JPH08279618A - Manufacture of thin film semiconductor device - Google Patents

Abstract

PURPOSE: To markedly lessen a rear-side exposure time in a thin film semiconductor device manufacturing process and to restrain a thin film semiconductor device from dispersing in parasitic capacitance by a method wherein a thin polycrystalline silicon film is used as an active layer, and a thin bottom-gate type film transistor is formed through a rear-side exposure process. CONSTITUTION: A light shading gate electrode 2 is formed on the surface of a transparent substrate 1, a gate insulating film 3 is formed thereon, and furthermore a thin polycrystalline silicon film 4 is formed on the gate insulating film 3. Then, an insulating film 5 is formed on the thin polycrystalline silicon film 4, a photoresist film is formed thereon, and a photoresist pattern 6 is formed conforming to the gate electrode 2. Then, the photoresist pattern 6 is worked into a channel stopper 7 conforming to the gate electrode 2. Lastly, the thin polycrystaline silicon film 4 is dopes with impurities using the channel stopper 7 as a mask to provide a source region S and a drain region D. By this setup, a thin bottom-gate film transistor can be formed integrated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin film semiconductor device. More specifically, the present invention relates to a method of forming a bottom gate type thin film transistor having a polycrystalline silicon thin film as an active layer by backside exposure.

[0002]

2. Description of the Related Art A thin film semiconductor device in which thin film transistors are integrated is suitable for, for example, a drive substrate (active element substrate) of an active matrix type liquid crystal display panel, and has been actively developed. Amorphous silicon thin films and polycrystalline silicon thin films are typically used as active layers of thin film transistors. As a structure of the thin film transistor, a bottom gate type and a top gate type having a stagger structure have been mainly developed. All of these are field effect transistors. In the bottom gate type, a gate electrode is patterned on the surface of a transparent substrate, and then a semiconductor thin film to be an active layer is formed on the gate electrode via a gate insulating film. In the top gate type, a semiconductor thin film to be an active layer is first formed on a transparent substrate, and then a gate electrode is patterned on the transparent substrate through a gate insulating film. The bottom gate type is superior in reliability while the manufacturing process is complicated. That is, since the active layer is separated from the transparent substrate via the gate insulating film, adverse effects of contaminants contained in the substrate are small. On the other hand, while the top gate type has a relatively simple manufacturing process,
Inferior in reliability. That is, since the active layer is in direct contact with the substrate surface, it may be contaminated.

[0003]

A thin film transistor using an amorphous silicon thin film as an active layer generally adopts a bottom gate structure. In this case, backside exposure processing is performed to simplify the manufacturing process, and various patterning is performed by self-alignment using the underlying gate electrode as a mask. However, since the amorphous silicon thin film has not so good light transmittance, there is a drawback that the back surface exposure takes a long time. Although it depends on the material of the photoresist used, an exposure time of, for example, 1 to 2 minutes is required. In addition, since the mobility μ of a thin film transistor using an amorphous silicon thin film as an active layer is small, (μ = 0.2 to 0.8 cm
² / Vs) It is extremely difficult to form a thin film transistor for pixel electrode switching and its drive circuit on the same substrate. Therefore, in reality, only the screen portion including the pixel electrode and the thin film transistor for switching is formed on the transparent substrate, and the driving circuit is externally attached. For example, an external drive IC is connected to an active matrix type liquid crystal panel by TAB or the like. Even if the drive circuit is formed on the same substrate, in a normal bottom gate type thin film transistor, there is a large variation in the gate parasitic capacitance due to the accuracy of the photolithography process. As a result, the driving frequency is remarkably lowered and the image quality is deteriorated.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, an object of the present invention is to produce a bottom gate type thin film transistor having a polycrystalline silicon thin film as an active layer with high efficiency and high precision. To do. The following measures have been taken in order to achieve this object. That is, according to the present invention, the thin film semiconductor device is manufactured by the following steps. First, a first step of patterning a light-shielding gate electrode on the surface side of a transparent substrate is performed. Next, a second step of forming a gate insulating film on the gate electrode is performed. Subsequently, a third step of forming a polycrystalline silicon thin film, which has better light transmittance than the amorphous silicon thin film, on the gate insulating film is performed.
Further, a fourth step of forming an insulator on the polycrystalline silicon thin film is performed. After that, after forming a photoresist film on the insulator, the photoresist film is exposed from the back surface of the transparent substrate by self-alignment using the gate electrode as a mask to form a photoresist pattern aligned with the gate electrode. 5 steps are performed. Further, a sixth step of etching the insulator through the photoresist pattern and processing it into a channel stopper matching the gate electrode is performed. Finally, the polycrystalline silicon thin film is doped with impurities by self-alignment using the channel stopper as a mask to integrally form a bottom gate type thin film transistor.

