JP4671183B2 - Defect evaluation method for semiconductor wafer surface - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor wafer surface defect evaluation method for evaluating defects on a semiconductor wafer surface according to semiconductor wafer processing, and in particular, evaluates a semiconductor wafer surface defect based on a defect image acquired before semiconductor wafer processing. About.
[0002]
[Prior art]
Semiconductor wafers (hereinafter simply referred to as wafers) are manufactured through various wafer processing steps (for example, epitaxial growth, annealing, cleaning, thermal oxidation, polishing, etc.). However, defects may occur on the wafer surface during these wafer processing steps or during the transition of each wafer processing step. The term “defect” as used herein refers to general defects that can occur on the wafer surface, such as crystal defects, damage during wafer processing, scratches, dust, scratches, and pits.
[0003]
One method for evaluating defects on the wafer surface is to use an LPD counter. The LPD counter acquires information such as increase / decrease and distribution of the number of LPDs. However, it is necessary to acquire an image of a defect in order to specify the type of defect.
[0004]
There is a scanning electron microscope (SEM) as an apparatus for acquiring an image of a wafer surface. In this apparatus, the wafer surface is scanned with an electron beam, and the amount of electrons generated from the surface is measured. The measured amount of electrons is converted into a luminance signal and acquired as an image of a defect on the wafer surface.
[0005]
There is also an atomic force microscope (AFM) as an apparatus for acquiring an image of the wafer surface. In this apparatus, an atomic force acting between a minute probe and the wafer surface is detected, and the wafer surface is scanned with the probe so that the atomic force is constant. The probe is irradiated with laser light, and the reflected light is incident on the photodetector to detect the amount of light displacement. According to this apparatus, a defect image can be obtained in the same manner as in the SEM.
[0006]
Furthermore, there is a confocal laser microscope as an apparatus for acquiring an image of the wafer surface. In this apparatus, a laser beam is irradiated on the wafer surface, and reflected light is detected. There is a difference in light intensity between the reflected light when there is no defect on the wafer surface and the reflected light when there is a defect. When the difference is a certain value or more, it is determined that the portion is a defect, the defect coordinates are acquired, and an image of the defect is acquired. According to this apparatus, an image of a defect can be acquired and the position of the defect can be specified.
[0007]
For example, Patent Document 1 describes a technique for detecting defects that collect in a colony using a confocal laser microscope after a cleaning and drying process, and acquiring an image thereof.
[0008]
(Patent Document 1)
Japanese Patent Laid-Open No. 2002-76082 [Problems to be Solved by the Invention]
Usually, after performing a certain wafer processing, as a method of evaluating defects existing on the wafer surface, the defect is measured by the LPD counter, and based on the result (position information of the defect), a microscope, SEM, AFM, etc. are used. And observed the actual defect.
[0009]
However, such an evaluation method has the following problems.
[0010]
For example, in the epitaxial growth process, the degree of defects that existed before the epitaxial growth may be reduced after the epitaxial growth. The degree of defect here refers to the size and concentration. In such a case, a defect having a size smaller than the resolution of the LPD counter is naturally not detected by the LPD counter. Therefore, the defect having a size equal to or smaller than the resolution of the LPD counter has no position information, and cannot be actually observed with a microscope, SEM, AFM, or the like.
[0011]
In addition, electrodes are formed after the gate oxidation treatment step, and probe inspection is performed. In this probe inspection, the oxide film breakdown voltage of each electrode is measured, and an electrode having a deteriorated oxide film breakdown voltage is specified. It is believed that the deterioration of oxide breakdown voltage is affected by defects that existed on the wafer surface before electrode formation, but it is impossible to grasp the substance of the defects from the wafer on which the electrodes were formed. .
[0012]
As described above, the conventional evaluation method does not accurately evaluate defects, but is insufficient for elucidating the cause of defect occurrence and improving processes for reducing defects.
[0013]
The present invention has been made in view of such a situation, and it is an object of the present invention to identify the cause of a defect on the wafer surface and accurately evaluate the wafer.
[0022]
[Means, actions and effects for solving the problems]
The first invention is
In the semiconductor wafer surface defect evaluation method for evaluating defects on the semiconductor wafer surface according to the semiconductor wafer processing,
Detecting defects on the surface of the semiconductor wafer before processing the semiconductor wafer, obtaining pre-processing image information of the portion where the defect exists, and pre-processing step of acquiring pre-processing position information of the portion where the defect exists,
Processing steps for performing semiconductor wafer processing;
A post-processing step of detecting defects on the surface of the semiconductor wafer after processing the semiconductor wafer and obtaining post-processing position information of the portion where the defects exist;
An evaluation step of evaluating defects on the surface of the semiconductor wafer detected in the pre-processing step by observing the pre-processing image information corresponding to the pre-processing position information that matches the post-processing position information. Features .
According to the first invention , for example, defects on the wafer surface are detected before wafer processing such as gate oxidation. At this time, the position of the defect is acquired as pre-processing position information, and the image of the defect is acquired as pre-processing image information. After the wafer processing is executed, the position of the defect existing on the wafer surface is acquired as post-processing position information. For the pre-processing position information that matches the post-processing position information, the image of the corresponding pre-processing image information is observed.
