The present invention relates to a film-forming device and a film-forming method for forming a film atomic layer by atomic layer with the use of a raw material gas and a reaction gas.
Nowadays, a film-forming method is known in which a thin film is formed atomic layer by atomic layer by ALD (Atomic Layer Deposition). Such ALD is performed by alternately supplying a raw material gas and a reaction gas as precursor gases onto a substrate so that a thin film is formed which has a structure in which atomic layer films are stacked on top of one another. Such a thin film obtained by ALD can have a very small thickness of about 0.1 nm, and therefore the film-forming method based on ALD is effectively used for producing various devices as a high-precision film-forming method.
For example, an ALD film-forming method using plasma is known in which oxygen radicals are formed by activating a reaction gas such as oxygen gas that reacts with a raw material gas with the use of plasma, and then the oxygen radicals are reacted with a component of the raw material gas adsorbed on a substrate (Patent Literature 1). Further, an ALD film-forming method not using plasma is also known in which a gas such as ozone that reacts with a raw material gas is reacted with a component of the raw material gas adsorbed on a substrate (Patent Literature 2).
Patent Literature 1: JP 2011-181681 A
Patent Literature 2: JP 2009-209434 A
Among these ALD film-forming methods, the method using plasma can form a dense film due to the activation of a reaction gas. However, the use of plasma sometimes damages a substrate surface or a film due to the bombardment of the substrate surface with ions in plasma. On the other hand, when a highly-active gas such as ozone or water is used without using plasma, such damage to a substrate surface or a film caused by using plasma can be prevented, but it is more difficult to form a dense film as compared to when plasma is used.
It is therefore an object of the present invention to provide a film-forming device and a film-forming method by which a film ranging from a dense film to a less-dense film can be freely formed on a substrate by plasma ALD with little damage to the surface of the substrate or the film.
Means to solve the Problem
An aspect of the invention is a film-forming device for forming a film atomic layer by atomic layer with a use of a raw material gas and a reaction gas.
The film-forming device includes:
The film-forming device according to embodiment 1, further including a first control part configured to determine, as a start point of production of the plasma, a time point when reflected power of power input to the plasma source crosses a value set within a range of 85 to 95% of the input power after the power is input.
The film-forming device according to embodiment 1 or 2, wherein the duration of production of the plasma includes a reaction time from start to end of a reaction between part of the component of the raw material gas and the reaction gas and a property-adjusting time for changing the property of a film formed by the reaction.
The film-forming device according to any one of embodiments 1 to 3, further including a second control part configured to control operations of the raw material gas supply part and the reaction gas supply part to repeat a cycle including supply of a raw material gas performed by the raw material gas supply part, supply of a reaction gas performed by the reaction gas supply part after the supply of the raw material gas, and plasma production using the reaction gas performed by the plasma source, wherein
The film-forming device according to embodiment 4, wherein the duration of production of the plasma of a first one cycle is shorter than the duration of production of the plasma of a last one cycle.
The film-forming device according to embodiment 5, wherein the duration of production of the plasma increases as a number of repetitions of the cycle increases.
The film-forming device according to any one of embodiments 4 to 6, wherein production of the plasma is performed more than once in at least one cycle, and a total duration of plasma production performed more than once is in a range of 0.5 millisecond to 100 milliseconds.
The film-forming device according to any one of embodiments 1 to 7, wherein the degree of the property has at least three different levels of the property.
Another aspect of the invention is a film-forming method for forming a film atomic layer by atomic layer with a use of a raw material gas and a reaction gas.
A film-forming method includes the steps of:
The film-forming method according to embodiment 9, wherein a time point when reflected power of power input to the plasma source to produce the plasma crosses a value set within a range of 85 to 95% of the input power after the power is input is determined as a start point of production of the plasma to determine an end point of input of the power to the plasma source.
