JPH07249749A - Production of soi board - Google Patents

Abstract

PURPOSE:To reduce voids at the interface by a factor of several to ten by activating the surface of SiO2 to be bonded through plasma processing thereby enhancing the bonding strength. CONSTITUTION:A substrate 100 deposited with an oxide and a previously prepared supporting substrate 110 deposited with a silicon oxide are set in a plasma processing system where they are subjected to surface activation by oxygen plasma. Both substrates are immersed into pure water and then dried before they are bonded on the processed surfaces. It is then heat treated and ground on the silicon substrate 100 side to expose a porous silicon 102 and only the porous part 101 is etched selectively and entirely. Consequently, an SOI substrate where single crystal silicon is deposited on silicon oxide is obtained and the density of void in the SOI film can be reduced by a factor of 4 as compared with a conventional SOI substrate which is not subjected to surface treatment.

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 an SOI substrate, and more particularly to a method for manufacturing an SOI substrate manufactured by a bonding method.

[0002]

2. Description of the Related Art The formation of a single crystal silicon semiconductor layer on an insulator is performed by using a Silicon on Insulator (S).
Much research has been done because this substrate has a number of advantages that are widely known as OI) technology and cannot be reached by a bulk silicon substrate for producing a normal silicon integrated circuit.

Among the SOI formation methods reported recently, the one called "bonded SOI" is particularly known as having excellent quality.
There is. This is because the mirror surfaces of two wafers, at least one of which has an insulating film formed by oxidation or the like, are brought into close contact with each other, and heat treatment is performed to strengthen the bond at the close contact interface. This is a technique of leaving a silicon single crystal thin film having an arbitrary thickness on the insulating film by polishing or etching. The most important step in this technology is the step of thinning the silicon substrate. That is, a silicon substrate having a thickness of several hundred μm must be uniformly polished or etched to a thickness of several μm or 1 μm or less, which is technically extremely difficult in terms of controllability and uniformity. There are roughly two methods for thinning silicon. One is a method of only polishing (BPSOI: Bonding and Polishing).
ng SOI), the other is a method in which an etching stop layer is provided directly above the thin film to be left (immediately below when manufacturing a single substrate), and the etching is performed in two steps (BESOI: Bond an).
d Etchback SOI). Since BESOI often has a silicon active layer epitaxially grown on an etching stop layer which has been previously formed, BESOI is currently considered to be advantageous in order to secure the uniformity of the film thickness. However, since the etching stop layer often contains impurities at a high concentration, distortion of the crystal lattice occurs due to this, and there is a problem that crystal defects propagate to the epitaxial layer. Further, there is a possibility that the impurities may diffuse during the oxidization of the epitaxial layer or the annealing after the bonding, which may change the etching characteristics.

Another important point in the bonding SOI is that an interface state is likely to occur at the bonding interface due to impurities in the atmosphere and irregularities on the substrate surface. The interface state is likely to cause deterioration of characteristics such as current leakage of the device. Therefore, in order to avoid this, a method in which the active layer is oxidized and then bonded is considered.
As a result, the underlying interface of the active layer is not a bonding interface,
It becomes a thermal oxidation interface, and the interface level can be kept low. However, in order to obtain an oxide film thickness that sufficiently satisfies the characteristics of SOI,
It is necessary to considerably oxidize the active layer, and as described above, B
In the case of ESOI, the impurity profile of the etching stop layer may change due to the heat generated during oxidation. Therefore, the active layer is thinly oxidized, the silicon oxide layer of the other substrate is thickened, and the silicon oxide films are bonded together. But here too, new problems arise. That is, the bonding strength between the silicon oxide films is lower than that between the bonding of silicon and the silicon oxide film, so that many voids called "voids" are generated at the bonding interface.

Goetz et al. Reported a method of bonding a quartz substrate and a silicon substrate whose surface was oxidized, as an example of bonding SiO ₂ and SiO ₂ with a stronger bonding force than in the past (GG. Goetz, Electroc
chemical Society, Bonding S
ymposium 1991, Extended ab
struct, pp. 65). This is because the surface of SiO ₂ is exposed to oxygen RF plasma and a DC bias is applied between the plasma and the silicon substrate to cause the oxygen ion plasma to collide with the SiO ₂ surface, and the energy is used to generate SiO 2.
It is a method of activating ₂ . Then, when activated SiO ₂ is bonded to each other, a bonding force several times higher than that of the bonded product without activation is generated. In other words, a fairly low temperature heat treatment is required to obtain the same bonding force. This is suitable for the case where heat treatment at high temperature is disliked such as BESOI and the case where a combination of different thermal expansion coefficients is used such as bonding of glass and silicon.

