JP5125194B2 - Manufacturing method of bonded wafer - Google Patents

Description

  The present invention relates to a method for manufacturing a bonded wafer using a so-called ion implantation peeling method, in which an ion-implanted wafer is peeled after bonding to produce a bonded wafer, and in particular, to a thin film on the surface of the bonded wafer after peeling. The present invention relates to a method for manufacturing a bonded wafer capable of removing a remaining damaged layer and the like.

  2. Description of the Related Art Conventionally, a method of manufacturing a bonded wafer by separating ion-implanted wafers after bonding (so-called ion-implantation peeling method) is known. Using this bonded wafer manufacturing method, for example, SOI (Silicon On Insulator). ) Wafers are manufactured.

  For example, in the case of manufacturing an SOI wafer, an oxide film is formed on at least one of two silicon wafers, and hydrogen ions or rare gas ions are implanted from the upper surface of one silicon wafer. After a microbubble layer (encapsulation layer) is formed inside, the surface into which the ions are implanted is brought into close contact with the other silicon wafer through an oxide film, and then heat treatment (peeling heat treatment) is applied to form the microbubble layer. This is a technique (see Patent Document 1) in which one wafer is peeled into a thin film as a cleavage plane to form an SOI wafer.

  In such a thin-film SOI layer (SOI film) formed by the conventional ion implantation delamination method, damage due to ion implantation remains, and the remaining damage affects device characteristics and the like. Therefore, in order to remove this, the SOI film after peeling has been subjected to a treatment such as sacrificial oxidation treatment to remove the damaged layer by ion implantation, and improvements have been made.

  However, the present inventors have investigated the thin film on the surface of the bonded wafer after peeling (the SOI film of an SOI wafer, etc.) that has been subjected to conventional processing such as sacrificial oxidation, and the surface of this thin film Was measured by AFM (Atomic Force Microscope), it was found that there was a dent (hereinafter referred to as a concave defect) having a diameter of 0.5 to 2 μm and a depth of 1 to 4 nm. The presence of such a concave defect will adversely affect the characteristics of future advanced devices.

JP-A-5-211128

  The present invention has been made in view of such problems, and is a method for manufacturing a bonded wafer manufactured by using an ion implantation separation method, which can remove damage caused by ion implantation and can be used after the separation. An object of the present invention is to provide a method for producing a bonded wafer in which the occurrence of a concave defect is suppressed without impairing the surface roughness on the surface of the thin film of the bonded wafer.

  In order to solve the above-described problems, the present invention at least bonds a bond wafer having a microbubble layer formed by gas ion implantation and a base wafer to be a support substrate, and uses the microbubble layer as a boundary to bond the bond wafer. In the method of manufacturing a bonded wafer by an ion implantation peeling method that peels and forms a thin film on a base wafer, a first step of forming a protective film on the surface of the thin film of the bonded wafer after peeling the bond wafer After performing a second step of heat treatment in a non-oxidizing gas atmosphere, and then performing a heat treatment in an oxidizing gas atmosphere to form a thermal oxide film on the surface layer of the bonded wafer, Performing a third step of removing the oxide film and the protective film, and then performing a fourth step of heat treatment again in a non-oxidizing gas atmosphere. That bonding to provide a method of manufacturing a wafer (claim 1).

In such a method for manufacturing a bonded wafer according to the present invention, a protective film is first formed on the surface of the thin film of the bonded wafer after the bond wafer is peeled off. Even if heat treatment is performed in a non-oxidizing gas atmosphere in the process, it is possible to effectively prevent the surface roughness of the thin film surface from being deteriorated. Further, by first forming a protective film on the surface, it is possible to prevent wafer contamination due to, for example, heavy metals from a heat treatment furnace.
Then, after forming the protective film in the first step, a second step is performed in which heat treatment is performed in a non-oxidizing gas atmosphere, and then a heat treatment is performed in an oxidizing gas atmosphere to thermally oxidize the surface layer of the bonded wafer. After forming the film, a third step of removing the thermal oxide film and the protective film is performed, and then a fourth step of heat-treating again in a non-oxidizing gas atmosphere is performed, thereby manufacturing a conventional bonded wafer. The method can remarkably suppress the occurrence of concave defects that frequently occur. As a result, device characteristics can be improved and stabilized, and yield can be improved.

