JPH04134869A - Manufacture of thin film semiconductor device - Google Patents

Abstract

PURPOSE:To increase an ON current of a thin film transistor and to reduce an OFF current by inserting a silicon thin film into an oxidation furnace and by increasing its temperature to a specified oxidation temperature at a temperature rise rate of 20 deg.C/minute or below to form a gate oxide film. CONSTITUTION:Only a crystal grain having crystal orientation of a small activation energy of crystal growth selectively grows by a low temperature anneal and a silicon thin film 1-3 of a large grain diameter is acquired by solid-state growth. Then, a gate oxide film 1-4 is formed by heat oxidation method. A temperature of an oxidation furnace is made to rise to a specified oxidation temperature Tb at a temperature rise rate of 20 deg.C/minute or below. In the case of dry oxidation which is carried out in dry oxygen atmosphere, Tb is usually set to 900 deg.C or higher. Since an oxidation speed is increased in initial oxidation, the silicon thin film is oxidized slowly even if inserted at a low temperature of 600 deg.C. A substrate surface attains the specified oxidation temperature Tb by increasing an oxidation furnace temperature. A very excellent gate oxide film 1-4 can be formed at Tb=1150 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a thin film semiconductor device, and in particular,
Insulated gate field effect transistor or TFT (
The present invention relates to a method for forming a gate insulating film of a thin film transistor.

[Prior art] In recent years, SOX (Silicon On In
Alternatively, as the need for 3D ICs, large liquid crystal display panels, high-speed, high-resolution contact image sensors, etc. increases,
Technologies for realizing high-performance thin-film semiconductor devices have become important. Furthermore, technology for forming high-quality gate insulating films at low temperatures is also becoming important. An oxide film (SiO2) is generally used as the gate insulating film. Examples of methods for forming an oxide film include thermal oxidation, CVD, photoCVD, plasma CVD, anodic oxidation, and high-pressure oxidation. Among the above methods, the electrical characteristics of the silicon oxide film interface formed by thermal oxidation are the best. Since the thermal oxidation method is a high temperature process of about 900 to 1200°C, (1) elements cannot be formed on inexpensive glass substrates; (2) Lateral diffusion of impurities. (3) Three-dimensional IC
This will have an adverse effect (such as diffusion of impurities) on the underlying elements.

(4) The poly-8i thermal oxide film has insufficient dielectric strength and a large interface state density. (5) There are problems such as large stress being applied to the Si/SiO2 interface.

[Problem to be solved by the invention] In the conventional thermal oxidation method, when inserting the substrate into the oxidation furnace,
The rate of temperature rise of the substrate was not controlled. When performing thermal oxidation at a predetermined oxidation temperature, for example 1000°C,
The substrate was suddenly inserted into an oxidation furnace set at a temperature ranging from room temperature to 1000°C.

Therefore, the oxide film was growing rapidly. It is known that the oxidation rate is particularly accelerated in the early stages of oxidation. Therefore, the oxide film formed by the conventional thermal oxidation method has problems such as a very large strain and a high density of interface states. Furthermore, there is a problem that the gate dielectric breakdown voltage is low, which adversely affects reliability. When a semiconductor device such as a thin film transistor is manufactured using such a gate oxide film,
There is a problem that the on-current and mobility become small, and the threshold voltage (Vth) and off-current become large.6 The present invention solves these problems and uses a thermal oxidation method to
The purpose is to form an excellent gate oxide film and realize a thin film semiconductor device such as a thin film transistor that has good transistor characteristics.

[Means for Solving the Problems] The method for manufacturing a thin film semiconductor device of the present invention includes: 1) a method for manufacturing a thin film semiconductor device having a gate oxide film formed by a thermal oxidation process, [a] an insulating non-containing film; a step of forming a silicon thin film on a crystalline material, [b] inserting the silicon thin film into an oxidation furnace;
The method is characterized in that it includes at least the step of forming a gate oxide film by heating the silicon thin film to a predetermined oxidation temperature at a heating rate of .degree. C./min or less.

