JP3265838B2 - Method for manufacturing thin film transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin film transistor, particularly a thin film transistor for driving a liquid crystal display used in a liquid crystal display device for displaying images.

[0002]

2. Description of the Related Art CRTs or cathode ray tubes, which have been put into practical use as displays for television receivers since about 1955, have expanded their uses, and have been used for televisions, computers, measuring instruments, etc. for almost 40 years for both consumer and industrial use. Various display devices have been able to maintain the leading role. However, with the increasing demand for portable electronic devices in the 1980's, light and thin words became popular, leading to radio, radio and cassette players, headphone stereos, etc. Competition has intensified.

On the other hand, the displays are also light and thin, and are characterized by a plasma display (PDP) and an electrochromic display (EC) using DC gas discharge.
D), a liquid crystal display (LCD) and others utilizing electrophoresis have been actively researched and developed for practical use. In particular, liquid crystal displays have rapidly solidified their use as desktop electronic calculators that have begun to be put into practical use at the same time, that is, display units of calculators and display panels of digital watches.
In addition, TFT liquid crystal displays, which appeared in 1990, have become thinner with the development of advanced color filter manufacturing technology.
In addition to light weight and low power consumption, the number of display colors, definition, and screen dimensions have come close to cathode ray tubes in terms of display capabilities.

Since then, the range of applications of liquid crystal displays has been expanded, and thin and lightweight displays are now mainly used for various displays such as portable small color television receivers, laptop computers, notebook personal computers, and in-vehicle navigator systems. Used as a device. Recently, it has been applied to small and high-definition displays such as viewfinders and projection displays (projectors) of small home video cameras.

In such a liquid crystal color television receiver and a liquid crystal viewfinder, an active matrix type liquid crystal display device using a thin film transistor (hereinafter, referred to as a TFT) made of amorphous silicon or polycrystalline silicon capable of obtaining high image quality is used. Used
These screens consist of tens of thousands to hundreds of thousands of pixels,
It must be manufactured in a state close to defect-free by extremely advanced manufacturing technology.

[0006] In the TFTs constituting hundreds of thousands of pixels formed without defects as described above, in order to prevent contamination due to ionic contamination or moisture penetration from outside, which causes leakage or corrosion and disconnection of aluminum wiring and the like. Requires a surface protection film. Conventionally, a film thickness of 500
Vapor-phase growth of a silicon nitride film of about 1000 nm at a low temperature has been performed. On the other hand, TFTs for driving the pixels formed in this manner are required to increase the on-current and reduce the off-current in order to improve display quality. Therefore, in general, this TF
The characteristics of the TFT were recovered by treating the T substrate at 380 ° C. for 30 minutes in a hydrogen gas atmosphere.

[0007]

However, this silicon nitride film has a problem that cracks occur at the temperature at the time of heat treatment in hydrogen gas which is performed in the last step of the TFT manufacturing method to recover the characteristics of the TFT. I was In particular, a heat treatment in a hydrogen gas at a high temperature is advantageous for recovering the characteristics of the TFT, and it is preferable to perform the heat treatment at a temperature of 400 ° C. or more. There has been a problem that a role as a protective film cannot be fulfilled.

[0008] The present invention is to solve the above problems,
At a relatively high processing temperature of the heat treatment in hydrogen gas performed to further improve the characteristics of the TFT,
It is an object of the present invention to provide a method of manufacturing a thin film transistor having a surface protective film capable of protecting various types of external contamination without causing a failure such as a crack in the protective film formed on the surface of the FT.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for forming a polycrystalline silicon film on a quartz substrate and then selectively leaving a polycrystalline silicon film to be a thin film transistor forming region; Forming a gate electrode made of an oxide film and a polycrystalline silicon film, forming a drain region and a source region of the thin film transistor by ion implantation, forming an interlayer insulating film such as a silicon oxide film on the entire surface, Forming a contact hole reaching the drain region and the source region in the insulating film, forming a conductive film containing aluminum as a main component over the entire surface, and then selectively etching to form an electrode wiring; The internal stress of the silicon nitride film for protecting the thin film transistor component is 3.0 × 10 ⁹
After being formed to have a compressive stress in the range of 4.2 × 10 ⁹ dynes / cm ² , the compressive stress becomes 1.6 × 10 ⁹ to
A heat treatment in a hydrogen gas at a temperature in the range of 400 to 500 ° C. so as to have a tensile stress of 2.7 × 10 ⁹ dynes / cm ² .

