JPH0666305B2 - Method for forming SOI substrate - Google Patents

Description

The present invention relates to a method for forming an SOI substrate.

[Conventional technology]

In order to achieve higher density and higher integration of semiconductor circuit elements, development of semiconductor three-dimensional circuit elements having a laminated structure in which semiconductor thin films and insulating films are alternately laminated on a substrate and devices are incorporated in each semiconductor thin film is being advanced. However, when manufacturing this kind of semiconductor three-dimensional circuit element, minute irregularities are generated on the surface of each semiconductor thin film or each insulating film in the intermediate stage of the process, and when these irregularities remain, these irregularities are generated. Since the quality of the growth film in the subsequent process is adversely affected, it is necessary to smooth the surface of the growth film having irregularities during the process.

Regarding the necessity of this surface smoothing, an SOI (silicon on insulator) formed by forming a single crystal insulating film on the substrate and then epitaxially growing a single crystal silicon film on the insulating film is further formed.
r) A substrate will be taken as an example for the detailed description.

The SOI substrate has attracted attention as an element material for obtaining integrated circuits with excellent characteristics.
The icon on sapphire) substrate has excellent features such as high speed due to reduction of stray capacitance and high integration due to reduction of element isolation area.

However, in the case of SOS substrates, it is difficult to increase the size of sapphire and it is expensive, so recently, SOI substrates using single crystal magnesia spinel (MgO ・ Al ₂ O ₃ ) as a single crystal insulating film have replaced sapphire. The research and development of forming technology are being actively conducted.

And, as a conventional method for forming a single crystal magnesia spinel film on a single crystal silicon substrate, for example, Japanese Patent Publication No.
The vapor phase epitaxial growth method (hereinafter referred to as VPE method) as described in Japanese Patent Publication No. -55119, Japanese Patent Publication No. 58-55120, etc. is well known.

Also, Extended Abstracts of the Fifteens Conference on Solid State Devices and Materials, Tokyo, 1983, pp31-34 [Extended Abstracts of the 15
th Conference on Solid State Devices and Material
s, Tokyo, 1983, pp31-34], as shown in FIG.
MgCl ₂ —Al—HCl—CO ₂ —H ₂ on the single crystal silicon substrate 1
After the single crystal magnesia spinel film 2 is formed by the -N ₂ -based VPE method, it is annealed at a temperature of 1100 ° C. in an oxygen atmosphere to oxidize the interface between the silicon substrate 1 and the magnesia spinel film 2 to form the silicon oxide film 3 Then, a single crystal silicon film 4 is epitaxially grown on the magnesia spinel film 2 and the silicon substrate 1 is formed by the double gate insulating film of the magnesia spinel film 2 and the silicon oxide film 3.
It has been reported that the dielectric isolation characteristics between the upper layer and the upper silicon film 4 are improved, and the gate insulation characteristics of an integrated circuit manufactured using an SOI substrate having such a double gate insulating film are improved. There is.

By the way, as described above, the change in crystallinity of the magnesia spinel film 2 when the magnesia spinel film 2 is formed on the silicon substrate 1 by the VPE method and then annealed at a high temperature in an oxygen atmosphere for about 2 hours is X. When examined by the line diffraction method, it became as shown in FIG.

That is, FIG. 10 shows the ratio of the X-ray diffraction intensity of the (400) magnesia spinel annealed at each annealing temperature, based on the X-ray diffraction intensity of the (400) magnesia spinel before annealing. The larger this ratio is, the more the crystallinity of the magnesia spinel film 2 increases. As is clear from FIG. 10, the higher the annealing temperature, the better the crystallinity of the magnesia spinel film 2.

However, when annealing is performed at a temperature of 1200 ° C., the crystallinity of the magnesia spinel film 2 is improved, but as can be seen from the electron micrograph of FIG. 11, the surface of the magnesia spinel film 2 is rough and the flatness is poor. In addition, the reflected electron beam diffraction pattern showing the surface crystal structure of the magnesia spinel film 2 in FIG.
Since the surface state and the crystal structure of the surface of the magnesia spinel film 2 when annealed at the temperature are not good,
There is a problem that the quality of the silicon film 4 epitaxially grown on the magnesia spinel film 2 is deteriorated.

