JPH10303427A - Preparation of semiconductor device and preparation of substrate for semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an adverse effect of impurity in a substrate on the operation of a semiconductor element formed on the substrate, by transforming an amorphous silicon film to a thermally oxidized film by heating in an oxidizing atmosphere, and forming a thin film semiconductor element on the thermally oxidized film. SOLUTION: An amorphous silicon film 102 to be the base of an underlying film is formed to a thickness of 30 nm on a quartz substrate 101 by a low pressure heat assisted CVD method. Then, the amorphous silicon film 102 is transformed to a thermally oxidized film 103 by carrying out heating in an oxygen atmosphere at 950 deg.C. In this case, the thickness of the thermally oxidized film is substantially doubled to about 60 nm. Then, an amorphous silicon film is formed on the thermally oxidized film 103 by a low pressure heat assisted CVD method, and the amorphous silicon film is crystallized by heating. In this case, the crystallized silicon film is obtained by carrying out heating in a nitrogen atmosphere at 850 deg.C for six hours. Since the fine thermally oxidized film 103 is formed as the underlaying film, diffusion of impurity from the quartz substrate 101, particularly, movement of OH groups, can be restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD [0001] The invention disclosed in the present specification is:
The present invention relates to a semiconductor device using a quartz substrate. In particular, it relates to a method of using a quartz substrate.

[0002]

2. Description of the Related Art An amorphous silicon film is formed on a glass substrate,
There is known a technique of crystallizing it to form a crystalline silicon film, and further using this silicon film to manufacture a thin film transistor (referred to as a TFT).

[0003] As a method of obtaining a crystalline silicon film, there are methods by heating and irradiation with laser light, but the method by heating is advantageous for stably obtaining predetermined characteristics.

However, the method of obtaining a crystalline silicon film by heating requires a high temperature such as 800 ° C. or 900 ° C., and cannot use a general glass substrate.

[0005] This is 80% for a general glass substrate.
When processing at a temperature such as 0 ° C or 900 ° C,
This is because deformation and expansion / contraction of the substrate become apparent.

In this case, it is necessary to use quartz as the substrate. However, high purity is required for use as a substrate constituting a semiconductor device. And
Such quartz substrates are generally expensive.

There are many ranks for quartz substrates. And those with low ranks are reasonably cheap.

However, a quartz substrate having a low rank contains a high concentration of OH groups in the substrate, and the OH groups affect the operation of a semiconductor device formed on the substrate. For example,
This causes the threshold value of the TFT to shift to the minus side.

In general, OH groups in a quartz substrate cause unstable operation of a semiconductor device manufactured on the substrate and cause variations in element characteristics.

According to the present inventors, the OH concentration in the low-grade quartz substrate is lower than the OH concentration in the high-grade quartz substrate.
It has been measured that the concentration is at least 15 times higher than the concentration.

[0011]

SUMMARY OF THE INVENTION An object of the present invention disclosed in the present specification is to solve a problem that occurs when a quartz substrate having a low rank as described above is used.

[0012]

Means for Solving the Problems One of the inventions disclosed in this specification is a step of forming an amorphous silicon film on at least a main surface of a substrate and a heat treatment in an oxidizing atmosphere. A step of transforming the crystalline silicon film into a thermal oxide film; and a step of forming a thin film semiconductor element on the thermal oxide film.

As a substrate, a quartz substrate can be typically used. In particular, the utility of the invention can be obtained when a low-grade quartz substrate is used.

At least the main surface is a surface on which a thin film semiconductor element (for example, a thin film transistor) is formed. As shown in the embodiment, an amorphous silicon film may be formed on the back surface of the substrate, and the amorphous silicon film may be transformed into a thermal oxide film.

As the oxidizing atmosphere, (1) an atmosphere of 100% oxygen. (2) An atmosphere containing a halogen element in an oxygen atmosphere. (3) An atmosphere containing oxygen and having an oxidizing action. And the like. Normal pressure is usually used as the pressure of the atmosphere. However, the pressure may be reduced or the pressure may be increased. Further, the water may be introduced.

