JP2964974B2 - Foreign matter inspection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter inspection method, and more particularly to a semiconductor wafer inspection method using laser light.

[0002]

2. Description of the Related Art A conventional method of inspecting a semiconductor device of this type will be described with reference to FIG.

FIG. 4A is a scattered light intensity waveform diagram obtained by scanning the surface of a substrate with a laser beam using a foreign matter inspection device, wherein the scattered light intensity detected on the vertical axis is plotted on the horizontal axis. Time (scan time) is shown, and five waveforms (a) to (e) are shown.

FIG. 4B shows an example of a result obtained by classifying the waveform of FIG. 4A by an arbitrary intensity of scattered light (the peak value of each waveform, the same applies hereinafter). FIG. 2 is a configuration diagram of an inspection apparatus for obtaining these scattered light intensity acquisition waveforms.

Referring to FIG. 2, a laser beam 1 output from a laser 3 is perpendicular to a surface of a semiconductor wafer (hereinafter, referred to as a wafer) 5 which is linearly and rotationally moved (spiral-shaped) by a substrate driving unit 7. Irradiated.

When there is no foreign matter 6 on the wafer 5, the laser light 1 which is vertically incident on the wafer surface is totally reflected and does not involve scattering of the laser light. Therefore, the light detector 4 attached at an arbitrary angle from the wafer surface does not detect light.

When there is a foreign substance 6 on the wafer 5, the laser beam 1 which is vertically incident on the wafer surface is scattered by the foreign substance 6, and is detected by the photodetector 4 as a scattered light intensity. FIG. 4 shows a scattered light intensity change waveform of the scattered light intensity obtained by continuously scanning the entire surface of the wafer 5 with the laser light 1 in a spiral shape.
(A).

In this type of conventional inspection apparatus, the intensity of the scattered light obtained in each waveform is adjusted to an arbitrary level (L1, L2,
L3), the scattered light was classified as a large foreign substance when the intensity of the scattered light was large, and as a small foreign substance when the intensity of the scattered light was small.

When the intensity of the scattered light is classified according to the magnitude of the foreign matter based on FIG. 4A, the intensity X of the scattered light is L1 <X <
The number of foreign substances (L1 level) corresponding to L2 is two. Similarly, a foreign substance (L) whose scattered light intensity X satisfies L2 <X <L3
2 levels) will be 2 months. The foreign matter at the L3 level has a scattered light intensity X of L3 <X and is zero. FIG. 4B shows these results.

In the case of a conventional inspection apparatus of this type, the size of a foreign substance is expressed only by the intensity of the scattered light. As a result, the difference in scattering rate depending on the type of foreign matter has made the relationship between the intensity of scattered light and the size of foreign matter unclear.

For example, when a laser beam is irradiated in the same situation, the intensity of the scattered light of the silicon fragment becomes larger than that of the resin fragment even if the size is the same due to the difference in the scattering rate.

Therefore, if the size classification of the foreign matter based only on the intensity of the scattered light is performed, the classification based on the size of the foreign matter becomes inaccurate when the foreign matter having a different scattering rate is mixed.

Next, a conventional technique disclosed in Japanese Patent Application Laid-Open No. 62-121339 entitled "Surface Defect Inspection Apparatus" will be described. This is an apparatus for determining the size of a foreign substance on the same basis without depending on the optical properties of the substrate material to which the foreign substance is attached. Therefore, since the difference in the scattering rate depending on the kind of the foreign matter is not particularly considered, it is impossible to correctly determine the size of the foreign matter having a different scattering rate on the same basis.

Next, a description will be given of a conventional technique disclosed in Japanese Patent Application Laid-Open No. Hei 4-245660 entitled "Method of Inspection of Foreign Substances". This is a method in which two laser beams are orthogonally irradiated at a low angle on a wafer substrate to irradiate a foreign substance, thereby accurately inspecting the number of adhered foreign substances, the attached position and the shape on the substrate. Therefore, even in this prior art, it is impossible to correctly classify the sizes of the foreign substances having different scattering rates because the difference in the scattering rate specific to the foreign substance type is not considered.

Finally, a conventional technique disclosed in Japanese Patent Application Laid-Open No. Hei 5-6929, entitled "Method and Apparatus for Inspecting Wafer Contaminants" will be described. In this method, the size of an unknown foreign substance is calculated from the relationship between reflected light and scattered light obtained by irradiating a foreign substance whose size is known in advance with laser light. In this case, since the relationship between the reflected light and the scattered light with respect to the foreign matter is checked in advance, it is considered that foreign matter having different scattering rates can be classified to some extent. However, it is impossible to check in advance all foreign substances adhering to the substrate, and therefore, it is not possible to classify all foreign substances on the substrate.

[0016]

As described above, the conventional problem is that when the size of foreign matter is classified only by the intensity of scattered light, if foreign matter having different scattering rates coexist, the size of the foreign matter is classified. Is inaccurate.

The reason is that, in the case of the conventional inspection method of this type, foreign matter is represented only by the magnitude of the scattered light, and as a result, the difference in the scattering rate depending on the type of the foreign matter causes the difference between the scattered light intensity and the foreign matter. This was because it made the relationship between the size and the size unclear.

