparatus of the present invention is given. However, the present invention can be implemented in a lot of different modes, and it is to be easily understood by those skilled in the art that various changes and modifications can be made without any departure from the spirit and scope of the present invention. Accordingly, the present invention is not to be taken as being limited to the described content of the embodiment mode included herein.
An example in which an electrically isolated TFT is used for a semiconductor element that is used in an integrated circuit of a wireless IC tag will be shown hereinafter; however, a semiconductor element that is used in an integrated circuit of a wireless IC tag is not limited to being a TFT, and any kind of element can be used. For example, in addition to a TFT, a memory element, a diode, a photoelectric element, a resistive element, a coil, a capacitive element, an inductor, and the like can typically be given.
At first, steps for fabrication of a thin film integrated circuit will be described using
Next, a base insulating film 1702 is formed over the separation layer 1701. The base insulating film 1702 is provided for the prevention of diffusion of an alkali metal such as Na or the like or an alkali earth metal that is contained in the first substrate into the semiconductor film and the prevention of adverse effects on the characteristics of a semiconductor element such as a TFT or the like. Furthermore, the base insulating film 1702 also has the function of protection of the semiconductor element during a step to be performed later in which the semiconductor element is separated from the substrate. The base insulating film 1702 may be a single layer or a film in which a plurality of insulating films are stacked together. Consequently, the base insulating film 1702 is formed using an insulating film of silicon oxide, silicon nitride, silicon oxide that contains nitrogen (SiON), silicon nitride that contains oxygen (SiNO), or the like that can suppress the diffusion of an alkali metal or an alkali earth metal into the semiconductor film.
Next, a semiconductor film 1703 is formed over the base insulating film 1702. It is preferable that the semiconductor film 1703 is formed after the base insulating film 1703 is formed without being exposed to the atmosphere. The film thickness of the semiconductor film 1703 is set to be from 20 nm to 200 nm, (desirably, from 40 nm to 170 nm, even more desirably, from 50 nm to 150 nm). In the present embodiment mode, an amorphous silicon film is formed as the semiconductor film 1703.
It is to be noted that, after an amorphous silicon film is formed for the semiconductor film 1703, the amorphous silicon film may be heated at 500° C. in an electric furnace for one hour in order to release hydrogen from the amorphous silicon film. Removing hydrogen is performed in order to prevent bumping of hydrogen gas in the semiconductor film 1703 at the time that the semiconductor film 1703 is irradiated with a laser beam and to prevent ablation of the semiconductor film 1703 but can be omitted if the amount of hydrogen contained in the semiconductor film 1703 is low.
Next, the substrate 1700 over which the semiconductor film 1703 is formed by the steps described above is transported to the prewashing unit that is used to eliminate impurities of the semiconductor manufacturing device of the present invention. Because an oxidized film layer 1740 is formed over the semiconductor film 1703 by heat treatment or the like that is performed when the film is formed or when hydrogen is removed from the film, impurities such as the oxidized film layer or the like that are not needed for doping are removed by a sheet-fed spin washing machine in the unit, and the semiconductor film 1703 is spun dry after being exposed.
The substrate 1700 from which impurities not needed for doping are removed is transported to the impurity introduction chamber and exposed to the impurity atmosphere for only the length of time required for attachment of an impurity at a desired concentration. Hereby, as shown in
Next, in the laser crystallization unit, as shown in
Next, as shown in
Next, as shown in
Instead of a resist mask, a mask of silicon oxide or the like may be used, as well. In this case, although a step in which a mask (referred to as a hard mask) of silicon oxide, silicon oxide that contains nitrogen, or the like is formed is added, because the amount of reduction in film thickness during etching is less for a mask than for a resist, the gate electrodes 1709 to 1711 can each be formed with a desired width. Furthermore, the gate electrodes 1709 to 1711 may also be formed as selected using a liquid droplet discharge method without any use of the masks 1712.
