JP3606432B2 - Manufacturing method of high flatness wafer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a high flatness wafer, and more particularly to a method for producing a high flatness wafer in which a semiconductor wafer having a high flatness can be obtained by grinding and polishing the surface of a semiconductor wafer after etching.
[0002]
[Prior art]
An example of a conventional silicon wafer manufacturing method will be described with reference to the flowchart of FIG.
First, in the slicing step (S301), the silicon wafer is sliced from the ingot. In the next chamfering step (S302), chamfering is performed on the outer peripheral portion of the silicon wafer. In the subsequent lapping step (S303), lapping is performed on both the front and back surfaces of the silicon wafer by a lapping machine. Then, in the next etching step (S304), the wrapped wafer is immersed in a predetermined etching solution (mixed acid or alkali + mixed acid) to remove distortion in the lapping process, distortion in the chamfering process, and the like.
Thereafter, the silicon wafer is bonded to a polishing board using wax, and the wafer surface is mirror-polished (S305). Then, after removing the wax and the like adhering to the back surface of the silicon wafer, a final finish cleaning step (S306) is performed.
[0003]
However, in such a conventional method for manufacturing a silicon wafer, as described above, acid etching is performed using a mixed acid after lapping the silicon wafer. As a result, the etching rate was relatively high, and during the acid etching, the silicon wafer and the acidic solution reacted strongly to generate a relatively large amount of bubbles. Due to these effects and the like, there is a problem that waviness is likely to occur on the wafer surface. There is also a problem that the taper generated by lapping is further emphasized by etching. Moreover, this problem of surface flatness has not been improved so much in the subsequent polishing process.
[0004]
As a conventional technique for solving these problems, for example, “Lamination support substrate and manufacturing method thereof” in Japanese Patent Application Laid-Open No. 10-22186, which was previously filed by the applicant of the present patent application and later published, is known. Yes.
In this prior art, the surface of a silicon wafer that has been cleaned after etching is ground using a vitrified grinding wheel having abrasive grains higher than # 2000, and then the wafer grinding surface is mirror-polished after cleaning. . By grinding the surface of the etched wafer before mirror polishing, waviness on the wafer surface caused by etching and sagging of the outer periphery of the wafer can be removed.
[0005]
[Problems to be solved by the invention]
However, in the silicon wafer manufacturing process, the back surface of the silicon wafer may be subjected to back surface processing such as sand blasting, poly back sealing, or LTO (deposition of low temperature oxide film).
At this time, conventionally, there has been no technical examination as to which process the back surface treatment process should be incorporated in during the wafer manufacturing process. Therefore, it has been said that the back surface treatment may be performed before the grinding step.
However, in fact, after repeating the experiment of grinding after the back surface treatment, a certain fact was found. That is, the back surface treatment layer formed on the back surface of the wafer and having fine irregularities by, for example, sandblasting may be damaged by cleaning after grinding (usually RCA cleaning using an alkaline cleaning liquid). was there. For this reason, the processing effect on the back surface of the wafer may be reduced by half, or in the worst case, it may disappear completely.
On the other hand, at the time of grinding, there is a possibility that the wafer back surface (processed surface) may be damaged by being attracted to the wafer holding portion of the grinding apparatus.
[0006]
OBJECT OF THE INVENTION
It is an object of the present invention to provide a method for producing a high flatness wafer in which the back surface treatment layer formed on the back surface of the semiconductor wafer is not melted by cleaning after grinding, and the back surface of the semiconductor wafer is hardly damaged during grinding of the wafer surface. And that is the purpose.
[0007]
[Means for Solving the Problems]
The invention described in claim 1 includes a step of etching a semiconductor wafer, a step of grinding the surface of the semiconductor wafer after the etching, and after grinding the surface, the ground surface of the semiconductor wafer is subjected to an alkaline cleaning liquid. A method of manufacturing a high flatness wafer, comprising: a step of cleaning using, a step of performing a predetermined back surface treatment on the back surface of the semiconductor wafer after the cleaning, and a step of mirror polishing the surface of the semiconductor wafer thereafter. .
