JPH1195259A - Thin film semiconductor device and method of manufacturing thin film semiconductor device - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To produce an array substrate for a polycrystalline silicon thin film transistor having a characteristic required for a thin film transistor in a pixel region and a driving circuit region in each region, and realize a high quality pixel display. It is an object to provide a display device. SOLUTION: When crystallizing amorphous silicon using laser annealing, the thickness of the underlayer 103 in the pixel region 10 and the drive circuit region 20 is changed, or a material having a different thermal conductivity is used. The pixel region and the drive circuit region are cooled at different cooling rates to form polycrystalline silicon regions having different crystallinities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor (
The present invention relates to an active matrix type liquid crystal display device using a switching element comprising a TFT.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have great advantages of thinness, light weight, and low power consumption. Therefore, they have been actively used for display devices of OA devices such as liquid crystal televisions, Japanese word processors and desktop personal computers. I have. At the same time, a liquid crystal display device using a thin film transistor or a thin film transistor array using polycrystalline silicon for an active layer has been actively developed for the purpose of improving the display device.

Conventionally, a thin film transistor using polycrystalline silicon for an active layer has been applied to a driving circuit of a pixel portion switching element by integrating a switching element and a thin film transistor in a pixel portion which is a display portion of a liquid crystal display device.
That is, a pixel unit thin film transistor for applying a voltage to a liquid crystal in a pixel, and application to a drive circuit unit thin film transistor for driving the pixel unit thin film transistor.

[0004] As the quality of the display is improved, the pixel portion thin film transistor and the drive circuit portion thin film transistor are required to have high performance. In particular, the pixel portion thin film transistor is required to have a low leakage current for holding the applied voltage, and the The circuit section thin film transistor is required to have high field-effect mobility for high-speed operation of the circuit.

In recent years, advances in process technology have made it possible to form high-performance polycrystalline silicon thin film transistors on insulating glass substrates at low process temperatures. In particular, when the crystallization process for obtaining polycrystalline silicon is changed from a solid phase growth method to, for example, an excimer laser annealing (hereinafter abbreviated as ELA) method, the field effect mobility is about 60 cm ² / V. 20 from s
0 cm ² / V. s is greatly improved. ELA
In the polycrystallization process by the method, the size of the crystal grain produced has a great influence on the characteristics of the thin film transistor. For example, polycrystalline silicon having a crystal grain size of 0.3 to 0.4 μm has a field effect mobility of about 200 cm ² / V. s.

[0006]

However, a thin film transistor having a high field-effect mobility tends to have a large leak current due to the ease of current flow, and is not suitable for a pixel portion thin film transistor requiring a low leak current. is there.

As described above, in a liquid crystal display device using polycrystalline silicon, a thin film transistor forming a pixel portion and a thin film transistor forming a driving circuit portion can be manufactured at the same time, but the required characteristics of the transistor are large. There is a difference.

On the other hand, the characteristics of polycrystalline silicon crystallized by laser annealing (the size of crystal grains that greatly affect the characteristics) greatly vary depending on the cooling rate of laser-irradiated amorphous silicon and the deviation of the depth of focus. .

According to the present invention, a polycrystalline silicon thin film transistor having specific characteristics required for a pixel portion thin film transistor and a drive circuit portion thin film transistor is manufactured at a specific position on an array substrate, and the polycrystalline silicon thin film transistor array substrate is used. Accordingly, it is an object to provide a liquid crystal display device which realizes high-quality pixel display.

[0010]

In order to solve the above-mentioned problems, a method of manufacturing a liquid crystal display device according to the present invention comprises an insulating glass substrate, a base layer formed on the substrate, and a base layer formed on the base layer. A liquid crystal display device comprising: a pixel region including a pixel portion polycrystalline silicon thin film transistor; and a drive circuit region including a drive circuit portion including a polycrystalline silicon thin film transistor formed on the base layer and driving the pixel region thin film transistor. When crystallizing amorphous silicon using laser annealing, by changing the thickness or thermal conductivity of the underlayer in the pixel region and the drive circuit region, the pixel region and the drive circuit are cooled at different cooling rates. The method is characterized in that the regions are cooled to form polycrystalline silicon regions having different crystallinities.

