JPH10303089A - Manufacture of laminated substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a laminated substrate by which voids can be eliminated, a heat treatment time for lamination can be reduced and an excessive thermal stress, contamination and OSF can be suppressed. SOLUTION: After both an active layer A substrate 11 and a supporting B substrate 12 are subjected to SC1 washing, they are subjected to diluted HF washing (HF:H2 O=1:50-400). By the diluted HF washing, Si-F couplings are once formed in the wafer surfaces. As the Si-F couplings are easily attacked by HF because of polarization, Si atoms in the wafer surfaces leave in the forms of SiF4 and the wafer surfaces are terminated by H-radicals. After the mirror surfaces of both the substrates are put on the other at a room temperature, they ate subjected to a heat treatment for lamination at 880-1100 deg.C for 20-120 minutes. As the Si surfaces are terminated by H-radicals, H2 O molecules are produced in the heat treatment for lamination and released through the boundary between both the lamination surfaces. With this constitution, a heat treatment time for lamination can be reduced and, further, the contamination of the substrates and OSF can be avoided.

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, and more particularly to a method of manufacturing a bonded substrate used for a power element, a composite element, and the like.

[0002]

2. Description of the Related Art Generally, in order to bond silicon wafers together, a surface having an OH group is required.
To control and form the wafer surface in this way, use SC1
(Standard Cleaning 1) A natural oxide film is formed on the surface by cleaning using a cleaning solution. Or
After this, the conc. Perform HF treatment and apply Si
A -F bond was generated once, and then F was replaced with an OH group by pure water rinsing (Japanese Patent Laid-Open No. 5-198549). Therefore, the bonding strengthening heat treatment is performed on the silicon surface (bonding surface) terminated by the OH group. Therefore, during this heat treatment, when H ₂ O escapes from the bonding interface, it is agglomerated and voids are easily generated in the outer peripheral portion of the wafer, and the yield of non-defective substrates is deteriorated.

In order to avoid this, the bonded substrate must be exposed to a high-temperature atmosphere of about 1200 ° C. for almost two hours. More specifically, the mirror surfaces of the silicon wafers subjected to the SC1 cleaning treatment are overlapped and adhered in a clean room at room temperature. Then, this laminated substrate that has been integrated
Hold at about 1200 ° C. for 2 hours.

[0004]

However, in such a conventional method for manufacturing a bonded substrate, the heat treatment after the superposition is performed at a high temperature exceeding 1100 ° C., so that the following problems occur. . That is, recently, there has been an increasing demand for lowering the temperature of the device process. For example, in some cases, a dielectric isolation substrate, a substrate subjected to selective polishing, a substrate for VDMOS, and the like are manufactured by using this bonding method. When laminating such patterned wafers, there was a problem that the amount of expansion and contraction of the pattern was increased in the high-temperature heat treatment. In such a high-temperature heat treatment, an OSF (Oxidation Indus) is formed on the active layer portion of the bonded substrate.
There was a possibility that a sed Stacking Fault would occur.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a bonded substrate by low-temperature heat treatment. Another object of the present invention is to manufacture a bonded substrate free from excessive thermal stress, for example, a pattern shift. Another object of the present invention is to provide a bonded substrate free from contamination and OSF. Further, another object of the present invention is to provide a bonded substrate in which generation of voids is small. Another object of the present invention is to enable a bonded substrate to be manufactured by a short heat treatment.

[0006]

According to a first aspect of the present invention, there is provided a process of preparing a first silicon wafer and a second silicon wafer, and a step of preparing the first silicon wafer and the second silicon wafer. A step of performing a dilute HF cleaning on each surface, a step of superposing the first silicon wafer and the second silicon wafer, and a step of superposing the superposed silicon wafers at 880 to 1100 ° C. for 20 to 12 hours.
And performing a heat treatment for 0 minutes to produce a bonded substrate. The reason for this temperature condition is that if the temperature is lower than 880 ° C., the void generation rate increases. If the temperature exceeds 1100 ° C., the heating temperature is too high, and excessive thermal stress such as pattern shift, contamination from a furnace, and OSF are likely to occur. The preferred heat treatment time is 20 to 120 minutes,
If the time is less than 0 minute, the heat treatment time is too short, and voids are easily generated at the bonding interface of the silicon wafer. Also,
If the time exceeds 120 minutes, the occurrence of OSF increases. Also,
Here, the dilute HF cleaning means cleaning using a lower concentration of HF (hydrofluoric acid) than HF cleaning of a general silicon wafer.