On the other hand, the void not only has a bonding strength,
It is very sensitive to irregularities on the bonding surface. In this respect, the BESOI described above is often disadvantageous. The reason for forming the etching stop layer is, for example, CV.
It is usual to perform heteroepitaxial growth with D or epitaxial growth in which a high concentration of impurities is doped, but in the case of CVD, especially in the case of heteroepitaxial growth, the flatness is often inferior to the flat surface obtained by polishing. Because. The etching stop layer may be formed by ion implantation or the like, but the flatness is deteriorated in this case as well.

The flatness of the bonding surface is good and BES
The thickness of the active layer is uniform like OI, and conventional BESOI
In the example where the selectivity of etch back is better by several orders of magnitude, the surface of the silicon substrate is made porous by anodization,
There is a technique of epitaxially growing a silicon active layer on this (see Japanese Patent Laid-Open No. 21338/1993). In this case, the porous layer corresponds to the etching stop layer referred to as BESOI. However, since porous silicon has an extremely high etching rate with respect to a hydrofluoric acid-based etching solution as compared with single crystal silicon, importance is attached to high selective etching characteristics rather than an etching stop layer. In this technique, the porous silicon layer is not formed by CVD, but the surface of a flat single crystal silicon substrate is anodized. Therefore, the flatness of the epitaxially grown active layer is improved as compared with BESOI in which the etching stop layer is formed by CVD or the like. However, even with this technique, the surface of the epitaxial growth layer is slightly less flat than the polished surface of the bulk. Therefore, when the active layer is oxidized and bonded to the other silicon oxide film, some voids may occur.

[0008]

As described above, as compared with the bonding of silicon and the silicon oxide film,
The bonding strength between the silicon oxide films is low, which causes a problem that many voids called "voids" are generated at the bonding interface.

Further, the voids are very sensitive not only to the bonding strength but also to the unevenness of the bonding surface, but the surface of the epitaxial growth layer is slightly less flat than the bulk polished surface. Therefore, there is a problem that some voids may be generated when the active layer is oxidized and bonded to the other silicon oxide film.

That is, the thickness of the active layer is uniform and the underlying SiO 2
₂ has a sufficient thickness, a small interface state, and a small number of voids, and there is a problem to be solved that an ideal SOI substrate has not yet been produced.

(Object of the Invention) The object of the present invention is to realize an ideal SOI in which the film thickness of the active layer is uniform, the underlying SiO ₂ has a sufficient thickness, the interface state is small, and the number of voids is small.
It is to provide a method for manufacturing a substrate.

[0012]

SOLUTION OF THE INVENTION SO of the present invention
In the method for producing the I substrate, a single crystal silicon layer is epitaxially grown on the porous silicon surface of a silicon substrate having a porous surface layer, and then the growth surface surface layer is oxidized to form a first substrate. Similarly, a supporting substrate (second substrate) having SiO ₂ on the surface is prepared, and both or one of them is exposed to plasma such as oxygen, X-ray, electron beam, etc. to chemically change the SiO ₂ surface. Activate. Then, the two substrates are brought into close contact with each other only by Van der Waals force at room temperature, and after heat treatment (or without heat treatment), the silicon substrate portion on the epitaxial growth side is first ground or etched, and then the porous portion is selected. Etching is performed to form a single crystal silicon thin film on SiO ₂ .

In carrying out the present invention, there are two important physical effects of porous silicon.

One is the etching characteristics of porous silicon. Normally, silicon is hardly etched with hydrofluoric acid, but it can be etched with hydrofluoric acid by making it porous. In addition, when a mixed etching solution of hydrofluoric acid and hydrogen peroxide is used, an etching rate ratio of about 10 5 times can be obtained between non-porous and porous. Therefore 1 μm
This enables selective etching that leaves even thin silicon layers in the front and back evenly and with good controllability.

Another effect is the epitaxial growth characteristics. Porous silicon maintains a single crystal structure as a crystal structure, and has pores with a diameter of several tens to several hundreds of angstroms at high density from the surface to the inside. The epitaxial layer grown on this surface has a characteristic that crystallinity substantially equal to that of the epitaxial layer on the non-porous single crystal substrate is obtained.

A feature of epitaxial growth on a porous layer is that stacking faults may occur from the growth interface although the density is very low. As a result, the stacking faults generated during the epitaxial growth are transferred to the other substrate by bonding, and the stacking faults observed in the silicon film of the SOI substrate thus formed appear to be in the opposite direction to normal.

From the above physical characteristics, it becomes possible to use a single crystal thin film equivalent to an epitaxial layer on a highly reliable single crystal silicon substrate as the active layer, and the conventional SO can be used.
An SOI substrate having excellent crystallinity and excellent film thickness uniformity can be applied as compared with the I substrate.

In the process of the present invention, the S of two substrates is
Since attaching the iO ₂ faces to each other, the epitaxial silicon film and SiO ₂ which is an active layer interface state at the interface (the thermal oxide film of the epitaxial layer) is sufficiently low, and SiO ₂
Since the layer thickness can be controlled arbitrarily, a substrate in which SOI characteristics are fully utilized can be manufactured.