[0010]

Therefore, according to the present invention, the polycrystalline silicon film formed on the quartz substrate is used as an active region, and the internal stress is 3.0 × 10 ^{9 to} 4.2 × 1 on the TFT provided with the electrode wiring.
0 ⁹ was formed by a plasma CVD device, a silicon nitride film having a compressive stress in the range of dynes / cm ^2, tensile wherein compressive stress of 1.6 × 10 ⁹ ~2.7 × 10 ⁹ dynes / cm ² Stress This TFT is set to 400 to 500 so that
Heat treatment in hydrogen gas at a temperature in the range of ℃ changes the compressive stress generated inside the silicon nitride film into an appropriate tensile stress. Therefore, the function as a surface protection film can be maintained without generating cracks or the like in the silicon nitride film. Further, since the heat treatment can be performed at a higher temperature than in the related art, the characteristics of the TFT can be recovered more effectively than in the related art.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a method for manufacturing a thin film transistor according to the present invention will be described below with reference to the drawings.

FIG. 1 is a process sectional view showing the manufacturing method of the embodiment. As shown in FIG. 1A, after a polycrystalline silicon film having a thickness of about 100 nm is formed on a transparent insulating substrate 1 made of quartz or the like, a polycrystalline silicon film 2 serving as a TFT formation region is selectively dried. Leave by etching.

Next, as shown in FIG. 1B, a gate oxide film 3 and a gate electrode 4 made of a polycrystalline silicon film are formed. Next, as shown in FIG. 1C, a drain region 5 and a source region 6 on the polycrystalline silicon film 2 are formed by ion implantation.

Next, as shown in FIG. 1D, after covering the entire surface with an interlayer insulating film 7 such as a silicon oxide film,
As shown in (e), a contact hole 8 reaching the drain region 5 and the source region 6 is provided in the interlayer insulating film 7, and a conductive film containing aluminum as a main component is formed on the entire surface, and then selectively etched. The electrode wiring 9 is formed.

Next, the TFT thus constructed
As shown in FIG. 1F, a silicon nitride film 10 is formed as a surface protection film on the entire surface of the substrate. The inside of the silicon nitride film formed at this time has a compressive stress of 3.0 × 10 ⁹
An internal stress in the range of ４4.2 × 10 ⁹ dynes / cm ² is formed. Note that a silicon oxide film may be formed below the silicon nitride film 10.

Next, as shown in FIG.
The TFT according to the present embodiment is completed by subjecting the quartz substrate 1 on which T is formed to a heat treatment in a hydrogen gas at a temperature in the range of 400 to 500 ° C.

Next, the internal stress of the silicon nitride film in this embodiment will be described. The internal stress was measured by measuring the amount of deformation (warpage) of the quartz substrate 1 with a flatness tester and calculating from the following equation (1).

Δ _f = 4 · E · D ² · δ / 3 (1-ν) · d · L ² (1) Here, the equation (1) represents the deformation amount δ and the internal stress δ _f . L is the interval at which the deformation amount δ is measured, d is the thickness of the silicon nitride film, D is the thickness of the quartz substrate, ν is the Poisson's ratio, E
Is the Young's modulus. The following relational expression (2) was obtained by substituting the numerical values of the materials used for the measurement into the expression (1).

Δ _f = 3.69 × 10 ¹¹ · δ (2) Next, after formation of the silicon nitride film 10 and at a temperature of 450
Silicon nitride film 10 after heat treatment in hydrogen gas at 100 ° C.
Table 1 shows the measurement results of the internal stresses of Table 1, and Table 2 shows a conventional example for reference. In Tables 1 and 2, the amount of deformation of the minus sign indicates a concave deformation, and the internal stress of the minus sign means a compressive stress.

[0020]

[Table 1]

[0021]

[Table 2]

As can be seen from Table 1, the silicon nitride film 1
The internal stress immediately after forming 0 is 3.0 × 10 ^{9 to} 4.2 ×
Although it has a compressive stress of 10 ⁹ dynes / cm ² , the polarity of the stress is reversed after heat treatment in hydrogen gas, and 1.6 × 1
0 ⁹ ~2.7 × 10 ⁹ has been changed to a tensile stress dyne / cm ^2.

