JP4943172B2 - Method for forming SOS substrate having silicon epitaxial film - Google Patents

Description

  The present invention relates to a method of forming an SOS substrate having a silicon epitaxial film for directly forming a silicon epitaxial film on a sapphire single crystal substrate, which is used for manufacturing an electronic / optical device such as a silicon semiconductor integrated circuit and a silicon photodiode.

  As the density of semiconductor integrated circuits increases, junctions with insufficient element isolation cause an increase in parasitic capacitance and leakage current, which becomes a major obstacle to the development of high-speed devices with low power consumption. As a device characterized by element isolation, there is a device using SOI (Silicon On Insulator) substrate technology, and among them, an SOS (Silicon using a sapphire single crystal excellent in insulation, which belongs to the category of this SOI device. On Sapphire) device is known. It is known that a semiconductor process similar to that of a normal silicon substrate can be applied to a silicon epitaxial film formed on a sapphire substrate, so that there is a merit in process design and an integrated device that operates at high speed with low power consumption is known. ing.

  Usually, this silicon epitaxial film is formed by a chemical vapor deposition (CVD) method. A substrate having a structure in which a silicon epitaxial film is formed on a sapphire single crystal substrate by a CVD method (hereinafter referred to as an SOS substrate) follows the crystallographic orientation of the sapphire single crystal substrate, for example, the main surface orientation of the sapphire single crystal substrate. Is a (1-102) plane, it is a well-known fact that the plane orientation of the silicon epitaxial film formed thereon forms a (100) plane self-organized crystal plane.

  However, in the case of such an SOS substrate, a large number of crystal defects are generated in the CVD-grown silicon epitaxial film due to strains caused by differences in lattice constants and thermal expansion coefficients between sapphire and silicon. For this reason, a device fabricated on such a silicon epitaxial film has not been able to obtain good characteristics.

  For this reason, with respect to the method for manufacturing the SOS substrate, many research reports have been made for the purpose of improving / reducing crystal defects generated in the above-described silicon epitaxial film (for example, Non-Patent Document 1 and Patent Document). 1).

  Non-Patent Document 1 discloses a manufacturing method called a three-step process in order to reduce the crystal defect density in the silicon epitaxial film on the SOS substrate.

In this manufacturing method, as a first step, a deposition temperature of 955 ° C. and a deposition rate are performed on a sapphire single crystal substrate surface having a (1-102) plane orientation in a SiH ₄ and H ₂ gas atmosphere by an atmospheric pressure CVD method. Under the condition of 0.33 μm / min, a silicon epitaxial film having a thickness of about 0.2 μm and having a (100) plane is formed. At this point, a large number of crystal defects exist in the formed silicon epitaxial film. Here, -1 indicating the plane orientation (1-102) represents a Miller index of 1 with a bar attached.

Next, as a second step, Si ⁺ ions are implanted from the surface of the SOS substrate toward the inside under conditions of an acceleration energy of 130 keV and a dose of about 1 × 10 ¹⁵ cm ⁻² at room temperature. By this ion implantation process, the silicon epitaxial film of the SOS substrate becomes an amorphous state due to damage during ion implantation, except for a very thin layer on the surface.

Finally, as the third step, the following process is continuously performed in the CVD apparatus. First, by performing annealing for 2 hours at a temperature of 960 ° C. in an H ₂ atmosphere, a silicon epitaxial film in an amorphous state is subjected to solid phase epitaxial regrowth using a very thin layer as a seed. At this time, the silicon epitaxial film is etched by about 0.05 μm. Subsequently, in a mixed gas of H ₂ and HCl, the silicon epitaxial film regrown by solid phase epitaxial growth is subjected to vapor phase etching to remove about 0.06 to 0.08 μm. By this vapor phase etching process, the ultrathin layer on the surface side used as a seed in the solid phase growth of the silicon epitaxial film regrown by solid phase epitaxial growth is completely removed. Subsequently, a silicon epitaxial film with a thickness of about 0.45 to 0.55 μm is additionally formed on the remaining solid phase epitaxially regrown silicon epitaxial film under the same conditions as the CVD method in the first step.

