JPS61104242A - Semiconductor wafer foreign matter inspection equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is suitable for detecting minute foreign matter in patterned edges and hills during semiconductor LSI Ueno/Special/cLSI manufacturing intermediate steps at high speed and with high sensitivity. This invention relates to a foreign matter inspection device.

[Background of the invention]

Conventional wafer E foreign matter inspection equipment uses (1) a combination of one-dimensional high-speed scanning of laser light and low-speed translational movement of the sample (:
The entire surface of the sample was scanned and detected using a linear scan based on a combination of high-speed rotation and low-speed translation of the sample as shown in Japanese Patent Application Laid-open No. 55-133551 (Public Patent No. 4). Furthermore, in Japanese Patent Application Laid-open No. 57-80546 (Public Known Example 1), scanning equivalent to the above (1) is realized by combining electrical scanning of a self-scanning type dimensional photoelectric conversion element array and low-speed movement of the sample. Furthermore, Automatic Microcirc
cuit and wafer inspection
Electronics Te5t, Vol.
4, Nn5. May1981, pp, 6
0-70. In (Known Example 2), a self-supporting vertical-dimensional photoelectric conversion element array is arranged at a radial position of the sample, and by combining this with rotational movement of the sample, scanning equivalent to the above (11) is realized.

However, in the methods of Known Examples 1 and 2, it is impossible to avoid "missing" a foreign object when the dead zone existing in adjacent areas of two individual photoelectric conversion element picture elements scans the foreign object. In order to strictly avoid this, it is necessary to install a plurality of photoelectric element arrays in an overlapping manner so as to cover the dead zone. This results in an unnecessarily large amount of signal processing circuitry and a decrease in reliability. However, even if the photoelectric element arrays are not overlapped, the size of the foreign object to be detected is sufficiently large compared to the above dead zone width, or the total dead zone width is negligible compared to the total photoelectric conversion element pixel width. If it is small, the above-mentioned "missing" will not be a big problem. From this point of view, the methods of Known Examples 1 and 2 ignore and do not discuss the 6 degrees missed due to the dead zone. [Detection of foreign matter on patterned wafer L] Foreign matter inspection work is essential for improving product yield and reliability. The automation of this work is disclosed in Japanese Patent Application Laid-Open No. 55-149829.
, %Kokai 1986-101390, JP-A-55-941
This is realized by a detection method using polarized light as shown in a series of patents such as No. 45 and Japanese Unexamined Patent Publication No. 56-30630. This principle will be explained using FIGS. 21 to 28.

As shown in FIG. 421, if only the illumination light 4 is compared with the surface of the wafer 1 at an inclination angle φ, reflected light and scattered lights 5 and 6 will be generated from the pattern 2 and the foreign object 3 at the same time. Cannot only be discriminated and detected when there is illumination? A device was devised to detect foreign matter 3 by using polarized laser light as light 4.

As shown in FIG. 22 (α), a pattern 2 existing on two wafers 1 is irradiated with S-polarized laser light 4. (Here, when the electric vector 10 of the laser beam 4 is parallel to the wafer surface, it is called S-polarized laser illumination.) In general, when viewed microscopically, the unevenness on the surface of the pattern 20 is sufficiently small compared to the wavelength of the illumination light; Therefore, the reflected light 5 also has an S polarization component 1.
1 is maintained. Therefore, if the analyzer 13 for blocking S-polarized light is installed in the optical path of the reflected light 5, one reflected light 5 will be blocked and will not reach the photoelectric conversion element 7. On the other hand, as shown in FIG. 22 (AIK), the scattered light 6 from the foreign object 3 includes a P-polarized component 12 in addition to the S-polarized component 11.

This is because the surface of the foreign object 3 is rough and the polarization is canceled, resulting in the generation of the P-polarized light component 12. Therefore, analyzer 13
If the P-polarized light component 14 passing through is detected by the photoelectric conversion element 7, the foreign object 3 can be detected.

Here, the pattern reflected light 5 is completely blocked by the analyzer 13 when the angle between the longitudinal direction of the pattern 2 and the laser beam 4 is at right angles as shown in FIG. If this angle is different from the right angle, light will not be completely blocked. This discussion is published in Proceedings of the Society of Instrument and Control Engineers, Vow, 17.
+Fh2 *P232~P242, 19'31
．． states. According to this.

