JP3917219B2 - Manufacturing method of bonded SOI wafer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a bonded SOI wafer, and more particularly to bonding of a bonded SOI wafer.
[0002]
[Prior art]
In the conventional method for manufacturing a bonded SOI wafer, as shown in FIG. 3, a base wafer 1 having a mirror finish on one or both sides and a mirror finish on one or both sides and a thermal oxidation treatment are performed. The active wafer 2 on which the insulating film (SiO ₂ ) 2a having a predetermined thickness is formed is washed with an aqueous solution of ammonia and hydrogen peroxide, respectively, and subjected to hydrophilic treatment, and then added using an adhesive jig. Adhere while pressing. Then, after a predetermined time has elapsed, the bonded wafer is subjected to bonding heat treatment. The elapsed time from bonding to bonding heat treatment is appropriately determined in consideration of the delivery date and the convenience of the heat treatment furnace.
[0003]
[Problems to be solved by the invention]
Accordingly, the elapsed time from the end of bonding to the bonding heat treatment varies from lot to lot, but depending on the lot, voids 3 are generated in the wafer periphery as shown in FIG. This figure shows, as an example, a result obtained by examining an bonded SOI wafer after 36 hours after bonding with an ultrasonic flaw detector. The void 3 is often generated in the range of 1.5 mm to 5 mm from the outer periphery of the wafer. The voids in the peripheral portion of the wafer tend to increase with the elapsed time from the end of the bonding process to the start of the bonding heat treatment step, and the void in the peripheral portion of the wafer does not occur after the bonding heat treatment step. If even one void is generated on the bonded wafer, the wafer must be discarded as a defective product. Therefore, the heat treatment process must be adjusted to shorten the elapsed time.
[0004]
Conventionally, for example, a directly bonded wafer using two silicon wafers has been used as an alternative to an epitaxial wafer. Japanese Patent Laid-Open No. 7-263290 discloses a manufacturing method for this bonded wafer, in which two silicon wafers are bonded together after washing with a hydrofluoric acid solution. This method has a problem that an SOI wafer having an insulating film as an intermediate layer cannot be manufactured because the surface oxide film is removed.
[0005]
The present invention has been made in view of the above circumstances, and provides a method for manufacturing a bonded SOI wafer in which voids are not generated even if there is no special restriction on the elapsed time from the end of the bonding process to the start of the bonding heat treatment process. For the purpose.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing a bonded SOI wafer according to the present invention includes a base wafer that has been mirror-polished on one side or both sides, and mirror-polished on one side or both sides, and then subjected to thermal oxidation treatment to obtain a predetermined In the method for manufacturing a bonded SOI wafer, the method includes a bonding step of bonding an active wafer on which an insulating film having a thickness of 5 mm is applied while pressing, and further a bonding heat treatment step of bonding and performing a bonding heat treatment. First, the method includes a hydrophobic treatment step for subjecting the base wafer to a hydrophobic treatment, and a hydrophilic treatment step for subjecting the active wafer to a hydrophilic treatment. Preferably, the hydrophobic treatment step applied to the base wafer is a wet treatment step using a hydrofluoric acid aqueous solution.
[0007]
The hydrophobic treatment step is a wet treatment step using a hydrofluoric acid aqueous solution. This hydrofluoric acid aqueous solution means an aqueous solution containing hydrofluoric acid as a main component, which is configured to have a hydrofluoric acid concentration sufficient to remove the natural oxide film, and contains other components. Also good.
[0008]
Moreover, a dry etching process may be used as the hydrophobic treatment process applied to the base wafer.
[0009]
Furthermore, a plasma etching process may be used as the dry etching process.
[0010]
The hydrophilic treatment step includes a washing step with an aqueous solution of ammonia and hydrogen peroxide, a washing step (SPM) with an aqueous solution of sulfuric acid and hydrogen peroxide solution, and the hydrophilic treatment includes hydrochloric acid and hydrogen peroxide. A cleaning step using an aqueous solution with water may be used.
[0011]
The present invention is an improvement of the pretreatment process performed prior to the bonding process. That is, the hydrophilic treatment is performed on the active wafer, and the hydrophobic treatment is performed on the base wafer. As a result, no void is generated in the peripheral portion of the wafer regardless of the length of the elapsed time from the bonding process to the bonding heat treatment process.
[0012]
Since the active wafer is subjected to a hydrophilic treatment, a clean surface can be obtained without much removal of the oxide film, while the hydrophobic treatment applied to the base wafer is a natural treatment of the base wafer surface. Since the surface is cleaned by a method such as etching with a hydrofluoric acid solution (HF) having a concentration capable of sufficiently removing the oxide film, the surface of the base wafer becomes a clean surface suitable for adhesion. In this way, by applying a hydrophilic treatment, removing the impurities and adding an OH group to the active wafer surface, and applying a hydrophobic treatment to remove the natural oxide film and clean the base wafer surface, It can be bonded well with extremely good adhesion, and even when the elapsed time from this bonding process to the bonding heat treatment becomes long, there is no generation of voids and it is possible to obtain a highly reliable bonded wafer Become.
[0013]
In addition, after performing a hydrophilic treatment process with respect to both a base wafer and an active wafer, you may make it perform a hydrophobic process only with respect to a base wafer.
DETAILED DESCRIPTION OF THE INVENTION
Next, a method of manufacturing a bonded SOI wafer according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing a manufacturing process of a bonded SOI wafer.
[0014]
First, a silicon wafer having one or both sides mirror-finished is used as a base wafer, and the base wafer 1 is subjected to a hydrophobic treatment. The hydrophobic treatment is to wash the base wafer 1 with a hydrofluoric acid solution having a concentration that can sufficiently remove the natural oxide film on the wafer surface. On the other hand, the active wafer 2 is one surface or both surfaces mirror-polished and then subjected to a thermal oxidation process to form an insulating film (SiO ₂ ) 2a having a predetermined thickness. Apply. The hydrophilic treatment may be any of cleaning with an aqueous solution of ammonia and hydrogen peroxide, cleaning with an aqueous solution of sulfuric acid and hydrogen peroxide (SPM), and cleaning with an aqueous solution of hydrochloric acid and hydrogen peroxide. After the base wafer 1 and the active wafer 2 that have been subjected to such treatment are bonded using a bonding jig while being pressed, bonding heat treatment is performed.
[0015]
The experimental results by the method for manufacturing the bonded SOI wafer are as follows.
[0016]
The concentration of HF for cleaning the base wafer was set to four levels of 1.5%, 5%, 10%, and 49%, and the base wafer was cleaned using a hydrofluoric acid solution having these concentrations. The active wafer was washed with an aqueous solution of ammonia and hydrogen peroxide to impart hydrophilicity. Thereafter, the two wafers were bonded using a bonding jig, and the bonding state was confirmed. Furthermore, the occurrence of voids was investigated for each elapsed time until the start of the adhesive heat treatment process. For comparison, both the base wafer and the active wafer were subjected to a hydrophilic treatment by a conventional method, and the same investigation as described above was performed.
[0017]
FIG. 2 shows the relationship between the elapsed time after bonding and the number of voids per wafer. In the bonded wafer according to the conventional method in which both the base wafer and the active wafer were subjected to hydrophilic treatment, voids were generated 1 hour after bonding, and about 100 were observed after 240 hours. On the other hand, the base wafer was washed with HF solutions having concentrations of 1.5%, 5%, 10%, and 49%, and the active wafer was washed with an aqueous solution of ammonia and hydrogen peroxide to impart hydrophilicity. Voids are not generated in the bonded wafer bonded afterwards. Therefore, it is confirmed that if HF cleaning with a concentration of 1.5% or more, which is a concentration that can sufficiently remove the natural oxide film on the base wafer, is performed, no voids will be generated even if at least 240 hours have elapsed after bonding. It was done. Regarding the adhesive strength, the base wafer was washed with the above four HF concentrations, and heat treatment was performed at the same temperature as when the conventional hydrophilic treatment was performed, but these strengths and the conventional hydrophilic treatment were performed. There was no difference from the strength of the case.
[0018]
In the embodiment, the hydrophobic treatment is performed with a hydrofluoric acid solution. However, the present invention is not limited to this, and other wet treatment methods, dry etching such as plasma etching, and the like are formed on the surface of the base wafer. Any method that can remove the natural oxide film formed may be used.
[0019]
【The invention's effect】
As described above, according to the present invention, by performing hydrophobic treatment by hydrofluoric acid cleaning on the base wafer and hydrophilic treatment on the active wafer, the elapsed time from the bonding step to the bonding heat treatment step can be 240 hours or less. For example, there is no generation of voids in the periphery of the wafer, and the defect rate due to voids can be significantly reduced. Accordingly, the time interval from the end of the bonding process to the bonding heat treatment process can be greatly extended, and the manufacturing process can be easily managed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a manufacturing process of a bonded SOI wafer.
FIG. 2 is a diagram showing a relationship between an elapsed time after bonding and the number of voids generated.
FIG. 3 is a schematic view showing a manufacturing process of a bonded SOI wafer according to a conventional technique.
FIG. 4 is a schematic diagram showing an example of a void generation state in a bonded SOI wafer according to a conventional technique.
[Explanation of symbols]
1 Base wafer 2 Active wafer 2a Insulating film

