JP2869721B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active-type electro-optical device, and more particularly to an active-type liquid-crystal electro-optical device, in which a clear gradation level can be set.

[0002]

2. Description of the Related Art Liquid crystal compositions have different dielectric constants in a horizontal direction and a vertical direction with respect to a molecular axis due to their material properties. Therefore, liquid crystal compositions may be horizontally or vertically aligned with an external electric field. Can be easily done. The liquid crystal electro-optical device displays ON / OFF by controlling the amount of transmitted light or the amount of dispersion by utilizing the anisotropy of the dielectric constant.

FIG. 2 shows the electro-optical characteristics of a nematic liquid crystal. When the applied voltage is small at Va (point A), the transmitted light amount is almost 0%, and when Vb (point B), the transmitted light amount is about 20%.
In the case of c (point C), it is about 70%, and in the case of Vd (point D), it is about 100%. In other words, if only the points A and D are used, black and white two-gradation display is possible, and if the rising portion of the electro-optical characteristic is used like points B and C, intermediate gradation display is possible.

Conventionally, in the case of a gray scale display of a liquid crystal electro-optical device using a TFT, the gray scale display is performed by changing the voltage applied to the gate of the TFT or the voltage applied between the source and drain to adjust the voltage in an analog manner. I was

[0005]

The method of displaying a gradation of a liquid crystal electro-optical device using a TFT will be further described. An N-channel thin film transistor conventionally used for a liquid crystal electro-optical device has a voltage-current characteristic as shown in FIG. The voltage-current characteristics shown in FIG. 3 are the characteristics of an N-channel thin film transistor using amorphous silicon and the characteristics of an N-channel thin film transistor using polysilicon.

By controlling the voltage applied to the gate electrode in an analog manner, the drain current can be controlled, and the magnitude of the electric field applied to the liquid crystal can be changed. Thereby, gradation display is possible.

However, assuming a liquid crystal electro-optical device having a pixel number of 640 × 400 dots, for example, it is very difficult to manufacture the characteristics of all 256,000 TFTs without variation. In reality, considering the mass productivity and the yield, 16 gradation display is considered to be the limit.

Further, the gate voltage is set to a constant value,
A method of performing gray scale display by controlling only N / OFF and controlling the source / drain voltage has been considered, but it is also considered that the limit is about 16 gray scales due to the instability of characteristics. Analog gradation display control largely depends on the characteristics of the TFT, and clear display requires difficulty.

As another method, a method of gradation display using a plurality of frames has been proposed. For example, as shown in FIG. 12, when gradation display is performed using, for example, 10 frames, the pixel A transmits 20 frames out of 10 frames and does not transmit the remaining 8 frames, so that the average is 20%. And can be displayed. Similarly, in pixel B, 70%
Can be displayed as 50% transmission.

However, when such a display is performed, the number of frames is substantially reduced, so that flicker is generated and display damage occurs. In order to solve this, an increase in frame frequency and the like have been devised, but this is a technology that has a limit because it is difficult to increase power consumption due to an increase in drive frequency or to increase the speed of an IC.

[0011]

Therefore, in order to clarify the applied voltage level, a reference voltage value which is not an analog value but is repeated at a constant cycle is input from the controller as a signal, and the reference signal is input to the TFT. The present invention is characterized in that a method of controlling the voltage applied to the TFT by controlling the connection timing by a digital value to cover the characteristic variation of the TFT is adopted in the present invention.

That is, a signal used for selecting an arbitrary pixel drive for gradation display of an electro-optical device using a display drive method having a display timing related to a time F for writing one screen and a time t for writing one pixel. The time t on one of the lines
Applying a selection signal to the reference signal having a voltage change having a period of and a signal line at an arbitrary timing within the time t;
It is characterized in that a voltage applied to the liquid crystal is determined and a gray scale can be displayed without changing the time F by actually applying a voltage to the pixel. In addition, this timing does not depend on data transfer, but a high-speed clock is applied to the driver IC itself mounted on the liquid crystal electro-optical device, and processing is performed in a signal processing portion. It is characterized in that high-speed control not limited to several tens of MHz, which was the limit of the above, can be performed.

FIG. 1 specifically shows a driving waveform of the electro-optical device according to the present invention. This is shown as an example in which the main drive waveform is put in the 2 × 2 matrix shown in FIG. Here, a half sine wave is used as the reference signal waveform. A sine wave 309 is applied to V _DD1 303 and V _DD2 304 corresponding to the scanning line direction.
310, and V _GG1 301, V
_GG2 302 is _supplied with a bipolar (hereinafter, referred to as "bipolar") signal. The part controlled by the digital value performs the timing of applying the bipolar signal. That is, 309,
The amount of charge and the potential accumulated at point A are determined by changing the timing of selecting a signal having a voltage change as shown at 310, and the potential 313 of the opposing electrode is arbitrarily determined so that the pixel and the liquid crystal can be charged. The magnitude of such an electric field is determined.

The timing at which the bipolar signal is applied is not determined by the transfer rate of the information signal, but is limited by the basic clock input to the driver IC directly connected to the liquid crystal electro-optical device in the configuration according to the present invention. That is, when a liquid crystal electro-optical device of 640 × 400 dots is considered, the driving frequency is 2
In order to calculate the number of gray scales using this numerical value, the drive frequency is determined by the product of the number of scanning lines, the number of frames, the bipolar pulse, and the number of gray scales. (400 × 60 × 2), so that the number of gray scales can be displayed up to 416 gray scales. It goes without saying that up to 832 gradations can be achieved by dividing the display screen into two. Examples will be described below, and further detailed description will be given.