At this time, it is preferable to form a thermal oxide film as a protective film in the first step.
Thus, if a thermal oxide film is formed as a protective film in the first step, a dense protective film can be easily formed.

The thermal oxide film formed as the protective film in the first step can be formed by RTA.
As described above, if the thermal oxide film formed as the protective film in the first step is formed by RTA (Rapid Thermal Annealing), it is possible to form a high-quality thermal oxide film in a short time.

Further, in the heat treatment in the second step, the heat treatment temperature can be set to less than 1200 ° C. (Claim 4).
In the present invention, since the protective film is formed on the surface of the thin film of the bonded wafer after peeling in the first step, the second step of heat treatment in a non-oxidizing gas atmosphere is performed, so the heat treatment in the second step Even if the temperature is less than 1200 ° C., it is possible to effectively prevent surface roughness from occurring on the surface of the thin film. Thereby, further suppression of impurity contamination can be achieved.

Then, after the fourth step, a fifth step of further performing a heat treatment in an oxidizing gas atmosphere to form a thermal oxide film on the surface of the thin film and removing the thermal oxide film can be performed. 5).
Thus, after the fourth step, if the fifth step of forming a thermal oxide film on the surface of the thin film by performing a heat treatment in an oxidizing gas atmosphere and removing the thermal oxide film is performed, the thickness of the thin film Can be easily adjusted to a desired thickness.

Further, in the heat treatment in the second step and / or the fourth step, it is preferable that the non-oxidizing gas atmosphere is Ar 100% (Claim 6).
In this way, in the heat treatment in the second step and / or the fourth step, particularly the second step, if the non-oxidizing gas atmosphere is Ar 100%, oxygen is not mixed in, so the heat treatment atmosphere becomes oxidizing. It is possible to more reliably prevent the occurrence of concave defects and more effectively prevent the occurrence of concave defects.

  With such a method for producing a bonded wafer according to the present invention, since the surface roughness of the thin film surface is not deteriorated and the concave defects generated on the thin film surface can be remarkably reduced, The device can be fully supported, the device performance is stabilized, and the yield can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.
As described above, when the present inventors investigated a thin film of a bonded wafer (for example, an SOI film of a bonded SOI wafer) manufactured by using a conventional ion implantation separation method, the surface thereof was measured by AFM. Then, it turned out that the concave defect has generate | occur | produced. This concave defect adversely affects the characteristics of the device.

Therefore, as a result of further examination of the concave defect by the present inventors, it was found that it exists at a density of about 1 × 10 ⁵ / cm ^{2 on} the surface of the thin film as shown in the following experiment. When concave defects are present on the surface of the thin film at such a density, it is not detected as much as 1 to 10 μm square as an AFM measurement area, but is detected when measuring a relatively wide area of about 30 μm square. A lot of things.

(Experiment 1-4)
Regarding the bonded wafer produced using the ion implantation separation method, the relationship between the treatment after the separation and the concave defect was investigated.
Here, a case of a bonded SOI wafer is taken as an example. First, as described below, an SOI wafer is manufactured by an ion implantation separation method in the same manner as in the prior art. That is, an SOI wafer is manufactured by a procedure as shown in FIG.
In the ion implantation delamination method of FIG. 2, in step (a), two silicon mirror wafers are prepared, and a base wafer 1 serving as a support substrate and a bond wafer 2 serving as an SOI film conforming to the device specifications are prepared. prepare.

  Here, a silicon single crystal ingot having a crystal orientation <100> produced by the Czochralski method, a conductivity type of p type, and a resistivity of 10 Ω · cm is sliced and processed to have a diameter of 300 mm. A silicon mirror wafer was produced. These were divided into bond wafers and base wafers.

Next, in the step (b), at least one of the wafers, here, the bond wafer 2 is thermally oxidized, and an oxide film 3 having a thickness of about 0.1 to 2.0 μm is formed on the surface (later becomes a buried oxide film). Form.
Here, the thickness is 0.4 μm.

In step (c), gas ions such as hydrogen ions or rare gas ions, in this case hydrogen ions, are implanted into one surface of the bond wafer 2 on which the oxide film 3 is formed on the surface, and the surface has an average ion penetration depth. Parallel microbubble layers (encapsulation layers) 4 are formed.
The ion implantation conditions here are such that the implanted ions are H ⁺ ions, the implantation energy is 50 keV, and the implantation dose is 5.0 × 10 ¹⁶ / cm ² .