Next, as shown in
Next, as shown in
Next, as shown in
Subsequently, by an etch-back method, parts of the insulating film 1721 and the gate insulating film 1708 are etched, and as shown in
Next, as shown in
Next, after the resist 1726 is removed by ashing or the like, thermal activation of the impurity regions may be performed. For example, after a silicon oxide film that contains nitrogen is formed at a film thickness of 50 nm, heat treatment may be performed in a nitrogen atmosphere at a temperature of 550° C. for four hours. Furthermore, the number of defects in a polycrystalline semiconductor film can be decreased by performance of heat treatment in a nitrogen atmosphere at a temperature of 410° C. for one hour after a silicon nitride film that contains hydrogen is formed at a film thickness of 100 nm. This process is used, for example, to terminate dangling bonds present in the polycrystalline semiconductor film and is referred to as a hydrogen treatment process or the like.
By the sequence of steps described above, an n-channel TFT 1730, a p-channel TFT 1731, and an n-channel TFT 1732 are formed. In the fabrication steps given above, by the conditions for the etching method being changed as appropriate and the size of the sidewalls being adjusted, a TFT with an LDD length of from 0.2 μm to 2 μm can be formed. Furthermore, a passivation film that is used to protect the TFTs 1730 to 1732 may be formed thereafter.
Next, as shown in
Next, contact holes are formed in the first interlayer insulating film 1733, the second interlayer insulating film 1734, and the gate insulating film 1708, and wirings 1735 to 1739 that are to be connected to the TFTs 1730 to 1732 are formed. It is to be noted that the wirings 1735 and 1736 are connected to the high-concentration impurity region 1727 of the n-channel TFT 1730, the wirings 1736 and 1737 are connected to the high-concentration impurity region 1720 of the p-channel TFT 1731, and the wirings 1738 and 1739 are connected to the high-concentration impurity region 1728 of the n-channel TFT 1732. Furthermore, the wiring 1739 is also connected to the gate electrode 1711 of the n-channel TFT 1732. The n-channel TFT 1732 can be used as a random number ROM memory element.
Next, as shown in
Next, an antenna 1742 is formed over the third interlayer insulating film 1741. For the antenna 1742, a conductive material that contains one or more of a metal, such as Ag, Au, Cu, Pd, Cr, Mo, Ti, Ta, W, Al, Fe, Co, Zn, Sn, Ni, or the like, or a metal compound containing one or more of the metals given can be used. The antenna 1742 is also connected to the wiring 1735. It is to be noted that the antenna 1742 is connected to the wiring 1735 directly in
The antenna 1742 can be formed using a printing method, a photolithography method, an evaporation method, a liquid droplet discharge method, or the like. In
When a liquid droplet discharge method or a printing method is used, conductive particles of Cu coated with Ag and the like can also be used. It is to be noted that when the antenna 1742 is formed using a liquid droplet discharge method, having the surface of the third interlayer insulating layer 1741 be treated in such a way that the adhesiveness of the antenna 1742 is increased is desirable. For a method by which the adhesiveness can be increased, specifically, for example, a method in which a metal or a metal compound by which the adhesiveness of a conductive film or an insulating film can be increased by catalytic action is attached to the surface of the third interlayer insulating film 1741; a method in which an organic insulating film, a metal, or a metal compound that has a high level of adhesiveness in regard to a conductive film or insulating film that is formed is attached to the surface of the third interlayer insulating film 1741; a method in which surface modification is performed by the surface of the third interlayer insulating film 1741 being treated by plasma treatment under atmospheric pressure or reduced pressure; and the like can be given.