Only the reflected light from the pattern within a range of ±30° from the right angle enters the objective lens installed above the wafer, so the pattern reflected light 5 in this range is reflected by the analyzer
Although the light is not completely blocked, the intensity is 2 to 3 μm.
Since the light is small enough to be distinguished from light scattered by foreign objects, it does not pose a problem in practical use.

Here, the inclination angle φ of the polarized laser beam 4 is set to about 1° to 3°. This is for the reason shown below. 23rd
In the experiment shown in the figure, 2μmlφ for S-polarized laser 4
The intensity Vs of the component 14 of the foreign object scattered light passing through the analyzer 13 and the intensity VP of the component passing the analyzer 14 of the pattern reflected light 5
Measurements were made using a 900-degree lens ($40X, N, A=0.55). The experimental results are shown in FIG.

The laser inclination angle φ was plotted on the horizontal axis, and the foreign matter/pattern discrimination ratio Vs/Vp was plotted. As can be seen from the figure, when the inclination angle φ is less than or equal to 0, Vs can be easily distinguished from Vp, so stable foreign object detection is possible. Further, considering design matters, φ=1° to f is optimal. (Unexamined Japanese Patent Publication No. 56-
30630) Here, the laser light source 15 is
The reason for using this is to enable stable detection of foreign substances that generate anisotropic scattered light.

Next, the foreign object inspection method using this detection principle is shown in Figure 25~
This will be explained in FIG.

As shown in FIG. 25 (α), a slit 8 is provided on the sample imaging plane to limit the detection range. This allows slit 8
Since only the scattered light within the projected area 8α of the aperture onto the sample is detected at one time.

Cumulative intensity of pattern reflected light P component within this area 14p
If the foreign matter scattered light P component 144 is sufficiently large compared to , the foreign matter 3 can be stably detected. Therefore.

This area 8α is the size of the foreign object to be detected (2 to 3 μm)
If the size is about the same as , the detection sensitivity will be optimal, but the number of scans will be increased as shown in FIG. 25 (6).

It has a long inspection time. Conversely, if the aperture area 8α is increased, inspection can be performed in a short time, but the detection sensitivity will deteriorate. Taking this into consideration, the area 8α is now 10
With 200μm, foreign matter of 2 to 3μm can be removed in about 2 minutes (1
50 (mφ sea urchin...) is inspected. This situation will be explained using FIG. 26 and FIG. 27.

First, FIG. 26 shows a plan view (α) and a cross-sectional view (h) of the wafer surface. The pattern 2 has (1) a slight depression in the pattern and (11) a part having an angle other than perpendicular to the irradiation direction of the laser beam 4, and a small amount of scattered light P component 14p is generated from each of these parts. do.

On the other hand, small foreign particles 3α and 2 with a size of about 0.5~2.αm
The large foreign matter 3b with a size of μm or more generates a P component 14cL having a larger intensity than each of the above mtli) locations.

FIG. 27 shows the signal output of the photoelectric conversion element 7 when the aperture 8α scans over the sample. In the same figure (α), P component 1
The distribution of sample E of 4p (pattern) and 14d (foreign matter) is shown. When the aperture 8α scans over this distribution, a video signal output Vp shown in FIG. 5(h) is obtained, and when this is binarized, a defect signal shown in FIG. 2(C) is obtained.

In this example, since the output from the small foreign object 3α and the edge of pattern 2 are the same, the threshold indicated by the broken line must be set at a position higher than this output, and as a result, the detection is limited to only large foreign objects. Ru.

However, in the manufacture of highly integrated LSIs, such as 256 Kbit memory LSIs, the presence of 1μm-sized foreign matter greatly affects the product yield.
m Foreign object detection sensitivity is required. If the aperture 8α is limited to less than 5×5 μm using the device shown in FIG.
, (li) is reduced compared to the case where the aperture 8α is 10 × 200 μm 2 , and as a result, it becomes possible to detect a 1 μm foreign object. However, in this case, the inspection time increases by about 40 times, making it impossible to synchronize with manufacturing throughput, which poses a problem in practical application.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a foreign matter inspection device that can distinguish minute foreign matter from patterns and detect it at high speed.

[Summary of the invention]

In the present invention, the size of the light receiving area of each painting is 5 x 5 μ (
By using multiple photoelectric conversion solid-state imaging devices (converted to the sample surface) and processing the output signals from each device in parallel at the same time.

This system is characterized in that foreign matter inspection can be performed with high sensitivity without deteriorating high-speed performance.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail using FIGS. 1 to 20.

