JPS6021524A - Position alignment apparatus - Google Patents

Abstract

PURPOSE:To automatically adjust the reference level and accurately detect the position of alignment marks of two objects by measuring interval of identification marks by sequentially comparing additional digitized data and reference slice level value within the storing means. CONSTITUTION:A microprocessor makes an access to a memory in the step 553 to search the peak data in the memory, a slice level is calculated from the peak data in the step 554 and the slice level data is compared with the data of memory in the step 555. This comparison is carried out for the addresses from 0 to 4095. In the step 556, the address where memory data changes from ''0'' to ''1'', or from ''1'' to ''0'' are searched. In this address, an optical signal has been detected and this address corresponds to position alignment mark signal. The peak interval of mark is calculated from this address in the step 557 and interval between marks can also be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for aligning two objects, and in particular, prior to aligning a semiconductor integrated circuit pattern on a mask or reticle to a predetermined position on a wafer (hereinafter referred to as alignment), the present invention relates to an apparatus for aligning two objects. Alternatively, the present invention relates to a position detection circuit that detects the position of an alignment mark on a reticle and the position of an alignment mark on a wafer.

The semiconductor manufacturing process includes a step of sequentially transferring several patterns onto a wafer to form a semiconductor integrated circuit. In this case, in order to accurately position another pattern on the wafer onto which the previous pattern has already been transferred, it is necessary to align the mask with the pattern and the wafer with high precision. This alignment is achieved by first determining the relative positional relationship between the alignment marks written on the mask and the wafer by photoelectrically detecting those marks, and then moving a predetermined amount of time based on this positional relationship. Ru.

By the way, alignment mark detection is performed by identifying that the peak level of the detection signal is higher than a predetermined reference level. However, conventionally, this reference level has been fixed, and depending on the type of wafer or mask that is the substrate for the alignment mark, it may be too high or too low, resulting in detection failure. In addition, when a failure occurred, there were some methods in which the reference level was manually adjusted again.

The present invention has been proposed in view of the above drawbacks, and provides a pattern printing apparatus having a position detection circuit that automatically adjusts a reference level and reliably detects the positions of alignment marks on two objects. With the goal.

The present invention will be described in detail below with reference to the drawings. FIG. 1 shows the external appearance of a pattern printing apparatus having a position detection circuit according to an embodiment of the present invention.

1 is a mask provided with an integrated circuit pattern, and is provided with mask alignment marks and mask/wafer alignment marks. 2 is the mask stage, mask 1
, and move the mask 1 in the plane and in the rotational direction. 3 is a reduction projection lens, 4 is a wafer provided with a photosensitive layer, and is provided with a mask/wafer alignment mark and a wafer alignment mark. 5 is a wafer
It's a stage. The wafer stage 5 holds the wafer 4 and moves it in the plane and in the rotational direction, and also controls the wafer printing position (inside the projection field) and the television.
Move between wafer alignment positions. 6 is an objective lens of a detection device for television wafer alignment; 7 is an objective lens of a detection device for television wafer alignment;
The image pickup tube or solid-state image sensor 1, 8 is a television receiver for viewing images.

Reference numeral 9 denotes a binocular unit, which serves to observe the surface of the wafer 4 through the projection lens 3. 1o is a light source 10a
This is an upper unit that houses an illumination optical system for converging the emitted mask illumination light and a detection device for mask/wafer alignment.

The wafer pot stage 5 holds the wafer transported by a wafer transport means (not shown) at a predetermined position, and first moves to a position where the alignment mark on the wafer is within the field of view of the television/wafer alignment objective lens 6. The positional accuracy at this time is due to mechanical alignment accuracy, and the field of view of the objective lens 6 is J: diameter 1.
Approximately 1 to 2 people. The alignment mark within this field of view is detected by the image pickup tube 7, and the alignment mark of the wafer from there is detected based on a reference mark for TV-wafer alignment (described later) provided in the optical system for TV-wafer alignment. The coordinate position of is detected. On the other hand, since the detection position for auto-alignment of the projection optical system and the position of the aforementioned reference mark for TV conference wafer alignment are set in advance, the auto-alignment position can be determined from the position of these two points and the coordinate position of the TV/wafer alignment mark. The amount by which the wafer stage 5 is fed is determined.

Position detection accuracy for TV/wafer alignment is ±5μ
It is approximately ±10 μm even when taking into consideration the error caused by the movement of the wafer stage from the TV/wafer alignment position to the mask/wafer alignment position. Therefore, fine alignment can be performed within a range of approximately ±10 μ, which is less than 1/10° of the field of view of conventional alignment, and alignment can be performed at a higher speed than conventional alignment.