On the other hand, when annealing is performed at a temperature of 1100 ° C or lower,
Compared to the case of 1200 ℃, the magnesia spinel film 2
Although the surface roughness of is decreased, as shown in FIG. 10, the rate of increase in crystallinity of the magnesia spinel film 2 due to annealing is
Since it is remarkably smaller than that at 1200 ° C., the film quality of the silicon film 4 epitaxially grown on this magnesia spinel film 2 is not sufficiently satisfactory.

Then, usually, in the pre-stage of the process of forming the insulating film or the semiconductor thin film, the substrate surface is mirror-polished to smooth the substrate surface.

[Problems to be Solved by the Invention]

However, there is no effective method other than polishing as described above as a method for smoothing the surface of the growth film in the middle of the process as described above. May occur, causing mechanical distortion or peeling of the film due to the hardness and adhesion strength of the grown film, and the process must be interrupted each time polishing is performed to set the wafer in the polishing apparatus. There is a problem in that it takes time.

The present invention has been made in view of such circumstances, the crystallinity of the single crystal insulating film, it is possible to significantly improve the surface characteristics, prevent the deterioration of the film quality of the single crystal silicon film, high-quality SO
It is an object of the present invention to provide a method for forming an SOI substrate that can obtain an I substrate.

[Means for Solving the Problems]

The method for forming an SOI substrate of the present invention comprises a step of forming a single crystal insulating film on a single crystal silicon substrate, a step of annealing the single crystal insulating film, and a normal line of this surface on the surface of the single crystal insulating film. Irradiating an ion beam at an incident angle of about 85 ° or more with respect to the direction to smooth the surface, and forming a single crystal silicon film on the smoothed single crystal insulating film, It is characterized by consisting of.

[Action]

According to the method for forming an SOI substrate of the present invention, after the single crystal insulating film is formed on the single crystal silicon substrate, the single crystal insulating film is annealed, so that the crystallinity of the single crystal insulating film is significantly improved. Further, although the surface of the single crystal insulating film after this annealing is rough, the surface of the single crystal insulating film is irradiated with an ion beam at an incident angle of about 85 ° or more with respect to the normal direction of this surface to irradiate the surface. Since the single crystal insulating film is smoothed, the crystallinity and surface characteristics are significantly improved without causing physical deformation such as peeling and contamination of the surface. After that, since the single crystal silicon film is formed over the single crystal insulating film having excellent crystallinity and surface characteristics, deterioration of the film quality of the single crystal silicon film can be prevented and a high-quality SOI substrate can be obtained.

Therefore, when an integrated circuit is manufactured using such an SOI substrate, the device characteristics can be improved.

〔Example〕

 Hereinafter, the present invention will be specifically described based on its examples.

FIG. 1 is a schematic diagram used for explaining the method of the present invention, in which 1 denotes a single crystal silicon substrate having a plane orientation (100). A single crystal spinel film 20 formed by the CVD method is laminated on the short crystal silicon substrate 1. FIG. 2 is an electron micrograph of the surface state of the single crystal spinel film 20, and the surface of the single crystal spinel film 20 has minute irregularities.

As a method for removing such minute unevenness, a fine processing technique using an ion beam using an ion beam milling device for etching a semiconductor film or the like is usually considered.

By the way, according to the catalog data published by Commonwells Inc. in the United States, the relationship between the incident angle of the ion beam and the etching rate with respect to the normal direction of the substance surface when various substances are etched by this ion beam milling device is As shown in the figure, most of the substances are etched when the incident angle of the ion beam is in the range of 0 ° to 80 °, and when the incident angle is more than 80 °, the etching rates of most of the substances decrease sharply. It can be seen that it is not etched much.