  As a result, according to this Non-Patent Document 1, a high-quality silicon epitaxial film in which crystal defects are reduced as compared with the silicon epitaxial film formed in the first step by the three-step process described above. Is disclosed.

  Further, Patent Document 1 discloses providing an SOS substrate that is excellent in crystallinity even when the silicon epitaxial film is thin and has few crystal defects such as micro twins in the production of the SOS substrate.

  According to the prior art disclosed in Patent Document 1, a silicon epitaxial film having a thickness of 1 μm or more is first formed on a sapphire single crystal substrate to produce an SOS substrate. Next, a heat treatment step of heat-treating the SOS substrate in an oxygen atmosphere at a temperature higher than the formation temperature of the silicon epitaxial film, and a step of etching away the silicon oxide film on the silicon epitaxial film formed in the heat treatment step Is configured to include a step of repeating until a desired film thickness of the silicon epitaxial film is reached.

  According to this prior art, the silicon epitaxial film has a thin film thickness of about 0.2 to 0.3 μm or less, and the crystallinity of the silicon epitaxial film is excellent, and the crystal defects such as micro twins are extremely small. It is disclosed that the substrate can be manufactured.

  In general, in the case of an epitaxial substrate such as the above-described SOS substrate, the lattice constant and the thermal expansion coefficient of the sapphire single crystal substrate and the silicon epitaxial film are greatly different from each other, resulting in innumerable crystal defects. Thus, it is observed in appearance that the surface roughness of the surface of the SOS substrate is deteriorated. It is a well-known fact that there is a correlation between the degree of surface roughness on the SOS substrate and the density of crystal defects generated inside the crystal of the epitaxial silicon film. That is, it is known that the larger the surface roughness, the higher the density of crystal defects (for example, see Non-Patent Document 2).

In Non-Patent Document 2, as a useful method for examining the defect density of a substrate surface during a semiconductor process, it is possible to inspect the measurement target substrate nondestructively and is sensitive to the unevenness of the measurement surface (degree of surface roughness). The correlation between the surface roughness of the SOS substrate and the defect density was confirmed by using an ultraviolet light reflectance measurement method (UVR: Ultra-Violet Reflectance) for measuring the change in reflectance of the SOS substrate, and the above-described contents are disclosed. .
JP 59-82744 A Appl. Phys. Lett. Vol.39, No.2, pp.163-165 (1981) Solid State Technology / February pp.104-109 (1983)

  However, although the crystal defects of the silicon epitaxial film of the SOS substrate manufactured by the three-step process described in Non-Patent Document 1 described above have been reduced, FIG. ), Crystal defects still exist as compared with the bulk silicon crystal, and therefore it cannot be said that the crystal defect reduction effect is sufficient.

  In addition, according to the method described in Patent Document 1 described above, the heat treatment step and the etching treatment step are repeatedly performed for about 10 cycles. Therefore, when this method is employed as a device manufacturing process, for example, the cost is reduced. Considering performance, it is difficult to adopt.

  Therefore, the inventor of this application pays attention to the surface roughness reflecting the defect density of the SOS substrate shown in Non-Patent Document 2, and the CVD method used for the formation process of the silicon epitaxial film is the atmospheric pressure CVD method or The following experiment was conducted to measure the surface roughness in each process of SOS substrate fabrication using the low pressure CVD method as a parameter. As a method for measuring the surface roughness, a known wafer surface roughness measuring device using light reflection was used.

  As the sapphire single crystal substrate used in the experiment, a substrate having a plane orientation (1-102) plane similar to that described in Non-Patent Document 1 was used. The size of the sapphire single crystal substrate used is a 6-inch diameter wafer.

First, in the first experiment using the atmospheric pressure CVD method, a silicon epitaxial film was formed on the sapphire single crystal substrate under the same conditions as those described in Non-Patent Document 1. That is, under normal pressure, the deposition temperature is 850 to 1150 ° C. in a SiH ₄ and H ₂ gas atmosphere, and the flow rate ratio of SiH ₄ gas to H ₂ gas is 5 × 10 ⁻⁴ to 2 × 10 ^−2. A silicon epitaxial film having a (100) plane with a thickness of about 2 μm was formed. At this time, the surface roughness of the SOS substrate was measured. Next, as in the conditions described in Non-Patent Document 1, Si ⁺ ion implantation is performed on this SOS substrate under the conditions of an acceleration energy of 130 keV and a dose of 1 × 10 ¹⁵ cm ⁻² . went. Next, after annealing for 2 hours at a temperature of 800 to 1100 ° C. in an H ₂ atmosphere to perform solid phase epitaxial regrowth, thermal oxidation is performed at 800 to 1100 ° C. under conditions of an O ₂ flow rate of 0.1 to 10 SLM. It was. After removing the silicon oxide film formed by the thermal oxidation treatment with a hydrofluoric acid-based etching solution, the surface roughness of the SOS substrate was measured again.

