JPH05198507A - Manufacture of semiconductor - Google Patents

Abstract

PURPOSE:To obtain a polycrystalline silicon semiconductor film which has an excellent electric characteristic by a method wherein a hydrogenated amorphous silicon film is formed at low temperatures and is heat-treated in a vacuum and then it is dehydrogenated to generate a dangling bond in the film and the excimer laser is cast on the film in a vacuum-unbroken state. CONSTITUTION:An SiO2 film or silicon nitride film is formed as a base protective film 12 on a glass substrate 11. Nextly, an intrinsic hydrogenated amorphous silicon semiconductor layer 13 is formed in the thickness of 100nm by the plasma CVD method. At that time, by setting the film formation temperature low, the formed amorphous silicon film is allowed to have in it a good quantity of water and bonds of silicon are neutralized with hydrogen as much as possible. Nextly, a device separation patterning is conducted and the sample is heated in a vacuum at 450 deg.C for one hour to be dehydrogenated completely and dangling bonds (unpaired bonds) are generated in high density in the film. With the vacuum state being maintained, the excimer laser is cast on the sample to crystallize it.

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 semiconductor film having good crystallinity and containing less impurities in the crystal film. The semiconductor film manufactured by the manufacturing method of the present invention,
It can be used for a semiconductor device such as a high performance thin film transistor having a high electric field mobility.

[0002]

2. Description of the Related Art Conventionally, plasma CVD or thermal CVD is used.
Hydrogenated amorphous silicon film formed by the method (amorphous silicon film containing a large amount of hydrogen and many of the silicon bonds are neutralized with hydrogen) (also written as a-Si: H) CW
It is well known that the hydrogenated amorphous silicon film is crystallized by irradiating a laser beam such as a laser or an excimer laser.

However, according to this method, since a large amount of hydrogen is contained in the amorphous silicon film as the starting film, a large amount of hydrogen is ejected from the film during laser irradiation and the quality of the film is significantly impaired. was there.

The following three methods are mainly used to solve the above problems. (A) First, for a hydrogenated amorphous silicon film as a sample,
Low energy density (below threshold energy of crystallization)
Of the starting film, which is a sample, by irradiating the sample with laser light, and then irradiating the sample with laser light having a high energy density to crystallize the sample. (It is called a multi-step irradiation method) (B) By forming a hydrogenated amorphous silicon film at a substrate temperature of 400 ° C. or higher, the hydrogen content in the starting film is reduced and the deterioration of the film quality due to laser irradiation is reduced. How to prevent. (C) A method of removing hydrogen in a hydrogenated amorphous silicon film by heat-treating it in an inert atmosphere.

[0005]

In order to obtain a high quality crystal film (generally a polycrystalline silicon film) by the above-mentioned method, there are the following problems.

In the method (1) (A), the efficiency of hydrogen desorption is poor, it is difficult to control the output energy of the laser, the number of times of laser irradiation is increased, and most of the laser light energy is absorbed on the film surface. Therefore, in the case of a thick film, there are problems such as difficulty in discharging hydrogen, and there is a problem in practicability. (2) In the method (B), the impurity content in the film tends to increase as the substrate temperature increases, and when the hydrogenated amorphous silicon film is formed at a high temperature, silicon clusters (silicon Since the microcrystalline component) is generated, there is a problem that the crystallization is hindered in the subsequent crystallization by the laser light. (3) In the method of (C), since hydrogen is released by heating, a dangling bond (unpaired bond) of silicon is formed, and this dangling bond easily bonds with oxygen and the like. As a result, oxygen easily penetrates into the film from the surface of the film to 10 to 20 nm, and subsequent irradiation of laser light causes the oxygen to diffuse deep into the film due to high temperature diffusion. As a result, there is a problem that the electrical characteristics (carrier mobility, etc.) of the crystal film are deteriorated due to the impurities such as oxygen.

[0007]

The present invention uses the methods described in the following (a) to (c) as a method for solving the above-mentioned problems.

