JPS6049241B2 - Wafer scribe line detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wafer scribe line detection device, and more particularly to a device that removes unnecessary signals by performing directional spatial filtering in a detection optical system.

A device that finds the wafer scribe line position and divides the wafer into each chip (e.g. wafer scriber) and a device that tests the normality of each chip (e.g. wafer tester)
Conventionally, one operator relies on visual observation using a microscope, TV, etc. to position each chip.

The 21C image is read on a TV and the pattern is analyzed.

3 alignment marks are determined and the chip position is determined.

However, each of the above methods has the following drawbacks. 1. Visual inspection reveals variations among workers, uneven working hours, and inefficiency.

2. Equipment for pattern analysis is large-scale and expensive.

3 The alignment mark must be determined in advance.
The process for this must be added separately to the wafer preparation, which is complicated and may limit the size of the wafer and the work.

As a scribe line position detection device free from such drawbacks, the applicant's earlier patent application 1983-143 has been proposed.
The device disclosed in No. 271 consists of the following principles and configurations.

Laser light (monochromatic, high-intensity light) or the like is focused near the scribe line on the wafer using a cylindrical lens system so as to be parallel to the line. The beam width is condensed to the same extent as the width of the disk life line, and the converged beam is made to scan the wafer by sinusoidal vibration using a vibrator in the optical path. If this is the destination optical system, the light receiving optical system is an optical system that receives only scattered light. Since the IC circuit pattern is generally smaller than the beam width, it causes scattering and diffraction and is received by the scattered light receiving optical system, but when the spot light falls on the scribe line, the scribe line is almost Since the width is equal to or larger than the spot, the incident light is directly reflected back along the optical path, and only a small amount of scattering occurs. This is the basis that enables the establishment of the present invention. That is, when only the scattered light is received and detected as a signal, the scattered light becomes a small signal only when the beam passes through the scribe line. At this time, when the vibration center of the beam coincides with the scribe line center, the time intervals of the minimum points of the scattered light intensity that occur during one period of sine vibration become equal. Furthermore, if the centers are shifted from each other, the time intervals between the minimum scattered light intensity points will differ. In order to properly obtain scattered light, it is more convenient to use a line spot as the focused spot than a point spot. This is because the wafer scribe line is a line. An electronic circuit is configured to detect and calculate this time difference. The peak position of the scattered light current received by the photoelectric element and waveform-shaped by the preamplifier and clipping circuit is determined by the differentiating circuit. Generate gate pulses in the differentiator circuit and alternately trigger the addition and subtraction counters. A high-speed pulse is input to the addition/subtraction counter, and when the addition/subtraction gate is applied alternately, a pulse corresponding to the time difference is obtained. When an additional drive circuit is added to the above circuit, this circuit can obtain the deviation between the center of the wafer scribe line and the center of vibration as the count number of the addition/subtraction counter. Also,
When the deviation between the vibration center and the scribe center is small, a linear relationship is established between the positional deviation and the pulse amount (positional deviation and pulse amount are proportional), and the amount of feedback to the wafer stage is is more accurate than when the difference is large, which has the advantage of making approach control easier. Signals obtained by the above optical system and electronic circuit system are fed back to the wafer stage system.

The wafer stage mechanism receives the amount of feedback given from the electronic circuit section, the direction and amount of positional deviation between the wafer scribe center and the beam vibration center. The wafer stage is moved according to this amount of feedback, and the operation is repeated until the positional deviation falls within the tolerance. Although the scribe line center detection device as described above has various advantages, it is based on the premise that there is no scattered light from the scribe line 4.

However, some scribe lines have a multi-layered shape or are separated, and when a laser spot light hits such a scribe line, scattered light is generated due to the layered layers and separation. For this reason, there is a possibility that the position of the scribe line cannot be set to the minimum position of the signal detected by the scattered light. Furthermore, when recognizing the scribe line position through image processing in ITV and the like, when the scribe line has a complicated shape as described above, it is difficult to recognize the position, and a large burden is placed on the software for the recognition. Therefore, an object of the present invention is to provide a device that eliminates scattered light from multi-stage, multi-layered scribe lines and detects only scattered light from an IC pattern on a detector.

The principle of the present invention is that the layers of a multi-stage, multi-layered scribe line generally run parallel to the scribe line, and therefore most of the scattered light from the scribe line is scattered in a direction perpendicular to the scribe line. However, because the IC pattern has a random shape, it is scattered in almost all directions.

The problem of the present invention is to insert a spatial filter (hereinafter referred to as a band-shaped light shielding plate) that blocks scattered light from the scribe line in a direction perpendicular to the scribe line near the entrance pupil of the scattered light receiving optical system in accordance with the above principle. It was resolved by this. In this case, it is desirable that the width of the band-shaped light-shielding plate be approximately equal to the length of the laser spot focused by the cylindrical lens. Further, the band-shaped light-shielding plate can rotate 900 times when the detection section is used for both the X and Y directions. In the electrical signal processing for detecting scattered light in the present invention, the scattered light signal is sliced at appropriate thresholds to generate pulses. Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows how irradiated laser light is scattered from above an IC chip.

