JP2829636B2 - Exposure equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus that precisely controls a mask chuck or a wafer chuck having a drive shaft.

[Prior Art] Conventionally, in an exposure apparatus, two systems of a die-by-die alignment system and a global alignment system are mainly used as an alignment sequence between a mask and a wafer. What is the die-by-die alignment method?
In this method, exposure is performed after alignment of the mask and the wafer is taken for each one shot. The global alignment method measures the alignment of the mask and the wafer at several representative locations within a single wafer, calculates the optimal position for other exposure shots based on these data, and then performs the alignment measurement. This is a method in which all shots are exposed at once without performing exposure.

[Problems to be solved by the invention] However, in the die-by-die alignment method,
Although the overlay accuracy for each shot is good, there is a disadvantage that the throughput is reduced and the chip rotation is accumulated. In addition, the global alignment method has a better throughput than the die-by-die alignment method, but has a disadvantage that the overlay accuracy for each shot is worse than the die-by-die alignment method. Therefore, at present, these methods are properly used in some cases.

When the wafer is exposed by the global alignment method, the exposure is performed in a sequence as shown in FIG. 5. In step 504 in the sequence, the wafer stage and the mask stage are not measured for the alignment state between the wafer and the mask. (Hereinafter, referred to as “blind feeding”), but at this time, if the coordinate axes of the mask stage and the wafer stage do not coincide, an overlay error between the mask and the wafer occurs. Conventionally, this error is not so much a problem because the driving amount is small, and no countermeasure has been taken against it. However, in recent years, where miniaturization of a circuit pattern is required, such an error cannot be ignored.

SUMMARY OF THE INVENTION An object of the present invention is to improve both the overlay accuracy and the throughput during alignment between a mask and a wafer in an exposure apparatus in view of the above-described problems of the related art.

Means for Solving the Problems In order to achieve the above object, according to the present invention, a mask stage for holding a mask and positioning at least in a rotation (θ) direction, and a wafer stage for holding a wafer and positioning at least in an XY direction In an exposure apparatus that sequentially positions a mask and a wafer and sequentially projects and exposes a pattern formed on the mask to a plurality of exposure positions on the wafer, a rotation center generated when the mask stage is driven to rotate in a rotational direction. Means for correcting the positioning of the wafer at the time of positioning between the mask and the wafer using data obtained by measuring the positioning error in the XY direction as viewed from the wafer side due to the movement of the wafer in advance.

The mask stage includes a plurality of radially arranged leaf springs that rotatably hold the mask, and an actuator that rotates the mask in a direction in which the leaf spring is deformed.

The measurement of the positioning error viewed from the wafer side is performed by measuring the output of a light receiving element fixed to the wafer, for example, receiving light emitted from a light emitting element fixed in position with respect to a mask.
This is done by processing.

[Operation] In this configuration, during exposure, the mask and the wafer are positioned by global alignment without using a die-by-die alignment method, thereby improving the throughput. Therefore, positioning at other exposure positions, that is, blind feeding is performed based on the alignment result performed at some exposure positions. In this case, correction such as rotating the mask according to the exposure position is usually required. And As a result, the X and Y positions of the mask viewed from the wafer side also change, causing an error. However, since the wafer is positioned at a feed amount corresponding to the exposure position in consideration of a data table obtained by measuring the error in advance, the error is corrected and accurate alignment is performed.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration of a mask θ stage portion in an exposure apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 106 denotes a mask θ stage base serving as a base of the mask θ stage 4; A radial leaf spring that flexibly supports the mask 2 only in the in-plane rotation direction (θ direction) with respect to the stage base 106 and rigidly supports the mask 2 in the other directions. 107 is a mask chuck for making the mask 2 detachable. , 103 and 104 are positioning Vs for mechanically positioning the mask 2.
A block and a positioning pin 102, a displacement sensor for measuring a relative rotation angle of the mask 2 with respect to the mask θ stage base 106 by an approximate linear displacement in a circumferential direction;
2 is a piezo element which is a driving displacement source of the mask θ stage 4, 113 is a lever enlargement mechanism for enlarging the displacement of the piezo element 112, and 101 is the displacement transmitted by the lever enlarging mechanism 113 to the utmost in the circumferential direction An elastic coupling 111 for transmitting the vibration is provided so as to attenuate the vibration of the mask θ stage 4.

Reference numeral 108 denotes a laser diode fixed to the mask θ stage 4, and its optical axis is dropped on the wafer stage side perpendicular to the mask 2 surface.

FIG. 2 shows the overall configuration of the exposure apparatus in this embodiment.