FIG. 1 shows how a solid-state image sensor array 20 is used in place of the slit 8 in the conventional example shown in FIG. 28.

FIG. 2 explains an example of the solid-state image sensor array 20. The light receiving section 20α is a silicon photodiode or a GaAsP photodiode, and among these, a PIN junction type is particularly suitable for the use of the present invention because of its characteristics of high speed response and high sensitivity. The width of each light receiving part 20tL (pixel) is 500 μm, and there is a width of 50 μm between adjacent pixels.
There is a dead zone of m. 1 if the number of pixels is 40
For example, if the total magnification of the detection system is 100x (40x magnification of objective lens 9 and 2.5x magnification of relay lens (not shown)), the size of one pixel is 5 x 5 μm on the sample surface.
2, which means that a range of 5×220 μm 2 is being scanned while being detected, and the inspection speed is comparable to that of the conventional method.

The effects of this solid-state image sensor array 20 will be explained with reference to FIG. For comparison, the case of the solid-state image sensor array 20 is shown in (α), (h), and (C) of the same figure, and (g) of the same figure,
(g), (7']K The case of the conventional example shown in Fig. 28 is shown. Fig. 28 (α) shows the state in which the solid-state image sensor array 20 scans and detects the wafer, and Fig. 28 (h) is each pixel (i, j, l, m) of the solid-state image sensor array 20
The video signal obtained from '1 + )'1 + n1 *
11'+ml.

The same figure (C) shows each video signal i1 r )'1 *n1,
Binarized signals L2 rj2 , k2 . lh, m2
FIG. Furthermore, the same figure (d) shows the state in which the slit 8 is scanned over the wafer and detected by the photoelectric conversion element 7,
(g) in the same figure shows the video signal V obtained from the photoelectric conversion element 7, and (2) in the same figure shows a binary signal obtained by binarizing this video signal using the threshold value of the VTR'. In addition, the figure (α
), (b).

In order to simplify the explanation, (C) has 5 pixels per pixel.

)°, ni, l, m). As is clear from this figure, if the output signal for one pixel is binarized using the threshold value VTH, 2 in the binarized signal becomes 1 even for a small foreign object 3α, and sensitivity is improved compared to the conventional method.

FIG. 4 shows a signal processing method for each pixel of the solid-state image sensor array 20. The outputs of each pixel L are simultaneously binarized in parallel in a binarization circuit 21 to produce a binarized signal (1).
is led to the OR circuit 22.

When a foreign object is detected in at least one picture, the output of the OR circuit becomes 1 and is input to the foreign object memory 23.

With this method, the outputs of 40 pixels are simultaneously processed in parallel, and inspection speed and detection sensitivity can be significantly improved compared to when a self-scanning image sensor is used.

However, the dead zone 20h of the solid-state image sensor array 20
gives rise to drawbacks which are explained below. This solution is the fifth
It is shown in FIGS.

As shown in FIGS. 5 and 7, when the arrangement direction of the solid-state image sensor array 20 and the scanning direction are perpendicular, the relationship between the dead zone 20h between the pixels and the small foreign object 3C is as shown in the same figure. In some cases, the small foreign object 3C may be overlooked. Figure 5 (α),
Ih'I is a diagram showing the state of being scanned.

Therefore, as shown in FIGS. 6 and 8, the arrangement direction of the solid-state imaging device array 20 and the scanning direction may be made to have an appropriate angle (for example, 4 angles).

The above oversights can be avoided. Figure 6 (α).

! b) and (C) are diagrams showing the state of being scanned.

This angle does not necessarily have to be d' if the shape of the single picture 20α is rectangular.

In FIG. 6, the small foreign object 3C is detected redundantly by pixels no and k, resulting in double counting. but,
As a way to avoid this double counting, JP-A-56-1
32549, JP-A-56-118187, JP-A-57-
66345, JP-A-56-126747, JP-A-56-
The method described in 11864.7 may be used.

FIG. 9 shows an example of application of the present invention in the case of stripe-shape scanning.

FIG. 1O shows the overall configuration of the embodiment. The wafer l is sucked onto the wafer chuck 4o by the vacuum tube 41, and
The stage 46 and the X stage 49 move in the XY directions. Foreign object information detected by the solid-state image sensor array 2° is sent to the foreign object memory 2 via a binarization circuit 21 and an OR circuit 22.
3 and is displayed on a display device 33.