Therefore, in the method of the present invention, specifically, while rotating the substrate 1 on which the spinel film 20 is formed in a horizontal plane, the incident angle θ becomes 80 ° or more with respect to the normal direction of the surface of the spinel film 20, By irradiating with an argon (Ar) ion beam IB, minute irregularities on the surface of the spinel film 20 are removed by etching, and like the conventional polishing method, the spinel film 20 is removed.
The surface of the spinel film 20 is smoothed without causing contamination of the surface or peeling of the spinel film 20.

The specific method of argon ion beam irradiation is as follows. That is, argon gas is ionized to obtain Ar ⁺ , this Ar ⁺ is led out from the extraction electrode and neutralized by the neutralizer (filament), and then Ar atoms are spun into the spinel film 20.
Irradiate to.

By the way, the energy of the argon ion beam IB is 500e
V, current density is 1.4mA / cm ² , incident angle θ is 60 each
As a result of taking electron micrographs of the surface state of the spinel film 20 at ゜, 85 ゜ and 87.5 ゜, as shown in Fig. 4 (a) and (b) for θ = 60 ゜, 85 ゜ and 87.5 ゜, respectively. , (C), and when the incident angle θ is 60 °, as shown in (a) of the figure, there are still irregularities on the surface of the spinel film 20, and at θ = 85 °, As can be seen from FIG. 7B, the spinel film 20 has almost no surface irregularities and becomes fairly smooth. At θ = 87.5 °, as shown in FIG. Is about 85 ° or more, a spinel film 20 having a smooth surface can be obtained, and even if a single crystal silicon film is formed on this spinel film 20, the quality of the single crystal silicon film may be deteriorated. Absent.

At this time, if the incident angle θ is around 75 ° or 80 °, θ =
It is natural that the surface of the spinel film 20 becomes smoother than in the case of 60 °, but when the single crystal silicon films are laminated as described above, the film quality of the single crystal silicon is such that there is no practical problem. A film cannot be obtained, and it is not suitable for smoothing the surface of the thin film also from the viewpoint of etching rate. By setting the incident angle θ at about 85 ° or more, the smoothing of the surface of the spinel film 20 is effectively performed. You can do it.

FIG. 5 shows the evaluation of the film quality of the spinel film after being irradiated with the ion beam. For comparison, FIG. 5 also shows the evaluation of the film quality of the spinel film before ion beam irradiation. Regarding the reflection electron beam diffraction [RHEED] pattern photograph, it can be seen that the spinel film after etching has a streak-like spot pattern, and the surface is smooth without amorphization. Regarding X-ray diffraction, the film thickness is reduced by etching, the diffraction intensity is reduced, and the rocking curve half-width is slightly increased.
Regarding the Mg composition, the reason why the Mg composition is large before etching is that a layer containing a large amount of Mg exists on the surface during growth of the spinel film, and there is no change in the Mg / Al composition ratio before and after etching. Further, regarding the electron binding energy (XPS), no change in the binding energy of Al, Mg, and O was observed before and after etching, indicating that relative crystallization did not occur.

As described above, the spinel film smoothed by the method of the present invention is not damaged by ion beam irradiation. Therefore, according to the method of the present invention, the spinel film can be smoothed without damaging the spinel film.

Next, when performing a smoothing process by irradiating an ion beam,
The rotation speed of the substrate and the degree of smoothing will be described. Sixth
(A)-(e) are electron micrographs of the surface of the spinel film after irradiation with an ion beam while rotating under the rotation conditions shown in Table 1 below.

It can be seen from FIG. 6 that the surface of the spinel film after etching is smooth when the total number of rotations is one or more. Ion energy is 500 eV and current density is 1.
Under 4mA / cm ² condition, if the rotation speed is sufficiently high (4r
It was possible to obtain sufficient smoothness in the spinel film after 10 minutes of etching treatment. From this, the condition necessary for smoothing is that the etching time is 10 minutes or more and the substrate is rotated once or more during this time.

Next, a specific method for forming an SOI substrate using the above-described smoothing method will be described.

First, a circular (100) single crystal silicon substrate 1 having a diameter of 3 inches shown in FIG. 9 was housed in a reaction chamber of an Al—HCl—MgCl ₂ —CO ₂ —H ₂ system vapor phase epitaxial growth apparatus, and a silicon substrate 1 is heated and held at 920 ° C., and a single crystal magnesia spinel film 2 having a thickness of 200 nm is grown on the silicon substrate 1.