FIG. 2 is a diagram showing an optical system of a pattern printing apparatus according to an embodiment of the present invention, and shows a state in which alignment mark detection signals on a mask and a wafer are sent to a position detection circuit. In the figure, a mask 1, a reduction projection lens 3, a wafer 4, and a wafer stage 5 are as shown in FIG. The projection lens 3 is schematically depicted for convenience. Reference numerals 11 and 11' are mask alignment marks, which are carved in immovable locations such as the lens barrel or a part of the device.

On the other hand, at the position 20,2 (l) of the mask 11-, there is a scanning line 60f as shown by the month number 75.76 in FIG. 3(A).
fliJ'j, 45°n:ri bite1Illi''
There are also defined lines and slit-like alignments and marks. Also, at the position indicated by 21.21' on wafer 4, month numbers 7], 72, 73.7 in Fig. 3 (A) are shown.
A line or slit-shaped alignment mark is provided at an angle of 45° with respect to the scanning line 6 ( ) as shown by 4 . Then, 6-shi positioning is usually performed using the I-go-getsu of both the left and right observation systems.

Note that the alignment marks on the mask 1 and the alignment marks on the wafer are interposed by a system other than the same-magnification projection system.At this time, the dimensions of both alignment marks do not change even if CI, projection or back projection is used. The dimension of the alignment mark is changed as shown in FIG. 2, and the reduction magnification is set to 4.times. when the dimension of the alignment mark of the wafer is divided by the dimension of the alignment mark of the il''Y mask.

Returning to FIG. 2, 22iJ is a laser light source, and 23 is an optical deflector such as an acousto-optic device. The optical deflector 2; 1 switches the light emission direction between upward, horizontal, and downward in response to a switching signal from the outside. 24 and 25 are convergent cylindrical lenses, which are arranged so that their generating lines are perpendicular to each other, and have the function of converting the cross-sectional shape of the laser beam into a linear one. 2
6 and 27 are trapezoidal prisms which have the function of refracting the light deflected upward and downward by the optical deflector 23 in opposite directions. 28
is a rotating polygon mirror (polygon) that rotates around the rotation axis 29.

Depending on the state of the optical deflector 23, the laser beam 30 emitted from the laser light source 22 is divided into a slit-shaped beam 30a1 which passes through the cylindrical lens 2/l and the prism 26, a slit-shaped beam 30b1 which passes through the cylindrical lens 25 and the prism 27, or The spot-shaped light ray 30c traveling straight takes one of the optical paths, but in each case it converges on a point 31 on the surface of the rotating polygon mirror 28. 32, 33, 34 are intermediate lenses, 35 is an optical path splitting mirror, 36 is a half mirror forming a visual observation system 37.degree. 38, 37 is a lens, and 38 is an eyepiece lens for forming an image of the wafer surface.

39 il, I: half mirror forming an illumination system not requiring visual observation /10.41, /101rl: condenser lens, 41 is a lamp. 42 is a photoelectric detection system 43°4
4+ A half mirror forming 45.46, 43 is a mirror, /I it lens, 45 is a spatial filter, 46 fd: condenser lens, 47 is a photodetector for detecting the alignment pattern signal, 57 is a A lens 58 is a photodetector for detecting a synchronization signal.

Further, 48, 49, 50, and 51 are total reflection mirrors, 52 is a prism, and 53 is an itf-θ objective lens.

Reference numeral 54 indicates the position of an alignment pattern for mask alignment provided on the mask 1''2.

As can be seen from Figure 2, the signal detection system consists of completely symmetrical left and right systems.If the operator side is the front side of the paper, the system indicated by a dash is the signal detection system on the right, and the system without a dash is the signal detection system on the left. I will call it.

Intermediate lenses 32, 33, 3.4 align the origin of vibration from the rotating polygon mirror 28 with the pupil 56 in the aperture position 55 of the objective lens 53.
to form. Therefore, the laser beam is scanned over the mask and wafer by the rotation of the rotating polygon mirror 28.

In addition, in the objective lens system, an objective lens 53, an aperture 55
, the mirror 51 and the prism 52 are movable in the XY directions by a moving means (not shown), and the observation and measurement positions of the mask 1 and wafer 4 can be changed arbitrarily. For example, when the mirror 51 moves in the direction indicated by arrow A in the X direction, the objective lens 53 and the aperture 55 simultaneously move in the A direction, and the prism 52 also moves in the A direction in order to keep the optical path length constant. The mirror 51 is moved by 1/2 of the amount of movement.

On the other hand, when moving in the Y direction, the entire optical system for observation and position detection moves in the Y direction (direction perpendicular to the plane of the paper).

