JP2017224680A - Manufacturing method of bonded wafer - Google Patents

Abstract

The present invention provides a method for manufacturing a bonded wafer, which can reduce the surface roughness of the peeled surface of the bonded wafer and reduce the surface roughness by a planarization heat treatment at a lower temperature. Gas ions are implanted from the surface of a bond wafer to form an ion implantation layer within the bond wafer. After bonding the bond wafer and the base wafer 2, the bonded wafer and the base wafer are held for 12 hours or more at room temperature until the bonding interface is bonded by the contribution of water molecules until the separation heat treatment is performed. To do. In the exfoliation heat treatment, whether the bonded bond wafer and base wafer are directly put into a heat treatment furnace set at a constant temperature of 400 ° C. or more and 500 ° C. or less without a heating step, and the heat treatment is performed at a constant temperature. Alternatively, the temperature is raised from a certain temperature to a predetermined temperature within + 50 ° C. and then heat-treated at the predetermined temperature. [Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a bonded wafer.

  In recent years, as a method of manufacturing a bonded wafer, a method of manufacturing a bonded wafer by bonding an ion-implanted wafer to another wafer and peeling the wafer (ion-implantation peeling method: a technique called Smart Cut Method (registered trademark)) Has begun to attract new attention.

  As a method of manufacturing an SOI wafer by such an ion implantation separation method, an oxide film is formed on at least one of two silicon wafers, and hydrogen ions or rare ions are formed from the upper surface of one silicon wafer (bond wafer). Gas ions such as gas ions are implanted to form a microbubble layer (encapsulation layer) inside the bond wafer. Then, the ion-implanted surface is brought into close contact with the other silicon wafer (base wafer) through an oxide film, and then a heat treatment (peeling heat treatment) is applied to form one wafer (bond wafer) with the microbubble layer as a cleavage plane. The thin film is peeled off, and further heat treatment (bonding heat treatment) is applied to firmly bond to form an SOI wafer (see Patent Document 1). In this method, an SOI wafer having an SOI layer with a highly uniform cleaved surface (peeling surface) and high film thickness uniformity can be obtained relatively easily.

  However, when a bonded wafer is manufactured by the ion implantation separation method, a damage layer due to ion implantation exists on the surface of the bonded wafer after separation, and the surface roughness is higher than the mirror surface of a normal product level silicon wafer. Will be big. Therefore, it is necessary to remove such a damaged layer and surface roughness in the production by the ion implantation separation method.

  Conventionally, in order to remove the damaged layer and the like, mirror polishing (removal allowance: about 100 nm) called “polishing polish” has been performed in the final step after the bonding heat treatment.

  However, if the thin film (SOI layer) of the bonded wafer is polished including a machining element, the amount of polishing is not uniform in the plane. Therefore, the thin film is achieved by implantation and peeling of hydrogen ions and the like. There arises a problem that the thickness uniformity deteriorates.

  As a method for solving such a problem, a flattening heat treatment for improving the surface roughness by performing a high temperature heat treatment instead of the touch polish has been performed.

  In particular, Patent Document 2 pays attention to the short period roughness and long period roughness of the surface roughness, and in the flattening heat treatment, rapid heating / rapid cooling apparatus (RTA apparatus) and heater heating type heat treatment furnace (batch type furnace) are used. There has been proposed a method of reducing both the short period roughness and the long period roughness of the surface roughness by performing a two-step heat treatment.

  Further, in Patent Document 3, in order to avoid OSF (oxidation-induced stacking fault) that is likely to occur when the peeled surface is directly oxidized, planarization heat treatment in an inert gas, hydrogen gas, or mixed gas atmosphere thereof is performed. By performing sacrificial oxidation treatment later, planarization of the peeled surface and avoidance of OSF are achieved at the same time. Further, it has been proposed to further reduce the long-period component of the surface roughness by carrying out polishing with a machining allowance of 70 nm or less before sacrificial oxidation.

  Further, in Patent Document 4, when bonding heat treatment for increasing the bonding strength of a bonded wafer after peeling is performed in an oxidizing atmosphere, 950 ° C. is used as the bonding heat treatment in order to surely avoid OSF that tends to occur on the peeling surface. It is disclosed that the heat treatment is performed at a temperature of 1000 ° C. or higher in an inert gas atmosphere containing 5% or less of oxygen after performing the oxidation heat treatment at a temperature below.