Claims (8)

A base wafer that has been mirror-polished on one side or both sides is bonded to an active wafer that has been mirror-polished on one or both sides and is then thermally oxidized to form an insulating film with a predetermined thickness. In a method for manufacturing a bonded SOI wafer, which includes an adhesion step and an adhesion heat treatment step in which an adhesion heat treatment is further performed to bond them together.
A method for producing a bonded SOI wafer comprising a hydrophobic treatment step for subjecting a base wafer to a hydrophobic treatment and a hydrophilic treatment step for subjecting an active wafer to a hydrophilic treatment prior to the bonding step. 2. The method for manufacturing a bonded SOI wafer according to claim 1, wherein the hydrophobic treatment step is a step of performing a wet treatment using a hydrofluoric acid aqueous solution on the base wafer. The method for manufacturing a bonded SOI wafer according to claim 1, wherein the hydrophobic treatment step is a dry etching step. 4. The method for manufacturing a bonded SOI wafer according to claim 3, wherein the dry etching step is plasma etching. The method for producing a bonded SOI wafer according to claim 1, wherein the hydrophilic treatment step is a cleaning step using an aqueous solution of ammonia and hydrogen peroxide. The method for producing a bonded SOI wafer according to claim 1, wherein the hydrophilic treatment step is a cleaning step using an aqueous solution (SPM) of sulfuric acid and hydrogen peroxide solution. The method for producing a bonded SOI wafer according to claim 1, wherein the hydrophilic treatment step is a cleaning step using an aqueous solution of hydrochloric acid and hydrogen peroxide. The hydrophilic treatment step is a step of subjecting both the base wafer and the active wafer to a hydrophilic treatment prior to the bonding step, and thereafter includes a hydrophobic treatment step of subjecting the base wafer to a hydrophobic treatment. A method for producing a bonded SOI wafer according to claim 1.

Images