According to a second aspect of the present invention, there is provided a method for manufacturing a bonded substrate, wherein an SOI substrate having an insulating film interposed between a first silicon wafer and a second silicon wafer is manufactured by bonding. A step of performing a dilute HF cleaning on each surface of the silicon wafer and the second silicon wafer, a step of overlapping the first silicon wafer and the second silicon wafer with an insulating film interposed therebetween, After the bonding, a heat treatment is performed at a temperature of 880 to 1100 ° C. for 20 to 120 minutes, thereby manufacturing a bonded substrate. These temperature conditions and heat treatment time are based on the same reason as in the first aspect of the present invention.

According to a third aspect of the present invention, there is provided a step of preparing a first silicon wafer having a mirror-polished polysilicon layer on its surface, a step of preparing a second silicon wafer, and a step of preparing the first silicon wafer. Performing a dilute HF cleaning on each surface of the silicon wafer and the second silicon wafer;
A step of superposing the polysilicon layer of the first silicon wafer on the surface of the second silicon wafer, and a step of producing a bonded substrate by heat-treating these at 880 to 1100 ° C. for 20 to 120 minutes. And a method for manufacturing a bonded substrate comprising: The first silicon wafer having a polysilicon layer on the surface includes both a case of an active layer wafer and a case of a support substrate wafer. Note that the effects of the present invention can be obtained even if both the first silicon wafer and the second silicon wafer have a polysilicon layer. The reasons for the above temperature conditions and heat treatment time are as follows.
This is the same as the case of the invention described in (1).

According to a fourth aspect of the present invention, there is provided a step of preparing a first silicon wafer having a polysilicon layer on the surface, a step of preparing a second silicon wafer having an insulating film on the surface, Performing dilute HF cleaning on the surface of the polysilicon layer of the first silicon wafer and the surface of the insulating film of the second silicon wafer, respectively, and overlapping the polysilicon layer of the first silicon wafer with the insulating film of the second silicon wafer This is a method for manufacturing a bonded substrate, which includes a step of bonding, and a step of manufacturing a bonded substrate by heat-treating these at 880 to 1100 ° C. for 20 to 120 minutes after being superposed. These temperature conditions and heat treatment times are limited for the same reason as in the first aspect of the present invention.

The invention according to claim 5 is the method for manufacturing a bonded substrate according to claim 3 or 4, wherein the first silicon wafer has a pattern formation layer covered with a polysilicon layer.

[0011] According to a sixth aspect of the present invention, the heat treatment comprises:
The method for producing a bonded substrate according to any one of claims 1 to 5, wherein the method is performed in an oxygen atmosphere or a nitrogen gas atmosphere.

According to a seventh aspect of the present invention, in the cleaning solution used for the dilute HF cleaning, when HF: H ₂ O = 1: X, 50 ≦ X ≦ 400. The method for manufacturing a bonded substrate according to any one of the above items. X
The value of was within this range, when X was less than 50, when F of the Si-F bond on the wafer surface was replaced with an OH group,
This is because the ratio of OH groups becomes too high, and the void generation rate at the outer peripheral portion of the wafer increases. If X exceeds 400, it takes too much time to remove the natural oxide film.

[0013]

According to the first aspect of the present invention, first, a first silicon wafer (PW: mirror surface wafer) and a second silicon wafer (PW) are prepared. Each of these silicon wafers is cleaned by immersing it in at least the SC1 solution, and finally, performing dilute HF cleaning. By dilute HF cleaning, HF molecules are first converted to Si-O on the wafer surface.
Reacts with the bond to form a Si-F bond. This Si-
Since the F bond is polarized, it is easily attacked by HF, whereby Si on the wafer surface is desorbed as SiF ₄ and the Si surface is terminated by H groups. Next, these first
And the second silicon wafer are overlapped, for example, at room temperature. The mirror surfaces of these silicon wafers are brought into close contact with each other. Then, the superposed wafers are heated at a temperature of 880 to 1100 ° C. for 20 to 1
Heat treat for 20 minutes. As a result, a bonded substrate free of voids can be manufactured. This is because H ₂ can easily be separated from the bonding interface. This, H ₂ is because the volume is very small. As a result of this low-temperature heat treatment, excessive heat stress and contamination hardly occur in the bonded substrate, and OSF is hardly generated.