Next, the magnesia spinel film 2 grown on the silicon substrate 1 is annealed in an oxygen atmosphere at a temperature of 1200 ° C. for 2 hours, and the interface between the magnesia spinel film 2 and the silicon substrate 1 is oxidized through the magnesia spinel film 2. To form a silicon oxide film 3.

At this time, annealing at a high temperature of 1200 ° C.
As is clear from FIG. 10, the crystallinity of the magnesia spinel film 2 is significantly improved, but on the other hand, as described above, the surface of the magnesia spinel film 2 is roughened or the crystal structure of the surface is deteriorated.

Next, in order to improve the surface characteristics of the magnesia spinel film 2, the surface of the magnesia spinel film 2 is exposed to an incident angle of 85 ° or more with respect to the normal direction of the surface by an ordinary ion milling device. The surface of the magnesia spinel film 2 is smoothed by irradiating it with an argon (Ar) ion beam to etch the surface of the magnesia spinel film 2 at a rate of 2 nm / min for about 10 minutes in the depth direction by about 20 nm.

At this time, the surface state of the magnesia spinel film 2 subjected to the ion beam etching is as shown in the electron microscope photograph of FIG. 7, which is more than that of the electron microscope photograph of FIG. 11 showing the conventional case where etching is not performed. As is apparent, the magnesia spinel film 2 was formed by ion beam etching.
The roughened surface is removed and the surface becomes flat, and the reflected electron beam diffraction pattern showing the crystal structure of the surface of the magnesia spinel film 2 subjected to ion beam etching becomes a streak pattern showing a single crystal as shown in FIG. Therefore, the surface characteristics of the magnesia spinel film 2 are remarkably improved by the ion beam etching.

Then, on the flattened magnesia spinel film 2, a monocrystalline silicon film 4 is epitaxially grown to a film thickness of 2 μm at a growth temperature of 950 ° C. by a thermal decomposition method of monosilane (SiH ₄ ) to form an SOI substrate.

By the way, the crystallinity of the silicon film 4 grown on the magnesia spinel film 2 subjected to ion beam etching after being annealed at 1200 ° C. for 2 hours in the oxygen atmosphere is determined by the rocking curve half of Si (422) X-ray diffraction. As a result of evaluation by measurement of the value width, the half value width was 0.10 °, and for comparison, a single crystal silicon film (annealed under the same annealing conditions as described above and grown on the single crystal magnesia spinel film without ion beam etching ( (Hereinafter referred to as a silicon film of A)) and a single crystal silicon film (hereinafter referred to as a silicon film of B) grown on a single crystal magnesia spinel film which has an annealing temperature of 1100 ° C. and is not subjected to ion beam etching. ) When the rocking curve full width at half maximum of X-ray diffraction was measured, the full width at half maximum of each of the A and B silicon films was 0.35 ° and 0.20 °. This is much larger than the half width of 0.10 ° in the case of the embodiment.

This is because, in the case of the silicon film A, the single crystal silicon film was grown on the magnesia spinel film whose surface was still roughened by annealing at a high temperature of 1200 ° C. In the case of the B silicon film, the single crystal silicon film was grown on the magnesia spinel film whose surface roughness is small but the increase in crystallinity is insufficient by annealing at 1100 ° C. This makes it impossible to obtain a single crystal silicon film having a sufficient film quality.

Table 2 below shows an n-MOS formed on an SOI substrate (single crystal silicon film) formed by the method for forming an SOI substrate of the present invention.
It is a table showing the characteristics of the FET (FET (a)), and Table 2 shows a single crystal silicon film laminated on the magnesia spinel film which is annealed under the same annealing conditions as a reference and is not subjected to ion beam etching. Created n-MOS FET
The characteristics of (FET (b)) are also shown.

