JPH0769142B2 - Alignment device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an alignment apparatus in an exposure apparatus or the like for manufacturing a semiconductor element, and particularly to a relative alignment between a mask and a substrate (photosensitive). Related to the device.

(Prior Art) This type of exposure apparatus exposes a circuit pattern formed on a mask onto a photoresist on a semiconductor wafer. However, in order to manufacture a semiconductor element, several layers to several dozen layers are formed on the wafer. It is necessary to form different circuit patterns by overlapping. In this case, the alignment mark formed on the mask and the alignment mark previously formed on the wafer are optically detected, and the mask and the wafer are adjusted so that the positional deviation of both marks is driven within a predetermined allowable range. Accurate superposition is performed by relatively moving. Various methods have been considered as methods for optically detecting the mark on the mask and the mark on the wafer. As an example, the mark on the mask and the mark on the wafer are scanned with a spot such as a laser beam, and the scattered light and diffracted light generated from both marks are photoelectrically detected to scatter and diffract the spot light on the scanning line. 2. Description of the Related Art There is known an automatic alignment device that detects the deviation of both marks from the light generation position.

(Problems to be Solved by the Invention) In a system in which the spot light scans the mask and the wafer at the same time, the mask and the wafer are photoelectrically detected while the spot light scans the mark on the mask and the mark on the wafer. And need to be stationary. However, particularly in a step-and-repeat exposure apparatus, the wafer is stepped by a stage that moves two-dimensionally, and the spot for auto-alignment is performed while the mask and the exposure area on the wafer are positioned with an accuracy within a few microns. Since the scanning is performed, the alignment between the mask and the wafer cannot be achieved with high precision due to the influence of the vibration of the stage. There is no problem if you perform auto alignment after waiting for the stage to stop completely, but if you try to perform alignment for each exposure with the step-and-repeat method, throughput will decrease as it is, which is not preferable. Absent.

The influence of the vibration of the stage as described above also occurs when the wafer (or reticle) of the spot light scanning system is aligned only.

(Means for Solving Problems) The present invention relates to a moving means (reticle stage or wafer stage) for moving an object (reticle or wafer) having a predetermined pattern (mark, standard pattern) and a light beam for the pattern. (Spot lights SP, SP ₁ , SP ₂ ) Alignment means (20, 21) for detecting positional deviation of an object with respect to a predetermined reference point (for example, a fixed point on the apparatus) by detecting light information from the pattern by scanning. , 22, 23, 24, 25, 3
0, 32). First, there is provided a first detecting means (scanning position detecting section 36) for outputting the first information (DS) regarding the scanning position of the light beam. Further, the second information (DR, DW) corresponding to the position change of the object (actually, the stage) with respect to the position shift detection direction by the alignment means.
Alternatively, a second detecting means (laser interferometer 5, 9) for outputting DRX, DRY) is provided. Then, arithmetic means for introducing the information (ADR, ADW or ADRX) of the difference between the first information and the second information into the arithmetic operation of the positional deviation detection by the alignment means, for example, the differential arithmetic unit 38 (counters 380, 382, 384, Subtractor 381, 38
3, or counters 480, 482, 483, adder / subtractor 481, subtractor 4
84) and are provided.

(Operation) With the above configuration, even if the object slightly moves during scanning with the light beam, the generation position of the optical information from the pattern (mark) that contributes to the positional deviation detection is apparently stationary. become. Therefore, the alignment detection operation can be executed even when the stage or the like is slightly moved.

(Embodiment) Next, an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 shows a schematic configuration when the alignment apparatus according to the present invention is applied to a projection type exposure apparatus. Reticle R
The pattern formed on (synonymous with mask) is the projection lens 1
An image is formed on the wafer W via. A light source and an optical system for illuminating the reticle R for exposure are not shown in FIG. The reticle R is provided with an alignment mark RM, and the wafer W has a mark WM overlapping with the mark RM.
Is provided. The wafer W is held on the wafer stage 2 which moves two-dimensionally, and the wafer stage 2 is moved on the surface plate 4 by the motor 3. The position of the wafer stage 2 is constantly measured by a laser interferometer length measuring device (hereinafter referred to as an interferometer) 5. A column 6 for mounting the projection lens 1 is provided on the surface plate 4, and a reticle stage 7 that holds the reticle R horizontally and moves two-dimensionally is arranged above the column 6. The moving stroke of the reticle stage 7 is much smaller than the moving stroke of the wafer stage 2, and is several mm or less at most. The reticle stage 7 is moved by a motor 8 and its position is constantly measured by an interferometer 9.