(A) A hydrogenated amorphous silicon film having a high density Si-H bond is formed at a low temperature by a vapor phase method. As the vapor phase method, a known method such as a physical vapor phase method such as a sputtering method or a vapor deposition method can be used in addition to a chemical vapor phase method such as a plasma CVD method, a thermal CVD method or a photo CVD method. At this time, it is necessary to form the hydrogenated amorphous silicon film at a substrate temperature of 350 ° C. or less, which is called a hydrogen desorption temperature from the hydrogenated amorphous silicon. This is because hydrogen is contained in the film as much as possible during film formation to increase the number of bonds between silicon and hydrogen (Si—H bonds). In order to maximize the bond between silicon and hydrogen (Si-H bond),
It is desirable to form a film at a substrate temperature as low as possible. However, practically, by forming a film at a substrate temperature of 100 to 200 degrees, a bond between silicon and hydrogen (Si-H
The goal of maximizing (coupling) can be achieved.

Further, by forming the film at a low temperature, it is possible to prevent generation of silicon clusters (microcrystals of silicon) in the film, and it is possible to desire more uniform crystallization in the subsequent crystallization step. ..

(B) The amorphous silicon film formed in the step (a) is heat-treated in a vacuum or in an inert atmosphere to release hydrogen in the film and to form a high-density dangling bond with silicon. To form. The heat treatment in a vacuum or in an inert atmosphere is to prevent the dangling bond of silicon from being combined with impurities such as oxygen as much as possible. The inert atmosphere means an atmosphere filled with a rare gas such as helium, argon, or neon, or nitrogen, hydrogen, a mixed gas thereof, or the like. Furthermore, the same effect can be expected in an atmosphere in which these gases are present under reduced pressure. Regarding the heating temperature, it is important that the substrate temperature is 350 ° C. or higher and 500 ° C. or lower. This is because the desorption temperature of hydrogen from the hydrogenated amorphous silicon is about 350 ° C., and the temperature at which the crystallization of the amorphous silicon starts is about 500 ° C. If the concentration of impurities in the film is low, especially if the concentration of oxygen is 45,
Since crystallization may start even at about 0 degrees, it is practically 4
It is preferable that the heating step for discharging hydrogen is performed at about 00 degrees. It is appropriate that the heating step for discharging hydrogen is performed for about 30 minutes to 6 hours.

This heating step is carried out in order to release a large amount of hydrogen contained in the amorphous silicon in the step (a) from the film, thereby forming a large amount of dangling bonds. The reason for producing this large amount of dangling bonds is to facilitate the crystallization in the crystallization process by laser irradiation or heating which will be performed later. This is because it is not preferable that the film be crystallized. Crystallization (including the cluster state in a minute region) should not be performed in this heat treatment step because a film once crystallized does not have to undergo crystallization energy (for example, laser irradiation energy). This is due to the fact that good electrical properties of the film cannot be obtained, but rather deteriorate.

After this, there is a crystallization process of the amorphous silicon film by laser irradiation or heating. During this crystallization process, the atmosphere is maintained in vacuum or inactive, and impurities are formed in the film. It is very effective to increase the crystallinity of the film in the subsequent crystallization process by laser irradiation or heating, to avoid bonding with dangling bonds as much as possible.

(C) The amorphous silicon film is crystallized by irradiating a laser or heating in a vacuum or in an inert atmosphere. It is extremely important that this step is performed without breaking the vacuum or the inert atmosphere subsequent to the step (b). This is because dangling bonds are formed at high density in the amorphous silicon film in the heating step (b), and silicon in the amorphous silicon film is extremely likely to react with impurities.

Further, at this time, laser irradiation while heating the substrate to about 300 to 500 degrees in order to reduce the cooling rate of the substrate temperature is effective in increasing the crystallinity. Further, when crystallization is performed only by heating, it can be performed in the range of 450 to 800 degrees, but in general, considering the heat resistant temperature of the glass substrate, the time is about 1 to 96 hours at about 600 degrees. It is applied and heated.

In the structure of the present invention, it is specified that the crystallization of amorphous silicon starts at 500 ° C. or higher, but if the oxygen concentration in the film is very low, the crystallization starts at about 450 ° C. The temperature range is limited to.