Examples of the semiconductor wafer include a silicon wafer and a gallium arsenide wafer. Further, the usage application of the wafer is not limited. For example, wafers for bonded wafers such as SOI (Silicon on Insulator) and dielectric separation wafers may be used.
Here, the surface of the semiconductor wafer has a high flatness, which means that the site flatness, for example, a site difference of SBIR (Site Back-side Ideal Range) at a site having an area of 25 mm × 25 mm is 0. It means that it is 40 μm or less.
[0008]
In addition, the grinding here is preferably performed by a high count grinding wheel capable of grinding the silicon surface, which is a non-damaged surface, with which the wafer surface is difficult to squeeze. Examples of the grindstone used for grinding include # 1500 to # 3000 resinoid grinding grindstones. The resinoid grinding wheel is a grindstone in which diamond abrasive grains are bonded using a high-quality synthetic resin as a binder.
Thus, since grinding with little damage is performed before polishing, high flatness can be obtained on the wafer surface after grinding. In addition, since the amount of polishing can be reduced, high throughput can be obtained. In this case, the grinding damage is, for example, 2 μm or less. If the damage is large, the amount of subsequent surface polishing increases.
[0009]
As a cleaning liquid used for cleaning performed after grinding, for example, alkaline KOH that dissolves the surface of the silicon wafer can be employed. For example, an alkaline solution that melts the surface of a silicon wafer. Even if the wafer surface layer is removed by 0.05 to 1.0 μm during this cleaning, the flatness of the semiconductor wafer is maintained. If the amount of erosion loss on the wafer surface by cleaning is less than 0.05 μm, the dropped abrasive grains may remain on the wafer surface. On the other hand, if the thickness exceeds 1.0 μm, the roughness increases and the shape of the wafer back surface changes.
[0010]
The back surface processing of the semiconductor wafer is not limited. Examples thereof include sandblasting, polysilicon back seal processing, and LTO (Low Temperature Oxidation) processing. Sand blasting is a processing method in which abrasive grains such as Si oxide are sprayed on the back surface of the wafer to cause mechanical damage, and this is used as a gettering site. Polysilicon back-seal processing is a processing method in which a polycrystalline silicon film is deposited on the back surface of a wafer and the grain boundaries of the polycrystalline silicon are used as gettering sites. Furthermore, LTO processing is a processing method in which an oxide film is formed on the back surface of a wafer before performing an epitaxial process for the purpose of preventing autodoping. WHT (Wafer Heat Treatment) for heat-treating the wafer is also a kind of this backside treatment.
[0011]
According to a second aspect of the present invention, in the high flatness wafer according to the first aspect, the back surface treatment is any one of a sand blast treatment, a polysilicon layer deposition treatment, an oxide film deposition treatment, and a donor killer heat treatment. It is a manufacturing method.
The invention according to claim 3 is the high flatness wafer according to claim 1 or 2, wherein the grinding step is performed using a # 1500 to # 3000 resinoid bond grinding wheel manufactured by DISCO Corporation. It is a manufacturing method.
As a resinoid bond grinding wheel manufactured by DISCO Corporation, for example, a # 2000 high count grinding wheel of resinoid bond having a product name “IF-01-1-4 / 6-B-M01” can be used.
[0012]
[Action]
According to this invention, the etched wafer is subjected to surface grinding, and then the wafer ground surface is washed with an alkaline cleaning liquid. At this time, abrasive grains and the like that fall off the grinding wheel and adhere to the wafer surface during grinding are washed away. Next, a predetermined back surface treatment is performed on the cleaned semiconductor wafer, and then the surface of the wafer after the back surface treatment is mirror-polished.