[0023]
According to the first aspect of the present invention , it is possible to grasp the substance of a defect before wafer processing that causes a defect after wafer processing.
[0024]
The second invention is the first invention ,
The pre-process is performed using a confocal laser microscope that scans the entire surface of the wafer and acquires an image of a portion where a defect exists.
[0025]
When using a confocal laser microscope that scans the entire surface of the wafer and obtains an image of the part where the defect exists, it acquires the positional information of the defect using an LPD counter, etc., and acquires it using SEM, AFM, etc. The work is easier and the work time is shortened than when the defect image information is acquired based on the position information.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a defect evaluation method for a semiconductor wafer surface according to the present invention will be described below with reference to the drawings.
[0027]
The present invention is directed to a wafer having a mirror-finished surface. Further, since the present invention is a nondestructive inspection, it may be performed on a wafer arbitrarily extracted from a plurality of wafers, or may be performed on all wafers.
[0028]
FIG. 1 is a processing flow of a wafer surface defect evaluation method according to the first embodiment.
[0029]
Step 11 is a step of inspecting the wafer surface before wafer processing. In this process, the state of the wafer surface is inspected with a confocal laser microscope. The confocal laser microscope used here has a function of scanning the entire surface of the wafer to detect a defect, specifying the position of the defect, and capturing an image of the defect. The resolution of the image acquired by the confocal laser microscope is high, and the finer defects are detected as the performance of the confocal laser microscope is improved.
[0030]
The position of the detected defect is converted into data and acquired as a position information file. The position information file acquired here is “defect coordinate file-1”. The detected defect image is converted into data and acquired as an image information file. The image information file acquired here is “defect image file-1”. At this time, “defect coordinate file-1” and “defect image file-1” corresponding to a predetermined number (for example, 100 points) are acquired in descending order of defects. Note that “defect coordinate file-1” and “defect image file-1” of all defects may be acquired.
[0031]
Step 12 is a process for performing wafer processing. For example, epitaxial growth, annealing, cleaning, thermal oxidation, polishing, etc. are performed as wafer processing.
[0032]
Step 13 is a step of inspecting the wafer surface after the wafer processing. In this step, the state of the wafer surface is inspected with a confocal laser microscope as in step 11.
[0033]
The position of the detected defect is converted into data and acquired as a position information file. The position information file acquired here is referred to as “defect coordinate file-2”. The detected defect image is converted into data and acquired as an image information file. The image information file acquired here is “defect image file-2”. At this time, “defect coordinate file-2” and “defect image file-2” of a predetermined number (for example, 100 points) are acquired in descending order of defects. Note that “defect coordinate file-2” and “defect image file-2” of all defects may be acquired.
[0034]
Further, images of the wafer surface at all coordinates acquired as “defect coordinate file-1” are taken. The wafer surface image is converted into data and acquired as an image information file. The image information file acquired here is assumed to be “defective image file-1 ′”.
[0035]
Step 14 is a step of comparing the acquired “defect image file-1”, “defect image file-1 ′”, and “defect image file-2”. The “defect image file-1”, “defect image file-1 ′”, and “defect image file-2” images are displayed on the display device, and the respective images are compared. The comparison may be performed by an operator or may be performed using another device. A typical comparison method will be described with reference to FIGS.
[0036]
2A is a schematic diagram showing an image of “Defect Image File-1”, and FIG. 2B is a schematic diagram showing an image of “Defect Image File-1 ′”. FIG. 2A and FIG. 2B are images of the same point.
[0037]
The image 20 in FIG. 2A has a defect 21, but the image 20 ′ in FIG. 2B has no defect. From the above results, it can be seen that the defect disappeared by executing the wafer processing in step 12.
[0038]
3A is a schematic diagram showing an image of “Defect Image File-1”, and FIG. 3B is a schematic diagram showing an image of “Defect Image File-1 ′”. FIG. 3A and FIG. 3B are images of the same point.
[0039]
A defect 31 exists in the image 30 in FIG. 3A, and a defect 31 ′ exists in the image 30 ′ in FIG. Comparing the image 30 with the image 30 ′, the degree of the defect 31 ′ is smaller than the degree of the defect 31. From the above results, it can be seen that the degree of defects is reduced by executing the wafer processing in step 12.
[0040]
As described above, even when the defect existing before the wafer processing is changed to a fine defect that is not detected as a defect by the confocal laser microscope after the wafer processing, the image is surely acquired. That is, according to the present embodiment, it is possible to detect a defect that has not been detected when a wafer surface is inspected using a confocal laser microscope only after wafer processing as in the prior art. Since such defects can be evaluated, it can be said that defect evaluation of a wafer can be performed more accurately.
[0041]
FIG. 4 is a schematic diagram showing an image of “Defect image file-2”.
[0042]
A defect 41 exists in the image 40 of FIG. The “defect image file-1” that is the same as the defect 41 is not acquired before the wafer processing. From this, it can be seen that the defect 41 occurred in the portion where the defect did not exist before the wafer processing by executing the wafer processing in Step 12.