[0015]

【Example】

Example 1 In this example, a wall-mounted television was manufactured using a liquid crystal display device having a circuit configuration as shown in FIG. The TFT at that time was made of polycrystalline silicon using laser annealing.

FIG. 6 shows an actual arrangement of electrodes and the like corresponding to this circuit configuration. For simplicity, only portions corresponding to 2 × 2 (or less) are described. FIG. 1 shows an actual drive signal waveform. For the sake of simplicity, the description will be made using signal waveforms in the case of a 2 × 2 matrix configuration.

First, a method for manufacturing a liquid crystal panel used in this embodiment will be described with reference to FIGS. FIG. 7 (A)
A silicon oxide film as a blocking layer 51 having a thickness of 1000 to 3000 mm is formed on a glass 50, such as quartz glass, which can withstand a heat treatment at an inexpensive temperature of 700 ° C. or less, for example, about 600 ° C. by using a magnetron RF (high frequency) sputtering method. To be manufactured. The process conditions are 100% oxygen atmosphere,
Film formation temperature 15 ° C, output 400-800W, pressure 0.5P
a. The film formation rate using quartz or single crystal silicon as a target was 30 to 100 ° / min.

A silicon film 52 was formed thereon by a plasma CVD method. The film formation temperature is from 250 ° C to 35
In this example, the temperature was set to 320 ° C., and monosilane (SiH
₄ ) was used. Not only monosilane (SiH ₄ ) but also disilane (Si ₂
H ₆ ) Alternatively, trisilane (Si ₃ H ₈ ) may be used. These were introduced into the PCVD apparatus at a pressure of 3 Pa, and 13.56 M
The film was formed by applying a high frequency power of Hz. At this time, an appropriate high frequency power is 0.02 to 0.10 W / cm ² , and in this example, 0.055 W / cm ² was used. The flow rate of monosilane (SiH ₄ ) was set to 20 SCCM, and the deposition rate at that time was about 120 ° / min. In order to control the threshold voltage (Vth) of the PTFT and the NTFT to be substantially the same, boron is used in a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm using diborane.
^-3 may be added during film formation. In addition, not only the plasma CVD but also a sputtering method and a low pressure CVD method may be used for forming the silicon layer to be a channel region of the TFT, and the method will be briefly described below.

When the sputtering method is used, the back pressure before the sputtering is set to 1 × 10 ⁻⁵ Pa or less, and single crystal silicon is used as a target in an atmosphere containing 20 to 80% of hydrogen mixed with argon. For example, argon was 20% and hydrogen was 80%.
The film formation temperature was 150 ° C., the frequency was 13.56 MHz, the sputter output was 400 to 800 W, and the pressure was 0.5 Pa.

In the case of forming by a reduced pressure gas phase method, 450 to 550 ° C. lower than the crystallization temperature by 100 to 200 ° C.
Disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ ) was supplied to the CVD apparatus at 30 ° C. to form a film. The reactor pressure is 30 ~
It was set to 300 Pa. The deposition rate was 50-250 ° / min. In order to control the threshold voltage (Vth) of the PTFT and NTFT substantially the same, boron may be added during the film formation at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ using diborane. .

The coatings formed by these methods are:
It is preferable that oxygen is 5 × 10 ²¹ cm ⁻³ or less. In order to promote crystallization, the oxygen concentration should be 7 × 10 ¹⁹ cm ⁻³ or less,
Preferably, it is desirable to be 1 × 10 ¹⁹ cm ⁻³ or less,
If the amount is too small, the leakage current in the off state increases due to the backlight, so this concentration was selected. If the oxygen concentration is high, crystallization is difficult, and the laser annealing temperature must be increased or the laser annealing time must be increased. Hydrogen is 4 × 10 ²⁰ cm ⁻³ and silicon 4 × 10 ²²
When compared with cm ^-3 , it was 1 atomic%.

In order to further promote crystallization of the source and the drain, the oxygen concentration is set to 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less.
Oxygen may be added only to the T channel formation region by ion implantation so as to have a concentration of 5 × 10 ^{20 to} 5 × 10 ²¹ cm ⁻³ .

By the above method, a silicon film in an amorphous state was formed to a thickness of 500 to 5000 °, in this embodiment, 1000 °.

Thereafter, as shown in FIG. 7B, a pattern was formed by opening only the source / drain regions of the photoresist 53 using the mask P1. A silicon film 54 serving as an n-type active layer was formed thereon by a plasma CVD method. The film was formed at a temperature of 250 ° C. to 350 ° C. In this embodiment, the temperature was set to 320 ° C., and monosilane (SiH ₄ ) and monosilane-based phosphine (PH ₃ ) having a concentration of 3% were used. These are introduced into the PCVD apparatus at a pressure of 5 Pa, and 13.56
The film was formed by applying a high frequency power of MHz. At this time, the high-frequency power is suitably 0.05~0.20W / cm ^2, in this embodiment using 0.120W / cm ^2.

