Patent Grant
7531784
The present invention relates to a semiconductor device, in particular, a semiconductor device including a photoelectric conversion device and a transistor. Further, the present invention relates to an electronic appliance using the semiconductor device.
A number of photoelectric conversion devices generally used for sensing an electromagnetic wave are known, and for example, a photoelectric conversion device having sensitivity in ultra-violet rays to infrared rays is collectively referred to as an optical sensor. An optical sensor having sensitivity in a visible light region with a wavelength of 400 to 700 nm is particularly referred to as a visible light sensor, and a large number of visible light sensors are used for devices which need illuminance adjustment, on/off control, or the like depending on human living environment.
In particular, in a display device, brightness in the periphery of the display device is detected to adjust display luminance thereof. This is because unnecessary electric-power can be reduced by detecting peripheral brightness and obtaining appropriate display luminance. For example, such an optical sensor for adjusting luminance is used for a mobile phone or a personal computer.
In addition, as well as peripheral brightness, luminance of a backlight of a display device, in particular, a liquid crystal display device is also detected by an optical sensor to adjust luminance of a display screen.
In such an optical sensor, a photodiode is used for a sensing part and an output current of the photodiode is amplified in an amplifier circuit. As such an amplifier circuit, for example, a current mirror circuit is used (for example, see Patent Document 1: Japanese Patent No. 3444093).
In a case of a conventional optical sensor, when detection is attempted for higher illuminance, an output current or an output voltage ranges widely; therefore, the following problems are given: the conventional optical sensor is not easily used as a photoelectric conversion device, and power consumption is increased.
In view of the foregoing problems, an object of the invention is to obtain a photoelectric conversion device capable of detecting a wider range of illuminance without expansion of an output voltage or output current.
A semiconductor device of the invention has a photoelectric conversion device that includes a photoelectric conversion element and an amplifier circuit electrically connected to the photoelectric conversion element, and a bias switching unit that reverses a bias to be applied to the photoelectric conversion device. By reversal of a bias to be applied to the photoelectric conversion device with use of the bias switching unit, a wider range of illuminance can be detected without expansion of a range of an output voltage or output current.
Note that the amplifier circuit has two or more transistors including at least a first transistor; incident light is sensed by the photoelectric conversion element; and a bias to be applied to the photoelectric conversion device is reversed and at the same time, detection by a current generated in the photoelectric conversion element and detection by a voltage generated in the photoelectric conversion element, which is applied between a gate and a source of the first transistor, are switched. Therefore, a property of the transistor included in the photoelectric conversion device, such as crystallinity of a channel formation region, a threshold value, or an S value (subthreshold value) is changed, whereby a range of detectable illuminance, an output current, an output voltage, and the like can be changed in accordance with a purpose.
One mode of the invention is a semiconductor device having an illuminance detecting function, and the semiconductor device has a photoelectric conversion device including a photoelectric conversion element and an amplifier circuit electrically connected to the photoelectric conversion element, and a bias switching unit for reversing a bias to be applied to the photoelectric conversion device. The amplifier circuit has two or more transistors including at least a first transistor. A gate electrode of the first transistor is electrically connected to a first electrode of the first transistor through the photoelectric conversion element. The photoelectric conversion element senses incident light. The bias switching unit reverses a bias at a predetermined level of illuminance, and at the same time, switches between detection by a current generated in the photoelectric conversion element and detection by a voltage generated in the photoelectric conversion element, which is applied between a gate and a source of the first transistor.
Another mode of the invention is a semiconductor device having an illuminance detecting function, and the semiconductor device has a photoelectric conversion device including a photoelectric conversion element and an amplifier circuit electrically connected to the photoelectric conversion element, and a bias switching unit for reversing a bias to be applied to the photoelectric conversion device. The amplifier circuit has two or more transistors including at least a first transistor. The photoelectric conversion element senses incident light. In a case where an illuminance level is a predetermined level or lower, the light is detected by a current generated in the photoelectric conversion element, whereas in a case where an illuminance level is higher than a predetermined level, the light is detected by application of a voltage generated in the photoelectric conversion element between a gate and a source of the first transistor. The bias switching unit reverses a bias at a predetermined level of illuminance.
Another mode of the invention is a semiconductor device having an illuminance detecting function, and the semiconductor device has a photoelectric conversion device including a photoelectric conversion element and an amplifier circuit electrically connected to the photoelectric conversion element, and a bias switching unit for reversing a bias to be applied to the photoelectric conversion device. The amplifier circuit has two or more transistors including at least a first transistor. A gate electrode of the first transistor is electrically connected to a first electrode of the first transistor through the photoelectric conversion element. The photoelectric conversion element senses incident light. In a case where an illuminance level is a predetermined level or lower, the light is detected by a current generated in the photoelectric conversion element, whereas in a case where an illuminance level is higher than a predetermined level, the light is detected by application of a voltage generated in the photoelectric conversion element between a gate and a source of the first transistor. The bias switching unit reverses a bias at a predetermined level of illuminance.
Another mode of the invention is a semiconductor device having an illuminance detecting function, and the semiconductor device has a photoelectric conversion device including a photoelectric conversion element and an amplifier circuit electrically connected to the photoelectric conversion element, and a bias switching unit for reversing a bias to be applied to the photoelectric conversion device. The amplifier circuit has at least a first transistor and a second transistor. A bias is applied through a first terminal and a second terminal of the photoelectric conversion device. The first terminal is electrically connected to a first electrode and a gate electrode of the second transistor and a gate electrode of the first transistor through the photoelectric conversion element, and is also electrically connected to a first electrode of the first transistor. The second terminal is electrically connected to second electrodes of the first transistor and the second transistor. The photoelectric conversion element senses incident light. In a case where an illuminance level is a predetermined level or lower, the light is detected by a current generated in the photoelectric conversion element, whereas in a case where an illuminance level is higher than a predetermined level, the light is detected by a voltage generated in the photoelectric conversion element. The bias switching unit reverses a bias at a predetermined level of illuminance.