In the second aspect of the present invention, the first silicon wafer and the second silicon wafer are overlapped with an insulating film interposed therebetween. That is, first,
These silicon wafers are subjected to SC1 and diluted HF cleaning. Then, in a state where these silicon wafers (surfaces are mirror surfaces) are stacked with an insulating film interposed therebetween, heat treatment is performed at a temperature of 880 to 1100 ° C. for 20 to 120 minutes. As a result, the SOI
A substrate can be manufactured.

According to the third aspect of the present invention, first, a first silicon wafer having on its surface a polysilicon layer whose surface is mirror-polished is prepared. Also, a second silicon wafer whose surface is mirror-polished is prepared. The surface (mirror surface) of these silicon wafers is S
After C1 cleaning, dilute HF cleaning is performed. Next, the polysilicon layer of the first silicon wafer is overlaid on and adhered to the surface of the second silicon wafer. The mirror surfaces are brought into close contact with each other. This superposition is performed, for example, at room temperature in a clean room. Then, after overlapping, this is heat-treated at 880 to 1100 ° C. for 20 to 120 minutes. As a result, it is possible to manufacture a bonded substrate in which the polysilicon layer is interposed between the silicon layers. This is because if the heat treatment is performed for less than 20 minutes, voids (unbonded portions) are generated at the bonded interface. If the time exceeds 120 minutes, the amount of expansion and contraction of the polysilicon layer becomes too large.

In the present invention, first, a first silicon wafer having a polysilicon layer is prepared.
Further, a second silicon wafer having an insulating film on the surface is prepared. Then, the surfaces of these silicon wafers, that is, the polysilicon layer surface and the insulating film surface are each subjected to dilute HF cleaning. Next, the surface of the polysilicon layer of the first silicon wafer and the surface of the insulating layer of the second silicon wafer are overlapped with each other and brought into close contact, for example, at room temperature. Then, after overlapping, these are 880-
Heat treatment is performed at 1100 ° C. for 20 to 120 minutes. Since the wafer surface is terminated with H groups by dilute HF cleaning, H ₂ is generated at the interface by the bonding heat treatment. However, H ₂ volume is very small, easy exit from the interface bonding even heat treatment time is relatively short. As a result,
A bonded substrate having a polysilicon layer, in which voids are less likely to occur in the outer peripheral portion of the wafer and less likely to cause contamination and OSF, can be manufactured with good productivity.

According to a fifth aspect of the present invention, a pattern layer is formed on the first silicon wafer. This pattern layer is covered with a polysilicon layer, and the surface of the polysilicon layer is mirror-polished. The first silicon wafer is superimposed on the second silicon wafer and heat-treated. Since the heat treatment temperature is relatively low at 880 to 1100 ° C., and the heat treatment time is relatively short at 20 to 120 minutes,
It is possible to manufacture a bonded substrate having a pattern forming layer interposed between silicon layers and having less excessive thermal stress such as pattern shift.

In the invention described in claim 6, the heat treatment is performed in an oxygen atmosphere or a nitrogen gas atmosphere. A dry O ₂ atmosphere or a wet O ₂ atmosphere may be used. Alternatively, heating in an N ₂ gas atmosphere may be used.

In the seventh aspect of the present invention, the cleaning liquid used for the dilute HF cleaning is such that when HF: H ₂ O = 1: X, 50 ≦ X ≦ 400. Before laminating the first silicon wafer and the second silicon wafer, the surfaces of these silicon wafers are subjected to dilute HF cleaning using an HF cleaning solution in the above range. As a result, compared to normal HF cleaning, the density of OH groups on the bonding surface of the silicon wafer is reduced, and the amount of H ₂ O generated at the bonding interface after the bonding heat treatment is reduced. Therefore, the rate of occurrence of voids in the peripheral portion of the bonded substrate can be further reduced.

[0020]

Embodiments of the present invention will be described below with reference to 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 graph showing a void generation rate of the bonded substrate according to the first example.

