WO2009141954A1 - Bonded wafer manufacturing method, and bonded wafer - Google Patents

Abstract

Provided is a bonded wafer manufacturing method, in which at least a wafer holding portion of a boat for holding a wafer in a peeling heat treatment is made of a material having a higher heat conductivity than that of quartz. After the wafer is inserted into a heat treatment furnace at a temperature lower than the peeling temperature, the temperature rise is continued till the bonded wafer is peeled in at least an ion-implanted layer. As a result, the bonded wafer manufacturing method can reduce a terrace width, in which a thin film is not transferred at a peeling heat treatment in an ion-implantation peeling method, and can suppress the film thickness irregularity of a marble pattern.

Description

Bonded wafer manufacturing method and bonded wafer

The present invention relates to a heat treatment for peeling a wafer with an ion implantation layer in the manufacture of a bonded wafer using an ion implantation peeling method.

As a wafer for a high-performance device, a bonded wafer is used in which a semiconductor wafer is bonded to another wafer and then a wafer on which an element is manufactured is thinned.
Specifically, for example, two mirror-polished silicon wafers are prepared, and an oxide film is formed on at least one of the wafers. After these wafers are bonded, heat treatment is performed at a temperature of 200 to 1200 ° C. to increase the bond strength. Thereafter, the element fabrication side wafer (bond wafer) is thinned to a desired thickness by grinding and polishing, etc., so that a bonded SOI wafer on which an SOI (Silicon On Insulator) layer is formed can be manufactured.

As a method for thinning the bond wafer, in addition to the above-described grinding / polishing method, an ion implantation layer such as hydrogen ions is formed in advance on the bond wafer before bonding, and after bonding to the base wafer, for example, 500 There is a method (also called Smart Cut (registered trademark)) in which a heat treatment is performed at about 10 minutes for about 10 minutes (see Japanese Patent Application Laid-Open No. 2005-79388), and the bond wafer is thinned by peeling off the ion-implanted layer. .

When a bonded wafer is manufactured by such a method, a part called a polishing sag and a chamfered part with a slightly reduced thickness exist in the peripheral part of the two mirror wafers to be bonded, and these parts are bonded. Otherwise, it remains as an unbonded portion with weak bonding strength. If the thin film is formed by heat treatment while such an unbonded portion exists, a part of the unbonded portion is peeled off during the thinning process. Therefore, the thinned bond wafer has a smaller diameter than the base wafer (base wafer), and minute irregularities are continuously formed in the peripheral portion.

Such a peripheral portion where the thin film is not transferred is called a terrace, and if the terrace width is large, the number of chips of the semiconductor device finally obtained is reduced. Such a terrace width problem is a particularly significant problem because an oxide film is formed on both the bond wafer and the base wafer, and when the oxide films are bonded together, the bonding strength between the oxide films becomes weak. .

Further, in order to reduce such a terrace width, even if an attempt was made to increase the bonding force at the periphery of the wafer by increasing the temperature during the heat treatment, the film thickness unevenness of the marble pattern was partially formed.

Therefore, the present invention has been made in view of the above problems, and can reduce the terrace width where the thin film is not transferred during the peeling heat treatment in the ion implantation peeling method, and can suppress the film thickness unevenness of the marble pattern. It aims at providing the manufacturing method of a bonded wafer.

In order to achieve the above object, the present invention provides an ion-implanted layer formed inside a wafer by ion-implanting at least one kind of gas ions of hydrogen ions and rare gas ions from the surface of the bond wafer. Bonding is performed by bonding the surface of the ion-implanted surface and the surface of the base wafer directly or through an insulating film, and then performing a peeling heat treatment to peel off the bond wafer at the ion-implanted layer to produce a bonded wafer. In the wafer manufacturing method, at least the wafer holding portion of the boat that holds the wafer in the peeling heat treatment is made of a material having a higher thermal conductivity than quartz, and the wafer is placed in a heat treatment furnace having a temperature lower than the peeling temperature. After the loading, at least until the bond wafer is peeled off at the ion implantation layer. To provide a method for producing a bonded wafer, characterized in that continuously heated.