The specific conductivity of the n-type silicon layer formed by this method was about 2 × 10 ⁻¹ [Ωcm ⁻¹ ]. The film thickness was 50 °. Thereafter, the resist 53 is removed by a lift-off method, and the source / drain region 5 is removed.
5, 56 were formed.

Using the same process, a p-type active layer was formed. The gas introduced at that time used monosilane (SiH ₄ ) and monosilane-based diborane (B ₂ H ₆ ) at a concentration of 5%. These were introduced into a PCVD apparatus at a pressure of 4 Pa, and high-frequency power of 13.56 MHz was applied to form a film.
At this time, the high-frequency power is suitably 0.05~0.20W / cm ^2, in this embodiment using 0.120W / cm ^2. The specific conductivity of the p-type silicon layer obtained by this method was about 5 × 10 ^-2 [Ωcm ^-1 ]. The film thickness was 50 °. Thereafter, source / drain regions 59 and 60 were formed by using a lift-off method as in the case of the N-type region.
Thereafter, the silicon film 52 was removed by etching using the mask P3 to form an N-channel type thin film transistor island region 63 and a P-channel thin film transistor island region 64.

Thereafter, the source, drain and channel regions were annealed with a laser using a XeCl excimer laser, and simultaneously the active layer was laser-doped. At this time, the laser energy has a threshold energy of 130 mJ / cm ^2.
mJ / cm ² is required. However, 220m from the beginning
When energy of J / cm ² or more is irradiated, hydrogen contained in the film is rapidly released, and the film is destroyed. For this purpose, it is necessary to first displace hydrogen and then melt it with low energy. In this embodiment, first 150 m
After purging hydrogen at J / cm ² , 230mJ
The crystallization was carried out at / cm ² .

Due to the annealing, the silicon film shifts from an amorphous structure to a highly ordered state, and a part of the silicon film exhibits a crystalline state. In particular, a region having a relatively high order in a state after the formation of silicon is particularly likely to be crystallized to be in a crystalline state. However, since the silicon existing between these regions is bonded to each other, silicon mutually pulls each other. When measured by laser Raman spectroscopy, a single crystal silicon peak 522 is obtained.
A peak shifted to a lower frequency side than cm ⁻¹ is observed. Its apparent particle size is 50 to 5 when calculated from the half width.
Although the area is 00 °, there are actually a large number of regions having high crystallinity and a cluster structure, and a film having a structure in which each cluster is bonded to each other by silicon (anchoring) can be formed. .

As a result, the coating exhibits a state substantially free of grain boundaries (hereinafter referred to as GB). Carriers can easily move from one cluster to another through anchored locations, resulting in higher carrier mobility than so-called GB polycrystalline silicon. That is, hole mobility (μh) = 10 to ²⁰⁰ cm ² /
VSec, electron mobility (μe) = 15 to 300 cm ² / V
Sec is obtained.

On this, a silicon oxide film was formed as a gate insulating film to a thickness of 500 to 2000 {for example, 1000}. This was made under the same conditions as those for forming the silicon oxide film as the blocking layer. During the film formation, a small amount of fluorine may be added to fix the sodium ions.

After this, 1-5 × 10 ²¹ cm of phosphorus is placed on the upper side.
^-3 silicon film or molybdenum (Mo), tungsten (W), MoSi ₂ or
A multilayer film with WSi ₂ was formed. This was patterned using a fourth photomask P4 to obtain FIG. NTFT
A gate electrode 66 for PTFT and a gate electrode 67 for PTFT were formed. For example, a channel length is 7 μm, and a gate electrode is 0.2 μm of phosphorus silicon, and 0.1 μm of molybdenum is placed thereon.
It was formed to a thickness of 3 μm.

When aluminum (Al) is used as a gate electrode material, the surface is anodically oxidized after patterning the aluminum with a fourth photomask 69, so that the self-alignment method can be applied. In addition, since the source / drain contact holes can be formed at positions closer to the gate, the characteristics of the TFT can be further improved by reducing the mobility and the threshold voltage.

Thus, a C / TFT can be manufactured without applying a temperature to 400 ° C. or more in all steps. Therefore, it is not necessary to use an expensive substrate such as quartz as a substrate material, and it can be said that the process is very suitable for the large-screen liquid crystal display device of the present invention.

In FIG. 8A, a silicon oxide film was formed on the interlayer insulator 68 by the above-mentioned sputtering method. This silicon oxide film is formed by LPCVD, optical CVD
Or a normal pressure CVD method. For example, 0.2-0.
6 μm thick, and then a fifth photomask P
5 was used to form an electrode window 79. After that, further, aluminum is formed on the entire surface to a thickness of 0.3 μm by a sputtering method, and leads 74 and contacts 73 and 75 are formed using a sixth photomask P6.
The surface was coated with an organic resin 77 for flattening, for example, a translucent polyimide resin, and the electrode drilling was performed again using the seventh photomask P7. Further, ITO (indium tin oxide) was formed on the entire surface by sputtering to a thickness of 0.1 μm, and a pixel electrode 71 was formed using an eighth photomask P8. This ITO is deposited at room temperature to 150 ° C.
Fulfilled by oxygen at 0-400 ° C. or by annealing in air.

The electrical characteristics of the obtained TFT are PTFT
And the mobility is 40 (cm ² / Vs), Vth is -5.9 (V),
NTFT has a mobility of 80 (cm ² / Vs) and a Vth of 5.0
(V).

