JP5738145B2 - Manufacturing method of SOI wafer - Google Patents

Description

The present invention relates to a method for manufacturing an SOI (Silicon On Insulator) wafer.

  In order to reduce the parasitic capacitance and increase the device speed, SOI wafers have been widely used. Among these SOI wafers, handle wafers called SOQ (Silicon on Quartz) and SOS (Silicon on Sapphire) are attracting attention as wafers composed of insulating transparent wafers.

  SOQ wafers are expected to be applied to optoelectronics utilizing the high transparency of quartz, or to high frequency devices utilizing low dielectric loss. In addition, since the handle wafer is made of sapphire, the SOS wafer has high thermal conductivity that cannot be obtained with quartz in addition to high transparency and low dielectric loss, so it is expected to be applied to high-frequency devices that generate heat. Is done.

  As a method of laminating a silicon thin film on a handle wafer, a method in which a silicon layer is heteroepitaxially grown on R-plane sapphire, a non-single crystal silicon is grown on glass, and then CG (Continuous Grains) is improved by laser annealing or the like. : Continuous grain boundary crystals) Silicon and the like have been developed. However, in order to stack high-quality single crystal silicon on the handle wafer, silicon is bonded to the handle wafer by bonding the bulk silicon wafer and the handle wafer, and then peeling off a portion of the silicon wafer and transferring it onto the handle wafer. It is ideal to form a thin film (Patent Document 1).

International Publication No. 2009/116664

  In a normal method for manufacturing an SOI wafer, bonding strength is increased by performing heat treatment after bonding two wafers (donor wafer, handle wafer). However, in the case of SOQ wafer and SOS wafer, if the donor wafer and the handle wafer are bonded at room temperature and then heat-treated at 300 ° C., for example, the thermal expansion coefficients of the donor wafer and the handle wafer are different, so the bonded wafer is damaged. There is a problem of doing. In order to avoid this problem, the temperature at the time of pasting can be raised to, for example, 200 ° C., thereby reducing the possibility that the wafer that has been pasted will be damaged during the subsequent heat treatment. This is because the strain due to heat treatment is proportional to “heat treatment temperature (T2) −bonding temperature (T1) = difference between heat treatment temperature and bonding temperature (ΔT)”.

  Further, when the two wafers are bonded at the same temperature when the two wafers are bonded, there is a problem that the wafer is deformed due to a rapid temperature change at the time of bonding, and bubbles are introduced into the bonded surfaces. For example, when a sapphire wafer (handle wafer) heated to 200 ° C. and an unheated donor wafer are bonded together, the heated sapphire wafer is temporarily and rapidly cooled to cause warpage and locality on the wafer. Deformation occurs, and bubbles are introduced into the bonding surface.

  In order to solve such a problem, the present inventors heated one wafer (lower wafer) to a desired temperature by placing it on the upper surface of the first heating device or the like. After holding the other wafer (upper wafer) in contact with the second heating device or the like installed above the first heating device or the like, and holding both wafers close to each other and heating both wafers to the same temperature The method of bonding was examined. However, if a heating source or a complicated mechanism is provided to hold the upper wafer, foreign matter or the like is generated and dropped and adheres to the bonding surface, resulting in an unbonded portion called a void on the bonding surface. To do. In addition, two heating sources are required, increasing the production cost.

  The present invention has been made in view of the above circumstances, and provides an SOI wafer manufacturing method capable of suppressing warpage and deformation of a wafer.

In order to solve the above-mentioned problem, the present inventor uses a silicon wafer as a donor wafer, quartz or sapphire as a handle wafer, and when the temperature difference between both wafers exceeds 50 ° C., Was deformed, and it was found that bubbles were introduced into the bonding surface.
That is, in the present invention, using a silicon wafer as a donor wafer, bonding the surface of the silicon wafer and the surface of the handle wafer to obtain a bonded wafer, and after bonding, a part of the silicon wafer An SOI wafer manufacturing method including at least a peeling step of peeling and transferring the silicon thin film made of the wafer onto the handle wafer, wherein the bonding step includes either the silicon wafer or the handle wafer. Is heated to 100-400 ° C. by placing it on the upper surface of the heating device, and the other wafer is held above the one wafer without contacting it at a certain distance from the one wafer. The temperature difference between the placed wafer and the held wafer is 50 ° C. or less. When it becomes, to provide a method for manufacturing an SOI wafer bonding the the placing location to wafer surface and the retained wafer surface.