2) The temperature of the oxidation furnace when inserting the silicon thin film is set so that the surface temperature of the silicon thin film is lower than the predetermined oxidation temperature.

[Example] An example will be described by taking as an example a case where the present invention is applied to a thin film transistor. FIG. 1 is a process cross-sectional view showing a method for manufacturing a thin film transistor in an embodiment of the present invention.

A non-single crystal semiconductor thin film is formed on an insulating amorphous material. As the insulating amorphous material, a quartz substrate, a glass substrate, a nitride film, a 5i02 film, etc. are used. When using a quartz substrate, the process temperature is allowed up to about 1200°C, but when using a glass substrate, , limited to low-temperature processes below 600°C. Furthermore, a quartz substrate or a glass substrate on which an oxide film or a nitride film is deposited may be used to suppress release and diffusion of impurities. The present invention will be described as an example in which a quartz substrate is used and a Si thin film is used as the non-single crystal semiconductor thin film.

Using a plasma CVD apparatus, as shown in FIG.
The amorphous Si film 1-2 is deposited by decomposition by high frequency glow discharge of 3.56 MHz.

The SiH partial pressure of the mixed gas is 10 to 20%, and the internal pressure in the debo is 0.5 to 1.5 torr.

The substrate temperature is suitably 250°C or less, about 180°C.

The amount of bound hydrogen was determined by infrared absorption measurement and was approximately 8ato.
mic%.

Subsequently, the amorphous Si film is heat-treated at 400° C. to 500° C. to release hydrogen. This step aims to prevent explosive desorption of hydrogen.

Next, the amorphous thin film 1-2 is grown in phase.

As a solid phase growth method, furnace annealing using a quartz tube is convenient. As the annealing atmosphere, nitrogen gas, hydrogen gas, argon gas, helium gas, etc. are used. Annealing may be performed in a high vacuum atmosphere of lXl0-6 to 1 x 10-10 Torr. Solid phase growth annealing temperature is 50
The temperature is 0°C to 700°C. In such low-temperature annealing, only crystal grains having a crystal orientation with a small activation energy for crystal growth grow selectively, and moreover, they grow slowly and to a large size. In the inventor's experiments, the annealing temperature was 600''C.
, a silicon thin film with a large grain size of 2 μm or more was obtained by in-phase growth with an annealing time of 16 hours. In FIG. 1(b), reference numeral 1-3 indicates a solid-phase grown silicon thin film. There is no problem in using the laser annealing method instead of the solid phase growth method.

Next, the in-phase grown silicon thin film 1-3 is patterned by photolithography to form an island shape as shown in FIG. 1(c).

Next, a gate oxide film 1-4 is formed by thermal oxidation as shown in FIG. 1(d). The thermal oxidation method includes a dry oxidation method, which is carried out in a dry oxygen atmosphere, and a wet oxidation method, which is carried out by mixing water vapor or the like. Although the dry oxidation method has a high oxidation temperature of 1°00°C or more, the film quality is excellent. The wet oxidation method can perform oxidation at a high oxidation rate even at a low temperature of 800° C. or lower. In the present invention, both methods can be used without problems. Here, an example will be explained using a dry oxidation method.

A first embodiment of the oxidation method according to the invention is shown in FIG.

This is a diagram showing a temperature rise curve of an oxidation furnace. The vertical axis shows the oxidation furnace temperature, and the horizontal axis shows the process time. Insertion of the substrate with the silicon thin film 1-3, which is a sample, is started from time to. High purity dry oxygen gas is introduced into the oxidation furnace. Ta indicates the insertion oxidation furnace temperature. For example, Ta is set at a low temperature of 600°C. At time t1, the substrate arrives at the center of the oxidation furnace. At this time, the insertion speed of the substrate is set so that the temperature increase rate of the substrate surface is 20° C./min. The distance from the entrance of the oxidation furnace to the center is 43c.
In the case of m, when the insertion speed was set to 100 mm/min or less, the temperature increase rate of the substrate surface was 20° C./min or less.

