JP3994523B2 - Inspection method of mirror chamfered part of silicon wafer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inspection method for a silicon wafer mirror chamfer. More specifically, the present invention relates to a method for inspecting a silicon wafer mirror chamfered portion that can detect surface abnormalities such as scratches and chips on the silicon wafer mirror chamfered portion and polysilicon remaining with extremely high sensitivity.
[0002]
[Prior art]
For example, when a silicon wafer is manufactured by the Czochralski method or the like, a cylindrical ingot is first cut into slices and then chamfered for the purpose of preventing edge chipping or adding an epitaxial growth step to prevent crowning. Is done. In a normal wafer manufacturing process, the chamfered portion is in a state where etching for removing processing distortion is performed, and the surface is rough. Therefore, in recent years, in order to prevent dust generation from the edge portion, mirror chamfering is performed to mirror the chamfered portion. At this time, if the mirror chamfering is insufficient, scratches, chips, steps, damage, and silicon chips remain on the chamfered portion, causing a device defect.
[0003]
In some cases, the silicon wafer may further include a step of growing polysilicon on the wafer surface by chemical vapor deposition in order to enhance the gettering ability. In this case, the mirror chamfering is performed again. However, if the mirror chamfering is insufficient, the polysilicon may remain in the chamfered portion in addition to scratches, chips, steps, damage, silicon flaws, etc. Cause.
[0004]
In particular, when an epitaxial growth process is added later, even if the residual polysilicon is very small, it grows and grows at the same time during the growth of the epitaxial layer, and is desorbed into particles during the device process. A major cause of device failure.
Therefore, after the mirror chamfering, particularly after the mirror chamfering before the epitaxial growth process, it is necessary to inspect the mirror chamfering portion with very high sensitivity.
[0005]
[Problems to be solved by the invention]
Conventionally, the inspection of the mirror chamfered portion has been performed by directly observing with an optical microscope after the mirror chamfering. However, this inspection method has very low sensitivity and could not detect minute burrs or polysilicon. In particular, because very small polysilicon remaining in the mirror chamfered portion before the epitaxial growth process could not be detected, this minute polysilicon also grew during the epitaxial growth process, resulting in enormous crystal grains, resulting in nodules at the edge. There is a problem that a silicon wafer having needle-like crystals and irregularities is produced.
[0006]
The present invention has been made in view of such a problem, and provides a method for inspecting a silicon wafer mirror chamfered portion that can detect surface abnormalities such as scratches, chips, and polysilicon residues in the silicon wafer mirror chamfered portion with extremely high sensitivity. For the purpose.
[0007]
[Means for Solving the Problems]
The present invention has been made to solve the above-mentioned problems, and the invention described in claim 1 is characterized in that a silicon wafer having a mirror chamfer is alkali-etched, and then the mirror chamfer is observed with a microscope. This is an inspection method for a wafer mirror chamfer.
[0008]
In alkali etching, the etching rate has a selectivity sensitive to the influence of the plane orientation of the silicon crystal surface. Therefore, even if there are surface abnormalities such as minute scratches, chips, or polysilicon residues in the chamfered portion of the wafer, the etching amount of these portions is sensitively different and the degree of surface roughness appears differently. That is, scratches, polysilicon residue, etc. existing on the surface of the silicon wafer chamfered portion are emphasized by alkali etching, and can be easily observed and detected with an optical microscope or an electron microscope with very high sensitivity.
[0009]
In this case, as described in claim 2 of the present invention, the alkali etching is preferably performed with an aqueous NaOH solution and / or an aqueous KOH solution.
These aqueous solutions have sufficient etching selectivity, exhibit the effects of the present invention, are easily available, and can be easily neutralized and detoxified, so that waste water treatment is also simple.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, although an embodiment of the present invention is described, the present invention is not limited to this.
Although the silicon wafer to be subjected to the inspection method of the present invention is mirror chamfered, any silicon wafer that has been mirror chamfered by any mirror chamfering method can be applied to the inspection method of the present invention. For example, a silicon wafer that has been mirror-finished by a conventional polishing method, etching method, or both can be inspected by the inspection method of the present invention.
[0011]
The mirror chamfering may be performed at any stage in the silicon wafer manufacturing process. For example, it is possible to chamfer a cylindrical ingot after cutting it into slices, and inspect the chamfered portion with the inspection method of the present invention. Further, after the polysilicon is grown on the wafer surface by chemical vapor deposition, mirror chamfering can be performed, and the mirror chamfered portion can be inspected by the inspection method of the present invention.
[0012]
The alkali etching is preferably an aqueous alkali solution, particularly an aqueous NaOH solution, an aqueous KOH solution, or a mixture thereof.
The etching rate is preferably 0.01 to 5 μm / min, particularly preferably 0.15 μm / min or less. By making the etching rate much smaller than the normal etching rate in this way, it is possible to produce selectivity selectively in the etching rate depending on the degree of surface abnormality such as scratches, burrs, and polysilicon residues. Differences occur in the degree of surface roughness, and detection with high sensitivity is possible with a microscope.
[0013]
The liquid temperature of aqueous alkali solution should just be 10-80 degreeC, for example. In particular, it is preferable to carry out at a room temperature of 15 to 25 ° C., because it does not require the trouble of temperature management by a heating facility, a temperature controller or the like.