As a result, a thin film transistor having a small leak current (small field effect mobility) can be formed in the pixel region, and a thin film transistor having a high field effect mobility can be formed in the drive circuit region, thereby realizing high quality image display. , A liquid crystal display device can be manufactured.

Further, the liquid crystal display device of the present invention comprises: an insulating glass substrate; a base layer formed on the substrate; a pixel region including a pixel portion polycrystalline silicon thin film transistor formed on the base layer; A driving circuit portion formed on the ground layer and including a polycrystalline silicon thin film transistor for driving the pixel region thin film transistor, wherein a thickness of a base layer of the pixel region is larger than that of the base layer of the driving circuit region. It is characterized by being thick.

Further, the liquid crystal display device of the present invention comprises an insulating glass substrate, a base layer formed on the substrate, a pixel region including a pixel portion polycrystalline silicon thin film transistor formed on the base layer, and A driving circuit portion including a polycrystalline silicon thin film transistor formed on the ground layer and driving the pixel region thin film transistor, the base layer of the pixel region having a higher thermal conductivity than the driving circuit region. It is characterized by being formed of a material.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1A and 1B are diagrams showing a configuration of a thin film transistor array substrate in a liquid crystal display device obtained according to the present invention. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the line AA ′ of FIG. FIG.

The structure and manufacturing method of the liquid crystal display device according to the present invention will be described with reference to FIGS. FIG. 2 is a flowchart showing a manufacturing process of the liquid crystal display device according to the present invention.
Non-alkali glass, alkali glass, and the like can be used as the insulating substrate material. A nitride film 102 or an oxide film 103 is formed on the substrate 101 by a plasma CVD device. This is provided as an undercoat for preventing diffusion of impurities (alkali impurities such as Na) in the glass substrate 101.

As the undercoat, a single layer of a nitride film or a single layer of an oxide film can be used.
It can also be used as a laminate, such as a nitride film / oxide film or an oxide film / nitride film. In this embodiment, a case where a stacked structure of a nitride film and an oxide film is used for an undercoat will be described.

The nitride film has a high blocking performance against Na and the like, and it is expected that thickening the film almost completely prevents impurities from being mixed into the glass substrate. Can not.

In the experiments, as the thickness of the nitride film increases, the probability of occurrence of cracks at the time of film formation or in a later process increases, and the amount of warpage of the substrate due to stress becomes 0.3 mm or more, so that the suction by the transfer system is performed. It has a significant effect on the process such as an error and a defect at the time of bonding with the counter substrate. In this embodiment, an example in which the thickness of the nitride film 102 is about 500 Å will be described.

The oxide film 103 has a relatively small internal stress and can be made relatively thick. In this embodiment, an oxide film 103 of 6000 angstroms is formed on the nitride film 102 (step S1).

Region 1 corresponding to a pixel portion of oxide film 103
By masking 0 with a resist, etching is performed until the thickness of the oxide film in the drive circuit section region 20 becomes about 2000 angstroms, that is, patterning of the oxide film 103 is performed (step S2).

In this way, the configuration of the undercoat in the pixel portion forming region 10 and the drive circuit portion forming region 20 of the array substrate is made different. Then, an amorphous silicon film having a thickness of 500 to 1000 Å is formed on the undercoat (step S3). This amorphous silicon film can be formed by, for example, a thermal decomposition method of disilane using a low pressure CVD apparatus.

Subsequently, annealing is performed at 400 ° C. to 500 ° C. for 1 hour to desorb hydrogen in the amorphous silicon. This is because, when crystallizing the amorphous silicon, film breakage due to rapid desorption of hydrogen in the amorphous silicon during the laser irradiation used, that is, so-called ablation does not occur.

Then, a polycrystalline silicon film 104 is formed by laser irradiation using an excimer laser (step S4). This laser irradiation step is performed while irradiating a predetermined region of the amorphous silicon with a long beam and moving the substrate in the longitudinal direction of the long beam.

