JPH02258690A - Method of forming semiconductor thin film - Google Patents

Abstract

PURPOSE:To improve controllability of grain boundary positions by providing a region with a high Si atom density at a desired position of an amorphous Si film, heat- treating the region at a specific temperature and growing a crystal from an amorphous Si film in the solid phase based on the crystal substance thereof. CONSTITUTION:A polycrystal Si thin film having about 1000Angstrom thickness is deposited on a ground material of glass using thermal decomposition of SiH4 by vacuum CVD. Si ions are then implanted into the whole surface of the polycrystal Si thin film at about 110keV implantation energy to provide an amorphous thin film and form the amorphous Si film. A resist is then applied onto the amorphous Si film and a pattern in which holes having about 1mum diameter are arranged at a prescribed interval in the form of lattice points is formed. The resultant resist part is then masked to carry out the second Si ion implantation at about 40keV implantation energy and form a substrate having a region with a high Si atomic density. The resist mask is finally shaved and separated and the film is heat-treated at about 600 deg.C for about 100hr in N2 atmosphere to afford the objective Si crystal thin film having crystal grain boundaries arranged in the form of lattice at a prescribed interval with hardly any grain diameter distribution.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method of forming a semiconductor thin film, and more particularly, to a method for forming a semiconductor thin film, and more particularly, a method for forming a semiconductor thin film, and more specifically, a method for forming a semiconductor thin film with a large particle size that enables high performance production of semiconductor devices such as TPT (thin film transistor). The present invention also relates to a method for forming a semiconductor thin film in which grain anchor positions are controlled.

[Prior Art] Conventionally, as a technology for forming a polycrystalline Si semiconductor thin film with a large grain size, there is a technology in which an amorphous St thin film is grown in a solid phase to form a polycrystalline St thin film with a large grain size and used for a thin film transistor. It has been reported (TNoguchi, T., Ohsh
ima&T, Hayashi; Polysil
iconFilms and Interfaces,
Boston, 1987. Mater.

Res, Sac, 5yllIip, Proc,
Vol, IOJ p, 293 (Elsecier 5
Science Publfshing, New Yo
rk.

19811)), the details of which are described below.

In this technique, first, an amorphous Si film is formed on a substrate. Note that the formation technology for the amorphous St layer includes a method of implanting Si ions into a polycrystalline Si layer to make it amorphous, and a method of thermally decomposing SiH4 using a chemical vapor method to form amorphous Si. A method of forming St, or a method of depositing St on a substrate kept at room temperature by electron beam evaporation is known.

Thereafter, when the amorphous St layer is heat-treated at 600° C. for several hours to several tens of hours in an N2 atmosphere, crystal nuclei are generated in the amorphous Si layer, and their size increases with the heat treatment time. The grains grow until they collide with each other, forming grain anchors. For example, an amorphous Si layer created by implanting 1,000 Si ions grows to a grain size of about 5 μm by heat treatment in a N2 atmosphere at 600° C. for 100 hours.

The carrier efficiency of a thin film transistor fabricated on a polycrystalline Si layer with such a large grain size is 100clI12/■S.
It has been observed that the particle size exceeds eC, and is an extremely useful method for increasing the particle size in device production.

[Problems to be Solved by the Invention] However, when the above-mentioned conventional example was actually repeated and examined in detail, the present inventors discovered that the following problems existed.

Nucleation in amorphous Si occurs at random positions, and after the growth of the nuclei, grains collide with each other to form grain boundaries, but the positions of these grain boundaries are naturally random and can be controlled. isn't it. In fact, if Si ions are implanted to make the polycrystalline Si layer amorphous and then heat treated at about 600°C, a polycrystalline layer with large grain sizes of up to 5 μm can be obtained.
The particle size distribution is broadly distributed in the range of 1 μm to 5 μm, and this distribution manifests itself as variations in device characteristics during device fabrication, which poses a great deal of practical difficulty. for example,
4 field effect transistors with a channel length of 10 μm
When fabricated on the large-grain polycrystalline Si layer of an inch substrate,
Electron mobility is ±10 for 110 cm'/v-sec
cm'/v-sec, and the threshold value has a variation of more than ±0.5V, which is significantly larger than that produced on a single crystal Si substrate, making it difficult to integrate and form a circuit. It becomes a big obstacle.

The present invention solves the above three problems of the conventional example, and the purpose of the present invention is to control the position of nucleation in the solid phase in order to reduce the particle size distribution after solid phase recrystallization. As a result, it is an object of the present invention to provide a method for forming a semiconductor thin film of Si crystal on an amorphous base material in which grain boundary positions are determined.

