JPH11145088A - Conformity evaluating method of semiconductor wafer polishing process using silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conformity evaluating method of mirror surface polishing process which is used for improving deterioration of oxide film withstand voltage which is to be caused by defect (fine scratch) introduced in a mirror surface polishing process of a silicon wafer. SOLUTION: An evaluating method is provided with a first process S-1 performing HF cleaning to an epitaxial wafer where SC-1 cleaning is performed after mirror surface polishing process is performed or a silicon wafer obtained by an FZ method, a second process S-2 performing the SC-1 cleaning, a third process S-3 measuring LPD(Light Point Defects) existing on the surface of the silicon wafer by using a particle counter, and a fourth process S-4 estimating the quality of the mirror surface polishing process on the basis of the above measured result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for evaluating the quality of mirror polishing of a semiconductor wafer using a silicon wafer.

[0002]

2. Description of the Related Art The main method of currently performing a mirror polishing process of a silicon wafer, that is, a process from chemical polishing to cleaning through mirror polishing, using the obtained silicon wafer is as follows. It is on the street. (1) Flatness measurement for evaluating surface droop caused by chemical polishing or mirror polishing based on deviation from a reference plane and a focal plane. (2) Appearance inspection for evaluating scratches introduced in the mirror polishing step, which can be visually confirmed under a condensing lamp. (3) As for evaluating the mirror polishing step and the cleaning step,
OSF inspection (evaluation of defects such as scratches caused by mechanical causes such as mirror polishing or ultrasonic cleaning as OSF by oxidative heat treatment), oxide film breakdown voltage measurement (evaluation of complex elements such as surface scratches, distortion, surface contamination, etc.) , Particle measurement (evaluation of dust adhering during polishing and cleaning), haze measurement (irradiation of condensing lamp on wafer to evaluate surface fogging), and micro roughness measurement (microscopic measurement due to etching during polishing and cleaning) Evaluate the swell). (4) Evaluation of surface cleanliness (evaluation of the degree of impurity contamination on the wafer surface) for evaluating the cleaning step.

[0003]

However, merely measuring and evaluating the flatness, cleanliness, etc. of a silicon wafer can be used to evaluate the presence or absence of a defect in the mirror-polishing process that may cause deterioration of the oxide film breakdown voltage. It is impossible to do. In particular, it is known that minute scratches formed on the silicon wafer in the mirror polishing process (including cleaning after polishing) are defects that contribute to deterioration of the oxide film breakdown voltage. Since light scattering does not occur even if it is performed, its detection is extremely difficult.

The present invention has been made in view of the above-mentioned conventional problems, and has established a method for simply detecting and evaluating processing defects such as polishing flaws, which have been conventionally difficult to detect. It is an object of the present invention to provide a method for evaluating the quality of a polishing process performed on a semiconductor wafer, particularly a silicon wafer, which can contribute to an improvement in film breakdown voltage.

[0005]

In order to achieve the above object, a first method of evaluating the quality of a semiconductor wafer polishing process using a silicon wafer according to the present invention is an epitaxial wafer which has been subjected to mirror polishing and cleaning. FZ
A first step of cleaning a silicon wafer by HF, a second step of cleaning with a SC-1 cleaning solution, and a second step of measuring the number of LPDs (Light Point Defects) detected on the surface of the wafer by a particle counter. It is characterized by comprising three steps and a fourth step of evaluating the quality of mirror polishing based on the measurement result. Conventionally, silicon wafers have been cleaned using an SC-1 cleaning solution immediately after mirror polishing, but with this cleaning alone, minute scratches formed when the silicon wafer is mirror-polished do not scatter light, so a particle counter is used. Not detectable. However, when the silicon wafer is subjected to HF cleaning as described above, the oxide on the surface is removed, and the SC-1 cleaning further etches the micro-scratch to enlarge and form pits, so that detection by a particle counter is possible. Becomes Therefore,
By counting the number of LPDs with a particle counter, the density of processing defects can be grasped, and the quality of mirror polishing can be evaluated.