JP-A-5-211128 International Publication No. 2001/028000 International Publication No. 2003/009386 JP 2010-98167 A

  When only a high-temperature heat treatment is performed without performing polishing as the separation surface flattening treatment, the higher the heat treatment temperature, the higher the flatness. According to Patent Document 2, it is said that it is more effective to set the temperature range of 1200 to 1350 ° C. as the heat treatment temperature by the RTA apparatus for improving the short period component, and the long period component is improved. Similarly, it is said that it is more effective to set a temperature range of 1200 to 1350 ° C. as a heat treatment temperature in a batch furnace. And in an Example, the heat processing of 1200 degreeC or more is performed in all the heat processing. Similarly, Patent Document 3 discloses only a heat treatment temperature of 1200 ° C. as Ar annealing for planarization heat treatment.

  As is clear from these descriptions, it is said that a heat treatment temperature of 1200 ° C. or higher is necessary in order to obtain a surface roughness that can be sufficiently applied to a device process by planarization treatment only by heat treatment. Even in mass production, a temperature of 1200 ° C. or higher was adopted.

  However, if heat treatment is performed at a temperature of 1200 ° C. or higher, the probability of occurrence of slip dislocation increases, resulting in a decrease in product yield, resulting in an increase in manufacturing cost.

  Therefore, if the surface roughness of the release surface after the release heat treatment can be reduced, it can be processed in a subsequent process so as not to apply a load to the planarization heat treatment for reducing the surface roughness.

  For example, when using migration by Ar annealing, a bonded wafer having a small peeled surface roughness can be processed at a low temperature, the occurrence of slip dislocation is reduced, and the increase in particles is also reduced. However, in a bonded wafer having a peeled surface with a large surface roughness, processing at a higher temperature is required to reduce the surface roughness. Therefore, it is necessary to take measures against slip, particles and the like. In addition, when the surface roughness of the peeled surface after the peeling heat treatment is large, there are many defects due to peeling of the bonded wafer, and sacrificial oxidation with a thicker oxide film is required to eliminate the defects.

  The present invention has been made in view of the above circumstances. For example, by reducing the surface roughness of a peeled surface after peeling of a bonded wafer such as an SOI wafer, a final planarization heat treatment is performed at a lower temperature. It aims at providing the manufacturing method of the bonded wafer which can reduce the surface roughness of the surface of a bonded wafer.

  In order to solve the above problems, in the present invention, at least one kind of gas ion of hydrogen ion or rare gas ion is ion-implanted from the surface of a bond wafer made of a silicon single crystal wafer, and an ion implantation layer is formed inside the bond wafer. After bonding the ion-implanted surface of the bond wafer and the surface of the base wafer directly or through an insulating film, the bond wafer is peeled off and pasted by the ion-implanted layer by performing a peeling heat treatment. In the bonded wafer manufacturing method for manufacturing a bonded wafer, after bonding the bond wafer and the base wafer, the bonded interface between the bonded wafer and the base wafer is bonded until the peeling heat treatment is performed. The bonded bonnet is bonded with the contribution of water molecules. The wafer and the base wafer are held at room temperature for 12 hours or more, and the peeling heat treatment raises the bonded wafer and the base wafer bonded together in a heat treatment furnace in which the furnace temperature is set to a constant temperature of 400 ° C. or more and 500 ° C. or less. Provided is a method for producing a bonded wafer that is directly charged without a temperature step and heat-treated at the constant temperature, or heated to a predetermined temperature within + 50 ° C. from the constant temperature and then heat-treated at the predetermined temperature.

  With such a bonded wafer manufacturing method, for example, the surface roughness of the peeled surface after peeling of the bonded wafer such as an SOI wafer can be reduced, so that the final surface can be obtained by planarizing heat treatment at a lower temperature. It is possible to reduce the surface roughness of the surface of the bonded wafer (surface of the SOI layer). In addition, by holding the bonded wafer at room temperature for 12 hours or more, the bonding strength between the bond wafer and the base wafer when being put into the heat treatment furnace can be increased, thereby suppressing the generation of voids. .