One substrate for a liquid crystal electro-optical device manufactured according to the above method was obtained.

FIG. 6 shows the arrangement of the electrodes and the like of the liquid crystal display device. N-channel type thin film transistor and P
The channel type thin film transistor is connected to the first signal line 3 and the second signal line.
At the intersection with the signal line 4. A matrix configuration using such a C / TFT is provided. NT
The FT 13 is connected to the second signal line 4 via a contact at the input end of the drain 10, and the gate 9 is connected to the first signal line 3.
It is connected to. The output terminal of the source 12 is connected to the pixel electrode 17 via a contact.

On the other hand, the PTFT 22 has an input terminal of the drain 20 connected to the second signal line 4 via a contact, a gate 21 connected to the signal line 3, and an output terminal of the source 18 connected to the same terminal as the NTFT via a contact. Are connected to the pixel electrode 17. By repeating such a structure left, right, up and down, 6
A liquid crystal display device having a large pixel size of 40 × 480 or 1280 × 960 can be obtained. In this embodiment, 1920 ×
400. Thus, a first substrate was obtained.

FIG. 13 shows a method for manufacturing the other substrate. A 1 μm-thick polyimide film obtained by mixing a black pigment with polyimide was formed on a glass substrate by spin coating, and a black stripe 81 was formed using a ninth photomask P9. Thereafter, a polyimide resin mixed with a red pigment was formed into a film having a thickness of 1 μm by a spin coating method, and a red filter 83 was manufactured using a tenth photomask P10. Similarly, using the masks P11 and P12, the green filter 85 and the blue filter 86
Was prepared. During the production, each filter was fired at 350 ° C. in nitrogen for 60 minutes. After that, the leveling layer 89 was formed using a transparent polyimide, also using the spin coating method.

Thereafter, ITO (indium tin oxide) was formed on the entire surface to a thickness of 0.1 μm by sputtering, and a common electrode 90 was formed using a fifth photomask 91. This ITO is deposited at room temperature to 150 ° C.
Fulfilled by oxygen at 300 ° C. or annealing in air,
A second substrate was obtained.

A polyimide precursor was printed on the substrate by using an offset method, and baked at 350 ° C. for 1 hour in a non-oxidizing atmosphere such as nitrogen. Thereafter, a known rubbing method was used to modify the surface of the polyimide, and at least initially, a means for aligning liquid crystal molecules in a certain direction was provided.

Thereafter, the nematic liquid crystal composition was sandwiched between the first substrate and the second substrate, and the periphery was fixed with an epoxy adhesive. A drive IC having a TAB shape and a PCB having a common signal and potential wiring were connected to leads on the substrate, and a polarizing plate was attached on the outside to obtain a transmissive liquid crystal electro-optical device.

FIGS. 9 and 10 are schematic structural views of the electro-optical device according to the present embodiment. The rear lighting device 22 in which the three liquid crystal panels 220 obtained in the above steps are arranged with three cold cathode tubes
Installation was performed in combination with 1. Thereafter, a tuner 223 for receiving a television wave was connected to complete the electro-optical device. Compared to a conventional CRT-type electro-optical device, the device has a planar shape, so that it can be installed on a wall or the like.

Next, a peripheral circuit of the liquid crystal electro-optical device for completing the present invention will be described with reference to FIG.

A driving circuit 352 is connected to the information signal side wirings 350 and 351 connected to the matrix circuit of the liquid crystal electro-optical device.
Is connected. The drive circuit 352 has two parts when divided in a drive frequency system. One is a data latch circuit system 353 similar to the conventional driving method,
This is mainly composed of a basic clock CLK 355 for sequentially transferring data 356, and 1-bit to 12-bit parallel processing is performed. The other is a component according to the present invention, which comprises a clock 357, a flip-flop circuit 358, and a counter 360 according to the division ratio required for gradation display. The counter 360 generates a bipolar pulse generation timing corresponding to the gradation display data sent from the data latch system 353. Further, Δt is set at 361 between the exit of the latch circuit and the data line.
→ It has been found that the gradation display data can be more finely controlled by using the ROM table of sin θ conversion.

The features of the present invention are exactly these parts. By adopting two driving frequencies, the number of frames for screen rewriting can be changed without changing the number of frames.
This is to enable clear digital gradation display. It is possible to avoid the occurrence of flicker and the like due to the decrease in the number of frames.

The driving circuit 364 connected to the signal lines 363 and 362 on the scanning side controls the sine wave transmitted from the sine wave oscillating circuit 365 by the flip-flop circuit 366 of the clock CLK 367 and adds a selection signal.

As described above, grayscale display is made possible by digitally voltage-controlling the timing of cutting the sine wave on the scanning line side by the bipolar pulse on the information line side.

For example, 768 of 1920 × 400 dots,
When a normal analog gray scale display is performed on a liquid crystal electro-optical device in which 000 sets of TFTs are formed in a 300 mm square, 16 gray scale displays are limited due to a variation in TFT characteristics of about ± 10%. there were. However, when the digital gradation display according to the present invention is performed, since it is hard to be affected by the variation in the characteristics of the TFT elements, it is possible to display up to 64 gradations, and in the color display, a variety of 262,144 colors are provided. The display has been realized.

Embodiment 2 In this embodiment, a viewfinder for a video camera using a liquid crystal electro-optical device having a diagonal of 1 inch is manufactured and the present invention is implemented.