Preferably, in the third step, a polycrystalline silicon thin film is formed on both the screen area defined on the transparent substrate and the peripheral area surrounding the screen area. In the seventh step, a thin film transistor for switching is formed in the screen area and a thin film transistor is formed in the peripheral area at the same time to form a circuit for driving the thin film transistor for switching. Then, an eighth step is performed to form a pixel electrode switched by the switching thin film transistor in the screen area. In this manner, a display thin film semiconductor device in which the pixel portion and the peripheral drive circuit portion are integrally formed is manufactured. When an active matrix type liquid crystal display device is assembled using this device as a drive substrate, the counter substrate on which the counter electrode is formed in advance is bonded to the transparent substrate through a predetermined gap, and liquid crystal is sealed in the gap. .

[0006]

According to the present invention, a gate electrode having a light-shielding property such as a metal film is patterned on the surface side of a transparent substrate, and a light insulating property is superior to that of an amorphous silicon thin film through a gate insulating film formed thereon. A polycrystalline silicon thin film is formed. A backside exposure process is performed by self-alignment using the underlying gate electrode as a mask to form a channel stopper on the polycrystalline silicon thin film. Since the back surface is exposed, the channel stopper is precisely aligned with the underlying gate electrode. Using the channel stopper as a mask, impurities are doped into the polycrystalline silicon thin film to form a bottom gate type thin film transistor. Since the polycrystalline silicon thin film has better light transmittance than the amorphous silicon thin film, the time required for the back surface exposure processing can be shortened and the manufacturing process can be made efficient. Since the channel stopper is patterned by self-alignment with respect to the gate electrode, the offset between the two can be minimized, and the parasitic capacitance that adversely affects the operating characteristics of the thin film transistor can be suppressed. Further, since the bottom gate type thin film transistor uses a polycrystalline silicon thin film, which is superior in mobility as compared with an amorphous silicon thin film, as an active layer,
Besides being used as a switching element for a pixel electrode, a peripheral drive circuit can be formed at the same time.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a process chart showing an example of a method of manufacturing a thin film semiconductor device according to the present invention. First, in step (A), a gate electrode 2 having a light-shielding property is patterned on the surface side of a transparent substrate 1 made of glass or the like. For example,
After forming a metal or alloy such as Mo or Ta by sputtering or the like, it is patterned into a predetermined shape by using photolithography and etching and processed into the gate electrode 2. Then, the gate insulating film 3 is formed on the gate electrode 2. For example, the gate insulating film 3 is formed by depositing SiO ₂ , SiN or the like by the CVD method. Alternatively, the surface of the gate electrode 2 made of metal may be anodized to be a part of the gate insulating film 3. Further, a polycrystalline silicon thin film 4 having a higher light transmittance than the amorphous silicon thin film is formed on the gate insulating film 3. For example, after forming an amorphous silicon thin film by the CVD method, excimer laser light is irradiated to once melt and recrystallize to convert into a high quality polycrystalline silicon thin film 4. After that, the insulator 5 is formed on the polycrystalline silicon thin film 4. For example, SiO ₂ is formed into a film having a predetermined thickness by the CVD method and the insulator 5 is provided. This insulator 5
After forming a photoresist film on the above, the photoresist is exposed from the back surface of the transparent substrate 1 by self-alignment using the gate electrode 2 as a mask to form a photoresist pattern 6 aligned with the gate electrode 2.

In step (B), the insulator 5 is etched through the photoresist pattern 6 to form a channel stopper 7 which is aligned with the gate electrode 2. The photoresist pattern 6 can be formed in a desired size by adjusting the back surface exposure intensity. By etching the insulator 5 using the photoresist pattern 6 as a mask, the dimensions of the channel stopper 7 can be freely controlled. If the amount of light entering the pattern of the gate electrode 2 by the diffraction of light by the backside exposure is ΔL, the width of the gate electrode 2 is W−2 × ΔL
Determines the channel length L. Generally, the smaller ΔL is, the smaller the gate parasitic capacitance of the thin film transistor becomes, and the higher performance operation characteristics can be obtained.