In the figure, reference numeral 3 denotes a wafer, which is chucked by a wafer chuck (not shown) on the wafer stage 24. 5
Is a coarse θ stage which is rotatable in the θ direction (around the z axis) and is held on the Z tilt stage 6. The Z tilt stage 6 can be moved in the Z direction and is held on the fine θ stage 7. The fine θ stage 7 is rotatable in the θ direction and is held on the fine X stage 8. Fine X stage 8
Is movable on the X axis and is held on the fine Y stage 9. The fine Y stage 9 is movable on the coarse X stage 10 in the Y axis direction. The coarse X stage 10 can be moved in the X direction and is held on the coarse Y stage 11.
The coarse Y stage 11 can be moved in the Y direction and is held by a frame 15.

The position X, Y and the attitude θ, ω _X , ω _Y of the stage 24 are determined by the laser interferometer beam 17 projected from the fixed position of the apparatus.
The light is reflected by a mirror 16 fixed on the tilt stage 6 and measured by an interferometer. Reference numeral 2 denotes a mask, which is chucked on a mask chuck (not shown) on the mask θ stage 4. The mask θ stage 4 is rotatable in a plane having the exposure light 1 as a normal line, and is held by a frame.

Reference numeral 12 denotes a plurality of detection optical meters (hereinafter referred to as pickups) for measuring a gap (interval) between the mask and the wafer and for measuring an alignment deviation between the mask and the wafer.
In particular, in this embodiment, four pickups are provided. Each pickup 12 is held on a pickup stage 13 that can move in the X and Y directions.

Reference numeral 23 denotes a light beam emitted from the pickup 12.
Since the light beam is projected obliquely, the pickup does not block the exposure light 1 during exposure. Therefore, there is no need to retract the pickup 12 during exposure.

The transfer pattern formed on the mask 2 by the exposure light 1 is printed on the transferred pattern on the wafer to which the previous layer has been transferred. Reference numeral 27 denotes a gap sensor which is installed on the Z tilt stage 6 and relatively measures the lower surface of a wafer chuck (not shown).

14 is a light receiving element installed on the Z tilt stage 6, 26
Denotes a light emitting element fixed on the frame, and is located at a position facing the wafer stage 24.

The light receiving element 14 can detect the light beam 23 emitted from the pickup 12 for alignment detection and the light beam emitted from the light emitting element 26. With respect to the projected beam received by the light receiving element 14, the center position of the beam is calculated, and the position of the center of the beam can be accurately measured by taking into account the position data of the wafer stage 24.

FIG. 8 shows the structure of the light receiving element 14. As shown in the figure, the light receiving element 14 has electrodes 801a to 801 on a flat silicon element 802.
d, and leads 803 of the electrodes 801a to 801d.
A package including one end of a to 803d is enclosed in one package 805. The coordinate values (P _x , P _y ) of the beam spot dropped on the silicon element 802 as viewed from the element middle point can be obtained from the following relationship.

Here, X ₁ , Y ₁ , X ₂ , and Y ₂ are photocurrents flowing between the center electrode 804 of the light receiving element and each of the electrodes 801 a to 801 d, respectively.
L indicates the distance from the center electrode 804 to each of the electrodes 801a to 801d.

The position of the beam spot in the stage coordinate system is determined by the values (P _x , P _y ) read from the light receiving element 14 and the measured values of the stage coordinates on the laser interferometer axis, and the arrangement (fixed value) of the light receiving element 14 on the wafer stage. ).

FIG. 3 is a block diagram showing a control unit of the exposure apparatus.
As shown in the figure, the exposure apparatus according to the present embodiment manages all functions under a main processor 301 located at the top. The main processor 301 is connected to each hardware unit via a communication path 302 and a communication I / F 303. In FIG. 3, a hardware unit including an alignment function, a stage control function, and a pickup stage control function is shown. Is extracted and shown. The name of this hardware unit will be referred to herein as a main body control block.

The main body control block controls the four pickups 12 (see FIG. 2) in the two axial directions (α axis, β axis) with respect to the alignment system.
Pickup stage controller 30 for positioning control on axis)
5. Fine AA.AF control units 309a to 309d for performing positional displacement and parallel alignment of the wafer 3 and the mask 2 on a plane,
A stage controller 313 for controlling the positioning of the wafer X and Y coarse movement stages 10 and 11 (see FIG. 2) and the wafer fine movement stages 6 to 9 is connected.

The main body control unit 304 is a control section in which a program for performing a predetermined sequence is stored, and which operates the respective control units according to the sequence. The main unit control unit 304 communicates with the upper main processor unit 301 via the communication path 302 and the communication I / F 303.
Are connected via the network to exchange data.