  At this time, it is preferable that the temperature at the time of taking out the bonded wafer from the heat treatment furnace after the heat treatment at the constant temperature or the predetermined temperature is the same as the temperature at the peeling heat treatment.

  If the temperature at the time of taking out the bonded wafer from the heat treatment furnace is the same as the temperature at the time of the peeling heat treatment, the temperature lowering step can be omitted, which is efficient and the manufacturing cost can be reduced.

  At this time, it is preferable that the holding time at the room temperature is 48 hours or more.

  In this way, the bonding strength between the bond wafer and the base wafer can be further increased.

  At this time, after the peeling heat treatment, a heat treatment for flattening the peeled surface of the bonded wafer from which the bond wafer has been peeled is performed, and the temperature of the heat treatment for flattening is within a temperature range of 1100 ° C. to 1175 ° C. Is preferred.

  If the planarization heat treatment is performed in such a temperature range, the probability of occurrence of slip dislocation is reduced, so that the product yield is improved, and as a result, the manufacturing cost can be reduced.

  At this time, it is preferable that the bond wafer and the base wafer be cleaned before the bond wafer and the base wafer are bonded together.

  As described above, in the present invention, by bonding the bond wafer and the base wafer before bonding the bond wafer and the base wafer, sufficient water molecules can be left on the surface of the bond wafer and the base wafer. When the bond wafer and the base wafer are bonded together, the bonded interface of the bonded wafers can be brought into a bonded state due to the contribution of water molecules.

  If it is the manufacturing method of the bonded wafer of this invention, since the surface roughness of the peeling surface after peeling of bonded wafers, such as an SOI wafer, can be reduced, it is final by planarization heat processing at lower temperature. It is possible to reduce the surface roughness of the surface of the bonded wafer (surface of the SOI layer). In addition, by holding the bonded wafer at room temperature for 12 hours or more, the bonding strength between the bond wafer and the base wafer when being put into the heat treatment furnace can be increased, thereby suppressing the generation of voids. .

It is the schematic which shows an example of the manufacturing method of the bonded wafer of this invention.

Hereinafter, the present invention will be described more specifically.
As described above, for example, by reducing the surface roughness of the peeled surface after peeling of a bonded wafer such as an SOI wafer or a direct bond wafer that does not pass through an insulating film, the final surface is processed by a planarization heat treatment at a lower temperature. There has been a demand for a method for manufacturing a bonded wafer that can reduce the surface roughness of the surface of the bonded wafer (the surface of the SOI layer).

  Normally, when performing a heat treatment by ion implantation, a wafer bonded to a heat treatment furnace held at a low temperature of about 350 ° C. is loaded as described in, for example, Japanese Patent Application Laid-Open No. 2003-347526. And holding for a predetermined time, and then raising the temperature to 500 ° C. or higher and holding it for a predetermined time. However, when such heat treatment is performed, the diffusion of ion-implanted hydrogen slightly progresses until the temperature reaches 500 ° C. at which peeling occurs, and the hydrogen concentration distribution in the implanted layer widens. When peeling occurs in this state, the width of the peeling region (width in the depth direction) becomes wide, and as a result, the surface roughness of the peeling surface increases.

  Therefore, in order to suppress the diffusion of hydrogen, the present inventors either directly input the temperature at which separation is possible without a heating step, or after raising the temperature from a certain temperature to a predetermined temperature within + 50 ° C. It has been found that the surface roughness of the peeled surface after peeling can be reduced by heat treatment at a predetermined temperature. However, when it is charged into the heat treatment furnace at a higher temperature than in the prior art, if the bonding force at the time of charging is weak, complete peeling cannot be obtained and voids are generated. As a countermeasure, the present inventors have bonded the bonded wafer and the base wafer at room temperature until the bonded interface is bonded by the contribution of water molecules until the separation heat treatment is performed. The inventors have found that the above problems can be solved by increasing the bonding strength between the bond wafer and the base wafer when being put into a heat treatment furnace by holding for a long time, and the present invention has been completed.

  Hereinafter, although the present invention is explained in detail, referring to drawings, the present invention is not limited to these.