If the metal or metal compound that is attached to the third layer interlayer insulating film 1741 is conductive, the sheet resistance of the metal or metal compound is controlled so that there is no disruption in the normal operation of the antenna 1742. Specifically, either the average thickness of the metal or metal compound that is conductive may be controlled so as to be from, for example, 1 nm to 10 nm, or a part of or all of the metal or metal compound may be made to be insulative by oxidation. Alternatively, regions other than those in which it is desired that adhesiveness be increased may be removed as selected by etching of the adhered metal or metal compound. Moreover, instead of the metal or metal compound being attached to the entire surface of the substrate in advance, the metal or metal compound may be attached to the substrate as selected in specified regions only using a liquid droplet discharge method, a printing method, a sol gel method, or the like. It is to be noted that there is no need for the metal or metal compound to be formed over the surface of the third interlayer insulating film 1741 in a perfectly continuous film shape, and the metal or metal compound may be formed in a dispersed manner to some extent.
After the antenna 1742 is formed, a protective layer 1745 is formed over the third interlayer insulating film 1741 so as to cover the antenna 1742, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
It is to be noted that, for the second substrate 1751, a flexible organic material of paper, plastic, or the like can be used.
Next, as shown in
Furthermore, the adhesive 1752 can be used to bond the cover material 1753 to the third layer interlayer insulating film 1741 and the antenna 1742. For the adhesive, a variety of types of curable adhesives, for example, reactive curable adhesives, thermal curable adhesives, light curable adhesives such as UV curable adhesives or the like, anaerobic adhesives, or the like, can be used.
By the steps given above, a wireless IC tag can be completed. By the fabrication method described above, an extremely thin integrated circuit with a total film thickness of greater than or equal to 0.3 μm and less than or equal to 3 μm, typically, a total film thickness of about 2 μm, can be formed between the second substrate 1751 and the cover material 1753.
It is to be noted that, in the present embodiment mode, an example is given in which the semiconductor manufacturing apparatus of the present invention is used for the introduction of impurities into a channel formation region; however, the semiconductor manufacturing apparatus of the present invention may be used for the introduction of impurities into an LDD region or into a source region or drain region, as well.
It is to be noted that the thickness of the integrated circuit is not only the thickness of a semiconductor element itself but is to be defined as also including the thicknesses of the various insulating films and interlayer insulating films that are formed between the adhesive 1750 and the adhesive 1752. Furthermore, the area occupied by the integrated circuit that is formed in a wireless IC tag can be made to be about 5 mm or less on each (25 mm2 or less), more desirably, from about 0.3 mm on each side (0.09 mm2) to about 4 mm on each side (16 mm2).
It is to be noted that, in the present embodiment mode, a separation method is given in which a separation layer is provided between the first substrate 1700, which is highly resistant to heat, and an integrated circuit, and the substrate and the integrated circuit are separated from each other by removal of the separation layer by etching; however, the fabrication method of a wireless IC tag of the present invention is not to be taken as being limited to having this configuration only. For example, the configuration may be one in which a metal oxide film is provided between a substrate, which is highly resistant to heat, and an integrated circuit, and the integrated circuit is separated from the substrate by weakening of this metal oxide film by crystallization. Alternatively, the configuration may be one in which a separation layer formed by use of an amorphous semiconductor film that contains hydrogen is provided between a substrate, which is highly resistant to heat, and an integrated circuit, and the substrate and the integrated circuit are separated from each other by removal of this separation layer by irradiation with a laser beam. Furthermore, the configuration may be one in which a substrate, which is highly resistant to heat, over which an integrated circuit is formed is eliminated mechanically or removed by etching with a solvent or gas, whereby the integrated circuit may be detached from the substrate.
It is to be noted that, in the present embodiment mode, an example is described in which an antenna is formed over the same substrate over which an integrated circuit is formed; however, the present invention is not limited to having only this structure. The structure may be one in which an antenna and an integrated circuit are formed over different substrates and are to be electrically connected to each other by bonding of substrates during a later step.
It is to be noted that the frequencies of electromagnetic waves used in radio frequency identification (RFID), in general, are often 13.56 MHz and 2.45 GHz, and forming wireless IC tags so that electromagnetic waves of these frequencies can be detected is extremely important for increasing versatility.