In this embodiment, a viewfinder is formed by forming a device using a high mobility TFT by a low-temperature process with a configuration of 387 × 128 pixels. FIG. 14 shows the arrangement of the active elements on the substrate of the liquid crystal display device used in this embodiment, and FIG. 15 shows the fabrication process showing the AA ′ section and the BB ′ section of FIG. In FIG. 15A, a blocking layer 5 is formed on a glass 50 which is inexpensive and can withstand heat treatment at 700 ° C. or less, for example, about 600 ° C. by using a magnetron RF (high frequency) sputtering method.
A silicon oxide film as No. 1 is formed to a thickness of 1000 to 3000 °. The process conditions were a 100% oxygen atmosphere, a film formation temperature of 15 ° C., an output of 400 to 800 W, and a pressure of 0.5 Pa. The film formation rate using quartz or single crystal silicon as a target was 30 to 100 ° / min.

A silicon film was formed thereon by LPCVD (low pressure gas phase), sputtering or plasma CVD. When formed by the reduced pressure gas phase method, the temperature is 1
450-550 ° C lower by 00-200 ° C, for example 530 ° C
CVD of disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ )
The film was supplied to the apparatus to form a film. Reactor pressure is 30 ~ 300
Pa. The deposition rate was 50-250 ° / min.
Threshold voltage (Vt) between PTFT and NTFT
In order to control substantially the same as in h), boron may be added at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ during film formation using diborane.

In the case of the sputtering method, the back pressure before the sputtering was set to 1 × 10 ⁻⁵ Pa or less, and single crystal silicon was used as a target in an atmosphere in which hydrogen was mixed with 20 to 80% of argon. For example, argon was 20% and hydrogen was 80%.
The film formation temperature was 150 ° C., the frequency was 13.56 MHz, the sputter output was 400 to 800 W, and the pressure was 0.5 Pa.

When a silicon film is formed by the plasma CVD method, the temperature is set to, for example, 300 ° C., and monosilane (SiH ₄ ) or disilane (Si ₂ H ₆ ) is used. These were introduced into a PCVD apparatus, and a high-frequency power of 13.56 MHz was applied to form a film.

The coatings formed by these methods are:
It is preferable that oxygen is 5 × 10 ²¹ cm ⁻³ or less. If the oxygen concentration is high, it is difficult to crystallize, and the heat annealing temperature must be increased or the heat annealing time must be increased.
If the amount is too small, the lamp is turned off by the backlight.
Current increases. Therefore, 4 × 10 ¹⁹ to 4 × 10 ²¹
The range was cm ⁻³ . Hydrogen is 4 × 10 ²⁰ cm ^-3 and silicon 4
It was 1 atomic% when compared with × 10 ²² cm ⁻³ .

After a silicon film in an amorphous state is formed to a thickness of 500 to 5000 °, for example, 1500 ° by the above method, heat treatment is performed at 450 to 700 ° C. for 12 to 70 hours in a non-oxide atmosphere at a medium temperature. For example, it was kept at a temperature of 600 ° C. in a hydrogen atmosphere. Since a silicon oxide film having an amorphous structure is formed on the surface of the substrate under the silicon film, no specific nucleus is present in this heat treatment, and the whole is annealed uniformly. That is, it has an amorphous structure at the time of film formation, and hydrogen is simply mixed therein.

By the annealing, the silicon film shifts from an amorphous structure to a highly ordered state, and a part of the silicon film exhibits a crystalline state. In particular, a region having a relatively high order in a state after the formation of silicon is particularly likely to be crystallized to be in a crystalline state. However, since the silicon existing between these regions is bonded to each other, silicon mutually pulls each other. When measured by laser Raman spectroscopy, a single crystal silicon peak 522 is obtained.
A peak shifted to a lower frequency side than cm ⁻¹ is observed. Its apparent particle size is 50 to 5 when calculated from the half width.
Although it is a microcrystal with a size of 00Å, there are actually a large number of regions with high crystallinity and a cluster structure, and a semi-amorphous structure film in which each cluster is bonded to each other by silicon (anchoring). Could be formed.

As a result, the coating exhibits a state substantially free of grain boundaries (hereinafter referred to as GB). Carriers can easily move from one cluster to another through anchored locations, resulting in higher carrier mobility than so-called GB polycrystalline silicon. That is, hole mobility (μh) = 10 to ²⁰⁰ cm ² /
VSec, electron mobility (μe) = 15 to 300 cm ² / V
Sec is obtained.

On the other hand, when the film is polycrystallized by high-temperature annealing at 900 to 1200 ° C. instead of annealing at the above-mentioned medium temperature, impurities in the film are segregated by solid phase growth from nuclei. , GB contain many impurities such as oxygen, carbon, and nitrogen, and have a high mobility in the crystal. However, a barrier is formed in the GB to hinder the movement of carriers there. As a result, a mobility of 10 cm ² / Vsec or more cannot be easily obtained. That is, in this embodiment, a silicon semiconductor having a semi-amorphous or semi-crystalline structure is used for such a reason.

In FIG. 15A, a silicon film is subjected to photoetching using a first photomask, and an NTFT region 13 (channel width 20 μm) is placed on the AA ′ cross-sectional side of the drawing to form a PTFT region. No. 22 was formed on the BB 'cross section side.