Since the surface of SiO _{2 at the} bonding interface is activated by plasma treatment, X-ray irradiation, or electron beam irradiation, the bonding strength is sufficiently increased and the generation of voids is suppressed.

Further, the selective etching of the porous silicon portion is preferably carried out with a mixed etching solution of hydrofluoric acid and hydrogen peroxide water, which allows etching with good controllability.

The plasma is preferably a single element gas of hydrogen, oxygen, nitrogen, a halogen gas, a rare gas, a compound gas other than a silane gas, or a mixed gas thereof. _{2 The} surface can be activated more effectively.

Embodiment Example FIG. 1 shows an embodiment example of the present invention.
And FIG. 6 will be described.

(FIG. 1-1) Porous silicon 101 is formed by anodizing a single crystal silicon substrate 100. At this time, the thickness to be made porous may be several μm to several tens of μm on one surface layer of the substrate. Further, the entire substrate may be anodized.

A method of forming porous silicon will be described with reference to FIG. First, a P-type single crystal silicon substrate 600 is prepared as a substrate. Even if it is N-type, it is not impossible, but in that case, it is necessary to be limited to a substrate having a low resistance, or it is necessary to irradiate the substrate surface with light to promote generation of holes. The substrate 600 is set in the device as shown in FIG. That is, one side of the substrate is in contact with the hydrofluoric acid-based solution 604, and the negative electrode 606 is provided on the solution side.
Is provided, and the opposite side is in contact with the positive metal electrode 605.

Further, as shown in FIG. 6-2, the positive electrode side 6
05 'may also have an electric potential via the solution 604'. In any case, porosification occurs from the negative electrode side in contact with the hydrofluoric acid solution.

As the hydrofluoric acid solution 604, concentrated hydrofluoric acid (49% HF) is generally used. Diluting with pure water (H ₂ O) is not preferable because etching will occur from a certain concentration, although it depends on the value of the flowing current. Further, bubbles are generated from the surface of the substrate 600 during the anodization,
For the purpose of efficiently removing the bubbles, alcohol may be added as a surfactant. Methanol, ethanol, propanol, isopropanol, etc. are used as alcohol. Further, a stirrer may be used instead of the surfactant, and the anodization may be performed while stirring the solution. Regarding the negative electrode 606, a material that is not corroded by the hydrofluoric acid solution, such as gold (Au) or platinum (Pt).
Etc. are used. The material of the positive electrode 605 may be a commonly used metal material, but the anodization is performed on the substrate 600.
Since the hydrofluoric acid-based solution 604 reaches the positive electrode 605 at the time when everything is done, it is preferable to coat the surface of the positive electrode 605 with a hydrofluoric acid solution-resistant metal film. The maximum current value for anodization is several hundred mA / cm ² , and the minimum value is not necessarily zero. This value is determined within a range that allows good quality epitaxial growth on the surface of porous silicon. Usually, when the current value is large, the rate of anodization increases, and at the same time, the density of the porous silicon layer decreases. That is, the volume occupied by the holes becomes large. This changes the conditions for epitaxial growth.

(FIG. 1-2) A non-porous single crystal silicon layer 102 is formed on the porous layer 101 formed as described above.
Epitaxially grow. Epitaxial growth is performed by general thermal CVD, low pressure CVD, plasma CVD, molecular beam epitaxy, sputtering method or the like. The grown film thickness may be the same as the design value of the SOI layer, but a film thickness of 2 μm or less is preferable. This is because when a single crystal silicon film with a thickness of 2 μm or more is in close contact with an insulating substrate containing SiO ₂ as a main component, heat treatment of this in the device process causes a difference in the thermal expansion coefficient of both materials, resulting in a bonding interface. This is because a large stress is generated and the silicon film is broken, the substrate is warped, or the interface is peeled off. If the film thickness is 2 μm or less, the stress can be relatively small.
Film breakage, peeling, warpage, etc. are unlikely to occur. More preferably, it is 0.5 μm or less. This is because if the film thickness is 0.5 μm or more, a slip line is likely to occur in a crystal in a minute region even if peeling, breakage, or the like does not occur during subsequent annealing.

(FIG. 1-3) The surface of the epitaxial layer 102 is oxidized (103). This is because when the epitaxial layer is directly bonded to the supporting substrate in the next step, impurities tend to segregate at the bonding interface, and the number of dangling bonds of atoms at the interface increases, resulting in thin film device characteristics. It becomes a factor that makes the instability.

The oxide film thickness may be such that it is not affected by contamination from the atmosphere taken into the bonding interface.

(FIG. 1-4) The substrate 100 having an epitaxial surface whose surface is oxidized, and Si serving as a supporting substrate.
A substrate 110 having O ₂ (103 ′) on its surface is prepared. The supporting substrate 110 is obtained by oxidizing a silicon substrate surface, quartz glass, crystallized glass, or SiO ₂ on an arbitrary substrate.
And the like.

