JPS6118858B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wafer and mask alignment device, and more specifically, to optically scan a surface provided with a real device pattern and an alignment mark, and after distinguishing between the real device pattern and the alignment mark, align the alignment mark. The present invention relates to a device that allows a portion to be properly optically scanned.

An alignment mark is provided between the mask and the actual device pattern on the wafer (hereinafter simply referred to as the scribe area), and this alignment mark is scanned with a scanning line that is significantly thinner than the scribe area, for example, a light spot with a significantly smaller diameter. , a device for detecting the amount of wafer displacement has already been proposed by the applicant of the present invention. (1972 patent application 26304
(No., Name: Masks or wafers for manufacturing semiconductor devices and equipment for aligning them).

In this earlier application, the applicant stated that it is very difficult to match the scribe area and the scan line because the scan line is very thin. In the device of the same prior application, the scribe area, that is, the mask and wafer, are moved relative to the scanning line, and the coincidence of the scanning line and the scribe area is determined from the scattering distribution state of light obtained from each scanning line. , When a signal indicating a match is obtained, the relative deviation amount between the mask and wafer is obtained from the mask and wafer alignment mark scanning signals.

The present invention relates to an improvement of the device of this earlier application,
The improvement is that the coincidence between the scanning line and the scribe area is determined based on the intensity of reflected light.

The present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a diagram showing the optical arrangement of the alignment apparatus of the present invention, in which 1 is a wafer and 2 is a mask. On the wafer 1, alignment marks formed by inclined surfaces as shown by numbers 3 and 4 in FIG. 2 are provided. Further, on the mask 2, alignment marks formed by inclined surfaces as shown by numbers 5, 6, 7, and 8 in FIG. 2 are provided. still,
This alignment mark is provided between the actual device patterns as shown in the third figure. Returning to the explanation of FIG. 1 again, 9 is the wafer 1.
10 is a rotating polygon mirror that rotates around a rotation axis 11;
3 and 14 are intermediate lenses, and 15 is a telecentric objective lens. Intermediate lenses 12, 13, 14
converts the polarized light from the rotating polygon mirror 10 into parallel light, and forms the deflection origin 16 (ie, the deflection origin) of the polarized light at the aperture position 17 of the objective lens 15. Therefore, spot light scanning is performed on the mask and wafer 2, 1 placed on the focal plane of the objective lens 15. 18 is a beam splitter.
This beam splitter 18 forms a photoelectric detection system. A lens 19 works together with the lens 14 to re-image the shake origin image 16. 20 is a spatial filter placed on the plane where re-imaging is formed. This spatial filter 20 has a light shielding portion of the same size as the shake origin image. Therefore, this filter 20 blocks the reflected light from the surface perpendicular to the optical axis of the objective lens 15, and allows the reflected light from the slope to pass through. Therefore, alignment marks 3 to 8
Transmits light. 21 is a condenser lens, 2
2 is a photodetector. This photodetector provides an alignment scanning signal as the spot moves. 23 is a beam splitter. This beam splitter 23 forms an observation system. 24 cooperates with lenses 15, 14, and 13 to place a mask, a wafer, and a mask on the field lens 25.
A lens for forming a 2,1 image, 26 is an eyepiece.

Note that the wafer and mask are moving in a direction perpendicular to the moving direction of the light spot. Therefore, the information scanned by each scanning line is read by the photoelectric element 22. At this time, the output of the photoelectric element 22 is significantly different between when there is a scanning line on the actual element pattern and when it is on a scribe line. That is, FIGS. 4a, b, and c each show the positional relationship between the wafer or mask and the scanning line, and a is the scanning line 4.
0 is the real element pattern part 41 and the real element pattern part 4
If the scanning line 40 is located in the scribe area 43 between 2, b and c are located in the scribe area 44 between
It shows the case where is located. The outputs of the photoelectric elements in these cases are indicated by a', b', and c', respectively. As is clear from a', b', and c', the output waveform for a' is significantly different from that for b' and c'. Therefore, by observing with an oscilloscope etc.
It can be easily determined whether the scanning line is on the scribe area or not.

If these judgments are to be made automatically, it is desirable to pass the output from the photoelectric element through a low-pass filter. That is, Figure 4 a'', b'', and c'' show the outputs obtained by passing the output of the photoelectric element through a low-pass filter.As is clear from these, the scanning line is in the scribe area. case
When the output level of a″ is in the real element pattern
It is lower than b″ and c″. Therefore, an appropriate reference level V _TH is determined, and if the output of the low-pass filter is lower than this level, it is determined that there is a scanning line on the scribe line.

FIG. 5 shows an electrical processing system to which this method is applied. 50 is an amplifier firer that amplifies the output of the photoelectric element 22. The output of the amplifier firer 50 is sent to a low pass filter 51. The output of the low pass filter is compared by comparator 52 with the reference level mentioned above. The results are input to the microcomputer 53. or,
Amplifier firer 5 is used to obtain one scan start or end signal from the output of amplifier firer 50.
The zero output is sent to timing circuit 54. The one-scan start and end signals from the timing circuit 54 are similarly input to the microcomputer 53. Furthermore, the output of the amplifier firer 50 is sent to a rectangular wave shaping circuit 55. Here, it is shaped into a pulse-like waveform. The pulse interval of this pulse wave is measured by a pulse interval counting circuit 56. This result is also sent to the microcomputer 53. This pulse wave is also sent to a pulse wave number counting circuit 57. This result is also sent to the microcomputer 53 in the same way. A circuit 58 drives and controls the Y motor 59, the θ (rotation direction) motor 60, and the X motor 61 using the output of the microcomputer 53.