FIG. 1 is a schematic view showing an example of a method for producing a bonded wafer according to the present invention.
In the bonded wafer manufacturing method of FIG. 1, first, for example, two silicon single crystal wafers are prepared as the bond wafer 1 and the base wafer 2 (FIGS. 1A and 1C).
Here, in FIG. 1, an insulating film (for example, an oxide film) 3 to be a buried oxide film layer is formed only on the bonding surface of the bond wafer 1, but the insulating film 3 is formed only on the base wafer 2. It may be formed on both wafers. Further, both wafers may be bonded directly without forming an insulating film.
As the insulating film formed at this time, for example, a thermal oxide film, a CVD oxide film, or the like can be formed. The insulating film may be formed only on the bonding surface, or may be formed on the entire wafer including the back surface.

  Next, at least one kind of gas ion of hydrogen ion and rare gas ion is ion-implanted from the surface of the insulating film 3 of the bond wafer 1 to form an ion-implanted layer 4 inside the bond wafer 1 (FIG. 1B). ). At this time, ion implantation conditions such as implantation energy, implantation dose, and implantation temperature can be appropriately selected so that a thin film having a predetermined thickness can be obtained.

  Next, the ion-implanted surface of the bond wafer 1 and the surface of the base wafer 2 are brought into close contact with each other and bonded together at a room temperature of about 18 to 30 ° C. (FIG. 1D).

  At this time, it is preferable to perform plasma treatment on at least one of the surfaces to be bonded. Thereby, the improvement effect of the bonding strength by holding | maintenance at room temperature mentioned later can be heightened further.

  Moreover, it is preferable to wash the bond wafer 1 and the base wafer 2 before bonding the bond wafer 1 and the base wafer 2 together. As described above, in the present invention, by bonding the bond wafer and the base wafer before bonding the bond wafer and the base wafer, sufficient water molecules can be left on the surface of the bond wafer and the base wafer. When the bond wafer and the base wafer are bonded together, the bonded interface of the bonded wafers can be brought into a bonded state due to the contribution of water molecules. The cleaning liquid used for this cleaning is not particularly limited, and examples thereof include a mixed solution of ammonia water and hydrogen peroxide water.

  After the bond wafer 1 and the base wafer 2 are bonded together, the bonded wafer is bonded at the room temperature in the state where the bonded interface of the bonded wafers is bonded by the contribution of water molecules until the peeling heat treatment described later is performed. Hold for at least 12 hours (FIG. 1 (e)). Immediately after bonding the bond wafer and the base wafer, the heat treatment of peeling is not performed, and the bonded wafer is left for a while to align the direction of water molecules at the bonding interface, thereby increasing the strength of the bonding interface. Can do. When the holding time at room temperature is less than 12 hours, the bonding strength between the bond wafer and the base wafer cannot be sufficiently increased.

  The holding time at room temperature may be 12 hours or longer, and preferably 48 hours or longer. By holding at room temperature for 48 hours or more, the bonding strength between the bond wafer and the base wafer can be further increased. In addition, as the upper limit of the time for holding at room temperature, the bonding strength is increased up to about 100 hours, but when the time exceeds 100 hours, no further increase in the bonding strength is observed, so the upper limit is set from the viewpoint of productivity. 100 hours is preferable. The holding time at room temperature can be adjusted within a range in which the yield can be secured according to the product specifications.

  Thereafter, the bonded wafer is subjected to a heat treatment (peeling heat treatment) for generating a microbubble layer in the ion implantation layer 4, and the bond wafer 1 is peeled off by the ion implantation layer 4 (microbubble layer). A bonded wafer 6 having a thin film (SOI layer) 5 formed thereon via an insulating film 3 is obtained (FIG. 1 (f)).

  In this exfoliation heat treatment, whether or not the bonded wafer and the base wafer bonded together in a heat treatment furnace whose temperature in the furnace is set to a constant temperature of 400 ° C. or more and 500 ° C. or less is directly put in without a heating step, and the heat treatment is performed at a constant temperature. Alternatively, the temperature is raised from a constant temperature to a predetermined temperature within + 50 ° C. and then heat-treated at the predetermined temperature. By performing the peeling heat treatment under such heat treatment conditions, the surface roughness of the peeling surface can be reduced.

