JPS5948540B2 - Foreign matter inspection method on wafer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION H. The present invention relates to a method for automatically inspecting foreign particles on a wafer.

By the way, there is a circuit pattern 2 on the wafer as shown in FIG.
exists.

In FIG. 1, a pattern 2 and a foreign object 3 are present on the wafer 1, but as in the conventional method, the laser 4 is tilted at a certain angle with respect to the wafer surface to determine whether or not the foreign object 3 is present there. If the reflected light from the wafer is focused by the objective lens directly above and received by the photoelectric conversion element, the reflected light from the circuit pattern etc. 2 and the reflected light from the foreign object 3 will be reflected by the photoelectric conversion element. The disadvantage is that it is not possible to distinguish between the two. An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to detect with high reliability whether or not foreign matter is present on the surface of a wafer on which a circuit pattern, etc., having unevenness formed linearly in the surface direction is formed. An object of the present invention is to provide a method for inspecting foreign substances on a wafer that allows easy inspection.

That is, in the present invention, a laser beam having a linearly polarized component is irradiated diagonally above the wafer, and since the surface of the wafer on which a circuit pattern is formed is planarly uneven, the reflected light also has the linearly polarized component. It remains a laser beam with a component,
Since the surface of the foreign object existing on the wafer is rough, we focused on the fact that when the laser beam is reflected from the surface of the foreign object, the polarized light is disturbed and has a component perpendicular to this component in addition to the linearly polarized component. Of this reflected light, the linearly polarized component is blocked by a polarization cut filter, and the perpendicular component is passed through, which is received by a photoelectric conversion element, thereby making it possible to recognize the presence of foreign matter.

Therefore, in order to achieve the above object, the present invention irradiates a predetermined position on a wafer with laser light having first and second linearly polarized components, respectively, from diagonally above in at least two directions around the predetermined position on the wafer. The diffusely reflected light obtained from the wafer by the laser beam having one linearly polarized light component is passed through the first polarization cut filter that blocks the first linearly polarized light component.
A first photoelectric conversion element receives and receives a component perpendicular to the linearly polarized component, and the second linearly polarized component is blocked by diffusely reflected light obtained from the wafer by a laser beam having a second linearly polarized component. The above-mentioned second light is passed through a second polarization cut filter.
A component perpendicular to the linearly polarized light component of is received by a second photoelectric conversion element, and the outputs obtained from each of the first and second photoelectric conversion elements are added to inspect the presence of foreign matter on the wafer. This is a method for inspecting foreign substances on wafers. The present invention will be specifically described below with reference to embodiments shown in the drawings.

In Figures 2 and 3, among the linearly polarized light components, the S-polarized laser 30 and the S-polarized laser 31 are alternately irradiated in the x direction, and the P polarized light is perpendicular to the S polarized light in the x direction. The polarized laser component 27 (considered in the X plane) is passed through the S polarization cut filter 3.
5 is detected by the photoelectric conversion element 37, and the S-polarized laser component 29 (considered in the X plane) during Y-direction illumination is detected by the photoelectric conversion element 38 through the P-polarization cut filter 35, and these are added and synthesized. did. That is, during x-direction S-polarized laser illumination, the S+P-polarized laser is reflected from the foreign object 3, so focusing on the component focused by the objective lens 33 and reflected to the right by the semi-transparent mirror 34, the S-polarized laser is removed by the S-polarized cut filter 35. If this is done, only the P-polarized laser component 27 will pass through the filter, and this will be detected by the photoelectric conversion element 37. This is named Vp. On the other hand, during Y-direction S-polarized laser illumination, the S+P-polarized laser is reflected from the foreign object 3, but if this is reflected in the x-direction, it is considered to be a P+S-polarized laser.

Similarly, if we focus on the component that is condensed by the objective lens 33 and passes through the semi-transparent mirror and goes upward, if we cut out the P polarization component with the P polarization cut filter 36, only the S polarization component will pass through the filter. Therefore, this is detected by the photoelectric conversion element 38. This will be named V8. Since the reflected light from the foreign object is V, +V5, it is sufficient to add V and V obtained above. Specifically, the X-feed table 41 is set on the base 40, the bearing 43 is attached on top of the X-feed table 41, and the wafer 1 is
A wafer stand 44 with a wafer placed on its upper surface is provided, and a rotary encoder 42 is connected thereto.