The thin film semiconductor device can be formed directly on the thermal oxide film. However, a structure in which an insulating film is further formed may be employed. Alternatively, a structure in which a film having high thermal conductivity such as a carbon film or an aluminum nitride film is provided as a heat dissipation layer and a semiconductor element is formed thereover may be used.

According to another aspect of the present invention, there is provided a process of forming an amorphous silicon film on at least a main surface of a substrate, and transforming the amorphous silicon film into a thermal oxide film by heat treatment in an oxidizing atmosphere. And a method for manufacturing a substrate for a semiconductor device.

The invention disclosed in this specification is useful not only in a process for manufacturing a semiconductor device but also as a method for manufacturing a substrate used in a semiconductor device.

In this specification, an example in which a quartz substrate is used as a substrate is shown, but a substrate having heat resistance enough to withstand the formation of a thermal oxide film can be used other than the quartz substrate.

As the substrate, a low-grade single-crystal silicon substrate (single-crystal silicon wafer) or a polycrystalline silicon substrate (polycrystalline silicon wafer) can be used.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An amorphous silicon film 102 is formed on a quartz substrate 101 containing a high concentration of low-grade OH groups.

The amorphous silicon film 102 is transformed into a thermal oxide film 103 by a heat treatment in an oxygen atmosphere.

Then, a TFT is formed on the thermal oxide film 103. By doing so, the characteristics of the TFT are changed to OH in the quartz substrate.
The group can be prevented from being adversely affected.

[0024]

【Example】

[Embodiment 1] FIG. 1 shows a manufacturing process of this embodiment. First, as shown in (A), an amorphous silicon film 102 serving as a base of a base film is formed on a quartz substrate 101 to a thickness of 30 nm by low pressure thermal CVD.
The film is formed by the method.

As a method of forming the amorphous silicon film 102,
The plasma CVD method can be used.
The use of the VD method is preferable because the film quality is dense. This becomes important later when the amorphous silicon film is transformed into a thermal oxide film.

The thickness of the amorphous silicon film is preferably selected from the range of 10 to 50 nm.

Next, the amorphous silicon film 102 is subjected to a heat treatment in an oxygen atmosphere at 950.degree.
Metamorphosis to 3. At this time, the thickness of the thermal oxide film is about twice that of about 6 times.
0 nm. (FIG. 1 (B))

It is useful to include a trace amount of a halogen element in an oxygen atmosphere during the formation of the thermal oxide film 103 because impurities can be vaporized and removed. in this case,
For example, an atmosphere containing HCl at 3% by volume in an oxygen atmosphere may be used.

Next, an amorphous silicon film (not shown) is formed on the thermal oxide film 103 by a low pressure thermal CVD method, and is crystallized by a heat treatment. Here, in a nitrogen atmosphere, 8
Heat treatment at 50 ° C. for 6 hours is performed to obtain a crystalline silicon film.

At this time, a dense thermal oxide film 10 is used as a base film.
Since the film 3 is formed, diffusion of impurities from the quartz substrate 101, in particular, movement of OH groups can be suppressed.

After obtaining a crystalline silicon film (not shown), the film is patterned to form a TF shown in FIG.
An active layer pattern 104 of T is formed.

Further, a gate insulating film 105 is formed by a plasma CVD method. As a method for forming the gate insulating film, a thermal oxidation method or a method combining the thermal oxidation method and the plasma CVD method may be used.

Next, a gate electrode 106 is formed using a silicon material having one conductivity type. Here, a gate electrode 106 is obtained by forming a silicon film doped with a high concentration of phosphorus by a low pressure thermal CVD method and patterning the silicon film.
(Fig. 1 (C))

As a material for the gate electrode, various silicide materials or a material obtained by laminating various materials in multiple layers can be used.

Next, phosphorus is doped by a plasma doping method to form the source region 107 and the drain region 10.
9 is formed in a self-aligned manner. At this time, the channel forming region 108 is also formed in a self-aligned manner. (Fig. 1 (D))

After the impurity doping, activation of the impurity doped by the heat treatment and annealing of the crystal structure damage caused during the doping are performed. This heat treatment is performed at 800 ° C. for 4 hours.

Although an example in which an N-channel type TFT is manufactured has been described here, if a P-channel type is manufactured, boron doping may be performed.