  According to the method for manufacturing an SOI wafer of the present invention, warpage and deformation of the wafer can be suppressed.

It is a figure which shows an example of the process of the manufacturing method of an SOI wafer. It is a figure which shows an example in which holding | maintenance is performed using a spacer. It is the photograph image | photographed from the sapphire wafer side about the bonded wafer with which the space | interval was hold | maintained at 50 micrometers. It is the photograph image | photographed from the sapphire wafer side about the bonded wafer with which the space | interval was hold | maintained at 3 mm.

Examples of the donor wafer used in the present invention include a single crystal silicon wafer and the like. For example, the donor wafer used in the present invention is generally marketed by the Czochralski method, and has electrical characteristics such as conductivity type and specific resistivity, crystal orientation The crystal diameter may be appropriately selected depending on the design value of the device provided with the SOI wafer manufactured by the method of the present invention, the process, the display area of the manufactured device, or the like.
If necessary, a silicon wafer having an oxide film formed on the surface or the entire surface may be used as the donor wafer. The oxide film can be formed by a general thermal oxidation method. Generally, it is obtained by heat treatment at 800 to 1100 ° C. under normal pressure in an oxygen atmosphere or a water vapor atmosphere. The thickness of the oxide film is preferably 50 to 500 nm. This is because it is difficult to control the oxide film thickness if it is too thin, and it takes too much time if it is too thick.
The handle wafer used in the present invention is preferably made of any material of quartz, glass, or sapphire. The handle wafer is preferably cleaned in advance such as RCA cleaning before use.
The difference in thermal expansion coefficient between the donor wafer and the handle wafer as described above is large. For example, the difference in thermal expansion coefficient between silicon and quartz is 2.0 × 10 ⁻⁶ / K, and the thermal expansion coefficient between silicon and sapphire is The difference is 3.2 × 10 ⁻⁶ / K. The present invention is not limited to these combinations, and can be applied even if the materials to be combined have the same difference in thermal expansion coefficient (2.0 × 10 ⁻⁶ / K or more).

Hereinafter, although the manufacturing method of the SOI wafer which concerns on this invention is demonstrated with reference to FIG. 1, this invention is not limited to these.
FIG. 1 is a diagram illustrating an example of steps of a method for manufacturing an SOI wafer.
First, a handle wafer 11 and a silicon wafer 12 as a donor wafer are prepared. Next, either the silicon wafer 12 or the handle wafer 11 is heated to 100 to 400 ° C. by placing it on the upper surface of the heating device 13. FIG. 1A shows an example in which the handle wafer 11 is placed on the upper surface of the heating device 13.
The heating device 13 may be any device that can heat the wafer to a desired temperature, and examples thereof include a hot plate.
The heating temperature is preferably 100 to 400 ° C, more preferably 200 to 400 ° C. For example, when quartz or glass is used as the handle wafer 11, the temperature is preferably 100 to 400 ° C., more preferably 200 to 400 ° C., and when sapphire is used as the handle wafer 11, preferably 100 to 300 ° C. ° C, more preferably 200 to 300 ° C. With such a heating temperature, the bonding strength between the silicon wafer 12 and the handle wafer 11 can be increased, and the bonded wafer may be damaged when the bonded wafer is returned to room temperature after the bonding process described later. Less is.

Here, before heating, a surface activation process may be performed on one or both of the silicon wafer 12 and the handle wafer 11. By applying this surface activation treatment, it is possible to increase the bonding strength of the bonded wafer immediately after the bonding process described later.
Examples of the surface activation treatment include ozone water treatment, UV ozone treatment, ion beam treatment, and plasma treatment.
When processing with plasma, for example, a silicon wafer and / or handle wafer that has been cleaned such as RCA cleaning is placed in a chamber, a plasma gas is introduced under reduced pressure, and then a high-frequency plasma of about 100 W is applied to 5 to The surface is subjected to plasma treatment for about 10 seconds. As a plasma gas, when processing a silicon wafer, when oxidizing the surface, plasma of oxygen gas, when not oxidizing, hydrogen gas, argon gas, nitrogen gas or a mixed gas thereof or hydrogen gas and helium gas A mixed gas can be used. Any gas may be used when processing the handle wafer. By treating with plasma, organic substances on the surface of the silicon wafer and / or handle wafer are oxidized and removed, and OH groups on the surface are increased and activated.
When processing with ozone water, it can be realized, for example, by immersing the wafer in pure water in which ozone is dissolved at about 10 mg / L.
When processing with UV ozone, it is possible to irradiate ozone light or ozone gas generated from the atmosphere with UV light (for example, wavelength 185 nm).
In the case of processing with an ion beam, for example, the surface of the wafer is processed under a high vacuum with a beam of an inert gas such as argon as in the case of sputtering, thereby exposing unbonded hands on the surface and increasing the bonding force. It is possible to increase.
In ozone water treatment, UV ozone treatment, and the like, activation is performed by decomposing organic substances on the surface of a silicon wafer or a handle wafer with ozone and increasing OH groups on the surface. On the other hand, in ion beam processing and plasma processing, activation is achieved by exposing highly reactive dangling bonds (dangling bonds) on the wafer surface or by adding OH groups to the dangling bonds. Do.
The activation of the surface can be confirmed by looking at the degree of hydrophilicity (wetting). Specifically, it can be measured simply by pouring water on the surface of the wafer and measuring its contact angle.