In the aforementioned structure, the amplifier circuit has a plurality of first transistors. In addition, the photoelectric conversion element has a p-type semiconductor layer, an n-type semiconductor layer, and an i-type semiconductor layer provided between the p-type semiconductor layer and the n-type semiconductor layer.
Note that in this specification, “being connected” means “being electrically connected”. Therefore, in the structure disclosed in the invention, another element which enables an electrical connection (for example, a switch, a transistor, a capacitor, an inductor, a resistor, a diode, or the like) may be interposed in the predetermined connection. It is needless to say that elements may be provided without another element being interposed, and “being electrically connected” means also “being directly connected”.
Note that in this specification, in order to reverse a bias to be applied to a photoelectric conversion device, potentials to be applied to the photoelectric conversion device may be reversed, and a potential difference is not always required to be the same before and after a reversal. Further, in this specification, description is made of a case where a transistor is a thin film transistor; however, it is not particularly limited thereto.
By the invention, a wider range of illuminance can be detected without expansion of a range of an output voltage or output current. Accordingly, a high-performance photoelectric conversion device can be obtained.
Although the invention will be fully described by way of an embodiment mode and embodiments with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications depart from the spirit and the scope of the invention, they should be construed as being included therein. Note that in a structure of the present invention described below, common portions and portions having a similar function are denoted by the same reference numerals in all diagrams, and description thereof is omitted.
A semiconductor device of Embodiment Mode 1 of the invention is described with reference to
One terminal 121 of the photoelectric conversion device 101 is connected to one electrode of the power source 103 through the bias switching unit 102, and the other terminal 122 of the photoelectric conversion device 101 is connected to the other electrode of the power source 103 through the resistor 104. Note that a current obtained from the photoelectric conversion device 101 is outputted as a voltage from the terminal V0 connected to the terminal 121, with use of the resistor 104.
Next, the photoelectric conversion device 101 is described with reference to
In the semiconductor device shown in
The bias switching unit 102 reverses potentials to be applied to the terminals 121 and 122 of the photoelectric conversion device 101, that is, a bias at a predetermined level of illuminance, with use of the power source 103. In
Further, by reversal of a bias to be applied to the photoelectric conversion device 101, an output voltage outputted from the terminal V0 is also reversed; therefore, an output may be obtained from the terminal V0 through a switching unit for reversing an output (not shown).
Light detection in a case where a voltage is applied to the photoelectric conversion device 101 with use of the power source 103a is described, taking the photoelectric conversion device 101 of the semiconductor device, with reference to
When the photoelectric conversion element 115 is irradiated with light, a current can be obtained, the thin film transistor 112 becomes conductive, and the current i flows to the thin film transistor 112, as described above. Note that in this case, the first electrode of the thin film transistor 112 is a drain electrode, the second electrode thereof is a source electrode, and the thin film transistor 112 is diode-connected. Further, a potential approximately equal to those of the gate electrode and the source electrode of the thin film transistor 112 is supplied to each of the gate electrode and the source electrode of the thin film transistor 113; therefore, the current i flows. Accordingly, an approximately 2×i current value I can be obtained from the photoelectric conversion device 101.
Next, description is made of a case where a predetermined level of illuminance at which the power source 103 is switched by the bias switching unit 102 shown in
When the thin film transistor 112 is in a nonconductive state and the photoelectric conversion element 115 is irradiated with light, an open-ciruit voltage Voc proportional to a logarithmic value of illuminance is generated. Therefore, each potential of the first electrode and the gate electrode of the thin film transistor 112 and the gate electrode of the thin film transistor 113 connected to them is Vss+Voc. Thus, a gate-source voltage of the thin film transistor 113 becomes Voc, whereby the thin film transistor 113 becomes conductive. Then, a current i′ flows to the thin film transistor 113. When Vdd>Vss+Voc is satisfied, the first electrode of the thin film transistor 112 is a source electrode, and the second electrode thereof is a drain electrode. Therefore, since a gate-source voltage Vgs of the thin film transistor 112 is 0, the thin film transistor 112 is in a nonconductive state. Note that description is made under the condition that an off current of the thin film transistor 112 is not considered here.
Thus, the current value i′ is obtained from the photoelectric conversion device 101. A relation of an output current from the photoelectric conversion device 101 to illuminance in that case is shown as a reference numeral 11 in
As described above, in this embodiment mode, an output voltage from the semiconductor device, that is, an output voltage from the terminal V0 in
By reversal of a bias to be applied to the photoelectric conversion device in this manner, a wider range of illuminance can be detected without expansion of a range of an output voltage or output current.