On the other hand, in the second experiment using the low pressure CVD method, a silicon epitaxial film was formed on the sapphire single crystal substrate using the low pressure CVD method. As formation conditions, under the reduced pressure of about 5 to 500 Torr, the atmospheric pressure CVD of the first experiment is performed under the condition that the SiH ₄ gas flow ratio to the H ₂ gas is in the range of 1 × 10 ⁻³ to 1 × 10 ^−1. A silicon epitaxial film having a (100) plane with a plane orientation of about 0.2 μm in thickness was formed at the same deposition temperature as the method. At this point, the surface roughness of the SOS substrate was measured as in the first experiment. Next, ion implantation, annealing, thermal oxidation treatment, and silicon oxide film etching were performed on the SOS substrate under the same conditions as in the first experiment, and then the surface roughness of the SOS substrate was measured again. .

  As a result of the above experiment, the surface roughness of these two types of SOS substrates was measured, and the results expressed as standard deviation values are shown in FIGS. In each figure, the horizontal axis indicates the distance from the center of the surface of the SOS substrate wafer to the X axis direction that is parallel to the main orientation flat of the wafer and the Y axis direction that is the vertical direction in units of mm. The axis indicates the standard deviation value of the surface roughness in the unit of nm. The fold line A and fold line B shown in each figure show the measurement results connecting the standard deviation values of the surface roughness in the X-axis and Y-axis directions of the orthogonal XY coordinates with the center of the surface of the SOS substrate wafer as the origin. ing.

  3A and 3B show the results of measuring the surface roughness of the SOS substrate in the first experiment, and FIG. 3A shows a state immediately after the silicon epitaxial film is formed by the atmospheric pressure CVD method. The measured values of the surface roughness and FIG. 3B show the measured values of the surface roughness after removing the silicon oxide film.

  Similarly, FIGS. 4A and 4B show the results of measuring the surface roughness of the SOS substrate in the second experiment, and FIG. 4A shows the formation of a silicon epitaxial film by the low pressure CVD method. The measured value of the surface roughness immediately after and the measured value of the surface roughness after removing the silicon oxide film are shown in FIG. 4B, respectively.

  As described above, from the measurement result of the first experiment, the value of the surface roughness of the SOS substrate immediately after forming the silicon epitaxial film by the atmospheric pressure CVD method shows a good value of about 1 to 2 nm excluding the outer peripheral portion of the wafer. It was. Moreover, it turned out that it has increased to the value of about 3-4 nm after passing through the subsequent process. On the other hand, from the measurement results of the second experiment, the surface roughness of the SOS substrate immediately after forming the silicon epitaxial film by the low pressure CVD method is about 5 nm except for the outer peripheral portion of the wafer, and even after the subsequent steps, the surface roughness is 5 nm. It was found that there was no change in surface roughness.

  As described above, the value of the surface roughness of the SOS substrate after removing the silicon oxide film is compared with the surface roughness immediately after forming the silicon epitaxial film due to the difference in the method of forming the silicon epitaxial film in the production of the SOS substrate. From the experimental results, it was found that increases or does not change. However, in all the experimental results, after removing the silicon oxide film of the SOS substrate subjected to the crystallinity improvement treatment, the value of the surface roughness is as large as about 3 to 5 nm, and is used as a device manufacturing process. For this reason, the flatness of the surface is insufficient. The influence of the surface roughness has a problem in that, for example, a patterning accuracy is lowered in a lithography process, and thus variations in device characteristics and yield are reduced.