Next, as shown in FIG. 1B, the other wafer (silicon wafer 12) is held above the handle wafer 11 without contacting the handle wafer 11 with a certain distance. The silicon wafer 12 is indirectly heated by the heat (convection heat, radiant heat) of the handle wafer 11.
The holding device 14 for holding the silicon wafer 12 is preferably a robot arm or vacuum tweezers. This is because the silicon wafer 12 can be brought as close as possible without contacting the handle wafer 11.
The constant distance L between the silicon wafer 12 and the handle wafer 11 is preferably 30 μm to 2 mm. This is because the silicon wafer 12 is sufficiently heated by the heat of the handle wafer 11 at such an interval.

Instead of the holding device 14 in FIG. 1B, a spacer 17 may be disposed on the handle wafer 11 as shown in FIG. By interposing the spacer 17 between the silicon wafer 12 and the handle wafer 11, the silicon wafer 12 is held.
The spacer 17 is not limited in shape and size as long as it can hold a silicon wafer 12 described later, and may be disposed at any position on the handle wafer 11, for example, at both ends of the handle wafer 11. .
The material of the spacer 17 is not particularly limited, but a material having high thermal conductivity is preferable, and examples thereof include a SUS metal piece.
Next, as shown in FIG. 2B-2, the other wafer (silicon wafer 12) is placed on the spacer 17 and held above the handle wafer 11. By interposing the spacer 17 between the silicon wafer 12 and the handle wafer 11, the silicon wafer 12 is heated by the heat (convection heat, radiant heat) of the handle wafer 11 without bringing the silicon wafer 12 into contact with the handle wafer 11. Indirect heating is possible.
The constant distance L between the silicon wafer 12 and the handle wafer 11 is preferably 30 μm to 2 mm. This is because the silicon wafer 12 is sufficiently heated by the heat of the handle wafer 11 at such an interval. The constant interval L can be set to a desired interval by changing the thickness of the spacer 17.

  As for the heating and holding described above, the silicon wafer 12 may be held while the handle wafer 11 is heated, or the handle wafer 11 may be heated and then the silicon wafer 12 may be held.

Next, as shown in FIG. 1C, the wafer was placed when the temperature difference between the placed wafer (handle wafer 11) and the held wafer (silicon wafer 12) was 50 ° C. or less. The wafer surface 11 s and the held wafer surface 12 s are bonded together to obtain a bonded wafer 15.
The temperature difference between the mounted wafer and the held wafer refers to the difference in surface temperature between the wafers. If the wafers 11 and 12 are bonded together when the temperature difference is 50 ° C. or less, the wafer 15 may be warped and locally deformed when the bonded wafer 15 is returned to room temperature. Low and there is little risk of air bubbles being introduced into the bonding surface. The lower limit value of the temperature difference depends on the size of the interval L, but since L is not zero, the lower limit value of the temperature difference is preferably not zero.
Since the distortion due to heating is proportional to “heating temperature (T2) −bonding temperature (T1) = difference between heating temperature and bonding temperature (ΔT)”, the bonded wafer 15 is damaged during the heating described later. The possibility can be reduced.

  Next, as shown in FIG. 1D, the bonded wafer 15 is heated to 100 to 400 ° C. if necessary. There are cases where it is necessary to heat the wafers 11 and 12 according to the temperature when the wafers 11 and 12 are bonded together, and there are cases where heating is performed to increase the bonding strength more reliably. The heating time is determined according to the heating temperature and the thermal conductivity of the material, and is selected from a range of 0.5 to 10 minutes, for example. Thus, by heating the bonded wafer 15, the bonding strength between the silicon wafer 12 and the handle wafer 11 can be increased. In addition, when heating is performed at such a temperature, there is little risk of occurrence of thermal strain, cracking, peeling, or the like due to a difference in thermal expansion coefficient due to the different materials.