1 to 3 show the case of a scribe line without stepped layers, etc., and the IC pattern S is the width ω of the laser focused light R.
Since it is a small vertical and horizontal cross pattern, the focused light irradiated on the IC pattern soil is scattered in all directions, but since the width of the scribe line is larger than the width ω of the focused light R, it is irradiated onto the scribe line. Focused light is not scattered. Therefore,
The scattered light signal reaches its minimum value when the focused light comes on the scribe line as shown in FIG. 1. 1. FIGS. 4 to 8 show the case where the step layer D etc. runs in the direction of the scribe line L, and when the focused light R is irradiated onto the scribe line L, the step layer D causes the scattered light D. F occurs. Therefore, as shown in FIG. 1, the scattered light signal has a peak 6a on the scribe line L. In the present invention, scattered light D. F is removed using a spatial filter (band-shaped light-shielding plate) using the directionality of its scattered light.

FIG. 17 shows the scattered light D. from the step layer D, etc. A gate signal obtained by slicing at a predetermined threshold level, which is a signal with F removed, is shown in FIG. As mentioned above, the stepped layer D runs in the direction of the scribe line, and the scattering D. Most of F is reflected in the direction of the stepped layer D, that is, in the direction perpendicular to the direction in which the scribe line runs. This has different properties from the scattered light reflected in all directions from the IC pattern S. Therefore, the scattered light D. is perpendicular to the direction of the scribe line. By cutting only F, the scattered light signal from the IC pattern S is generated, but the scattered light signal from the scribe line due to the step layer is excluded. It will be done.
FIG. 2 shows an embodiment in which the light-shielding band of the present invention is inserted into a scattered light condensing system.

This is a case where a scribe line L runs in the X and y directions on the wafer 26, and there are stepped layers D, etc. parallel to the scribe line. Here, the scribe line L running in the x direction will be explained. Focused light 2 irradiating onto the wafer 26
0 is a focused light beam that is vibrated in the y direction and has a width ω in the y direction and a length 1 in the X direction, for example, the width ω is 20 to
The length l of 30 pm is about 1 to several degrees. Only the scattered light from the wafer 26 is reflected by the donut-shaped mirror 21 via the donut-shaped lens 22, condensed by the condensing lens 23, and incident on the light receiver 25 to generate a scattered light signal. X
Since most of the light scattered by the stepped layer D running in the direction occurs in the y direction, if a band-shaped light shielding plate 26 is provided in the y direction of the condenser lens 24, most of the scattered light from the stepped layer D in the X direction is removed. be able to. The width of this band-shaped light shielding plate 26 corresponds to the length 1 of the spot of the focused light 20. On the other hand, since the scattered light from the IC pattern has omnidirectionality, only a part of the scattered light from the IC pattern is removed by the light shielding plate 24, while the majority enters the light receiver 25 and generates a scattered light signal. I can do it. The vibration direction of the focused light 20 is rotated by 90 degrees with respect to the scribe line running in the y direction, and the light shielding plate 24 is rotated by 90 degrees accordingly. Of course, optical systems may be provided separately in the x direction and the y direction. FIG. 3 shows the overall configuration of an optical system in an embodiment of the present invention. 1 is a laser, 2 is a beam expansion system, 3 is a sindrical lens, 4 is a total reflection mirror and an oscillator, 5 is a beam splitter, 6 is an interlock, 7 is an image rotator, 8 is a beam splitter, 9 is a donut shaped mirror , 10 is a donut-shaped condenser lens, 11
1 is an imaging lens, 12 is a light receiving element, 13 is a total reflection mirror, and 14 and 15 are light shielding plates.

The diameter of the light from the laser 1 is expanded by a beam expansion system 2 and enters a cylindrical lens 3.

Here, the beam receives power such that it converges in one direction, x or y, on the wafer. It is reflected by the vibrator 4 and split into two beams by the half mirror 5. The direction of the light beam traveling to the image rotator 7 changes by 900 compared to other light beams. By switching the interlock 6, two light beams are selected and it is determined whether to perform measurement in the X direction or the Y direction on the wafer. The beam splitter 8 matches the two beams separated by the half mirror 5, but of course only one beam enters the surface of the beam splitter 8 during measurement. That is, if the path 5-13-8 is defined as the X direction, the path 5-7-8 corresponds to the y direction. Measurements are made individually for either one. The beam changes its direction at the total reflection mirror 13, passes through the center of the donut-shaped condenser lens 9 and the donut-shaped mirror 10, and is directly incident on the wafer surface. The beam width ω in the converging direction on the wafer is determined by the so-called N. A. It depends on the width of the scribe line and is preferably narrower than the scribe line width. Specifically, around 20 to 40 pm is required. Also, the length I of the beam in the non-convergence direction is 1T0t~
A few words are enough. Further, regarding the vibration amplitude, it is desirable that the vibration amplitude be larger in consideration of the optical system and the offset of the wafer, and although there is a limit due to the measurement accuracy, an amplitude of around 1.5 liters is sufficient.
During beam vibration, total reflection light occurs from the scribe line and scattered light occurs from the pattern surface, but as a light receiving lens,
Since the donut-shaped lens 10 is used, only scattered light is received.