On the other hand, in the conventional example shown in Table 2, the internal stress after the formation of the silicon nitride film is 2.7 × 10 ⁹ to 2.2.
8 × 10 ⁹ dynes / cm ² tensile stress
This is because the tensile stress is further increased by the heat treatment in a high-temperature hydrogen gas.
0 ^{10 to} 11.1 × 10 ¹⁰ dynes / cm ² . This large tensile stress causes the conventional silicon nitride film to crack.

As described above, according to the above embodiment, the internal stress at the time of forming the silicon nitride film is 3.0 × 10 ^{9 to} 4.2 ×.
By controlling so as to have a compressive stress in the range of 10 ⁹ dynes / cm ² , even if the heat treatment in hydrogen gas is performed at a temperature in the range of 400 to 500 ° C., an excessive tensile stress as in the related art is generated inside. It does not occur, so that the TFT can be protected from obstacles such as cracks.

If the compressive stress after the formation of the silicon nitride film is less than 2.0 × 10 ⁹ dynes / cm ² , the tensile stress after the heat treatment in hydrogen gas becomes excessive, causing the silicon nitride film to crack. Becomes When the compressive stress exceeds 5.0 × 10 ⁹ dynes / cm ² , cracks do not occur in the silicon nitride film, but the warp of the transparent insulating substrate such as a quartz substrate becomes excessive, so that during the automatic transfer and the exposure process, Problems occur, and in extreme cases, the transparent insulating substrate may crack.

If the heat treatment temperature during the heat treatment in hydrogen gas is lower than 400 ° C., the characteristics of the TFT are not sufficiently recovered.
If the temperature exceeds 00 ° C., cracks occur in the silicon nitride film.

In this embodiment, an example of a silicon nitride film has been described. However, the present invention is not particularly limited to this range, and similar effects can be expected in a silicon oxynitride film.

[0028]

According to the present invention, a TFT provided with an electrode wiring using a polycrystalline silicon film formed on a quartz substrate as an active region is provided.
After forming a silicon nitride film having a compressive stress in the range of 3.0 × 10 ^{9 to} 4.2 × 10 ⁹ dynes / cm ² by a plasma CVD apparatus on the silicon nitride film, the compressive stress becomes 1.6. Since the TFT is heat-treated in a hydrogen gas at a temperature within a range of 400 to 500 ° C. so as to have a tensile stress of × 10 ^{9 to} 2.7 × 10 ⁹ dynes / cm ² , cracks or the like may occur in the silicon nitride film. Therefore, the function as a surface protective film can be maintained without causing the heat treatment, and the heat treatment can be performed at a higher temperature than in the related art, so that the effect of restoring the characteristics of the TFT can be further improved as compared with the related art. What
The internal stress is 2.0 × 10 ^{9 to} 5.0 × 10 ⁹ dynes /
The same effect can be obtained even when the area is in the range of cm ² .

[Brief description of the drawings]

FIGS. 1A to 1G are process cross-sectional views illustrating a method for manufacturing a thin film transistor according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 quartz substrate (transparent insulating substrate) 2 polycrystalline silicon film 3 gate oxide film 4 gate electrode 5 drain region 6 source region 7 interlayer insulating film 8 contact hole 9 electrode wiring 10 silicon nitride film

────────────────────────────────────────────────── (5) References JP-A-63-132433 (JP, A) JP-A-63-165 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 29/786 H01L 21/336 H01L 21/318

Claims (1)

(57) [Claims] 1. A step of forming a polycrystalline silicon film on a quartz substrate and then selectively leaving a polycrystalline silicon film to be a thin film transistor forming region, and a step of forming a gate electrode comprising a gate oxide film and a polycrystalline silicon film. Forming a drain region and a source region of the thin film transistor by ion implantation, forming an interlayer insulating film such as a silicon oxide film over the entire surface, and forming a contact hole reaching the drain region and the source region in the interlayer insulating film. Forming a conductive film containing aluminum as a main component over the entire surface and then selectively etching to form an electrode wiring; and forming a silicon nitride film for protecting the thin film transistor component including the electrode wiring. Its internal stress
After being formed by a plasma CVD apparatus so as to have a compressive stress in a range of 3.0 × 10 ^{9 to} 4.2 × 10 ⁹ dynes / cm ² , the compressive stress is 1.6 × 10 ^{9 to} 2.7 ×. 10 ⁹
400 to 5 so that a tensile stress of dyne / cm ² is obtained.
Performing a heat treatment in a hydrogen gas at a temperature in the range of 00 ° C.