Furthermore, among the above control units, the fine AA.AF control unit 3
09a to 309d and the stage control unit 313 are the communication I / Fs 306 and 3 respectively.
Data is exchanged with the main unit control unit 304 via the communication paths 307 and 311 via the 08, 310 and 312.

The main unit control unit 304
Each of the control units connected to the CPU has a CPU mounted therein, and all hardware signal processing is completed therein. With this configuration, each control unit can be operated independently and hierarchized.

FIG. 4 is a detailed block diagram of the stage control unit 313 in FIG. This unit is the main unit control unit
With 304, information is exchanged via communication I / Fs 310 and 312 and communication path 311. The wafer stage control unit 401 has a CPU (not shown) inside, and calculates the drive amount of each actuator mounted inside the wafer stage with respect to the target position of the stage sent from the main body control unit 304. . In addition, it also has a processing function of converting data sent from the PSD length measuring system control unit 409, which receives a signal output from the light receiving sensor (PSD) 14 on the wafer stage, into appropriate position data. . Reference numeral 402 denotes a laser interference measurement length unit that performs position measurement on five axes excluding an axis (Z axis) normal to the wafer surface. 403 is a minute displacement sensor control unit, which is a minute displacement sensor
The Z-axis displacement of the wafer stage is measured by performing drive 27 and signal processing. Reference numeral 404 denotes an X, Y coarse movement controller, which is a wafer X, Y coarse movement stage 1 shown in FIG.
The electric cylinders 0 and 11 are controlled. Reference numeral 405 denotes a θ coarse movement controller. The coarse movement axis is mounted on the X and Y drive axes of the stages 8 to 11, the Z, ω _X and ω _Y drive axes of the stage 6 and the fine movement axis of the stage 7 as shown in FIG. Wafer stage by moving the θ coarse movement axis of stage 5
The position change 24 is a mirror 16 for reflecting the optical axis 17 from the interferometer.
Is not reflected in the movement. Therefore, in this embodiment, θ
By using an inchworm actuator as the actuator for the coarse movement axis, position fluctuation after the θ axis coarse adjustment is eliminated. 406 is driven by three piezo actuators
This is a tilt stage controller for positioning Z, ω _X , ω _Y , and controls the position of the tilt stage 6 mounted on the X, Y drive axis and the θ fine movement axis by a command from the wafer stage control unit 401. Reference numeral 407 denotes a fine movement stage controller, which controls a minute displacement actuator of the fine X, Y drive axes of the stages 8, 9. Reference numeral 408 denotes a mask θ controller that controls the mask θ fine movement stage 4 mounted on the mask stage.

FIG. 5 shows an exposure sequence by the global alignment method. The operation of the device will be described with reference to FIG.
First, in step 501, alignment measurement is performed on an exposure area for several shots representative of the wafer 3 loaded on the wafer chuck. The shot for alignment measurement is, for example, 60 in FIG.
The remaining shots 602, which are shots indicated by 1a to 601e and for which alignment measurement has not been performed, are interpolated and predicted based on alignment measurement data obtained from the peripherally measured shots 601a to 601c (step 50).
2). In step 503, the amount of drive of each axis of the wafer stage 24 and the mask stage 4 for aligning the shot on the wafer 3 to be exposed with the pattern drawn on the mask 2 is calculated.

Here, for example the coordinates of the movement target position P P (x, y, z , θ, ω X, ω Y) if give absolute coordinates, such as the drive target position of each axis of the case (X, Y, Θ, Z ₁ , Z ₂ , Z ₃ ) are for three piezo actuators that drive the tilt stage toward Z ₁ , Z ₂ , Z ₃ For the piezo actuator of the mask stage, _{Ｍ M} = L _M θ (4), and the target values X and Y of the X and Y stages are X = x−f _T (Z ₁ , Z ₂ , Z ₃ ) − f _M (Θ _M ) (5) Y = Y−g _T (Z ₁ , Z ₂ , Z ₃ ) −g _M (Θ _M ) (6) However, A _T is the distance to the point from the conversion matrix, mask center of the piezoelectric actuator 112 in the mask stage L _M is minutely displaced determined from the positional relationship to be disposed of three piezoelectric actuators. Function f _T and g _T respectively X, the Y-axis, a generation amount of movement by the Abbe length tilt stage caused by tilting the tilt stage, f _M, g _M is joined as a new correction terms by the present invention This is the amount of movement of the center of rotation of the mask stage in the X and Y directions due to the drive of the mask θ stage 4. The amount of generated movement is not originally intended to be achieved, but includes variations in rigidity of the leaf springs 109 supporting the mask stage 4 by a plurality of sheets, and the piezo actuator 1.
This is caused by the expansion and contraction of a leaf spring arranged in the direction of the force applied to the point of action, which is generated by the force generated at 12 acting at one point around the mask stage 4.
The functions f _M and g _M are created when the exposure apparatus in the present embodiment is started, and the creation procedure will be described later.