In step (d), the base wafer 1 is superposed and adhered to the hydrogen ion implantation surface of the bond wafer 2 into which hydrogen ions have been implanted via the oxide film 3. Usually, the wafers are bonded to each other without using an adhesive or the like by bringing the surfaces of the two wafers into contact with each other in a clean atmosphere at room temperature.
Also in this experiment, the wafers were bonded together at normal temperature as usual.

Next, in the procedure (e), the bond wafer is peeled off with the encapsulating layer 4 as a boundary, thereby separating into a peeled wafer 5 and an SOI wafer 6 (SOI film 7 + embedded oxide film 3 + base wafer 1). For example, if heat treatment is performed at a temperature of about 400 ° C. to 600 ° C. in an inert gas atmosphere, the separation wafer 5 and the SOI wafer 6 are separated by rearrangement of crystals and aggregation of bubbles in the encapsulating layer. The damaged layer 8 remains on the SOI film 7 on the surface of the SOI wafer that has been peeled off.
In this experiment, the peeling heat treatment was performed at 500 ° C. for 2 hours in an N ₂ gas atmosphere.

For the SOI wafer after peeling thus obtained,
Experiment 1: Heat treatment in non-oxidizing gas atmosphere (Ar 100%, 1200 ° C., 1 hr)
Experiment 2: Sacrificial oxidation treatment (after removing the thermal oxide film formed on the wafer surface (SOI film surface) with 15% HF after heat treatment at 900 ° C. for 1 hour in a pyrogenic atmosphere) and then non-oxidizing Heat treatment in a gas atmosphere (Ar 100%, 1200 ° C., 1 hr)
Experiment 3: Sacrificial oxidation treatment (after removing the thermal oxide film formed on the wafer surface (SOI film surface) with 15% HF after heat treatment at 900 ° C. for 2 hours in a pyrogenic atmosphere) and then non-oxidizing Heat treatment in a gas atmosphere (Ar 100%, 1200 ° C., 1 hr)
Experiment 4: After chemical etching (SC-1 solution (mixed solution of NH ₄ OH / H ₂ O ₂ / H ₂ O) at 76 ° C. for 140 minutes), heat treatment in a non-oxidizing gas atmosphere (Ar 100%, 1200 ° C., 1 hr)
After adding a sacrificial oxidation treatment (pyrogenic atmosphere, heat treatment at 950 ° C. for 3 hours, and removing the thermal oxide film with 15% HF), the surface of the SOI film was measured by AFM, and a concave defect was obtained. investigated.

As a result, the concave defect was 3.7 × 10 ⁷ / cm ² in Experiment 1, 1.3 × 10 ⁵ / cm ² in Experiment ² , 1.0 × 10 ⁵ / cm ² in Experiment 3, and 0 / in Experiment 4. cm ² .
Thus, since this concave defect is observed remarkably when heat treatment is first performed in a non-oxidizing gas atmosphere, the cause of the occurrence is considered to be caused by the etching action in the non-oxidizing gas atmosphere. (Experiment 1). It can also be seen that when sacrificial oxidation is first performed, the concave defects are generated at a lower density than when heat treatment is first performed in a non-oxidizing gas atmosphere (Experiment 1, Experiment 2, and 3). Furthermore, it can also be seen that the density of the concave defects depends on the sacrificial oxide film thickness after peeling (Experiments 2 and 3). However, on the other hand, the thickening of the sacrificial oxide film only suppresses the concave defects. Found that there was a limit.

  Then, instead of removing the damage of the ion implantation by the sacrificial oxidation treatment, the concave defect is not observed when the damaged layer is removed by chemical etching as much as the sacrificial oxidation and then heat-treated in a non-oxidizing gas atmosphere. I found out (Experiment 4). However, this method of removing the damaged layer by chemical etching is not a practical method because the essential uniformity of the SOI film thickness deteriorates.

  From these results, the oxidizing atmosphere has the effect of oxidizing and removing the damaged region of the ion implantation and growing the defect generated in the damaged portion, and the grown defect and the distortion accompanying it grow in the subsequent non-oxidizing atmosphere. The present inventors speculated that a concave defect was generated by being locally etched by the etching action of the heat treatment in FIG.

