JP2013238534A - Wafer surface evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method that enables accurate evaluations in the case of performing evaluations by applying a laser beam and detecting the scattered light from a wafer surface with a detector.SOLUTION: Provided is a method that performs evaluations of a wafer surface by applying a laser beam to the wafer surface and detecting the scattered light from the wafer surface with a detector. In the method, the plurality of detectors are arranged to detect the scattered light respectively, and on the basis of their respective detection results, the evaluations are performed.

Description

  The present invention relates to a method for evaluating a wafer surface, and more particularly to a method for irradiating a wafer surface with laser light and evaluating the wafer surface from the scattered light.

  With the miniaturization of devices, adverse effects on devices due to foreign matters such as particles adhering to the surface of a semiconductor wafer can no longer be ignored. For this reason, it is necessary to prevent the generation of these foreign substances and to accurately evaluate the foreign substances on the wafer surface.

For example, a particle counter is often used when evaluating the wafer surface.
In general, a particle counter irradiates a wafer surface with laser light and detects scattered light generated from the surface to measure foreign matter or the like.

  In addition, other than foreign substances (for example, scratches, crystal defects, etc.) are also detected, and thus the detected ones are usually classified as LPD (Light Point Defect) instead of particles.

  In this way, the scattered light is detected and the bright spot is detected as LPD. However, the scattered light is not uniformly scattered in all directions, but the wavelength of the laser light, the size of the defect, The direction changes depending on the density. In the case of scratches, the scattering in the direction parallel to the scratch direction is weak and the scattering in the vertical direction is strong (see Patent Document 1).

JP 2009-236519 A

  As described above, the wafer surface is evaluated using laser light by a particle counter or the like. At that time, if the particles are very close (overlapping), there is a function to combine large particles as if they were measured twice, and a function to judge a flaw when particles are continuous. Generally, it is added to the particle counter.

  As a result of intensive research on the conventional detection method and evaluation method by the present inventors, there is actually no problem in evaluation even though foreign matters such as particles are attached and a problem exists. It turned out that it might be judged.

  The present invention has been made in view of the above problems, and in the case where evaluation is performed by irradiating laser light and detecting scattered light from the wafer surface with a detector, the evaluation can be performed with high accuracy. It aims to provide a possible method.

  In order to achieve the above object, the present invention is a method for evaluating a wafer surface by irradiating a laser beam on the wafer surface and detecting scattered light from the wafer surface using a detector, wherein the detector A wafer surface evaluation method is provided, in which a plurality of detectors are arranged, scattered light is detected using the plurality of detectors, and evaluation is performed based on each detection result.

With such an evaluation method of the present invention, by disposing a plurality of detectors and detecting scattered light, scattered light that is difficult to detect with one detector can be detected with another detector. As a result, scattered light can be detected with high sensitivity, and the wafer surface can be evaluated with high accuracy.
Conventionally, even when scattered light is detected using a plurality of detectors, evaluation is performed by summing up the respective detection results or taking the average of them.
On the other hand, in the evaluation method of the present invention, since the evaluation is performed based on the detection results of each of the plurality of detectors, the feature of each detection result is faded by summing or averaging as in the past Can prevent evaluation. That is, the evaluation can be performed in a state before the characteristic detection result for each detector is thinned, and the evaluation can be performed with higher sensitivity and higher accuracy than in the past.

At this time, when detecting the scattered light, it is possible to detect the scattered light scattered by any of scratches, foreign matter, crystal defects, and haze on the wafer surface.
These are often cited as evaluation items of the wafer surface, and the present invention can evaluate them with higher accuracy than before.

  As described above, according to the wafer surface evaluation method of the present invention, scattered light can be detected with high sensitivity, and the wafer surface can be evaluated with higher accuracy than before.

It is the schematic which shows an example of the evaluation apparatus of a wafer surface. (A) Side view in case of oblique incidence method, (B) Top view of a part of the apparatus, (C) Side view in case of vertical incidence method. It is a flowchart which shows an example of the evaluation method of the wafer surface in this invention. It is a measurement figure which shows the detection result for every detector 3L1-3L6 of Example 1. FIG. It is a measurement figure which shows the detection result for every detector 3H1-3H4 of Example 1. FIG. It is a measurement figure which shows the detection result for every detector 3L1-3L6 of Example 2. FIG. It is a measurement figure which shows the detection result for every detector 3H1-3H4 of Example 2. FIG. It is a measurement figure which shows the detection result for every detector of Example 3.