What is important in the constitution of the present invention is that a hydrogenated amorphous silicon film having a high bond density of silicon and hydrogen is first formed as a starting film. Then, hydrogen is removed from this starting film by a heating annealing process that promotes dehydrogenation from the film to obtain an amorphous silicon film having a high-density dangling bond. The use of such a membrane is
An amorphous silicon film having a high density of dangling bonds of silicon has a strong atomic level lattice vibration and is in an extremely thermally unstable state. Therefore, the energy required for crystal nucleus generation and crystal growth is small, Because it is easy to change. Then, the dangling bonds are generated at a high density by laser irradiation and heating for crystallization to crystallize the amorphous silicon film which is easily crystallized to obtain a polycrystalline silicon film.

It is important that the amorphous silicon semiconductor film is not exposed to the outside air in the above steps, that is, from the film formation to the crystallization. This is to prevent the dangling bond from bonding with oxygen and the like as much as possible. In order to achieve this object, an apparatus having a chamber equipped with a high vacuum exhaust system, a quartz window for laser irradiation, a heating device for a heating process, etc. is required. Industrially, a multi-chamber type device equipped with the above equipment is useful. Hereinafter, the structure of the present invention will be described with reference to examples.

[0018]

EXAMPLE 1 Here, an n-channel type insulating gate thin film field effect transistor using polycrystalline silicon (poly-Si) formed according to the present invention is shown as an application example of the present invention. In addition, in this embodiment, an excimer laser (KrF (wavelength 248
nm)) was used.

FIGS. 1 to 5 show steps of manufacturing an insulating gate thin film field effect transistor (hereinafter referred to as TFT) manufactured in this embodiment. In this example, a glass substrate or a quartz substrate was used as the substrate. This is because the TFT manufactured in this example is intended to be used as a switching element or a driving element of an active matrix type liquid crystal display device or an easy sensor. However, when the structure of the present invention is used in another semiconductor device, a silicon single crystal substrate or a polycrystalline substrate may be used as the substrate, or another insulator may be used.

In FIG. 1, a SiO ₂ film or a silicon nitride film is formed as a base protective film 12 on a glass substrate 11 which is a substrate. In this example, the SiO ₂ film 12 was formed to a thickness of 200 nm by RF sputtering in an atmosphere of 100% oxygen. The film forming conditions were an O ₂ flow rate of 50 sccm, a pressure of 0.5 pa, an RF power of 500 W, and a substrate temperature of 150 degrees.

Next, 100 n of intrinsic or substantially intrinsic (meaning that no impurities are artificially added) hydrogenated amorphous silicon semiconductor layer 13 is formed by plasma CVD.
It is formed to a thickness of m. This hydrogenated amorphous silicon semiconductor layer 1
3 is a semiconductor layer forming a channel formation region. The film forming conditions are as follows: atmosphere silane (SiH ₄ ) 10
0% Film formation temperature 160 degrees (Substrate temperature) Film formation pressure 0.05 Torr Input power 20W (13.56MH)
z). In this example, silane is used as a raw material gas for forming amorphous silicon. However, when polycrystallizing amorphous silicon by thermal crystallization, disilane is used to lower the crystallization temperature. In particular, trisilane may be used.

When the film forming atmosphere is 100% silane,
This is based on the experimental result that an amorphous silicon film formed in a 100% silane atmosphere is more easily crystallized than an amorphous silicon film formed in a silane atmosphere diluted with hydrogen, which is generally performed. Is.

The reason why the film forming temperature is low is that a large amount of hydrogen is contained in the formed amorphous silicon film and the bond of silicon is neutralized by hydrogen as much as possible.

Also, high frequency energy (13.56 MH
The input power of z) is as low as 20 W (generally hundreds of watts) in order to prevent the formation of clusters of silicon, that is, portions having crystallinity during film formation as much as possible. This is also based on the experimental fact that if the amorphous silicon film has a little crystallinity, it will adversely affect crystallization (irregularity in crystallinity) at the time of subsequent laser irradiation.

Next, device isolation patterning was performed to obtain the shape shown in FIG. Then, the sample is placed in a vacuum (10 ⁻⁶ Torr
In the following), heating was carried out at 450 ° C. for 1 hour to thoroughly dehydrogenate hydrogen and to form dangling bonds in the film at high density.