  As a result of further earnest research, we discovered the following. First, by performing heat treatment in a non-oxidizing gas atmosphere, damage due to ion implantation is recovered, and thereby the growth of defects occurring in the damaged portion during heat treatment in an oxidizing gas atmosphere in the subsequent sacrificial oxidation treatment is performed. Can be prevented. In this way, even if heat treatment is subsequently performed in a non-oxidizing gas atmosphere, the damage has been recovered in the first place, and the defect in the damaged part does not grow. It has been found that it is possible to effectively prevent the occurrence of a general etching and remarkably suppress the occurrence of concave defects. However, if non-oxidizing heat treatment was applied immediately after peeling, surface roughness and wafer contamination were likely to occur, and further improvements were required.

  Therefore, the present inventor previously formed a protective film on the surface of the wafer before performing the first heat treatment in the non-oxidizing gas atmosphere on the peeled SOI wafer, thereby providing a non-oxidizing gas atmosphere. It has also been found that even if the heat treatment is performed under the condition, the contamination and surface roughness of the SOI film surface can be prevented from deteriorating, and the present invention has been completed.

Hereinafter, the manufacturing method of the bonded wafer of this invention is demonstrated with reference to figures. Here, a case where a bonded SOI wafer is manufactured will be described as an example, but the present invention is naturally not limited to this. Any bonded wafer may be used.
FIG. 1 shows an example of the process flow of the method for manufacturing a bonded wafer of the present invention. In addition, when preparing the SOI wafer after peeling produced using the ion implantation peeling method, it can prepare according to the procedure similar to that shown in Experiment 1-4 and FIG.

(First step)
In the present invention, a protective film is first formed on the surface of the SOI film for an SOI wafer having a thin SOI film on the surface.
In this manner, by forming a protective film in advance for heat treatment performed in a later step, it is possible to effectively prevent the surface roughness of the SOI film from being deteriorated due to the heat treatment. .
Further, this protective film can prevent heavy metal from a heat treatment furnace or the like from entering the SOI film and causing metal contamination during heat treatment.

  Although this protective film is not particularly limited, for example, a thermal oxide film can be formed as a protective film by heat-treating an SOI wafer in an oxidizing gas atmosphere. If it is a thermal oxide film, it is easy to form a dense film easily.

  In particular, if it is formed by RTA, a good quality thermal oxide film can be formed in a very short time. Furthermore, by performing RTA treatment at this stage, it is possible to eliminate oxygen precipitate nuclei existing in the base wafer, and it is confirmed that oxygen precipitates are formed more than necessary in the base wafer by subsequent high-temperature heat treatment. As a result, an effect of preventing unnecessary warping of the SOI wafer can be obtained.

Note that the oxidation conditions at this time, the thickness of the thermal oxide film to be formed, and the like are not particularly limited, and can be determined each time according to the conditions of the heat treatment performed thereafter. Any conditions that can form a film that can serve as a protective film may be used.
Moreover, it is not limited to thermal oxidation, It can also form by CVD method etc.

(Second step)
After forming the protective film on the surface of the SOI film as described above, heat treatment is performed in a non-oxidizing gas atmosphere.
As described above, by performing heat treatment in a non-oxidizing gas atmosphere on the SOI wafer, damage caused by the previous ion implantation in the SOI film can be recovered. On the other hand, when the heat treatment temperature in the non-oxidizing atmosphere is 1200 ° C. or higher, a concave defect is also generated by etching the damaged portion. It is thought that it disappears by migration in the lower heat treatment.

In addition, although the heat processing temperature at this time is not specifically limited, For example, it can be set to less than 1200 degreeC. When the temperature is lower than 1200 ° C., the protective film formed on the surface of the SOI film is not completely removed during the heat treatment, and etching of the damaged portion can be sufficiently suppressed.
Naturally, it is possible to set the temperature to 1200 ° C. or higher. However, by performing heat treatment at a lower temperature such as less than 1200 ° C., heavy metal contamination from the heat treatment furnace is less likely to occur, and it can be performed more easily and at low cost. .

