JPS62208629A - Reduction stepper - Google Patents

Abstract

PURPOSE:To enable a wafer to be exposed to an optimum position by a method wherein any slips of focussing positions due to the ruggedness on the surface of wafer or the slope of a wafer stage etc. are corrected. CONSTITUTION:A wafer stage 14 is lifted and lowered to level-adjust a measuring point A on a wafer 13 to the focussing level of a lens 11 so that a light 15 from a photoemitter 1 may enter into a photodetector 6 with the maximum incident light intensity while the slip Z1 of a measuring point A on the wafer 13 in the vertical direction from the backside of lens 11 at this time may be measured by a measuring part 20. Likewise, the slips Z2, Z3, Z4, Z5 of respective measuring points B, C, D, E are measured to input total slips Z1-Z5 in a focussing part 21 so that the mean value thereof may be calculated to be set up as the optimum focussing level in case of exposure for shoot-the range of wafer 13. In such a constitution, a level-adjusting mechanism 22 is driven to lift and lower the wafer stage 14 for level-adjusting the wafer 13 so that a pattern P on a reticle may be transfer-exposed to the wafer 13 on the position thereof through the contraction projecting lens 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a reduction projection type exposure apparatus used in the alignment exposure process after resist coating.

[Conventional technology]

Conventionally, automatic focusing mechanisms in reduction projection type exposure apparatuses include a pressure detection method using an air micrometer, a volume sensor method, and a reflection imaging method using an optical sensor. Each method has its advantages and disadvantages, and cannot be generalized, but
Reflection imaging methods are becoming mainstream due to their accuracy and reliability.

[Problem that the invention seeks to solve]

In the case of the reflection imaging method using the conventional optical sensor described above, a method is adopted in which light is applied to one point on the wafer and the reflected light is detected through a positioned slit plate or the like.

When using this type of method, the positioning accuracy in the Z-axis direction at the measurement point is high, but since the focusing operation is performed at one point within the shot (usually at the center of the exposure axis), the wafer may warp or the wafer may warp. If the stage itself is tilted, the measurement point may be in optimal focus (Best 1~Focus), but there will be a significant shift in focus (defocus) around the shot, resulting in a significant drop in resolution. was.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reduction projection type exposure apparatus that corrects deviations in focal position caused by unevenness on the surface of a wafer, inclination of a wafer stage, etc., and enables exposure at an optimal position. .

[Means for solving problems]

The present invention relates to a reduction projection type exposure apparatus that transfers a reticle pattern onto a wafer through a reduction projection lens, which includes a plurality of light emitting elements that independently irradiate light to each of a plurality of measurement points set on a wafer, and the projection lens. Each of the above al! A pair of light receiving elements that individually receive light from each light emitting element reflected from the wafer surface at one fixed point, a height adjustment mechanism for a wafer stage on which a wafer is mounted, and a lens at each measurement point on the wafer. A measurement unit that measures the amount of deviation with respect to the focal height position, and 1! ) The average value of the amount of deviation from the lens focal height position of each dI fixed point is determined, and the height position of the average value is set as the focal height position during exposure, and the wafer is placed at the set focal height position. The reduction projection type exposure apparatus is characterized by having a focusing section that issues a drive command necessary for positioning to the height adjustment mechanism.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, a plurality of measurement points A are set on the wafer 13 on one side of the exposure axis 12 of the reduction projection lens 11 installed directly above the wafer stage 14.
Lights 15 to 19 are applied independently to each of B, C, D, and E.
The light emitting elements 1, 2, 3, 4-, and 5 that emit light are arranged diagonally on one side of the wafer 13, and are placed at the focal height positions A' to E' of the projection lens 11 at a position inverted by 90 degrees. Light receiving elements 6.7, 8, 9.10 that individually receive light from the light emitting elements 1 to 5 reflected from the wafer surface at certain measurement points A, B, C, D, and E are placed diagonally on the wafer 13. to be placed. The wafer stage 14 is supported by a height adjustment mechanism 22, which raises and lowers the wafer stage 14, and receives light at each measurement point A-E shifted in the height direction of the wafer 13 mounted on two sides of the stage 14. The height is adjusted to focal height positions A' to E' of the lens 11 where the incident light intensity of each element is maximum. Furthermore, each measurement point A- of the wafer 13 whose height has been adjusted by the height adjustment mechanism 22
A measurement unit 20 that measures the amount of deviation in the height direction with respect to the lens focal positions A' to E' of E, and each measurement point A to E with respect to the lens focal positions A' to E' in response to the output from the measurement unit 20.
Find the average value of the amount of deviation in the height direction of and a focusing section 21 that emits the image to the height adjustment mechanism 22.