Next, in step 504, a drive command is given to the axis of each stage to align the mask and the wafer. Step 505
In, the aligned wafer is exposed by blind feeding.
Then, in step 506, it is determined whether or not exposure has been completed for all shots. If the exposure has been completed, the exposure for the wafer is determined to be completed. If not, the process for the next shot is started.

FIG. 6 shows a wafer 3 by the global alignment method.
This shows upper alignment measurement shots 601a to 601e. Reference numeral 602 denotes a shot that is blindly fed to a position predicted from a surrounding alignment measurement shot without performing alignment measurement and is exposed (hereinafter, referred to as an unmeasured shot).
It is.

FIG. 7 is a flowchart of the sequence of generating the functions f _M and g _M described in the description of FIG. Referring to the figure, when the exposure apparatus is started, first, the wafer stage and the mask stage are initialized (steps 701 and 70).
2) is performed in parallel.

Next, in step 703, the LD 108 on the mask stage is turned on, and the light flux is dropped in a direction perpendicular to the mask 2.
In step 704, the light receiving element 14 on the wafer stage searches for a spot of the laser beam dropped from the LD 108, and in step 705 the wafer stage 2
The position of 4 is paired with the feed position of the mask stage and stored in the memory in the wafer stage control unit 401.

In step 706, it is determined whether or not all the measurement points to be sampled have been measured. If all the measurement points have not been measured yet, the mask θ stage 4 is stepped and the measurement at the next measurement point is started. (Step 707). When all the measurements are completed, the data stored in the wafer stage control unit 401 is transferred to the main body control unit 301, and a process of creating a table interpolated by the measured sample points every time the mask stage is stepped is performed. . In step 709, step 7
Functions (or conversion tables) f _M and g _M are generated based on the table created in step 08, and transferred to the wafer stage control unit 401.

[Effects of the Invention] By applying the present invention, the accuracy of exposure by the global alignment method is improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a mask chuck and a mask stage according to an embodiment of the present invention, FIG. 2 is a schematic configuration diagram of an exposure apparatus using the apparatus of FIG. 1, and FIG. 2 is a block diagram of an electrical hardware configuration for controlling the exposure apparatus of FIG. 2, FIG. 4 is a block diagram of an electrical hardware configuration of the stage control unit in FIG. 3, and FIG. 5 is a global alignment to which the present invention is applied. FIG. 6 is a layout view of global alignment measurement shots on the wafer, and FIG. 7 is a movement amount f _{M of} the rotation center of the mask stage in the X and Y directions due to the drive of the mask θ stage. FIG. 8 is a flowchart for obtaining g _M , and FIG. 8 is a detailed view of the light receiving element in FIG. 2: mask, 3: wafer, 4: mask θ stage, 14: light receiving element, 24: wafer stage, 108: laser diode (L
D), 112: Piezo actuator.

Continuation of the front page (72) Inventor Shunichi Uzawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Nobutoshi Mizusawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Shigeyuki Suda 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Tetsushi Nose 3-30-2, Shimomaruko 3-chome, Ota-ku, Tokyo Inside Canon Inc. (56) Reference Reference JP-A-63-310116 (JP, A) JP-A-1-144626 (JP, A) JP-A-63-118 (JP, A) JP-A-61-44429 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H01L 21/027

Claims (3)

(57) [Claims] 1. A mask stage for holding a mask and positioning at least in a rotation (θ) direction and a wafer stage for holding a wafer and positioning at least in an XY direction, wherein the mask and the wafer are sequentially positioned and formed on the mask. In an exposure apparatus for sequentially projecting and exposing a pattern to a plurality of exposure positions on a wafer, a positioning error in the XY direction seen from the wafer side due to movement of a rotation center generated at the time of positioning drive in the rotation direction of the mask stage is performed. An exposure apparatus comprising means for correcting the positioning of a wafer at the time of positioning between a mask and a wafer using data measured in advance. 2. The apparatus according to claim 1, wherein the mask stage includes a plurality of radially arranged leaf springs for rotatably holding the mask, and an actuator for rotating the mask in a direction in which the leaf spring is deformed. The exposure apparatus according to claim 1. 3. A light-emitting element having a fixed position with respect to a mask, and a light-receiving element having a fixed position with respect to a wafer and receiving light emitted from the light-emitting element. 2. The exposure apparatus according to claim 1, wherein the measurement is performed based on an output of the light receiving element.