With such a method for manufacturing a bonded wafer, the wafer is placed in a heat treatment furnace having a temperature lower than the peeling temperature at the time of the peeling heat treatment, and the temperature at which the peeling occurs is maintained by raising the temperature until peeling. It can be made higher than the temperature at the time of peeling. Thereby, since it peels when the bond strength in the wafer surface, especially the wafer peripheral part with low bond strength is high, the terrace width can be reduced. Also, at least the wafer holding part is made of a material having a higher thermal conductivity than quartz, so that the temperature of the wafer holding part rises in the same way as the temperature of the wafer rises during the temperature rise during heat treatment. As a result, it is possible to prevent partial temperature unevenness in the wafer surface due to the contact of the part, so that favorable peeling occurs even in the contact part, and the occurrence of unevenness of the film thickness of the marble pattern is prevented, and the defect of the peeling surface is reduced. A high-quality thin film can be obtained. For this reason, the width of the thin film with high quality is widened, and the number of chips of the finally obtained semiconductor device can be increased, so that the product yield is improved.

At this time, in the exfoliation heat treatment, it is preferable that the wafer is put into the heat treatment furnace having a temperature of less than 500 ° C. and the temperature is continuously raised to a temperature of 500 ° C. or more until the bond wafer is exfoliated at least in the ion implantation layer. .
Thus, by setting the temperature at the time of wafer introduction to less than 500 ° C., peeling does not occur immediately after being put into the heat treatment furnace, and the bond strength is higher when peeling is generated at the highest possible temperature. Therefore, it is preferable to raise the temperature so that peeling occurs at a temperature of 500 ° C. or higher.

At this time, in the exfoliation heat treatment, it is preferable that the wafer is put into the heat treatment furnace having a temperature of 400 ° C. or lower and the temperature is continuously increased at 2 ° C./min or more until the bond wafer is exfoliated at least in the ion implantation layer. .
In this way, when the temperature is 400 ° C. or lower, it can be surely prevented that peeling occurs immediately by introducing it into the heat treatment furnace. By raising the temperature at 2 ° C./min or higher after the wafer is charged, a higher temperature can be obtained. Thus, peeling can occur when the bond strength is increased.

At this time, it is preferable that a silicon single crystal wafer is used as the bond wafer and the base wafer, and the material of at least the wafer holding portion of the boat is Si or SiC.
Thus, when the bond wafer and the base wafer are silicon single crystal wafers, if the wafer holding part is made of Si or SiC material, the thermal conductivity is close to that of silicon. A temperature difference is unlikely to occur between the other portions of the wafer and there is little temperature unevenness in the wafer surface.

At this time, it is preferable that an insulating film is formed in advance on the surfaces of the bond wafer and the base wafer, and bonded together via the insulating films during the bonding.
The method for producing a bonded wafer according to the present invention can achieve good peeling even in the case where the bonding strength is high, even when bonding is performed through insulating films having low bonding strength, so that the film thickness is uniform. And a terrace width is reduced.

Moreover, it is a bonded wafer which has a thin film on the base wafer manufactured by the manufacturing method of the bonded wafer of this invention, Comprising: The defect density detected by selectively etching this thin film is 10 pieces / cm < ² > or less. A bonded wafer is provided.
If it is a bonded wafer manufactured by the manufacturing method of the present invention, since the temperature at the time of peeling becomes high, peeling occurs in a state where the bonding strength is high, and the temperature is uniform within the wafer surface, and good peeling Since the surface roughness of the peeled surface is improved, a bonded wafer having a high-quality thin film with a defect density of 10 pieces / cm ² or less detected by selective etching of the thin film is obtained.