For example, when a laser beam is irradiated in the same situation, the intensity of the scattered light of the silicon fragments becomes larger than that of the resin fragments due to the difference in the scattering rate. Therefore, in this type of conventional inspection method, even if the pieces have the same size, the silicon pieces are determined to be foreign matters larger than the resin pieces.

An object of the present invention is to provide an inspection method capable of correctly determining the size of foreign substances having different scattering rates on the same basis.

[0020]

SUMMARY OF THE INVENTION A feature of the present invention is a method for inspecting foreign matter on a substrate surface using a laser beam, wherein the substrate surface is scanned with the laser beam and the laser beam is irradiated on the foreign matter. There is a foreign matter inspection method for classifying foreign matter using the intensity of scattered light and the width of the intensity distribution obtained sometimes. Here, it is preferable that the substrate is a semiconductor wafer in a manufacturing stage of a semiconductor device. In this case, the foreign matter includes a piece of silicon and a piece of resin, and the piece of silicon and the piece of resin can be classified. Further, the width of the intensity distribution can be indicated by a time longer than a predetermined scattered light intensity level. Alternatively, the width of the intensity distribution can be indicated by the time calculated by (integrated value of scattered light intensity distribution) / (intensity of scattered light: peak value of waveform) in each waveform.

That is, the present invention focuses on the fact that the relationship between the intensity of scattered light and its intensity distribution has a unique relationship with foreign matter emitted from any foreign matter, and adjusts the intensity of the scattered light and the width of the intensity distribution appropriately. Values.

[0022]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an inspection method according to a first embodiment of the present invention. FIG. 1A is similar to FIG.
FIG. 4 is a waveform diagram of the scattered light intensity obtained by scanning the substrate surface with laser light, wherein the detected scattered light intensity is plotted on the vertical axis, and time (scanning time) is plotted on the horizontal axis. Two waveforms are shown.

That is, FIG. 1A is a conceptual diagram of a scattered light intensity acquisition waveform obtained by scanning a substrate surface, for example, a wafer surface, with a laser beam in the inspection method according to the first embodiment of the present invention. . FIG. 1B is an example of a result obtained by classifying the waveform of FIG. 1A by the intensity of an arbitrary scattered light, that is, the peak value of the waveform and the width (time) of the intensity waveform. The inspection apparatus shown in FIG. 2 can be used to obtain these scattered light intensity acquisition waveforms.

For example, 30 m output from the laser beam 3
The laser beam 1 of W is applied perpendicularly to the surface of the wafer 5 that is in a linearly rotating motion (a spiral shape) by the substrate driving unit 7. When there is no foreign matter 6 on the wafer 5, the laser light 1 vertically incident on the wafer surface is totally reflected and does not involve scattering of the laser light. Therefore, in the photodetector 4 mounted at an arbitrary angle from the wafer surface, for example, at an angle of 30 degrees,
No light detection.

When there is a foreign matter on the wafer 5, the laser beam 1 which has been incident perpendicularly on the wafer surface is scattered by the foreign matter 6, and the light detecting means attached at an arbitrary angle from the wafer surface, for example, at an angle of 30 degrees. The light is detected by the detector 4 as scattered light intensity.

The scattered light intensity change of the scattered light obtained by spirally scanning the entire surface of the wafer 5 with the laser light 1 is continuously addressed, and a part of the scattered light intensity acquisition waveform is shown.
It is FIG. 1 (A).

In the inspection method of the present invention, the intensity (peak value of the waveform) X of the obtained scattered light is set to an arbitrary level (L1, L2).
2, L3), and furthermore, the width Y of the scattered light intensity distribution is also classified at an arbitrary level (W1, W2, W3), and the foreign matter is classified two-dimensionally.

When the intensity of the scattered light and the width of the intensity distribution are classified into foreign matter types and sizes based on FIG. 1A, for example, the intensity of the scattered light is L1 <X <L2, and the intensity distribution width is W1 <Y. <W2
Is one (L1W1 level).

Similarly, when the intensity of the scattered light is L2 <X <L3,
There is also one foreign matter (L2W3 level) whose intensity distribution width satisfies W3 <Y.

For a foreign substance at the L3 level, the intensity of the scattered light is L3 <
X, zero. FIG. 1 shows these results.
(B).

In FIG. 1A, for example, the scattered light intensity waveform obtained from silicon fragments has a narrow waveform (c).
And the scattered light intensity waveform obtained from the resin fragments is a broad waveform (d).

For example, when the intensity of the scattered light is
V, 15 mV, and 40 mV, and furthermore, the width Y of the scattered light intensity distribution defined by the width between waveform portions crossing a predetermined scattered light intensity level (a low level at which the presence of foreign matter does not matter) L0, The threshold value of the time during which scattered light is detected during scanning is 0.05 ms, 0.07 ms, 0.
Foreign matter is classified two-dimensionally by performing classification in 10 ms. As a result, for example, the intensity X of the scattered light is 10 mV <X
15 mV, intensity distribution width Y is 0.05 ms <Y <0.07
The number of foreign substances (L1W1 level) corresponding to m seconds is one.
Similarly, the number of foreign substances (L2W3 level) having a scattered light intensity of 10 mV <X15 mV and an intensity distribution width of 0.1 ms <Y is also one. L3 level foreign matter has a scattered light intensity of 40 mV
<X, zero. FIG. 1B shows these results.