The mark RM on the reticle R and the mark WM on the wafer W are scanned by the laser light from the laser light source 20.
The laser light from the laser light source 20 is shaped into a predetermined cross-sectional shape by the beam shaping optical system 21, passes through the half mirror 22 and enters the scanner mirror (vibrating mirror) 23, where it is deflected with a predetermined amplitude and aligned. A sheet-shaped spot is formed on the reticle R by the objective optical system 24 for forming an image. The spot light is reciprocally scanned by the reticle R so as to cross the mark RM, and the spot light is re-imaged on the wafer W through the projection lens 1 in the transparent portion of the reticle R as it is. The spot light on the wafer W is also reciprocally scanned so as to cross the mark WM. Light information from the mark WM (scattered light,
Diffracted light) returns to the reticle R via the projection lens 1,
Mark RM of reticle R passes through the transparent part of reticle R
Objective optical system 24, scanner mirror with optical information from
It is reflected by the half mirror 22 via 23 and reaches the photoelectric detector 25. In this embodiment, the photoelectric detector 25 separately receives the optical information from the mark RM and the optical information from the mark WM, and outputs the respective photoelectric signals Ar and Aw. Laser source 20, beam shaping optical system 21, half mirror 22, scanner mirror
23, the objective optical system 24, and the photoelectric detector 25 constitute an alignment optical system of the alignment means of the present invention. The photoelectric signal Ar corresponding to the mark RM and the photoelectric signal Aw corresponding to the mark WM are amplified by the amplifier unit 30, respectively, and then input to the signal processing unit 32 that detects the relative deviation amount between the reticle R and the wafer W. To do. The information DD regarding the amount of deviation detected by the signal processing unit 32 is sent to the main control system 34, and
34 drives the motor 3 or the motor 8 based on the information DD,
The wafer stage 2 or the reticle stage 7 is moved by the displacement amount.

Now, in the present embodiment, a scanning position detection unit (hereinafter simply referred to as a detection unit) 36 that outputs information DS regarding the scanning position of the spot light by the scanner mirror 23 is provided. The detection unit 36 outputs information DS corresponding to the position of the spot light on the reticle R or the wafer W based on the information on the deflection angle of the scanner mirror 23. In this example, information DS
Is a pulse signal generated for each unit scanning amount of the spot light on the wafer W. The pulse of the information DS is generated with the same resolution as the pulse of the position information DW from the interferometer 5 for the wafer stage 2. That is, interferometer 5
, For example, every time the wafer stage 2 moves 0.02 μm
In the case of the resolution for generating a pulse, the information DS is also set to be one pulse each time the spot light moves 0.02 μm on the wafer W. As such a detection unit 36, a method in which a rotary encoder is directly attached to the axis of the scanner mirror 23, another reference light is radiated to the scanner mirror 23, and a lattice slit and a photoelectric detector that receive the reflected light (spot) are provided. In combination with the above, a method of detecting pulsed light when the reflected light scans the lattice slit can be used.

Information DS and position information DW are the position information from interferometer 9.
It is input to the differential operation unit 38 together with DR. The position information DR from the interferometer 9 is also set to be one pulse for each unit movement amount of the reticle stage 7. In this embodiment, the resolution of the position information DR is projected by the projection lens 1 with respect to the resolution of the position information DW. It should be lowered by the magnification. That is, assuming that the projection magnification is 1/5, the interferometer 9 has a reticle stage 7 of 0.1
It is defined that one pulse is generated for every μm movement. The differential operation unit 38 is based on the information DR and the information DS,
The scanning position information ADR associated with the position of the reticle stage 7 of the spot light is calculated in real time, and the scanning position information ADW associated with the position of the wafer stage 2 of the spot light is calculated based on the information DW and the information DS. Is calculated in real time. The scanning position information ADR and ADW are sent to the signal processing unit 32, and the signal processing unit 32 processes the photoelectric signal Ar based on the information ADR and processes the photoelectric signal Aw based on the information ADW.