As described above, according to the method for manufacturing a bonded wafer of the present invention, the wafer is put into a heat treatment furnace having a temperature lower than the peeling temperature during the peeling heat treatment, and then the temperature is continuously raised until peeling, thereby making the conventional method Peeling occurs at higher temperatures. Due to this high temperature, peeling occurs when the bonding strength is increased in the wafer surface, particularly in the periphery of the wafer having a low bonding strength in the past, so that a separation surface having a small terrace width and few defects such as voids can be obtained. . In addition, since the wafer holding part of the boat that holds the wafers during the peeling heat treatment is made of a material having a higher thermal conductivity than quartz, the temperature of the wafer and the wafer holding part is relatively close even if the temperature in the heat treatment furnace is increased. Since the temperature is raised by the temperature, there is almost no temperature difference between the contact portion and the other portion of the wafer surface, and the in-plane uniform peeling occurs, so the uneven portion of the marble pattern does not occur and the film thickness is uniform. It can be a highly thin film. For this reason, the width of the thin film with high quality is widened, and the number of chips of the finally obtained semiconductor device can be increased, so that the product yield is improved.

It is a flowchart which shows an example of the process of the manufacturing method of the bonded wafer of this invention. It is a top view of the bonded wafer (a) manufactured by the manufacturing method of the bonded wafer of this invention, and the bonded wafer (b) manufactured by the conventional manufacturing method. It is a figure which shows the relationship of the temperature and time of the peeling heat processing of an Example and a comparative example.

In the manufacture of bonded wafers, it has been difficult to reduce the terrace width with high film thickness uniformity of the thin film to be peeled.
In order to narrow such a terrace width, it is necessary to peel the wafer in a state where the bond strength at the bonding interface at a temperature at which peeling occurs is as high as possible. That is, if the bond strength at the temperature at which peeling occurs is strong, the peripheral portion where the polishing sagging is also improved in adhesion, so that the peripheral portion is further transferred. In the case of bonding oxide films, since the bonding strength is lower than that of bonding of a semiconductor and an oxide film or bonding of semiconductors, the terrace width tends to be easily increased.

As a result of intensive investigations, the inventors determined that the bond strength at the bonding interface strongly depends on the heat treatment temperature, and becomes stronger as the temperature is higher. It has been found that when the peeling heat treatment is performed, the temperature of the portion where the wafer contacts the heat treatment boat is different from the other regions during the temperature rise, and the temperature becomes nonuniform within the wafer surface.

For example, when a bonded wafer is manufactured using semiconductor silicon, if a heat treatment for peeling is performed using a quartz heat treatment boat, the thermal conductivity of silicon is 156 W / mK, quartz is as small as 2 W / mK, and quartz is Since it is transparent and hardly absorbs heat, the temperature of the portion of the wafer that contacts the boat during the temperature rise is considered to be lower than in other regions. When wafer peeling occurs in this state, the temperature in the vicinity of contact with the boat is lower than in other areas, so the bond strength at the bonding interface is low, and the cavity that is the driving force for peeling in the ion implantation layer Growth will not progress. As a result, in the region in the vicinity of the contact portion of the wafer with the boat, the film is forcibly peeled off, and striped film thickness unevenness is formed (hereinafter referred to as a marble pattern).

In order to avoid this, in the normal ion implantation delamination method, when semiconductor silicon is delaminated, for example, after raising the temperature to 500 ° C., the temperature in the furnace is kept at 500 ° C. for about 30 minutes for a temperature within the wafer surface. By causing peeling in a state that is as uniform as possible, the occurrence of a marble pattern in the transferred semiconductor silicon layer is avoided and the film thickness uniformity is improved. This is because the wafer peeling does not occur immediately after the furnace temperature reaches 500 ° C., but the temperature in the wafer surface becomes uniform while maintaining the temperature for a certain period of time, and at the same time peeling occurs. It is considered that peeling occurs without causing a marble pattern by applying a necessary amount of heat to the semiconductor silicon.
However, since this method focuses only on improving the film thickness uniformity of the transferred semiconductor silicon layer (that is, suppressing the occurrence of a marble pattern), the semiconductor silicon layer peeled off by this method is included. There is a disadvantage that the terrace width of the bonded wafer is relatively large.