At this time, normally, without the protective film, in the heat treatment in the non-oxidizing atmosphere, the surface roughness of the SOI film is likely to be deteriorated at a temperature lower than 1200 ° C., so that the heat treatment is preferably performed at a heat treatment temperature of 1200 ° C. or higher. However, in the present invention, as described above, since the protective film is formed in advance, even in such a low temperature, the damage in the SOI film can be recovered without deteriorating the surface roughness of the SOI film. Can do.
Moreover, as a minimum of heat processing temperature, in order to recover damage efficiently, it is good to set it as 1000 degreeC or more, for example.

(Third process)
Next, sacrificial oxidation treatment is performed. That is, first, heat treatment is performed in an oxidizing gas atmosphere to form a thermal oxide film on the surface layer of the SOI wafer, and then the thermal oxide film is removed with an HF aqueous solution or the like. At this time, the thermal oxide film formed as the protective film in the first step is also removed.
As described above, it is possible to remove the remaining damaged region by this sacrificial oxidation treatment, but in the first place, the heat treatment under an oxidizing gas atmosphere also has the effect of growing defects generated in the damaged portion due to ion implantation. Therefore, after performing this third step, if a heat treatment is performed in a non-oxidizing gas atmosphere, which is the fourth step, the defects grown in the third step and the distortion associated therewith are etched in the fourth step, resulting in a concave shape. Defects will occur.

  However, in the present invention, before the third step of performing the sacrificial oxidation treatment, the damaged portion is recovered by performing a heat treatment in a non-oxidizing gas atmosphere in the second step. Therefore, even when heat treatment is performed in an oxidizing gas atmosphere in the third step, the number of damages itself is reduced, so that the number of growing defects is also reduced. For this reason, the occurrence of local etching in the fourth step due to the grown defects and distortion is also reduced, so that the number of concave defects caused by this etching action can be significantly reduced.

The heat treatment conditions in the third step and the method for removing the formed thermal oxide film are not particularly limited and can be determined each time. The sacrificial oxidation treatment may be performed by a method similar to the conventional method.
Further, the heat treatment in the non-oxidizing gas atmosphere in the second step and the heat treatment in the oxidizing gas atmosphere in the sacrificial oxidation treatment in the third step can be performed continuously.
Further, the heat treatment from the first step to the third step can be performed continuously using the same heater heating type heat treatment furnace (batch furnace).

(Fourth process)
After the third step, heat treatment is performed again in a non-oxidizing gas atmosphere.
As described above, the number of defects that have occurred in the damaged portion and should grow due to the steps up to the third step has been extremely reduced, and the number of grown defects and the distortions associated therewith are naturally reduced. In the process, the number of local etching caused by these is extremely suppressed.
In addition, the concave defect generated in the second process can be eliminated because migration occurs in the fourth process.

In the fourth step and the heat treatment in the non-oxidizing gas atmosphere in the second step, the heat-treating atmosphere may be a non-oxidizing gas atmosphere and is not particularly limited.
Even if oxygen is mixed even at 1%, an oxidizing atmosphere is formed, and the effect of suppressing the occurrence of concave defects cannot be obtained. Therefore, in these steps (particularly the second step), for example, Ar is preferably 100%. .

(Fifth process)
After performing the first to fourth steps as described above, as a fifth step, if necessary, for example, further sacrificial oxidation treatment is performed to adjust the thickness of the SOI film to a desired thickness. can do.
This sacrificial oxidation treatment itself can be the same as the conventional method. This method is as described in the third step.

  According to the method for producing a bonded wafer of the present invention as described above, damage caused by ion implantation remaining in the thin film after peeling is removed without deteriorating contamination and surface roughness of a thin film such as an SOI film. The method can remarkably suppress the occurrence of concave defects on the surface of the thin film, which frequently occurred. That is, it is possible to obtain a bonded wafer having more excellent device characteristics.

The present invention will be described in detail below with reference to examples of the present invention, but these examples do not limit the present invention.
(Example 1-5)
An SOI wafer is manufactured using the bonded SOI wafer manufacturing method of the present invention.
A silicon mirror wafer having a diameter of 300 mm is prepared by slicing and processing a silicon single crystal ingot having a crystal orientation <100> produced by the Czochralski method and having a p-type conductivity and a resistivity of 10 Ω · cm. Was made. These were divided into a bond wafer and a base wafer, and an SOI wafer having a thin-film SOI film on the surface was obtained as a sample in accordance with each procedure in FIG.