. When I checked with a thermocouple, it tracked well. Next, the oxidation furnace temperature is raised to a predetermined oxidation temperature Tb at a heating rate of 20° C./min or less. In the case of dry heat treatment, Tb is usually set at 900° C. or higher, but a lower temperature may be used. At the beginning of oxidation, the oxidation rate is accelerated, so 60
Even when inserted at a low temperature of 0°C, the silicon thin film is slowly oxidized. By increasing the oxidation furnace temperature,
The substrate surface reaches the predetermined oxidation temperature Tb at time t2. At Tb'=1150'C, a very good gate oxide film was formed. The gist of the present invention is to
This means that the insertion oxidation furnace temperature is lower than the oxidation temperature. That is, Tb>Ta. When the substrate temperature reaches Tb, the oxidation furnace temperature is kept constant and a time t3 is set to perform the oxidation treatment in order to form a predetermined oxide film thickness. At time t3, the gas introduced into the oxidation furnace is switched from oxygen gas to nitrogen gas.

Nitrogen annealing is performed until time t4, but this is not always necessary.When the substrate is finally taken out, the temperature is slowly lowered until time t5 in order to prevent the occurrence of defects due to rapid cooling of the substrate. It is desirable that the temperature decreasing rate at this time be smaller than the temperature increasing rate.

An embodiment of the second oxidation method according to the present invention is shown in FIG.

This is an example in which the temperature of the insertion oxidation furnace was increased from Ta to Tc in the method explained in Fig. 2 (Ta<Tc).
. For example, by increasing the insertion oxidation furnace temperature from 600°C to 900°C, initial oxidation will proceed.

An example of the third oxidation method according to the present invention is shown in FIG.

This is an example in which the temperature increase rate of the oxidation furnace is reduced in the method explained in FIG. 3. By increasing the heating rate from 20° C./min to 2° C./min, the time required for heating increases tenfold. Therefore, since the processing time at a relatively low temperature becomes longer, the effect of in-phase growth appears and the silicon crystal grain size becomes larger.

A conventional oxidation method is shown in FIG. 5. The OM furnace temperature was always set at a predetermined oxidation temperature Tb. The silicon thin film was inserted into this oxidation furnace all at once, so the temperature of the substrate surface could only be controlled by the speed at which the substrate was inserted.

The rate of temperature increase on the surface of the silicon thin film at this time was measured and was approximately 36° C./min. The field effect mobility of a thin film transistor having a gate oxide film formed by this conventional oxidation method was the smallest value of 10 cm<2>/V-s or less. Further, the off-state current was as large as about 50 pA at a drain voltage of 5 volts. In other words, the oxidation method using a heating rate of 36'C/min does not provide sufficient characteristics.

In this way, the oxidation step is completed. In order to explain the manufacturing process of a thin film transistor, we will return to FIG. 1 again for explanation. As shown in FIG. 1(e), the gate electrode 1-5
form. The gate electrode material may be polycrystalline silicon thin film, molybdenum silicide, metal film such as aluminum or chromium, or ITO.
A transparent conductive film such as or 5no2 can be used. As the film forming method, there are methods such as CVD method, Suba-Ivy method, vacuum evaporation method, and plasma CVD method.

Doped a-3i:H solid-phase grown low resistance silicon thin films can also be used. A detailed explanation will be omitted here.

