JP3214001B2 - Alignment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Table of Contents] The present invention will be described in the following order. BACKGROUND OF THE INVENTION Problems to be Solved by the Invention Means for Solving the Problems (FIGS. 1 and 2) Function (FIGS. 1 and 2) Example (FIGS. 1 and 2) Effects of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment apparatus, and is suitably applied to, for example, an alignment apparatus of an apparatus for manufacturing a semiconductor integrated circuit, a liquid crystal display device, or the like.

[0003]

2. Description of the Related Art Conventionally, as one of manufacturing processes of a semiconductor integrated circuit, a pattern of a reticle or a photomask (hereinafter, referred to as a reticle) is transferred and exposed on a semiconductor wafer (photosensitive substrate) on which a resist layer is formed. There is a photolithography process.

In this photolithography process, a step-and-repeat type projection exposure apparatus is used as an apparatus for transferring a reticle pattern onto a semiconductor wafer with high resolution.

Japanese Patent Application Laid-Open No. Sho 60-130742 discloses a projection exposure apparatus of this type as an alignment apparatus for accurately overlapping a projected image of a reticle pattern and a circuit pattern (chip) formed in a matrix on a semiconductor wafer. A laser step alignment (LSA) system of a TTL (Through The Lens) system as disclosed in Japanese Patent Application Laid-Open No. H10-209,036 is provided.

In this alignment apparatus, an alignment beam composed of an elongated strip of spot light is irradiated onto an alignment mark (diffraction grating mark) formed on a wafer via a projection lens, and diffracted light (or scattering) generated from the mark is irradiated. Light) is photoelectrically detected.

[0007]

In this type of projection exposure apparatus, a projection optical system is used as a method for correcting the distortion of a projected image generated by reticle bending or distortion of a projection lens. It is considered that at least one of the constituent optical elements (lens elements) is driven in the optical axis direction or tilted with respect to the optical axis.

[0008] However, when the lens element is moved, the light path of the alignment beam changes due to the change in the incident position of the alignment beam for detecting the alignment mark via the projection lens with respect to the projection lens. As a result, the irradiation position of the alignment beam on the semiconductor wafer (that is, the position relative to the optical axis of the projection lens), the intensity distribution, and the like change due to the aberration of the projection lens and the like, and the alignment mark can be correctly detected. However, there is a problem that the overlay (alignment) accuracy of the projected image of the reticle pattern and the chip may be reduced. In particular, in order to synthesize a circuit pattern with high accuracy by overlay exposure using a plurality of reticles, the position of a reference alignment mark must be accurately detected.

The present invention has been made in view of the above points, and prevents a decrease in alignment accuracy due to a shift in an irradiation position of an alignment beam even when at least one optical element constituting a projection optical system is moved. What you want to do.

[0010]

According to a first aspect of the present invention, a pattern on a photomask R is provided on a photosensitive substrate W via a projection optical system PL for image-forming and projecting the pattern on the photosensitive substrate W. In the alignment device 50 that detects the alignment mark for alignment, at least one optical element constituting the projection optical system is movable, and the projection optical system when the optical element of the projection optical system PL is driven. Alignment light position correcting means 1 for correcting a change in the irradiation position on the photosensitive substrate of the alignment light SP for detecting an alignment mark irradiated through the PL.
02A, 102B, 104A, 104B, 105, 12
0 is provided. Further, in the second invention, measuring means 16, 19, 12 for measuring the irradiation position of the alignment light SP and the relative position of the pattern on the photomask R.
0 is provided.

[0011]

The optical path of the alignment beam SP can be corrected, so that the image forming characteristics of the screen (projected image) projected on the wafer W, in particular, image distortion (distortion) are driven by some lens elements of the projection optical system. In this case, a change in the optical path of the alignment beam SP can be corrected. Therefore, the irradiation position of the alignment beam SP can always be kept constant.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 shows a projection exposure apparatus using an alignment apparatus according to the present invention. Exposure light irradiating the reticle R with a uniform illuminance from above the reticle R passes through the reticle R, and then is exposed on both sides (or The light is incident on a (one side) telecentric projection optical system PL, and the projection optical system PL forms and projects a projection image of a circuit pattern formed on the reticle R onto a wafer W having a resist layer formed on the surface. The projection optical system PL is composed of a plurality of lens elements.
For example, a plurality of lens elements near the reticle R are configured to be movable. Thereby, the projection optical system PL
, In particular, distortion and the like can be arbitrarily changed (details will be described later).