In the first embodiment, silicon wafers (silicon surfaces) are directly bonded to each other.
As shown in FIG. 1, in this case, two mirror-polished silicon wafers (A plate for active layer, B plate for support layer) 11,
In both cases, SC1 washing and dilute HF washing (HF: H
₂ O = 1: 50-400). By the dilute HF cleaning, HF molecules react with Si—O bonds on the wafer surface to form Si—F bonds. Since the Si—F bond is polarized, it is susceptible to HF attack, whereby Si on the wafer surface is desorbed as SiF _4, and the wafer surface is terminated with H groups. Then, after bonding these mirror surfaces together at room temperature, the bonded substrate 13
Is subjected to a lamination heat treatment. This heat treatment temperature is 8
At 80 to 1100 ° C, the time is 120 minutes. The heat treatment was performed in a N ₂ gas atmosphere.

At this time, since the surface of the silicon wafer is terminated with H groups by the dilute HF cleaning, H ₂ is generated at the bonding interface by the bonding heat treatment. H ₂ volume is very small. Therefore, H ₂ generated at this bonding interface
Is easy to escape from the bonding interface even if the heat treatment time is relatively short. Further, thereafter, a void inspection by ultrasonic irradiation is performed, and the A plate is made to have a predetermined thickness by chamfering and grinding and polishing of the A plate, and the A plate is cleaned.

FIG. 2 shows the relationship between the bonding heat treatment temperature and the void generation rate. As shown in this graph,
The heat treatment at 880 ° C. or higher reduced the void generation rate.
This void generation rate is based on the inspection by ultrasonic irradiation (ultrasonic flaw detection method). Further, since the heat treatment temperature is set to a relatively low temperature (880 to 1100 ° C.), even if the heat treatment is performed for a relatively short time of 120 minutes, contamination of the bonded substrate (such as heavy metal contamination from a heat treatment furnace). ) Is less likely to occur. OSF is less likely to occur. The measurement of the OSF was performed by a known method. That is, the measurement was performed by a measuring method of observing with a microscope after selective etching such as secco etching.

FIG. 3 shows a second embodiment of the present invention. In this embodiment, SOI (Silicon On Ins) is used.
ulrator) A procedure for producing a substrate will be described. The silicon wafer to be used has an oxide film of a predetermined thickness deposited on one of the mirror surfaces of the A plate for the active layer and the B plate for the support. A bonded SOI substrate is manufactured by forming an SiO ₂ film having a predetermined thickness on the surface of the A plate or the B plate and overlaying them. These silicon wafers
In both cases, SCl cleaning, rinsing, dilute HF cleaning (HF: H ₂
O = 1: 50-400), and after being rinsed with pure water, they are superposed. Alternatively, a silicon wafer having an oxide film for an active layer may be subjected to SCl cleaning. This is because particles on the oxide film can be removed by this SC1 cleaning. Lamination is performed at room temperature,
Subsequent heat treatment is performed at 880 to 1100 ° C. for 20 to 12 hours.
It shall be performed for 0 minutes. Grinding and polishing of the active layer after the heat treatment are the same as in the above embodiment. Also in this embodiment, an SOI substrate with less generation of voids can be manufactured as in the above embodiment.

FIG. 4 shows a third embodiment of the present invention. In the third embodiment, bonding of silicon wafers with a polysilicon film interposed therebetween is shown. First, a first silicon wafer (A plate) for an active layer and a second silicon wafer (B plate) coated with a polysilicon film are prepared. This first silicon wafer is a CZ wafer having one surface subjected to mirror polishing. In addition, the second silicon wafer has a polysilicon film of a predetermined thickness deposited on the mirror-finished wafer by, for example, CVD. Next, the first silicon wafer and the second silicon wafer are first
After washing with SC1 solution and rinsing, washing with diluted HF solution is performed. This dilute HF cleaning solution is HF: H ₂ O = 1: (50 to 40
0). The cleaning time is set so that SiO _X can be removed from the wafer surface. Then, running water rinsing with pure water was performed. Subsequent drying was performed by spin drying.

Next, within 30 minutes after the drying, the wafers were superposed and bonded at room temperature under predetermined conditions. The first silicon wafer is bonded to the second silicon wafer. This bonding is performed at room temperature. Then, the bonded substrate is heat-treated. For example, heating is performed at 880 to 1100 ° C. for 20 to 120 minutes in a dry O ₂ atmosphere. Then, the bonded substrate was inspected and confirmed for any voids at the bonded interface by, for example, ultrasonic measurement. Also in this embodiment, a bonded substrate with reduced generation of voids can be obtained as in the above embodiments.