With the wireless IC tag of the present embodiment mode, there are advantages in that shielding of electromagnetic waves can be reduces more effectively with the wireless IC tags of the present embodiment mode than with RFID formed using semiconductor substrates and attenuation of signals caused by the shielding of electromagnetic waves can be prevented. Consequently, because semiconductor substrates need not necessarily be used, manufacturing costs of the wireless IC tags can be reduced dramatically.
It is to be noted that, in the present embodiment mode, an example was described in which an integrated circuit is separated from the substrate over which it is formed and attached to a substrate that has flexibility; however, the structure of the present invention is not limited to having this kind of structure only. For example, if a substrate that has an allowable temperature limit high enough to withstand heat treatment performed during the fabrication process of the integrated circuit, as with a glass substrate, is used in the IC tag, the integrated circuit need not necessarily be separated from the substrate over which it is formed.
By use of the semiconductor manufacturing apparatus of the present invention, an impurity can be introduced into a semiconductor film at low concentration and at a high level of accuracy. As a result, variations in threshold voltage of semiconductor devices formed by use of these semiconductor films can be suppressed, and high performance semiconductor devices can be fabricated at high productivity and high yield. Furthermore, because no expensive doping apparatus is used in the introduction of the impurity into the semiconductor film, it becomes possible to provide semiconductor devices at low cost.
By the present invention, for impurities within a surface of a substrate and between substrates, because an impurity can be introduced into an active layer of a semiconductor element at low concentration and at a high level of accuracy, a high performance semiconductor device can be manufactured at high yield. Furthermore, by use of a semiconductor device of the present invention, an electronic device can be fabricated with good throughput and high quality. Specific examples of these kinds of electronic devices will be described using
In addition, the thin film transistors fabricated using the laser irradiation apparatus of the present invention can be used as thin film integrated circuits or contactless thin film integrated circuit devices (also referred to as wireless IC tags and radio frequency identification (RFID, wireless authentication)). Thin film integrated circuits and contactless thin film integrated circuit devices fabricated using fabrication methods given in other embodiment modes can be used in tags and memory.
In
In addition, a wireless IC tag can be used as memory. In
Furthermore, the wireless IC tag can be used as described hereinafter. In accounting, at the time of payment, information relating that payment has been made is written to the wireless IC tag, and whether payment has been made or not is checked by a checking device provided at an exit that checks to see if the information that payment has been made has been written to the wireless IC tag. If the wireless IC tag is taken out of the store without payment having been made, an alarm rings. With this method, payment being forgotten to be made and shoplifting can be prevented.
In consideration of protection of customer privacy, the following method can also be used. In payment at a cash register, any of the following may be conducted: (1) data input to the wireless IC tag is locked by a pin number or the like; (2) the data itself that is input to the wireless IC tag is encrypted; (3) data input to the wireless IC tag is erased; and (4) data input to the wireless IC tag is destroyed. Then, a checking device that is provided at an exit checks to see if any one of the processes of (1) to (4) has been conducted or if the data in the wireless IC tag has not been processed so that whether the payment has been made or not is checked. In this way, whether the payment has been made or not can be checked in the store, and reading out of the information in the wireless IC tag outside the store against the will of the possessor of the wireless IC tag can be prevented.
Several methods can be given for destruction of the data that is input to the wireless IC tag in (4). For example, (a) only the data is destroyed by writing of either one or both of “0” (“off”) and “1” (“on”) in at least a part of the electronic data in the wireless IC tag or (b) a current is made to flow excessively through the wireless IC tag so that a part of a wiring included in a semiconductor element in the wireless IC tag is destroyed.
Because manufacturing costs of these wireless IC tags that are described above are higher than those of barcodes used conventionally, there is a need for a reduction in costs. According to the present invention, however, because uniform laser annealing of a semiconductor film is possible, semiconductor devices with favorable product quality and no variation can be manufactured effectively, which is effective for a reduction in costs. Furthermore, any wireless IC tag can be manufactured so as to be highly reliable and to have high product quality with no variation in performance.