A wafer W is mounted on a wafer stage 12 which can be moved two-dimensionally in the X and Y directions by a motor 202 in a step-and-repeat manner, and a reticle R for one exposure area (shot area) on the wafer W is provided. When the transfer exposure is completed, stepping is performed to the next shot position. Two-dimensional position (movement amount) of wafer stage 12
Is a laser light wave interferometer (interferometer) as shown in FIG.
A moving mirror 17 that constantly detects the laser beam from the interferometer 18 is fixed to an end of the wafer stage 12 by, for example, a resolution of about 0.01 μm.

By repeatedly performing pattern exposure on the same wafer W while stepping the wafer stage 12 as described above, a reticle pattern is formed on the wafer W on which development and etching processing has been performed. It will be formed in the shape.

Here, an alignment device 50 for detecting the position of the wafer W is provided in FIG.
The details are disclosed in, for example, JP-A-60-130742, JP-A-2-272305, and the like, and will be briefly described here. The alignment device 50 adjusts the shape of the alignment beam SP supplied from the alignment light source (He-Ne laser or the like) 100 by the beam shaping optical system 101, and then uses the alignment beam SP for position correction made of parallel flat glass. Harving 102A, 102
The optical path is corrected by B and the inclination correcting harvings 104A and 104B. Then, the light enters the projection optical system PL via the beam splitter 106, the objective lens 107 and the mirror system 108, and is placed on the wafer stage 12. Irradiation is performed on the wafer W.

On the surface of the wafer W, a wafer mark is formed at the boundary (street line) of each shot area, and the diffracted light and the scattered light (diffuse light) generated when the wafer mark and the alignment beam SP are relatively scanned. This is referred to as an alignment detection light), reverses the optical path of the alignment beam SP, and is guided to a detector 109 in a beam splitter 106.

The detector 109 photoelectrically converts the alignment detection light to obtain an alignment detection signal corresponding to each intensity of the diffracted light and the scattered light, and sends it to the alignment signal processing circuit 110. Alignment signal processing circuit 110 calculates the position of the wafer mark based on the alignment detection signal and the position signal from interferometer 18, and sends the calculation result to main controller 120.

Main controller 120 sends a predetermined drive command to controller 19 based on the wafer mark position information from alignment signal processing circuit 110 so that the position of wafer W is at an optimum position. The motor 202 is controlled via the controller 202.

By controlling the movement of the wafer stage 12 based on the position of the wafer mark formed on the wafer W in this manner, the positioning of the wafer W at a target position can be controlled. I have.

Here, in the alignment apparatus 50, the optical path of the alignment beam SP can be corrected by the position correcting herbs 102A and 102B and the tilt correcting herbs 104A and 104B.

That is, the position correcting harves 102A and 102B are arranged at or near a position conjugate with the image forming plane (ie, the wafer surface), and operate based on a control signal from the alignment control unit 105.
Driven by C and 102D. Thus, the optical path of the alignment beam SP is changed to correct the irradiation position of the alignment beam SP on the wafer surface. Further, the tilt correction harbings 104A and 104B are pupil conjugate positions with respect to the projection optical system PL,
Alternatively, the alignment control unit 10
5 is driven by the driving units 104C and 104D which operate based on the control signal from the projection optical system P.
The inclination of the principal ray of the alignment beam SP on the image side (wafer side) of L with respect to the optical axis of the projection optical system PL (hereinafter, referred to as telecentric inclination) is corrected. still,
Both the position correction and the inclination correction have two
Although a pair of parallel flat glasses is used, each parallel flat glass is configured to be one-dimensionally tiltable. If the two flat parallel glass is configured to be two-dimensionally tiltable, one set may be used.

Accordingly, at least one lens element (6, 7, or 8) constituting the projection optical system is moved.
Alternatively, when the optical path of the alignment beam SP fluctuates due to some disturbance or the like, the position-correcting harving 1
02A, 102B and the inclination-correcting harbing 104A,
By correcting the optical path by 104B, the irradiation position of the alignment beam SP irradiated onto the wafer W via the projection optical system PL can always be kept constant. It should be noted that the position correcting harbing 102
A and 102B are lens elements (6, 7,...) In order to always keep the irradiation position of the alignment beam SP constant.
8) The tilting is performed by the amount corresponding to the movement amount of 8).
02A, 102B and lens elements 6, 7,
8 is tilted to cancel (correct) the telecentric tilt of the alignment beam SP caused by the movement of the alignment beam SP.