Finally, in step (C), the channel stopper 7
With the mask as a mask, the source region S and the drain region D are provided by doping (injecting) impurities into the polycrystalline silicon thin film 4 by self-alignment. As a result, bottom gate type thin film transistors (TFTs) are integrally formed. The implantation of impurities is performed by ion doping, for example.
In this method, after the source gas is ionized, the polycrystalline silicon thin film is doped with impurities by accelerating without mass separation. This ion doping method is suitable for manufacturing a large-area thin film semiconductor device. However, the present invention is not limited to this, and ion implantation can also be used as an impurity implantation method. In this method, after ionizing a source gas, mass separation is performed and acceleration is performed to inject ions of a desired impurity species into a polycrystalline silicon thin film in a beam shape. In this specification, all the implantation methods are collectively referred to as impurity doping. Then, the drain wiring 8D is connected to the drain region D to be patterned, and the source wiring 8S is connected to the source region S to be patterned.

FIG. 2 is a graph showing data comparing the polycrystalline silicon thin film and the amorphous silicon thin film in evaluating the accuracy of the back surface exposure process. The horizontal axis of this graph represents the exposure amount (J / cm ² ), and the vertical axis represents the amount ΔL (μm) that entered the gate pattern due to the diffraction of light by the backside exposure. When an amorphous silicon thin film (a-Si) is used for the active layer, it is necessary to set the film thickness dimension to a large value in order to obtain stable TFT characteristics in the process.
Degree is needed. On the other hand, when a polycrystalline silicon thin film (Poly-Si) is used for the active layer of the TFT, its thickness can be set to about 30 nm. Generally, ΔL is set to 1 in order to suppress the parasitic capacitance of the bottom gate type TFT.
It is necessary to control within μm. In this case, the back surface exposure amount through the a-Si film having a large light absorption coefficient is Poly-
This is about four times as large as that of a Si film, which requires a long exposure process.
Thus, when a bottom gate type TFT is formed by the backside exposure process, the active layer is formed from the a-Si film to the Poly-S.
By changing to the i film, the exposure amount can be remarkably reduced.

FIG. 3 is a process drawing showing another example of the method for manufacturing a thin film semiconductor device according to the present invention. The basic steps are the same as in the example shown in FIG. 1, and corresponding parts are designated by corresponding reference numerals to facilitate understanding. In this example, a pixel electrode and a thin film transistor for switching the pixel electrode are integrated and formed in a screen area set on the transparent substrate, and a circuit for driving the switching thin film transistor is integrated and formed in a peripheral area set on the same substrate. There is. The thin film semiconductor device having such a configuration is suitable as an active element substrate of an active matrix display device. First, in step (A), a gate electrode 2x is patterned on a screen area X set on the surface of the transparent substrate 1, and another gate electrode 2y is simultaneously formed on a peripheral area Y also set on the surface of the transparent substrate 1. Patterning is formed. These gate electrodes 2x and 2y are covered with a common gate insulating film 3. Further, a polycrystalline silicon thin film 4 is formed on the gate insulating film 3 over both the screen region X and the peripheral region Y surrounding the screen region X. Further, an insulator 5 made of SiO ₂ or the like is formed on the polycrystalline silicon thin film 4. After forming a photoresist film on the insulator 5, the photoresist is exposed from the back surface of the transparent substrate 1 by self-alignment using the gate electrodes 2x, 2y as a mask, and the photoresist pattern aligned with each gate electrode 2x, 2y. Create 6x and 6y. By properly adjusting the back surface exposure intensity, photoresist patterns 6x and 6y having desired dimensions can be formed.

Proceeding to step (B), the insulator 5 is etched using the photoresist patterns 6x and 6y as masks, and the channel stoppers 7 aligned with the gate electrodes 2x and 2y, respectively.
Process to x, 7y. Subsequently, in step (C), the polycrystalline silicon thin film 4 is patterned into an island shape to separate the element regions. Then, each channel stopper 7x, 7
Impurities are implanted into the polycrystalline silicon thin film 4 by self-alignment using y as a mask. As a result, a thin film transistor (TFT-SW) for switching is integrated and formed in the screen region X, and a thin film transistor (TFT-CKT) is also integrated in the peripheral region Y to form a circuit for driving the TFT-SW. Here, P (phosphorus) is used as an impurity.
Is ion-doped or ion-implanted to form N-channel TFT-SW and TFT-CK.
Forming a T. The portion of the polycrystalline silicon thin film 4 into which the impurity P is injected is the source region S of each thin film transistor.
And the drain region D. After that, the source wiring 8S is formed by connecting to the source region S of the TFT-SW. At the same time, the drain wiring 8D is formed by connecting to the drain region D of the TFT-CKT, and the source wiring 8S is formed by connecting to the source region S.