A second method of evaluating the quality of a semiconductor wafer polishing process using a silicon wafer according to the present invention is as follows.
A first step of measuring, with a particle counter, the number of LPDs detected on the surface of a silicon wafer by the CZ method which has been subjected to mirror polishing and cleaning, a second step of cleaning the wafer with HF, and SC -1 The third step of cleaning with a cleaning liquid, the fourth step of measuring the number of LPDs detected on the surface of the wafer with a particle counter, and the difference between the number of LPDs measured in the first and fourth steps is calculated. The method is characterized by comprising a fifth step and a sixth step of evaluating the quality of mirror polishing based on the calculated difference in the number of LPDs. A silicon wafer obtained by slicing an ingot of single crystal silicon by the CZ method has grown generated during the process of growing a single crystal.
-In defects are included, and pits due to COP (Crystal Originated Particle) are generated in SC-1 cleaning after mirror polishing. Therefore, this method uses LPD in the first step.
The number, that is, the number of pits of the COP is counted. When this silicon wafer is subjected to HF cleaning, oxides on the surface are removed, and further SC-1 cleaning is performed to etch and expand minute scratches due to polishing. Therefore, the number of LPDs measured in the fourth step is equal to the number of pits due to minute scratches. This is the total number of pits by COP. Therefore, the number of pits due to minute scratches is clarified by calculating the difference between them, and the quality of the mirror polishing can be evaluated from the density.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a method for evaluating the quality of polishing a semiconductor wafer using a silicon wafer according to the present invention will be described with reference to the drawings.
Epitaxial wafers or silicon wafers produced by the FZ method have no grown-in defects, especially COPs, as observed in silicon wafers produced by the CZ method, and
The cleaning and the SC-1 cleaning have an advantage that only defects caused by mirror polishing are detected. Therefore, as shown in FIG. 1, the evaluation procedure in this evaluation method is to perform mirror polishing on an epitaxial wafer or a silicon wafer by the FZ method on a polishing processing line to be evaluated, and perform SC-1 cleaning. Used as a silicon wafer to be evaluated. First, in the first step (S-1), the silicon wafer to be evaluated is immersed in 10% HF for 5 minutes or more to be washed, and then in the second step (S-2), it is washed with the SC-1 cleaning solution for about 10 minutes. . The HF is at room temperature and SC-
One cleaning solution is at a temperature of 70C to 80C. Then the third
In step (S-3), the number of LPDs generated on the surface of the silicon wafer to be evaluated is counted by a particle counter. This value is the number of defects caused by mirror polishing. Then, in a fourth step (S-4), the quality of the mirror polishing is evaluated by comparing the number of defects calculated from the number of defects with a predetermined allowable number of defects. The allowable number of defects may be determined as appropriate depending on the required wafer quality, but need not be specified if a relative comparison is made for each polishing apparatus.

[0008] As an experimental example for evaluating the quality of the mirror polishing process, an epitaxial wafer having a diameter of 6 inches is mirror-polished on a polishing line to be evaluated, and the LPD value is evaluated by applying the evaluation method of the present invention. That is, the number of defects caused by mirror polishing was obtained. The concentration of HF was set to 10%, and the immersion time was set to 5 minutes or 2/30. Also, H
The time of SC-1 cleaning performed after F cleaning is 1 minute, 10 minutes 2
Standard. In the following LPD measurement using a particle counter, pits of 0.12 μm or more were targeted, but the present invention is not limited to this.

The surface of the epitaxial wafer to be evaluated was measured with a particle counter, and the number of LPDs was determined. Then, the number of LPDs was compared with a predetermined allowable number of LPDs to evaluate the quality of the mirror polishing. Furthermore, LP
The coordinate position where D was recognized was observed by SEM (scanning electron microscope) and AFM (atomic force microscope). Observation by SEM was performed at an accelerating voltage of 5 kV.
Analysis by FM was performed.

FIG. 2 shows the number of LPDs of not less than 0.12 μm detected by the particle counter after the HF cleaning + SC-1 cleaning. Note that LPD is not detected by HF cleaning alone regardless of time. HF cleaning time from 5 minutes to 30
When extended to minutes, the number of LPDs increased. Further, even if the HF cleaning time is the same, the SC-1 cleaning time is increased from 1 minute to 10 minutes.
When the number of LPDs is extended to minutes, the number of LPDs increases. This is H
In the F cleaning step, pits (hereinafter, referred to as HF pits) caused by polishing scratches or scratches can be formed, but the size does not reach a size that can be detected as LPD.
This is because the HF pits are etched and the LPD size increases through the SC-1 cleaning step. The observation range by the SEM and the AFM is significantly smaller than the observation range by the particle counter. However, when the HF pit detected by the particle counter is observed by the SEM, the AFM, or the like, as shown in FIG.
It can be seen that it has a linear shape different from the OP.

