JP2000315634A - Silicon wafer for bonding and manufacture of bonded substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing bonded substrate by which wafers can be bonded firmly to each other with less voids. SOLUTION: After two silicon wafers 11 and 12 are cleaned by HF cleaning, the wafers 11 and 12 are rinsed with pure water, cleaned by SC1 (standard cleaning), washed with water, and dried. When the wafer is cleaned by the HF cleaning, oxide films are removed and the surfaces of the wafers 11 and 12 become hydrophobic. When the SC1 cleaning is performed, surface layers are etched and terminal with an OH group. Consequently, the SiOH coverage θon the surfaces of the wafers 11 and 13 become >=40%. After a bonded substrate 13 is obtained by bonding the wafers 11 and 12 to each other at a room temperature, the substrate 13 is heat-treated in a dry oxygen atmosphere. The heat-treating temperature is adjusted to 1,200 to 1,280 deg.C and the heat-treating period is set at 60 minutes. During the heat treatment, Si atoms are terminated with the OH group on >=40% surfaces of the wafers 11 and 12 and the heat- treating temperature becomes 1,200 to 1,280 deg.C. Consequently, the wafers 11 and 12 can be bonded to each other with less voids.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a bonded substrate, for example, a method of manufacturing a bonded substrate such as an SOI or a bonded dielectric separation wafer.

[0002]

2. Description of the Related Art Generally, in order to bond silicon wafers together, it is necessary that dangling bonds of silicon atoms on the wafer surface be terminated with OH groups. In order to control the surface of a silicon wafer in this way, conventionally, as described in, for example, Japanese Patent Publication No. 62-27040, a silicon wafer is immersed in sulfuric acid / hydrogen peroxide, aqua regia or nitric acid, and this is boiled. The way to do it was known. Therefore, the subsequent lamination strengthening heat treatment is
This is performed on the silicon surface (bonded surface) terminated by the H group. Specifically, the mirror surfaces of the silicon wafers are overlapped and adhered in a clean room at room temperature. Then, this was heated to 880 to 110 using a heat treatment furnace.
The heating is performed at a relatively low temperature of 0 ° C. In addition,
The coverage θ of OH groups on the wafer bonding surface according to this conventional method was 38% or less.

[0003]

However, in the conventional method of manufacturing a bonded substrate, when bonding silicon wafers to each other, these silicon wafers are mixed in a mixed solution of sulfuric acid / hydrogen peroxide, aqua regia or After boiling in a nitric acid solution to reduce the OH group coverage θ of each bonding surface of the silicon wafer to 38% or less, and laminating them, a bonding strengthening heat treatment was performed at a relatively low temperature of 880 to 1100 ° C. . As a result, during this heat treatment, when H ₂ O escapes from the bonding interface where the flatness is reduced due to the boil, the H ₂ O is agglomerated and voids (unbonded portions) are likely to be generated at the outer peripheral portion of the wafer. As a result, the yield of non-defective substrates was low.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method of manufacturing a bonded substrate capable of performing firm bonding with few voids. Another object of the present invention is to provide a silicon wafer for manufacturing a bonded substrate.

[0005]

An object of the present invention is to provide a mirror-polished silicon wafer, comprising:
H bond coverage is 40% of the surface of the silicon wafer
The above is a bonding silicon wafer.

A preferable SiOH bond coverage θ is 50%.
That is all. If it is less than 40%, the hydrogen bond generated when the bonding surfaces are overlapped is weak, and the number of cycloacid bonds due to the bonding heat treatment is small, so that the void generation rate increases. As a method of controlling the SiOH bonding on the bonding surface of the silicon wafer, for example, after HF cleaning, SC1
(Standard Cleaning 1) Cleaning or SC2 (Standard Cleaning 2)
There is a method of performing washing. Other examples include a method of performing SC1 cleaning or SC2 cleaning alone.

For example, as a specific example, when the former HF cleaning and SC1 cleaning or SC2 cleaning are sequentially performed, first, a silicon wafer is treated with a hydrofluoric acid solution (HF: H ₂ O = 0.05:
Wash for 1 to 10 minutes according to 1). Then, a 50 ° C. SC1 washing solution (NH ₄ OH: H ₂ O ₂ : H ₂ O = 0.
5: 1.0: 5) for 5-10 minutes. Or, SC2 cleaning liquid at room temperature _{(H 2 O: HCl = 1000} : 1) by washing for 5 to 10 minutes. Then, it is washed with water and dried. The cleaning with the SC1 cleaning solution and the cleaning with the SC2 cleaning solution may be performed successively.

According to a second aspect of the present invention, a mirror-polished surface of a silicon wafer is washed with a hydrofluoric acid solution, and thereafter, the surface is washed with a SC1 solution or an SC2 solution, whereby the silicon wafer surface is cleaned. This is a bonding silicon wafer having a coverage of SiOH bonds of 40% or more.