Finally, in step (E), the TFT-SW
And the TFT-CKT is covered with an interlayer insulating film 9 made of PSG or the like. A contact hole is opened in the interlayer insulating film 9 to partially expose the drain region D of the TFT-SW. A transparent conductive film made of ITO or the like is formed on the interlayer insulating film 9 by sputtering or the like, and then patterned into a predetermined shape by photolithography and etching to form the pixel electrode 10. The pixel electrode 10 is electrically connected to the drain region D of the TFT-SW and is switching-driven by the TFT-SW. In this way, by using the polycrystalline silicon thin film 4 as the active layer, it becomes possible to form the pixel section and the drive circuit section on the same transparent substrate 1. The thin film semiconductor device having such a structure is used for assembling an active matrix type display device. In this case, the counter substrate on which the counter electrode is formed in advance may be bonded to the transparent substrate 1 through a predetermined gap, and the liquid crystal may be sealed in this gap.

FIG. 4 is a schematic partial sectional view showing another example of a thin film semiconductor device manufactured according to the present invention. The basic structure is similar to that shown in FIG. 3E, and corresponding parts are designated by corresponding reference numerals to facilitate understanding. In the structure shown in FIG. 3E, only the N-channel TFT-CKT is formed in the peripheral region Y to form the drive circuit. On the other hand, in the example shown in FIG. 4, in the peripheral region Y, in addition to the N-channel type thin film transistor (Nch-TFT-CKT), the P-channel type thin film transistor (Pch-TFT-CKT) is integratedly formed. . Thus, in this example, the CMOS is used to form the drive circuit unit. In the case of this example, first, an N-type impurity (for example, P) is ion-doped, and the drain region D and the source region S of the TFT-SW and the Nch-TFT-CKT are formed.
A drain region D and a source region S are formed. Subsequently, a P-type impurity (for example, B) is selectively ion-doped to form the drain region D and the source region S of the Pch-TFT-CKT. After that, by patterning the source wiring 8S, the drain wiring 8D, and the pixel electrode 10, the pixel portion and the driving circuit portion can be formed on the same substrate 1. Also in this example, the corresponding channel stoppers 7x, 7yn, and 7yp are formed by the back surface exposure process using the gate electrodes 2x, 2yn, and 2yp as masks. Therefore, ΔL can be controlled within 1 μm by setting the exposure intensity to an appropriate value without depending on the alignment accuracy of the photolithography process that has been conventionally performed. Therefore, the parasitic capacitance of each TFT can be remarkably reduced, the variation in the parasitic capacitance can be suppressed, and the image quality can be improved.

FIG. 5 is a process drawing showing still another example of the method for manufacturing a thin film semiconductor device according to the present invention. Basically, it is similar to the example shown in FIG. 3, and corresponding parts are given corresponding reference numerals to facilitate understanding. In this example,
The LDD structure is adopted in order to suppress the leak current of the thin film transistor formed in the screen region X. In contrast,
The LDD region is not used for the thin film transistor formed in the peripheral region Y in order to secure a sufficient drive current. In this case, first, as shown in step (A), a photoresist pattern 11 is formed so as to overlap the channel stopper 7x. On the other hand, no photoresist pattern is overlaid on the channel stopper 7y. In this state, N-type impurities are implanted at high concentration into the polycrystalline silicon thin film 4. As a result, the drain region D and the source region S are formed. Next, in step (B), the used photoresist pattern 11 is removed. In this state, N-type impurities are ion-irradiated at a relatively low concentration and implanted into the region previously masked with the photoresist pattern 11. As a result, the thin film transistor (L
DD-TFT-SW) is formed. On the other hand, the peripheral area Y
Is a bottom gate type TFT-CK having a normal structure
T is formed.

Finally, FIG. 6 shows an example of an active matrix type display device assembled using the thin film semiconductor device manufactured according to the present invention. As shown
The display device has a panel structure including a transparent substrate 101, a counter substrate 102, and a liquid crystal 103 held between them. A pixel portion 104 and a driving circuit portion are integrated and formed on the transparent substrate 101. The drive circuit unit is the vertical drive circuit 105.
And a horizontal drive circuit 106. Further, a terminal portion 107 for external connection is formed on the upper end of the peripheral portion of the transparent substrate 101. The terminal portion 107 is connected to the vertical drive circuit 105 and the horizontal drive circuit 106 via the wiring 108. In the pixel portion 104, gate wirings 109 intersecting each other
And the signal wiring 110 is formed. Gate wiring 10
9 is connected to the vertical drive circuit 105, and the signal wiring 110 is connected to the horizontal drive circuit 106. A pixel electrode 111 and a thin film transistor 112 for switching and driving the pixel electrode 111 are formed at the intersection of the gate line 109 and the signal line 110. The drain region of the thin film transistor 112 is connected to the corresponding pixel electrode 111, the source region is connected to the corresponding signal line 110, and the gate electrode is connected to the corresponding gate line 109.