In the present invention, the size of the pixel is set to about 5×5 μm 2 or less, so if a defocus occurs during inspection due to undulations on the wafer surface, the foreign object detection sensitivity will be significantly reduced. Therefore, it is essential to use a configuration in which the automatic focus detection section 30 detects the amount of defocus during the inspection and feeds it back to the driver 31 of the focus mechanism motor 43.

The principle of this automatic focus function was announced on pages 223-224 of the preprint collection of the 22nd 5ICE Academic Conference, and
70540, this principle will be explained using FIGS. 11 to 13.

This method is most suitable for the present invention because it is characterized by stable automatic focusing without being affected by the pattern on the sample.

FIG. 11 shows the main parts of the automatic focus detection section 30.

The striped patterns 60α and 60h on the striped pattern glass plate are each projected onto the sample by the objective lens 9, but the respective focal point positions are set slightly too high and slightly lower than the focused focal point of the image sensor array 20. It has been determined. The images of the respective striped patterns 60α and 60h on the sample are captured by the objective lens 9.
The image sensor 6 is magnified by the transmissive mirrors 34 and 62 and reflected by the semi-transmissive mirrors 34 and 62.
1.

Figure 12 (α) shows that the wafer is too low (if Z<(l),
shows a projected fringe pattern imaged on the image sensor 61J;
FIG. 12 (Li) shows the video signal waveform detected by the image sensor 61 in the case shown in FIG. 12 (α).

FIG. 12(b) shows a projection pattern imaged on the image sensor 61 in the case of the focused position (Z=O), and FIG.
0 indicates the video signal waveform detected by the image sensor 61 in the case shown in FIG. 12(h). FIG. 12(C) shows the projected fringe pattern imaged on the image sensor 61E when the wafer is too high (Z>O), and FIG. 61 shows a video signal waveform detected at 61.

Therefore, when the image sensor array 20 is in focus, the detection signals of the image sensor 61 become equal at locations corresponding to the striped patterns 60α and 60b, and the difference signal between the two becomes zero. on the other hand,
If it rises too much (or falls too much), the image sensor 20
Since the deviation from the in-focus point corresponds to the magnitude of the output of the difference signal, the servo signal shown in FIG. 13 is obtained. The figure shows an example of actual measurement of the difference signal when the sample surface is an aluminum surface and when the sample surface has a complicated pattern (memory cell surface). This allows ±0
．． Since focusing within 5 μm is possible, stable foreign object detection is possible when the objective lens 9 has a magnification of 40×. As an autofocus mechanism.

For example, a motor 43 as shown in FIG. Slope 45.
1 ball 44. The configuration using the plate spring 42 is simple.

Next, another embodiment of the present invention will be described. That is, as shown in FIG. 14, using a linear image sensor 200 composed of a charge-coupled device whose dead zone 200h is inclined with respect to the arrangement direction of the array 200α, the wafer is moved in a direction perpendicular to the arrangement direction as shown in FIG. If it is scanned relative to 1, the same effect as in the embodiment described above can be achieved.

Moreover, as shown in FIG. 16, each light receiving section 201α (...).

Even if i, )', k, l, . . . ) are arranged in a diamond shape, the same effect as in the embodiment described above can be obtained. Note that 201b indicates a dead zone area.

Moreover, as shown in FIG. 17, each light receiving section 202α (...).

Even if i, )', k, l, . . . ) are arranged in a staggered pattern, the same effect as in the embodiment described above can be obtained.

Note that 202A indicates a dead zone area.

In this way, the solid-state image sensor array is shown in FIGS. 18, 19,
As shown in Fig. 20, bonding pad portions 200g, 201g, 202g wiring 200d, 201d, 202d are essential for connection to external pins, and light receiving portions 200α, 201α, 202α are wider than the light receiving field concave. There is a need to. Therefore, in order to increase the detection resolution, optical light shielding parts 200C and 201? , Paste 202c by printing etc., bonding butt part 200g
, 201g, 202g, and other areas outside the light receiving range.

Furthermore, the present invention is not limited to wafers, but can also be applied to the inspection of other products such as photomasks and reticles.