As described above, since the wafer back surface treatment is performed after grinding the wafer surface, the wafer back surface treatment layer formed on the back surface side of the semiconductor wafer is melted down by the cleaning liquid having an etching action during the cleaning after the grinding. Can be avoided.
In addition, the semiconductor wafers subjected to the grinding process in this way are etched wafers that have not yet been subjected to the back surface treatment, that is, grinding abrasive grains or the like during back surface processing adhere to the front and back surfaces of the wafer, or fine on the back surface of the wafer. This is a semiconductor wafer that is not shaped with irregularities (occurred during sandblasting). Therefore, even when the semiconductor wafer is ground and held by the wafer holding portion of the grinding apparatus during the wafer grinding, even if the wafer back surface is scratched, the scratch can be removed by subsequent alkali cleaning. Also, the falling abrasive grains of the grinding wheel can be removed by washing with this alkaline solution or the like. Also, contamination due to grinding can be removed. Therefore, it is possible to prevent the semiconductor wafer from being damaged due to these abrasive grains.
[0013]
In particular, according to the invention described in claim 3, the surface of the semiconductor wafer is ground using a # 1500 to # 3000 resinoid bond grinding wheel manufactured by DISCO Corporation. This grinding wheel is a high count resinoid bond grinding wheel capable of grinding a silicon surface which is a non-damaged surface. Therefore, the wafer surface that has been etched and has no damage can be ground by this high-quality grinding wheel with little damage (for example, a damage depth of about 2 μm) and without revealing the surface. Also, grinding can be performed with a higher throughput than electric field dressing.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing a method for manufacturing a high flatness wafer according to an embodiment of the present invention.
As shown in FIG. 1, in this embodiment, the high flatness is roughly obtained through the steps of slicing, chamfering, lapping, etching, cleaning, grinding, cleaning, back surface treatment, WHT, polishing, and cleaning. A silicon wafer is produced. Hereinafter, each process will be described in detail.
[0015]
The silicon ingot pulled up by the CZ method is sliced into an 8-inch silicon wafer having a thickness of about 860 μm in the slicing step (S101).
Next, in the chamfering step (S102), the peripheral edge of the sliced wafer is chamfered into a predetermined shape using a chamfering grindstone. As a result, the peripheral edge of the silicon wafer is formed into a predetermined rounded shape (for example, a MOS type chamfered shape).
Next, the chamfered silicon wafer is lapped in a lapping step (S103). In this lapping process, a silicon wafer is placed between lap surface plates kept parallel to each other, and a wrap liquid, which is a mixture of alumina abrasive grains, a dispersant and water, is placed between the lap surface plate and the silicon wafer. Pour. Then, both surfaces of the wafer are mechanically wrapped by rotating and sliding under pressure. The wrap amount of the silicon wafer is about 40 to 80 μm in total on both the front and back surfaces of the wafer.
[0016]
Next, the chamfered silicon wafer is etched (S104). Specifically, the silicon wafer is immersed in a mixed acid solution (normal temperature to 50 ° C.) in which hydrofluoric acid and nitric acid are mixed.
Thereafter, a cleaning process (S105) for cleaning the silicon wafer with an RCA-based cleaning liquid is performed.
Then, the surface of the silicon wafer is ground using a resinoid bond grinding wheel manufactured by Disco Corporation, product name “IF-01-1-4 / 6-B-M01” (S106). This grinding wheel is a special grindstone developed to process a non-damaged surface with a high count of # 2000. The product name of this grinding apparatus is “DFG840”.
[0017]
The grinding amount at this time is about 2 to 10 μm. As a result, when the wafer surface is polished in the post-process, the polishing amount is 2 to 8 μm, which is about half that of the conventional one. As described above, since the grinding is performed with a high-grinding grinding wheel, the wafer can be ground with little damage (2 μm or less) and without exposing the surface thereof.