Hereinafter, the present invention will be described more specifically.
Conventionally, the wafer surface is evaluated using a particle counter or the like. Some of these use multiple detectors, but it may be judged that there is no problem in the evaluation even though there are problems such as particles adhering. It was. As a result of further diligent research conducted by the present inventors, conventionally, even if the scattered light is detected using a plurality of detectors, the evaluation is based on the sum and average of the detection results, As a result, it has been found that the characteristics of each detection result are diminished and accurate evaluation cannot be performed as described above. In view of this, the present inventors have found that it is important to perform evaluation based on characteristic detection results from each detector, and have completed the present invention.

Hereinafter, the wafer surface evaluation method of the present invention will be described in detail as an example of an embodiment with reference to the drawings. However, the present invention is not limited to this.
FIG. 1 shows an example of a wafer surface evaluation apparatus that can be used in the wafer surface evaluation method of the present invention. (A) is a side view in the case of the oblique incidence method, and (B) is a top view of a part of the apparatus. It is a side view in case (C) is a normal incidence system.
This evaluation apparatus 1 mainly includes a laser oscillator 2 for irradiating the surface of the wafer W to be evaluated with laser light, and a detector 3 for detecting scattered light scattered by particles or the like. And a computer 4 for data processing and a stage 5 for mounting the wafer W.

The laser oscillator 2 is not particularly limited as long as it can irradiate the surface of the wafer W with laser light. For example, a conventional one can be used.
Further, the arrangement of the laser oscillator 2 with respect to the wafer W, that is, the irradiation position of the laser beam is not particularly limited. It is movable and the arrangement position can be adjusted as appropriate. For example, as shown in FIG. 1A, it can be disposed at a position obliquely above the wafer W, that is, at a position where the incident angle of the laser beam is low (oblique incidence method).
Alternatively, as shown in FIG. 1C, the laser beam can be arranged directly above the wafer W so that the laser beam can be incident perpendicularly to the surface of the wafer W (vertical incidence method).

The detector 3 is not particularly limited as long as it can detect scattered light from the surface of the wafer W. For example, a conventional one can be used.
The number of detectors 3 may be plural, and the number is not particularly limited. As an example, 10 units (3L1 to 3L6, 3H1 to 3H4) are arranged in FIG.
By increasing the number, the scattered light can be detected from various angles, the scattered light can be detected with high sensitivity, and more information about the surface of the wafer W can be obtained and evaluated with higher accuracy. it can. The number can be determined as appropriate in consideration of the cost.

Further, the arrangement position is not particularly limited. In the example shown in FIG. 1, four units (3H1 to 3H4) are arranged at a high angle position with respect to the surface of the wafer W, and six units (3L1 to 3L6) are arranged at a low angle position.
Here, as shown in FIG. 1B, 3L1, 3L2, and 3L3 detectors are arranged in order from the irradiation side on the right side in the laser light irradiation direction at a low angle position. In addition, detectors 3L6, 3L5, and 3L4 are arranged on the left side in the laser light irradiation direction in order from the irradiation side.
Further, at the high angle position, 3H1 is disposed on the laser beam irradiation side, 3H3 is disposed on the opposite side, 3H2 is disposed on the right side along the irradiation direction, and 3H4 is disposed on the left side.

  In addition, the computer 4 is connected to the detector 3, acquires a signal from the detector 3 that has detected the scattered light, processes the data, and obtains a detection result for each of the detectors 3L1 to 3L6 and 3H1 to 3H4. Anything that can do. In addition to the respective detection results, a result obtained by summing (or averaging) the respective detection results may be obtained.

  Further, the stage 5 can be rotated or slid, and is not particularly limited as long as it can rotate or slide the wafer W placed thereon. For example, a conventional one can be used.