Subsequently, as shown in FIG. 1(f), the gate electrode 1-
5 as a mask, impurity ions are implanted to form a source region 1-6 and a drain region 1-7 in a self-aligned manner. As the impurity, P+ or As2 is used when manufacturing an Nch transistor, and B1 or the like is used when manufacturing a Pch transistor. In addition to the ion implantation method, impurity addition methods include a laser doping method, a plasma doping method, and an ion shower method. The arrows 1-8 represent impurity ion beams. Said insulating amorphous material 1-1
When a quartz substrate is used as the substrate, a thermal diffusion method can be used. Impurity temperature is from 1×1015 to 1×102°
It should be about Cm-3. If the thickness of the gate oxide film 1-4 is, for example, 1200, the phosphorus ions are 80 to 120K.
Boron ions are implanted at an accelerating voltage of about 30 to 80 keV.

Next, as shown in FIG. 1(g), the glabellar insulating film 1-
Layer 9. As the interlayer insulating film material, an oxide film, a nitride film, or the like is used. The film thickness may be any thickness as long as the insulation is good, but it is usually from several thousand to several micrometers.

A simple method for forming a nitride film is LPCVD or plasma CVD.
Alternatively, a mixed gas of silane gas and nitrogen gas is used.

Here, hydrogen plasma method or hydrogen ion implantation method,
Alternatively, if hydrogen ions are introduced by a method such as hydrogen diffusion from a plasma nitride film, defects such as dangling bonds existing at the gate oxide film interface or crystal grain boundaries in the silicon film are inactivated, and the electrical properties is dramatically improved. Such a hydrogenation step may be performed before laminating the interlayer insulating film 1-9.

Next, as shown in FIG. 1(h), contact holes are formed in the interlayer insulating film and the gate insulating film, contact electrodes are formed, and a source electrode 1-10 and a drain electrode 1-1 are formed.
11. The source electrode and drain electrode are formed of a metal material such as aluminum. In this way, a thin film transistor is formed.

The field effect mobility of the thin film transistor manufactured by the oxidation method of the present invention was 20 to 300 m2/v·S, which is two to three times improved compared to the conventional method. Furthermore, the off-state current when the drain voltage was 5 volts was about 5 pA, which was one order of magnitude smaller.

[Effect of the invention] Conventionally, a silicon thin film having a large crystal grain size of 2 μm or more was used using the solid phase growth method, but in the oxidation process, it was inserted all at once into an oxidation furnace at a temperature of 1000°C or more, so the silicon thin film was formed. The gate oxide film has a very large strain,
The interface state at the S i /S i O2 interface was very large. Therefore, although thin film transistors manufactured by conventional methods use silicon thin films with large grain sizes, their off-state currents are large and their on-state currents are small. Furthermore, Vth was also large. Reliability was low due to poor interfacial properties. The field effect mobility is at most 10cm”/
It was as small as V-s. Furthermore, the off-state current was as large as about 50 pA when the drain voltage was 5 volts.

In the present invention, a substrate is inserted at a certain insertion speed into an oxidation furnace set at a temperature lower than a predetermined oxidation temperature.

Then, from the point where the substrate is set in the furnace, the temperature is raised to a predetermined oxidation temperature at a certain heating rate. Further, the insertion speed and the temperature increase rate are controlled so that the temperature increase rate of the substrate surface is 20'C/min or less. Therefore, the oxidation reaction proceeds slowly, with very little strain, and the S i / S i O
A gate oxide film with excellent two-interface characteristics is formed. In addition to the conventional conditions, a new parameter, the temperature increase rate of the oxidation furnace, has been added as a parameter for controlling the oxide film and interface properties, making it possible to control gate oxide film properties more precisely than before. It's now possible.

Furthermore, it is possible to process from a low temperature of about 60 cm.
At the same time as the silicon thin film is oxidized, due to the effect of solid phase growth, the silicon thin film becomes a silicon thin film with few defects and a large crystal grain size. In the case of silicon films deposited as polycrystalline thin films from the beginning, solid-phase growth cannot be expected to have much effect;
As described in the examples, if a silicon film initially deposited as an amorphous thin film is used, great effects of solid phase growth can be expected. Of course, there is no problem in applying a polycrystalline silicon thin film to the present invention.