Note that the thickness of the SOI film was 400 nm, and the thickness of the buried oxide film was 150 nm. As ion implantation conditions, the implanted ions were H ⁺ ions, the implantation energy was 50 keV, and the implantation dose was 5.0 × 10 ¹⁶ / cm ² . Further, the peeling heat treatment was performed at 500 ° C. for 2 hours in an N ₂ gas atmosphere.

  The peeled SOI wafer thus obtained was first subjected to thermal oxidation at 1000 ° C. for 30 seconds in an oxygen atmosphere by RTA to form a thermal oxide film having a thickness of 4 nm as a protective film (FIG. 1st step).

Next, as a second step, heat treatment was performed in an Ar 100% atmosphere by changing the heat treatment temperature and the heat treatment time in each of Examples 1 to 5.
Example 1: Heat treatment temperature 1000 ° C., heat treatment time 1 hr
Example 2: Heat treatment temperature 1050 ° C., heat treatment time 1 hr
Example 3: Heat treatment temperature 1100 ° C., heat treatment time 1 hr
Example 4: Heat treatment temperature 1200 ° C., heat treatment time 1 hr
Example 5: Heat treatment temperature 1200 ° C., heat treatment time 4 hr

  Thereafter, sacrificial oxidation treatment was performed as a third step. Specifically, after heat treatment at 900 ° C. for 1 hr in a pyrogenic atmosphere, the thermal oxide film formed on the wafer surface layer is removed with a 15% HF aqueous solution (the thermal oxide film formed in the first step). Are also removed).

Next, as a fourth step, heat treatment was performed again in a non-oxidizing gas atmosphere. Here, heat treatment was performed at 1200 ° C. for 1 hr in an Ar 100% atmosphere.
Then, as a fifth step, after heat treatment at 950 ° C. for 3 hours in a pyrogenic atmosphere, the thermal oxide film formed on the wafer surface layer is removed with a 15% HF aqueous solution, so that the SOI film has a desired thickness. It adjusted so that it might become.

  The surface of the SOI film of the SOI wafer thus obtained was first measured at 30 μm square by AFM measurement. In any of Examples 1 to 5, the surface roughness was 0.28 nm or less in RMS value. Yes, this is significantly better than the value (0.50 nm) of Comparative Example 2 described later, in which no protective film was formed and the present invention was not carried out.

Further, when the AFM measurement was performed at 30 μm square, the density of the concave defects was 6.2 × 10 ³ / cm ² in Example 1, 3.8 × 10 ³ / cm ² in Example ² , and Example 3 5.8 × 10 ² / cm ² , Example 4 was 0 / cm ² , and Example 5 was 0 / cm ² . These are remarkably superior to Comparative Example 1 (9.0 × 10 ⁴ / cm ² ) in which the present invention was not carried out without performing the heat treatment in the non-oxidizing gas atmosphere as the second step.

  In Examples 1 to 5, it can be seen that the density of the concave defects decreases as the heat treatment temperature in the second step increases. By making the temperature higher, recovery of the damaged part by ion implantation in the second step is efficiently performed, and as a result, the number of concave defects is considered to be further reduced, but the heat treatment temperature of this second step is It can be determined appropriately according to various conditions such as the SOI film thickness of the sample.

(Comparative Example 1)
In the same manner as in each example, an SOI wafer sample after peeling was obtained according to FIG.
A first step was performed on this sample in the same manner as in each example, and a thermal oxide film as a protective film was formed.
Next, unlike each example in which heat treatment in a non-oxidizing gas atmosphere of Ar 100% was performed as the second step, heat treatment in an oxidizing gas atmosphere having an Ar / O ₂ ratio of 99/1 (1100 ° C., 1 hr).
Thereafter, the third to fifth steps were performed in the same manner as in the respective examples to obtain an SOI wafer having a desired SOI film thickness.

With respect to the surface of the SOI film of the SOI wafer thus obtained, the surface roughness and the density of concave defects were measured by the same measurement method as in each example. As a result, the surface roughness was 0.30 nm, which was almost the same as that of each example, but the density of the concave defects was 9.0 × 10 ⁴ / cm ² .