The silicon film melted by the laser irradiation solidifies while gradually lowering its temperature, and becomes polycrystalline by growing crystals. At this time, the cooling rates of the silicon in the pixel forming section 10 and the driving circuit forming section 20 are different depending on the configuration (film thickness) of the base film, and the crystallinity is different. In general, when the irradiation intensity during ELA is high, the grain size of the crystal grains is large, and when the cooling rate after ELA is high, the grain size of the crystal grains is small.

As shown in FIG. 1B, the cooling rate of the pixel section forming region 10 having a large SiO2 film thickness is high, and the cooling rate of the drive circuit forming section 20 having a small SiO2 film thickness is low. FIG.
2 shows the average grain size of the crystal grains of polycrystalline silicon crystallized by ELA. Irradiation influence is 320 (mJ / cm
^In the case of ² ), the crystal grains of about 0.15 μm are formed in the pixel portion forming region 10 having an oxide film thickness of 6000 Å, and the crystal grains having a thickness of 0.2 to 0.25 μm are formed in the drive circuit portion forming region having an oxide film thickness of 2,000 Å. Crystal grains were obtained.

Also, as in this embodiment, the pixel portion forming region 10
When the height is different between the drive circuit portion forming region 20 and the
A difference in the degree of crystallization occurs due to a difference in the depth of focus at the time of A, and a difference in crystallization due to a difference in the heat conduction state (cooling rate) can be promoted.

After forming polycrystalline silicon by laser annealing, in step S5, elements such as transistors are separated. Then, an oxide film 105 is formed by the plasma CVD method (Step S6). Subsequently, the gate electrode 106 is formed (Step S7). Using the gate electrode 106 as a mask, ion implantation of the source 107 and the drain 108 in the polycrystalline silicon layer 104 is performed in
This is performed according to the type (step S8).

The interlayer insulating film 109 is formed on the thin film transistor after the above steps (Step S9). Subsequently, an annealing process is performed for the purpose of reducing the resistance of the source / drain portion (Step S10).

Then, a contact hole is formed at a predetermined position (step S11), and a metal wiring 110 which is in ohmic contact with the ohmic junction is formed in the source portion 107 through the contact hole (step S12).
Further, the transparent electrode 111 is brought into contact with the drain portion 108 (Step S13), and is processed into a predetermined shape.

The thin film transistor array substrate thus manufactured is superposed on the counter substrate (step S1).
4) A liquid crystal display device is obtained by injecting liquid crystal (step S15) and laminating.

In this embodiment, the region of the nitride film 500 Å / oxide film 2000 Å and the nitride film 500 Å / oxide film 6 are used as the undercoat.
Although 000 Å was used, it is also possible to set a single-layer undercoat as described below, for example.

(1) Change the film thickness between the pixel portion and the drive circuit portion with the same type of film. (2) Form an undercoat with a different film and the same film thickness between the pixel portion and the drive circuit portion. (3) Drive with the pixel portion FIG. 4 shows the average crystal grain size of polycrystalline silicon when an oxide film of 2000 Å, 4000 Å and a nitride film of 2000 Å, 4000 Å are used for the undercoat. . It can be seen that polycrystalline silicon having different sizes (average particle diameters) can be formed by selecting the type and thickness of the base film.

As described above, the polycrystalline silicon regions having different crystallinity (crystalline state) are prepared for each region, and the optimum thin film transistors are formed in the pixel region and the drive circuit region, respectively. TFTs can be manufactured for the pixel portion and the drive circuit portion, respectively.
High-quality image display with high contrast can be realized.

[0034]

According to the present invention, the following effects can be obtained. 1) The characteristics of the transistors in the pixel portion and the drive circuit portion can be set by laser annealing of single energy irradiation.

2) The thin film transistor in the pixel portion can be formed by a thin film transistor having a small leak current, and the driving circuit portion can be formed by a thin film transistor having a high field effect mobility.