Next, the wafer surface evaluation method of the present invention using the evaluation apparatus 1 will be described.
FIG. 2 is a flowchart showing an example of this evaluation method.
(Step 1: Detection of scattered light using a plurality of detectors)
First, a wafer W to be evaluated is placed on the stage 5 and prepared.
Then, a laser beam is applied to a predetermined position of the wafer W from the laser oscillator 2 disposed obliquely above the wafer W. The stage 5 scans the entire surface of the wafer with laser light by rotating or sliding the wafer W. Here, the laser oscillator 2 is disposed obliquely above the surface of the wafer W to irradiate the laser beam. Instead, the laser oscillator 2 is disposed immediately above the wafer W so that the laser beam is perpendicular to the wafer surface. A method of irradiating can also be used and can be determined appropriately each time.

The scattered light from the surface of the wafer W is detected using a plurality of detectors 3 (3L1-3L6, 3H1-3H4) arranged.
Examples of the scattered light include scratches, foreign matters such as particles attached to the wafer surface, and light scattered by crystal defects. Moreover, it is scattered by the haze which is a wave | undulation with a periodicity of about several to several tens of nm on the wafer surface. In the present invention, it is possible to evaluate the causes of scattering with higher sensitivity and higher accuracy.

(Process 2: Evaluation from each detection result)
The scattered light data detected by each of the detectors 3L1 to 3L6 and 3H1 to 3H4 is sent to the computer 4 for data processing, and a detection result is obtained for each detector. Then, the wafer surface is evaluated based on each detection result.
In the present invention, the scattered light is detected by using the plurality of detectors 3 as described above, and the wafer surface is evaluated based on the detection result for each detector. Therefore, an extremely accurate evaluation can be obtained.

  In the conventional method, since the detection results of the respective detectors are summed or averaged, characteristic data from each of the detectors has been diluted. In other words, even if data related to scattered light, that is, scratches, is actually detected by each detector, the final data is that some of the data has faded or has disappeared. was there.

  However, in the present invention, rather than performing evaluation based on data in which characteristic data have faded or disappeared due to summation and averaging as in the prior art, each detector 3L1-3L6, 3H1-3H4 detected with high sensitivity. Since the evaluation is performed based on characteristic data, the evaluation can be performed with higher accuracy.

  In addition, the result which totaled or averaged each detection result can also be obtained as reference data. As described above, the surface of the wafer W is evaluated from each detection result, and further, the evaluation can be performed by comparing with the reference data. Thereby, the evaluation regarding the wafer surface can be further enhanced.

EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated more concretely, this invention is not limited to these.
Example 1
Using the evaluation apparatus 1 (LS6800UV manufactured by Hitachi High-Technology Corporation) shown in FIG. 1, the wafer surface was evaluated for scratches, foreign matter, and crystal defects. The wafer to be evaluated was obliquely irradiated with laser light, and scattered light was detected by a plurality of detectors 3 (3L1-3L6, 3H1-3H4). Then, the data was processed by the computer 4, and the detection results were obtained for each detector and evaluated.

FIG. 3 shows the detection results for each of the detectors 3L1 to 3L6. In the center, the sum of the detection results from the detectors 3L1 to 3L6 is also shown for reference.
Moreover, the detection result for every detector 3H1-3H4 is shown in FIG. In the center, the sum of the detection results from the detectors 3H1 to 3H4 is also shown for reference.

  3 and 4, it can be seen that a characteristic detection result is obtained for each detection position, that is, for each detector. By detecting from a plurality of directions, it can be seen that even a scratch that is difficult to detect only from one direction can be detected from another direction.

  Since the laser light scattering direction changes depending on the direction of the surface of the wafer, such as a scratch, the scratches at different angles are detected depending on the position of the detector. Since the wafer slides while being rotated by the stage 5, the detectors 3L1 to 3L3 and 3H2 capture clockwise scratches, and the detectors 3L4 to 3L6 and 3H4 capture counterclockwise scratches.

  In addition, the detectors 3L1, 3L6, 3H1 mainly detect scratches in the circumferential direction in order to detect scratches in the direction in which the laser light incident on the wafer is scattered backward (that is, on the irradiation side). . The detectors 3L3, 3L4, and 3H3 capture a radial scratch. Further, the detectors 3L2, 3L5, 3H2, and 3H4 capture a scratch at an intermediate angle.