The film-forming method according to embodiment 9 or 10, wherein the duration of production of the plasma includes a reaction time from start to end of a reaction between part of the component of the raw material gas and the reaction gas and a property-adjusting time for changing the property of a film formed by the reaction.
The film-forming method according to any one of embodiments 9 to 11, wherein a cycle including supply of the raw material gas, supply of the reaction gas performed after the supply of the raw material gas, and plasma production using the reaction gas performed by the plasma source is repeated, and
The film-forming method according to embodiment 12, wherein during repetition of the cycle, the duration of production of the plasma of a first one cycle is shorter than the duration of production of the plasma of a last one cycle.
The film-forming method according to embodiment 13, wherein during repetition of the cycle, the duration of production of the plasma increases as a number of repetitions of the cycle increases.
The film-forming method according to embodiment 15, wherein the film has a refractive index increasing from its substrate side to its uppermost layer side.
The film-forming method according to any one of embodiments 12 to 15, wherein production of the plasma is performed more than once in at least one cycle, and a total duration of plasma production performed more than once is in a range of 0.5 millisecond to 100 milliseconds.
The film-forming method according to any one of embodiments 9 to 16, wherein the degree of the property has at least three different levels of the property.
The film-forming method according to any one of embodiments 9 to 17, wherein the substrate is a flexible substrate.
The film-forming method according to any one of embodiments 9 to 18, wherein the film contains a metal component, and the substrate is a plate having a composition not containing the metal component.
The above film-forming device and film-forming method make it possible to freely form a film ranging from a dense film to a less-dense film with little damage to the surface of a substrate or the film.
Hereinbelow, a film-forming method and a film-forming device according to the present invention will be described in detail.
When supplied into the film-forming space, the raw material gas is adsorbed onto the substrate so that an atomic layer of a certain component of the raw material gas is uniformly formed. When the reaction gas is supplied into the film-forming space, the ALD device 10 allows an electrode as a plasma source to produce plasma using the reaction gas to form radicals of a component of the reaction gas to enhance reaction activity. The radicals are reacted with the component of the raw material gas on the substrate to form a film in atomic layer unit. The ALD device 10 forms a film having a predetermined thickness by repeating the above process as one cycle. At this time, the duration of plasma production per cycle is in the range of 0.5 millisecond to 100 milliseconds. Further, the density of power input to the plasma source is in the range of 0.05 W/cm2 to 10 W/cm2. Here, the density of power input to the plasma source is a value obtained by dividing input power by the area of a plasma-producing region. The area of a plasma-producing region is the cross-sectional area of a plasma-producing region taken along a plane parallel to the substrate. When the plasma source is a parallel plate electrode 14, the density of power input to the plasma source is almost equal to a value obtained by dividing input power by the area of an upper electrode 14a. This makes it possible to freely form a film ranging from a dense film to a less-dense film with little damage to the surface of the substrate or the film. Particularly, in a case where a dense film is to be formed, the duration of plasma production is set to be long within the above range, and in a case where a less-dense film is to be formed, the duration of plasma production is set to be short within the above range. It is to be noted that a dense film and a less-dense film are different in properties, and therefore the duration of plasma production is set according to preset information about the property (at least one property selected from refractive index, dielectric strength, and dielectric constant) of a film to be formed, for example, according to the degree of refractive index of a film to be formed. The degree of the property preferably has, for example, at least three different levels of the property.
At this time, the duration of plasma production preferably includes a reaction time from the start to the end of a reaction between part of a component of the raw material gas and the reaction gas and a property-adjusting time for changing the value of the property of a film formed by the reaction. Particularly, the property of the film can be changed by changing the property-adjusting time.
The following description will be made with reference to a case where an aluminium oxide film is formed on a substrate with the use of TMA (Trimethyl Aluminium) containing an organic metal as a raw material gas and oxygen gas as a reaction gas.