According to SEM observation, HF pits having a length exceeding 5 μm were found to be SC-SC irrespective of the HF cleaning time.
This was observed when one washing time was 10 minutes. This indicates that the influence of SC-1 cleaning is dominant on the size (length) of the HF pit. That is, H
The determination of the density of the F pit depends on the HF cleaning time,
The determination of the size that can be detected as depends on the SC-1 wash time. Therefore, in this evaluation method, it is preferable that the cleaning time with 10% HF is set to 5 minutes or more and 30 minutes or less, and SC-1 cleaning is performed for about 10 minutes.

When the quality of a mirror polishing line for a silicon wafer is evaluated, it is possible to use a silicon wafer by the CZ method instead of the epitaxial wafer polished on the line to be evaluated as described above. This will be described as an example. In the case of using a silicon wafer by the CZ method, as shown in FIG. 4, in order to exclude the influence of the COP already detected by the SC-1 cleaning immediately after the mirror polishing, as shown in FIG.
C-1 The first step (S
In the step -1), the first LPD measurement by the particle counter is performed. The measured value at this time is defined as LPD1. LPD
The number included in 1 is mainly the number of COPs, and includes a small number of particles adhering to the wafer surface.

Next, as in the case of the epitaxial wafer, cleaning with HF in the second step (S-2) and cleaning with the SC-1 cleaning liquid in the third step (S-3) are performed.
In a fourth step (S-4), a second LPD measurement is performed by a particle counter. The measured value at this time is LPD2. The LPD 2 includes the number of pit-like defects caused by scratches or minute scratches formed in the polishing process together with the COP and the like. Then, the fifth step (S-
By subtracting LPD1 from LPD2 in 5), the number of defects caused by polishing is obtained. Then, the sixth step (S-
In 6), the quality of the mirror polishing is evaluated by comparing the number of defects with a predetermined allowable number of defects. Of course, in the case of relative comparison, it is not necessary to determine the allowable number of defects.

FIG. 5 shows an example of the result of applying the present invention. In any of the polishing processes A, B and C, HF
If cleaning + SC-1 cleaning is not performed, the number of LPDs is 2 × 10 ²
Although about the same value was shown, by performing HF cleaning + SC-1 cleaning, a processing difference between polishing apparatuses becomes clear.

[0015]

As described above, according to the present invention, a semiconductor wafer which has conventionally been difficult to detect, particularly,
It is possible to easily detect minute defects caused by mirror polishing of a silicon wafer and evaluate the quality of the mirror polishing process based on the result. By improving the mirror polishing process based on the evaluation result, the oxide film breakdown voltage of the silicon wafer can be improved.

[Brief description of the drawings]

FIG. 1 is a process chart showing an evaluation procedure of a first embodiment of the present invention.

FIG. 2 is a diagram showing the number of detected LPDs according to cleaning conditions of HF and SC-1.

FIG. 3 is a diagram illustrating an example of an image obtained by observing an LPD with an AFM.

FIG. 4 is a process chart showing an evaluation procedure according to a second embodiment of the present invention.

FIG. 5 is a diagram showing LPD numbers when HF cleaning + SC-1 cleaning is not performed and when HF cleaning + SC-1 cleaning is performed.

Claims (2)

[Claims] 1. A first step of cleaning an epitaxial wafer or a silicon wafer by the FZ method, which has been subjected to mirror polishing and cleaning processing, with HF, a second step of cleaning with an SC-1 cleaning liquid, L to be detected
A silicon wafer comprising a third step of measuring the number of PDs (Light Point Defects) with a particle counter and a fourth step of evaluating the quality of mirror polishing based on the measurement result. The quality evaluation method of the used semiconductor wafer polishing process. 2. CZ subjected to mirror polishing and cleaning
Measurement of the number of LPDs detected on the surface of a silicon wafer by a particle counter
A second step of cleaning the wafer with HF;
C-1 The third step of cleaning with a cleaning liquid, the fourth step of measuring the number of LPDs detected on the surface of the wafer with a particle counter, and calculating the difference between the number of LPDs measured in the first and fourth steps. And the calculated LPD
The sixth to evaluate the quality of mirror polishing based on the difference in number
And a semiconductor wafer polishing process using a silicon wafer.