According to a third aspect of the present invention, there is provided a step of preparing a first silicon wafer and a second silicon wafer each having a mirror-polished bonded surface;
Subjecting each bonded surface of the silicon wafer and the second silicon wafer to a hydrophilic treatment so that the coverage of SiOH bonds is 40% or more;
A method for manufacturing a bonded substrate, comprising: a step of stacking a bonded surface of a first silicon wafer and a bonded surface of a second silicon wafer; and a step of manufacturing a bonded substrate by heat-treating the stacked silicon wafer. It is.

According to a fourth aspect of the present invention, in the method for manufacturing a bonded substrate according to the third aspect, the surface of the silicon wafer is washed with hydrofluoric acid and then with an SC1 solution or an SC2 solution in the hydrophilic treatment. It is.

According to a fifth aspect of the present invention, there is provided the method of manufacturing a bonded substrate according to the third or fourth aspect, wherein the overlaid silicon wafer is heat-treated at 1200 to 1280 ° C. This is a method for manufacturing a bonded substrate.

[0012] The reason for the temperature condition is that if the temperature is lower than 1200 ° C, the degassed substance from the bonding interface hardly disappears, so that the void generation rate increases. Also, 12
If the temperature exceeds 80 ° C, the heating temperature is too high, causing excessive thermal stress, contamination from the furnace, and OSF (Oxidation Induced Stack).
ing Fault) is likely to occur. A preferred heat treatment time is 30 to 120 minutes. If the heat treatment time is less than 30 minutes, the heat treatment time is too short, and voids are easily generated at the bonding interface of the silicon wafer. If the time exceeds 120 minutes, thermal stress becomes remarkable. Further, the atmosphere in the furnace is an oxidizing atmosphere. For example, a dry oxygen atmosphere is used.

[0013]

According to the invention as set forth in claims 1 to 5, first,
A first silicon wafer (mirror wafer: PW) and a second silicon wafer (PW) are prepared. These silicon wafers are subjected to SC1 cleaning or SC2 cleaning after HF cleaning, for example. Or SC1 cleaning and S
Apply both C2 cleans. As a result, the coverage θ of the SiOH bond on the bonding surfaces of both silicon wafers becomes 40% or more.

That is, in the former method, the silicon oxide surface is removed by HF cleaning the surface of the silicon wafer. Thereafter, this is subjected to SC1 cleaning, so that Si on the silicon wafer surface has OH groups (coverage θ =
40% or more). In the case of cleaning with the SC2 cleaning solution instead of the SC1 cleaning, Si on the wafer surface is similarly terminated by OH groups having a coverage θ of 40% or more.

In the latter method, even if the silicon wafer surface is cleaned with the SC1 cleaning solution alone, the Si surface is terminated by OH groups. Alternatively, even if the surface of the silicon wafer is cleaned by SC2 alone, the OH groups are terminated.

Next, the first silicon wafer and the second silicon wafer are overlapped, for example, at room temperature. That is, the mirror surfaces of these silicon wafers are brought into close contact with each other. Thereafter, the bonded wafer is heat-treated at, for example, 1200 to 1280 ° C. As a result, a firmly bonded bonded substrate with few voids is produced. As described above, the heat treatment of the silicon wafer at a high temperature is performed because the silicon wafer surface is coated with, for example, SiOH bonds having a coverage θ of 40% or more,
This is because, when the bonding heat treatment is performed at a heat treatment temperature of less than 1200 ° C., the rate of occurrence of voids becomes relatively high.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. In the first embodiment, silicon wafers (silicon surfaces) are directly bonded to each other. FIG. 1 is a flow sheet showing a method for manufacturing a bonded substrate according to a first embodiment of the present invention. As shown in FIG. 1, two mirror-polished silicon wafers (active layer A
(Plate, B plate for support layer) 11 and 12 are prepared. Thereafter, both the silicon wafers 11 and 12 are subjected to HF cleaning (H
F: H ₂ O = 0.05: 1), rinse with pure water, and then SC1 (NH ₄ OH: H ₂ O ₂ : H ₂ O =
0.5: 1: 5) Washing is performed. Then, it is washed and dried.

At this time, since the silicon wafer is subjected to HF cleaning, the oxide film on the surface is removed, and the wafer surface becomes hydrophobic. In addition, at the time of SC1 cleaning, the surface layer is etched and simultaneously terminated with OH groups. As a result, on the surface of the silicon wafer, the coverage θ of the SiOH bond becomes 40% or more. Then, after bonding these mirror surfaces to each other at room temperature, a bonding heat treatment is performed on the bonded substrate 13. This heat treatment temperature is 1200 to 1
280 ° C., time is 60 minutes. This heat treatment was performed in a dry oxygen atmosphere.