Next, a silicon oxide film 110 is formed to a thickness of 700 nm by a plasma CVD method. Further, a silicon nitride film 111 is formed to a thickness of 150 nm by a plasma CVD method.

Next, a polyimide resin film 112 is formed by spin coating. The minimum thickness of the polyimide resin film is 500 nm. Other than polyimide, polyamide, polyimide amide, polyamide, acrylic,
A material such as epoxy can be used. Further, a multilayer film of these materials can be used.

The silicon oxide film 110, the silicon nitride film 111, and the polyimide resin film 112 form an interlayer insulating film.

Next, a contact hole is formed, and then a source electrode 113 and a drain electrode 114 are formed of a three-layered film of a titanium film, an aluminum film, and a titanium film.

Here, the thickness of the titanium film is 100 nm, and the thickness of the aluminum film is 400 nm.

Thus, the N-channel TFT shown in FIG. 1E is completed.

In the structure shown in this embodiment, a thermal oxide film 1 having a dense film quality is formed on a quartz substrate 101 as a base film.
Since 03 is formed, it is possible to suppress the adverse effect of the OH group in the quartz substrate 101 on the characteristics of the TFT.

Even when a low-grade quartz substrate having a high OH group concentration is used, a TFT having high characteristics and high reliability, a circuit using the TFT,
An apparatus using FT can be obtained.

[Embodiment 2] This embodiment relates to a method of improving the method of forming the underlayer as shown in FIGS. 1A and 1B and obtaining higher reliability.

Here, a low-pressure thermal CVD method is used as a method for forming an amorphous silicon film serving as a starting film of a base film, and a method of holding a substrate during film formation is devised.
It is characterized in that an amorphous silicon film is formed on the back side of the substrate.

FIG. 2 shows the manufacturing process of this embodiment. First, a quartz substrate 101 is prepared. Next, the substrate is held so that the front and back surfaces of the substrate are exposed, and an amorphous silicon film 201 is formed by low-pressure thermal CVD. (Fig. 2 (A))

At this time, the amorphous silicon film 2
01 is formed. Although the film is not formed on the edge of the substrate due to holding the substrate, the ratio of this portion is extremely small.

Next, the amorphous silicon film 201 is formed by a thermal oxidation method.
Is transformed into a thermal oxide film. Here, the amorphous silicon film 201
The substrate 101 is held in the same state as when forming the
A heat treatment at 950 ° C. is performed in an atmosphere of 0%. In this step, the amorphous silicon film 201 is transformed into a thermal oxide film 202. (FIG. 2 (B))

It is useful to include a trace amount of a halogen element in an oxygen atmosphere when forming the thermal oxide film 103 because impurities can be vaporized and removed. in this case,
For example, an atmosphere containing HCl at 3% by volume in an oxygen atmosphere may be used.

After that, the TFT may be manufactured according to the manufacturing process shown in the first embodiment.

[Embodiment 3] In this embodiment, a process in the case where the invention shown in this specification is used and a method using a nickel element is employed as a method for forming a crystalline silicon film will be described.

FIGS. 3 and 4 show the manufacturing process of this embodiment. First, an amorphous silicon film 102 is formed on a quartz substrate 101 to a thickness of 300 nm by using a low pressure thermal CVD method.
(FIG. 3 (A))

Next, the amorphous silicon film 102 is formed by thermal oxidation.
Is transformed into a thermal oxide film 103. (FIG. 3 (B))

Here, if a manufacturing process as shown in FIG. 2 is adopted, a thermal oxide film can be formed also on the back surface side of the substrate. That is, a quartz substrate wrapped in a thermal oxide film can be obtained.

Next, an amorphous silicon film 301 is formed to a thickness of 50 nm by using a low pressure thermal CVD method. (FIG. 3 (C))

Next, a mask 302 made of a silicon oxide film having a thickness of 90 nm formed by a plasma CVD method is formed.

The mask 302 made of the silicon oxide film includes:
An opening 303 is provided. This opening 303 is
It has a longitudinal shape extending from the depth direction of the drawing to the front direction.

After disposing the mask 302, a nickel acetate solution is applied to obtain a state in which the nickel element is held in contact with the surface as indicated by 304.