Note that in
As described above, for detection of illuminance, characteristics of the photoelectric conversion element 115 are used in the range A, and the open-circuit voltage Voc obtained from the photoelectric conversion element 115 and characteristics of the thin film transistor 112 are used in the range B. Thus, characteristics of the thin film transistor are changed, whereby an output current in the range B can be changed. By control of the characteristics of the thin film transistor, an output current can be obtained within a predetermined range in the range B; therefore, ranges of an output current in the ranges A and B can be more approximated. For example, in a case where a threshold voltage of the thin film transistor 113 is controlled, a relation of an output current to illuminance (reference numeral 11 in
In addition, by control of an S value (subthreshold value) of the thin film transistor, a slope of a relation of an output current to illuminance (reference numeral 11 in
Further, a difference between an output current in the range A and that in the range B may be the same ranges of output voltages by selection of a resistance value of a resistor connected to the photoelectric conversion device 101, that is, the resistor 104 in accordance with the power source 103 in
Note that in the above description, for detection of illuminance, characteristics of the photoelectric conversion element 115 is used in the range A at a predetermined level of illuminance, and the open-circuit voltage Voc obtained from photoelectric conversion element 115 and characteristics of the thin film transistor 112 are used in the range B at a predetermined level of illuminance. Instead, characteristics to be used may be interchanged at a predetermined level of illuminance. For example, in
Note that in this embodiment mode, an n-channel thin film transistor is used for each thin film transistor included in the current mirror circuit 114. Alternatively, p-channel transistor may be used.
Thus, by the invention, by reversal of a bias to be applied to the photoelectric conversion device, a wider range of illuminance can be detected without expansion of a range of an output voltage or output current. Further, characteristics of the thin film transistor included in the photoelectric conversion device, such as a threshold value or an S value, is changed, whereby a range of detectable illuminance, an output current, an output voltage, and the like can be changed in accordance with a purpose.
In
The photoelectric conversion element 115 in
First, the p-type semiconductor layer 111p may be formed by deposition of a semi-amorphous silicon film containing an impurity element belonging to Group 13, for example, boron (B) by a plasma CVD method. Alternatively, after formation of a semi-amorphous silicon film, an impurity element belonging to Group 13 may be introduced.
Note that a semi-amorphous semiconductor film includes a semiconductor which has an intermediate structure between an amorphous semiconductor and a semiconductor having a crystalline structure (including a single crystal and a polycrystal). The semi-amorphous semiconductor film has a third condition which is stable in terms of free energy, and is a crystalline substance having a short-range order and lattice distortion, and the semi-amorphous semiconductor film having the crystal grain size of 0.5 to 20 nm can be dispersed in a non-single crystalline semiconductor film. As for the semi-amorphous semiconductor film, Raman spectrum thereof is shifted to a wavenumber side lower than 520 cm−1, and the diffraction peaks of (111) and (220) that are said to be caused by a Si crystal lattice are observed in X-ray diffraction. In addition, the semi-amorphous semiconductor film contains hydrogen or halogen of at least 1 atomic % or more to terminate a dangling bond. In the present specification, such a semiconductor film is referred to as a semi-amorphous semiconductor (SAS) film for the sake of convenience. Moreover, a noble gas element such as helium, argon, krypton or neon is contained to further promote lattice distortion so that stability is enhanced and a favorable semi-amorphous semiconductor film can also be obtained. Note that a microcrystalline semiconductor film (microcrystal semiconductor film) is also included in the semi-amorphous semiconductor film.
Also, the SAS film can be obtained by glow discharge decomposition of gas containing silicon. As typical gas containing silicon, SiH4 is given, and Si2H6, SiH2Cl2, SiHCl3, SiCl4, SiF4 or the like may be used instead. The gas containing silicon is diluted with hydrogen, or gas in which one or more of noble gas elements of helium, argon, krypton and neon are added to hydrogen; whereby, the SAS film can be formed easily. It is preferable that the dilution ratio be set to be in a range of 2 to 1000 times. Moreover, carbide gas such as CH4 or C2H6, germanium gas such as GeH4 or GeF4, F2 or the like may be mixed in the gas containing silicon to adjust an energy band width to be 1.5 to 2.4 eV or 0.9 to 1.1 eV.
After the p-type semiconductor layer 111p is formed, a semiconductor layer which does not contain an impurity imparting a conductivity type (referred to as an intrinsic semiconductor layer or an i-type semiconductor layer) 111i and the n-type semiconductor layer 111n are sequentially formed. Accordingly, the photoelectric conversion layer 111 including the p-type semiconductor layer 111p, the i-type semiconductor layer 111i and the n-type semiconductor layer 111n is formed.
Note that, in this specification, the i-type semiconductor layer refers to a semiconductor layer in which the concentration of an impurity imparting p-type or n-type conductivity is 1×1020 cm−3 or less, and the concentration of oxygen and nitrogen is 5×1019 cm−3 or less. Note that photoconductivity is preferably 1000 times or more dark conductivity. In addition, 10 to 1000 ppm of boron (B) may be added to the i-type semiconductor layer.
As the i-type semiconductor layer 111i, for example, a semi-amorphous silicon film may be formed by a plasma CVD method. In addition, as the n-type semiconductor layer 111n, a semi-amorphous silicon film containing an impurity element belonging to Group 15, for example, phosphorous (P) may be formed, and alternatively, an impurity element belonging to Group 15 may be introduced after the semi-amorphous silicon film is formed.
As the p-type semiconductor layer 111p, the intrinsic semiconductor layer 111i and the n-type semiconductor layer 111n, an amorphous semiconductor film may be used instead of a semi-amorphous semiconductor film.
Each of the wiring 319, a connection electrode 320, a terminal electrode 351, a source electrode and a drain electrode 341 of the thin film transistor 112 and a source electrode and a drain electrode 342 of the thin film transistor 113 has a stacked layer structure of a refractory metal film and a low resistance metal film (such as an aluminum alloy or pure aluminum). Here, the wiring and these electrodes each have a three-layer structure in which a titanium film (Ti film), an aluminum film (Al film) and a Ti film are sequentially stacked.