Also, the limit on the size of two pixels is 1.
It has been confirmed through experiments that there is no practical problem when detecting foreign particles of 5 μm to 2 μm.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to realize an automatic foreign matter inspection apparatus that can detect minute foreign matter with high sensitivity and stability while maintaining high speed inspection.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of the foreign object inspection device of the present invention, Fig. 2 is a perspective view showing details of the solid-state image sensor shown in Fig. 1, and Fig. 3 is a comparison between the present invention and a conventional example. FIG. 4 is a diagram showing a signal processing circuit of the solid-state image sensor shown in FIG. 1. FIG. 5 is a diagram showing the positional relationship between a dead zone and a foreign object. FIG. 6 is a diagram showing the positional relationship between the dead zone and foreign matter in the present invention, FIG. 7 is a diagram showing the relative scanning direction of the solid-state image sensor with respect to the wafer in FIG. FIG. 9 is a diagram showing the relative scanning direction of the solid-state imaging device with respect to the wafer, and FIG. 9 is a diagram showing the relative spiral scanning of the solid-state imaging device with respect to the wafer. Fig. 10 is a block diagram showing the embodiment shown in Fig. 1 in more detail, Fig. 11 is a perspective view showing the automatic focus detection section shown in Fig. 10, and Fig. 12 is for explaining automatic focus detection. diagram,
FIG. 13 is a diagram showing the relationship between the difference output obtained from the automatic focus detection section shown in FIG. 11 and the focus shift, and FIG.
Figure 15 is a diagram showing another solid-state image sensor different from the one shown in the figure.
4 is a diagram showing the state of scanning relative to a wafer using the solid-state FA image device shown in FIG. Figure 17 is a diagram showing the light receiving section of another solid-state image pickup device that is different from that shown in Figure 16, Figure 18 is a diagram showing in more detail what is shown in Figure 14, and Figure 19 is similar to Figure 16. FIG. 20 is a diagram showing more specifically what is shown in FIG. 17, FIG. 21 is a cross-sectional view showing the wafer, and FIG.
2 is a diagram showing the circuit pattern of wafer b and the state of reflection from a foreign object with respect to the irradiated laser light, FIG. 23 is a schematic perspective view showing the first example of the conventional foreign object detection method, and FIG. Output ratio Vs/V when the inclination angle φ is changed by
25 is a schematic perspective view showing a second example of the conventional foreign object detection method, FIG. 26 is a diagram showing the state of reflection from the circuit pattern on the wafer and the foreign object, and FIG. 27 is a graph showing measurement data of p.
The figure shows the relationship between video signals obtained by relatively scanning the slits on the wafer as shown in Fig. 25, and Fig. 28 shows the conventional foreign object detection method similar to the second example shown in Fig. 25. FIG. ■...Wafer, 2...Pattern 3...
Foreign matter, 4...Illumination light C1
10...S polarized light, 5...Reflected light 6...
Scattered light, 9...Objective lens 11...S polarized light component, 12.14...P polarized light component 13...
Analyzer, 15... Polarized laser light source 20... Solid-state image sensor array for photoelectric conversion 20α... Light receiving section, 20b...
・Dead zone 21...Binarization circuit, 22...OR circuit 2
3... Foreign object memo IJ, 30... Automatic focus detection section 31... Driver 1 63... Illumination light 60α
, 60b... Striped pattern 61... Image sensor. Fig. 67 Fig. 7 Fig. 8 Fig. 11 Fig. % 12 Fig. (ku) Cb) (C) m m [II (d) (e><su) 13th Fig. 15 Fig. 16 U\J Fig. 77 /6 囌 /q 5 20th [21st page 23rd figure 25 (his) 26th figure vI27,. ) -111''- 197'J-

Claims (1)

[Claims] 1. In an inspection device comprising an illumination device, a detection optical device, and a sample scanning means, a solid-state image sensor array for photoelectric conversion is arranged at an enlarged image position on the sample surface, and the image sensor array is A foreign matter inspection device that detects foreign matter on the surface of a sample at high speed using an electric circuit that performs parallel and simultaneous processing on each output signal. 2. Having an appropriate angle between the sample scanning direction of the solid-state image sensor array for photoelectric conversion and the solid-state image sensor array arrangement direction,
2. The foreign object inspection device according to claim 1, wherein the foreign object inspection device avoids overlooking foreign objects due to dead zones between individual solid-state image sensors. 3. Intensity of scattered light from the pattern on the wafer surface and foreign matter at each pixel, assuming that the size of each picture of the solid-state image sensor array for photoelectric conversion is converted to a range of 10 x 10 μm^2 or less on the sample surface. The foreign matter inspection device according to claim 1, characterized in that the detection signal ratio corresponding to the detection signal ratio is increased. 4. The foreign matter inspection apparatus according to claim 1, which is equipped with an automatic focus function to correct and avoid defocus caused by wafer surface waviness in real time during inspection.