  Here, it is preferable that the temperature at the time of taking out the bonded wafer from the heat treatment furnace after the heat treatment at a constant temperature or a predetermined temperature is the same as the temperature at the peeling heat treatment. If the temperature at the time of taking out the bonded wafer from the heat treatment furnace is the same as the temperature at the time of the peeling heat treatment, the temperature lowering step can be omitted, which is efficient and the manufacturing cost can be reduced.

  Bonded heat treatment for increasing the bond strength at the bonding interface, and planarization heat treatment for flattening the peeled surface of the bonded wafer from which the bond wafer has been peeled off, if necessary, for the bonded wafer produced as described above. Then, heat treatment such as sacrificial oxidation treatment for adjusting the thickness of the thin film can be performed.

  In particular, in the present invention, it is preferable to perform the temperature of the planarization heat treatment within a temperature range of 1100 ° C. to 1175 ° C. If the planarization heat treatment is performed in such a temperature range, the probability of occurrence of slip dislocation is reduced, so that the product yield is improved, and as a result, the manufacturing cost can be reduced.

  If it is the manufacturing method of the bonded wafer of this invention which was demonstrated above, since the surface roughness of the peeling surface after peeling of bonded wafers, such as an SOI wafer, can be reduced, it is at lower temperature. The surface roughness of the final bonded wafer surface (the surface of the SOI layer) can be reduced by the planarization heat treatment.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example and a comparative example, this invention is not limited to these.

Example 1
First, a plurality of wafers shown in Table 1 are used as bond wafers and base wafers made of silicon single crystal, and an SOI wafer is manufactured by performing cleaning, bonding, room temperature holding, and peeling heat treatment under the conditions shown in Table 1. did. The room temperature holding time was 12 hours. The peeling heat treatment was performed at a constant temperature of 450 ° C. and the heat treatment time was 3 hours.

  The obtained SOI wafer is further subjected to sacrificial oxidation treatment that also serves as bonding heat treatment, planarization heat treatment, and sacrificial oxidation treatment for adjusting the film thickness of the SOI layer, and bonded SOI with a SOI layer thickness of 90 nm. A wafer was produced. In addition, as shown in Table 2, the planarization heat treatment was performed separately for 2 hours on the obtained SOI wafer under the temperature conditions of 1100 ° C., 1150 ° C., and 1175 ° C.

  The surface roughness (1 μm square RMS) of the SOI layer (final SOI layer) of the obtained bonded SOI wafer was measured with an AFM (atomic force microscope) and shown in Table 2. Note that, when the surface roughness of the peeled surface immediately after peeling is measured, there is a large variation due to the measurement point and it is difficult to compare, so here, the surface surface of the final SOI layer (that is, after performing the planarization heat treatment) Roughness was measured and compared.

(Example 2)
A bonded SOI wafer was prepared in the same manner as in Example 1. However, the room temperature holding time was 48 hours. Further, the peeling heat treatment was performed by raising the temperature from a constant temperature of 450 ° C. to a predetermined temperature of 500 ° C. (+ 50 ° C.) (temperature raising rate: 10 ° C./min) and a heat treatment time of 0.5 hours.
Further, the surface roughness of the surface of the final SOI layer was measured in the same manner as in Example 1, and the results are shown in Table 2.

(Example 3)
A bonded SOI wafer was prepared in the same manner as in Example 1. However, the room temperature holding time was 96 hours. Further, the peeling heat treatment was performed by raising the temperature from a constant temperature of 400 ° C. to a predetermined temperature (+ 50 ° C.) of 450 ° C. (heating rate of 10 ° C./min) and a heat treatment time of 3 hours.
Further, the surface roughness of the surface of the final SOI layer was measured in the same manner as in Example 1, and the results are shown in Table 2.

(Comparative Example 1)
A bonded SOI wafer was prepared in the same manner as in Example 1. However, the room temperature holding time was 1 hour. The peeling heat treatment was performed at a constant temperature of 450 ° C. and the heat treatment time was 3 hours. Further, as shown in Table 2, the planarization heat treatment was obtained under the temperature conditions of 1100 ° C., 1150 ° C., 1175 ° C., and 1200 ° C. with the heat treatment time being 2 hours, 2 hours, 2 hours, and 1 hour, respectively. Separately for SOI wafers.
Further, the surface roughness of the surface of the final SOI layer was measured in the same manner as in Example 1, and the results are shown in Table 2.