Moreover, protective electrodes 318, 345, 348, 346 and 347 are formed so as to cover the wiring 319, the connection electrode 320, the terminal electrode 351, the source electrode and the drain electrode 341 of the thin film transistor 112 and the source electrode and the drain electrode 342 of the thin film transistor 113, respectively.
The protective electrodes protect the wiring 319 and the like in an etching step for forming the photoelectric conversion layer 111. As a material for the protective electrode 318, a conductive material having slower etching speed than that of the photoelectric conversion layer to an etching gas (or an etchant) for the photoelectric conversion layer 111 is preferable. In addition, a conductive material which does not react with the photoelectric conversion layer 111 to become an alloy is preferable as the material for the protective electrode 318. Note that the other protective electrodes 345, 348, 346 and 347 are also formed by the similar material and manufacturing process to the protective electrode 318.
Alternatively, a structure in which the protective electrodes 318, 345, 348, 346 and 347 are not formed may be employed.
In addition, in order to prevent deterioration of the ON current value due to a hot carrier, the n-channel thin film transistors 112 and 113 may have a structure in which an LDD region and a gate electrode are placed so as to be overlapped with each other with a gate insulating film interposed therebetween (in this specification, referred to as a GOLD (Gate-drain Overlapped LDD) structure). In a case where a GOLD structure is used, the effect that an electric field in the vicinity of a drain region is reduced and deterioration due to hot carrier injection is prevented is more enhanced than in a case where an LDD region and a gate electrode are not overlapped with each other. With such a GOLD structure, electric field intensity in the vicinity of a drain region is reduced and hot carrier injection is prevented, and thus, it is effective for prevention of deterioration phenomenon.
The thin film transistors 112 and 113 included in the current mirror circuit 114 may be a bottom gate thin film transistor, for example, an inversely staggered thin film transistor, instead of the top gate thin film transistor described above.
In addition, a wiring 314 is connected to the wiring 319, and also becomes a gate electrode by being extended to an upper side of the channel formation region of the thin film transistor 113 of the amplifier circuit.
A wiring 315 is connected to the terminal 121 connected to the n-type semiconductor layer 111n through the connection wiring 320 and the protective electrode 345, and is connected to a drain wiring (also referred to as a drain electrode) or a source wiring (also referred to as a source electrode) of the thin film transistor 113.
Since light to be detected passes through interlayer insulating films 316 and 317, a material having a high light transmitting property is preferably used as the materials for both of them. Note that for the insulating film 317, an inorganic material such as a silicon oxide (SiOx) film is preferably used so that fixing intensity is improved. Also for a sealing layer 324, an inorganic material is preferably used, and the insulating films can be formed by a CVD method or the like.
In addition, a terminal electrode 350 is formed by the same process as the wirings 314 and 315, and the terminal electrode 351 is formed by the same process as the wiring 319 and the connection electrode 320. Note that the terminal 122 is connected to the terminal electrode 350 through the auxiliary electrode 348 and the terminal electrode 351.
Note that the terminal 121 is mounted on an electrode 361 of a substrate 360 by a solder 364. The terminal 122 is formed through the same process as the terminal electrode 121, and is mounted on an electrode 362 of the substrate 360 by a solder 363.
In
In such a photoelectric conversion device, a bias to be applied is reversed, so that a wide range of illuminance can be detected without an output voltage or an output current range being expanded. Further, a property of a thin film transistor included in the photoelectric conversion device, such as a threshold value or an S value, is changed, whereby a detection range of light, an output voltage or the like can be changed in accordance with a purpose.
In this embodiment, current characteristics obtained when a bias applied to the photoelectric conversion device is reversed is described with reference to
In
According to
In the case of ELC, when a predetermined intensity by which a bias to be applied to a photoelectric conversion device is set to be 100 l× and a range of an output current is set to be 20 nA to 5 μA, a lower limit of a range of detectable illuminance can be approximately 0.5 l× and an upper limit thereof can be 100,000 l× or more. Therefore, a wider range of illuminance can be detected without expansion of a range of an output current.
Note that
Note that this embodiment can be implemented in appropriate combination with any of the embodiment mode and the other embodiments.
In this embodiment, description is made of a semiconductor device having a photoelectric conversion device to which the present invention is applied and a manufacturing method of the semiconductor device. Note that each of
First, an element is formed over a substrate (first substrate 310). In this embodiment, AN 100, which is one of glass substrates, is used as the substrate 310.
Subsequently, a silicon oxide film containing nitrogen (with a film thickness of 100 nm) to be the base insulating film 312 is formed by a plasma CVD method, and a semiconductor film such as an amorphous silicon film containing hydrogen (with a film thickness of 54 nm) is stacked without being exposed to an atmospheric air. Further, the base insulating film 312 may be formed by stacking a silicon oxide film, a silicon nitride film, and a silicon oxide film containing nitrogen. For example, a film in which a silicon nitride film containing oxygen with a film thickness of 50 nm and a silicon oxide film containing nitrogen with a film thickness of 100 nm are stacked may be formed as the base insulating film 312. It is to be noted that the silicon oxide film containing nitrogen and the silicon nitride film serve as a blocking layer that prevents an impurity such as an alkali metal from diffusing from the glass substrate.