In order to reduce the terrace width, it is necessary to perform peeling in a state where the bonding strength at the bonding interface is as high as possible. For that purpose, it is necessary to cause peeling at a temperature as high as possible. For this purpose, it is necessary to perform heat treatment so that the wafer is peeled off within a short time, for example, within a few minutes after the temperature is raised or held constant at a higher temperature than usual.
However, when heat-treated boats having different thermal properties are used, the temperature in the vicinity of the contact portion with the boat at the time of peeling in the wafer surface is different from that in other regions, causing a defect such as a marble pattern.

As a result of extensive investigations, the present inventors have found a problem that arises when a material having different thermal conductivity and heat absorption characteristics is used as a peeling heat treatment boat in the peeling heat treatment in the ion implantation peeling method. The present invention has been completed by finding a peeling heat treatment method capable of reducing the terrace width while avoiding it.
That is, the present invention is a peeling heat treatment method in the production of bonded wafers using the ion implantation peeling method, and the material of the wafer holding part, which is a part that comes into contact with the wafer during the peeling heat treatment, is frequently used as a boat. It has a higher thermal conductivity than quartz, and its thermal conductivity and heat absorption characteristics are the same as or close to those of the semiconductor wafer to be manufactured, and the wafer is peeled off during temperature rise. Is.

A bonded wafer using a general silicon wafer (a bonded wafer in which a high-temperature bonding heat treatment is performed after bonding at room temperature and then thinned by grinding and polishing) is performed by setting the bonding heat treatment to 1000 ° C. or higher. The bond at the bonding interface is a strong siloxane bond. However, in the ion implantation peeling method, the heat treatment temperature when peeling the bonded wafer is as low as about 500 ° C. At this time, since the bonding state of the bonding interface is a weak bond centered on a silanol group, the bonding force of the bonding interface is defeated by the peeling force, and the terrace width is widened, causing void defects and blister defects. The possibility was high. Therefore, in the ion implantation separation method, it is necessary to increase the bond strength at the bonding interface when separation occurs.

In order to peel off the wafer with a high bonding interface bond strength as much as possible, it is desirable to cause peeling during the temperature rise. Therefore, in the present invention, by using a heat treatment boat made of a material having the same thermal conductivity as that of the wafer (a material having a higher thermal conductivity than quartz), the temperature in the wafer surface is uniform even during the temperature rise. It is possible to maintain the property at a relatively high level.

In other words, even when the temperature is rising, the decrease in the wafer temperature near the contact portion with the boat can be suppressed, and the wafer temperature during the peeling heat treatment can be kept almost uniform in the plane. As a result, the wafer can be peeled off at the highest possible temperature, so that the peeling can be carried out with the highest bonding force at the bonding interface, and the SOI width can be reduced by reducing the terrace width and void defects. The quality is improved and the merit of improving productivity is obtained.

Hereinafter, a method for manufacturing a bonded wafer according to the present invention will be described in detail with reference to FIG. 1 as an example of the embodiment, and a case of manufacturing a bonded wafer by an ion implantation separation method will be described in detail. It is not limited.
FIG. 1 is a flowchart showing an example of an embodiment of a method for producing a bonded wafer according to the present invention.

First, in the step (a) of FIG. 1, for example, two silicon single crystal bare wafers are prepared as the bond wafer 10 and the base wafer 20. There are various types of wafers such as polished wafers (PW), epitaxial wafers, heat-treated wafers, etc., but they can be applied to the present invention regardless of their types. The wafer material is not limited to silicon, and the present invention can also be applied to compound semiconductors or quartz, metals, etc. in addition to semiconductor materials, and also to patterned wafers such as devices.
At this time, in FIG. 1, the insulating films 12 and 21 are formed on both the bond wafer 10 and the base wafer 20 in advance. However, the insulating films may be formed on only one of the wafers. Both may not be formed.