Then, both of these substrates, or one of them, is exposed to X-rays or electron beams in a plasma atmosphere or exposed to S on the surface.
Activates iO ₂ .

Oxygen is preferably used as the gas used for exposure to the plasma atmosphere, but in addition to this, the atmosphere (mixture of oxygen / nitrogen), nitrogen, hydrogen, or an inert gas such as argon or helium, or a molecular gas such as ammonia. Is possible.
The energy to irradiate the substrate is a few volts with DC bias.
It is preferable to control in the range of about 400 V, and if a bias of more than 400 V is applied, SiO ₂ is etched at a considerable rate and the surface is roughened, which is not preferable. Irradiation energy need not be controlled by the DC bias, but can be sufficiently controlled by controlling the self-bias of the plasma itself. Self-bias is, for example, R that creates plasma
It greatly depends on the F power, and also depends on the gas species and the gas pressure.

X-rays can be used in the air or in an oxygen atmosphere. The electron beam has the limitation that it must be performed in a vacuum.

(FIGS. 1-5) Both of the above-prepared substrates are cleaned and then bonded. The washing method is preferably only rinsing with pure water, and other methods such as hydrogen peroxide solution diluted with pure water and hydrochloric acid or sulfuric acid sufficiently diluted with pure water are also possible.

Pressing the substrates over the entire surface after bonding has the effect of increasing the bonding strength.

Then, the bonded substrates are heat-treated.
The heat treatment temperature is preferably high, but if it is too high, the porous layer 101 may change its structure or impurities contained in the substrate may diffuse into the epitaxial layer. You need to choose a time. Specifically, about 600 to 1100 ° C. is preferable. Also, some substrates cannot be heat treated at high temperatures. For example, when the support substrate 110 is quartz glass, the temperature is 200 ° C. due to the difference in thermal expansion coefficient between silicon and quartz.
It can be heat-treated only at a temperature below a certain level. If this temperature is exceeded, the bonded substrates will be peeled or cracked due to stress. However, the heat treatment needs only to withstand the stress at the time of grinding or etching the bulk silicon 100 performed in the next step. Therefore, the process can be performed by optimizing the surface treatment conditions for activation even at a temperature of 200 ° C. or lower.

(FIG. 1-6) Next, the epitaxial growth layer 1
02 is left, and the silicon substrate portion 100 and the porous portion 10
1 is selectively removed. First, the silicon substrate portion 100 is ground with a surface grinder or the like, or is removed with an alkali solution such as potassium hydroxide or ammonia water or an organic alkali solution such as trimethylammonium. In the case of etching, it is effective to perform the etching in a warm solution of 100 ° C. or lower. Since the alkaline solution hardly etches SiO ₂ , if the supporting substrate is glass or a silicon substrate covered with an oxide film, only the silicon substrate portion can be selectively etched. Also, hydrofluoric acid and nitric acid,
Alternatively, it can be removed by etching with an acid mixture solution in which acetic acid or the like is added. However, since the hydrofluoric acid / nitric acid-based etchant also slightly etches the supporting substrate, it is better to avoid using it for a long time. The silicon substrate portion 100 is etched, and when the porous portion 101 is exposed, the etching is temporarily stopped, and the subsequent porous portion 101 is selectively etched in a hydrofluoric acid solution. Epitaxial growth part 1
Since 02 is not porous, it hardly reacts with hydrofluoric acid and remains as a thin film. Further, as a matter of course, the support substrate 110 is S
When iO ₂ is used as a main component, it easily reacts with a hydrofluoric acid solution, so it is not preferable to soak it in the hydrofluoric acid solution for a long time. However, if the porous silicon layer is thin, it does not take so much time to etch it, so there is no concern. If the support substrate 110 is not desired to be etched at all, it is advisable to deposit a substance that is difficult to react with a silicon nitride film or other hydrofluoric acid by CVD or the like on the surface opposite to the bonding surface in advance. Alternatively, if the porous portion 101 is also diluted to some extent with an alkaline solution, an organic alkaline solution, or a hydrofluoric acid / nitric acid solution before the substrate is immersed in an etching solution, the time required for selective etching of the epitaxial layer and the porous layer can be shortened. Therefore, the supporting substrate does not need to react so much.

Epitaxial film 102 and porous layer 101
The hydrofluoric acid-based solution used for the selective etching is a mixture of hydrofluoric acid and hydrogen peroxide solution (H ₂ O ₂ ). Selective etching of porous silicon is possible with hydrofluoric acid and nitric acid, or a mixed solution of acetic acid added to it, but in this case the selectivity is not so good and the single crystal silicon thin film to be left is also etched to some extent. Therefore, it is necessary to precisely control the time.

By carrying out the above steps, a single crystal silicon thin film can be obtained on the insulating substrate.

[0040]

【Example】

(Embodiment 1) The details of the first embodiment of the present invention will be described with reference to FIGS.