[0043]
As described above, when a defect that did not exist before the wafer processing exists after the wafer processing, it is considered that the wafer processing itself has a cause of the occurrence of the defect. That is, according to the present embodiment, the cause of the defect and the wafer processing to be improved can be specified. Further, the improvement method varies depending on the generated defect, and the optimal improvement method can be specified by analyzing the defect 41.
[0044]
It should be noted that the wafer surface defect evaluation method in the present embodiment can be performed without using a confocal laser microscope. For example, the coordinates of the defect may be acquired using an LPD counter, and an image of the acquired coordinate portion may be acquired using SEM or AFM. However, such a method requires a special technique and takes time as compared with the case of using a confocal laser microscope. Conversely, when using a confocal laser microscope, it can be said that the operation is easy and the operation time is shortened.
[0045]
FIG. 5 is a processing flow of the wafer surface defect evaluation method according to the second embodiment. Note that the wafer processing performed here is assumed to be gate oxidation processing.
[0046]
Step 51 is a step of inspecting the wafer surface before the oxidation treatment, and is the same as step 11 in FIG. Here, “defect coordinate file-1” and “defect image file-1” are acquired.
[0047]
Step 52 is a step of performing a gate oxidation process. An oxide film is formed on the wafer surface by gate oxidation.
[0048]
Step 53 is a step of inspecting the wafer surface after wafer processing. In this step, the state of the wafer surface is inspected by a confocal laser microscope as in step 51. Here, “defect coordinate file-2” and “defect image file-2” are acquired.
[0049]
Step 54 is a process of forming an electrode on the oxide film.
[0050]
Step 55 is a step of performing a probe inspection. As a result of the probe inspection, it is assumed that a defect exists before the electrode is formed at a position where an electrode having an oxide film withstand voltage equal to or lower than a predetermined voltage exists. The detected electrode position is converted into data and acquired as a position information file. The position information file acquired here is referred to as “defect coordinate file-3”.
[0051]
Step 55 is a step of evaluating defects existing on the wafer surface before the gate oxidation process based on the acquired “defect coordinate file-3”. “Defect image file-1” corresponding to “Defect coordinate file-1” that matches “Defect coordinate file-3” is referred to. The image of “Defect image file-1” is displayed on the display device and evaluated. The evaluation may be performed by an operator or may be performed using another device.
[0052]
In the present embodiment, as shown in the first embodiment, “defect coordinate file-1” and “defect image file-1”, “defect coordinate file-2”, and “defect image file-2” Changes in defects before and after the gate oxidation process have been confirmed. However, this confirmation is not essential in this embodiment. That is, step 53 may not be performed.
[0053]
Further, although the gate oxidation process has been described in the present embodiment, the present invention is not limited to this. For example, in the processing flow of FIG. 1 described as the first embodiment, “defect image file-1” corresponding to “defect coordinate file-1” that matches “defect coordinate file-2” is also referred to. This is the scope of the invention.
[0054]
According to the present embodiment, it is possible to grasp the substance of defects before wafer processing that cause defects after wafer processing.
[0055]
It should be noted that the wafer surface defect evaluation method in the present embodiment can be performed without using a confocal laser microscope. For example, before wafer processing, the coordinates of the defect may be acquired using an LPD counter, and an image of the acquired coordinate portion may be acquired using SEM or AFM. However, such a method requires a special technique and takes time as compared with the case of using a confocal laser microscope. Conversely, when using a confocal laser microscope, it can be said that the operation is easy and the operation time is shortened.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a processing flow according to a first embodiment;
FIG. 2A is a schematic diagram showing an image of “Defect Image File-1”, and FIG. 2B is a schematic diagram showing an image of “Defect Image File-1 ′”.
FIG. 3A is a schematic diagram showing an image of “Defect Image File-1”, and FIG. 3B is a schematic diagram showing an image of “Defect Image File-1 ′”.
FIG. 4 is a schematic diagram showing an image of “Defect image file-2”.
FIG. 5 is a diagram illustrating a processing flow of the second embodiment;
[Explanation of symbols]
20, 20 ', 30, 30', 40 Image 21, 31, 32, 41 Defect

Claims (2)

In the semiconductor wafer surface defect evaluation method for evaluating defects on the semiconductor wafer surface according to the semiconductor wafer processing,
Detecting defects on the surface of the semiconductor wafer before processing the semiconductor wafer, obtaining pre-processing image information of the portion where the defect exists, and pre-processing step of acquiring pre-processing position information of the portion where the defect exists,
Processing steps for performing semiconductor wafer processing;
A post-processing step of detecting defects on the surface of the semiconductor wafer after processing the semiconductor wafer and obtaining post-processing position information of the portion where the defects exist;
An evaluation step of evaluating defects on the surface of the semiconductor wafer detected in the pre-processing step by observing the pre-processing image information corresponding to the pre-processing position information that matches the post-processing position information. A method for evaluating defects on the surface of a semiconductor wafer. The defect evaluation method for a semiconductor wafer surface according to claim 1, wherein the pre-processing step is performed using a confocal laser microscope that scans the entire surface of the wafer to acquire an image of a portion where a defect exists.

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