This seems to be because in Comparative Example 1, the heat treatment performed in the second step was a heat treatment in an oxidizing gas atmosphere.
In each example in which the present invention is implemented, the heat treatment in the second step after the first step is an Ar 100% atmosphere and a non-oxidizing gas atmosphere, so that damage caused by ion implantation in the SOI film can be recovered. The number of defects generated in the damaged portion is reduced, the number of defects grown in the third step is reduced, and the grown defects that are locally etched in the fourth step and the distortion caused thereby are also reduced. As a result, finally, the number of concave defects can be remarkably suppressed.

  However, in Comparative Example 1, since the heat treatment performed in the second step is in an oxidizing gas atmosphere, the effect of growing defects generated in the damaged portion works, and finally the number of occurrences of concave defects increases. End up.

(Comparative Example 2)
In the same manner as in each example, an SOI wafer sample after peeling was obtained according to FIG.
Unlike the examples in which a thermal oxide film was formed as a protective film, the following process was performed on this sample without forming the protective film.
In the subsequent steps, the second to fifth steps were performed in the same manner as in each example (the second step was the same heat treatment as in Example 3), and an SOI wafer having a desired SOI film thickness was obtained.

With respect to the surface of the SOI film of the SOI wafer thus obtained, the surface roughness and the density of concave defects were measured by the same measurement method as in each example. As a result, the surface roughness was 0.50 nm, which was larger than each example. The density of the concave defects was 6.0 × 10 ³ / cm ² , which was similar to that in Example 1.

Unlike the examples, the surface roughness of Comparative Example 2 was larger than that of each example, and the protective film was formed before the heat treatment in the non-oxidizing gas atmosphere in the second step. This is probably because they did not. In particular, as in Example 1 and Comparative Example 2, when the heat treatment temperature in the second step is less than 1200 ° C., the surface roughness is more likely to deteriorate if a protective film is not formed than in the case of 1200 ° C. or higher. .
On the other hand, in Example 1 in which a protective film was formed in advance and the present invention was carried out, the heat treatment temperature in the second step was less than 1200 ° C. as in Comparative Example 1, but the surface roughness was excellent at 0.28 nm. It has become. Moreover, the presence or absence of the protective film is directly linked to the presence or absence of contamination during heat treatment.

  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.

  For example, although an SOI wafer has been described as an example in the present example, the present invention is not limited to this and can be applied to various bonded wafers.

It is a flowchart which shows an example of the process of the manufacturing method of the bonding wafer of this invention. It is a flowchart which shows an example of the procedure which manufactures SOI wafer using an ion implantation peeling method.

Explanation of symbols

1 ... Base wafer, 2 ... Bond wafer, 3 ... Oxide film,
4 ... Microbubble layer (encapsulation layer), 5 ... Peeling wafer, 6 ... SOI wafer,
7 ... SOI film, 8 ... Damage layer.

Claims (6)

At least a bond wafer having a microbubble layer formed by gas ion implantation is bonded to a base wafer serving as a support substrate, and the bond wafer is peeled off at the microbubble layer as a boundary to form a thin film on the base wafer. In a method of manufacturing a bonded wafer by an ion implantation separation method,
After the first step of forming a protective film on the surface of the thin film of the bonded wafer after peeling off the bond wafer, the second step of heat-treating in a non-oxidizing gas atmosphere is performed, and then the oxidizing property is performed. After performing a heat treatment in a gas atmosphere to form a thermal oxide film on the surface layer of the bonded wafer, a third step of removing the thermal oxide film and the protective film is performed, and then again in a non-oxidizing gas atmosphere A method for producing a bonded wafer, comprising performing a fourth step of heat treatment.   The method for producing a bonded wafer according to claim 1, wherein a thermal oxide film is formed as a protective film in the first step.   The method for manufacturing a bonded wafer according to claim 2, wherein the thermal oxide film formed as the protective film in the first step is formed by RTA.   The method for manufacturing a bonded wafer according to any one of claims 1 to 3, wherein the heat treatment temperature in the second step is set to less than 1200 ° C.   2. The fifth step of performing a heat treatment in an oxidizing gas atmosphere to form a thermal oxide film on the surface of the thin film and removing the thermal oxide film after the fourth step is performed. The manufacturing method of the bonded wafer as described in any one of Claim 4 to 5.   The bonded wafer according to any one of claims 1 to 5, wherein in the heat treatment in the second step and / or the fourth step, the non-oxidizing gas atmosphere is Ar100%. Manufacturing method.

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