In addition, if it is the manufacturing method of this invention, as shown in FIG. 1, even if it is a bonded wafer with low bonding strength, such as when an insulating film is formed on both wafers and bonded via the insulating films, Since the bonding strength can be increased and the separation can be performed at the time of the separation heat treatment, a bonded wafer having a reduced film thickness and a high film thickness uniformity can be manufactured.
As the insulating film formed at this time, for example, a thermal oxide film, a CVD oxide film, or the like can be formed. In addition, the insulating film formed on each wafer may be formed only on the bonding surface in addition to being formed on the entire surface of the wafer including the back surface.

Next, in the step (b), at least one kind of gas ion of hydrogen ion or rare gas ion is ion-implanted from the surface of the insulating film 12 of the bond wafer 10 to form the ion-implanted layer 11 inside the wafer. At this time, other ion implantation conditions such as implantation energy, implantation amount, and implantation temperature can be appropriately selected so that a thin film having a predetermined thickness can be obtained. In addition, since the temperature at the time of peeling in the subsequent peeling heat treatment changes mainly depending on the implantation amount at the time of ion implantation, the temperature at the time of peeling can be adjusted to some extent by appropriately adjusting the implantation amount. .

Next, in the step (c), the insulating film 12 of the bond wafer 10 and the insulating film 21 of the base wafer 20 are adhered and bonded together.
Prior to this bonding, the bonding strength of either or both wafers can be increased by plasma treatment. Further, for example, RCA cleaning can be performed before bonding to remove particles and organic substances adhering to the wafer surface, thereby performing better bonding. In this case, it is preferable to perform bonding as soon as possible after cleaning because particle contamination or the like may be received from the atmosphere of the bonding process or the BOX storing the wafer.

Next, in the step (d), a bonded wafer in which the bond wafer 10 is peeled off by the ion implantation layer 11 and a thin film 31 is formed on the base wafer 20 via the insulating films 12 and 21 by performing a peeling heat treatment. 30 is produced.
By this peeling heat treatment, a defect layer called a cavity is formed in the ion implantation layer 11 in the bond wafer 10, and this defect layer is connected in the horizontal direction inside the bond wafer 10, whereby the bond wafer 10 is peeled off. Thereby, a part of the bond wafer 10 is transferred to the base wafer 20 to become the thin film 31, and the bonded wafer 30 is formed.

In the present invention, the material of at least the wafer holding portion of the boat that holds the wafer in the peeling heat treatment is a material having a higher thermal conductivity than quartz, and the wafer is put into a heat treatment furnace having a temperature lower than the peeling temperature. Thereafter, the temperature is continued to rise until the bond wafer is peeled off at least by the ion implantation layer.
In this way, by continuing to raise the temperature until the bond wafer peels, it is possible to cause peeling at the highest possible temperature, that is, when the bonding strength of bonding is increased, it is possible to cause peeling. It is possible to reduce the terrace width at the wafer peripheral portion where the bonding strength is weak and the thin film is difficult to be transferred. In addition, by making the wafer holding part a material with higher thermal conductivity than quartz, the temperature difference at the contact part with the wafer at the time of temperature rise is reduced, and the temperature of the contact part and other parts within the wafer surface is uniform. Thus, good peeling occurs and a thin film with high film thickness uniformity can be obtained.

Here, the temperature lower than the peeling temperature when the wafer is put into the heat treatment furnace is a temperature at which peeling does not occur at least immediately after the wafer is charged, and the temperature rises when the temperature is too low such as room temperature. However, it takes longer than necessary, and there is a risk that peeling will occur while the temperature does not reach the highest level. Conventionally, holding at 500 ° C. for 10 to 30 minutes has caused peeling. It is desirable to put the wafer into a heat treatment furnace having a temperature of about 200 to 500 ° C. Further, the temperature at which the temperature rises and peeling occurs varies depending on the heat treatment conditions and the like, but when the temperature is raised to about 600 ° C., almost all wafers in the heat treatment furnace are peeled off.
Further, the method for confirming the peeling of the bond wafer is not particularly limited, but it can be confirmed that the peeling is performed by the peeling sound.