It has become possible to create a silicon thin film with excellent crystallinity on an amorphous insulating substrate, and it has also become possible to form an even better gate oxide film. Therefore, thin film transistors and SOI
This will greatly contribute to the development of technology. The number of photo processes does not increase at all.

Even though an excellent silicon thin film can be obtained, the cost does not increase.

When a thin film transistor is made using the gate oxide film obtained according to the present invention and a large-grain polycrystalline silicon thin film, excellent characteristics can be obtained. Compared to the conventional art, the N current of the thin film transistor increases and the OFF current decreases. In addition, the threshold voltage is also reduced, and transistor characteristics are greatly improved.

The imbalance in characteristics between the N channel and the P channel is also improved. Field effect mobility is 10cm2/y
, s to about 20-30 Cm2/V-5.

Furthermore, the off-state current when the drain voltage is 5 volts has been reduced from the conventional 50 pA to 5 pA.

Since it is possible to fabricate thin film transistors with excellent characteristics on an amorphous insulating substrate, sufficient high-speed operation can be achieved even when applied to an active matrix substrate in which a driver circuit is integrated on the same substrate. Furthermore, it has great effects on reducing power supply voltage, reducing current consumption, and improving reliability.

When the present invention is applied to a contact image sensor in which a photoelectric conversion element and its scanning circuit are integrated on the same chip, it is possible to increase the reading speed, increase the resolution, and increase the gradation. Once high resolution is achieved, which produces this effect, it will be easier to apply it to contact type image sensors for color reading. Of course, this has great effects in reducing power supply voltage, reducing current consumption, and improving reliability.

Also, since it can be produced by a low-temperature process,
Close-contact image sensor chip can be made longer,
- A reading device for large facsimile machines such as A4 size or A3 size can be realized using a book chip. Therefore, it is possible to avoid the troublesome and unreliable technique of joining two sensor chips, and the mounting yield is also improved.

In addition to quartz and glass substrates, sapphire substrates (
A 1203) or MgO・A l 2031BP
, a crystalline insulating substrate such as CaF2 can also be used.

Although the description has been given above using a thin film transistor as an example, the present invention can also be applied to elements using thin films such as bipolar transistors or heterojunction bipolar transistors. In addition, SO such as a three-dimensional device
The present invention can also be applied to elements using I technology.

[Brief explanation of the drawing]

FIGS. 1(a) to 1(h) are process cross-sectional views of a thin film transistor showing an embodiment of the present invention. FIG. 2 is a diagram showing a temperature rise curve of the oxidation furnace in the first oxidation method of the present invention. The vertical axis shows the oxidation furnace temperature, and the horizontal axis shows the process temperature. FIG. 3 is a diagram showing a temperature rise curve of the oxidation furnace in the second oxidation method of the present invention. The vertical axis shows the oxidation furnace temperature, and the horizontal axis shows the process temperature. FIG. 4 is a diagram showing a temperature rise curve of the oxidation furnace in the third oxidation method of the present invention. The vertical axis shows the oxidation furnace temperature, and the horizontal axis shows the process temperature. FIG. 5 is a diagram showing a temperature rise curve of an oxidation furnace in a conventional oxidation method. The vertical axis shows the oxidation furnace temperature, and the horizontal axis shows the process temperature.

Claims (1)

[Claims] 1) A method for manufacturing a thin film semiconductor device having a gate oxide film formed by a thermal oxidation process, comprising: [a] forming a silicon thin film on an insulating amorphous material; [b] ] The silicon thin film was inserted into an oxidation furnace and heated at 20°C/
1. A method of manufacturing a thin film semiconductor device, comprising at least the step of forming a gate oxide film by heating the silicon thin film to a predetermined oxidation temperature at a heating rate of 1 minute or less. 2) The temperature of the oxidation furnace at the time of inserting the silicon thin film is set so that the surface temperature of the silicon thin film is lower than the predetermined oxidation temperature.
A method of manufacturing the thin film semiconductor device described above.