  Therefore, in the present invention, as a result of earnest research, in order to obtain a practical SOS substrate having a good surface roughness with few crystal defects, in the method for forming a silicon epitaxial film, an atmospheric pressure CVD method and a low pressure CVD method are used. It was found that the conventional problems can be solved by forming a silicon epitaxial film continuously.

  The present invention has been made in view of the above-described conventional problems.

  Accordingly, an object of the present invention is to use an atmospheric pressure CVD method and a low pressure CVD method in succession in a method for forming a silicon epitaxial film in producing an SOS substrate in which a silicon epitaxial film is directly formed on a sapphire single crystal substrate. By forming a silicon epitaxial film, an SOS substrate having a silicon epitaxial film for obtaining an SOS substrate having a good surface roughness even after steps such as ion implantation, annealing, thermal oxidation, and removal of the silicon oxide film is performed. It is to provide a forming method.

  That is, according to the first aspect of the present invention, in manufacturing an SOS substrate in which a silicon epitaxial film is directly formed on a sapphire single crystal substrate, an SOS substrate having a silicon epitaxial film including the following first to seventh steps is manufactured. A forming method is provided.

  In the first step, a sapphire single crystal substrate is prepared.

  In the second step, a first silicon epitaxial film deposited by an atmospheric pressure CVD method is formed on the first main surface which is the surface of the sapphire single crystal substrate.

  In the third step, a second silicon epitaxial film deposited by a low pressure CVD method is formed on the first silicon epitaxial film.

In the fourth step, ion implantation of Si ⁺ ions is performed from the surface of the second silicon epitaxial film toward the inside of the first silicon epitaxial film to make the first and second silicon epitaxial films amorphous. .

  In the fifth step, the first and second silicon epitaxial films in the amorphous state are subjected to solid phase epitaxial regrowth by annealing in a hydrogen atmosphere.

  In the sixth step, a silicon oxide film is formed on the second silicon epitaxial film which has been solid-phase epitaxially regrown, so that thermal oxidation is performed until the second silicon epitaxial film which has been solid-phase epitaxially regrown is changed to a silicon oxide film. Oxidize by the method.

  In the seventh step, the silicon oxide film formed in the sixth step is removed by etching to obtain an SOS substrate consisting only of the first silicon epitaxial film that has been solid-phase epitaxially regrown.

  According to the second invention, as the first step, the sapphire single crystal substrate having a plane orientation of the (1-102) plane or the (0001) plane of the sapphire single crystal substrate. It is preferable to prepare

  According to the first invention, the first silicon epitaxial film by the atmospheric pressure CVD method having a good surface roughness value immediately after the formation of the silicon epitaxial film, ion implantation, annealing treatment, thermal oxidation treatment process, and silicon oxidation By forming the second silicon epitaxial film by the low pressure CVD method in which the value of the surface roughness does not change even after the process such as film removal, the surface roughness value does not change from that immediately after the CVD process. The effect that the SOS substrate which consists only of the 1st silicon epitaxial film of surface morphology by the atmospheric pressure CVD method can be expected.

  According to the second invention, a sapphire single crystal substrate having a plane orientation of either the (1-102) plane or the (0001) plane is used, and the first is above the plane. And the second silicon epitaxial film are sequentially formed so that the surface orientations of the formed first and second silicon epitaxial films are the (100) plane or ( 111) surface.

  Embodiments of the present invention will be described below with reference to the drawings. These drawings only schematically show the shape, size, and arrangement relationship of each component to the extent that the present invention can be understood, and the numerical and other conditions described below are merely mere. This is a preferred example, and the present invention is not limited to the embodiments of the present invention. In the cross-sectional view, in order to prevent complication of the drawing, some hatching or the like representing the cross-section is omitted.

(Embodiment)
1 (A) to 1 (D) and FIGS. 2 (A) to 2 (C), an outline of a manufacturing process flow of an SOS substrate having a silicon epitaxial film for explaining an embodiment of the present invention is shown. Show. Each drawing shows a cross section of a main part in a main process for manufacturing an SOS substrate according to the present invention.

  FIG. 1A is a view for showing a cross-sectional structure of a sapphire single crystal substrate 100 used in the embodiment of the present invention.