At this time, it is preferable that the wafer is put into a heat treatment furnace having a temperature of less than 500 ° C., and the temperature is continuously increased to a temperature of 500 ° C. or more until at least the ion-implanted layer 11 peels the bond wafer 10.
Conventionally, it was peeled off by holding at about 500 ° C. for a predetermined time. Therefore, even if it was put into a heat treatment furnace having a temperature of less than 500 ° C., it was not peeled off immediately, and the temperature was continuously raised to 500 ° C. By causing peeling at a temperature of, peeling can occur at a higher temperature than before, and peeling can be caused in a state where the bond strength is higher.

In addition, it is preferable that the wafer is placed in a heat treatment furnace having a temperature of 400 ° C. or lower, and the temperature is continuously increased at 2 ° C./min or higher until the bond wafer 10 is peeled off at least by the ion implantation layer 11.
If the wafer is put into a heat treatment furnace having a temperature of 400 ° C. or lower, the temperature can be increased to a high temperature without causing separation immediately. The temperature can be raised to a temperature at which the bond strength is further increased while maintaining uniformity.

Further, when the bond wafer 10 and the base wafer 20 are silicon single crystal wafers, it is desirable that the material of at least the wafer holding portion of the boat for peeling heat treatment is Si or SiC.
Since the silicon single crystal wafer and Si or SiC are close in thermal conductivity, there is no temperature difference at the time of temperature rise, and the temperature at the contact part with the wafer holding part is the same temperature as in other wafer surfaces, which is good. Peeling occurs and a thin film with high film thickness uniformity without a marble pattern can be obtained. In addition, if the material of the entire boat as well as the wafer holding part is made of a material (Si or SiC) having a higher thermal conductivity than quartz, the temperature uniformity during the temperature rise in the entire heat treatment furnace is also improved. Therefore, it is more preferable.

The bonded wafer 30 thus manufactured is subjected to, for example, a bonding heat treatment for increasing the bonding strength at the bonding interface at 1000 ° C. or higher in an oxidizing atmosphere or a non-oxidizing atmosphere, and the thin film 31 side is subjected to heat treatment, micro polishing, etc. The final bonded wafer is completed by performing the flattening process.

The bonded wafer 30 manufactured as described above has a defect density of 10 pieces / cm ² or less detected by selectively etching the thin film 31.
The bonded wafer manufactured by the method for manufacturing a bonded wafer according to the present invention has a good peeling property in a state where the bonding strength is increased. A bonded wafer having

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to this.

(Example): Use of SiC boat, peeling at around 600 ° C. during heating, bonding of oxide films First, 25 sets of mirror-polished silicon single crystal wafers having a diameter of 8 inches (200 mm) were prepared as material wafers. . A 200 nm oxide film was formed on the bond wafer, and a 500 nm oxide film was formed on the base wafer. A bond wafer is injected with hydrogen ions at an acceleration voltage of 80 keV and an injection amount of 7 × 10 ¹⁶ / cm ² , and is subjected to pre-bonding cleaning including RCA cleaning, and then bonded to the base wafer at room temperature. It was.

Next, a SiC heat treatment boat having a thermal conductivity close to that of silicon was prepared, and exfoliation heat treatment was performed in a horizontal furnace that is a resistance heating heat treatment furnace (batch furnace) capable of performing heat treatment on a large number of sheets at once. In the peeling heat treatment, a wafer is introduced at 300 ° C. in a nitrogen atmosphere, and the temperature is raised to 600 ° C. at 5 ° C./min. During the temperature rising, the bond wafer is peeled off by the ion implantation layer and transferred to the base wafer. A wafer was produced. At this time, it was confirmed that peeling occurred during the temperature rise of 500 to 600 ° C. by detecting the peeling sound. The relationship between temperature and time at this time is shown in FIG.