Then, the amorphous silicon film is crystallized by a solid-phase growth method, a laser crystallization method, a crystallization method using a catalytic metal, or the like to form a semiconductor film having a crystalline structure (a crystalline semiconductor film), for example, a polycrystalline silicon film. Here, a polycrystalline silicon film is obtained by a crystallization method using a catalytic element. A nickel acetate solution containing nickel of 10 ppm by weight is applied by a spinner. It is to be noted that a nickel element may be dispersed over the entire surface by a sputtering method instead of application of the solution. Then, heat treatment is performed for crystallization to form a semiconductor film having a crystalline structure. Here, a polycrystalline silicon film is obtained by heat treatment for crystallization (at 550° C. for 4 hours) after the heat treatment (at 500° C. for one hour).
Next, an oxide film over the surface of the polycrystalline silicon film is removed by a dilute hydrofluoric acid or the like. Thereafter, in order to increase a crystallization rate in the polycrystalline silicon film and repair defects left in crystal grains, irradiation with laser light (XeCl: wavelength of 308 nm) is performed in the atmosphere or the oxygen atmosphere.
As the laser light, excimer laser light with a wavelength of 400 nm or less; or a second harmonic or a third harmonic of a YAG laser is used. Here, pulse laser light with a repetition frequency of approximately 10 to 1000 Hz is used, the pulse laser light is condensed to 100 to 500 mJ/cm2 by an optical system, and irradiation is performed with an overlap rate of 90 to 95%, whereby a surface of the silicon film may be scanned. In this embodiment, irradiation with laser light having a repetition frequency of 30 Hz and energy density of 470 mJ/cm2 is performed in the atmosphere.
Note that since laser light irradiation is performed in an atmospheric air or in an oxygen atmosphere, an oxide film is formed on the surface by the laser light irradiation. Note that an example in which the pulse laser is used is shown in this embodiment. Instead, a continuous wave laser may be used. In order to obtain crystal with large grain size at the time of crystallization of a semiconductor film, it is preferable to use a solid laser which is capable of continuous oscillation and to apply the second to fourth harmonic of a fundamental wave. Typically, a second harmonic (532 nm) or a third harmonic (355 nm) of an Nd: YVO4 laser (a fundamental wave of 1064 nm) may be applied.
In a case of using a continuous wave laser, laser light which is emitted from a continuous wave YVO4 laser of 10 W output is converted into a harmonic by a non-linear optical element. Also, there is a method by which YVO4 crystal and a non-linear optical element are put in an oscillator and a high harmonic is emitted. Then, the laser light having a rectangular shape or an elliptical shape on an irradiated surface is preferably formed by an optical system to be emitted to an object to be processed. At this time, an energy density of approximately 0.01 to 100 MW/cm2 (preferably, 0.1 to 10 MW/cm2) is necessary. The semiconductor film may be moved at approximately a rate of 10 to 2000 cm/s relatively with respect to the laser light so as to be irradiated.
Subsequently, in addition to the oxide film which is formed by the above laser light irradiation, a barrier layer formed of an oxide film having a thickness of 1 to 5 nm in total is formed by treatment of the surface with ozone water for 120 seconds. The barrier layer is formed in order to remove the catalytic element which is added for crystallization, for example, nickel (Ni) from the film. Although the barrier layer is formed using ozone water here, the barrier layer may be formed by deposition of an oxide film having a thickness of approximately 1 to 10 nm by a method of oxidizing a surface of the semiconductor film having a crystalline structure by UV-ray irradiation in an oxygen atmosphere; a method of oxidizing a surface of the semiconductor film having a crystalline structure by oxygen plasma treatment; a plasma CVD method; a sputtering method; an evaporation method; or the like. Alternatively, the oxide film formed by the laser light irradiation may be removed before formation of the barrier layer.
Then, an amorphous silicon film containing an argon element which serves as a gettering site is formed to be 10 to 400 nm thick, here 100 nm thick, over the barrier layer by a sputtering method. The amorphous silicon film containing an argon element is formed under an atmosphere containing argon with the use of a silicon target. In a case where an amorphous silicon film containing an argon element is formed by a plasma CVD method, deposition conditions are as follows: flow ratio of monosilane to argon (SiH4: Ar) is 1:99, deposition pressure is set to be 6.665 Pa, RF power density is set to be 0.087 W/cm2, and deposition temperature is set to be 350° C.
Thereafter, heat treatment in a furnace heated at 650° C. is performed for 3 minutes to remove a catalytic element (gettering). Accordingly, the catalytic element concentration in the semiconductor film having a crystalline structure is reduced. A lamp annealing apparatus may be used instead of the furnace.
Subsequently, the amorphous silicon film containing an argon element, which is a gettering site, is selectively removed using the barrier layer as an etching stopper, and thereafter, the barrier layer is selectively removed with a diluted hydrofluoric acid. Note that nickel has a tendency to move to a region having high oxygen concentration at the time of gettering; therefore, it is preferable that the barrier layer formed of an oxide film be removed after gettering.
Note that, in a case where crystallization with the use of a catalytic element is not performed to a semiconductor film, the above steps such as forming the barrier layer, forming the gettering site, heat treatment for gettering, removing the gettering site, and removing the barrier layer are not required.
Subsequently, a thin oxide film is formed on the surface of the obtained semiconductor film having a crystalline structure (for example, a crystalline silicon film) with ozone water, and thereafter, a mask formed from a resist is formed using a first photomask and etching treatment into a desired shape is performed to form semiconductor regions that are separated into an island shape (in this specification, referred to as island-shaped semiconductor regions) 331 and 332 (see
Next, a very small amount of an impurity element (boron or phosphorus) is added in order to control a threshold value of a thin film transistor, if necessary. Here, an ion doping method is used, in which diborane (B2H6) is not separated by mass but excited by plasma.