FIG. 5 shows a fourth embodiment of the present invention. In this embodiment, a pattern is formed on the surface of the wafer, and an A plate 22 (the surface of the polysilicon layer is mirror-polished) covered with the polysilicon layer 21 is bonded to a B plate 23. After SC1 washing, rinsing, diluted HF washing, and rinsing, they are superposed at room temperature. Mirror surfaces are superimposed. Furthermore, after performing a heat treatment at 880 to 1100 ° C. for 120 minutes, a known method (ultrasonic wave,
IR etc.).

FIG. 6 is a graph showing the pattern expansion / contraction ratio in the bonded substrate according to the fourth embodiment of the present invention. As can be seen from this graph, the heat treatment exceeding 1100 ° C. increases the expansion ratio. The measurement was performed by a known method.

[0029]

According to the present invention, the following effects can be obtained. (1) No large thermal stress occurs on the bonded substrate. (2) It is possible to manufacture a bonded substrate free from pattern displacement and the like. (3) Contamination of the bonded substrate is also reduced. (4) A bonded substrate free of OSF can be manufactured. (5) The concentration profile at the bonding interface of the bonded substrate can be changed steeply. (6) It is possible to prevent the occurrence of voids at the outer peripheral portion of the wafer of the bonded substrate. (7) The heat treatment time can be shortened. (8) Productivity can be improved.

[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 graph showing a void generation rate and an OSF generation rate of the bonded substrate according to the first embodiment of the present invention.

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

FIG. 4 is a flow sheet showing a method for manufacturing a bonded substrate according to a third embodiment of the present invention.

FIG. 5 is a flow sheet showing a method for manufacturing a bonded substrate according to a fourth embodiment of the present invention.

FIG. 6 is a graph showing the expansion and contraction rate of a pattern on a bonded substrate according to a fourth embodiment of the present invention.

[Explanation of symbols]

 11 first silicon wafer, 12 second silicon wafer, 13 bonded substrate, 21 polysilicon film.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Toru Taniguchi 1-5-1, Otemachi, Chiyoda-ku, Tokyo Mitsubishi Materials Silicon Corporation

Claims (7)

[Claims] A step of preparing a first silicon wafer and a second silicon wafer; a step of performing dilute HF cleaning on each surface of the first silicon wafer and the second silicon wafer; Superposing the silicon wafer and the second silicon wafer on each other;
Producing a bonded substrate by performing a heat treatment at 00 ° C. for 20 to 120 minutes. 2. A bonded substrate manufacturing method for manufacturing an SOI substrate having an insulating film interposed between a first silicon wafer and a second silicon wafer by bonding the first silicon wafer and the second silicon wafer. Performing a dilute HF cleaning on each surface of the wafer; superposing the first silicon wafer and the second silicon wafer with an insulating film interposed therebetween; and 880 to 1100 At a temperature of 20C
Producing a bonded substrate by performing a heat treatment under conditions for 120 minutes. 3. A step of preparing a first silicon wafer having a mirror-polished polysilicon layer on its surface, a step of preparing a second silicon wafer, and a step of preparing the first silicon wafer and the second silicon wafer. Performing a dilute HF cleaning on each surface of the wafer, superposing a polysilicon layer of the first silicon wafer on the surface of the second silicon wafer, and superposing these at 880 to 1100 ° C. for 20 minutes.
Producing a bonded substrate by performing a heat treatment for up to 120 minutes. 4. A step of preparing a first silicon wafer having a polysilicon layer on the surface, a step of preparing a second silicon wafer having an insulating film on the surface, and the polysilicon of the first silicon wafer. Performing a dilute HF cleaning process on each of the layer surface and the insulating film surface of the second silicon wafer; and superposing the polysilicon layer of the first silicon wafer and the insulating film of the second silicon wafer. Later, these are treated at 880-1100 ° C. for 20 minutes.
Producing a bonded substrate by performing a heat treatment for up to 120 minutes. 5. The method for manufacturing a bonded substrate according to claim 3, wherein the first silicon wafer has a pattern formation layer covered with a polysilicon layer. 6. The method according to claim 1, wherein the heat treatment is performed in an oxygen atmosphere or a nitrogen gas atmosphere. 7. The cleaning liquid used for the dilute HF cleaning includes:
HF: H ₂ O = 1: when the X, method for manufacturing a substrate laminated according to any one of claims 1 to 6 is 50 ≦ X ≦ 400.