JPH1097987A - Method and device for scanning type exposure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce focusing error by measuring a position of a substrate plane to be exposed in exposure optical-axis direction at a position away by a specified distance, near side in scanning direction, for the exposure area of a projection optical system, and employing a means for controlling/correcting position based on the result. SOLUTION: A wafer stage 3 is provided on a stage stool 7, with a focus sensor comprising a light-projecting means 21 and a photo-detecting means 22 for detecting whether a wafer on the wafer stage 3 is positioned on the focus plain of a projection optical system 2 or not provided. The stage stool 7 causes deflection due to dead load and surface precision at work. This is measured for each machine type, and a deflection amount is decided by the position of the wafer stage 3. With a table for each XY position and correction value of the wafer stage 3 prepared in advanced, the Z-axis of the wafer stage 3 driven based on the value wherein the measurement value by a focus sensor is corrected with that correction value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an exposure apparatus used for manufacturing a semiconductor device or the like by exposing a design pattern on a resist on a substrate and a device manufacturing method using the same.

[0002]

2. Description of the Related Art In a one-shot exposure type exposure apparatus, when a projection optical system is constituted by a lens, an image forming area has a circular shape. However, since the semiconductor integrated circuit generally has a rectangular shape, the transfer area in the case of batch exposure is a rectangular area inscribed in a circular imaging area of the projection optical system. Therefore, even the largest transfer area has a diameter of 1 /
正方形 2 is a square with sides. On the other hand, the transfer area is enlarged by scanning and moving the reticle and wafer synchronously using a slit-shaped exposure area having a diameter approximately equal to that of the circular imaging area of the projection optical system. A scanning exposure method (step and scan method) has been proposed. In this method, when a projection optical system having an imaging area of the same size is used, a larger transfer area is secured as compared with the step-and-repeat method in which collective exposure is performed for each transfer area using a projection lens. be able to. That is, since there is no restriction by the optical system in the scanning direction, it is possible to secure only the stroke of the scanning stage, and it is possible to secure approximately √2 times the transfer area in the direction perpendicular to the scanning direction. .

An exposure apparatus for manufacturing a semiconductor integrated circuit is required to have an enlarged transfer area and an improved resolution in order to cope with the manufacture of a chip having a high degree of integration. The fact that a smaller projection optical system can be employed is advantageous from the viewpoint of optical performance and cost, and the exposure method of the step-and-scan method is attracting attention as a mainstream of future exposure apparatuses.

In the step-and-scan method, during scanning, the attitude of the wafer in the direction of the optical axis of the projection optical system is controlled so that focus adjustment corresponding to the unevenness of the wafer in the transfer area, which is difficult with the batch exposure method, is performed. Since it can be performed, a larger margin can be provided for the undulation of the wafer and the pattern inspection. For this purpose, it is necessary to provide a means for sequentially measuring and controlling the attitude of the wafer surface during scanning exposure in order to adjust the wafer surface and the image surface of the projection optical system to the most appropriate state in the exposure area. is there. Measuring the wafer surface at a position separated in the scanning direction with respect to the slit-shaped exposure region as this measurement means is advantageous in control because position information in the focus direction can be obtained before a predetermined surface enters exposure. It is. But,
Since it is not a measurement value on the exposure surface, there is a problem that if the scanning direction of the exposure surface is not perpendicular to the exposure optical axis, the measurement value will not be accurate.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a scanning exposure apparatus which measures a substrate surface at a position apart from a slit-shaped exposure region in a scanning direction and focuses the substrate surface at the slit position. It is an object of the present invention to reduce a focus error generated when a scanning direction of a surface of a substrate stage on which a substrate such as a wafer is mounted is not perpendicular to an exposure optical axis.

[0006]

In order to achieve the above object, according to the present invention, a part of the pattern of an original is projected onto a substrate via a projection optical system, and is perpendicular to the optical axis of the projection optical system. In a scanning type exposure apparatus that exposes the substrate with the pattern of the original by scanning the original and the substrate together, the substrate exposed surface at a position at a predetermined distance in the scanning direction with respect to the exposure area of the projection optical system. Means for measuring the position in the exposure optical axis direction, means for controlling the position in the exposure optical axis direction of the substrate exposure surface based on the measurement result, and the measurement result in accordance with the position in the image plane direction of the substrate And means for correcting

As the correction data, for example, the amount of the correction with respect to the position of the substrate in the image plane direction is measured in advance and stored as a table or an arithmetic expression.

[0008]

In a scanning exposure apparatus, a measurement point of a focus sensor for measuring a position (focus) of an exposed surface of a substrate in an exposure optical axis direction is arranged in front of an exposure area in a scanning direction.
Performs focus look-ahead. When the surface of the stage base is distorted due to the weight of the stage, processing, or the like, an error occurs because the exposure position does not match the focus measurement point.