Subsequently, the oxide film is removed with an etchant containing a hydrofluoric acid, and at the same time, the surfaces of the island-shaped semiconductor regions 331 and 332 are washed. Thereafter, an insulating film containing silicon as its main component, which becomes a gate insulating film 313, is formed. Here, a silicon oxide film containing nitrogen (composition ratio: Si=32%, 0=59%, N=7%, and H=2%) is formed to have a thickness of 115 nm by a plasma CVD method.
Subsequently, after a metal film is formed over the gate insulating film 313, patterning is performed using a second photomask to form gate electrodes 334 and 335, wirings 314 and 315, and a terminal electrode 350 (see
As the gate electrodes 334 and 335, the wirings 314 and 315, and the terminal electrode 350, instead of the above film, a single-layer film formed from an element selected from titanium (Ti), tungsten (W), tantalum (Ta), molybdenum (Mo), neodymium (Nd), cobalt (Co), zirconium (Zr), zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), aluminum (Al), gold (Au), silver (Ag), and copper (Cu), or an alloy material or a compound material containing the above element as its main component; a single-layer film formed from nitride thereof, for example, titanium nitride, tungsten nitride, tantalum nitride or molybdenum nitride; or a stacked-layer film of them may be used.
Subsequently, an impurity imparting one conductivity type is introduced to the island-shaped semiconductor regions 331 and 332 to form a source region and a drain region 337 of the thin film transistor 112 and a source region and a drain region 338 of the thin film transistor 113 (see
Next, a first interlayer insulating film (not shown) including a silicon oxide film is formed to be 50 nm thick by a CVD method, and thereafter, a step is performed, in which the impurity element added to each of the island-shaped semiconductor regions is activated. This activation process is performed by a rapid thermal annealing method (RTA method) using a lamp light source; an irradiation method with a YAG laser or an excimer laser from the back side; heat treatment using a furnace; or a method which is a combination of any of the foregoing methods.
Then, a second interlayer insulating film 316 including a silicon nitride film containing hydrogen and oxygen is formed, for example, to be 10 nm thick.
Subsequently, a third interlayer insulating film 317 formed of an insulating material is formed over the second interlayer insulating film 316 (see
Then, heat treatment (heat treatment at 300 to 550° C. for 1 to 12 hours, for example, at 410° C. for 1 hour in a nitrogen atmosphere) is performed to hydrogenate the island-shaped semiconductor regions. This step is performed to terminate a dangling bond of the island-shaped semiconductor regions by hydrogen contained in the second interlayer insulating film 316. The island-shaped semiconductor regions can be hydrogenated regardless of whether or not the gate insulating film 313 is formed.
Alternatively, as the third interlayer insulating film 317, an insulating film using siloxane and a stacked structure thereof may be used. Siloxane is composed of a skeleton structure of a bond of silicon (Si) and oxygen (O). An organic group containing at least hydrogen (such as an alkyl group or an aryl group) is used as a substituent. Instead, a fluoro group may be used as a substituent.
In a case where an insulating film using siloxane and a stacked structure thereof are used as the third interlayer insulating film 317, after formation of the second interlayer insulating film 316, heat treatment to hydrogenate the island-shaped semiconductor regions can be performed, and then, the third interlayer insulating film 317 can be formed.
Subsequently, a mask formed from a resist is formed using a third photomask, and the first interlayer insulating film, the second interlayer insulating film 316, the third interlayer insulating film 317 and the gate insulating film 313 are selectively etched to form a contact hole. Then, the mask formed from a resist is removed.
Note that the third interlayer insulating film 317 may be formed if necessary. In a case where the third interlayer insulating film 317 is not formed, the first interlayer insulating film, the second interlayer insulating film 316, and the gate insulating film 313 are selectively etched after formation of the second interlayer insulating film 316 to form a contact hole.
Next, after formation of a metal stacked film by a sputtering method, a mask formed from a resist is formed using a fourth photomask, and then, the metal film is selectively etched to form the wiring 319, the connection electrode 320, the terminal electrode 351, the source electrode and the drain electrode 341 of the thin film transistor 112, and the source electrode and the drain electrode 342 of the thin film transistor 113. Then, the mask formed from a resist is removed. Note that the metal film of this embodiment is a stacked-layer film of a Ti film with a thickness of 100 nm, an Al film containing a very small amount of Si with a thickness of 350 nm, and a Ti film with a thickness of 100 nm.
In addition, as shown in
The top gate thin film transistors 112 and 113 using a polycrystalline silicon film can be manufactured through the process described above. Note that S values of the thin film transistors 112 and 113 can be changed depending on crystallinity of a semiconductor film and an interfacial state between a semiconductor film and a gate insulating film.
Subsequently, after formation of a conductive metal film (such as titanium (Ti) or molybdenum (Mo)) which is not likely to be an alloy by reacting with a photoelectric conversion layer (typically, amorphous silicon) which is formed later, a mask formed from a resist is formed using a fifth photomask, and then, the conductive metal film is selectively etched to form a protective electrode 318 which covers the wiring 319 (see
Note that in a case where the wiring 319, the connection electrode 320, the terminal electrode 351, the source electrode and the drain electrode 341 of the thin film transistor 112, and the source electrode and the drain electrode 342 of the thin film transistor 113 are formed as a single-layer conductive film, that is, as shown in
Subsequently, a photoelectric conversion layer 111 including a p-type semiconductor layer 111p, an i-type semiconductor layer 111i and an n-type semiconductor layer 111n is formed over the third interlayer insulating film 317.