Next, as shown in FIG. 1E, the silicon thin film 12 </ b> B formed of a part of the silicon wafer 12 in the bonded wafer 15 after heating is peeled off and transferred onto the handle wafer 11.
The peeling transfer method is not particularly limited, and examples thereof include a SiGen method and a SOITEC method. For example, hydrogen ion implantation is performed on a donor wafer (silicon wafer) in advance to a depth corresponding to the thickness of a thin film to be transferred (before FIG. 1A). The silicon thin film can be peeled along and transferred onto the handle wafer.

Through the steps as described above, an SOI wafer 16 as shown in FIG. 1F can be obtained.
As described above, according to the SOI wafer manufacturing method of the present invention, warpage and deformation of the wafer can be suppressed.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited thereto.

Example 1
A 6-inch sapphire wafer was used as a handle wafer, and the sapphire wafer was placed on a heating plate and heated at 250 ° C. Next, a metal piece having a width of 2 mm and a length of 3 mm was placed as a spacer on the sapphire wafer. Next, a silicon wafer was placed on the spacer and held above the sapphire wafer. The interval between the silicon wafer and the sapphire wafer was changed depending on the thickness of the spacer, and the temperature of the silicon wafer at each interval was measured. The time during which the temperature of the silicon wafer was constant was about 3 minutes regardless of the interval. The temperature of the silicon wafer was measured by a thermocouple attached to the silicon wafer. It processed for 3 minutes at the said heating temperature. The measurement results are shown in Table 1.

In addition, wafers held at intervals of 50 μm and 3 mm were bonded together. The photograph which image | photographed from the sapphire wafer side about the obtained bonded wafer is shown in FIG.3 and FIG.4, respectively.

From Table 1, when the interval was in the range of 30 μm to 2 mm, no bubbles were generated on the bonding surface. Further, the temperature difference between the silicon wafer and the sapphire wafer in this range was 50 ° C. or less.
In FIG. 3, generation | occurrence | production of the bubble was not confirmed, but generation | occurrence | production of the bubble a was confirmed in FIG.

(Example 2)
The same procedure as in Example 1 was performed except that the sapphire wafer was heated at 300 ° C. The measurement results are shown in Table 2.

  From Table 2, when the interval was in the range of 30 μm to 2 mm, no bubbles were generated on the bonding surface. Further, the temperature difference between the silicon wafer and the sapphire wafer in this range was 50 ° C. or less.

11 Handle wafer 11s Surface 12 Silicon wafer 12s Surface 12B Silicon thin film 13 Heating device 14 Holding device 15 Bonded wafer 16 SOI wafer 17 Spacer a Bubble

Claims (6)

Using a silicon wafer as a donor wafer, and bonding the surface of the silicon wafer and the surface of the handle wafer to obtain a bonded wafer;
A method of manufacturing an SOI wafer including at least a peeling step of peeling a silicon thin film formed of a part of the silicon wafer and transferring the film onto the handle wafer after the bonding;
The handle wafer is a sapphire wafer;
In the bonding step, either the silicon wafer or the handle wafer is heated to 100 to 300 ° C. by placing the wafer on the upper surface of a heating apparatus, and the other wafer is fixed from the one wafer. The wafer is held above the one wafer without contact at intervals, and when the temperature difference between the wafer placed above and the wafer held is 50 ° C. or less, the wafer placed A method for manufacturing an SOI wafer in which a surface and a surface of the held wafer are bonded together. The method for manufacturing an SOI wafer according to claim 1, further comprising a step of heating the bonded wafer to 100 to 400 ° C. before the peeling step .   3. The method for manufacturing an SOI wafer according to claim 1, wherein the peeling is performed along an ion implantation layer introduced to a depth corresponding to a thickness of a thin film to be transferred to the silicon wafer in advance.   The method for manufacturing an SOI wafer according to claim 1, wherein the predetermined interval is 30 μm to 2 mm.   The method for manufacturing an SOI wafer according to claim 1, wherein the holding is performed using a robot arm, vacuum tweezers, or a spacer interposed between the donor wafer and the handle wafer. The method for manufacturing an SOI wafer according to claim 1, wherein a difference in coefficient of thermal expansion between the silicon wafer and the handle wafer is 2.0 × 10 ⁻⁶ / K or more.