(FIG. 1-1) A 5-inch P-type (100) single crystal silicon substrate (0.
1 to 0.2 Ωcm) was prepared, and this was set in an apparatus as shown in FIG. 6A to carry out anodization to make the surface of the silicon substrate 100 20 μm in porous silicon 101. A 49% HF solution was used as the solution 604 at this time, and the current density was 100 mA / cm ² . The porosification rate at this time is 8.4 μm / min. And a 20 μm thick porous layer was obtained in about 2.5 minutes.

(FIG. 1-2) The porous silicon 101
A single crystal silicon layer 102 is formed on the upper surface by CVD to 0.5.
μm epitaxially grown. The deposition conditions are as follows.

Gas used: SiH ₄ / H ₂ gas flow rate: 0.62 / 140 (1 / min.) Temperature: 750 ° C. Pressure: 80 Torr Growth rate: 0.12 μm / min. (FIG. 1-3) The substrate prepared by the above method was processed in a steam atmosphere at 900 ° C. to obtain a 0.1 μm oxide film 10.
Got 3.

(FIG. 1-4) Substrate 1 having the above oxide film
00 and a supporting substrate (silicon wafer) 110 having a 0.5 μm thick silicon oxide film prepared in advance were set in a plasma processing apparatus, and each surface was activated by oxygen plasma. The processing conditions are as follows.

RF frequency ... 13.58 MHz RF power ... 400 W Oxygen flow rate ... 30 sccm Pressure ... 15 pa. Treatment time: 5 minutes Note that the bias was not controlled between the plasma and the substrate, and the surface treatment was performed only by the self-bias of the plasma.

(FIGS. 1-5) Both the above-mentioned surface-treated substrates were immersed in pure water for 5 minutes and spin-dried, and then the treated surfaces were bonded together. After that, heat treatment was performed at 800 ° C. for 6 hours.

(FIG. 1-6) Silicon substrate 1 after heat treatment
The 00 side was ground by 610 μm by a surface grinding device to expose the porous silicon 102.

This substrate was subsequently immersed in a selective etching solution to selectively etch only the porous portion 101. At this time, the composition of the selective etching solution and the etching rate for porous silicon were HF: H ₂ O ₂ = 1: 5 1.6 μm / min. Met. Therefore, the porous portion of less than 20 μm was completely etched in about 13 minutes. Incidentally, the etching rate of the single crystal silicon layer 102 at this time is 0.0006 μm.
/ Hour, which remained without being etched.

As a result, an SOI substrate having a single crystal silicon film of about 0.4 μm on a silicon oxide film of 0.6 μm is completed, and the void density of the SOI film is about that of the conventional non-surface-treated one. It decreased to 1/4.

(Second Embodiment) The second embodiment of the present invention will be described in detail with reference to FIG.

(FIG. 2-1) A 4-inch P-type (100) silicon substrate 200 having a resistivity of 0.01 .OMEGA..cm having a thickness of 300 .mu.m is prepared, and its surface layer is only 20 .mu.m as in the first embodiment. The porous silicon 201 was used.

(FIG. 2-2) The first layer is formed on the obtained porous surface.
Similarly to the embodiment, the epitaxial layer 202 is formed with 0.15.
It was formed to a thickness of μm.

(FIG. 2-3) The substrate prepared by the above method was oxidized in water vapor at 1000 ° C. for 0.1 μm.

(FIG. 2-4) The surface of the above-described substrate and a 4-inch synthetic quartz substrate 210 prepared in advance was subjected to plasma treatment in the same manner as in the first embodiment.

(FIG. 2-5) The silicon substrate 200 and the quartz substrate 210 were immersed in pure water for 5 minutes, and then their treated surfaces were bonded to each other. Subsequently, heat treatment was performed at 180 ° C. for 24 hours.

(FIG. 2-6) First, a silicon substrate portion 200 having a thickness of 280 μm was treated with hydrofluoric acid / nitric acid / acetic acid 1: 10: 1.
Etching was carried out with a 0 mixed solution. When the porous silicon layer 201 was exposed on the surface, the porous layer 201 was selectively etched with a 1: 5 mixed solution of hydrofluoric acid / hydrogen peroxide solution. At this time, the etching rate of hydrofluoric acid / nitric acid / acetic acid with respect to the single crystal silicon was about 2 μm / min, so that it was about 140 minutes, and the etching rate with respect to the porous silicon of hydrofluoric acid / hydrogen peroxide was about 1.6 μm / min. Since it was a minute, the entire porous layer could be etched in about 13 minutes.
The quartz substrate 210 was only etched by a few μm.

As a result, an SOI substrate having a silicon single crystal thin film of 0.1 μm on a quartz substrate is completed, and the SOI substrate is
The void density of 1 was reduced to about 1/5 of that of the conventional quartz substrate type without surface treatment.