The p-type semiconductor layer 111p may be formed by deposition of a semi-amorphous silicon film containing an impurity element belonging to Group 13 such as boron (B) by a plasma CVD method, or may be formed by introduction of an impurity element belonging to Group 15 after formation of semi-amorphous silicon film.
Note that the wiring 319 and the protective electrode 318 are in contact with the bottom layer of the photoelectric conversion layer 111, in this embodiment, the p-type semiconductor layer 111p.
After the p-type semiconductor layer 111p is formed, the i-type semiconductor layer 111i and the n-type semiconductor layer 111n are sequentially formed. Accordingly, the photoelectric conversion layer 111 including the p-type semiconductor layer 111p, the i-type semiconductor layer 111i and the n-type semiconductor layer 111n is formed.
As the i-type semiconductor layer 111i, for example, a semi-amorphous silicon film may be formed by a plasma CVD method. In addition, as the n-type semiconductor layer 111n, a semi-amorphous silicon film containing an impurity element belonging to Group 15, for example, phosphorus (P) may be formed, or after formation of a semi-amorphous silicon film, an impurity element belonging to Group 15 may be introduced.
Alternatively, as the p-type semiconductor layer 111p, the intrinsic semiconductor layer 111i and the n-type semiconductor layer 111n, an amorphous semiconductor film may be used instead of a semi-amorphous semiconductor film.
Next, a sealing layer 324 formed from an insulating material (for example, an inorganic insulating film containing silicon) is formed to have a thickness of 1 to 30 μm over the entire surface to obtain a state shown in
Subsequently, after the sealing layer 324 is etched to provide an opening, terminals 121 and 122 are formed by a sputtering method. Each of the terminals 121 and 122 is a stacked-layer film of a titanium film (Ti film) (100 nm), a nickel film (Ni film) (300 nm), and a gold film (Au film) (50 nm). The thus obtained terminal 121 and terminal 122 have a fixing intensity of higher than 5 N, which is sufficient fixing intensity as a terminal electrode.
Through the process described above, the terminal 121 and the terminal 122 which can be connected by a solder are formed, and a structure shown in
Thus, a large quantity of photo IC chips (2 mm×1.5 mm each), that is, photoelectric conversion device chips can be manufactured from one large-sized substrate (for example, 600 cm×720 cm). Next, the substrate is cut separately to take out a plurality of photo IC chips.
A cross-sectional view of one taken photo IC chip (2 mm×1.5 mm) is shown in
In addition, in order to reduce the total thickness of an optical sensor chip, the substrate 310 may be ground to be thinned by CMP treatment or the like, and then, cut separately by a dicer to take out a plurality of optical sensor chips.
In
Lastly, the obtained optical sensor chip is mounted on a mounting surface of a substrate 360 (see
Thus, a semiconductor device can be manufactured. Note that in order to detect light, light may be blocked using a housing or the like in a portion where light does not enter the photoelectric conversion layer 111 from the substrate 310 side. Note that any material may be used for a housing as long as it has a function of blocking light; for example, a housing may be formed using a metal material, a resin material having a black pigment, or the like. With such a structure, a highly reliable semiconductor device having a function of detecting light can be manufactured.
In this embodiment, an example in which an amplifier circuit included in a semiconductor device is formed using an n-channel thin film transistor is described. Alternatively, a p-channel thin film transistor may be used. Note that a p-channel thin film transistor can be formed similarly to an n-channel thin film transistor except that a p-type impurity such as boron (B) is used instead of an impurity imparting one conductivity type to an island-shaped semiconductor region. Next, an example in which an amplifier circuit is formed using a p-channel thin film transistor is described.
Note that this embodiment can be implemented in appropriate combination with any of the embodiment mode and the other embodiments.
In this embodiment, an example of a semiconductor device in which an amplifier circuit is formed using a bottom gate thin film transistor and a manufacturing method thereof is described with reference to
First, a base insulating film 312 and a metal film 511 are formed over a substrate 310 (see
In addition, as the metal film 511, instead of the above film, a single-layer film formed from an element selected from titanium (Ti), tungsten (W), tantalum (Ta), molybdenum (Mo), neodymium (Nd), cobalt (Co), zirconium (Zr), zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), aluminum (Al), gold (Au), silver (Ag) and copper (Cu), or an alloy material or a compound material containing the above element as its main component; or a single-layer film formed from nitride thereof such as titanium nitride, tungsten nitride, tantalum nitride, or molybdenum nitride may be used.
Note that the metal film 511 may be formed directly on the substrate 310 instead of formation of the base insulating film 312 over the substrate 310.
Next, the metal film 511 is patterned to form gate electrodes 512 and 513, wirings 314 and 315 and a terminal electrode 350 (see
Subsequently, a gate insulating film 514 which covers the gate electrodes 512 and 513, the wirings 314 and 315 and the terminal electrode 350 is formed. In this embodiment, the gate insulating film 514 is formed using an insulating film containing silicon as its main component, for example, a silicon oxide film containing nitrogen (composition ratio Si=32%, O=59%, N=7%, H=2%) having a thickness of 115 nm by a plasma CVD method.