On top of this, a silicon oxide film was formed as a gate insulating film to a thickness of 500 to 2000 {for example, 1000}. This was made under the same conditions as those for forming the silicon oxide film as the blocking layer. During the film formation, a small amount of fluorine may be added to fix the sodium ions.

After this, 1-5 × 10 ²¹ cm of phosphorus is placed on the upper side.
^-3 silicon film or molybdenum (Mo), tungsten (W), MoSi ₂ or
A multilayer film with WSi ₂ was formed. This was patterned using a second photomask to obtain FIG. 15B. NTFT
And a gate electrode 21 for PTFT were formed. In this embodiment, the channel length for NTFT is 10 μm.
m, the channel length for the PTFT was 7 μm, and the gate electrode was formed of 0.2 μm of silicon-doped silicon and 0.3 μm of molybdenum thereon. In FIG. 15C, boron was added to the PTFT source 18 drain 20 by ion implantation at a dose of 1 to 5 × 10 ¹⁵ cm ⁻² . Next, as shown in FIG. 15D, a photoresist 61 was formed using a photomask. Phosphorous is used as a source 10 and a drain 12 for NTFT in a range of 1 to 5 × 10
^It was added by ion implantation at a dose of ¹⁵ cm ^-2 .

When aluminum (Al) is used as the gate electrode material, the surface is anodized after patterning with a second photomask, so that the self-alignment method can be applied. Since the source / drain contact hole can be formed at a position closer to the gate, the characteristics of the TFT can be further improved in terms of reduction in mobility and threshold voltage.

Next, annealing was performed again at 600 ° C. for 10 to 50 hours. The source 10 and the drain 12 of the NTFT and the source 18 and the drain 20 of the PTFT were formed as P ⁺ and N ⁺ by activating impurities. Channel formation regions 19 and 11 are formed below the gate electrodes 21 and 9 as semi-amorphous semiconductors.

In this way, a C / TFT can be manufactured without applying a temperature to 700 ° C. or more in all steps, even though it is a self-aligned system. Therefore, it is not necessary to use an expensive substrate such as quartz as a substrate material, and this is a process very suitable for the large pixel liquid crystal display device of the present invention.

In this embodiment, the thermal annealing is performed as shown in FIG.
(D) was performed twice. However, the annealing in FIG. 15 (A) is omitted depending on the required characteristics, and both of them are omitted in FIG. 15 (D).
The manufacturing time may also be reduced by using a tool. FIG.
In (E), a silicon oxide film was formed on the interlayer insulator 65 by the above-described sputtering method. This silicon oxide film may be formed by an LPCVD method, a photo CVD method, or a normal pressure CVD method. For example, it was formed to a thickness of 0.2 to 0.6 μm, and then a window 66 for an electrode was formed using a photomask. Further, as shown in FIG. 15 (F), aluminum is formed on the entire surface by sputtering, and leads 7 are formed.
After the contact 1 and the contact 72 were formed using a photomask, the surface was coated with an organic resin 69 for flattening, for example, a translucent polyimide resin, and the electrode drilling was performed again using the photomask.

An ITO (indium tin oxide film) was formed by a sputtering method so that the two TFTs had a complementary structure and their output terminals were connected to an electrode of one pixel of the liquid crystal device as a transparent electrode. . It was etched using a photomask to form the electrode 17. This I
TO was formed at room temperature to 150 ° C. and achieved by oxygen at 200 to 400 ° C. or in air. In this manner, the NTFT 13, the PTFT 22, and the electrode 17 of the transparent conductive film were formed on the same glass substrate 50. The obtained T
The electrical characteristics of FT are PTFT and the mobility is 20 (cm ² / V
s), Vth is -5.9 (V), and the mobility is 4 for NTFT.
0 (cm ² / Vs) and Vth were 5.0 (V).

According to the method as described above, one substrate for a liquid crystal device was manufactured. FIG. 14 shows the arrangement of the electrodes and the like of the liquid crystal display device. NTFT13 and PTF
T22 is provided at the intersection of the first signal line 3 and the second signal line 4. A matrix configuration using such a C / TFT is provided. The NTFT 13 is connected to the second signal line 4 via a contact at the input end of the drain 10, and the gate 9 is connected to the signal line 3 on which a multilayer wiring is formed. The output terminal of the source 12 is connected to the pixel electrode 17 via a contact.

On the other hand, the PTFT 22 has the input terminal of the drain 20 connected to the second signal line 4 via a contact, the gate 21 connected to the signal line 3, and the output terminal of the source 18 connected to the same terminal as the NTFT via a contact. Are connected to the pixel electrode 17. The present embodiment is configured by repeating such a structure left, right, up and down.

Next, as a second substrate, ITO (injection) was formed by sputtering on a substrate in which a silicon oxide film was laminated to a thickness of 2000 mm on a soda lime glass by sputtering.
Tin oxide film). This ITO is between room temperature and 15
Films were formed at 0 ° C. and achieved with oxygen at 200-400 ° C. or in air. A color filter was formed on this substrate using the same method as in "Example 1" to obtain a second substrate.

A polyimide precursor was printed on the substrate by using an offset method, and baked at 350 ° C. for 1 hour in a non-oxidizing atmosphere such as nitrogen. Thereafter, the surface of the polyimide was modified using a known rubbing method, and at least initially, means for aligning the liquid crystal molecules in a certain direction was provided to obtain first and second substrates.