In addition to the drive control of the wafer stage 12 described above, the controller 19 controls the drive of the reticle stage RS by the control unit 20 by the lens elements 6, 7, 8 (FIG. 2) and the motor 201. It has been done.

That is, as shown in FIG. 2, in the projection optical system PL of the projection exposure apparatus, the lens elements 6, 7 and 8 are driven three-dimensionally (parallel movement (vertical movement) in the direction of the optical axis AX and the optical axis By performing the two-dimensional tilt with respect to the plane perpendicular to AX, the imaging characteristics of the screen (projected image) projected on the wafer W, particularly the image distortion (distortion), are corrected.

That is, the lens elements 6 and 7 are integrally fixed by the lens support member 4, and the lens element 8 is fixed to the lens support member 5. Further, the lens elements 9 and below provided below the lens element 8 are fixed to the main body (barrel) of the projection optical system PL.

The lens support member 5 is connected to the main body of the projection optical system PL by three drive elements 11A, 11B, and 11C (11C not shown) that can expand and contract in the optical axis direction. In addition, the lens support member 4 is configured to
The lens support member 5 is connected to the lens support member 5 by 0A, 10B, and 10C (10C is not shown).

The driving elements 11A, 11B and 11C are arranged at positions rotated by 120 ° along the circumference of the lens element 8, respectively.
Are independently controlled by the lens element control unit 20, so that the lens elements 6, 7 and 8 can be integrally and three-dimensionally driven.

Similarly, each of the driving elements 10A, 10B, and 10C extends along the periphery of the lens
And the driving element 1
By independently controlling 0A, 10B, and 10C by the lens element control unit 20, the lens elements 6 and 7 can be driven three-dimensionally.

In addition, a high-precision by installing a capacitive position sensor, a differential transformer or the like as a position detecting element in the vicinity of the driving element and monitoring a change amount of the driving element corresponding to a voltage or a magnetic field applied to the driving element, is provided. Driving can be performed.

In the above configuration, an example of a position correction control sequence of the alignment beam SP when the movable part (lens elements 6, 7, 8) of the projection optical system PL is moved will be described.

A plurality of reticle marks (M ₁₁ , M ₁₂ ,...) Formed on reticle R are detected by photoelectric sensor 16 mounted on wafer stage 12 via projection optical system PL and reference member 15. I do.

The photoelectric sensor 16 is connected to the interferometer system (1).
Wafer stage 12 whose coordinates are controlled by (7, 18)
The reticle marks (M ₁₁ , M ₁₂ ,...), Which are scanned in the X and Y directions and projected on the reference member 15 provided at substantially the same height as the wafer W, A detection signal detected through the reference mark (slit mark) is stored in a memory in the controller 19 in synchronization with the coordinate data of the interferometer 18. The controller 19 calculates the signal interval of the fetched detection signal, compares it with the reticle mark interval of the design value obtained in advance, and calculates a magnification change, distortion, and the like. The measurement operation is disclosed in, for example, JP-A-59-94032, and a detailed description thereof will be omitted.

Here, the controller 19 sends a correction command to minimize the magnification change amount and distortion amount to the lens element control unit 20, and the lens element control unit 20 adjusts the lens by the correction amount corresponding to the correction command. In order to correct the positions of the elements 6, 7, 8
A to 10C and 11A to 11C are driven.

At this time, the lens element control unit 20
The amount of movement of the lens elements 6, 7, 8 is controlled by the controller 1.
9 to the main controller 120. Main controller 1
Numeral 20 calculates the irradiation position of the alignment beam SP on the wafer W and the telecentric inclination (or the amount of change thereof) generated by the movement of the lens elements 6, 7, 8 and corrects them so that each amount of change can be corrected. Alignment control unit 10
5 Note that the main controller 120 calculates the relationship between the drive amounts of the lens elements 6, 7, and 8 and the irradiation position of the alignment beam SP and the telecentric inclination, which are obtained in advance through experiments, simulations, and the like, in the form of a table or a mathematical expression. It is assumed that it is stored in the memory.

The alignment control unit 105 corrects the position of the alignment beam and the tilt of the telecentric lens based on the input correction amount, so as to correct the position correction harbing 102A, 1H.
02B and the tilt correction harvings 104A and 104B are driven.

Accordingly, the irradiation position of the alignment beam SP is corrected to the position before driving the lens elements 6, 7, 8 so that even if the lens elements 6, 7, 8 are driven, the irradiation position of the alignment beam SP is corrected. Can always be kept constant. Also, the telecentric inclination at this time is corrected to almost zero.