Next, island-shaped semiconductor regions 515 and 516 are formed over the gate insulating film 514. The island-shaped semiconductor regions 515 and 516 may be formed by the similar material and manufacturing process to those of the island-shaped semiconductor regions 331 and 332 described in Embodiment 2 (see
After the island-shaped semiconductor regions 515 and 516 are formed, a mask 518 is formed covering portions except for regions which becomes a source region and a drain region 521 of a thin film transistor 501 and a source region and a drain region 522 of a thin film transistor 502, and an impurity imparting one conductivity type is introduced (see
Next, the mask 518 is removed, and a first interlayer insulating film which is not shown, a second interlayer insulating film 316 and a third interlayer insulating film 317 are formed (see
Contact holes are formed in the first interlayer insulating film, the second interlayer insulating film 316 and the third interlayer insulating film 317, and a metal film is formed, and further, the metal film is selectively etched to form the wiring 319, the connection electrode 320, the terminal electrode 351, the source electrode and the drain electrode 531 of the thin film transistor 501 and the source electrode and the drain electrode 532 of the thin film transistor 502. Then, the mask formed from a resist is removed. Note that the metal film of this embodiment is a stacked-layer film of a Ti film having a thickness of 100 nm, an Al film containing a very small amount of silicon having a thickness of 350 nm and a Ti film having a thickness of 100 nm.
In addition, instead of the wiring 319 and a protective electrode thereof 318; the connection electrode 320 and a protective electrode thereof 533; the terminal electrode 351 and a protective electrode thereof 538; the source electrode and the drain electrode 531 of the thin film transistor 501 and a protective electrode thereof 536; and the source electrode and the drain electrode 532 of the thin film transistor 502 and a protective electrode thereof 537, each wiring and electrode may be formed using a single-layer conductive film, in the same manner as the wiring 404, the connection electrode 405, the terminal electrode 401, the source electrode and the drain electrode 402 of the thin film transistor 112 and the source electrode and the drain electrode 403 of the thin film transistor 113 in
Through the above process, bottom gate thin film transistors 501 and 502 included in an amplifier circuit 503 can be manufactured (see
Subsequently, the photoelectric conversion layer 111 including the p-type semiconductor layer 111p, the i-type semiconductor layer 111i and the n-type semiconductor layer 111n is formed over the third interlayer insulating film 317 (see
Next, the sealing layer 324 and the terminals 121 and 122 are formed (
Moreover, the substrate 360 having the electrodes 361 and 362 is mounted using the solders 364 and 363. Note that the electrode 361 over the substrate 360 is mounted on the terminal 121 by the solder 364. In addition, the electrode 362 over the substrate 360 is mounted on the terminal 122 by the solder 363 (see
In a semiconductor device shown in
Note that this embodiment can be implemented in appropriate combination with any of the embodiment mode and the other embodiments.
In this embodiment, a circuit which switches a bias is described as an example of the bias switching unit in
The circuit shown in
In
In addition, in
In
Note that the output voltage, which is obtained by outputting the current obtained from the photoelectric conversion device as a voltage, may be used for the photo sensor output VPS, or a voltage in which the output voltage is amplified in an amplifier circuit may be used instead.
In
Note that in the circuit shown in
The photo sensor output VPS is inputted to the gate electrode of the p-channel thin film transistor 911 of the comparator 903, and is compared with a voltage value from the reference voltage generating circuit 902. In a case where the photo sensor output VPS is lower than a voltage value from the reference voltage generating circuit, the photo sensor output VPS is connected to a power source 103a of a power source 103, and a current flows in a direction shown in
By reversal of a bias to be applied to the photoelectric conversion device with use of the bias switching unit described above, a wider range of illuminance can be detected without expansion of a range of an output voltage or output current.
Note that this embodiment can be implemented in appropriate combination with any of the embodiment mode and the other embodiments.
In this embodiment, an example in which a semiconductor device obtained by the present invention is incorporated in various electronic devices as an optical sensor is described. As electronic appliances to which the present invention is applied, a computer, a display, a mobile phone, a TV set and the like are given. Specific examples of those electronic appliances are shown in
The optical sensor 712 senses light which is transmitted through the light-transmitting material portion 711, controls luminance of the display panel (A) 708 and the display panel (B) 709 in accordance with illuminance of sensed external light, or controls illumination of the operation keys 704 in accordance with illuminance obtained by the optical sensor 712. Accordingly, power consumption of a mobile phone can be reduced.
In a mobile phone shown in
Also, in a mobile phone shown in
As the display portion 733 provided in the computer of
The optical sensor portion 754 which is manufactured using the present invention detects the light amount from the backlight 753, and luminance of the liquid crystal panel 762 is adjusted when information thereof is fed back.
When the release button 801 is pressed down halfway, a focusing adjusting mechanism and an exposure adjusting mechanism are operated, and when the release button is pressed down fully, a shutter is opened. The main switch 802 switches ON or OFF of a power source of a digital camera by being pressed or rotated. The finder window 803 is placed at the upper portion of the lens 805 of a front side of the digital camera, and is a device for recognizing an area which is taken or a focus position from the finder eyepiece window 811 shown in
When the optical sensor to which the present invention is applied is incorporated in the camera shown in
In addition, the optical sensor of the present invention can be applied to other electronic appliances such as a projection TV and a navigation system. That is, the optical sensor of the present invention can be used for any device which is necessary to detect light. A result of light detection is fed back to an illumination control device or the like included in an electronic appliance, whereby power consumption can be reduced.
Note that this embodiment can be implemented in appropriate combination with any of the embodiment mode and the other embodiments.
This application is based on Japanese Patent Application serial no. 2006-122993 filed in Japan Patent Office on 27th, Apr., 2006, the entire contents of which are hereby incorporated by reference.
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