  First, in the first step, a sapphire single crystal substrate 100 is prepared. Therefore, in the first step, a sapphire single crystal substrate having a plane orientation (1-102) plane is used as the sapphire single crystal substrate 100. Here, one surface of the sapphire single crystal substrate 100 was defined as a first main surface 102 (FIG. 1A).

Next, the sapphire single crystal substrate 100 is transferred into a CVD apparatus, and the first main surface 102 of the sapphire single crystal substrate 100 is cleaned at 850 to 1150 ° C. in an H ₂ atmosphere under normal pressure. Perform thermal cleaning for 30 minutes.

Next, as a second step, a first silicon epitaxial film 104 is formed on the first main surface 102 of the sapphire single crystal substrate 100 using an atmospheric pressure CVD method. Therefore, in this second step, at atmospheric pressure, at a deposition temperature of 850 to 1,150 ° C., SiH ₄ gas flow rate ratio _{H 2} gas is 5 × ¹⁰ -4 ~1 × ^{10 -2} range of conditions, 0. A first silicon epitaxial film 104 having a thickness of 1 μm is formed. The formed first silicon epitaxial film 104 forms the plane orientation (100) plane in a self-organized manner on the sapphire single crystal substrate 100 having the plane orientation (1-102) plane (FIG. 1 ( B)).

Subsequently, without exposing the inside of the CVD apparatus to the atmosphere, following the above-described atmospheric pressure CVD process of the second process, the inside of the CVD apparatus is depressurized to form a third process on the first silicon epitaxial film 104. Then, the second silicon epitaxial film 106 is formed by using the low pressure CVD method. Therefore, in this third step, the SiH ₄ gas flow ratio with respect to H ₂ gas is in the range of 1 × 10 ⁻³ to 1 × 10 ⁻¹ at a deposition temperature of 850 to 1150 ° C. under a reduced pressure of about 5 to 500 Torr. Under the conditions, a second silicon epitaxial film 106 having a thickness of 0.1 μm is formed (FIG. 1C).

Next, as a fourth step, ion implantation 108 of Si ⁺ ions is performed from the surface of the second silicon epitaxial film 106 toward the inside of the first silicon epitaxial film 104, and the first and second silicon epitaxial films are formed. The films 104 and 106 are made amorphous. Therefore, in this fourth step, the ion implantation 108 of Si ⁺ ions is performed at the room temperature from the surface of the second silicon epitaxial film 106 toward the internal first silicon epitaxial film 104 at an acceleration energy of 130 keV and a dose amount. Ion implantation is performed under conditions of 1 × 10 ¹⁵ cm ⁻² . As a result, the first and second silicon epitaxial films 104 and 106 become the first and second silicon epitaxial films 104 ′ and 106 ′ that are both in an amorphous state (FIG. 1D).

Subsequently, as a fifth step, the amorphous silicon first and second silicon epitaxial films 104 ′ and 106 ′ are annealed in a hydrogen atmosphere to cause solid phase epitaxial regrowth. Therefore, in the fifth step, in order to cause solid phase epitaxial regrowth of the first and second silicon epitaxial films 104 ′ and 106 ′ in the amorphous state described above, at a temperature of 800 to 1100 ° C. under normal pressure, H Annealing is performed under the condition of ₂ flow rates of 0.1 to 10 SLM. As a result, the first and second silicon epitaxial films 104 ′ and 106 ′ in the amorphous state become the first and second silicon epitaxial films 104 ″ and 106 ″ subjected to solid phase epitaxial regrowth (FIG. 2A )).

Next, as the sixth step, the solid phase epitaxial regrowth SOS substrate is oxidized by a thermal oxidation method. This oxidation process is performed until the entire second silicon epitaxial film 106 ″ changes to a silicon oxide film. Therefore, in this sixth step, an O ₂ flow rate of 0. An oxidation process is performed by a thermal oxidation method under conditions of 1 to 10 SLM to form a silicon oxide film 110 having a thickness of 0.23 μm. By this oxidation process, the second silicon epitaxial film 106 ″ that has been solid-phase epitaxially regrown All change to the above-described silicon oxide film 110 (FIG. 2B).