[Means for Solving the Problems] The method for forming a semiconductor thin film of the present invention provides a method for forming a semiconductor thin film in a desired position of an amorphous Si film, which is a sufficiently minute region for crystal growth from a single nucleus; is different from St in the amorphous Si film.
A region is provided where the St atom density is higher than the St atom density, and a crystalline substance grown from a single nucleus is formed in the region, and heat treatment is performed at a temperature at which no nuclei are generated in the amorphous Si film, which is different from the region. , characterized in that the amorphous Si film is crystal-grown in a solid phase based on the crystalline substance.

[Effect]

The details of the operation and structure of the present invention will be explained below along with the knowledge obtained in making the present invention.

The key point of the present invention is how to control the growing position of crystals in the solid phase. That is, in an amorphous Si film, nuclei are generated preferentially in a specific position, and generation of nuclei in other areas is suppressed.

The present inventor deposited a polycrystalline Si film on a base material made of, for example, 5ift, and then implanted Si ions to make the polycrystalline St layer amorphous. We discovered a phenomenon in which the crystallization temperature (crystallization temperature) depends on the ion implantation energy.

Therefore, we investigated why the crystal nucleation temperature depends on the ion implantation energy and discovered the following. The details are described below.

By changing the implantation energy, the Si after becoming amorphous
It was first found that the distribution of implanted Si ions changes in the layer (amorphous t-layer), and that the distribution of vacancies also changes accordingly.

The mechanism of nucleation is determined by the phase transition of Si atoms from an amorphous phase to a crystalline phase, or the rate of movement of the crystalline phase/amorphous phase interface. The movement speed of the crystalline phase/amorphous phase interface is determined by the movement speed of Si atoms across the interface, and the movement speed strongly depends on the vacancy density and the Si atom density. The temperature (crystallization temperature) changes.

FIG. 1 shows the correlation between Si ion implantation energy and crystallization temperature. The conditions at this time are as follows.

St ion implantation amount: Critical implantation amount (approximately 1015 cm-2
) Constant implantation layer: Polycrystalline St layer of 1000 people Heat treatment time = 20 hours Projected range of St" ions (controlled by implantation energy): ■Implantation energy 40kev; center of implantation layer ■Implementation energy 70kev; implantation layer When the implantation is performed at the interface between the base material and the base material at 40 keV, all of the implanted ions and generated vacancies are present in the implanted layer, but when the implantation is at 70 keV, almost all the vacancies are distributed within the implanted layer. Only about half of the Si atoms are in the injection layer, and S
The i-atom density is higher in the former, resulting in a denser amorphous structure.

In general, Si atoms from the amorphous phase to the crystalline phase migrate via vacancy sons. Therefore, the difference in the density of the Si atoms to be moved affects the crystallization temperature, and the crystallization temperature is about 50° C. lower for the 40 keV implanted layer with the projected range at the center of the film.

In the end, the difference in the energy of the implanted ions is the vacancy density and the Si
The present inventors have discovered that crystallization temperature changes when there is a difference in the density of SL atoms, which occurs as a difference in atomic density.

The above phenomena are used to control the location of nuclear generation.

As shown in FIG. 2, regions with a high Si atom density and a sufficiently high vacancy concentration are locally formed in the amorphous Si film (A).

The amorphous 5iFA may be formed, for example, by implanting ions into a polycrystalline Si film on a base material. Furthermore, if this ion implantation is performed with high energy so that the projected range is at the interface between the underlying material and the polycrystalline Si layer, the entire layer can be easily made into an amorphous Si layer.

In order to form a region with a high Si atom density in the amorphous 5tli, ions may be implanted only into the region that is to become a region with a high Si atom density using, for example, a masking technique. At this time, if the implantation energy is low so that the projected range is at the center in the film thickness direction, the amorphous Si
Since the surface of the region of the layer having a high Si atom density can be made to have an even higher Si atom density, the crystallization temperature can be lowered.

This thin film does not generate nuclei in areas with low Si atom density,
Heat treatment is performed at a temperature that allows nucleation to occur only in regions with high Sii ion density. The temperature may be determined in advance through experiments or the like. For example, as shown in Figure 1,
When Si ion implantation is performed at 80 KeV and further amorphousization is performed partially at 40 KeV, heat treatment may be performed at 620° C. for 10 hours in an N2 atmosphere.

Si crystal nuclei are generated from regions with high Si atom density,
The crystal grows while maintaining a single domain up to a region where the Si atom density is low. This is because the activation energy for the growth of dust-generated crystal nuclei is lower than the activation energy for overcoming the surface energy to generate nuclei.

The growth continues, and eventually nuclei are generated from adjacent regions with a high Si atom density, collide with the grown crystal at an open position, and a grain boundary is formed there.