At the time of this heat treatment, 4
At 0% or more, Si atoms are terminated with OH groups, and the heat treatment temperature is 1200 to 1280 ° C. Thereby, the silicon wafers 11 and 12 having few voids are bonded to each other. Then, the bonded substrate 1
3 is subjected to a void inspection by ultrasonic irradiation. Then, the A plate 11 is chamfered, and the A plate 11 is ground and polished to a predetermined thickness. Finally, the A plate 11 is cleaned.

Next, a method of manufacturing a bonded substrate according to a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the bonding surface has an OH group coverage θ = 40.
This is an example in which a method of performing SC1 cleaning alone is employed as a method for increasing the percentage by percentage. FIG. 2 is a flow sheet showing a method for manufacturing a bonded substrate according to a second embodiment of the present invention. As shown in FIG. 2, SC1 (NH ₄ O) was added to the two prepared mirror-polished silicon wafers 11 and 12.
H: H ₂ O ₂ : H ₂ O = 0.5: 1: 5)
After that, it is washed and dried.

At this time, by cleaning the silicon wafer with SC1, the wafer surface layer is etched and terminated with OH groups at the same time. As a result, the surface of the silicon wafer is terminated by OH groups having a coverage θ = 40% or more. The post-process such as the lamination heat treatment is the same as in the first embodiment. Other configurations, operations, and effects are the same as those of the first embodiment, and a description thereof will not be repeated.

Next, a method for manufacturing a bonded substrate according to a third embodiment of the present invention will be described with reference to FIG. FIG.
9 is a flowchart showing a method for manufacturing a bonded substrate according to a third embodiment of the present invention. As shown in FIG.
The method of manufacturing a bonded substrate according to the third embodiment is an example based on the second embodiment and employing a dielectric isolation wafer as the bonded substrate. First, a silicon wafer 20 having a mirror-finished surface to be an active layer wafer is prepared and prepared (FIG. 3A). Next, a mask oxide film 21 is formed on the surface of the silicon wafer 20 (FIG. 3B).

Next, a resist film 22 is deposited on the oxide film 21. Then, windows of a predetermined pattern are formed in the resist film 22. Subsequently, a window having the same pattern is formed in oxide film 21 through this window, and a part of the surface of silicon wafer 20 is exposed. Next, the resist film 22 is removed.
Further, this silicon wafer 20 is treated with an etching solution (I
(PA / KOH / H ₂ O) for a predetermined time. As a result, a concave portion (dent) having a predetermined pattern is formed on the surface of the silicon wafer. Therefore, anisotropic etching is performed on the wafer surface (FIG. 3C), and the cross-section V
A character-shaped dielectric isolation groove 23 is formed.

Next, the mask oxide film 21 is washed and removed with a dilute HF solution (FIG. 3D). At this time, a dopant may be introduced into bulk Si. Subsequently, a dielectric isolation oxide film 24 having a predetermined thickness is formed on the surface of the silicon wafer by an oxidizing heat treatment (FIG. 3E). Then, the wafer surface is cleaned.

Next, a seed polysilicon layer 25 is deposited on the surface of the silicon wafer 20 by low-temperature CVD at about 600.degree. After the cleaning, a high-temperature polysilicon layer 26 is grown to a predetermined thickness on the polysilicon layer 25 by a high-temperature CVD method at about 1250 ° C. (FIG. 3).
(F)). Subsequently, the outer peripheral portion of the wafer is chamfered, and the back surface of the wafer is flattened as necessary. Then, the high-temperature polysilicon layer 26 on the wafer surface is ground and polished to a thickness of 30 μm (FIG. 3 (g)). Alternatively, a low-temperature polysilicon layer 27 having a thickness of 3 μm is deposited on the wafer surface by a low-temperature CVD method at 600 ° C. if necessary, and the surface is polished.

Then, SC1 (NH ₄ OH:
(H ₂ O ₂ : H ₂ O = 0.5: 1: 5) Washing is performed. SC
By performing one cleaning, the surface of the low-temperature polysilicon layer 27 is etched by several layers and simultaneously terminated with OH groups. As a result, the surface of the low-temperature polysilicon layer 27
% Or more of Si is terminated by an OH group. Thereafter, the wafer is washed with water and dried.

On the other hand, a support substrate wafer 30 whose surface is covered with the oxide film 31 is prepared (FIG. 3 (h)). Then, similarly, SC
1 Apply washing. As a result, Si on the surface of oxide film 31
The dangling bond of the atom is terminated by an OH group. At this time, the coverage θ of the SiOH bond is 40% or more. afterwards,
This wafer is washed with water. Next, the silicon wafer 20 for the active layer wafer is bonded on the support substrate wafer 30 with its mirror surfaces superimposed (FIG. 3 (i)).