The ALD device 10 according to this embodiment is a capacitively-coupled plasma-producing device using a parallel plate electrode as a plasma source. However, the structure of a plasma source to be used is not particularly limited, and another plasma-producing device may also be used, such as an electromagnetically-coupled plasma-producing device using two or more antenna electrodes, an ECR plasma-producing device utilizing electron cyclotron resonance, or an inductively-coupled plasma-producing device.
ALD Device
The ALD device 10 includes a film-forming vessel 12, a parallel plate electrode 14, a gas supply unit 16, a controller (first control part, second control part) 18, a high-frequency power source 20, a matching box 22, and an exhaust unit 24.
The film-forming vessel 12 maintains a constant reduced-pressure atmosphere created in its film-forming space by exhaustion through the exhaust unit 24.
In the film-forming space, the parallel plate electrode 14 is provided. The parallel plate electrode 14 has an upper electrode 14a and a lower electrode 14b as electrode plates, and is provided in the film-forming space to produce plasma. The upper electrode 14a of the parallel plate electrode 14 is provided so as to face the substrate-placing surface of a susceptor 30 provided in the film-forming space. On the substrate-placing surface, a substrate is to be placed. That is, a substrate is to be placed in the film-forming space. The upper electrode 14a is connected to the high-frequency power source 20 through the matching box 22 by a power feeder extending from above the film-forming vessel 12. The matching box 22 has an inductor and a capacitor therein, and adjusts the inductance of the inductor and the capacitance of the capacitor for matching to the impedance of the parallel plate electrode 14 at the time of plasma production. The high-frequency power source 20 supplies a high-frequency pulsed power of 13.56 to 27.12 MHz to the upper electrode 14a for a short period of time of 100 milliseconds or shorter.
The surface of the lower electrode 14b acts as a substrate-placing surface and is grounded. The susceptor 30 has a heater 32 therein. During film formation, a substrate is heated by the heater 32 so as to be maintained at, for example, 50° C. or higher but 400° C. or lower.
The susceptor 30 is configured so that an elevating shaft 30a provided at the bottom of the susceptor 30 is freely moved in a vertical direction in
The gas supply unit 16 introduces, into the film-forming space, a raw material gas containing an organic metal, a first gas that does not chemically react with the raw material gas, and a second gas that oxidizes a metal component of the organic metal.
Specifically, the gas supply unit 16 has a TMA source 16a, an N2 source 16b, an O2 source 16c, valves 17a, 17b, and 17c, a pipe 18a that connects the TMA source 16a and the film-forming space in the film-forming vessel 12 through the valve 17a, a pipe 18b that connects the N2 source 16b and the film-forming space in the film-forming vessel 12 through the valve 17b, and a pipe 18c that connects the O2 source 16c and the film-forming space in the film-forming vessel 12 through the valve 17c. The TMA source 16a, the valve 17a, and the pipe 18a constitute a raw material gas supply part. The O2 source 16c, the valve 17c, and the pipe 18c constitute a reaction gas supply part.
The valves 17a, 17b, and 17c are activated under the control of the controller 18 to introduce TMA as a raw material gas, N2 gas, and O2 gas into the film-forming space at predetermined timings, respectively.
The exhaust unit 24 exhausts the raw material gas, the nitrogen gas, and the oxygen gas, introduced into the film-forming space through the left wall of the film-forming vessel 12, from the film-forming space through an exhaust pipe 28 in a horizontal direction. At some point in the exhaust pipe 28, a conductance variable valve 26 is provided. The conductance variable valve 26 is adjusted under instructions from the controller 18.
The controller 18 controls the timing of supply of each of the raw material gas, the nitrogen gas, and the oxygen gas and the timing of supply of power to the parallel plate electrode 14. Further, the controller 18 controls the opening and closing of the valve 26.
Specifically, concurrently with the supply of oxygen gas into the film-forming space, the controller 18 sends a trigger signal to the high-frequency power source 20 to control the start of power supply to the upper electrode 14a of the parallel plate electrode 14 so that the parallel plate electrode 14 produces plasma using oxygen gas.
