JPH08110586A - Aligner - Google Patents

Abstract

PURPOSE: To provide technique for preventing yield from lowering because of faulty resolution caused by a foregin matter adhering to a wafer chuck by finding out the foreign matter adhering to the wafer chuck in an early stage. CONSTITUTION: In an autofocusing mechanism 10 for an alginer 1 equipped with an illumination system 2 for exposing a photoresist applied to a wafer 11, a projection system 3 reducing and projecting a pattern formed on a reticle 8 to the wafer 11, the wafer chuck 12a arranged on an XY table 12 and sucking and fixing the wafer 11, and the autofocusing mechanism 10 provided with a measuring point in the center of shot and performing automatic focusing; a focusing difference decision device 13 provided with plural measuring points other than the center of shot, performing focus-monitoring for all the measuring points, comparing a focusing difference between continuous shot and the same shot of the continuous wafer 11 and deciding tolerance is connected to the mechanism 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of semiconductor manufacturing, and is particularly effective when applied to an exposure apparatus used in semiconductor fine processing technology.

[0002]

2. Description of the Related Art In a semiconductor device manufacturing process, a projection exposure apparatus is often used as equipment for transferring a mask pattern of an integrated circuit onto a semiconductor substrate coated with photoresist. Regarding the projection exposure apparatus, for example, “Semiconductor Lithography Technology” (published by Sangyo Tosho KK), pages 87 to 93.
Page. That is, the projection exposure apparatus is an apparatus for projecting an image of a mask pattern on the surface of a wafer by interposing an optical system between the mask and the wafer for printing. Since the mask and wafer are completely separated from each other, there are no drawbacks of the contact exposure method, and since the pattern image is formed by focusing on the wafer surface by the imaging optical system, the gap is precisely controlled like the proximity exposure method. You don't even have to. A projection exposure apparatus has been used as a main force for mass production of fine and high-density VLSI.

The optical system used in the projection exposure apparatus is roughly divided into a lens and a mirror, and the image magnification can be equal or reduced. Further, the image formation area is often limited to a small area, and the mask and the wafer are continuously moved to expose the entire surface of the wafer, or one section (field) is exposed and the wafer is moved one step to move the adjacent area. It is necessary to adopt a step-and-repeat method for exposing the field.

In the reduction projection exposure apparatus of this system, the parallel light flux formed by the condenser lens passes through the mask (reticle), and the mask image is reduced by the reduction projection lens and imaged on the wafer surface. Reduction rate is 1/2, 1 /
4, 1/5, 1/10, etc. In this method, since the mask pattern is an enlarged view, the demand for the mask dimension accuracy becomes gentle, and since foreign matter attached to the mask is also projected in a reduced scale, it may not be a problem on the wafer.

Regarding the reduction projection exposure apparatus (step and repeater, hereinafter referred to as stepper),
Others "VLSI Manufacturing and Testing Equipment Guidebook 198"
7th Edition Electronic Materials Separate Volume "(published by the Industrial Research Board), pp. 101 to 109.

[0006]

However, the depth of focus of the stepper is narrower than that of the 1/1 projection exposure apparatus. For example, the depth of focus F = λ / 2 (NA) squared (λ is the exposure When the wavelength and NA are approximately calculated by the numerical aperture of the optical system, the depth of focus F of the 1/1 projection exposure apparatus is ± 8 μm.
On the other hand, in the stepper with λ = 0.436 and NA = 0.54, the depth of focus F is 0.75 μm, which is very small.

Therefore, when a foreign matter is generated on the wafer chuck, the foreign matter sandwiched between the wafer chuck and the wafer causes the wafer on the wafer chuck to tilt. As a result, the distance between the wafer and the reduction lens is changed, which causes defective resolution. Depending on the stepper, an autofocus mechanism having a function of comparing with the focus value of the previous shot to determine the amount of ups and downs when the XY stage is driven is provided. Figure 5
(A) is a top view of a conventional autofocus mechanism, (b)
The cross section is shown in FIG. This autofocus mechanism is to generate detection light from the light emitting element 18, reflect it at the shot center measurement point, detect it by the light receiving element 19, and measure the position of the wafer surface.

However, such an autofocus mechanism is not sufficient for the determination of foreign matter on the chuck because it only determines the shot center and does not consider the XY stage tilt component.