The present invention has been made by paying attention to the fact that the distortion (deformation) of the surface plate is determined by the position of the stage.
The change in the scanning direction (zy plane) of the substrate caused by the deformation of the stage base is measured in advance, and the correction amount for the stage position and the scanning direction is prepared in the form of a table, an arithmetic expression, or the like. At this time, the focus measurement value is corrected using the table, the arithmetic expression, or the like.

Thus, it is possible to correct a focus error caused by the deformation of the stage base.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing a state of an exposure apparatus according to an embodiment of the present invention as viewed from the side, and FIG. 2 is a perspective view showing an appearance of the exposure apparatus. As shown in these drawings, this exposure apparatus uses a projection optical system 2 to project a part of an original pattern on a reticle stage 1 through a wafer stage 3.
The reticle and the wafer are synchronously scanned in the Y direction relative to the projection optical system 2 to expose the reticle pattern to the wafer, and this scanning exposure is performed on a plurality of transfer areas on the wafer. (Shot) is a step-and-scan type exposure apparatus which performs step movement for repeated execution.

The reticle stage 1 is driven in the Y direction by a linear motor 4, and the wafer stage 3 (3a to 3d)
The X stage 3a is driven in the X direction by the linear motor 5, and the Y stage 3b is equipped with the linear motor 5, and is driven in the Y direction by the linear motor 6. The synchronous scanning of the reticle and the wafer is performed by driving the reticle stage 1 and the Y stage 3b at a constant speed ratio in the Y direction (for example, 4: -1, where "-" indicates that the directions are opposite). Do. A X-tilt stage 3c is mounted on the X stage 3a, and a wafer chuck 3d for holding the wafer 51 is mounted thereon. X stage 3a is air bearing 52
As a result, it is constrained on the stage base 7 in the Z direction and guided in the X direction. Z tilt stage 3c is X stage 3a
Is driven in the Z tilt direction by a plurality of linear motors 15. Z tilt stage 3c and X stage 3a
The relative position in the Z-tilt direction is measured by the sensor 16 between.

The wafer stage 3 is provided on a stage base 7, and the stage base 7 is connected to three stages through three dampers 8.
It is supported on a floor at a point. Reticle stage 1,
The projection optical system 2 and the illumination system 14 are provided on a lens barrel base 9, and the lens barrel base 9 is a base frame 10 mounted on a floor or the like.
It is supported above via three dampers 11 and columns 12. The damper 8 is an active damper for actively damping or removing vibrations in six axial directions. However, a passive damper may be used, or the damper 8 may be supported without a damper.

The exposure apparatus further includes a distance measuring means 13 such as a laser interferometer or a micro encoder for measuring the distance between the lens barrel base 9 and the stage base 7 at three points.

The light projecting means 21 and the light receiving means 22 constitute a focus sensor for detecting whether or not the wafer on the wafer stage 3 is located on the focus surface of the projection optical system 2. That is, the wafer is irradiated with light from an oblique direction by the light projecting means 21 fixed to the lens barrel base 9, and the position of the reflected light is detected by the light receiving means 22, whereby the direction of the optical axis of the projection optical system 2 is adjusted. Of the wafer surface is detected.

In this configuration, when the wafer is loaded onto the wafer stage 3 via the transport path between the two columns 12 at the front of the apparatus by the transport means (not shown) and the predetermined alignment is completed, the exposure apparatus While repeating the scanning exposure and the step movement, the reticle pattern is exposed and transferred to a plurality of transfer areas on the wafer. At the time of scanning exposure, the reticle stage 1 and the Y stage 3b are moved at a predetermined speed ratio in the Y direction (scanning direction) to scan a pattern on the reticle with slit-like exposure light,
By scanning the wafer with the projected image, a pattern on the reticle is exposed to a predetermined transfer area on the wafer. During the scanning exposure, the height of the wafer surface is measured by the focus sensor.
Height and tilt are controlled in real time, and focus correction is performed. When the scanning exposure for one transfer area is completed, the X stage 3a and / or the Y stage 3b are driven to move the wafer stepwise in the X direction and / or the Y direction, thereby starting the scanning exposure position for the other transfer area. And scanning exposure is performed.
The combination of the step movement in the X and Y directions and the movement for scanning exposure in the Y direction allows each of the plurality of transfer areas on the wafer to be sequentially and efficiently exposed. The arrangement of the transfer area, the scanning direction of either positive or negative Y, the order of exposure to each transfer area, and the like are set.

