JPH04318446A - Foreign matter detecting system - Google Patents

Abstract

PURPOSE:To make a foreign matter inspecting system commonly usable for both a researching and inspecting lines by performing X-direction scanning by changing the step interval in the Y-direction of an X-Y stage in corresponding to the narrow and wide visual fields of a microscope produced by a change in the magnification of a repeating lens. CONSTITUTION:An objective 311 having 40 magnifications is provided in the direction perpendicular to a wafer 1 and the fixed section 61 of a mobile table 6 is fixed. A repeating lens section 7 provided with repeating lenses 312A and 312B respectively having 2.5 and 1 magnifications is fitted to the mobile section 62 of the table 6 and the section 7 is manually selected. A microscope 31A for research having 100 magnifications is constituted by using the 2.5-power lens and a microscope 31B for inspection having 40 magnifications is constituted by using the 1-power lens. At the time of performing inspections, one of the repeating lenses is selected and an X-Y stage 5 is moved in the Y direction in steps for scanning. Any lens magnification other than those mentioned above can be used according to the actual condition.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION The present invention is an inspection method for foreign matter attached to a patterned wafer.

0002

2. Description of the Related Art Wafers used for manufacturing semiconductor ICs are inspected using a foreign matter inspection device because pattern wiring is formed on a mirror-surfaced wafer, and the quality deteriorates if foreign matter adheres to the surface of the wafer. Optical methods are exclusively used to detect foreign objects, in which the surface of the wafer is irradiated with a laser beam, the foreign objects are detected by receiving the scattered light, and this detection signal is processed by an appropriate processing circuit. The foreign object data obtained is displayed as a map on a display device.

Now, a wafer (
On a patterned wafer (or simply referred to as a wafer), the irradiated laser beam is reflected by the pattern as well as the foreign matter, so it is extremely important to distinguish between the two and detect only the foreign matter. In response to this, a method and device for distinguishing between the two and detecting only the foreign matter were developed, and the first application was filed in Japanese Patent Application No. 103596/1983, Foreign Matter Inspection Apparatus (hereinafter referred to as Detection Method 1 for convenience). Next, ``Unexamined Japanese Patent Publication No. 104243/1983, Foreign Matter Detection Method and Apparatus Therefor'' (hereinafter referred to as Detection Method 2) has been published. Detection method 1's detection optical system is effective for wafers with low pattern height differences (relatively easy to detect foreign objects), and detection method 2 is effective for wafers with high pattern height differences (relatively difficult to detect foreign objects). It is said to be suitable. Furthermore, a slightly simplified device combining these detection optical systems was filed, and was disclosed in Japanese Patent Application Laid-Open No. 63-296348,
"Wafer Foreign Matter Inspection System" has been released to the public.

[0004] FIG.
No. 96348, Wafer Foreign Matter Inspection Apparatus", in which an irradiation system 2 is provided for a wafer 1 to be inspected,
A pair of opposing light sources 21a and 21b emit an S-polarized laser beam with wavelength λ1 at a low angle θ1 (1 to 5 degrees).
), and from similar light sources 22a and 22b, a laser beam of wavelength λ2 and S polarization is irradiated at a high angle θ2 (for example, 30°). A light receiving system 3 having a microscope 31 is provided in a direction perpendicular to the wafer 1, and the reflected light of each laser beam is focused by an objective lens 311 of the microscope 31 and outputted from a relay lens 312. The output reflected light is separated into wavelengths λ1 and λ2 by a wavelength separation mirror 32, which are received by CCD elements 34a and 34b, respectively, and outputted as voltages VL and VH. Output voltage VL
and VH in the signal processing unit 4, a divider 41 calculates a ratio VL/Vh, and a comparator 42 compares this ratio with a threshold m to detect a foreign object and obtain a detection signal pa. The detection optical system in this case corresponds to detection method 1 described above. Regarding the above, the wavelength separation mirror 3
When a polarizing beam splitter 33 is used instead of 2, each reflected light is not wavelength-separated but is separated into S and P polarized waves, each of which is transmitted to the CCD element 3.
The light is received by 5a and 35b, voltages VL and VH are output, and the ratio VL/VH is calculated in the same manner as above to obtain the foreign object signal pa. This case corresponds to detection method 2 above.