As thus described, the range of application for a semiconductor device manufactured by use of the present invention is extremely wide, and a semiconductor device that is manufactured by use of the present invention can be applied to electronic devices of any field.
Hereinafter, even more detailed descriptions of embodiments of the present invention will be given; however, the present invention is not to be taken as being limited to these embodiments, and it goes without saying that the present invention is to be specified by the range of the patent claims given.
In the present embodiment, results of an experiment in which a crystalline semiconductor film that contains an impurity at low concentration was formed over a substrate according to the fabrication steps given in Embodiment Mode 1 are shown.
For the substrate, a glass substrate with a thickness of 0.7 mm, manufactured by Coming Incorporated, was used. Furthermore, for a base insulating film, a stacked-layer structure of a silicon nitride oxide film and a silicon oxynitride film was used, and each of the films was formed in a parallel-plate CVD plasma apparatus. Specifically, the substrate was heated to a temperature of 300° C.; for film formation gases (flow rates), SiH4 (10 sccm), NH3 (100 sccm), N2O (20 sccm), and H2 (400 sccm) were made to flow at a pressure of 40 Pa; and a plasma was formed with RF power at an RF frequency of 27 MHz set to be 50 W and the distance between electrodes set to be 30 mm, whereby the silicon nitride oxide film was formed at a film thickness of 50 nm.
Subsequently, the substrate over which the silicon nitride oxide film was formed was moved to a different process chamber and heated to a temperature of 400° C.; for film formation gases (flow rates), SiH4 (4 sccm) and N2O (800 sccm) were made to flow at a pressure of 40 Pa; and a plasma was formed with RF power at an RF frequency of 27 MHz set to be 50 W and the distance between electrodes set to be 15 mm, whereby the silicon oxynitride film was formed at a film thickness of 100 nm.
Next, over the base insulating film, for a semiconductor film, an amorphous silicon film was formed in a parallel-plate CVD plasma apparatus. Specifically, the substrate was heated to a temperature of 250° C.; for film formation gases (flow rates), SiH4 (25 sccm) and H2 (150 sccm) were made to flow at a pressure of 66.7 Pa; and a plasma was formed with RF power at an RF frequency of 27 MHz set to be 50 W and the distance between electrodes set to be 25 mm, whereby a silicon nitride oxide film was formed at a film thickness of 66 nm.
After the amorphous semiconductor film was formed under the film formation conditions given above, the substrate over which the amorphous semiconductor film was formed was heated to a temperature of 500° C. in an electric furnace for one hour for performance of dehydrogenation treatment.
Then, the substrate over which an oxide film layer that is not needed was formed by heat treatment at the time that the semiconductor film layer was formed or dehydrogenation treatment was performed or was formed over the semiconductor film at the time that the substrate was transported was transferred to the prewashing unit, which is used for removal of impurities, of the semiconductor manufacturing apparatus of the present invention. For the prewashing unit that is used for removal of impurities, after the oxidized film layer was removed by rotation of the washing machine while 0.5 wt % of fluoric acid was being discharged for 70 seconds using a sheet-fed spin washing machine, the substrate was washed with water that contains CO2, an oxide film was formed over the surface of the semiconductor film and the substrate rotated and dried while ozonated water was being discharged for 40 seconds.
Next, the substrate was transferred to the impurity introduction unit. For the impurity introduction method, the substrate was left in the process chamber for two hours during which 5% B2H6 gas diluted with hydrogen was made to flow at a rate of 30 sccm and boron was attached over the surface of the amorphous semiconductor film.