FIG. 2 is a circuit block diagram showing a specific configuration of the differential operation section 38 and the signal processing section 32 in FIG. First photoelectric signal
Ar is input to the automatic gain controller (AGC) circuit 320a that optimizes the peak and bottom levels of the signal waveform. The photoelectric signal from the AGC circuit 320a is input to an analog-digital converter (ADC) 322a and converted into a digital value corresponding to the magnitude of the signal level. The ADC 322a performs conversion into a digital value in response to the information DS (pulse signal) from the scanning position detector 36. Then, the digital value from the ADC 322a is input to the memory circuit 324a in which writing and reading can be arbitrarily switched. On the other hand, information DR from interferometer 9
The (pulse signal) is input to the counter circuit 380 and converted into a numerical value corresponding to the position of the reticle stage 7. Normal,
The measurement pulse signal from the interferometer is discriminated into an up pulse signal and a down pulse signal corresponding to the forward and backward movements of the stage, and is output. Therefore, the counter circuit 380 is also actually configured as an up / down counter. Further, the information DS from the detection unit 36 also reciprocally scans the spot light,
The pulse signals are discriminated into up pulse signals and down pulse signals, and these pulse signals are input to a counter circuit (up / down counter) 382 and digitized. In this embodiment, as will be described later in detail, since the photoelectric signal is read only in the forward path (or the backward path) of the reciprocal scanning of the spot light,
The information DS input to the counter circuit 382 may be only the up pulse signal (or the down pulse signal). Then, the digital subtractor 381 subtracts the numerical value D ₁ of the counter circuit 380 from the numerical value D ₂ of the counter circuit 382, and uses the value as the scanning position information A described above.
It is output to the memory 324a as DR. Memory 324a is information ADR
Is accepted as an address value (address). Therefore, the waveform of the photoelectric signal Ar is stored in the memory 324a in correspondence with the scanning position of the spot light.

The photoelectric signal Aw is also converted into a digital value via the AGC circuit 320b and the ADC 322b and stored as a waveform in the memory circuit 324b. The address value of the memory 324b is determined by the scanning position information ADW from the subtractor 383, and the subtractor 383 outputs the information.
Counter circuit (up / down counter) that digitizes DW (pulse signal) D ₃ of counter 384 and D ₂ of counter circuit 382
The value subtracted from is output as information ADW. The counter circuits 380, 382, 384 are simultaneously initialized by a signal SYC generated in synchronization with a predetermined scanning start point of spot light. The signal waveform data D ₄ and D ₅ stored in the memories 324a and 324b as described above are read into the bit slice processor (BSP) 326 which performs high-speed waveform recognition and data processing, and this BSP 26 stores both data D ₄ , the shift amount between the marks RM and WM is calculated based on D ₅ and the information DD corresponding to the shift amount is output.

Next, regarding the alignment operation of the present embodiment, a third
It will be described with reference to the drawings. FIG. 3 (a) shows a planar arrangement of the mark RM and the mark WM. Here, the spot light SP is used.
Are scanned along the scan line SL parallel to the x direction. The mark RM is a two-line pattern and extends parallel to the y direction. The mark WM is a diffraction grating pattern extending in the y direction so as to be sandwiched between the two marks RM. The spot light SP is in the direction (y direction) orthogonal to the scanning line SL.
When the spot light SP scans the mark RM, a waveform of the photoelectric signal Ar as shown in FIG. 3B is obtained. Further, when the spot light SP scans the mark WM through the transparent portion of the reticle R, a waveform of the photoelectric signal Aw as shown in FIG. 3C is obtained.

First, the main control system 34 steps the wafer stage 2 so that the mark RM and the mark WM are substantially aligned.
Then, the levels of the photoelectric signals Ar and Aw are peak-held on the return path when the spot light SP scans the scanning line SL, and the AGC
The gains of the circuits 320a and 320b are optimized. Then, the signal SYC is generated at the starting point of the outward path of the scanning of the spot light SP, and the counter circuits 380, 382, 384 are initialized. For this initialization, for example, it is only necessary to set the value of each counter circuit to zero. At this initialization timing, the main control system 34 sets the position R in the x direction of the reticle R measured based on the information DR from the interferometer 9. And the position W of the wafer W in the x direction measured based on the information DW from the interferometer 5. And remember.
Assuming that neither the reticle R nor the wafer W has moved in the x direction after the initialization, the numerical value D ₂ of the counter circuit 382 is sequentially incremented on the outward path of the scanning of the spot light SP, and each of the counter circuits 380 and 384. Since the numbers D ₁ and D ₃ both remain zero, the outputs ADR and A
DW is ADR = D ₂ and ADW = D ₂ . Therefore, at the time when the scanning of the spot light SP on the outward path is completed, the waveform as shown in (b) of FIG.
In 4b, a waveform as shown in FIG. 3 (c) is stored from address 0. Then, the BSP326 reads both waveforms and performs the position detecting process as shown in FIG. In FIG. 3 (d), the horizontal axis x represents the wafer-converted position in the memory 324, and the mark RM on the left side is at the position x ₁ with reference to the zero address (position R.) and the mark RM on the right side. Is at the position of x ₂ with reference to the zero address (position R.). BSP326 is the midpoint R _m that divides x ₁ and x ₂ into two equal parts with l, and the position W _m of the mark WM on the memory.
And calculate. Then, the BSP 326 outputs the amount of deviation between the positions R _m and W _m (for example, the number of addresses × 0.02 μm) as information DD. The amount of deviation (R _m −W _m ) is R on the reticle stage 7. Position, wafer stage 2 is at W. This is the amount of deviation that occurred at the position of.

Now, the main control system 34 determines the current position XW of the wafer W read from the interferometer 5 and the current position of the reticle R read from the interferometer 9.
The motor 3 or the motor 8 is driven so that the relationship with XR satisfies the expression (1).

XR-XW = (R.-W .) + (R m -W m) ...... (1) In this way the mark WM is aligned as sandwiched exactly the center of the mark RM, the alignment is completed It has been done.

Now, the signal waveform is stored in the memory 32 by scanning the spot light SP.
If, for example, the wafer stage 2 slightly moves in the x direction by ΔW during the reading to 4, the numerical value D ₃ of the counter circuit 384 changes to a value corresponding to ΔW, and In ADW (the value of subtractor 383), the value D ₃ is Δ
When it changes by W, it decreases by ΔW. Therefore, the waveform stored in the memory 324b also shifts laterally (in the address direction) after the change to ΔW. This state is shown in FIG. In the case where the differential operation unit 38 as in this embodiment is not provided, the peak on the waveform corresponding to the mark WM of the wafer W is ΔW on the address of the memory 324b compared to when the wafer stage 2 is stationary. It will shift. However, by determining the address of the memory 324 by the differential operation, the peak on the waveform always appears at the same address position as when the wafer stage 2 was stationary.

Similarly, when the reticle R is displaced by ΔR in the x direction, the waveform of the same state as when the reticle R is stationary is obtained on the address of the memory 324a by the function of the differential calculation unit 38. Of course, even if both the reticle R and the wafer W are slightly moved, each waveform in the memory 324 is stored in the state at the time of initializing each counter of the differential operation section 38.

As described above, in this embodiment, the position R of the reticle R is set at the time of initialization. And the position W of the wafer W. However, the value D ₁ of the counter circuit 380 and the counter circuit 384
The reticle stage 7 and the wafer stage 2 may be moved so that the main control system 34 directly reads the numerical value D _{3 of the} above. That is, the numerical value D ₁ is the position R if the value at initialization is zero. Corresponding to the amount of deviation (XR-R.), The numerical value D ₃ is the position W if the initial value is zero. It corresponds to the amount of deviation from (XW-W.). Numerical values D ₁ , D ₃ are reticle R after initialization,
It can change with the fine movement of the wafer W. Therefore, the equation (2) is established, and the equation (3) is derived by substituting the equation (1).

D ₁ −D ₃ = (XR−XW) − (R. −W.) …… (2) D ₁ −D ₃ = R _m −W _m …… (3) Therefore, the shift amount (R _The motor 3 or the motor 8 may be servo-driven so that ( _m −W _m ) becomes equal to the difference between the numerical values D ₁ and D ₃ .

As described above, in the present embodiment, the photoelectric detector 25 performs photoelectric detection separately for the mark RM and the mark WM, which is recognized by the edge scattered light generated in the direction of the scanning line SL, and the mark WM is scanned. This is because the light information of the marks RM and WM is spatially separated because it is recognized by the diffracted light generated in the direction orthogonal to the line SL. Of course, both the marks RM and WM may be recognized by a single light receiving element. In this case, the same photoelectric signal waveform is stored in both memories 324a and 324b, and peaks corresponding to both marks RM and WM appear in the waveform. Then, only the position R _{m of the} mark RM needs to be detected from the waveform in the memory 324a, and only the position of the mark WM needs to be detected from the waveform in the memory 324b.

Further, as the detection unit 36 shown in FIG.
When using a position sensor that outputs an analog signal proportional to the deflection angle of 23 (or the scanning position of the spot light),
The counter circuit 382 in FIG. 2 can be an analog-digital converter. Also, counter circuits 380, 382, 38
When the resolutions of the outputs of 4 do not match on the wafer W, the resolutions can be adjusted by using digital multipliers and frequency dividers. Further, since the photoelectric signal waveform is stored in the memory circuit 324 once during the scanning of the spot light SP in one direction, if the shape change of the mark WM, noise, etc. are affected, the position is inevitably accurate. It is not always possible to detect.
In this case, during the scanning of the spot light SP, the waveform storage and the calculation of the position deviation are repeatedly performed several times, and the deviation amount (R _m −
It is good to find the average value of W _m ). At that time, the counter circuit 38
Initialization of 0, 382, 384 is performed only once at the first scan, and waveform storage by the second and subsequent scans is performed without initializing each numerical value D ₁ , D ₃ of the counter circuits 380, 384. Try to use it as it is.

Next, another embodiment of the present invention will be described with reference to FIGS. In FIG. 4, the spot lights SP ₁ and SP ₂ extend in directions orthogonal to each other and are both inclined by 45 ° with respect to the scanning line SL. The mark RM of the reticle R is a parallelogram tilted window provided apart in the x direction, and the 45 ° edges E ₁ , E ₂ , E ₃ , E ₄ on both sides are used. Further, the mark WM of the wafer W is assumed to use two linear patterns inclined by 45 ° in opposite directions. When both spot lights SP ₁ and SP ₂ are scanned as shown in (a) of FIG. 4, as shown in (b) of FIG. 4, edges E ₁ , E ₂ , E ₃ , E ₄ , marks
A photoelectric signal AS including the pulses P ₁ , P ₂ , P ₃ , P ₄ , P ₅ , P ₆ corresponding to WM is obtained. 45 with respect to the scanning line SL as shown in FIG.
When the mark tilted by deg. Is detected, the two-dimensional shift between the reticle R and the wafer W in the x direction and the y direction can be recognized at the same time. For example, in the waveform as shown in FIG. 4B, by measuring the interval between the pulses P ₁ and P ₄ (or P ₃ and P ₆ ), the mark RM in the y direction (scanning line SL It is possible to detect the deviation in the orthogonal direction), and it is possible to detect the deviation in the y direction of the mark WM from the interval between the pulses P ₂ and P ₅ . Therefore, in the actual alignment, pulse P ₁ and
P ₂ (or P ₄ and P ₅₎ interval and pulse P ₂ and P ₃ (or P ₅ and P ₆₎
The reticle R or the wafer W so that the distance is equal to the fine motion in the x direction (direction of the scanning line SL), and a pulse P ₂
The reticle R and the wafer W may be relatively finely moved in the y direction so that the interval of P _{5 and} the interval of the pulses P ₁ and P ₄ both become predetermined values.

When using the alignment mark as shown in Fig. 4,
As an example, the circuit configuration shown in FIG. 5 is used. FIG. 5 shows only the differential operation unit and the memory circuit only for position detection on the reticle R side, and the same structure is used for position detection on the wafer side. The reticle stage 7 detects the positions in the x direction and the y direction independently by the interferometer 9. The position information DRX (pulse signal) in the x direction is counted by the counter 480, and the result is sent to the adder / subtractor 481. To be

On the other hand, position information (pulse signal) in the y direction from the interferometer 9
The DRY is counted by the counter 482 and the result is also added / subtracted by the adder / subtractor 48.
Sent to 1. The adder / subtractor 481 switches between adding the numerical values from the counters 480 and 482 or subtracting the numerical value of the counter 482 from the numerical value of the counter 480 in response to the operation flag CF input from the outside. The result of the addition / subtraction is output to the subtractor 484. The scanning position information DS from the detection unit 36 is digitized by the counter 483, and the value is sent to the subtractor 484. The subtractor 484 subtracts the value of the adder / subtractor 481 from the value of the counter 483 and outputs the address value of the memory circuit 485.
Output in real time as ADRX. The memory circuit 485 sequentially stores the sampled digital value AS 'of the photoelectric signal AS as shown in FIG. 4 (b). The BSP 326 detects the position of the mark RM of the reticle R in the x direction based on the output D _4r from the memory circuit 485.

Now, in such a configuration, the operation flag CF is set to, for example, the subtraction mode until the spot light SP ₁ (SP ₂ ) has passed the edges E ₁ and E ₂ (mark WM), and the spot light SP ₂ (S ₂
P ₁ ) is set to enter the addition mode when scanning edges E ₃ and E ₄ (mark WM). Thus the signal taken into the memory circuit 485 waveform is corrected the effect of fine movement in the y direction of the reticle R, the pulse P _1,
P _3, P _4, P ₆ is generated at the position at the time of on, it is initialized by the initialization signal SYC address.

Although the alignment between the reticle and the wafer has been described in each of the embodiments of the present invention, the same can be applied to an apparatus having an alignment optical system that detects only a mark on the wafer by spot light.

As described above, according to the present invention, at the time of scanning the alignment beam, even if the reticle or the wafer is moving while the alignment mark of the reticle or the wafer is present within the scanning range, Since the same detection signal (waveform data) as when stationary is obtained, the alignment accuracy can be improved. Conversely, in order to enter the alignment mark detection operation without waiting for the reticle stage or wafer stage to settle, the step-and-repeat exposure apparatus can be used to align multiple shots on a wafer. The effect that the throughput is improved compared to the method is obtained. Further, the alignment apparatus according to the present invention is not limited to the exposure apparatus, but may be a laser processing apparatus (laser repair machine) or a wafer if an alignment method for detecting an alignment mark (or standard pattern) by scanning with a light beam or the like is adopted. It can be widely applied to the inspection device for the above pattern line width.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration when a positioning apparatus according to an embodiment of the present invention is incorporated in a projection type exposure apparatus, and FIG. 2 is a circuit block diagram showing a main circuit configuration of alignment processing, and FIG. FIG. 4 is a diagram showing the alignment mark and the state of the signal waveform, FIG. 4 is a diagram showing the alignment mark of another shape and the state of the signal waveform, and FIG. 5 is another alignment process suitable for the detection of the mark in FIG. 3 is a circuit block diagram showing the circuit configuration of FIG. (Explanation of symbols of main parts) R ... reticle, W ... wafer, RM, WM ... alignment mark, 2 ... wafer stage, 7 ... reticle stage, 20 ... laser light source, 23 ... scanner mirror, 32 ... Alignment signal processor, 36 ... Scan position detector, 38 ... Differential calculator

Claims (2)

[Claims] 1. A moving means for moving an object having a predetermined pattern, and scanning the pattern with a light beam,
An apparatus having an alignment unit that detects light information from the pattern to detect a positional shift of the object with respect to a predetermined reference point; first detection unit that outputs first information regarding a scanning position of the light beam; Second detection means for outputting second information relating to a position change of the object corresponding to a direction of detecting the positional deviation by the alignment means; information for a difference between the first information and the second information for the positional deviation by the alignment means An alignment device provided with a calculation means to be introduced into a detection calculation. 2. A moving means for relatively moving a mask having a first mark and a substrate having a second mark, the first mark and the second mark are scanned by a light beam, and the first mark and In an apparatus having an alignment means for detecting optical information from a second mark to detect a relative positional deviation between the mask and the substrate, a scanning position of the light beam with reference to a predetermined point on the apparatus. First detecting means for outputting first information regarding the change in relative position between the mask and the substrate corresponding to the direction of positional deviation detected by the alignment means; second detecting means for outputting; An alignment device comprising: an arithmetic unit that introduces information on the difference between the first information and the second information into the arithmetic operation for detecting the positional deviation by the alignment unit.