As described above, an St crystal thin film with specified grain boundary positions is formed by controlling the nucleation position in amorphous Si (B
).

At this time, the crystal grain size is equal to the interval between regions with high Si atom density, and can be arbitrarily determined, and the variation in the grain size is extremely small.

[Example] 1000 polycrystalline Si thin films were deposited by thermal decomposition of SiH by low pressure chemical vapor deposition (CVD) on a base material made of 4-inch glass. The formation temperature was 620°C.

The grain size of the deposited polycrystalline Si thin film was less than 500 Å.

Next, Si ion implantation was performed twice. First, polycrystalline Si
31 ions were implanted on the entire surface of the thin film at an implantation dose of 5×101Sc m
-', implanted with an implantation energy of 110 keys, polycrystalline S
The entire thin film was made amorphous to form an amorphous Si film.

Further, a resist was applied onto the amorphous XSi film, and two types of patterns were formed using ordinary glue lithography, in which holes with a diameter of 1 μm were arranged in the form of lattice points at intervals of 5 μm and 10 μm. A second Si film is applied using the patterned resist as a mask.
Ion implantation was performed. The injection volume is the same as the first time <5X10
15 am-'', the injection energy is -40 key, and S
A substrate having a region with high t-atom density was formed.

After peeling off the resist mask, 6
When heat treated at 00℃ for 100 hours, 1000
Grain boundaries are approximately 5μm to 110μm, as is the flat human film.
They are arranged in a lattice shape with intervals, and the particle size distribution is an average of 5 μm and 10
It was found by observation using a transmission electron microscope that the difference was ±1 μm with respect to μm.

When 100 field effect transistors with a channel length of 3 μm were fabricated using a normal IC process on the St thin film with a particle size distribution of 5 μm±1 μm prepared as described above, the electron mobility was 200±5 cm2/ v-sec
, The variation in threshold value was ±0.2V. Since it is possible to arrange the channel portion of the transistor so that no grain boundaries exist (grain boundary positions are known in advance), high performance and narrow distribution of device characteristics have been achieved.

In addition, in the above explanation, the case of amorphous Si@, which is amorphous polycrystalline Si film, was given as an example.
The same effect can be obtained by using an amorphous Si film containing hydrogen at 550° C. by VD method or by glow discharge method as a starting material. In this case, there is no need to deeply implant ions into the entire structure to make it amorphous. In addition, the as-deposited amorphous Si film is 7
It was confirmed that crystallization did not occur up to 00°C. Ion implantation may be performed without a mask using a focused ion implantation method.

[Effect of the invention] By locally changing the Si implantation energy in amorphous Si to form a region with high vacancy concentration and SL atoms, the grain boundary position can be controlled while maintaining a flat and thin film, and the grain size distribution can be changed. A small amount of St crystal thin film was formed. Since grain boundary positions can be set in advance, devices can be fabricated while avoiding grain boundaries that adversely affect device performance, making it possible to improve the performance of device characteristics and narrow variations.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between ion implantation energy and crystallization temperature. FIG. 2 is a conceptual diagram showing an embodiment of the present invention.

Claims (5)

[Claims] (1) A region at a desired position of the amorphous Si film that is sufficiently small to allow crystal growth from a single nucleus, and which is smaller than the Si atom density in the amorphous Si film that is different from the region. A high-density region is provided, and a crystalline material grown from a single nucleus is formed in the region, and heat treatment is performed at a temperature at which no nuclei are generated in the amorphous Si film, which is different from the region, and the crystalline material is formed as a base. A method for forming a semiconductor thin film, characterized in that the amorphous Si film is crystal-grown in a solid phase. (2) The amorphous Si film having the region with high Si atom density is made by implanting ions into the entire surface of the polycrystalline Si film to make the polycrystalline Si film amorphous, and then implanting ions only into the above region. 2. The method of forming a semiconductor thin film according to claim 1, wherein the semiconductor thin film is formed by using a method of forming a semiconductor thin film. (3) An amorphous Si film is formed on the substrate, and the first ion implantation is performed with high energy so that the projected range where the implanted ion concentration is maximum is at the interface between the substrate and the amorphous Si film. 3. The method of forming a semiconductor thin film according to claim 2, wherein the second ion implantation is performed at low energy so that the projected range is locally in the center of the amorphous Si film in the film thickness direction. . (4) The method for forming a semiconductor thin film according to any one of claims 1 to 3, wherein a single region having a high Si atom density is provided. (5) The method for forming a semiconductor thin film according to any one of claims 1 to 3, wherein a plurality of regions having a high Si atom density are provided.