Next, the substrate was transferred to the laser crystallization unit. Here, for a laser oscillator, the second harmonic (532 nm) of a YVO4 pseudo continuous wave mode-locked laser where output was 20 W and the oscillation mode was TEM00 with a repetition rate of 80 MHz±1 MHz was used. Furthermore, a linear laser beam with a laser beam with a width of approximately 500 μm along the long axis and a width of approximately 20 μm along the short axis was formed with an optical system. Then, the substrate was placed on a stage that has x and y axes; while the stage was moved in the x-axis direction, which is to be the direction along the short axis of the linear laser beam, at a speed of 350 mm/s, the substrate was irradiated linearly with the linear laser beam from edge to edge; the stage was moved 500 μm, which is to be the width of the long axis of the linear laser beam, in the y-axis direction, which is to be the direction along the long axis of the linear laser beam; and while the stage was moved in the x-axis direction in a direction differing from the previous direction by 180°, at a speed of 350 mm/s, the substrate was irradiated linearly with the linear laser beam from edge to edge, in the same way. In this way, by the substrate being irradiated back and forth with the linear laser beam, laser crystallization was performed over the entire surface of the substrate.
It is to be noted that, with the optical system used to form the laser beam into the linear laser beam, after a laser beam emitted from a laser oscillator was transmitted through an attenuator that can be used to change the transmittance of the laser beam and the beam size of the laser beam is doubled by a beam expander, the long axis direction of the laser beam was shielded using a slit with a width of 1 mm. Then, after the laser beam was transmitted through a long-axis cylindrical lens, which was arranged so that the image of the long axis direction of the laser beam immediately after passing through the slit was reduced and transcribed so as to be approximately 500 μm wide on the surface that was to be irradiated, and the direction in which the laser beam progresses was changed to the direction of incident light using an incident-light mirror, the width of the short axis on the surface that was to be irradiated was adjusted so as to be approximately 20 μm by a short-axis cylindrical lens, whereby a linear laser beam was formed such that the width of the long axis on the surface that was to be irradiated was approximately 500 μm and the short axis thereon was approximately 20 μm.
In the laser crystallization process described above, an amorphous silicon film was irradiated with the linear laser beam and melted at the same time as boron was diffused throughout the melted silicon film. That is, at the same time as the melted silicon film was crystallized, boron was activated at a high activation rate, and a polycrystalline silicon film that contains boron at a low concentration was formed.
Results of the concentration of boron introduced throughout the polycrystalline silicon film that were measured using secondary ion mass spectrometry (SIMS) are shown in
It is to be noted that, because measurement accuracy of concentration within a film cannot be obtained if the thickness of the object to be measured is thin, in consideration of measurement accuracy, measurements were taken using a substrate formed of an amorphous silicon film that was formed at a thickness of 100 nm as a monitor substrate. The measured concentration of boron throughout the polycrystalline silicon film was approximately 2×1017 atoms/cm3, and it was confirmed that approximately the same concentration of boron could be introduced as when conventional channel doping was used, with a desired threshold voltage of 0.9 V.
Furthermore, the concentration of boron dispersed throughout the polycrystalline silicon film was introduced approximately uniformly with respect to the direction of depth from the surface. In addition, it was shown that because boron was not introduced throughout the amorphous silicon film in the case in which laser crystallization was not performed, boron was introduced throughout the semiconductor film by the laser crystallization step.
By the results given above, it was shown that introduction of an impurity into an active layer at low concentration as well as at approximately uniform concentration can be realized with good productivity by use of the semiconductor manufacturing apparatus of the present invention.
In the present embodiment, results of an experiment in which, in the impurity introduction unit of the semiconductor manufacturing apparatus of the present invention, an impurity was generated using a chemical solution and an FFU and exposed in a stocker will be described.