When the width of the terrace portion of the peeled SOI wafer was examined, in the conventional peeling heat treatment (corresponding to Comparative Example 1 below), the widest portion of the terrace width of each wafer was 2.2 mm to 3.2 mm, which varied depending on the location. However, in this result, it could be reduced to 2.6 mm at the maximum. As a result, it was possible to eliminate defects caused by the terrace width for users whose terrace width was defined as 3 mm. As a result of evaluating the film thickness uniformity of the peeled wafer with a film thickness measuring device, the film thickness uniformity was kept at 500 ° C. for a predetermined time, and no difference was found in the film thickness variation compared to the peeled data. Moreover, as shown to Fig.2 (a), it was able to confirm that the marble pattern which becomes the striped pattern shape by the film thickness of the thin film becoming non-uniform | heterogenous did not generate | occur | produce in the contact part vicinity.

After the bonded SOI wafer is subjected to a bonding heat treatment at 950 ° C., the SOI layer surface is planarized (trace polishing and sacrificial oxidation). The final quality of the SOI layer (thin film) of the completed SOI wafer is the SOI layer. The mixed acid etching was performed, and the number of pits was evaluated. As a result of evaluating the pit density, it was found that the pit density was 10 pieces / cm ² at the maximum, and most of them were very low, less than 10 pieces / cm ² . This is because, during the temperature rise using a SiC heat treatment boat having a thermal conductivity close to that of silicon, the in-plane temperature is highly uniform and as high as possible (ie, the bond strength is as high as possible). As a result of peeling, the surface roughness of the peeling surface is improved, and local deep pits and surface roughness are suppressed.

From the above results, by using a peeling heat treatment boat made of a material having the same thermal conductivity as the material to be manufactured, wafer peeling occurs with the bonding force at the bonding interface as high as possible, so the terrace width is narrow. At the same time, it was found that the final quality was improved and the product yield was improved.

(Comparative example 1): Quartz boat use, hold | maintained at 500 degreeC for 30 minutes, the coupling | bonding of oxide films First, 25 sets of mirror-polished silicon single crystal wafers of 8 inches in diameter were prepared as material wafers. A 200 nm oxide film was formed on the bond wafer, and a 500 nm oxide film was formed on the base wafer. A bond wafer is injected with hydrogen ions at an acceleration voltage of 80 keV and an injection amount of 7 × 10 ¹⁶ / cm ² , and is subjected to pre-bonding cleaning including RCA cleaning, and then bonded to the base wafer at room temperature. It was.

Next, a quartz heat treatment boat having a thermal conductivity lower than that of silicon was prepared, and peeling heat treatment was performed in a horizontal furnace. The peeling heat treatment was performed in a nitrogen atmosphere, the temperature was raised to 500 ° C. at 5 ° C./min, and held at 500 ° C. for 30 minutes, and the bond wafer was peeled off and transferred to the base wafer by the ion implantation layer. Even if a quartz boat having a low thermal conductivity is used, the temperature distribution in the furnace can be made uniform by maintaining the temperature at 500 ° C. for a while. The relationship between temperature and time at this time is shown in FIG.

When the width of the terrace portion of the peeled wafer was examined, the widest portion of the terrace width of each wafer was found to vary from 2.2 mm to 3.2 mm. As a result, for the users whose terrace width is defined as 3 mm, defects due to the terrace width frequently occur and the manufacturing yield deteriorates. The final quality of the SOI layer was evaluated by the number of pits obtained by etching the SOI layer with mixed acid. As a result of evaluating the pit density, the pit density fluctuated in the range of 10 to 40 pieces / cm ² , and the quality of the SOI layer was not defective, but its numerical level increased.
From the above results, it was found that peeling occurs in the ion-implanted layer at the bonding interface bond strength at 500 ° C., so that the terrace width is widened, the final quality is lowered, and the product yield is lowered.