FIG. 3 shows a positional relationship between a slit (exposure slit) projected on the wafer by the projection optical system 2 and a focus measurement point (hereinafter, referred to as a spot) by the focus sensor. 2 shows the focus measurement target point of FIG. In the apparatus of the present embodiment, the exposure slit 30 is 7 × 25 mm, and the maximum size of the transfer area 40 is 25 × 25 mm.
32.5 mm. A total of seven spots are set, one at the center of the exposure slit 30 and three at a position shifted by 12 mm from the center of the exposure slit 30 in the scanning direction. When scanning the wafer upward (UP scanning) from the bottom in the figure, when scanning the wafer from top to bottom (DOWN scanning) using three channels of spots a ₁ , a ₂ , and a ₃ , , wafer height 3 channels of spot c _1, c _2, c ₃ a (Z direction position), measured at 10 points in the wafer measurement direction (M0～M9) for each spot. These measurement data are then used as data for focus correction when the wafer is further scanned and each measurement point (M0 to M9) comes to the center of the exposure slit 30. That is, focus correction is performed by pre-reading the focus of each measurement point (pre-read measurement). The spot S is an acquisition measurement spot on the slit.

Meanwhile, the stage base 7 bends as shown in FIG. 5 (a) due to its own weight and surface accuracy during processing. For this reason, the scanning direction of the wafer stage 3 generates an inclination θ from the Y direction in the optical axis plane (YZ plane) (FIG. 5).
(B)) When the wafer surface at the pre-read measurement point a is scanned while keeping the wafer height with respect to the wafer stage 3 constant, the wafer surface shifts by ΔZ at the slit position P separated by L from the pre-read measurement point a. That is, if the measurement value at the pre-read measurement point a is not changed, a so-called Abbe error is calculated by ΔZ = Lθ
Will only have. In FIG. 5, reference numeral 51 denotes a wafer, 5
2 is an air bearing.

The deflection of the weight of the stage base 7 can be measured for each model, and the amount of the deflection is determined by the position of the wafer stage 3. Therefore, in this embodiment, a table of each XY position of the wafer stage 3 and a correction value is prepared in advance. At the time of scanning exposure, the wafer stage 3 is Z-driven based on a value obtained by correcting the measurement value of the focus sensor (21, 22) by this correction value, and the wafer surface position is corrected (focus correction). Thus, when the stage base 7 is deformed, it is possible to correct a focus error caused by a mismatch between the focus measurement point (spot) and the focus correction (slit) position. The correction value is a value for correcting a deviation between each XY position of the wafer stage 3 during scanning from the focus measurement point to the slit, and varies depending on the scanning direction.

Next, a method of creating the correction value table will be described with reference to FIG.
This will be described with reference to FIG. In the present embodiment, 256
Considering the M correspondence, the allowable focal depth of the projection optical system is 0.8
μm, the measurement accuracy of the distance measuring means 13 is 0.1 μm, the target accuracy of the stage is 0.1 μm, and the target accuracy of the focus correction is 0.2 μm.

A jig 61 having a sufficiently flat reference surface of the order of 20 to 30 nm is mounted on the wafer stage 3 instead of the wafer chuck. This jig has a dimension larger than the wafer chuck by the thickness of the wafer. next,
By driving the wafer stage 3 in the XY directions, a predetermined position P (x _p , y _p ) on the jig 61 (where x _p and y _p are coordinate systems of the wafer stage 3) is exposed to an exposure lens (projection optical system). Bring to the center of 2. At this position, seven spots a ₁ , a ₂ , a ₃ , S (p ₂ ), c
While measuring the surface positions at ₁ , c ₂ and c ₃ , the wafer stage 3 is Z-tilt driven to adjust the surface of the jig 61 to a reference surface (exposure image surface). Next, the wafer stage 3 is moved from the position by the pre-reading distance L in the scanning direction while controlling the Z-tilt system so that the measurement value of the sensor 16 becomes constant (stage platen reference mode). That is, the point P is moved to (x _p , y _p + L) and the point p
₁ , p ₂ and p ₃ are brought to the positions of spots c ₁ , c ₂ and c ₃ . At this time, the values measured at the spots c ₁ , c ₂ , and c ₃ by the focus sensor are scanned in the −Y direction by scanning exposure (D
When OWN scanning is performed, the correction value is a correction value for the pre-read detection value of the point P (p ₁ , p ₂ , p ₃ ) obtained at the spots c ₁ , c ₂ , c ₃ . However, at this time, it is obtained from the measured value of the distance measuring means 13. A change in the measurement value of the focus sensor due to a relative posture change between the stage base 7 and the barrel base 9 must be corrected. By the correction, the effect of only the change in the strain due to the flatness of the stage base 7 and the load is taken out.

Further, the sensor measurement values at the spots a ₁ , a ₂ , and a ₃ obtained by moving the point P to (x _p , y _p -L) when the scanning movement (UP scanning) in the + Y direction is performed. It becomes a correction value.