First, a silicon nitride oxide film with a film thickness of 50 nm and a silicon oxynitride film with a film thickness of 100 nm were stacked together as a base insulating layer over a glass substrate, and an amorphous silicon film with a film thickness of 66 nm was formed over the base insulating film as an amorphous semiconductor film by a plasma CVD method. Next, after heat treatment was performed at 500° C. for one hour for dehydrogenation treatment, heat treatment was performed at 550° C. for four hours, the substrate was treated with 0.5 vol. % HF for 90 seconds using the sheet-fed spin washing machine in the prewashing unit before the introduction of impurities, and a silicon oxide film and impurities formed over the amorphous silicon film were removed. Subsequently, in a boron atmosphere in which a filter that contains boron was used for the filter of the FFU unit of the impurity introduction unit, the substrate was exposed for 24 hours using the stocker, and boron was attached over the amorphous silicon film.
Next, in the laser crystallization unit, laser crystallization was performed using a pseudo continuous wave laser, and boron was introduced into the silicon film while a polycrystalline silicon film was formed at the same time. Here, for the laser crystallization method, the entire surface of the substrate was irradiated with the laser beam under the same conditions as the conditions outlined in Embodiment 1.
In
For the case in which the substrate was not exposed to the boron atmosphere, a concentration of boron of approximately 2×1016 atoms/cm3 was introduced into the polycrystalline silicon film. Moreover, for the case in which the substrate was exposed to the boron atmosphere for 24 hours, a concentration of boron of approximately 9×1016 atoms/cm3 was introduced into the polycrystalline silicon film. From these results, it could be seen that the concentration of boron introduced into the polycrystalline silicon film could be controlled even at a low concentration by exposure of the substrate to the boron atmosphere.
Furthermore, in the FFU, measurement results of the amount of boron introduced in the case in which a boronless filter and a chemical filter were employed instead of a filter that contains boron are shown in
Moreover, after laser crystallization, a resist was applied over the polycrystalline silicon film that was formed, the resist was exposed to light and developed so that the resist was formed into a given shape, etching was performed using the formed resist as a mask, and island-shaped polycrystalline semiconductor films were formed. A TFT was formed using these island-shaped polycrystalline semiconductor films.
It is to be noted that the shape of a channel in the polycrystalline semiconductor film was set with the channel length being 1 μm and the channel width being 8 μm. Furthermore, phosphorus or boron was introduced into respective source regions or drain regions in the island-shaped polycrystalline semiconductor films by an ion doping apparatus, and a plurality of n-channel TFTs and p-channel TFTs was formed.
Results of an examination by regression analysis of a correlation between the threshold voltage Vth and the length of time of exposure to the boron atmosphere of n-channel TFTs that were formed are shown in
In
Moreover, in
From the results of
In the present embodiment, results of an experiment in which, in the impurity introduction unit of the semiconductor manufacturing apparatus of the present invention, a substrate was exposed to an impurity atmosphere that was generated using tri-n-octyl borate, which is an ester borate compound, as the chemical solution will be described.
First, a silicon nitride oxide film with a film thickness of 50 nm and a silicon oxynitride film with a film thickness of 100 nm were stacked together as a base insulating layer over a glass substrate, and an amorphous silicon film with a film thickness of 150 nm was formed over the base insulating film as an amorphous semiconductor film by a plasma CVD method. Next, dehydrogenation treatment was performed, the substrate from which a silicon oxide film and impurities formed over the amorphous silicon film were removed in the prewashing unit before the introduction of impurities was exposed for 5 minutes to a boron atmosphere that was generated by hydrolysis of tri-n-octyl borate, and boron was attached over the amorphous silicon film.
Next, in the laser crystallization unit, laser crystallization was performed using a pseudo continuous wave laser, and boron was introduced into the silicon film while a polycrystalline silicon film was formed at the same time. Here, for the laser crystallization method, the entire surface of the substrate was irradiated with the laser beam under the same conditions as the conditions outlined in Embodiment 1.
In
This application is based on Japanese Patent Application serial no. 2007-057424 filed with the Japan Patent Office on Mar. 7, 2007, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-057424 | Mar 2007 | JP | national |