Example 3 (FIG. 3-1) Resistivity 0.0 having a thickness of 400 μm 0.0
5 inch P type (100) silicon substrate 30 of 1 Ω · cm
0 was prepared, and the porous layer 301 was formed to a thickness of 20 μm from the surface.

(FIG. 3-2) An epitaxial layer 302 having a thickness of 0.5 μm was formed on the porous surface of the obtained substrate in the same manner as in Example 1.

(FIG. 3-3) The surface of the epitaxial layer 302 of the above substrate was oxidized to 0.2 μm in water vapor at 1000 ° C. to obtain a SiO ₂ layer 303. As a result, the thickness of the silicon single crystal portion of the epitaxial layer was 0.4 μm and the thickness of the oxide film portion was 0.2 μm.

(FIG. 3-4) The substrate 300 prepared by the above method and the synthetic quartz substrate 310 prepared in advance were subjected to plasma treatment. The processing conditions are as follows.

RF frequency ... 13.56 MHz RF power ... 450 W Gas species ... Oxygen / nitrogen mixture Flow rate ratio ... 40 sccm / 160 sccm Pressure ... 20 pa. Processing time ... 8 minutes (FIG. 3-5) The above-mentioned treated substrates were washed with 10% hydrogen peroxide solution, further rinsed with pure water, and then dried to bond the substrates to each other. Then, a pressure of 70 tons was applied to the bonded substrates for 10 minutes.

(FIG. 3-6) The silicon substrate side was directly etched with a solution without heat-treating the substrate. First, the thermal oxide film 303 covering the silicon substrate is removed with dilute hydrofluoric acid, and then Tetra Methyl.
It was immersed in a 2.4% aqueous solution of ammonium hydride (trade name: SD-1) and treated at 90 ° C. for about 5 hours. As a result, the bulk silicon portion 300 on the silicon substrate side was entirely etched, and the porous layer 301 was exposed. Subsequently, the porous portion 301 was selectively etched with a hydrofluoric acid / hydrogen peroxide aqueous solution.

(FIG. 3-7) The single crystal silicon thin film 302 on the quartz substrate 310 obtained by the above process was patterned into an island shape according to the designed area, shape and arrangement of the element. After the patterning, as a first step of forming an element, each island region was exposed to an oxygen atmosphere of 1000 ° C.
It was oxidized by 05 μm. Therefore, this oxidation step is also combined with the heat treatment, and as a result, an SOI substrate having a single crystal silicon thin film with a thickness of about 0.4 μm on the transparent substrate was obtained.

(Fourth Embodiment) The fourth embodiment of the present invention will be described in detail with reference to FIG.

(FIG. 4-1) A 5-inch P-type (100) silicon substrate 400 having a resistivity of 0.01 Ω · cm having a thickness of 400 μm is prepared, and a porous layer 401 is formed from the surface to a thickness of 20 μm. did.

(FIG. 4-2) An epitaxial layer 402 having a thickness of 0.5 μm was formed on the porous surface of the obtained substrate in the same manner as in Example 1.

(FIG. 4-3) The surface of the epitaxial layer 402 of the substrate was oxidized by 0.05 μm in water vapor at 900 ° C. to obtain a SiO ₂ layer 403.

(FIG. 4-4) The substrate 400 prepared by the above method and a 5 inch diameter and a thickness of 625 μm prepared in advance.
m synthetic quartz substrate 410 was plasma treated. The processing conditions are as follows.

RF frequency ... 13.56 MHz RF power ... 450 W Gas species ... Oxygen / nitrogen mixture Flow rate ratio ... 40 sccm / 160 sccm Pressure ... 20 pa. Processing time ... 3 minutes (FIG. 4-5) The above-mentioned treated substrates were washed with 10% hydrogen peroxide solution, rinsed with pure water and then dried, and the substrates were bonded to each other. Then, a pressure of 70 tons was applied to the bonded substrates for 10 minutes. Furthermore, the same substrate 180
A heat treatment was performed at ℃ for 24 hours.

(FIG. 4-6) From the silicon substrate side of the above substrate, a silicon substrate of 100 μm was formed using a surface grinding machine.
Grinded until left. That is, 100 μm including the porous layer and the epitaxial layer on a 625 μm thick quartz substrate.
The m-thick silicon substrates are in a bonded state.
This was heat-treated at 300 ° C. for 24 hours.

(FIG. 4-7) Part 4 of the remaining bulk
00 was subsequently ground with a surface grinder and the porous silicon portion 401 was etched with a hydrofluoric acid / hydrogen peroxide mixture. As a result, an SOI substrate including a single crystal silicon thin film 402 having a thickness of about 0.4 μm is completed on the quartz substrate, and the void density of the SOI is about 1/10 as compared with the conventional quartz substrate type without surface treatment. Diminished.

(Fifth Embodiment) The fifth embodiment of the present invention will be described in detail with reference to FIG.