When a film is to be formed on a substrate, the controller 18 first controls the flow rate of the valve 17a to introduce TMA gas into the film-forming space in which the substrate is placed on the substrate-placing surface. By controlling the flow rate, TMA gas is supplied into the film-forming space for, for example, 0.1 seconds. During the supply of TMA gas into the film-forming space, the exhaust unit 24 always exhausts gas from the film-forming space. That is, when TMA gas is supplied into the film-forming space, part of the TMA gas is adsorbed onto the substrate in the film-forming space, but the remaining unnecessary TMA gas is exhausted from the film-forming space.
Then, the controller 18 stops the supply of TMA into the film-forming space through the valve 17a, and then controls the supply of oxygen gas through the valve 17c to start the supply of oxygen gas into the film-forming space. The supply of oxygen gas into the film-forming space is performed for, for example, 1 second. The controller 18 sends a trigger signal to the high-frequency power source 20 to instruct the high-frequency power source 20 to start the supply of power to the upper electrode 14a through the matching box 22 for a certain period of time during the supply of oxygen gas. The high-frequency power source 20 includes a power source control part 20a that controls the start of power supply according to the trigger signal. The power source control part 20a adjusts a power supply time so that the duration of plasma production becomes, for example, 0.01 seconds. More specifically, information about the property (at least one property selected from refractive index, dielectric strength, and dielectric constant) of a film to be formed, for example, the degree of refractive index is previously set and input to the high-frequency power source 20 by an operator or the like, and the time set within the range of 0.5 millisecond to 100 milliseconds according to the preset information is defined as the duration of plasma production. The information about the property, for example, the magnitude of refractive index preferably has, for example, at least three different refractive index levels. The controller 18 determines the start point of plasma production (as the first control part) so that the actual time during which plasma is continuously produced is in close agreement with the set duration of plasma production. The high-frequency power source 20 counts time to stop the input of power at the end point of plasma production that is the time point when the set duration of plasma production has elapsed after the start point of plasma production determined by the controller 18. It is to be noted that in this embodiment, the controller 18 determines the start point of plasma production (as the first control part), but the power source control part 20a may determine the start point of plasma production (as the first control part). The count and the stop of power input by the high-frequency power source 20 are performed by the power source control part 20a.
The input of power to the upper electrode 14a allows the parallel plate electrode 14 to produce plasma using oxygen gas in the film-forming space. During the supply of oxygen gas into the film-forming space, the exhaust unit 24 always exhausts gas from the film-forming space. More specifically, when oxygen gas is supplied into the film-forming space, part of the oxygen gas is activated by plasma, oxygen radicals produced by the activation react with part of a component of TMA adsorbed on the substrate placed in the film-forming space, and the remaining unnecessary oxygen gas, oxygen radicals produced by plasma, and oxygen ions are exhausted from the film-forming space.
Then, the supply of power to the upper electrode 14a is stopped, and the supply of oxygen gas into the film-forming space through the valve 17c is stopped. Then, the controller 18 again controls the flow rate by the valve 17a so that TMA gas is supplied into the film-forming space. By repeating such a cycle including the supply of TMA gas into the film-forming space, the supply of oxygen gas into the film-forming space, and the production of plasma using oxygen gas, an aluminium oxide film having a predetermined thickness can be formed on the substrate.
It is to be noted that the supply of nitrogen gas from the nitrogen gas source 16b into the film-forming space may always be performed or may sometimes be stopped during each of the periods of TMA gas supply, oxygen gas supply, and plasma production. Nitrogen gas functions as a carrier gas or a purge gas. An inert gas, such as argon gas, may be used instead of nitrogen gas.
Oxygen gas may also be used instead of nitrogen gas as long as a reaction with the raw material gas does not occur.