As described above, in the above-mentioned wafer foreign object inspection apparatus, foreign objects can be detected effectively by selectively using detection method 1 or 2 in response to pattern steps that change sequentially according to the wafer process. .

The field of view of the microscope 31 and the scanning width of the laser beam will now be explained. The surface of the wafer is magnified by a microscope 31, and the reflected light is imaged on CCD elements 35a and 35b within its field of view A, as shown in Figure (b).
It detects foreign objects by scanning the CCD element.CC
The pixel range of the D element 35a or 35b becomes the scanning width W of the laser beam. In this case, the magnification of the microscope is related to the detection sensitivity of foreign matter, and the higher the magnification, the better the sensitivity. Conventionally, a microscope with a magnification of 100x is constructed using a 40x objective lens and a 2.5x relay lens, and the diameter Wa of the field of view A is approximately 700 μm when converted to the surface of the wafer. The scanning width w of the laser beam is also approximately 200 μm.

[0007]

In the above, the laser beam scans the wafer using an XY scanning method, which is shown in FIG. 4(a). The orientation of wafer 1 is XY with its orientation flat OF as the X direction.
The wafer is placed on a stage (not shown), and the entire surface of the wafer is scanned by reciprocating the stage in the X direction and sequentially stepwise moving in the Y direction. In this case, it is necessary to keep the scanning speed relative to the wafer constant, but since the stage is decelerated near the turning point for reciprocating, the overall scanning speed is low and the inspection time is therefore long. There is. Although this is acceptable in the case of research-based foreign matter inspection, it is desirable to shorten the inspection time as much as possible when a large number of wafers are inspected in succession on an inspection line. In response to this, it is possible to move the wafer at a higher speed, but this cannot be expected due to the structure of the XY stage and its moving mechanism. On the other hand, in the above-mentioned microscope, the range of the field of view A converted to the wafer surface changes depending on the magnification, and the narrower the field of view, the narrower the scanning width w and the longer the inspection time. The above magnification of 100x corresponds to the above-mentioned detection method 2, that is, a pattern with high steps where detection of foreign objects is relatively difficult, but when applied to an inspection line, a slight decrease in detection sensitivity is allowed. In particular, by lowering the magnification, the field of view A is enlarged, the scanning width w becomes wider, and the inspection time can be shortened. However, since the foreign matter inspection device is used for both research and inspection lines, it is necessary to adopt a method that can be applied to both.

[0008] This invention was made in view of the above,
The purpose of this invention is to provide a foreign substance inspection method that can be used commonly for research and inspection lines, maintains the same detection sensitivity as before for research, and shortens inspection time for inspection lines.

[0009]

[Means for Solving the Problems] The present invention comprises an It is equipped with an irradiation system that irradiates at a low angle and the other at a high angle, and a light receiving system that is installed perpendicular to the wafer, and consists of an objective lens and a relay lens, and condenses the reflected light of each laser beam. A microscope that forms an image of the wafer surface, a selectable wavelength separation mirror and polarization beam splitter that separates the reflected light in wavelength or polarization direction, and a wavelength separation mirror and polarization beam splitter that receives the reflected light that has been separated in wavelength or polarization direction. , a foreign matter inspection method in a wafer foreign matter inspection apparatus having a light receiving system composed of two CCD elements on which an image of the surface of the wafer is formed, wherein two relay lenses with different magnifications are selectably provided, Scanning in the X direction is performed by changing the step interval in the Y direction of the XY stage in response to the narrowing and widening of the field of view of the microscope due to the magnification of the selected relay lens.