Then, a predetermined bonding heat treatment is performed on the bonded wafer. At that time, the heat treatment temperature is 1200 to 1280 ° C. The heat treatment time is 60 minutes. The atmosphere for the heat treatment is a dry oxygen atmosphere. Thereafter, a void inspection is performed by an ultrasonic flaw detection method. If it is determined that the wafer is non-defective, as shown in FIG. 3 (j), the outer peripheral portion of the active layer wafer is chamfered and, if necessary, the oxide film 31 on the back surface of the support substrate wafer 30.
After the removal, the surface of the active layer wafer is ground and polished. The polishing amount of the active layer wafer is set until the dielectric isolation silicon island 20A partitioned by the dielectric isolation oxide film 24 appears. In this way, a rigid bonded dielectric separation wafer with few voids (bonded substrate)
Is produced.

Next, data obtained when an experiment was actually conducted on the relationship between the coverage ratio θ of OH groups on the wafer surface and the bonding heat treatment temperature using two mirror-finished silicon wafers will be described. The conditions at the time of the experiment are as follows. For each experimental condition, 25 active layer wafers are prepared (one of them is for monitoring). (1) First, as a preparation for the bonding surface, all the samples on the active layer wafer side are subjected to SC1 cleaning of the wafer surface. (2) Next, cleaning before bonding is performed. That is, 50
SC1 washing solution (NH ₄ OH: H ₂ O ₂ : H ₂ O) at ± 5 ° C.
= 0.5: 1: 5), the two bonded silicon wafers are subjected to SC1 cleaning. The storage of wafers is performed at room temperature 22 ± 3 ° C, humidity 30-60%, class 10
Use a clean room. The storage time is 1 to 13 hours.

(3) The coverage θ of OH groups on the wafer surface is measured by Fourier transform total reflection infrared absorption spectroscopy (FT-I
R-ATR), each sample is evaluated one by one, and the coverage θ of OH groups on the wafer surface is calculated. (4) The bonding heat treatment is performed in a dry oxygen atmosphere.
The heat treatment time is 60 minutes. Table 1 shows the relationship between the coverage θ of OH groups on the surface of the silicon wafer and the temperature of the bonding heat treatment when the bonding heat treatment was performed under the above conditions. As a post-process, the outer periphery of the bonded wafer is
Chamfer by mm. Then measure the voids. This measurement is performed by an ultrasonic inspection method using an ultrasonic inspection apparatus. The inspection condition is that the ultrasonic frequency is 30 MHz
When the reflection intensity is 50% or more, it is regarded as a void. In this way, the void occupancy rate (void area / wafer area × 100) is obtained. The numerical values in Table 1 are the average values of 24 silicon wafers. Good products with void occupancy of 0.2% or less.

[0031]

[Table 1]

As is evident from Table 1, the covering ratio θ of the OH group exceeds 40%, and the laminating heat treatment temperature is 120%.
In the case of 0 to 1280 ° C., good products having a void occupancy of 0.2% or less were obtained.

[0033]

According to the present invention, it is possible to manufacture a bonded substrate which has few voids and is firmly joined.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing a method for manufacturing a bonded substrate according to a first embodiment of the present invention.

FIG. 2 is a flow sheet showing a method for manufacturing a bonded substrate according to a second embodiment of the present invention.

FIG. 3 is a flow sheet showing a method for manufacturing a bonded substrate according to a third embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 11 silicon wafer (first silicon wafer), 12 silicon wafer (second silicon wafer), 13 bonded substrate, 20 active layer wafer (first silicon wafer), 30 support substrate wafer (second silicon wafer) ).

Claims (5)

[Claims] 1. A silicon wafer for bonding, which is a mirror-polished silicon wafer, wherein the coverage of SiOH bonds is 40% or more of the surface of the silicon wafer. 2. The surface of a mirror-polished silicon wafer is washed with a hydrofluoric acid solution, and then the SC1 solution or S
A silicon wafer for bonding in which the surface is cleaned with a C2 liquid so that the coverage of SiOH bonds on the surface of the silicon wafer is 40% or more. 3. A step of preparing a first silicon wafer and a second silicon wafer each having a mirror-polished bonded surface; and bonding each bonded surface of the first silicon wafer and the second silicon wafer to SiOH. A step of subjecting each of the first and second silicon wafers to a hydrophilic treatment so that the bonding coverage is 40% or more;
And a step of manufacturing a bonded substrate by heat-treating the stacked silicon wafer. 4. In the hydrophilization treatment, the surface of the silicon wafer is washed with hydrofluoric acid, and then the SC1 solution or the SC2 solution is washed.
The method for producing a bonded substrate according to claim 3, wherein the substrate is washed with a liquid. 5. The method according to claim 1, wherein the superposed silicon wafers are
The method for manufacturing a bonded substrate according to claim 3 or 4, wherein the heat treatment is performed at 200 to 1280 ° C.