The point P (x _p, y _p) to finely set at a position corresponding to the entire surface of the wafer, to obtain a large number of correction values, (x _p,
y _p ) Create a correction table of paired correction values. in this case,
It is preferable that the correction value is obtained for at least P points corresponding to the spatial frequency of the undulation of the wafer stage. In addition, instead of the correction table, a correction value is represented by a function F (x _p ,
y _p ).

The Z-tilt system of the wafer stage 3 is controlled by the correction value obtained in this manner to control the Z-tilt system based on the value obtained by correcting the focus measurement value during the scanning exposure. Is at most 0.2 μm /
Despite being 12 mm, no substantial focus error was detected.

[Embodiment of Manufacturing of Micro Device] FIG. 7 shows a flow of manufacturing a micro device (a semiconductor chip such as an IC or an LSI, a liquid crystal panel, a CCD, a thin film magnetic head, a micromachine, etc.). In step 1 (circuit design), the circuit of the semiconductor device is designed. Step 2 is a process for making a mask on the basis of the circuit pattern design. On the other hand, in step 3 (wafer manufacturing), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the prepared mask and wafer. The next step 5 (assembly) is called a post-process, and is a process of forming a semiconductor chip using the wafer produced in step 4, and includes processes such as an assembly process (dicing and bonding) and a packaging process (chip encapsulation). including. In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device manufactured in step 5 are performed. Through these steps, a semiconductor device is completed and shipped (step 7).

FIG. 8 shows a detailed flow of the wafer process. Step 11 (oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms an insulating film on the wafer surface. Step 13 (electrode formation) forms electrodes on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted into the wafer. Step 15
In (resist processing), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the above-described exposure apparatus to print and expose the circuit pattern of the mask onto the wafer. Step 17 (development) develops the exposed wafer. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), unnecessary resist after etching is removed. By repeating these steps, multiple circuit patterns are formed on the wafer.

By using the manufacturing method of this embodiment, a highly integrated semiconductor device, which was conventionally difficult to manufacture, can be manufactured at low cost.

[0028]

As described above, according to the present invention, the scanning direction of the substrate (z-
The change in the y-plane) is measured, and the correction amount for the position of the stage and the scanning direction is prepared in the form of a table or a function in advance, and at the time of exposure, the focus measurement value is calculated using the table or an arithmetic expression. By performing the correction, it is possible to reduce a focus error caused by a distortion of the surface of the stage surface plate when performing the pre-reading of the focus, and to improve the focus accuracy.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a state of an exposure apparatus according to one embodiment of the present invention when viewed from a side.

FIG. 2 is a perspective view showing an appearance of the exposure apparatus of FIG.

FIG. 3 is a diagram showing an arrangement of a focus sensor in the apparatus of FIG.

FIG. 4 is a diagram showing focus measurement points in a shot in the apparatus of FIG. 1;

FIG. 5 is an explanatory diagram exaggeratingly showing the deflection of the stage base in the apparatus of FIG. 1;

FIG. 6 is an explanatory diagram of a method of obtaining a focus measurement correction value in the apparatus of FIG.

FIG. 7 is a diagram showing a flow of manufacturing a micro device.

FIG. 8 is a diagram showing a detailed flow of a wafer process in FIG. 7;

[Explanation of symbols]

1: reticle stage, 2: projection optical system, 3: wafer stage, 3a: X stage, 3b: Y stage, 3c:
Z-tilt stage, 3d: wafer chuck, 4: linear motor, 6: linear motor, 7: stage base, 8:
Damper, 9: lens barrel surface plate, 10: base frame, 11:
Damper, 12: support, 13: distance measuring means, 14: illumination system, 15: linear motor, 16: sensor, 18, 19:
Center of gravity, 20: cross section of exposure light, 21: light projecting means, 22: light receiving means, 23: laser interferometer, 30: slit, 51:
Wafer, 52: air _{bearings, a 1, a 2, a} 3, c 1
, C ₂ , c ₃ , S: spot, M0 to M9: focus measurement point, S1 to S36: shot, 61: jig.

Claims (4)

[Claims] 1. A pattern of an original is projected on a substrate through a projection optical system, and a part of the pattern of the original is scanned perpendicularly to an optical axis of the projection optical system. In a scanning type exposure apparatus that exposes a substrate, means for measuring a position in a direction of an exposure optical axis of a surface to be exposed on a substrate at a position at a predetermined distance before a scanning direction with respect to an exposure region of the projection optical system, and Scanning exposure comprising: means for controlling the position of the surface to be exposed on the substrate in the direction of the exposure optical axis, and means for correcting the measurement result in accordance with the position of the substrate in the image plane direction. apparatus. 2. The apparatus according to claim 1, further comprising storage means for storing in advance the amount of the correction for the position of the substrate in the image plane direction. 3. The apparatus according to claim 1, further comprising storage means for storing in advance the calculation method of the correction for the position of the substrate in the image plane direction. 4. A device manufacturing method using the apparatus according to claim 1.