As can be seen from Table 2, SO produced according to the present invention
The characteristics of the n-MOS FET (FET (a)) formed on the I substrate are excellent, and this is due to the improvement of the crystallinity of the single crystal silicon film accompanying the smoothing treatment of the magnesia spinel film. .

Although the annealing is performed in the oxygen atmosphere in this embodiment, the annealing may be performed in another oxidizing atmosphere, for example, a nitrogen atmosphere containing water vapor.

〔The invention's effect〕

According to the method for forming an SOI substrate of the present invention, after the single crystal insulating film is formed on the single crystal silicon substrate, the single crystal insulating film is annealed, so that the crystallinity of the single crystal insulating film is significantly improved. Further, although the surface of the single crystal insulating film after this annealing is rough, the surface of the single crystal insulating film is irradiated with an ion beam at an incident angle of about 85 ° or more with respect to the normal direction of this surface to irradiate the surface. Since the single crystal insulating film is smoothed, the crystallinity and surface characteristics are remarkably improved without causing physical deformation such as peeling and contamination of the surface. After that, since the single crystal silicon film is formed over the single crystal insulating film having excellent crystallinity and surface characteristics, deterioration of the film quality of the single crystal silicon film can be prevented and a high-quality SOI substrate can be obtained.

Therefore, when the integrated circuit is manufactured using the SOI substrate formed by the method of the present invention, the device characteristics can be improved, and the method of the present invention exhibits excellent effects.

[Brief description of drawings]

FIG. 1 is a schematic diagram used for explaining the method of the present invention, FIG. 2 is an electron micrograph of the crystal structure of the surface of a single crystal spinel film which is not irradiated with an ion beam, and FIG. 3 is the incidence of an ion beam. 4 (a) to (c) are graphs showing the relationship between the angle and the etching rate of various substances, and the surface of the single crystal spinel film when the incident angles of the ion beam are 60 °, 85 °, and 87.5 °, respectively. 5 is an electron micrograph of the structure of the crystal of Fig. 5, Fig. 5 is a characteristic diagram shown together with a photograph of the structure of the crystal of the single crystal spinel film, and Fig. 6 is a structure of the crystal of the surface of the single crystal spinel film when the rotation speed is changed. 7 is an electron micrograph of the crystal structure of the surface of the single crystal magnesia spinel film in the method for forming an SOI substrate of the present invention, and FIG. 8 is a single crystal magnesia in the method for forming an SOI substrate of the present invention. Crystal structure of the surface of the spinel film Fig. 9 is a sectional view of an SOI substrate, and Fig. 10 is the relationship between the annealing temperature and the X-ray diffraction intensity of a single crystal magnesia spinel film formed by the VPE method on a single crystal silicon substrate. FIG. 11 is an electron micrograph of the crystal structure of the surface of the single crystal magnesia spinel film in the conventional method, and FIG. 12 is a photo of the structure of the same crystal by backscattered electron diffraction. 1 ... Single crystal silicon substrate, 2 ... Single crystal magnesia spinel film, 4 ... Single crystal silicon film, 20 ... Single crystal spinel film, 18 ... Argon ion beam

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-59-69930 (JP, A)

Claims (5)

[Claims] 1. A step of forming a single crystal insulating film on a single crystal silicon substrate, a step of annealing the single crystal insulating film, and a surface of the single crystal insulating film having a thickness of about 85 in a direction normal to the surface. Characterized by comprising a step of irradiating an ion beam at an incident angle of ° or more to smooth the surface and a step of forming a single crystal silicon film on the smoothed single crystal insulating film. Method for forming SOI substrate. 2. The method for forming an SOI substrate according to claim 1, wherein the single crystal insulating film is annealed in an oxidizing atmosphere. 3. The method for forming an SOI substrate according to claim 2, wherein the single crystal insulating film is a single crystal magnesia spinel film. 4. The method for forming an SOI substrate according to claim 3, wherein the single crystal insulating film is annealed at a temperature of about 1200 ° C. or higher. 5. The single crystal silicon substrate on which the single crystal insulating film is formed is rotated at least once in a horizontal plane when the ion beam is irradiated. A method for forming an SOI substrate according to claim 1.