According to the structure described above, the present invention is capable of measuring the lens focal height position A' to each measurement point A-E shifted in the height direction of the wafer 13.
Adjust the height to E' and find the deviation in the height direction of each measurement point A - E with respect to the lens focal height position A' to E'.
The amount of deviation is averaged, and the iV average value is used as the optimum focus position during exposure.The height of the wafer 13 is adjusted to the optimum position directly below the lens 11, focusing is performed, and exposure is performed. .

That is, if the surface of the wafer 13 has undulations or irregularities as shown in FIGS. 2 to 4, each measurement point on the wafer will shift in the height direction, causing the lens focal point height position A'
In the case of the measurement point on the wafer 13 that overlaps ~E', the light from the light emitting element is reflected by the same surface (z) of the wafer 13, so the light intensity entering the light receiving element paired with the light emitting element is maximum. becomes. On the other hand, in the case of a measurement point on the wafer 13 that is shifted in the height direction from the lens focal height positions A' to E', the light from the light emitting element is reflected on the surface of the wafer 13 and enters the light receiving element. Light intensity decreases. Based on this principle, the amount of deviation in the height direction of each measurement point with respect to the lens focal height position is determined. Specifically, as shown in FIG. 2, the wafer stage 14 is raised and lowered to adjust the height of the measurement point A on the wafer 13- to the focal height position A' of the lens 11.
Light 15 emitted from the light emitting element 1 is made to enter the light receiving element 6 with maximum incident light intensity.

At this time, 1lll of the wafer 13-1- in the vertical direction from the bottom surface of the lens 11 + the deviation of the fixed point A M z 1
is measured by the measuring section 20.

In addition, as shown in FIG. 13-F, the deviation lz2 of measurement point B is measured by the running part 20 of nl.

Further, as shown in FIG. 4, the wafer 13 is layered in two layers, and the measurement point C on the wafer 13 is adjusted in height to the focal height position C' of the lens, and the wafer 13 is ]3'' The displacement plate Z at the second measurement point C is measured by the measuring section 20.

Measurement point I] using the wafer stage in the same manner.

The height of E is adjusted, and the measurement unit 20 measures the deviation iZ4+Z5 of E at each measurement point in the vertical direction from the f-plane of the lens 11.

The deviation amounts 71 to Z5 of all the measurement points A-E obtained as described above are input to the focusing section 21, and the average value is calculated, and the height position of the average value is determined at the time of exposure for the shot in the wafer. The optimum focus height position Z is set as the optimum focus height position Z, and the height adjustment mechanism 22 is driven by a command from the focus adjustment unit 21 to raise and lower the wafer stage 14. The height of the wafer 13 is adjusted to the focal height position Z, the wafer 13 is focused on the lens 11, and the reduction projection lens 11 is adjusted at that position.
pattern P on the reticle through the wafer 13-1-
Perform transfer exposure.

In the previous embodiment, five measurement points were set on the wafer, but the number may be arbitrary.

In one embodiment of the present invention, a focusing mechanism having the structure shown in the figure was used, but the present invention is characterized by performing height adjustment operations at multiple points within the pattern transferred onto the wafer. The structure of the focusing mechanism does not matter as long as the method of finding the optimal focus position by averaging the amount of deviation is used.

〔Effect of the invention〕

As explained above, the present invention has two or more light-emitting elements and corresponding light-receiving elements, performs a height adjustment operation at a measurement point on a wafer, and calculates the amount of deviation from the focal point of each measurement point. Because the optimum focus position of the shot is determined by averaging processing and the exposure operation is performed with the wafer adjusted to the height fJII at that position, there are no irregularities on the wafer surface due to undulations or a tilt of the wafer stage. This also has the effect of correcting this, allowing exposure under optimal conditions, and minimizing the decrease in resolution.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing one embodiment of the present invention, FIG.
Figures 4 and 4 are o of Figure 1 for detailed explanation of the present invention.
-o' sectional view. 1 to 5 - Light emitting element 6 to 10... Light receiving element 11... Reduction projection lens 12... Exposure axis 13.
...Wafer 14...Wafer stage 15-19, light 20...Measurement section 21...
Focusing section

Claims (1)

[Claims] (1) In a reduction projection exposure apparatus that transfers a reticle pattern onto a wafer through a reduction projection lens, a plurality of light emitting elements and the projection lens independently irradiate light to each of a plurality of measurement points set on the wafer. a plurality of pairs of light receiving elements that individually receive light from each light emitting element reflected from the wafer surface at each measurement point located at a focal height position of , and a height adjustment mechanism for a wafer stage on which the wafer is mounted; A measurement unit that measures the amount of deviation of each measurement point on the wafer from the lens focal height position; and a focusing unit that sets the height position as a focal height position during exposure and issues a driving command necessary for aligning the wafer to the set focal height position to the height adjustment mechanism. Features: Reduction projection type exposure equipment.