Here, in FIG. 1, the lens element 6,
The amount of deviation of the alignment beam position caused by the movement of 7, 8 is calculated, and based on the calculation result, the position correcting herbs 102A, 102B and the tilt correcting herbs 104A, 104B are driven. The position and the relative position of the reticle marks (M ₁₁ , M ₁₂ ,...) May be controlled to be always constant.

That is, the change in the light intensity of the alignment beam SP is detected by the photoelectric sensor 16 in the same manner as the method of detecting the reticle mark (M ₁₁ , M ₁₂ ,...) On the reticle using the photoelectric sensor 16. The relative position between the reticle mark at a predetermined position on the reticle and the irradiation position of the alignment beam SP is determined in synchronization with the interferometer coordinates of the wafer stage 12, and the alignment control unit 105 is controlled so that the relative position is always constant. If this is the case, the irradiation position of the alignment beam SP can always be kept constant even when the lens elements 6, 7, 8 are driven in the same manner as described above. It should be noted that regarding the telecentric inclination, the driving amount of the lens elements 6, 7, 8 (or the position-correcting
A, the amount of change (based on the amount of inclination of 102B) or the amount of change based on the value measured using the reference mark on the reference member 15 as disclosed in Japanese Patent Application Laid-Open No. 2-272305. What is necessary is just to correct by inclining the correction harving 104A, 104B.

According to the above configuration, the change in the position of the alignment beam SP and the inclination of the telecentric beam caused by driving the lens elements 6, 7, and 8 are compared with the image plane of the projection optical system PL in the optical path of the alignment beam. The alignment beam can be corrected by shifting the alignment beam substantially at the substantially conjugate position and at the substantially conjugate position with respect to the pupil plane of the projection optical system PL. Even when the lens elements 6, 7, 8 are driven, the alignment beam SP is always irradiated at a constant irradiation position. Can be held. If the telecentric inclination of the alignment beam SP caused by the movement of the lens elements 6, 7, 8 and the inclination of the position-correcting harbing 102A, 102B is within a predetermined allowable value, the inclination-correcting harving is used for the correction. There is no need to tilt 104A, 104B.

In the above-described embodiment, a case is described in which the amount of change in the alignment beam position that changes in accordance with the movement of the lens elements 6, 7, 8 is calculated, and the alignment beam position is corrected based on the calculation result. However, the present invention is not limited to this.
D, line sensor, etc.) 160 (FIG. 1) may be provided on the wafer stage 12 to detect the irradiation position of the alignment beam SP and feed it back to match the target position.

That is, the wafer W on the wafer stage 12
At the same height position, a detector 160 whose coordinates are controlled by the interferometer system (17, 18) is provided, and the detector 160 is moved so that the detector 160 is irradiated with the alignment beam SP. The position of alignment beam SP detected based on the reference is input to main controller 120. Main controller 120
Detects the irradiation position of the alignment beam SP in the rectangular coordinate system XY (that is, the image field of the projection optical system PL) based on the position information input from the detector 160 and the coordinate values corresponding to the position of the detector 160, A command to correct the optical path of the alignment beam SP is sent to the alignment control unit 105 up to a position where the detection result becomes a target (for example, a position before driving the lens elements 6, 7, 8). Therefore, the irradiation position of the alignment beam SP is determined by the detector 160 and the main controller 12.
0, the alignment control section 105 and the alignment beam correcting means (102A, 102B, 104A, 104B) are controlled so as to adjust to the target position by a feedback loop. In the above embodiment, the case where the lens elements 6, 7, and 8 constituting the projection optical system PL are moved has been described. In addition to the lens elements, the alignment beam SP is disposed between the reticle R and the wafer W. Optical components that pass through (eg, field lens,
The same effect can be obtained by applying the present invention when moving parallel plate glass or the like.

In the above embodiment, the change of the irradiation position of the alignment beam SP on the wafer W caused by the movement of the lens elements 6, 7, 8 is determined by the projection optical system P.
Correction is made by adjusting the incident position of the alignment beam incident on L, so that the irradiation position (relative position to the optical axis of the projection optical system) within the image field of the projection optical system PL is always kept constant. Was. However,
The amount of change in the irradiation position of the alignment beam SP during the movement of the lens elements 6, 7, 8 is obtained by calculation or actual measurement as in the above-described embodiment, and the amount of change is given to the main control device 120 as an offset. The wafer W may be positioned offset from the reference position (for example, the optical axis of the projection optical system) by an offset so as to offset the alignment error caused by the change amount. The alignment accuracy due to the change can be made substantially zero.