Here, the nickel element comes into contact with the surface of the amorphous silicon film 301 exposed at the bottom of the opening 303. (FIG. 3 (D))

In this state, in a nitrogen atmosphere, 600
Heat treatment at 8 ° C. for 8 hours. In this step, crystal growth proceeds in a direction parallel to the substrate as indicated by an arrow 305 from a region where the opening 303 into which the nickel element is selectively introduced is provided. This crystal growth is called lateral growth. (FIG. 3 (E))

In this way, a silicon film 306 having been laterally grown as shown in FIG. 4A is obtained. Next, a mask 3 made of a silicon oxide film
Remove 02.

Then, HCl is added in an oxygen atmosphere at 3% by volume.
In a contained atmosphere, heat treatment is performed at 950 ° C. for 30 minutes.

In this step, the thermal oxide film 307
It is deposited to a thickness of nm. At this time, the thickness of the silicon film 306 decreases from 50 nm to 35 nm.

In this step, nickel remaining in the film is vaporized in the atmosphere as nickel chloride. Thus, the nickel element concentration in the silicon film is reduced.

Then, by patterning the exposed silicon film, an activation enhancement pattern 308 shown in FIG. 4B is obtained.

Further, a gate insulating film 309 is formed. Here, first, after forming a thermal oxide film to a thickness of 20 nm,
Further, a silicon oxide film is formed to a thickness of 50 nm by a plasma CVD method.

Thus, a gate insulating film 309 having a thickness of 70 nm is formed. Further, the finally remaining active layer 3
08 has a thickness of 25 nm.

Next, a film of a material containing aluminum as a main component is formed to a thickness of 400 nm by a sputtering method. And by patterning it, 310
Is formed. Reference numeral 311 denotes a resist mask used at this time. (FIG. 4 (B))

Next, in a state where the resist mask remains, anodic oxidation is performed using the aluminum pattern 310 as an anode to form a porous anodic oxide film 312. This step is performed using an aqueous solution containing 3% by volume of oxalic acid as an electrolytic solution. The thickness of this porous anodic oxide film is 4
00 nm.

Next, the resist mask 311 is removed, and anodic oxidation is performed again. Here, a solution obtained by neutralizing an ethylene glycol solution containing 3% by volume of tartaric acid with aqueous ammonia is used as the electrolytic solution.

In this step, an anodic oxide film 313 having dense film quality is formed. The thickness of the anodic oxide film 313 having this dense film quality is 70 nm.

Next, 31
The regions 5 and 316 are doped with phosphorus in a self-aligned manner. (FIG. 4 (C))

Next, the exposed silicon oxide film is removed. Thus, a state in which the silicon oxide film (film in which the thermal oxide film and the plasma CVD film are stacked) 317 is obtained as shown in FIG.

Next, phosphorus doping is performed again by the plasma doping method. This step is performed under light doping conditions compared to the previous step.

In this doping step, 318, 3
Light doping is performed on the 19 regions. (FIG. 4
(D))

After the doping is completed, annealing is performed by irradiating a laser beam to activate the dopant and anneal the doped region damaged at the time of doping.

In this way, the source region 315,
Drain region 316, low concentration impurity regions 318, 31
9. A channel formation region 30 is formed.

In this embodiment, since aluminum is used as the gate electrode, the heat treatment (700 ° C.
(Temperatures above 800 ° C. are required) are not possible.
Generally, heat treatment of aluminum is limited to about 400 ° C.

Next, a silicon oxide film 32 is used as an interlayer insulating film.
0, a silicon nitride film 321 and a resin film 322 are stacked. Then, a contact hole is formed, and a source electrode 323 and a drain electrode 324 are formed.

Thus, the TFT shown in FIG. 4E is completed.

[Embodiment 4] In this embodiment, examples of various apparatuses utilizing the present invention will be described. The invention disclosed in this specification is based on T
It can be used for FT integrated circuits.

FIG. 5A shows a mobile computer (mobile computer), which includes a main body 2001 and a camera unit 2.
002, an image receiving unit 2003, an operation switch 2004, and an active matrix display device 2005.
The present invention can be applied to the display device 2005 and internal circuits.