Further, in the chamber where the hydrogen was discharged, an excimer laser was irradiated while maintaining a vacuum state to crystallize the sample. The conditions of this process are KrF
Using an excimer laser (wavelength 248 nm), laser irradiation energy density 350 mJ / cm ² pulse number 1 to 10 shots substrate temperature 400 ° C. After laser irradiation, in a hydrogen depressurized atmosphere (about 1 To
rr), the temperature was lowered to 100 degrees.

In the present example, the heating step for dehydrogenating the sample and the crystallization by excimer laser light irradiation were carried out in the same vacuum chamber using the apparatus shown in FIG. By using such a vacuum chamber, a vacuum state can be easily maintained from the heating step to the crystallization step by laser irradiation, and a film in which impurities (especially oxygen) are not mixed can be obtained. Of course, it is not necessary to use such a vacuum chamber exclusively for laser annealing, but it is possible to move the sample by using a high-vacuum exhaust device and using a plasma CVD device having a window of quartz or the like so that the laser can be irradiated from the outside. Alternatively, the steps from film formation to laser irradiation may be continuously performed.

In FIG. 6, 21 is a vacuum chamber, 2
2 is a quartz window for irradiating a laser from the outside of the vacuum chamber 21, 23 is a laser beam when the laser is irradiated, 24 is a sample (sample), 25 is a sample holder, 26 is a heater for heating the sample, 27 Is an exhaust system. As the exhaust system, a rotary pump for low vacuum and a turbo molecular pump for high vacuum were used, and efforts were made to minimize the residual concentration of impurities (particularly oxygen) in the chamber.

After crystallization by an excimer laser using the vacuum chamber of FIG. 6, a SiO ₂ film having a thickness of 50 nm is formed by RF sputtering, and only the gate region is patterned by using a photoresist. The insulating film 15 shown in 2 was formed. This insulating film is provided to protect the channel forming region under the insulating film from being contaminated by impurities (particularly oxygen). Further, the photoresist 16 on the insulating film 15 was left without being removed. A channel formation region is formed under the gate insulating film 15.

Then, an n ⁺ type amorphous silicon film 17 to be the source and drain regions is formed by plasma CVD under the following conditions to a thickness of 50 nm. Film forming atmosphere H ₂ : SiH ₄ = 50: 1 (PH ₃
Addition of 1%) Substrate temperature 150 to 200 degrees Film forming pressure 0.1 Torr Input power 100 to 200 W It is desirable that the film formation be kept at 200 degrees or less so that the resist is not cured by heat. Further, here, by adding an impurity imparting P-type conductivity (for example, B ₂ H ₆ is used), a P-channel TFT
Can be obtained.

In this situation the shape of FIG. 2 is obtained. Then, the lift-off method is used to remove the n ⁺ -type amorphous silicon film from the gate region to obtain the shape shown in FIG. In this method, the remaining photoresist is removed to simultaneously remove the film (n ⁺ type amorphous silicon film in this case) formed around and around the photoresist together with the photoresist.

Further, as indicated by an arrow in FIG.
By irradiating the F excimer laser, energy is applied to the n ⁺ -type amorphous silicon film to be the source and drain regions (171 and 172) to activate the source and drain regions (one included in the source and drain regions). Activation of impurities imparting conductivity type) was performed.

The laser irradiation conditions at this time were as follows using a KrF excimer laser (248 nm). Energy density 250 mJ / cm ² Number of pulses 10 to 50 shots Substrate temperature 350 degrees Of course, here, KrF excimer laser (wavelength 248
It goes without saying that a laser other than (nm) may be used.

After the above steps, the sheet resistance of the n ⁺ type amorphous silicon film to be the source and drain regions is 100 to 20.
It decreases to about 0 Ω / cm ² . Further, the silicon oxide film 15, which is a protective film protecting the channel forming region (the region under 15), is removed after the above process.

After the activation of the impurities in the source and drain regions, Si is formed by RF sputtering as shown in FIG.
The O ₂ film 18 was formed to a thickness of 100 nm. The film forming conditions are the same as the method for forming the gate oxide film.