Thereafter, the nematic liquid crystal composition was sandwiched between the first substrate and the second substrate, and the periphery was fixed with an epoxy adhesive. Since the pitch of the leads on the substrate was as fine as 46 μm, they were connected using the COG method. In this embodiment, a method is used in which gold bumps provided on an IC chip are connected with an epoxy-based silver-palladium resin, and the IC chip and the substrate are filled and fixed with an epoxy-modified acrylic resin for fixing and sealing. Was. Thereafter, a polarizing plate was attached on the outside to obtain a transmission type liquid crystal display device.

FIG. 16 shows driving waveforms used in this embodiment. A ramp waveform was used instead of the sine wave used in the first embodiment. The ramp wave has a simple structure, and the gradation data
It has an advantage in that conversion to t is easy.

FIG. 17 shows a configuration diagram of the viewfinder according to the present embodiment. The liquid crystal electro-optical device 370 manufactured by the above method and the cold cathode tube 371 having planar light emission were used.

For example, 384 × 128 dots 49, 15
Two sets of TFTs are placed in a 50 mm square (36 mm from a 300 mm square substrate).
When a normal analog gray scale display is performed on a liquid crystal electro-optical device prepared in a multi-panel display, 16 gray scale display is the limit because there is about ± 10% variation in TFT characteristics. . However, when the digital gradation display according to the present invention is performed, since it is hard to be affected by the characteristic variation of the TFT element, it is possible to display up to 128 gradations, and in the color display, 2,097,152 colors are various and delicate. Color display has been realized.

Embodiment 3 In this embodiment, a projection type image display device as shown in FIG.

In this embodiment, three liquid crystal electro-optical devices 20 are used.
1 is used to assemble a projection unit for a projection type image display device. Each of them has a configuration of 640 x 480 dots, and 307,200 in 4 inch diagonal.
A pixel was produced. The size per pixel was 127 μm square.

As a configuration of the projection type image display device, the liquid crystal electro-optical device 201 is composed of three primary colors of light, red and red.
It is installed separately for green and blue, and red filter 2
02, green filter 203, blue filter 204
, Reflector 205, prism mirrors 206, 207 and 1
A 50 W metal halide light source 208 and a focusing optical system 209 are provided.

The substrate of the liquid crystal electro-optical device used in the electro-optical device of this embodiment was a substrate having a matrix circuit of C / MOS configuration by using the same process as that manufactured in “Embodiment 2”. .

FIG. 19 schematically shows the structure. On the substrate 21
0, the fumaric acid-based polymer resin and the nematic liquid crystal were added to 65:
A mixture dissolved in xylene as a common solvent at a ratio of 35 was formed to a thickness of 10 μm by die casting. Thereafter, the solvent was removed in a nitrogen atmosphere at 120 ° C. for 180 minutes to form a liquid crystal dispersion layer 211. In this case, it was found that when the pressure was slightly reduced from the atmospheric pressure, the tact time could be reduced.

Thereafter, ITO (indium tin oxide film) was formed by a sputtering method to obtain a counter electrode 212. This ITO was formed at a temperature from room temperature to 150 ° C. Thereafter, using a printing method, a translucent silicone resin was applied to a thickness of 30 μm, and baked at 100 ° C. for 30 minutes to obtain a liquid crystal electro-optical device.

FIG. 20 shows the functional configuration of the driving IC used in this embodiment. The configuration on the information electrode side is the same as in "Example 1". The drive circuit 400 connected to the scan-side wirings 406 and 407 outputs the ramp wave transmitted from the ramp wave oscillation circuit 405 to the flip-flop circuit 4 of the clock CLK 408.
03 and 404, and a selection signal is added.

In this way, gradation display is enabled by digitally voltage-controlling the timing of cutting out the ramp wave on the scanning line side by the bipolar pulse on the information line side.

For example, 307 × 2 of 640 × 480 dots
When a normal analog gradation display is performed on a liquid crystal electro-optical device in which 00 sets of TFTs are formed in a 300 mm square,
Since there is about ± 10% variation in TFT characteristics,
Six gradation display was the limit. However, when the digital gradation display according to the present invention is performed, the display is hardly affected by the variation in the characteristics of the TFT elements, so that it is possible to display up to 256 gradations.
A variety of 16 colors can be displayed in subtle colors.

When displaying software such as a television image, for example, even a “rock” made of the same color has a slightly different color due to the degree of light corresponding to the minute depressions. When an attempt is made to display a color close to the natural colors, it is difficult to perform the display with 16 gradations, and it is not suitable for expressing these subtle depressions. With the gradation display according to the present invention, it is possible to impart these minute color changes.

This liquid crystal electro-optic can be used not only for the front projection television shown in FIG. 18, but also for the rear projection television.

[Embodiment 4] In this embodiment, an electro-optical device for a portable computer was manufactured using a reflective liquid crystal display device as shown in FIG.

The first substrate used in this example was manufactured in the same process as in Example 1. On the substrate 21
A mixture formed by dissolving a nematic liquid crystal obtained by mixing 15% of a fumaric acid-based polymer resin and a black pigment in xylene, which is a common solvent, in a ratio of 65:35 to a thickness of 10 μm using a die casting method. And then in a nitrogen atmosphere for 120
The solvent was removed at 180 ° C. for 180 minutes to form a liquid crystal dispersion layer 211.