The scattered light passes through a donut-shaped total reflection mirror 9, an imaging lens 11, and is focused on a light receiving element 12. As mentioned above, if there is a stepped layer or the like in the scribe line, there will be scattered light from it, but this is blocked by the light shielding bands 14 and 15. FIG. 4 shows the electrical waveform processing for positioning the scribe line using the scattered light signal.

Figure 4 1 shows the center of the scribe line and the oscillating focused light beam 2
This shows the locus of the beam center when the center of zero is shifted.
A broken line 40 indicates the center of the scribe, and a solid line 41 indicates the locus of the focused beam on the wafer. Figure 4-2 is the reference gate COs.
ine waveform is shown. FIG. 4-3 shows a state in which the scattered light signal from the light receiving element 12 and the slice level signal 42 are observed simultaneously. Figure 4-4 is the reference gate signal output, CO
This corresponds to 2 cycles of 3 of the sine waveform. FIG. 4-5 shows pulses of the period sliced according to FIG. 4-13. FIG. 4-6 shows the detection pulse output, and a first detection pulse 43, a second detection pulse 44, and a third detection pulse 45 are generated at the rising edge of the pulse shown in FIG. 3-5. 4-7 and 4-8 correspond to the detection pulse interval of the first control gate signal 46 and the second control gate signal 47 of FIG. 4-6. FIG. 4-9 shows the clock output of the clock signal 31. The signal waveform shown in FIG. 4 will be explained below. Figure 3-
1 shows the case where the center of the scribe line and the center of beam vibration are different. In this case, the scattering and optical signals are as shown in FIG. 41 intersection) takes the minimum value. This minimum value usually has a sharp peak, but in a scribe line with steps, the waveform can be shaped by a band-shaped light shielding plate as shown in Figure 1.
- Peaks are smoothed as in g.

Therefore, since it is not appropriate to detect the peak, the scattered light signal is cut at the slice level. The signal shaped as shown in FIG. 4-5 is converted into a pulse as shown in FIG. 4-6, and three control gate signals are generated as shown in FIG. 4-7 and 8, respectively. FIG. 4-9 is a high-speed clock and is the input of the addition/subtraction counter. As shown in FIG. 4-4, the reference gate pulse is 312 times the beam vibration period. During this period, the scattered light intensity always decreases by three times, and the counter gate signal for UP, which is the first control gate signal 46, and the counter gate signal for DOWN, which is the second control gate signal 47, are always output in correspondence. The Rukoto. These UP and DOWN signals are input in an addition/subtraction counter input gate control circuit, and the input order is synchronized with the reference gate pulse signal.

The addition/subtraction counter output indicates the deviation between the laser beam vibration center and the scribe line. For example, R
It is connected to the input terminal of a C meter, minicomputer, or microprocessor to smooth the output, integrate it, and use it as a feedback signal. As described above, according to the present invention, the spatial characteristics of scattered light are taken into consideration, and since the light-shielding zone removes only scattered light in a specific direction, the target signal can be detected without complex electrical signal processing or information processing. can be detected.
By skillfully utilizing the extremely characteristic property that scattered light from a scribe line only emerges in a direction perpendicular to the scribe line, it has the advantage of being able to solve problems that are difficult in conventional detection. The scribe line detection device of the present invention can be widely used in automatic position detection parts of IC measuring machines and manufacturing machines such as wafer probers and wafer scribers that require wafer alignment.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the state of focused light scattered from an IC pattern and a scribe line, FIG. 2 is a diagram showing a light-shielding band inserted into a scattered light collection system according to the present invention, and FIG. 3 is a diagram showing the present invention. FIG. 4 is an overall view of the optical system and a diagram showing waveforms of signal processing in the present invention. Explanation of symbols of main parts, light receiving optical system...21,
22, 23, 25 (Figure 2), 9, 10, 11, 12 (
(Fig. 3), light shielding plate...24 (Fig. 2), 14,
15 (Figure 3).

Claims (1)

[Claims] 1. A light transmitting optical system that irradiates and scans a semiconductor integrated circuit wafer with focused light having a predetermined vibration cycle, a light receiving optical system that receives only scattered light of the focused light from above the wafer, and the received scattered light. is converted into an electrical signal, the minimum value of the signal is detected as a scattered light signal from the wafer scribe line position, and the detected minimum value determines the scanning center of the focused light irradiated onto the wafer and the wafer scribe line. In a wafer scribe line detection device comprising a circuit that measures positional deviation from the wafer line; in a direction perpendicular to the direction in which the scribe line runs at a position near the entrance pupil of an optical system that receives only scattered light from the wafer. A wafer scribe line detection device characterized by installing a band-shaped light shielding plate that blocks scattered light.