[0017]

As described above, according to the present invention, a polycrystalline silicon thin film is used as an active layer, and a back gate exposure process is used to form a bottom gate type thin film transistor. Since a polycrystalline silicon thin film, which is superior in light transmittance to an amorphous silicon thin film, is used, the back surface exposure time can be greatly shortened. The back surface exposure enables self-alignment with respect to the pattern of the gate electrode, and can suppress variations in parasitic capacitance of thin film transistors. Since back surface exposure can suppress variations in parasitic capacitance of thin film transistors, it is possible to form a pixel portion and a drive circuit portion on the same substrate, and it is possible to realize a compact and high quality active matrix liquid crystal display.

[Brief description of drawings]

FIG. 1 is a process chart showing an example of a method of manufacturing a thin film semiconductor device according to the present invention.

[FIG. 2] Offset amount ΔL of backside exposure amount and channel size
It is a graph which shows the relationship with.

FIG. 3 is a process drawing showing another example of the method for manufacturing a thin film semiconductor device according to the present invention.

FIG. 4 is a schematic view showing another example of the method for manufacturing a thin film semiconductor device according to the present invention.

FIG. 5 is a process drawing showing still another example of the method for manufacturing a thin film semiconductor device according to the present invention.

FIG. 6 is a schematic perspective view showing an example of an active matrix type liquid crystal display device assembled using the thin film semiconductor device manufactured according to the present invention.

[Explanation of symbols]

 1 Transparent Substrate 2 Gate Electrode 3 Gate Insulating Film 4 Polycrystalline Silicon Thin Film 5 Insulator 6 Photoresist Pattern 7 Channel Stopper

Claims (3)

[Claims] 1. A first step of patterning a gate electrode having a light-shielding property on the surface side of a transparent substrate, a second step of forming a gate insulating film on the gate electrode, and comparing with an amorphous silicon thin film. A third step of forming a polycrystalline silicon thin film having excellent light transmittance on the gate insulating film; a fourth step of forming an insulator on the polycrystalline silicon thin film; and a step of forming an insulator on the insulator. A fifth step of forming a photoresist pattern aligned with the gate electrode by exposing the photoresist by self-alignment from the back surface of the transparent substrate using the gate electrode as a mask after forming a photoresist film on the transparent substrate, and the photoresist pattern. The sixth step of etching the insulator through the groove to process it into a channel stopper that aligns with the gate electrode, and impurities by self-alignment using the channel stopper as a mask. 7. A method of manufacturing a thin film semiconductor device, which comprises performing a seventh step of integrally forming a bottom gate type thin film transistor by doping a polycrystalline silicon thin film. 2. The third step forms a polycrystalline silicon thin film over both the screen area defined on the transparent substrate and the peripheral area surrounding the transparent area, and the seventh step comprises switching for switching on the screen area. A circuit for driving the switching thin film transistor by forming a thin film transistor in the peripheral region at the same time as forming the thin film transistor is formed, and in addition, the eighth step is performed to form the pixel electrode switched by the switching thin film transistor in the screen region. The method for manufacturing a thin film semiconductor device according to claim 1, wherein the thin film semiconductor device is formed. 3. A first step of patterning a gate electrode having a light-shielding property on the surface side of a transparent substrate, a second step of forming a gate insulating film on the gate electrode, and comparing with an amorphous silicon thin film. A third step of forming a polycrystalline silicon thin film having excellent light transmittance on the gate insulating film; a fourth step of forming an insulator on the polycrystalline silicon thin film; and a step of forming an insulator on the insulator. A fifth step of forming a photoresist pattern aligned with the gate electrode by exposing the photoresist by self-alignment from the back surface of the transparent substrate using the gate electrode as a mask after forming a photoresist film on the transparent substrate, and the photoresist pattern. The sixth step of etching the insulator through the groove to process it into a channel stopper that aligns with the gate electrode, and impurities by self-alignment using the channel stopper as a mask. Seventh step of integrally forming a bottom gate type thin film transistor by doping the polycrystalline silicon thin film, and eighth step of connecting to the thin film transistor to form a pixel electrode
A method for manufacturing an active matrix type display device, comprising: a step of bonding a counter substrate on which a counter electrode is formed in advance to the transparent substrate through a predetermined gap, and filling a liquid crystal in the gap.