On the other hand, the wafer table 44 is driven by a motor (described at the end) and is sent in the X direction while rotating. Furthermore, semiconductor lasers 45 to 48 are used as a blinkable light source. The microscope and semiconductor laser are all fixed to the base. The laser irradiation point is one point 39 on the wafer, but since the wafer is rotated and sent in the x direction, the laser irradiation point is relatively scanned in a line from the entire surface of the wafer. The output of the rotary encoder 42 is shown in FIG. 4A.

Using this signal, the x-direction illumination semiconductor laser 30
is lit as shown in FIG. 4B ("1" is the lighting section).

) Next, the Y direction illumination semiconductor laser 31 is turned on as shown in FIG. The output of the photoelectric conversion element 38 during illumination in the Y direction is shown in FIG. 4E. The waveform shown in FIG. 4F shows the combination of the output of the photoelectric conversion element 37 and the output of the photoelectric conversion element 38. This synthesis circuit is shown in FIG.

The output of the photoelectric conversion element 37 is A/D converted in accordance with the timing pulse 50. Once this output is full adder (full adder)
adder) 59 and store it.

Next, the output of the photoelectric conversion element 38 is A/D converted according to the timing pulse 51, and a full adder (fu11 adder) is applied.
Add at 59. The result of addition by the full adder 59 is input to the microcomputer 60 using the output 61 of the rotary encoder 42 as a timing. At the same time, the position of the x-feed table 41 is input to the microcomputer as a truck signal 63. The output of the rotary encoder 42 is cleared every rotation, and the Z of the rotary encoder 42
49 pulses are counted based on the ERO signal 62.

FIG. 6 shows the relationship between the wafer 1, the output positions 66-70 of the rotary encoder 42, and the tracks 71-73.

When a foreign object is detected, the output of the foreign object, the rotary encoder output position and the tractor number at that time are stored in the microcomputer. With the above steps, the wafer foreign matter inspection is completed. This device can be used in two ways: for wafer quality control and for online wafer inspection.

As explained above, according to the present invention, there is a remarkable effect that foreign matter on a patterned wafer can be detected stably and easily.

In addition, unlike the conventional method of visually inspecting foreign substances on wafers, which took 3 to 4 hours to inspect per wafer, the present invention allows inspection to be performed within 1 minute, which has a remarkable effect. be effective.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a case in which a laser is irradiated onto a wafer obliquely, FIG. 2 is a schematic perspective view showing an embodiment of an apparatus for implementing the method of detecting foreign matter on a wafer of the present invention, and FIG. The figure shows a foreign substance on a wafer in the X direction using the apparatus shown in Figure 2.
and a fourth diagram showing the state of irradiation with the S-polarized laser in the Y direction.
The figure shows a timing chart for polarization laser switching in the device shown in Figure 2, and Figure 5 shows the synthesis of the output signal of the photoelectric conversion element during x-direction illumination and the output signal of the photoelectric conversion element during Y-direction illumination. FIG. 6 is a diagram showing a schematic configuration of a synthesis circuit, and is a diagram showing a locus on a wafer of scanning detection points. Explanation of symbols, 1...Wafer, 2...Pattern, J3...Foreign object, 30...X direction S polarized laser, 31...・Y direction S polarized laser, 33...Objective lens, 35...S polarized light cut filter, 36...P polarized light power cut filter, 37, 38...Photoelectric Conversion element, 44.
...Wafer stand, 45-48...Semiconductor laser.

Claims (1)

[Claims] 1 Laser light having first and second linearly polarized light components is irradiated onto a predetermined position on the wafer from diagonally above in at least two directions around the wafer, and the wafer is irradiated with laser light having the first linearly polarized light component. A component perpendicular to the first linearly polarized light component is received by a first photoelectric conversion element through a first polarization cut filter that blocks the first linearly polarized light component, and a second linearly polarized light component is received by a first photoelectric conversion element. The reflected light obtained from the wafer by the laser beam having the component is passed through a second polarization cut filter that blocks the second linearly polarized light component, and the component perpendicular to the second linearly polarized light component is converted into a component perpendicular to the second linearly polarized light component by a second photoelectric conversion element. A method for inspecting foreign matter on a wafer, comprising: detecting the presence of foreign matter on the wafer by receiving light and adding outputs obtained from each of the first and second photoelectric conversion elements.