The matching box 22 is adjusted so that impedance matching is established when plasma is produced in the film-forming space. Even when impedance matching is adjusted, plasma is not instantaneously produced at the time when power is supplied to the upper electrode 14a as a plasma source. The time from the start point of power input to the time point when plasma is produced varies. This is because even when conditions where plasma is likely to be produced can be created by placing a voltage between the upper electrode 14a and the lower electrode 14b, the nucleus of electric discharge that produces plasma needs to be produced. The nucleus is produced by various causes, and the time point when the nucleus is produced varies by several hundred milliseconds. In the present embodiment, the duration of plasma production T1 is short as illustrated in
The duration of plasma production T1 preferably includes a reaction time from the start to the end of a reaction between part of a component of the raw material gas and the reaction gas and a property-adjusting time for changing the degree of the property (at least one property selected from refractive index, dielectric strength, and dielectric constant) of a film formed by the reaction. Particularly, the property of the film can be changed by changing the property-adjusting time following the end of the reaction. As described above, in the present embodiment, a reaction between part of a component of the raw material gas and the reaction gas and adjustment of the property of a film'can be performed by plasma produced at a time. One atomic layer film or, at most, about two atomic layer films is/are formed by the reaction between part of a component of the raw material gas and the reaction gas, and therefore plasma is required to act on only the formed atomic layer film(s). For this reason, the duration of plasma production can be set to 100 milliseconds or shorter.
At this time, the duration of plasma production T1 was changed within the range of 5 milliseconds to 500 milliseconds, and the refractive index of a film formed at this time was measured with a spectroscopic ellipsometer. The refractive index of an aluminium oxide film formed by ALD is 1.63 to 1.65 when the film is sufficiently dense. As can be seen from
As illustrated in
It is to be noted that power input to the upper electrode 14a is in the range of 15 to 3000 W so that input power per unit area determined by dividing input power by an area of the electrode (upper electrode 14a) of 300 cm2 is in the range of 0.05 W/cm2 to 10 W/cm2.
For example, when the duration of plasma production T1 is set to 10 milliseconds, a film that is relatively less dense and has a refractive index of about 1.60 can be formed. On the other hand, when the duration of plasma production T1 is set to 20 milliseconds, a film that is relatively dense and has a refractive index of about 1.62 can be formed. Conventionally, a dense aluminium oxide film (film having a high refractive index) is formed by producing plasma using oxygen gas (by producing oxygen plasma) to form oxygen radicals and reacting the oxygen radicals with a component of TMA, and a less-dense aluminium oxide film (film having a low refractive index) is formed by reacting ozone gas with a component of TMA gas. Therefore, in a case where a less-dense film and a dense film are to be formed on one substrate as a lower layer and an upper layer, respectively, a film-forming device needs to be changed because a reaction gas to be used is different between when the film as a lower layer is formed and when the film as an upper layer is formed. A system that produces oxygen plasma and a system that provides ozone gas can be incorporated into one film-forming device, which however increases the cost of the film-forming device. On the other hand, the film-forming device according to the present embodiment can freely switch between forming a dense film and forming a less-dense film simply by adjusting the duration of plasma production T1.
The film formed in the embodiment contains a metal component such as aluminium. On the other hand, the substrate on which a film is to be formed may be a plate having a composition not containing a metal component, such as aluminium. The substrate ma be a plate made of, for example, a resin. Alternatively, a glass substrate or a ceramic substrate may be used.