After that, contact holes were patterned to obtain the shape shown in FIG. Further, aluminum serving as an electrode was vapor-deposited to perform wiring electrode patterning. And 3
A device was completed by performing hydrogen annealing in a hydrogen atmosphere at 50 degrees. (Fig. 5)

FIG. 7 is a graph showing the I _D -V _G characteristics of the TFT (insulating gate type field effect transistor) manufactured in this example. In FIG. 7, I _D is the drain current and V _G is the gate voltage. FIG. 7 shows a case where the drain voltage is 10V and a case where the drain voltage is 1V.

Table 1 shows the TF produced in this example.
Comparison data of various characteristics of T and a TFT obtained by a conventional manufacturing method are shown.

The manufacturing process of the comparative example will be described below. The difference between the comparative example and Example 1 is that in Example 1, the vacuum state was maintained between the heating step for hydrogen desorption and the laser irradiation for crystallization. In the example, different chambers were used in the heating process for hydrogen discharge and the process for laser irradiation, so the sample from the heating furnace that performed the heating process for hydrogen discharge to the vacuum chamber for laser irradiation The difference is that the surface of the sample, that is, the surface of the amorphous silicon semiconductor film, was exposed to the outside air when the sample was moved.

The other manufacturing steps are exactly the same as in Example 1. Therefore, by comparing this comparative example with Example 1, in the structure of the present invention in which dangling bonds are generated at a high density by performing dehydrogenation, a vacuum atmosphere was maintained during the steps from dehydrogenation to crystallization. You can see the importance of doing in a state. Table 1 shows the electrical characteristics of Example 1 and this comparative example.

[0041]

[Table 1]

Looking at Table 1, field effect mobility, ON / O
It can be seen that this example is excellent in all of the FF current ratio, the threshold voltage, and the S value.

In Table 1, the field effect mobility is an index showing the speed at which carriers cross a channel, and the larger this value is, the faster the switching speed is and the higher the operating frequency is.

The ON / OFF current ratio is VD = 1
(V), VG = 30 (V), the value of ID and the ID-VG curve in that case (shown in FIG. 7) are defined by the ratio of the minimum value of ID. The larger the OFF current ratio, the smaller the leak current at the time of OFF, indicating that the switching element is excellent.

The lower the threshold voltage, the smaller the power consumption. The low threshold voltage is an important problem in an active matrix type liquid crystal display device or the like which has to drive hundreds of thousands of TFTs.

The S value is (d (ID) / d (VG)) ^{-1 at} the rising portion of the curve in the graph showing the relationship between the gate voltage (VG) and the drain current (ID) as shown in FIG. Is the minimum value of and is a parameter indicating the steepness of the ID-VG curve. The smaller the S value, the more excellent the switching characteristics can be evaluated to be.

From the above, it can be seen that by adopting the constitution of the present invention, a high-performance TFT can be obtained, and at the same time, a polycrystalline silicon semiconductor excellent in electrical characteristics can be obtained. In particular, the comparison with the comparative example shows that it is important to shift from the heating step for dehydrogenation to the step for crystallization while maintaining the vacuum state.

It is needless to say that the TFT obtained in this embodiment can be applied not only to the switching element of the liquid crystal display device but also to the element of the integrated circuit, and the structure of the present invention can be applied to the structure of the TFT in this embodiment. However, it is also effective in a method of manufacturing a TFT in which source and drain regions are formed by ion implantation which is self-aligned (self-aligned).

[Embodiment 2] In this embodiment, the TFT manufactured in Embodiment 1 is heated by crystallization means. The heating temperature for this crystallization is 600
And the heating time is 48 hours.

Further, in this embodiment, the device isolation patterning performed in Embodiment 1 is performed after crystallization by heating. That is, after forming an amorphous silicon semiconductor film in which the bonds of silicon and hydrogen, which are intrinsic or substantially intrinsic (meaning that impurities are not artificially mixed in) to be a channel formation region, are present at high density are formed. , Keep it in a vacuum state without exposing it to the outside air, dehydrogenate at a temperature of 350 to 500 degrees (450 degrees or less if the oxygen concentration in the film is low), and then keep the vacuum state. Crystallization is performed at a temperature of 600 ° C., and then device isolation patterning is performed.

The heating process for discharging hydrogen is 400
The heating process for crystallization is 600 ° C for 48 hours.
Went in time. In other steps, the same steps as in Example 1 were performed. Also in this embodiment, hydrogen is discharged from an amorphous silicon film in which hydrogen is excessively bonded to silicon to form a large amount of dangling bonds, and the amorphous silicon film having a large amount of dangling bonds is vacuumed. It is important to carry out heating for crystallization while maintaining the temperature.