(Comparative Example 2): Use of quartz boat, peeling at around 600 ° C. during temperature rise, bonding of oxide films First, 25 sets of mirror-polished silicon single crystal wafers having a diameter of 8 inches were prepared as material wafers. A 200 nm oxide film was formed on the bond wafer, and a 500 nm oxide film was formed on the base wafer. A bond wafer is injected with hydrogen ions at an acceleration voltage of 80 keV and an injection amount of 7 × 10 ¹⁶ / cm ² , and is subjected to pre-bonding cleaning including RCA cleaning, and then bonded to the base wafer at room temperature. It was.

Next, a quartz heat treatment boat having a thermal conductivity lower than that of silicon was prepared, and peeling heat treatment was performed in a horizontal furnace. The peeling heat treatment was performed in a nitrogen atmosphere, and the temperature was raised to 600 ° C. at 5 ° C./min. During the temperature rising, peeling of the bond wafer and transfer to the base wafer occurred. The relationship between temperature and time at this time is shown in FIG.
As a result, the peeling heat treatment occurs in a state where the bonding interface bond strength is higher than the peeling at 500 ° C., but the temperature of the region in contact with the boat of the wafer is lower than the other regions.

As a result of evaluating the film thickness uniformity of the peeled wafer with a film thickness measuring instrument, the marble pattern as shown in FIG. It occurred in most of the wafers put in the process.
From the above results, even if the heat treatment temperature at the time of wafer peeling is higher than 500 ° C., if a heat treatment boat made of quartz having a low thermal conductivity is used, the temperature in the wafer surface during temperature rise becomes non-uniform. Therefore, it turned out that a marble pattern will occur.

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

Claims (6)

1. At least one type of hydrogen ion or rare gas ion is ion-implanted from the surface of the bond wafer to form an ion-implanted layer inside the wafer, and the ion-implanted surface of the bond wafer and the surface of the base wafer are formed. In a method for manufacturing a bonded wafer in which a bonded wafer is manufactured by peeling the bond wafer from the ion implantation layer by performing a peeling heat treatment after bonding directly or through an insulating film,
   The material of at least the wafer holding portion of the boat holding the wafer in the peeling heat treatment is a material having a higher thermal conductivity than quartz, and after placing the wafer in a heat treatment furnace having a temperature lower than the peeling temperature, at least the A method for producing a bonded wafer, wherein the temperature is continuously increased until the bond wafer is peeled off at the ion-implanted layer.
   
2. In the peeling heat treatment, the wafer is put into the heat treatment furnace having a temperature of less than 500 ° C., and the temperature is continuously raised to a temperature of 500 ° C. or more until the bond wafer is peeled at least in the ion implantation layer. Item 2. A method for producing a bonded wafer according to Item 1.
   
3. In the peeling heat treatment, the wafer is put into the heat treatment furnace having a temperature of 400 ° C. or lower, and the temperature is continuously raised at 2 ° C./min or more until the bond wafer is peeled at least in the ion implantation layer. The manufacturing method of the bonded wafer of Claim 1 or Claim 2.
   
4. 4. The silicon wafer according to claim 1, wherein a silicon single crystal wafer is used as the bond wafer and the base wafer, and a material of at least a wafer holding portion of the boat is Si or SiC. Manufacturing method of bonded wafer.
   
5. The insulating film is formed in advance on the surface of the bond wafer and the base wafer, and the bonding is performed through the insulating films at the time of the bonding. The manufacturing method of the bonded wafer as described in claim | item.
   
6. A bonded wafer having a thin film on a base wafer manufactured by the method for manufacturing a bonded wafer according to any one of claims 1 to 5, wherein the defect is detected by selectively etching the thin film. A bonded wafer having a density of 10 / cm ² or less.

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