0010

[Function] In the foreign object inspection method described above, two relay lenses with different magnifications are selectable, and the Y of the XY stage is Scanning is performed in the X direction by changing the step interval in the direction, and when using a relay lens with high magnification, the field of view is narrow and high detection sensitivity can be obtained, but on the other hand, the scanning width of the laser beam is narrow and inspection is difficult. It's a long time. On the other hand, when using a relay lens with a low magnification, the detection sensitivity is slightly lowered, but the scanning width can be widened and the inspection time can be shortened.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention. A wafer 1 to be inspected is placed on an XY stage 5 and moved in the X or Y direction, and the wafer is irradiated with each laser beam and scanned by the irradiation system 2 shown in FIG. 3 described above. On the other hand, an objective lens 311 with a magnification of 40× in the direction perpendicular to the wafer
is provided, and a fixing part 61 of the moving table 6 is fixed to the upper part thereof. The moving parts 62 of the moving table each have a magnification of 2.
A relay lens unit 7 having 5× and 1× relay lenses 312A and 312B is attached, and a relay lens is selected by manually moving the relay lens unit. For research use, a microscope 31A with a magnification of 100x is constructed using mainly 2.5x, and for inspection lines, a microscope 31B with a magnification of 40x is constructed using mainly 1x. In the inspection, one of the relay lenses is selected and the XY stage 5 is moved in steps in the Y direction with a scanning width corresponding to the selected relay lens. The reflected light of the laser beam passes through the microscope 31A or 31B, and as in the case of FIG. 3 described above, the wavelength separation mirror 3
2 or polarization beam splitter 33, and the CCD elements 34a and 3
4b, voltages VL and VH are output, and these are processed by the signal processing section 4 to obtain a foreign object signal pa.

FIG. 2 shows the field of view A of the microscope and the scanning width w of the laser beam corresponding to the relay lens selected in FIG.
shows. (a) is the case when a 2.5× relay lens 312A is used, the diameter Wa1 of the field of view A1 is approximately 700 μm converted to the wafer surface, and the scanning width w1 of the laser beam is
is also about 200 μm, and (b) shows that the XY stage 5 moves the wafer stepwise in the Y direction and scans it in the X direction with a scanning width w1. Then (c) is 1.0
In the case of the × relay lens 312B, the diameter of its field of view A2 is about 1750 μm, the scanning width w2 is about 500 μm, and the inspection time is significantly shortened to 1/2.5.

In the above embodiment, the objective lens is 40×, and the relay lenses are 2.5× and 1.0×.
Although these lenses were used, it is of course possible to use lenses with other magnifications depending on the actual situation.

[0014]

As explained above, in the foreign object inspection method according to the present invention, two lenses with different magnifications are selectable as relay lenses of the microscope, and the field of view of the microscope is changed by the higher or lower magnification of the selected relay lens. In response to narrow and wide conditions, scanning is performed in the X direction by changing the step interval in the Y direction of the stage, and a relay lens with high magnification is selected to achieve high detection sensitivity, or a relay lens with low magnification is selected. , the test time is shortened at the expense of a slight decrease in sensitivity, and the operational efficiency of the device is improved by being used for both research and test lines, which has a significant effect.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the field of view and scanning method of the microscope in FIG. 1.

FIG. 3 is a configuration diagram of the wafer foreign matter inspection apparatus disclosed in the patent and an explanatory diagram of the field of view of the microscope.

4 is an explanatory diagram of a method of scanning a wafer with a laser beam in the wafer inspection apparatus of FIG. 3. FIG.

[Explanation of symbols]

1... Patterned wafer (simply wafer), 2... Irradiation system,
21a, 21b, 22a, 22b...Light source, 3...Light receiving system, 31, 31A, 31B...Microscope, 311...Objective lens, 312, 312A, 312B...Relay lens, 32...Wavelength separation mirror, 33...Polarizing beam splitter, 34a ，
34b... CCD element, 4... Signal processing section, 41... Divider, 42... Comparator, 5... XY stage, 6... Moving table, 61... Fixed part, 62... Moving part, 7... Relay lens part.

Claims (1)

[Claims] 1. An XY stage on which a patterned wafer to be inspected is placed and moved in the X or Y direction, and a laser beam of different wavelengths directed toward the surface of the wafer, one of which is set at a low angle and the other is set at a high angle. An irradiation system that irradiates at an angle,
a light receiving system installed in a direction perpendicular to the wafer, comprising an objective lens and a relay lens, and condensing the reflected light of each of the laser beams to form an image of the surface of the wafer; , a selectable wavelength separation mirror and a polarizing beam splitter that separate the reflected light in wavelength or direction of polarization, and an image of the surface of the wafer is formed by receiving the reflected light separated in the wavelength or direction of polarization. In the wafer foreign matter inspection apparatus having the light receiving system constituted by two CCD elements, the two relay lenses having different magnifications are selectably provided, and the microscope is adjusted according to the magnification of the selected relay lens. A foreign matter inspection method characterized in that scanning in the X direction is performed by changing the step interval in the Y direction of the XY stage in response to a narrow or wide field of view.