Here, a flat display, which has been difficult to display using a dispersion type liquid crystal display because of the use of a black dye, shows a black color when light is scattered (when no electric field is applied) and a white color when transmitted (when an electric field is applied). It can be displayed and can be displayed like characters written on paper.

As a reverse structure, it is possible to express white when scattering and black when transmitting without mixing a black pigment. However, in this case, the back side shown below needs to be black. This is also possible to display like characters written on paper.

Thereafter, ITO (indium tin oxide film) was formed by a sputtering method to obtain a counter electrode 212. This ITO was formed at a temperature from room temperature to 150 ° C. Thereafter, using a printing method, a white silicon resin was applied to a thickness of 55 μm and baked at 100 ° C. for 90 minutes to obtain a liquid crystal electro-optical device.

[0092]

The present invention is characterized in that digital gray scale display is performed in contrast to the conventional analog gray scale display. As an effect, assuming, for example, a liquid crystal electro-optical device having a pixel number of 640 × 400 dots, it is very difficult to manufacture all the 256,000 TFTs without variation in characteristics. In consideration of mass productivity and yield, 16 gray scale display is considered to be the limit. However, in order to clarify the applied voltage level, a reference voltage value is input from the controller as a signal instead of an analog value in order to clarify the applied voltage level. By controlling the timing at which the reference signal is connected to the TFT by a digital value, the voltage applied to the TFT is controlled, thereby controlling the TFT.
The present invention is characterized in that a method for covering the characteristic variation of the present invention is adopted, and therefore, it is possible to display clear digital gradation.

Another advantage is that by using two driving frequencies, clear digital gradation display is possible without changing the number of frames for screen rewriting.
It is possible to avoid the occurrence of flicker and the like due to the decrease in the number of frames.

For example, 256,0 dots of 640 × 400 dots
When a normal analog gradation display is performed on a liquid crystal electro-optical device in which 00 sets of TFTs are formed in a 300 mm square,
Since there is about ± 10% variation in TFT characteristics,
Six gradation display was the limit. However, when the digital gradation display according to the present invention is performed, the display is hardly affected by the variation in the characteristics of the TFT elements, so that it is possible to display up to 256 gradations.
A variety of 16 colors can be displayed in subtle colors. In the case of displaying software such as television images, for example, even a “rock” made of the same color has a slightly different color due to its minute dents and the like. If you try to display something close to the colors of nature,
Difficulty is required for 16 gradations. With the gradation display according to the present invention, it is possible to impart these minute color changes.

[Brief description of the drawings]

FIG. 1 shows a driving waveform according to the present invention.

FIG. 2 shows electro-optical characteristics of a nematic liquid crystal.

FIG. 3 shows current-voltage characteristics of a TFT made of polysilicon and amorphous silicon.

FIG. 4 shows a matrix configuration according to the invention.

FIG. 5 shows a matrix circuit according to an embodiment.

FIG. 6 shows a planar structure of a device according to an example.

FIG. 7 illustrates a TFT process according to an embodiment.

FIG. 8 illustrates a TFT process according to an embodiment.

FIG. 9 shows a structure of a liquid crystal display device (television) according to the embodiment.

FIG. 10 shows a configuration of a liquid crystal display device (television) according to an embodiment.

FIG. 11 shows a system configuration of a drive circuit according to an embodiment.

FIG. 12 shows a frame gradation display according to a conventional example.

FIG. 13 shows a process of a color filter according to an example.

FIG. 14 shows a planar structure of a device according to an example.

FIG. 15 illustrates a TFT process according to an embodiment.

FIG. 16 shows another driving waveform according to the present invention.

FIG. 17 shows the structure of a viewfinder according to an embodiment.

FIG. 18 shows a structure of a front projection television according to an embodiment.

FIG. 19 shows a liquid crystal electro-optical device according to an example.

FIG. 20 shows a system configuration of a drive circuit according to an embodiment.

FIG. 21 shows a configuration of a portable personal computer according to an embodiment.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-156725 (JP, A) JP-A-63-200572 (JP, A) JP-A-63-136673 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) H01L 29/786 H01L 21/336 G02F 1/136 500

Claims (2)

(57) [Claims] A step of forming an island-shaped semiconductor layer including a channel region on an insulating surface; and a step of forming a source / drain region on the island-shaped semiconductor layer in an N-type or P-type conductive type. Forming a source / drain region by irradiating the semiconductor film with a laser beam; and forming a gate electrode made of aluminum on the channel region of the island-shaped semiconductor layer. Forming via a gate insulating film, and oxidizing the surface of the gate electrode by anodic oxidation
If, forming an interlayer insulator to cover the island-shaped semiconductor layer having the gate insulating film and a gate electrode formed thereon, one at least of the source and drain regions provided in the island-shaped semiconductor layer A step of forming a contact hole in the interlayer insulator on one of them, and a step of forming a wiring connected to at least one of the source and the source and the drain provided in the island-shaped semiconductor layer, Forming a thin film transistor, forming a flattening organic resin layer over the thin film transistor, and forming a pixel electrode connected to the thin film transistor on the flattening organic resin layer. Of manufacturing a semiconductor device. 2. The method according to claim 1, wherein the flattening organic resin layer is made of polyimide having a light transmitting property.