Here, a more detailed evaluation is performed with respect to FIG.
Comparing the summation results with the detection results for each detector, it was found that some of the flaws detected by each detector disappeared in the summation results.
In each detection result of FIG. 3, scratches or the like that have disappeared in the summation result are indicated by arrows surrounded by a square. It can be seen that at least one piece of data from the detector 3L1, such as two places in 3L2, two places in 3L3, one place in 3L4, and two places in 3L5, is lost in the summation result.
In addition, since the gain setting of 3L6 was too large, noise was detected and correct scratch data could not be obtained.

  Further, in FIG. 4, when the summation result and the detection result for each detector are compared, at least one data from the detector 3H1, one place in 3H2, and two places in 3H4, such as scratches, It turns out that it has disappeared.

  In this way, scratches that are missed because they have disappeared in the summation result can be easily detected without being overlooked by the evaluation method of the present invention. Since the evaluation is performed based on the result of high sensitivity detected from each detector, it is possible to evaluate the scratches on the wafer surface with higher accuracy.

(Example 2)
Evaluation was performed in the same manner as in Example 1 except that the wafer to be evaluated was vertically irradiated with laser light from directly above.

FIG. 5 shows detection results for each of the detectors 3L1 to 3L6. In the center, the sum of the detection results from the detectors 3L1 to 3L6 is also shown for reference.
Moreover, the detection result for every detector 3H1-3H4 is shown in FIG. In the center, the sum of the detection results from the detectors 3H1 to 3H4 is also shown for reference.

As shown in FIGS. 5 and 6, characteristic detection results were obtained for each detector.
Moreover, in FIG. 5, even if the sum total result and the detection result for each detector are compared, there is no particular difference. Although it is possible to evaluate each detection result with high accuracy, in the case of the present detection conditions of scattered light (wafer, normal incidence, oblique detection), there was no particular disappearance of scratches in the total result. it is conceivable that.

On the other hand, in FIG. 6, when the summation result and the detection result for each detector are compared, the detection result of the detector 3H4 clearly has more scratches than the summation result. It can be seen that a part of data such as scratches detected by the detector 3H4 disappears in the summation result.
In this way, scratches and the like that were not captured by the evaluation based on the summation result as in the prior art can be captured by the evaluation method of the present invention, and the evaluation can be performed with higher accuracy.

(Example 3)
The haze was evaluated using the evaluation apparatus 1 shown in FIG. Five wafers of samples A to E were prepared as evaluation targets. These have different polishing conditions. These wafers were obliquely irradiated with laser light, and scattered light was detected by a plurality of detectors 3 (3L1 to 3L6, 3H1 to 3H4). Then, the data was processed by the computer 4, and the detection results were obtained for each detector and evaluated.

  FIG. 7 shows detection results for each of the detectors 3L1 to 3L6 and 3H1 to 3H4. For reference, the total result (usually MAP) as in the conventional method is also shown.

  First, in the normal map, there is no significant difference between samples A to E. Therefore, in the conventional method, there is not much difference in evaluation between samples A to E.

However, looking at the detection results for each detector (3L2, 3H2, 3H4 among them), it can be seen that there is a large difference in haze for each sample.
For example, in the detection results of all the sample detectors 3H2, the sample A detector 3L2, the sample B detector 3H4, and the sample E detector 3H4, the haze is too strong and overflows during measurement. In this case, since the measurement is performed from the center toward the outer periphery, the smaller the filled circle is, the faster the overflow occurs, and the wafer has a poor haze. Thus, in the present invention, since haze is evaluated based on each characteristic detection result, the difference between samples A to E can be evaluated with high accuracy.

  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.

1 ... Wafer surface evaluation device, 2 ... Laser oscillator,
3, 3L1-3L6, 3H1-3H4 ... detector, 4 ... computer,
5 ... Stage.

Claims (2)

A method for evaluating a wafer surface by irradiating a wafer surface with laser light and detecting scattered light from the wafer surface using a detector,
A method for evaluating a wafer surface, wherein a plurality of the detectors are arranged, scattered light is detected using the plurality of detectors, and evaluation is performed based on each detection result.   2. The method for evaluating a wafer surface according to claim 1, wherein when the scattered light is detected, scattered light scattered by any one of a scratch, foreign matter, crystal defect, and haze on the wafer surface is detected.

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