It is to be noted that when a dense film is formed so as to be in direct contact with a substrate, the film is likely to be peeled off from the substrate due to the tensile stress of the film. Further, the dense film is hard, and is therefore likely to be peeled off from the substrate when the substrate is bent. For these reasons, in order to ensure the adhesion of a film to a substrate, part of the film that is in contact with the substrate is preferably soft and less dense. Therefore, it is preferred that a less-dense film is formed on a substrate as a lower layer, and a dense film is formed as an upper layer on the less-dense film. In this case, the degree of denseness may be gradually increased from the lower layer toward the upper layer. For example, a film can be formed whose refractive index increases from its substrate side toward its uppermost layer side. The refractive index can be measured with a spectroscopic ellipsometer. In this case, the formed film is less likely to be peeled off even when the substrate is a flexible substrate that is highly deformable. In this case, the substrate on which a film is to be formed may be a plate (including a film) having a composition not containing a metal component contained in the film to be formed or a plate (including a film) made of, for example, a resin. Alternatively, the substrate may be a glass substrate or a ceramic substrate. Generally, a substrate on which a film is to be formed has, for example, a thermal expansion coefficient different from that of the film to be formed, but even when a film is formed on such a substrate, peeling-off of the formed film due to the difference in thermal expansion is less likely to occur as long as the film is formed so that its refractive index increases from its substrate side toward its uppermost layer side.
In order to form such a film, it is preferred that, as in the case of the present embodiment, the film-forming device 10 is used by which a film property can be controlled by adjusting the duration of plasma production T1.
In the present embodiment, one cycle including supply of a raw material gas such as TMA gas, supply of a reaction gas, such as oxygen gas, performed after the supply of the raw material gas, and plasma production using the reaction gas by the plasma source such as the upper electrode 14a is repeated. At this time, it is preferred that the duration of plasma production Ti is controlled to be different between at least two cycles. This makes it possible to form a film having portions different in film property.
Particularly, during the repetition of the above cycle, the high-frequency power source 20 preferably controls the plasma source such as the upper electrode 14a so that the duration of plasma production T1 of the first one cycle is shorter than that of the last one cycle. This makes it possible to form a film whose lower layer on its substrate side is less dense and whose upper layer is dense.
Further, during the repetition of the above cycle, the high-frequency power source 20 preferably controls power supplied to the upper electrode 14a so that the duration of plasma production T1 increases as the number of repetitions of the cycle increases. This makes it possible to form a film whose degree of denseness gradually increases from its substrate-side lower layer toward its upper layer.
It is to be noted that in the present embodiment, plasma production using oxygen gas is performed once per cycle, but pulsed plasma may be produced, more than once, for a duration shorter than the duration of plasma production T1. In this case, the cumulative total time of plasma production may be equal to the duration of plasma production T1. That is, plasma production may be performed more than once in at least one cycle so that the total duration of plasma production performed more than once is in the range of 0.5 millisecond to 100 milliseconds.
It is to be noted that in the embodiment, TMA gas is used as an example of the raw material gas, but the raw material gas is not limited to TMA gas. For example, TEA (tetraethylammonium) gas or DMAOPr (dimethylaluminum isopropoxide) gas may also be used. Further, the film to be formed is not limited to aluminium oxide, and may be an oxide of Si, Mg, Ti, Cr, Fe, Ni, Cu, Zn, Ga, Ge, Y, Zr, In, Sn, Hf, or Ta. Further, the reaction gas is not limited to oxygen gas, and may be nitrogen gas, N2O, NH3, H2, or H2O.
The film-forming device and the film-forming method according to the present invention have been described above in detail, but the present invention is not limited to the above embodiment. It is obvious that various changes and modifications may be made without departing from the scope of the present invention.
10 film-forming device
12 film-forming vessel
12
a projecting wall
14 Parallel plate electrode
14
a upper electrode
14
b lower electrode
16 gas supply unit
16
a TMA source
16
b N2 source
16
c O2 source
17
a,
17
b,
17
c valves
18 controller
18
a,
18
b,
18
c pipes
20 high-frequency power source
20
a power source control part
22 matching box
24 exhaust unit
26 conductance variable valve
28 exhaust pipe
30 susceptor
30
a elevating shaft
30
b elevating system
32 heater
Number | Date | Country | Kind |
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2013-215437 | Oct 2013 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2014/056622 | 3/13/2014 | WO | 00 |