In the case of the inspection method of the present invention, by using the intensity of the scattered light and the width of the intensity distribution for the classification of the foreign matter, it is possible to correctly determine the size of the foreign matter having a different scattering rate on the same basis. . For example, due to the difference in the scattering rate when irradiating laser light in the same situation, the scattered light intensity of the silicon fragments is larger than that of the resin fragments, but the width of the intensity distribution becomes smaller, so that the foreign substances are classified two-dimensionally. Then, they are classified into different areas.

That is, even when foreign substances having different scattering rates are mixed, the relationship between the intensity of the scattered light and the width of the intensity distribution is as follows.
Since there is a unique relationship between foreign matter coming from an arbitrary foreign matter, the size can be accurately classified into foreign matter types.

Next, a second embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 3 is a diagram showing an inspection method according to the second embodiment of the present invention. Like FIG. 1A, FIG.
FIG. 9 is a conceptual diagram of a scattered light intensity acquisition waveform obtained by scanning a substrate surface, for example, a wafer surface, with laser light in the inspection method according to the second embodiment of the present invention. FIG.
A result obtained by classifying the time width Y calculated by dividing the waveform of (A) by an arbitrary scattered light intensity X and an integrated value of the intensity distribution by the scattered light intensity (peak value of each waveform) by w value. This is an example. The inspection apparatus shown in FIG. 2 can also be used to obtain these scattered light intensity acquisition waveforms.

That is, the scattered light intensity change of the scattered light obtained by the same method as in the first embodiment is continuously addressed, and FIG.
In (A), the intensity (peak value of the waveform) X of the obtained scattered light is classified at an arbitrary level (L1, L2, L3),
Further, the integral value of the scattered light intensity distribution (each waveform (a), (b),
In (c) and (d), the Y value calculated by dividing the upper right hatched area) by the scattered light intensity X is classified at an arbitrary level (w1, w2, w3), and the two-dimensional value is obtained. Classify foreign substances.

When the size of the foreign substance is classified based on the intensity X of the scattered light and the width Y thereof based on FIG. 3A, for example, the intensity X of the scattered light is L1 <X <L2, and the width Y is w1 <Y. The number of foreign substances (L1w1 level) corresponding to <w2 is one. Similarly, there is only one foreign matter (L2w3 level) whose scattered light intensity X satisfies L1 <X <L2 and width value Y satisfies w3 <Y. The L3 level foreign matter has a scattered light intensity of L3 <X and is zero. FIG. 3B shows these results. As described above, it is also possible to classify by the w value in the same manner as in the first embodiment.

In the second embodiment, since the scattered light intensity waveform is classified based on the integral value, even when the S / N ratio of the waveform is small, the classification is directly performed based on the time width of the waveform. , Can be accurately compared.

On the other hand, since the integration is not performed in the first embodiment, the foreign substance inspection can be performed in a shorter time than in the second embodiment.

[0042]

As described above, according to the present invention, it is possible to correctly determine the size of an unknown foreign matter having a different scattering rate on the same basis. For example, the size of each piece of silicon on the wafer can be determined by distinguishing the piece of silicon from the piece of resin.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention,
(A) shows the scattered light intensity acquisition waveform, and (B) shows the result of classifying (A).

FIG. 2 is a diagram showing the concept of a foreign matter inspection device using laser light.

FIG. 3 is a diagram showing a second embodiment of the present invention;
(A) shows the scattered light intensity acquisition waveform, and (B) shows the result of classifying (A).

FIGS. 4A and 4B are diagrams showing a conventional technique, wherein FIG. 4A shows a scattered light intensity acquisition waveform, and FIG. 4B shows a result of classifying (A).

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser light 2 scattered light 3 laser 4 photodetector 5 wafer (substrate) 6 foreign matter 7 substrate drive unit

Claims (5)

(57) [Claims] 1. A method for inspecting foreign matter on a substrate surface using laser light, wherein the substrate surface is scanned with laser light, and the intensity of scattered light obtained when the laser light is applied to the foreign matter and the intensity thereof A foreign matter inspection method characterized by classifying foreign matter using a width of distribution. 2. The foreign matter inspection method according to claim 1, wherein the substrate is a semiconductor wafer in a stage of manufacturing a semiconductor device. 3. The foreign matter inspection method according to claim 1, wherein the foreign matter includes silicon fragments and resin fragments, and the silicon fragments and the resin fragments are classified. . 4. The foreign matter inspection method according to claim 1, wherein the width of the intensity distribution is indicated by a time longer than a predetermined scattered light intensity level. 5. The foreign matter inspection method according to claim 1, wherein the width of the intensity distribution is calculated by (integral value of scattered light intensity distribution) / (intensity of scattered light).