When the lens elements 6, 7, 8 are moved, the irradiation position of the alignment beam SP can be shifted two-dimensionally in the image field of the projection optical system PL. Also, at least the change amount in the mark measurement direction (for example, the X direction) of the change amount of the irradiation position on the wafer W may be corrected, and the irradiation position is slightly shifted in the non-measurement direction (for example, the Y direction). But you can ignore it. In this case, there is an advantage that the driving amount of the position correcting harbings 102A and 102B can be small. However, this is effective when the wafer mark is a one-dimensional mark.

Further, in the above embodiment, the irradiation position of the alignment beam (or the change amount thereof) is obtained by calculation. However, after the lens elements 6, 7, 8 have been moved, the reference member 15 and the photoelectric sensor 16 ( The irradiation position is measured by using FIG. 2), and based on the measured value, the position correcting herbs 102A and 102B and the inclination correcting herbs 104A and 104A are used.
104B may be driven or stored as an offset. The alignment beam S
The method of measuring the irradiation position of P is not limited to the method using the reference member 15 and the photoelectric sensor 16. For example, a reflective diffraction grating mark is formed on the reference member 15 and The irradiation position may be measured by detecting the mark. Further, according to a detection method (image processing method or the like) of the alignment system, a reference mark (slit mark) of the reference member 15 is irradiated with illumination light transmitted to a lower portion thereof by an optical fiber or the like, and the reference mark is irradiated by the alignment system. By detecting, the irradiation position may be measured. The means for measuring the imaging characteristics of the projection optical system PL, particularly the projection magnification and distortion, is also used as the reference member 15.
The present invention is not limited to the photoelectric sensor 16 and may be any other method.

In the above embodiment, the alignment system of the TTL system has been described as an example.
The same effect can be obtained by applying the present invention to an alignment system of the (e Reticle) type. Furthermore, TT
In any of the L method and the TTR method, the detection method may be arbitrary. For example, an image processing method using a CCD camera or the like, or a method using interference fringes as disclosed in JP-A-2-272305. But it doesn't matter. In the above embodiment, a projection lens system including a plurality of lens elements is considered as the projection optical system PL. However, at least one optical element is used in a mirror browsing system or a system combining a reflection system and a refraction system. The present invention can be applied to driving. The present invention can be applied to the case where the imaging characteristics of the projection optical system are adjusted at the time of assembling adjustment of the exposure apparatus, for example, when the thickness of the washer is changed to change the distance between the lens elements. Further, the position correction harbings 102A and 102B may be arranged between the projection optical system PL and the wafer W.

[0047]

As described above, according to the present invention, an alignment for detecting an alignment mark formed on a photosensitive substrate via a projection optical system in which at least one optical element constituting the projection optical system is movable. By correcting the alignment beam position of the apparatus in accordance with the movement of the optical element of the projection optical system, the alignment beam position can be constantly controlled. Therefore, even when a pattern is overlapped and exposed using a plurality of photomasks, the detection position of the reference alignment mark can be accurately detected without changing, and the overlay accuracy can be further improved. In addition, since the alignment beam position can be periodically corrected, the long-term drift of the alignment beam itself can be corrected, and deterioration of the overlay accuracy due to the drift of the alignment beam position can be prevented.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing a projection exposure apparatus using an alignment apparatus according to the present invention.

FIG. 2 is a partial cross-sectional view illustrating a detailed configuration of a movable section of the projection optical system.

[Explanation of symbols]

6, 7, 8, 9 ... lens element, 19 ... controller, 20 ... lens element controller, 50 ... alignment device, 102A, 102B, 104A, 10
4B: Harving, 105: Alignment control unit,
109 Detector 110 Alignment signal processing circuit 120 Main controller PL Projection optical system
R: reticle, W: wafer, SP: alignment beam.

Claims (2)

(57) [Claims] 1. An alignment apparatus for detecting a positioning alignment mark provided on a photosensitive substrate via a projection optical system for forming and projecting a pattern on a photomask onto a photosensitive substrate. At least one of the constituent optical elements is movable, and the alignment mark detection alignment light emitted through the projection optical system when the optical element of the projection optical system is driven is on the photosensitive substrate. An alignment apparatus comprising: an alignment light position correcting means for correcting a change in an irradiation position in the apparatus. 2. The alignment apparatus according to claim 1, further comprising measuring means for measuring an irradiation position of the alignment light and a relative position of a pattern on the photomask.