(Comparative Example 2)
A bonded SOI wafer was prepared in the same manner as in Example 1. However, the room temperature holding time was 96 hours, and the peeling heat treatment was performed by raising the temperature from a constant temperature of 350 ° C. to a predetermined temperature of 500 ° C. (+ 150 ° C.) (heating rate 10 ° C./min), and the heat treatment time was 0.5 hours Went as. Further, as shown in Table 2, the planarization heat treatment was obtained under the temperature conditions of 1100 ° C., 1150 ° C., 1175 ° C., and 1200 ° C. with the heat treatment time being 2 hours, 2 hours, 2 hours, and 1 hour, respectively. Separately for SOI wafers.
Further, the surface roughness of the surface of the final SOI layer was measured in the same manner as in Example 1, and the results are shown in Table 2.

(result)
As shown in Table 2, in Examples 1 to 3 in which the bonded SOI wafer was manufactured by the bonded wafer manufacturing method of the present invention, the relatively low temperature planarization heat treatment at 1100 to 1175 ° C. It was found that a good surface roughness equal to or better than the surface roughness in the conventional method (planarization heat treatment temperature: 1200 ° C.) can be obtained.
Moreover, since the planarization heat processing in Examples 1-3 is performed at 1175 degrees C or less, it has also confirmed that generation | occurrence | production of the slip dislocation by heat processing was suppressed compared with the case of 1200 degreeC.

  On the other hand, in Comparative Example 1 in which the room temperature holding time was less than 12 hours (1 hour) and Comparative Example 2 in which the temperature was raised from a certain temperature to a predetermined temperature exceeding + 50 ° C. (+ 150 ° C.), a relatively high temperature of 1100 to 1175 ° C. In the flattening heat treatment at a low temperature, the surface roughness of the surface of the final SOI layer was worse than those in Examples 1 to 3.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

1 ... bond wafer, 2 ... base wafer, 3 ... insulating film,
4 ... Ion implantation layer, 5 ... Thin film, 6 ... Bonded wafer.

Claims (5)

A surface of a bond wafer made of a silicon single crystal wafer is ion-implanted with at least one gas ion of hydrogen ions and rare gas ions to form an ion implantation layer inside the bond wafer, and the ion-implanted surface of the bond wafer In the method for manufacturing a bonded wafer, the bonded wafer is manufactured by peeling the bond wafer with the ion implantation layer by performing a peeling heat treatment after bonding the substrate and the surface of the base wafer directly or through an insulating film. ,
After bonding the bond wafer and the base wafer, the bonding interface between the bonded bond wafer and the base wafer is bonded with the contribution of water molecules until the peeling heat treatment is performed. Hold the combined bond wafer and base wafer for more than 12 hours at room temperature,
In the exfoliation heat treatment, the bonded wafer and base wafer are directly put into a heat treatment furnace set at a constant temperature of 400 ° C. or more and 500 ° C. or less without a heating step, and the heat treatment is performed at the constant temperature. Or a method of manufacturing a bonded wafer, wherein the temperature is raised to a predetermined temperature within + 50 ° C. from the constant temperature and then heat-treated at the predetermined temperature.   The temperature at the time of taking out the bonded wafer from the heat treatment furnace after the heat treatment at the constant temperature or the predetermined temperature is the same as the temperature at the time of the peeling heat treatment. Manufacturing method of bonded wafer.   The method for producing a bonded wafer according to claim 1 or 2, wherein the time for holding at room temperature is 48 hours or more.   After the peeling heat treatment, a heat treatment for flattening a peeling surface of the bonded wafer from which the bond wafer has been peeled is performed, and the temperature of the flattening heat treatment is performed within a temperature range of 1100 ° C. to 1175 ° C. The manufacturing method of the bonded wafer as described in any one of Claims 1-3.   The method for producing a bonded wafer according to any one of claims 1 to 4, wherein the bond wafer and the base wafer are cleaned before the bond wafer and the base wafer are bonded together. .

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