Although silicon has been mainly described in the above description, the structure of the present invention is also useful when crystallizing another amorphous semiconductor film. In the above embodiment, the heat treatment and the laser writing process were performed in a vacuum, but the atmosphere is not particularly limited, and the same effect can be expected in the above-mentioned inert atmosphere. ..

Needless to say, the polycrystalline semiconductor film produced by the structure of the present invention can be applied to photoelectric conversion devices and other semiconductor devices.

[0054]

According to the present invention, a step of forming a hydrogenated amorphous silicon film at a low temperature and producing a large amount of Si-H bonds in the film, which is the constitution of the present invention, and the hydrogenated amorphous film formed by the above step A step of forming a large amount of dangling bonds in the film by subjecting the silicon film to heat treatment in a vacuum and dehydrogenation, and irradiating an excimer laser from the step without breaking the vacuum. By taking a step or a heating step for crystallization, a polycrystalline silicon semiconductor film having excellent electrical characteristics can be obtained, and a TFT using the polycrystalline silicon semiconductor film has extremely high characteristics. It became clear that I had it.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of the manufactured insulating gate thin film field effect transistor in Example 1;

FIG. 2 is a diagram showing a manufacturing process of the manufactured insulating gate thin film field effect transistor in Example 1;

FIG. 3 is a diagram showing a manufacturing process of the manufactured insulating gate thin film field effect transistor in Example 1;

FIG. 4 is a diagram showing a manufacturing process of the manufactured insulating gate thin film field effect transistor in Example 1;

FIG. 5 is a diagram showing a manufacturing process of the manufactured insulating gate thin film field effect transistor in Example 1;

FIG. 6 shows an outline of the vacuum chamber used in Example 1.

FIG. 7 is a graph showing the electrical characteristics of the insulated gate field effect transistor manufactured in Example 1.

[Explanation of symbols]

11 glass substrate 12 underlying SiO ₂ film 13 polycrystalline silicon film 14 KrF excimer laser light (wavelength 248 nm) 15 SiO ₂ film 16 photoresist 17 n ⁺ type amorphous silicon film 171 source or drain region 172 drain or source region 18 SiO ₂ film 19 Aluminum layer 21 Vacuum chamber 22 Quartz window 23 Laser light 24 Sample 25 Sample holder 26 Heater 27 Exhaust system

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 29/784

Claims (3)

[Claims] 1. A step of forming an amorphous silicon semiconductor film containing silicon as a main component on a substrate by a vapor phase method, and a step of heat-treating the amorphous silicon semiconductor film formed by the step, In the method for manufacturing a semiconductor, including the step of irradiating the amorphous silicon semiconductor film heat-treated by the step with laser, the vapor phase method is performed at a temperature of 350 ° C. or lower, and the heat treatment is 350 ° C. or higher. And a temperature of 500 ° C. or less, and the step of performing laser irradiation from the heat treatment is performed in a vacuum or in an inert atmosphere. 2. The hydrogen in the amorphous silicon semiconductor film is released by heating and annealing the amorphous silicon semiconductor film formed on the substrate and having a large amount of bonds between hydrogen and silicon in vacuum. A step of producing a large amount of dangling bonds and a step of crystallization by performing laser irradiation on the amorphous silicon semiconductor film having a large amount of dangling bonds in the state where the vacuum state is maintained from the step, to perform crystallization. And a step of obtaining a silicon semiconductor film. 3. A step of forming an amorphous silicon semiconductor film containing silicon as a main component on a substrate by a vapor phase method, the amorphous silicon semiconductor film formed by the step being 350 degrees or more, and In a semiconductor manufacturing method including a step of performing heat treatment at a temperature of 500 ° C. or lower, and a step of heating the amorphous silicon semiconductor film at a temperature of 500 ° C. or higher after the step, the amorphous silicon semiconductor film is In the step of, the semiconductor manufacturing method is characterized in that it is always maintained in an atmosphere isolated from the outside air, and is maintained in a high vacuum state or an inert atmosphere except during film formation.