Active matrix type display device 200
As 5, either a reflection type or a transmission type can be used. Further, a device using an EL element can be used instead of the liquid crystal display device. This is the same in other examples.

FIG. 5B shows a projection type display device called a front projection type. This device includes a main body 2201, a light source 2202, an active matrix type reflective liquid crystal display device 2203, and an optical system 2204. Further, a screen 2205 (or an alternative projection surface) is required separately from the main body.

FIG. 5D shows a portable telephone, which has a main body 230.
1, an audio output unit 2302, an audio input unit 2303, an active matrix type liquid crystal display device 2304, operation switches 2305, and an antenna 2306.

FIG. 5E shows a video camera,
401, active matrix type liquid crystal display device 240
2, a voice input unit 2403, operation switches 2404, a battery 2405, and an image receiving unit 2406.

FIG. 5F shows a projection type display device called a rear projection type. This device has a main body 2
Reference numeral 501 denotes a light source 2502, an active matrix type reflection type liquid crystal display 2503, a polarization beam splitter 2
504, reflector (reflection mirror) 2505, 250
6, and a screen 2507.

The present invention can be used for a substrate constituting a reflection type liquid crystal display.

Here, an example of a liquid crystal display has been described, but an active matrix type EL display device can also be used. Also in this case, the invention disclosed in this specification can be used for a substrate constituting a panel.

[0092]

By employing the invention disclosed in this specification, it is possible to solve a problem that occurs when a low-rank quartz substrate is used. That is, when a quartz substrate having a low rank is used, it is possible to suppress the influence of impurities in the substrate from adversely affecting the operation of the semiconductor element formed on the substrate.

[Brief description of the drawings]

FIG. 1 is a diagram showing a process for manufacturing a thin film transistor (TFT) over a quartz substrate.

FIG. 2 is a view showing a process of forming a base film over a quartz substrate.

FIG. 3 is a diagram illustrating a process for manufacturing a thin film transistor (TFT) over a quartz substrate.

FIG. 4 is a diagram illustrating a process for manufacturing a thin film transistor (TFT) over a quartz substrate.

FIG. 5 is a diagram showing an outline of a device using the invention.

[Explanation of symbols]

 Reference Signs List 101 quartz substrate 102 amorphous silicon film 103 thermal oxide film 104 active layer 105 gate insulating film 106 gate electrode 107 source region 108 channel formation region 109 drain region 110 silicon oxide film 111 silicon nitride film 112 polyimide resin film 113 source electrode 114 drain Electrode 201 Amorphous silicon film 202 Thermal oxide film 301 Amorphous silicon film 302 Silicon oxide film 303 Opening 304 Nickel element held in contact with surface 305 Crystal growth direction 306 Silicon film 307 Thermal oxide film 308 Active layer 309 Gate insulating film 310 Aluminum pattern 311 Resist mask 312 Porous anodic oxide film 313 Anodized film having dense film quality 314 Gate electrode 315 Source region 316 Drain region 30 Channel formation region 317 Light insulating film 318 low concentration impurity region 319 low concentration impurity region 320 silicon oxide film 321 silicon nitride film 322 resin film 323 source electrode 324 drain electrode

Claims (6)

[Claims] A step of forming an amorphous silicon film on at least a main surface of a substrate; a step of transforming the amorphous silicon film into a thermal oxide film by heat treatment in an oxidizing atmosphere; Forming a thin-film semiconductor element on an oxide film. 2. The method for manufacturing a semiconductor device according to claim 1, wherein a quartz substrate is used as the substrate. 3. The method for manufacturing a semiconductor device according to claim 1, wherein the amorphous silicon film is formed by a low pressure thermal CVD method. 4. A step of forming an amorphous silicon film on at least a main surface of a substrate, and a step of transforming the amorphous silicon film into a thermal oxide film by heat treatment in an oxidizing atmosphere. A method for manufacturing a substrate for a semiconductor device, comprising: 5. The method according to claim 4, wherein a quartz substrate is used as the substrate. 6. The method for manufacturing a substrate for a semiconductor device according to claim 4, wherein the amorphous silicon film is formed by a low pressure thermal CVD method.