3) By using the nitride film for the undercoat, the contamination of impurities from the glass substrate is suppressed, and the reliability of the thin film transistor is improved. With the above effects,
TFTs having required characteristics can be manufactured in each of the pixel portion and the driving circuit portion, and high-quality image display with high contrast can be realized.

[Brief description of the drawings]

FIG. 1 is a plan view and a cross-sectional view of a liquid crystal display device according to the present invention.

FIG. 2 is a process chart showing a thin film transistor array substrate manufacturing process in the liquid crystal display device of the present invention.

FIG. 3 is a diagram showing an average grain size of polycrystalline silicon in different regions of an undercoat.

FIG. 4 is a diagram showing an average grain size of polycrystalline silicon depending on the type of undercoat.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Pixel area 20 ... Drive circuit area 101 ... Glass substrate 102 ... SiN (undercoat) 103 ... SiO2 (undercoat) 104 ... Polysilicon 105 ... Gate oxide film 106 ... Gate metal 109 ... Interlayer insulating film 110 ... Signal line 111 ... interlayer insulating film 112 ... transparent electrode

Claims (7)

[Claims] An insulating glass substrate; a base layer formed on the substrate; a pixel region including a pixel portion polycrystalline silicon thin film transistor formed on the base layer; and a pixel region formed on the base layer; A driving circuit portion for driving the pixel region thin film transistor, comprising a driving circuit region including a polycrystalline silicon thin film transistor, wherein a thickness of a base layer of the pixel region is larger than a thickness of the base layer of the driving circuit region. Semiconductor device. 2. An insulating glass substrate, a base layer formed on the substrate, a pixel region including a pixel portion polycrystalline silicon thin film transistor formed on the base layer, and a pixel region formed on the base layer, A driving circuit portion for driving the region thin film transistor, comprising a driving circuit region including a polycrystalline silicon thin film transistor, wherein the underlying layer of the pixel region is formed of a material having a higher thermal conductivity than the driving circuit region. Characteristic thin film semiconductor device. 3. An insulating glass substrate, a base layer formed on the substrate, a pixel region including a pixel portion polycrystalline silicon thin film transistor formed on the base layer, and a pixel region formed on the base layer, A driving circuit portion for driving the region thin film transistor, comprising a driving circuit region including a polycrystalline silicon thin film transistor, wherein a relative step is provided between base layers of the pixel region and the driving circuit region. Thin film semiconductor device. 4. A first method for forming a base layer on an insulating glass substrate.
A second step of forming an amorphous silicon layer on the underlayer, and a third step of crystallizing the amorphous silicon layer using laser annealing to form a polycrystalline silicon layer. A fourth step of forming a gate oxide film, a fifth step of forming a gate electrode and processing it into a predetermined shape, and using the gate electrode as a mask in a self-aligned manner with the gate electrode. Forming a source / drain ohmic junction in the crystalline silicon layer; and forming a pixel region including the pixel portion thin film transistor array and a drive circuit portion thin film transistor array for driving the pixel portion thin film transistor array. In the method for manufacturing a thin film semiconductor device, the method further includes a step of forming a drive circuit region including the step of forming the underlayer. The way the different thermal conducting state in the pixel region and a driver circuit region, a thin film semiconductor device manufacturing method characterized by forming the base layer in step. 5. A first step of forming the underlayer, wherein in the third step of crystallizing the amorphous silicon, underlayers having different thicknesses are formed in the pixel region and the drive circuit region. 5. The method for manufacturing a thin film semiconductor device according to claim 4, wherein: 6. The first step of forming the underlayer is performed using a material having different thermal conductivity in the pixel region and the drive circuit region in the third step of crystallizing the amorphous silicon. 5. The method according to claim 4, wherein a formation layer is formed. 7. A first step of forming the underlayer so that a focal depth of the laser annealing is shifted between the pixel region and the drive circuit region in the third step of crystallizing the amorphous silicon. 5. The method according to claim 4, further comprising the step of providing a relative step between the underlying layers of the pixel region and the drive circuit region.