Next, the operation of this electrical system will be explained. First Y
Assume that the motor is rotating and the wafers and masks 1 and 2 are moving in a direction perpendicular to the moving direction of the spot, and further assume that the relationship between the scanning line, the mask, and the wafer is as shown in Figure 4c. . In this case, since the output of the comparator 52 indicates a mismatch between the scribe area and the scanning line, the output of the microcomputer does not cause any change in the θ motor and the X motor. Therefore, the Y motor rotates further to move the mask and wafer. Next, if there is a scanning line in the actual element pattern, but the input of the comparator 52 represents a signal indicating that there is a scanning line in the scribe area, (depending on the actual element pattern, such an output may occur). (This cannot be said to be true.) In this case, the determination is made based on the output of the pulse number counting circuit. That is, the number of pulses indicating the number of scribe lines is always 6 or less in the alignment mark of FIG. 2. Therefore, the output of the pulse number counting circuit is 7 per scan.
If the number of pulses is more than 1, it is determined that there is no scanning line on the scribe area, and the θ motor and the X motor are the same as before. The number of pulses for one scan is counted by the pulse number counting circuit in a microcomputer by calculation with the output of the timing circuit.

Next, the case where the scanning line comes to the scribe area will be explained. In this case, naturally the circuits 52, 57
The output of is a determination that a scan line exists in the scribe area. In this case, as a result of the output of the timing circuit and the calculation of the pulse interval counting circuit 56, the interval between the alignment marks is determined by the microcomputer 5.
Measured within 3. Further, signals from the other scanning optical system and a system having the same configuration as the circuits 50 to 57 are input to the microcomputer 53. Therefore, the alignment mark interval measurement results from the left and right systems are calculated in the microcomputer 52 based on a predetermined calculation formula, and the amount of deviation of the wafer and mask is input from the microcomputer 52 to the drive circuit 58. Based on the output of this drive circuit, the Y, θ, and X motors are operated as necessary to perform mask and wafer alignment.

In the electrical system shown in FIG. 5, an example using the low-pass filter 51 has been described, but it is also possible to use an integrator instead of the low-pass filter. FIG. 6 shows an example using an integrator.

SW1 and SW2 are switches, 60 is an integrator, 6
1 is an AD converter. The output of amplifier 50 in FIG. 7a is input to timing circuit 54.
It is assumed that this output is obtained when the scanning line and the scribe area match. The scan start and end signals (FIG. 7b) of this timing circuit are sent to the microcomputer in the same manner as before. Furthermore, the signal of this timing circuit is sent to switch SW1, which is turned on by a rising signal as shown in FIG. . That is, the integrator 60 integrates the output of the amplifier 50 between the rising signal and the falling signal in FIG. 7c. After the integration is completed, the AD converter is activated by the output of the timing circuit 54 (FIG. 7d) to produce an integral value of the integrator and send it to the microcomputer 53. The output of this integrator 60 is shown in FIG.
As shown in the figure, the value is low when the scanning line matches the scribe area, and high when the scan line does not match. Therefore, it is determined whether or not they match based on this level. The subsequent operations are the same as in the previous example, so they will be omitted. However, the switch SW2 formed by the falling signal of the scan period signal Fig. 7b
Due to the ON signal, switch SW2 is closed,
The integral value of the integrator is cleared and returns to the initial state.

As described above, compared to the device of the prior application, the device of the present invention has the advantage that it does not require an optical filter to examine the distribution state of scattered light and can determine whether the scribe area and the scanning line match with a simple configuration. have. Furthermore, the apparatus of the present invention has good accuracy because it detects the previous coincidence by counting the number of pulses in one scan, in addition to the above-mentioned judgment mechanism.

[Brief explanation of the drawing]

FIG. 1 is an optical layout diagram of the alignment apparatus of the present invention, FIGS. 2 and 3 are diagrams showing alignment marks provided in the scribe areas of the mask and wafer, and FIG. 4 is a diagram showing the relationship between the mask, wafer, and scanning lines. Figure 5 is a block diagram of the electrical system that processes the electrical signal obtained by the photoelectric element in Figure 1, and Figure 6 is a diagram showing the electrical system with a different configuration from Figure 5. System block diagram, Figure 7 is 6
FIG. 3 is an output waveform diagram of each circuit of the electrical system shown in the figure. In the figure, 1 is a wafer, 2 is a mask, 3 to 8 are alignment marks, 9 is a laser light source, 10, 1
1 is a rotating polygon mirror, 13, 14, 15, 19, 21
is a lens, 20 is a filter, 22 is a photoelectric element,
50 is an amplifier firer, 51 is a low-pass filter, 52 is a comparator, 53 is a microcomputer, 54 is a timing circuit, 55 is a waveform shaper, 56 is a pulse interval measuring device, 57 is a pulse number counter, and 58 is a motor drive. Circuit, 59-61 are motors.

Claims (1)

[Scope of Claims] 1. An alignment mark provided in a strip-like region between actual device patterns on a mask or wafer is optically scanned along a scanning line, and a scan obtained by this optical scanning is performed. In an alignment device that introduces a signal into an arithmetic circuit, calculates the amount of mutual positional deviation between the mask and wafer, and adjusts the mutual positional relationship between the mask and wafer based on this calculated value, this device means for changing the relative positional relationship between the mask and the wafer and the scanning line; and a means for discriminating based on the intensity of light, and the mask and wafer are adjusted based on the calculated value of the arithmetic circuit obtained when a signal from the discriminating means indicating that alignment mark scanning is being performed. An alignment device characterized by: 2. In the alignment device according to claim 1, the determining means includes a photoelectric element that converts reflected light into an electrical signal, and a circuit that determines whether the output value of this photoelectric element is greater than a predetermined value. An alignment device comprising: