JP2829649B2 - Alignment device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment apparatus used in an exposure apparatus for performing high-accuracy relative alignment between an original such as a mask and a substrate to be exposed such as a semiconductor wafer. .

2. Description of the Related Art In an exposure apparatus for manufacturing a semiconductor integrated circuit, a mask on which a pattern of an integrated circuit is formed and a semiconductor wafer to which the pattern is to be transferred need to be overlapped with high accuracy before exposure. is there. For example, in the case of a 256 megabit DRAM class integrated circuit, the pattern line width is 0.25
It is on the order of microns, and the overlay accuracy is required to be 0.06 microns or less.

However, using a conventional alignment device,
Such high-precision positioning has been difficult.

[Problems to be Solved by the Invention] The present invention has been made in view of such problems of the related art, and an object of the present invention is to provide an alignment apparatus capable of performing more accurate alignment.

[Means for Solving the Problems] In order to achieve the above object, according to the present invention, there is provided a measuring means for detecting a relative displacement amount between a substrate to be exposed and an original, and a measuring means for correcting the relative displacement between the substrate and the original. An alignment apparatus comprising: a correction driving unit that corrects and drives at least one of them; and a control unit that determines whether the relative positional deviation amount is within a predetermined tolerance and controls an operation of the correction driving unit. The apparatus is characterized in that at least one correction drive is performed even if the relative displacement is within the tolerance.

In one embodiment of the present invention, the correction driving is performed once at the end after the relative displacement has entered the tolerance.

In this operation, for example, first, the correction drive is performed based on the relative position shift amount measured by the measuring unit, and then the determination process is performed on the relative position shift amount corrected by the immediately preceding correction drive. It is realized by doing.

[Operation] In a conventional alignment apparatus, an alignment mark formed on an original, for example, a mask and a substrate to be exposed,
For example, a linear deviation amount in a direction parallel to the X, Y coordinate axes with an alignment mark formed on a semiconductor wafer is measured, and a plurality of linear deviation amount data ΔX _m , ΔY obtained from a plurality of pairs of masks and on-wafer microphones. _{Based on n} , a linear shift amount (ΔX, ΔY) and a rotational shift amount (Δθ) of the entire shot between the mask and the wafer are calculated. Then, it is determined whether or not these deviation amounts (ΔX, ΔY, Δθ) are within a predetermined tolerance. If the deviation amounts are within the tolerance, the positioning process is terminated. The mask and the wafer are positioned relative to each other by correcting and driving the mask and the wafer relatively.

Here, with reference to FIG. 10, the value T of the tolerance generally indicates an error (AA measurement error) a in the linear deviation amount measurement system, an alignment mark on the mask caused by a temperature or a process, and an alignment mark on the wafer. Position error (MW error) b of the mark, position error caused by minute vibration of the stage by a servo for positioning the mask and the wafer at a desired position, measurement error of a stage position detection system (for example, a laser interferometer), and the like. (Stage stability) A value is set by giving a margin to the sum (a + b + c) of c. It is needless to say that the tolerance value T must be in a range that sufficiently satisfies the overlay (alignment) accuracy in the exposure apparatus, and each measurement system, alignment mark, stage stability, and the like are extremely high in accuracy. It is assumed that

In such an alignment apparatus, for example, the deviation amount (ΔX, ΔY, Δθ) measured and calculated when the wafer is sent to the alignment position is accidentally set to the tolerance T.
If it is within the position, the positioning process is terminated as it is. However, the calculated shift amounts (ΔX, ΔY, Δ
θ) includes the respective errors a, b, and c, so that the true deviation is within ± (T + a + b + c) with respect to the target value 0 even if the calculated deviation is within the tolerance T. Become.
That is, in the conventional alignment apparatus, when the tolerance value is T, the actual alignment error is ± (T + a + b
+ C), which is more than twice the sum (a + b + c) of the respective errors.

Note that the tolerance value T is calculated by the sum (a + b + c).
Making it smaller is not advisable, as it entails an accidental factor that alignment within this tolerance can take a long time or make alignment difficult.

On the other hand, in the present invention, the correction drive is always performed at least once regardless of whether the calculated deviation amount is within the tolerance. In this case, since the calculated shift amount at the point where the true shift amount is A is A ± (a + b + c), the true shift amount after at least one correction drive is A−ＡA ± (a + b +
c)｝ = ± (a + b + c). Since the tolerance value T is set to be larger than the sum of the errors (a + b + c) as described above, the alignment error always falls within the tolerance by at least one correction drive. Therefore, according to the present invention, the alignment error always becomes the tolerance value T
And the accuracy of the measurement system, the stage system, and the like can be improved as compared with the conventional device having the same accuracy.

[Effects] As described above, according to the present invention, alignment accuracy can be improved.

Embodiment FIG. 1 shows a configuration of a mask wafer alignment and an exposure stage portion of a step and repeat exposure apparatus (stepper) according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes exposure light, for example, X-rays emitted from SOR. Reference numeral 2 denotes a mask on which a pattern to be transferred is formed. Reference numeral 3 denotes a wafer to which a pattern of a mask is transferred, 4 denotes a mask θ stage for rotating the mask 2 in its plane, 5 denotes a coarse movement stage for rotating the wafer 3 in its plane, and 6 denotes a wafer 3 (Moves in the direction toward the exposure light), ω _X (rotates around the X axis), ω
A Z tilt stage 7 for driving _Y (rotating around the Y axis); and 7 for rotating the wafer 3 minutely in its plane.
A fine movement stage, 8 is an X fine movement stage for finely driving the wafer in the X direction, 9 is a Y fine movement stage for finely driving the wafer in the Y direction, 10 is an X coarse movement stage, and 11 is a Y coarse movement stage. . θ coarse movement stage 5, Z tilt stage 6, θ fine movement stage 7, X fine movement stage 8, Y fine movement stage 9, X coarse movement stage 10, and Y coarse movement stage 11.
Constitutes a wafer stage 24.

Reference numeral 12 denotes a pickup that irradiates light to alignment marks formed on the mask 2 and the wafer 3 and detects scattered light from these marks. In this embodiment, a total of eight alignment marks are formed on the scribe line of each shot on the wafer 3 in the vicinity of each side of the shot, one priority mark and one spare mark. As shown in FIG. 2, one alignment mark includes an AA mark 201 for detecting a mask-wafer overlay error in a direction parallel to a side where the mark is arranged, and an AA mark 201 for detecting a mask 2 and a wafer 3. A diffraction grating serving as an AF mark 202 for detecting an interval is formed together with a semiconductor circuit pattern in a preceding process. Eight alignment marks 203 and 204 that are paired with the alignment marks on the wafer 3 are also formed on the mask 2 with gold or the like together with the semiconductor circuit pattern to be transferred.

In FIG. 2, reference numeral 205 denotes a semiconductor laser which is a light emitting element, reference numeral 206 denotes a collimator lens that converts a light beam output from the semiconductor laser 205 into parallel light, and reference numeral 207 denotes output from the semiconductor example laser 205 and is converted into parallel light by the collimator lens 206. Projection beam 208, AA mark 201 on wafer and AA mark 20 on mask
An AA light receiving beam to which positional shift information (AA information) is given by an optical system composed of 3; 209 is a gap information (AF information) by an optical system composed of an AF mark 202 on a wafer and an AF mark 204 on a mask. A given AF light receiving beam, 210 is an AA sensor which is a line sensor such as a CCD for converting the position of the AA light receiving spot 211 formed by the AA light receiving beam 208 into an electric signal as AA information, and 212 is an AF light receiving beam 209. AF position of the AF spot 213 to be formed
It is an AF sensor that is a line sensor such as a CCD that converts the information into an electric signal.

FIG. 3 shows a configuration of a control system of the exposure apparatus shown in FIG.
The apparatus shown in FIG. 1 includes a mirror unit that expands an X-ray radiated from an SOR into a sheet beam in a horizontal direction in the vertical direction to form a planar beam, an alignment unit that aligns a mask and a wafer, and an aligned mask. A body unit including an exposure unit for exposing the wafer with the planar X-ray, a posture control unit for controlling the postures of the mirror unit and the body unit, and a chamber and an air conditioning unit for controlling the atmosphere of the mirror unit and the body unit Etc. are provided.

In FIG. 3, reference numeral 301 denotes a main processor unit for controlling the operation of the entire apparatus, 302 denotes a communication line connecting the main processor unit 301 and the main unit, 303 denotes a main body side communication interface, 304 denotes a main unit control unit, 305 is a pickup stage control unit, and 307 and 306, 308 are fine AA / AF control units 309a, 309b, for driving the θ, X, Y fine movement stage and the mask θ stage for fine alignment with the main unit control unit 304 and the main unit in the main unit. Communication line and communication interface connecting to 309c, 309d, 311 and 310,312
Reference numeral denotes a communication line and a communication interface for connecting the main body control unit 304 and the stage control unit 313 for controlling pre-alignment and step movement of the wafer in the main body unit.

FIG. 4 is a diagram showing a step-and-repeat exposure method. For simplicity, for FIG. 1,
The mask θ stage 4 as a driving unit of the mask 2, the wafer stage 24 as a driving unit of the wafer 3, and the pickup 12
The pickup stage 13 which is a driving means of the above is omitted.

In the figure, reference numeral 12 (12a to 12d) denotes a mask 2 and a wafer 3
418 is a transfer pattern drawn on the mask, 419 is a transferred pattern formed on the wafer by the preceding process, and 420 is a mask alignment mark for aligning the mask with the wafer stage , 421 alignment marks on the mask to align the transferred pattern 418 with the transferred pattern 419, 4
22 is an alignment mark on the wafer for the same purpose, 423 is a light beam projected from the pickup 12 for the same purpose, 401 is a scribe line between shots, and an alignment mark 421 on the mask and an alignment mark on the wafer are provided on the scribe line. 422 is drawn.

To align the mask 2 and the wafer 3, first,
In a state where the mask 2 and the wafer 3 are supported to face each other, light beams 423 are projected from the pickups 12a to 12d, and a gap between the mask and the wafer is formed through the corresponding alignment mark 421 on the mask and alignment mark 422 on the wafer. Measure. Based on information obtained from the four pickups, a gap correction driving amount is calculated, and the wafer stage is driven.
By driving 24 (not shown), the gap between the mask and the wafer is set to the exposure gap.

Next, light beams 423 are projected from the pickups 12a to 12d, and the corresponding alignment marks 421 on the mask are respectively projected.
Of the mask and the alignment mark 422 on the wafer in the plane direction of the mask and the wafer are measured. Based on the information obtained from the four pickups, the correction drive amount of the entire shot is calculated, and the mask is moved on the mask by driving the mask θ stage 4 (not shown) and the wafer stage 24 (not shown). The transferred pattern 418 is aligned with the transferred pattern 419 on the wafer. When the alignment is achieved, exposure is performed to transfer the transfer pattern 418 onto the wafer 3. Then, the wafer stage 24 (not shown) is driven so that the next exposure shot comes under the mask. Similarly, the alignment and the exposure are repeated to expose all the shots.

FIG. 5 is a flowchart for one batch of the step-and-repeat exposure sequence. One batch is a unit that can be printed on one wafer without replacing the mask in the middle. In the start state, the mask 2 and the wafer 3 are chucked by the mask θ stage 4 and the wafer stage 24, respectively, and the pickup 12 aligns the projection beam 423 on the mask for AF (auto focus) / AA (auto alignment) measurement. Each of the marks 421 is irradiated.

First, in step 501, it is determined whether or not the mask needs to be replaced. The process proceeds to step 504 when exposing with the currently chucked mask, and proceeds to step 502 when exposing with the mask replaced. In step 502, the currently chucked mask is detached from the mask stage 4 using a mask traverser (not shown) and stored in a mask cassette (not shown), and the mask used for exposure is removed from the mask cassette using a mask traverser. Take it out and chuck it on the mask stage 4. In step 503, the pickup 12 is used to align the mask alignment mark 420 drawn on the mask 2 with a reference mark (not shown) provided on the wafer stage.

Next, in step 504, the wafer stage 24 is driven,
The position (shot position, that is, the transferred pattern 419) on the wafer to be exposed now is opposed to the transfer pattern 418 on the mask. In step 505, the gap between the mask and the wafer is measured using the on-mask alignment mark 421 and the on-wafer alignment mark 422, and the z-direction and tilt correction driving is performed. When the AF is completed, in step 506, the displacement in the X and Y directions between the mask and the wafer is measured using the alignment mark 421 on the mask and the wafer alignment mark 422 to perform the correction drive, and AA is performed. Detailed processing contents of AA (step 506) will be described later.

When AA is completed, one-shot exposure is performed in step 507, and the presence or absence of the next exposure shot is determined in step 508. If there is, the process returns to step 504;

FIG. 6 is a flowchart showing the contents of the AA process in step 506 in FIG. It shows AA measurement for one shot, X, Y, θ deviation amount calculation, and correction driving.

First, in step 601, a layout check on the wafer of the shot to be exposed (current shot) is performed. 1
FIG. 7 shows an example of a shot layout of a wafer.
S1 to S3 are shots. FIG. 8 shows the alignment mark arrangement for one shot. a to d are priority marks for measuring the displacement between the mask and the wafer, and a 'to d' are preliminary marks, which are provided on both the mask and the wafer. Each mark can detect a displacement in either the X or Y direction at that position, and a, a ', b, b'
In the directions c, c ', d, d', a shift in the Y direction can be detected. Therefore, in order to know the X, Y, θ shift of one shot, at least 3
Measurement of marks on two sides is required.

When the shot S1 is to be exposed, all marks a to d can be measured because the entire shot is on the wafer. Therefore, proceed to step 602 to select each pickup 1
By projecting the light projecting beam 423 for AA from 2, measurement is performed at four points, and the measurement result is checked in step 603. Here, a measurement error caused by a measurement failure due to a missing or crushed mark or a large shift between the mask 2 and the wafer 3 is repelled.

FIG. 9 is a graph showing the characteristics of the output signal from the pickup 12 with respect to the amount of displacement between the wafer and the mask in the X and Y directions. In the figure, the AA measurement range is the AA measurement range, and the area (Zone II) where the shift amount vs. output characteristic is non-linear and monotonous following the linear area is nonlinear.
Is an area where a measurement error occurs and is repelled in step 603. When all four marks can be measured, four points are determined to be OK, and the X, Y, and θ shift amounts are calculated in step 604.
Proceed to. If only three marks can be measured in step 603, it is determined that three points are OK, and the process proceeds from the above-described four-point measurement sequence (steps 602 to 604) to step 609 of the three-point measurement sequence (steps 607 to 609) branched in step 601. Join. If only two marks or less can be measured, the measurement sequence for two or less points is determined as NG (step 61).
The process proceeds to step 612 of (0 to 613) to measure a preliminary mark corresponding to the mark that was NG.

When the shot S2 in FIG. 7 is to be exposed, the mark a in FIG.
The point is measured, branching from step 601 and step 607
Performs AA measurement at three points excluding mark a. In step 608, the measurement result is checked in the same manner as in step 603. If three points are OK, the process proceeds to step 609; In step 609, X, Y, and θ correction amounts are calculated based on the three-point data, including those branched in step 603 of the four-point measurement sequence. Assuming that a cannot be measured and that displacement data ΔX _D , ΔY _L , and ΔY _{R of the} mask and the wafer are obtained from b, c, and d, respectively, the displacements ΔX, ΔY, Δθ of the entire shot are represented by ΔX = ΔX _D + Δθ · L _X / 2 ΔY = (ΔY _L + ΔY _R ) / 2 Δθ = (ΔY _L −ΔY _R ) / L _Y The value obtained by inverting the sign of each shift amount is the correction amount. L _X and L _Y are the distances between marks for detecting displacement in the same direction, respectively.
The value or design value obtained in 1006 is used. When marks other than a cannot be measured, 3
Three unknowns ΔX, ΔY, Δθ can be obtained from the measured data of the points. Then, in step 605, correction driving of X, Y, θ is performed.

When shot S3 in FIG. 7 is to be exposed, only b and c in FIG. 8 can be measured. Although the measurement of d 'is possible, in the present embodiment, the measurement of d' is performed later because the pickups interfere with each other depending on the shape and mark arrangement of the pickup.

First, the process branches from step 601 to step 610.
AA measurement of 2 marks is performed. In step 611, the measurement result is checked, and in step 612, the missing data is supplemented. In step 612, the error branch from the four-point measurement or the three-point measurement merges. When only two points or less can be measured as in the shot S3, d 'can be measured as described above, so that the pickup 12 corresponding to d is measured.
The d is driven by using the pickup stage 13d to move over the preliminary mark d ', and d' is measured. When the NG is merged from the four-point measurement or the three-point measurement, the preliminary mark corresponding to the NG mark is measured. If the pickup 12 is moved here, after the measurement is completed, it is necessary to return the pickup position to the original position for the measurement of the next shot. Then, in step 613, the total number of valid data is checked.
If there are four points, the process proceeds to step 604, and if there are three points, the process proceeds to step 609 to calculate the X, Y, and θ shift amounts. If still less than two points are obtained, an error is terminated and manual alignment is performed or the shot is skipped and the next shot is started. Alternatively, it is also possible to perform alignment by estimating from information of surrounding shots and performing alignment.

When the processing in step 604 or 609 is completed, the process proceeds to step 605.

In step 605, a correction drive based on the calculated shift amounts X, Y, θ calculated in step 604 or 609 is performed. Then, at step 606, the correction drive amount is checked. If the correction amount, that is, the calculated value of the deviation amount in step 604 or 609 is within the tolerance, the AA processing is terminated.

In this embodiment, when four points are measured in step 602 and three points are OK in step 603, the shot shift amount is obtained from the data of the three points. Instead, the process may proceed to step 612 to measure the preliminary mark corresponding to the NG mark. The effect of the measurement error can be reduced at four points than at three points.
Since the measurement data at another point is obtained by picking up an object that can be aligned at a point and the measurement data at the other point is obtained, the throughput is reduced. Therefore, which one to select is a trade-off between time and accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a step-and-repeat exposure apparatus according to an embodiment of the present invention. FIG. 2 is an explanation of a fine AA / AF system for detecting a deviation between a wafer and a mask in a plane direction and a vertical direction. Schematic diagram, FIG. 3 is a hardware configuration diagram of a control system of the exposure apparatus of FIG. 1, FIG. 4 is an explanatory diagram of a step-and-repeat exposure method, and FIG.
FIG. 6 is a flowchart showing the contents of the AA process in step 506 of FIG. 5, FIG. 7 is an explanatory diagram showing a shot layout of one wafer, and FIG. 8 is a diagram of one shot. FIG. 9 is a graph showing the characteristics of the output signal from the pickup with respect to the amount of displacement between the wafer and the mask in the X and Y directions, and FIG. 10 is a graph showing the alignment accuracy between the conventional example and the present invention. It is explanatory drawing for a comparison. 1: X-ray (exposure light) 2: Mask (original plate) 3: Wafer (substrate to be exposed) 4: Mask θ stage 12, 12a to 12d: Pickup 13: Pickup stage 24: Wafer stage 304: Main unit control unit 305: Pickup Stage controller 309a, 309b, 309c, 309d: Fine AA / AF controller 421: Alignment mark on wafer 422: Alignment mark on mask 423: Projection beam ΔX _U , ΔX _D , ΔY _L , ΔY _R : Deviation of alignment mark Quantity measurement

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shunichi Uzawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Tetsushi Nose 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-64-71125 (JP, A) JP-A-61-271830 (JP, A) JP-A-61-87330 (JP, A) JP-A-58-176934 (JP, A) A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 21/027

Claims (3)

(57) [Claims] 1. A measuring means for detecting a relative displacement between a substrate to be exposed and an original, a correction driving means for correcting and driving at least one of the substrate and the original to correct the relative displacement, and the relative position. It is determined whether or not the amount of deviation is within a predetermined tolerance, and if it is, it is determined that the alignment has been completed on condition that at least one correction drive has been performed, and the correction drive is terminated. An alignment apparatus comprising: a control unit. 2. The apparatus according to claim 1, wherein said control means determines completion of said positioning on condition that said at least one correction drive has been performed after said relative displacement has entered a predetermined tolerance. 2. The alignment device according to 1. 3. The control unit executes the determination process on the relative position shift amount corrected by the immediately preceding correction drive after the correction drive unit performs the correction drive at least once. The alignment device according to claim 2.