As described above, the silicon wafer to be subjected to the grinding process is an etched wafer that has not yet been subjected to the back surface treatment, that is, a silicon wafer in which fine irregularities (for example, generated during sandblasting) are not formed on the back surface of the wafer. It is.
[0018]
Next, the surface-ground silicon wafer is cleaned with an alkaline cleaning solution (S107). As this cleaning solution, a 10 to 50% KOH solution is employed. By this cleaning, diamond abrasive grains and the like that fall off the grinding wheel and adhere to the wafer surface during grinding are washed away. Also, other contamination during grinding is removed. By this cleaning, the wafer surface is melted by 0.5 μm.
[0019]
Next, a predetermined back surface treatment is performed on the cleaned semiconductor wafer (S108). Here, sandblasting is employed for the backside treatment. That is, by spraying silicon oxide abrasive grains on the back surface of the silicon wafer, the wafer back surface is mechanically damaged.
The silicon wafer whose back surface has been treated in this manner is put into a heating furnace and subjected to a WHT (Wafer Heat Treatment) process (S109). That is, it is heated for 10 minutes in a heating furnace at 650 ° C. At that time, if an abnormal defect has occurred in the wafer during the grinding process or the like, the abnormality is emphasized during the heat treatment. Therefore, the quality of the silicon wafer can be easily determined.
[0020]
Subsequently, the surface of the silicon wafer is mirror-polished (S110). The polishing amount at this time only needs to remove the damage in the grinding step of S106. Therefore, 2 to 8 μm is sufficient.
Subsequently, a cleaning step (S111) is performed. Specifically, it is an alkaline cleaning.
Through such a manufacturing process, a high-quality silicon wafer in which the wafer back surface treatment layer is not melted by the cleaning liquid is manufactured.
[0021]
FIG. 2 is a graph showing the degree of melting damage in the backside treatment of the silicon wafer according to this example in comparison with the conventional example.
The flatness is indicated by SBIR. FIG. 2 shows that the flatness of the silicon wafer according to this embodiment is improved over that of the conventional example. The flatness is measured by a known method using a known device.
[0022]
【The invention's effect】
According to the present invention, the back surface processing step of the semiconductor wafer is performed after the wafer surface is ground and the ground surface is cleaned . Therefore, the back surface processing layer formed on the back surface of the wafer during the cleaning after the grinding is dissolved. There is no damage, and the rear surface processed during wafer surface grinding is not attracted and scratched.
[0023]
In particular, according to the invention described in claim 3, since the grinding process of the surface of the semiconductor wafer is performed using a resinoid bond grinding wheel of # 1500 to # 3000 manufactured by DISCO Corporation, The surface can be ground with little damage and without revealing the surface. Also, grinding can be performed with a higher throughput than electric field dressing.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a method for manufacturing a high flatness wafer according to an embodiment of the present invention.
FIG. 2 is a graph showing the degree of erosion of the backside treatment of a silicon wafer according to one embodiment of the present invention compared to a conventional example.
FIG. 3 is a flowchart showing a method for manufacturing a high flatness wafer according to conventional means.

Claims (3)

Etching a semiconductor wafer;
  Grinding the surface of the semiconductor wafer after this etching;
  After grinding the surface, a step of washing the ground surface of the semiconductor wafer with an alkaline washing liquid;
  After this cleaning, a step of performing a predetermined back surface treatment on the back surface of the semiconductor wafer;
  Then, the manufacturing method of the high flatness wafer provided with the process of mirror-polishing the surface of a semiconductor wafer. 2. The method for manufacturing a high flatness wafer according to claim 1, wherein the back surface treatment is any one of sand blast treatment, polysilicon layer deposition treatment, oxide film deposition treatment, and donor killer heat treatment. The said grinding process is a manufacturing method of the high flatness wafer of Claim 1 or Claim 2 performed using the disco Co., Ltd. # 1500- # 3000 resinoid bond grinding wheel.

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