(FIG. 5A) A 4-inch P-type (100) silicon substrate 500 having a resistivity of 0.01 .OMEGA..cm having a thickness of 300 .mu.m is prepared, and its surface layer is 20 .mu.m as in the first embodiment. The porous silicon 501 is used.

(FIG. 5-2) The first layer was formed on the obtained porous surface.
An epitaxial layer 502 of 0.15 is formed in the same manner as in the embodiment.
It was formed to a thickness of μm.

(FIG. 5-3) The substrate prepared by the above method was oxidized in water vapor at 1000 ° C. to a thickness of 0.1 μm.

(FIG. 5-4) 0.7 prepared in advance
The surface of a 4-inch silicon substrate 510 having a silicon oxide film with a thickness of μm was plasma-treated in the same manner as in the first embodiment. At this time, plasma treatment was not performed on the substrate epitaxially grown on the porous silicon.

(FIGS. 5-5) The above two substrates were washed with 10% hydrogen peroxide solution, rinsed with pure water, dried and then bonded to each other. Then, the bonded substrates were placed under a pressure of 70 tons and a temperature of 200 ° C. for 1 hour. Further, the taken-out substrate was annealed at 1000 ° C. for 30 minutes.

(FIGS. 5-6) As in the first embodiment, the bulk portion 500 and the porous silicon portion 501 on the first substrate side were removed by grinding and selective etching of the above substrate.

As a result, an SOI substrate having a 0.1 μm single crystal silicon film on a 0.8 μm silicon oxide film is completed, and the void density of the SOI film is about 1 as compared with the conventional one not surface-treated. It decreased to / 10.

Example 6 (FIG. 6-1) Resistivity 0.0 having a thickness of 400 μm 0.0
5 inch P type (100) silicon substrate 60 of 1 Ω · cm
0 was prepared, and a porous layer 601 having a thickness of 20 μm was formed from the surface thereof.

(FIG. 6-2) An epitaxial layer 602 having a thickness of 0.5 μm was formed on the porous surface of the obtained substrate in the same manner as in Example 1.

(FIG. 6-3) The surface of the epitaxial layer 602 of the above substrate was oxidized to 0.2 μm in water vapor at 1000 ° C. to obtain a SiO ₂ layer 603. As a result, the thickness of the silicon single crystal portion of the epitaxial layer was 0.4 μm and the thickness of the oxide film portion was 0.2 μm.

(FIG. 6-4) The substrate 600 prepared by the above method and the synthetic quartz substrate 610 prepared in advance were irradiated with soft X-rays (wavelength 2 nm) for 30 seconds in the atmosphere.

(FIG. 6-5) The above-mentioned treated substrates were washed with 10% hydrogen peroxide solution, rinsed with pure water and then dried to bond the substrates to each other. Then, a pressure of 70 tons was applied to the bonded substrates for 10 minutes.

(FIG. 6-6) The silicon substrate side was directly etched with a solution without heat treatment of the substrate. First, the thermal oxide film 603 covering the silicon substrate is removed with diluted hydrofluoric acid, and then tetramethyl.
It was immersed in a 2.4% aqueous solution of ammonium hydride (trade name: SD-1) and treated at 90 ° C. for about 5 hours. As a result, the bulk silicon portion 600 on the silicon substrate side was entirely etched, and the porous layer 601 was exposed. Subsequently, the porous portion 601 was selectively etched with a hydrofluoric acid / hydrogen peroxide aqueous solution.

(FIG. 6-7) The single crystal silicon thin film 602 on the quartz substrate 610 obtained by the above process was patterned into an island shape in accordance with the designed area, shape and arrangement of the element. After the patterning, as a first step of forming an element, each island region was exposed to an oxygen atmosphere of 1000 ° C.
It was oxidized by 05 μm. Therefore, this oxidation step is also combined with the heat treatment, and as a result, an SOI substrate having a single crystal silicon thin film with a thickness of about 0.4 μm on the transparent substrate was obtained.

(Steps almost the same as in Example 3) (Example 7) (FIG. 7-1) Resistivity 0.0 having a thickness of 400 μm 0.0
5 inch P type (100) silicon substrate 70 of 1 Ω · cm
0 was prepared, and a porous layer 701 having a thickness of 20 μm was formed from the surface thereof.

(FIG. 7-2) An epitaxial layer 702 having a thickness of 0.5 μm was formed on the porous surface of the obtained substrate in the same manner as in Example 1.

(FIG. 7-3) The surface of the epitaxial layer 702 of the above substrate was oxidized by 0.05 μm in water vapor at 900 ° C. to obtain a SiO ₂ layer 703.

(FIG. 7-4) The substrate 700 prepared by the above method and a 5 inch diameter and a thickness of 625 μm prepared in advance.
m synthetic quartz substrate 710 is set in each vacuum device,
The electron beam was irradiated with an acceleration energy of 0.5 KeV.