The concentration of the aqueous alkali solution is preferably 1 to 60% by weight, particularly 10 to 20% by weight.
[0014]
Conventionally, since the etching rate of alkali etching is slow, the etching rate is increased by using a high temperature of 60 to 80 ° C. and a concentration of 40 to 60% by weight. However, in the present invention, conversely, by reducing the etching rate by lowering the temperature and / or concentration, selectivity can be produced in the etching rate according to the degree of surface abnormality.
[0015]
Alkaline etching is performed by immersing a silicon wafer in an alkaline aqueous solution. The dipping method may be a normal method. That is, the silicon wafer is placed in a fluororesin carrier and immersed in an alkaline aqueous solution. As the container for containing the alkaline aqueous solution, a vinyl chloride-based container is sufficient if it is not necessary to raise the temperature. For raising the temperature, a container such as quartz or pyrex is used. During the immersion, stirring may or may not be performed. This is because the alkaline aqueous solution does not cause uneven etching unless it is stirred as in the case of an acidic aqueous solution such as a seco solution or a mixed acid solution.
[0016]
The removal amount by etching is preferably 0.2 to 5 μm, particularly preferably 0.5 to 2 μm. If the etching amount is less than 0.2 μm, sufficient sensitivity for detection may not be obtained. Conversely, if the etching amount is more than 5 μm, there will be no residue or polysilicon residue. In consideration of etching time and the like, a practical range of 0.5 to 2 μm is preferable.
[0017]
After completion of the alkali etching, the silicon wafer is washed and dried as necessary, and the mirror chamfered portion is observed with a microscope. As a microscope, an optical microscope, a scanning electron microscope (SEM), etc. are preferable.
[0018]
【Example】
Hereinafter, the present invention will be specifically described with reference to Examples.
(Example)
Polysilicon is grown by chemical vapor deposition on each of three silicon wafers having a diameter of 200 mm, a surface orientation <100>, a conductivity type P type, and a resistivity of 10 Ωcm manufactured by the Czochralski method, and then chamfered. Was polished for 60 seconds, 90 seconds, and 150 seconds to obtain three silicon wafers having a mirror chamfer.
[0019]
On the other hand, an aqueous NaOH solution having a liquid temperature of 23 ° C. and a concentration of 10% by weight was placed in a vinyl chloride container. The above three types of silicon wafers contained in a fluororesin carrier were immersed in this and etched for 20 minutes without stirring. The etching amount was 0.5 μm. Then, each silicon wafer was washed and dried, and observed with an optical microscope (magnification 200).
[0020]
As a result of observation, the chamfered portion of the silicon wafer having the longest polishing time of 150 seconds was smooth, but as the polishing time was shortened to 90 seconds and 60 seconds, the chamfered portion of the silicon wafer was strongly streaked. It was observed that the polysilicon residual portion was selectively etched.
FIG. 1 shows a typical example of observations of 150 seconds polished and 60 seconds polished.
[0021]
(Comparative example)
The sample was observed with an optical microscope (magnification 200) in the same manner as in Example 1 except that alkali etching was not performed.
As a result of the observation, the chamfered portion of any silicon wafer was observed to be smooth regardless of the polishing time, and the polysilicon remaining portion could not be detected at all.
FIG. 2 shows a typical example of observations of 150 seconds polished and 60 seconds polished.
[0022]
The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention shows 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. Are included in the technical scope.
[0023]
For example, in the above-described embodiment, etching is performed mainly by immersing the entire silicon wafer in an alkaline aqueous solution. However, etching may be performed only on a peripheral portion of the silicon wafer, for example, a chamfered portion.
[0024]
【The invention's effect】
The method for inspecting a silicon wafer mirror chamfered portion of the present invention can easily and highly sensitively inspect the processing state of the chamfered portion. Therefore, not only a very small surface abnormality of the wafer chamfered portion can be detected, but also the chamfering polishing time which cannot be performed conventionally can be optimized, and the production efficiency can be improved. Further, since defective products can be completely detected, troubles in the subsequent process can be prevented, and the yield of device manufacturing can be improved.
[Brief description of the drawings]
FIG. 1 is an observation result diagram of an example.
(A) is a case where the polishing time is 150 seconds, and (b) is a case where the polishing time is 60 seconds.
FIG. 2 is an observation result diagram of a comparative example.
(A) is a case where the polishing time is 150 seconds, and (b) is a case where the polishing time is 60 seconds.

Claims (5)

After the polysilicon is grown on the wafer surface by chemical vapor deposition, the chamfered portion is mirror chamfered and the silicon wafer having the mirror chamfered portion is alkali-etched, and the streaky pattern on the mirror chamfered portion is observed with a microscope. A method for inspecting a silicon wafer mirror chamfered portion, wherein polysilicon residue is detected by observing.   2. The silicon wafer mirror chamfer inspection method according to claim 1, wherein the alkali etching is performed with an aqueous NaOH solution and / or an aqueous KOH solution.   The silicon wafer mirror chamfer inspection method according to claim 1 or 2, wherein an etching rate of the alkali etching is set to 0.01 to 5 µm / min.   4. The method for inspecting a silicon wafer mirror chamfered portion according to claim 1, wherein the temperature of the alkali aqueous solution of the alkali etching is set to 15 to 25 ° C. 5.   5. The method for inspecting a silicon wafer mirror chamfered portion according to claim 1, wherein an amount of removal by the alkali etching is 0.2 to 5 μm.

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