  Finally, as the seventh step, the silicon oxide film 110 is removed by etching to obtain the SOS substrate 120 in which only the first silicon epitaxial film 104 ″ subjected to solid phase epitaxial re-growth is left. By selectively removing the silicon oxide film 110 formed in the six steps with a hydrofluoric acid-based etching solution, the SOS substrate 120 having only the first silicon epitaxial film 104 "regrown by solid phase epitaxial growth is obtained (FIG. 2 (C)).

  As described above, according to the embodiment of the present invention, the surface roughness value immediately after the formation of the silicon epitaxial film is good, the silicon epitaxial film by the atmospheric pressure CVD method, ion implantation, annealing treatment, thermal oxidation treatment process, In addition, the surface roughness value does not change even after the process such as the removal of the silicon oxide film, and the surface roughness value is not changed from that immediately after the CVD process by stacking the silicon epitaxial film by the low pressure CVD method. An SOS substrate having only a silicon epitaxial film by an atmospheric pressure CVD method having a good surface morphology can be obtained.

  Furthermore, in the above-described embodiment, a silicon epitaxial film having a plane orientation (100) plane is formed using a sapphire single crystal substrate having a first main plane having a plane orientation (1-102) plane. The present invention can be applied to an SOS substrate in which a silicon epitaxial film having a plane orientation (111) plane is formed using a sapphire single crystal substrate having a plane orientation (0001) plane, and the same good results can be obtained. Can be expected.

  In the above-described embodiment, the second silicon epitaxial film may be formed by using an MBE (Molecular Beam Epitaxy) method using a solid source or a gas source as the second silicon epitaxial film formation method. Good.

  Further, even when the SiGe mixed crystal semiconductor layer is epitaxially grown on the silicon substrate, the first SiGe layer is formed by the atmospheric pressure CVD method in the same manner as the method described in the above embodiment of the present invention. The same effect can be expected by forming the second SiGe layer by the low pressure CVD method.

It is a figure for demonstrating the manufacturing process of the SOS substrate of embodiment of this invention. It is a figure for demonstrating the manufacturing process of the SOS substrate of embodiment of this invention following FIG. 1 (D). It is the figure which showed the surface roughness of the SOS board | substrate after each process in a 1st experiment using a normal pressure CVD method. It is the figure which showed the surface roughness of the SOS substrate after each process in 2nd experiment using the low pressure CVD method.

Explanation of symbols

100: sapphire single crystal substrate 102: first main surface 104: first silicon epitaxial film 104 ′: first silicon epitaxial film 104 ″ in an amorphous state: first silicon epitaxial film 106 grown by solid phase epitaxial re-growth: Second silicon epitaxial film 106 ': second silicon epitaxial film 106 "in an amorphous state: second silicon epitaxial film 108 grown by solid phase epitaxial growth: ion implantation of Si ⁺ ions 110: silicon oxide film 120: SOS substrate

Claims (2)

In producing an SOS substrate in which a silicon epitaxial film is directly formed on a sapphire single crystal substrate,
A first step of preparing a sapphire single crystal substrate;
A second step of forming a first silicon epitaxial film deposited by an atmospheric pressure CVD method on a first main surface which is a surface of the sapphire single crystal substrate;
A third step of forming a second silicon epitaxial film deposited on the first silicon epitaxial film by a low pressure CVD method;
From the surface of the second silicon epitaxial film, Si ⁺ ions are implanted in the direction toward the inside of the first silicon epitaxial film to make the first and second silicon epitaxial films amorphous. Process,
A fifth step of solid-phase epitaxial regrowth by annealing the first and second silicon epitaxial films in the amorphous state in a hydrogen atmosphere;
By forming a silicon oxide film on the solid phase epitaxially regrown second silicon epitaxial film, thermal oxidation is performed until the solid phase epitaxially regrown second silicon epitaxial film changes to the silicon oxide film. A sixth step of oxidation treatment;
And a seventh step of obtaining an SOS substrate consisting only of the first silicon epitaxial film obtained by the solid phase epitaxial regrowth by etching away the silicon oxide film formed in the sixth step. A method for forming an SOS substrate.   The sapphire single crystal substrate having a plane orientation of the (1-102) plane or the (0001) plane of the sapphire single crystal substrate is prepared as the first step. A method for forming an SOS substrate having the silicon epitaxial film according to Item 1.

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