(FIG. 7-5) The above-mentioned treated substrates were washed with 10% hydrogen peroxide solution, rinsed with pure water and then dried to bond the substrates to each other. Then, a pressure of 70 tons was applied to the bonded substrates for 10 minutes. Further, the substrate was heat-treated at 180 ° C. for 24 hours.

(FIG. 7-6) From the silicon substrate side of the above substrate, a silicon substrate of 100 μm was formed using a surface grinding machine.
Grinded until left. That is, 100 μm including the porous layer and the epitaxial layer on a 625 μm thick quartz substrate.
The m-thick silicon substrates are in a bonded state.
This was heat-treated at 300 ° C. for 24 hours.

(FIG. 7-7) The remaining bulk portion 7
00 was subsequently ground with a surface grinder and the porous silicon portion 701 was etched with a hydrofluoric acid / hydrogen peroxide mixture. As a result, an SOI substrate having a single crystal silicon thin film 702 with a thickness of about 0.4 μm is completed on the quartz substrate, and the void density of the SOI is about 1/10 of that of the conventional quartz substrate type not surface-treated. Diminished.

(Almost the same steps as in Example 4)

[0096]

As described in detail above, according to the present invention,
The surface layer of the silicon substrate is made porous, then the single crystal silicon is epitaxially grown, and then the surface of the growth layer is oxidized, and the substrate having SiO ₂ is bonded to the surface, and the bulk silicon portion on the silicon substrate side and the porous surface are made porous. In a method for manufacturing an SOI substrate obtained by removing a silicon portion, a bonding SiO ₂ surface is activated by plasma treatment, X-ray, or electron beam treatment to increase the strength of bonding and It has become possible to reduce the number of voids generated from a fraction to one.

Further, since the bonding strength is increased, the effect that the annealing temperature after the bonding can be kept low can be obtained.

Further, according to the present invention, it is possible to manufacture an ideal SOI substrate in which the film thickness of the active layer is uniform, the underlayer SiO ₂ has a sufficient thickness, the interface state is small, and the number of voids is small. You can also get the effect.

[Brief description of drawings]

FIG. 1 is a schematic process drawing for explaining a process of an embodiment example and a first embodiment of the present invention.

FIG. 2 is a schematic process drawing for explaining a second embodiment of the present invention.

FIG. 3 is a schematic process drawing for explaining a third embodiment of the present invention.

FIG. 4 is a schematic process drawing for explaining a fourth embodiment of the present invention.

FIG. 5 is a schematic process drawing for explaining a fifth embodiment of the present invention.

FIG. 6 is a schematic view of an apparatus for making a silicon substrate porous.

[Explanation of symbols]

100, 200, 300, 400, 500, 600
Single crystal silicon substrate 101, 201, 301, 401, 501 Porous silicon substrate 102, 202, 302, 402, 502 Epitaxial growth layer 103, 203, 303, 403, 503 Epi oxide film 103 ', 503' Support substrate silicon Oxide film 110, 210, 310, 410, 510 S on the surface
Support substrate 107 having an iO ₂ layer 107, 207, 307, 407, 507 Plasma 604, 604 'Etching solution 605, 605' Positive electrode 606, 606 'Negative electrode

Claims (7)

[Claims] 1. A step of producing a first substrate in which a porous layer, an epitaxial layer, and a silicon oxide film are sequentially formed on a silicon single crystal substrate, and a second substrate having a silicon oxide film on its surface is prepared. Irradiating the silicon oxide film surface of at least one of the first substrate and the second substrate with X-rays to activate the silicon oxide film surface, the first substrate and the second substrate Bonding the substrate of (1) through the activated silicon oxide film, and removing the silicon single crystal substrate and the porous layer of the bonded substrate to form the above-mentioned substrate on the second substrate. And a step of forming a substrate having the epitaxial layer with a silicon oxide film interposed therebetween, a method for manufacturing an SOI substrate. 2. The method for manufacturing an SOI substrate according to claim 1, wherein the X-ray is an electron beam. 3. The method for manufacturing an SOI substrate according to claim 1, wherein the X-ray is plasma. 4. The SOI according to claim 1, wherein the porous layer is formed by making the surface layer of the silicon single crystal substrate porous by anodization.
Substrate manufacturing method. 5. The silicon single crystal substrate and the porous layer of the bonded substrates are removed by grinding or etching the non-porous silicon single crystal substrate portion on the side of the adhered silicon substrate. The method for producing an SOI substrate according to claim 1, wherein after the removal, the step of selectively etching the porous silicon portion is performed. 6. The method for manufacturing an SOI substrate according to claim 5, wherein the selective etching of the porous silicon portion is performed by a mixed etching solution of hydrofluoric acid and hydrogen peroxide. 7. The plasma uses hydrogen, oxygen, nitrogen, a halogen gas, a rare gas single element gas, a compound gas other than a silane gas, or a mixed gas thereof. The method for manufacturing an SOI substrate as described in 1.