The scanning beam 61 of the optical path 30a passing through the cylindrical lens 24 makes an angle θ=45° with respect to the scanning axis 60, and is approximately parallel to the mark 71°72.75 in FIG. When scanning is performed in this state, the photodetectors 47 and -47 obtain S, S, and S signals as shown in FIG. 3(B). s, s.

7] 75 72 71 75 S7□ are signals corresponding to the alignment marks 71, 75, and 72, respectively. Furthermore, even if there is minute dust on the scanning surface, it is not detected in the case of a spot-shaped beam and is averaged as an output for practical use.

On the other hand, the optical path 30b passing through the cylindrical lens 25
The scanning Billmulo 2 of is θ−− for the scanning 1141160
45° inclined marks 73, 74. ．． 76, the detection signal is parallel to S73.76 in FIG. 3(b). S76゜S74
becomes. Therefore, the detection signal S71'S75' S7
2'S73. The interval between S76 and S74 is 1f111
Then, the deviation l between the mask and the wafer can be detected, and when they match, the intervals between the detection signals become equal.

Incidentally, the present applicant 1-j has proposed auto-alignment in Japanese Patent Application Laid-Open No. 5:190872 or Japanese Patent Application Laid-Open No. 53-9:1754.

Hereinafter, the alignment of the alignment mark 20 on the mask 1 and the alignment mark 21 on the surface of the wafer 1, that is, the outline of the mask-wafer alignment has been explained using FIGS. 2 and 3.

Next, the configuration of an alignment mark position detection circuit of a pattern printing apparatus according to an actual Mli example of the present invention will be described.

FIG. 4 is a block diagram of a position detection circuit according to an embodiment of the present invention. 47, 4.7 is a photodetector that converts the optical signal of the alignment mark already explained into an electrical signal.1.
Reference numeral 58 and 58' denote a photodetector that detects the scanning timing by converting the laser beam scanning the mask and wafer into an electrical signal.

Reference numeral 101 denotes a synchronization detection circuit which binarizes and waveforms the output signals of the photodetectors 58 and 58 and outputs a synchronization signal 161 and control signal 03 as shown in FIG. 3(c). Reference numeral 102 is an analog switch, which performs a switching operation in response to a control signal 103, and a photodetector 47.4.
7' are combined (FIG. 3(B) shows the output signal of the photodetector 47). 104 is an AD converter, which converts the analog signal level of the analog switch 102 into an 8-bit digital signal at a fixed timing. A latch 105 temporarily stores the digital signal of the AD converter 104. AI) Timing signal controlling converters 11-104 and latch 105 (
(not shown) is output from a control circuit 155, which will be described later.

150 is an adder with an input A port 8 bits long, an input B port 16 bits long, and an output Y port 16 bits long, which adds the output data (T) of the latch 105 and the data (B) for the latch 153, and 151. 152
is 16 bits x 4. It is a K-word random access memory, and address and read/write control is performed by the output of the data selector 154 (YOI Y ).
) is controlled by The output of memory 152 is input to latch 153, and the output of latch 153 is input to B port of adder 150 as described above.

On the other hand, the input and output of the memory 152 are connected to the data bus 121 of the microprocessor (not shown) via buffers 1.57 and 158, respectively.

154 is a data selector, and its output signal (R/w
The output signal (R/w signal, ADR signal) is either the output signal (R/w signal, ADR signal) of the control circuit 12-155 or the output signal (R/w signal, ADR signal) of the microprocessor output via the address and control bus 122. ADR signal), and the selection is made by the control circuit 15.
5 is controlled by a select signal 156 outputted by the controller 5.

Note that the select signal 156 is controlled by a microprocessor.

Next, the operation of the position detection circuit according to the embodiment of the present invention will be explained with reference to the drawings. FIG. 5(5) is a flowchart showing the control sequence of the microprocessor that controls the position detection circuit of FIG. 4. Also, Figure 5 (B
) is a flowchart for explaining in detail the state of execution of the measurement shown in FIG. This will be explained in detail below. Clear memory 152 (step 550).

That is, the microprocessor controls the control circuit 15
5 controls to output the select signal 156 to the data selector 154. As a result, the data selector 154
is the microprocessor address and control bus 122
Select. Memory 152 is directly accessed by the microprocessor and all storage areas of memory 152 are cleared by writing zeros.

Next, at 155 it? 111 start is commanded to the control circuit 155, and in step 552, the state waits for the end of the open side. The measurement is separated from the control of the microprocessor and is performed by hardware under the control circuit 155.

To explain this opening side operation using FIG. 5 (13), after the opening side start 551, in step a560, the address counter (not shown) for the memory 152 provided in the control/roll circuit 155 is cleared. .

Next, when a synchronization signal is detected at 561, the data at address 0 of the memory (which is zero because it is initially cleared) is read at 562, and the first sampling signal is read at AD converter 104. Koshinkan is digitized. These two data are stored in latches 105 and 15, respectively.
3 and is input to the adder 150 at the same timing and added (step 56;
51 to memory 152 (step 564
), the address counter for memory 152 is incremented by 1 (step 565).

The optical signal digitized by the following timing signal is
It is stored at address 1 in the memory 152 according to the instruction of the address counter.

Thereafter, each digital data of the optical signal for one scan is sequentially stored in a predetermined address of the memory 152 by the same operation. This operation continues until the end of the synchronization signal (loop 562→567). The number of words in address 4 of the memory is determined by the period of the synchronization signal and the sampling interval of the AD converter 104, and the address does not advance to address 4095 (4K) before the synchronization signal ends.

The scan is repeated up to a predetermined number of times (loop 560→567). The number of scans is determined according to the required accuracy. The relationship between the required accuracy and the number of scans is disclosed in Japanese Patent Application No. 57-208765 filed by the present applicant.

When the predetermined number of measurements are completed, a termination signal is generated to the control circuit 15514 microprocessor in step 568, and the measurement is completed. At the time when the measurement is completed, the waveform obtained by adding up the waveform shown in FIG. 3(B) by the number of times of scanning is often stored in the memory 152 as digital data.

Returning again to FIG. 5(A). After the measurement is completed, the microprocessor accesses the memory 152 in step 553 to search for peak data in the memory 152, and then in step 55
In step 4, the slice level is calculated from the peak data, and in step 555, this slice level data and memory 1 are
52 data are compared. The comparison result is e.g. data”
' o '' (if the data in memory is smaller than the slice level data), and data II 11+ (if the data in memory is smaller than the slice level data).
It is written into memory 152 again. This comparison is performed from address O to address 4095. Next, in step 556, the process searches for an address where the memory data changes from 0 to 1' and from J to II OIT.This address is the address where the optical signal was detected, and the third address is T71. T71', T75°T75・
Corresponds to... Therefore, in step 557, the peak interval between marks is calculated from this address, and the interval between marks can be determined.

As described above, according to the embodiment of the present invention, the slice level is automatically determined in accordance with the peak value of the actual alignment mark signal, so that it is possible to prevent the alignment mark signal from being overlooked, and it is also possible to manually determine the slice level. This has the effect of saving the trouble of resetting the slice level. Further, since the number of measurement scans can be selected depending on the required positioning accuracy, work efficiency is improved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a positioning device according to an embodiment of the present invention, FIG. 2 is a diagram showing an optical system of a positioning device according to an embodiment of the present invention, and FIG. 3 (4) is a perspective view of a positioning device according to an embodiment of the present invention. is a schematic diagram of alignment marks on a wafer. FIG. 3(B) is a diagram showing the detection signal corresponding to the alignment mark in FIG. 3, and FIG. 3(C) is the synchronization detection circuit 1,
FIG. 4 is a block diagram of the position detection circuit, and FIG. FIG. 5(B) is a flowchart for explaining in detail the execution state of the first measurement shown in FIG. 5(A). 47.47, 58.58...Photodetector 101...Synchronization detection circuit 102...Anaphroswitch 103...Anaphroswitch control signal 104...A
D converter 1 (15, 151+, 153... latch 121.
・Data bus 122...Address and control bus 150...Adder 152...Memory 154...Data selector 155...Control circuit 156...Select signal 1.57, 158...Buffer 161... ...Synchronized bow-6 19- (A) Fig. 5 Fig. 5

Claims (1)

[Claims] A first identification mark on a first object and a second identification mark on a second object.
A positioning device that measures the distance between the objects and the identification mark and properly aligns the objects based on this distance, comprising a photoelectric conversion means for detecting the identification mark, and an output signal level of the photoelectric conversion means. digital conversion means for sequentially digitizing; storage means for storing the digitized data in a predetermined address order; and addition of the digitized data in the storage means and the digitized data of the identification mark obtained by the next scan. , an adding means for sending the added data to the storage means so that it is stored again in a predetermined address order; and a reference slice based on the added digitized data obtained by scanning a predetermined number of times and stored in the storage means. The device comprises a setting means for setting a level, and a comparison means for successively comparing the magnitude relationship between the added digitized data in the storage means and the reference slice level value, and the interval between the identification marks is determined based on the comparison result of the comparison means. A positioning device characterized by having a position detection circuit for measuring.