The inventor of the present invention paid attention to the fact that when a foreign substance adheres to the wafer chuck, a resolution defect continuously occurs at the same position, and has made earnest studies.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a technique for preventing a decrease in yield due to poor resolution due to foreign matter adhering to a wafer chuck, by early detecting foreign matter adhering to the wafer chuck.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0012]

The outline of the representative one of the inventions disclosed in the present application will be briefly described as follows. That is, an illumination system for exposing the photoresist coated on the wafer to light, a projection system for reducing the pattern formed on the reticle and projecting it onto the wafer, and a wafer chuck provided on an XY table for adsorbing and fixing the wafer, A measurement point is provided at the center of the shot,
The autofocus mechanism of the exposure system equipped with an autofocus mechanism that automatically adjusts the focus is provided with multiple measurement points other than the center of the shot, and focus monitoring is performed at all measurement points to obtain continuous shots and continuous wafers. Compare the focus difference of the same shot of
A focus difference determination device for determining tolerance is connected.

[0013]

[Function] The auto focus mechanism is provided with a plurality of measurement points other than the center of the shot, and focus monitoring is performed at all the measurement points, and the focus difference between consecutive shots and the same shot of consecutive wafers is compared to determine the tolerance. By connecting the difference determination device, it is possible to confirm whether or not there is a focus difference at the same position in succession for a plurality of wafers, thereby confirming whether the foreign matter is on the back surface of the wafer.
It is possible to determine whether the focus difference is due to scratches or the foreign matter on the chuck.

Further, by correcting the inclination of the XY stage, it is possible to eliminate variations between devices, reduce tolerance, and improve detection accuracy.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 schematically shows the stepper of the present invention.
The stepper 1 mainly includes an illumination optical system 2 and a projection optical system 3 having a reticle 8 as a boundary. Illumination optical system 2
Is a Hg lamp 4, an elliptical mirror 5, an integrator 6,
The exposure light for forming a device pattern on the wafer is formed by the condenser lens 7 and the like. The projection optical system 3 includes a reduction projection lens 9 and an autofocus mechanism 1.
0, an XY stage 13, a wafer chuck 12, etc., and reduces the image of the reticle 8 with a reduction lens 9,
The device pattern is imaged on the wafer 11. The reduction ratio of the reduction lens 9 is 1/2, 1/4, 1/5, 1/1
There is 0 etc. The autofocus mechanism 10 is composed of a light emitting element and a light receiving element. That is, the wafer position is detected by reflecting light emitted from a light emitting element such as a light emitting diode on the upper surface of the wafer, detecting the position of the reflected light with a position sensor including a light receiving element, and converting the value into the wafer position. By doing. In the present invention, the wafer position is detected at a plurality of points per shot,
For example, two to five measurement points are set to achieve more precise focus adjustment. FIG. 2A is a schematic top view of the autofocus mechanism 10, and FIG. 2B is a sectional view thereof. In this embodiment, five measurement points are provided at the center and four corners in the one-shot range 18, and when the light 16 is emitted from each of the light emitting elements 14a to 14e, the respective measurement points 17a to 17e. Then, the focus is measured by being detected by the position sensors 15a to 15e. As described above, by providing a plurality of measurement points for focus measurement, more precise focus adjustment can be achieved and the tilt of the XY stage can be detected.

Next, the autofocus mechanism 10 of the present invention.
A method of detecting a foreign substance using the focus difference determination device 13 will be described. FIG. 3 is a model when focus measurement is performed at five positions (A to E) within one shot on the wafer. In this case, first, focus measurement of n shots (A to E) is performed, and the measurement result is stored in the storage unit of the focus difference determination device 13. Next, the focus measurement of (A ′ to E ′) of (n + 1) shots is performed, the measurement result is stored in the storage unit of the focus difference determination device 13, and the (A to E) of the n shots stored in the storage unit are stored. Focus value and (n + 1) shots (A 'to E')
The difference between the focus value and the focus value is calculated by the calculation unit of the focus difference determination device 13, and the tolerance determination is performed individually. As a result, if the focus difference exceeds the tolerance value,
The position at which the wafer is raised is detected at that point, and the presence of foreign matter adhering to the wafer chuck or foreign matter on the back surface of the wafer is determined.

FIG. 4 is a flow chart showing a foreign matter adhered to the wafer chuck. First, as described with reference to FIG. 3, the focus difference determination device 13 compares the tolerance of the focus value at each point within one shot. As a result, if the value is below the tolerance value, the exposure is performed. If the tolerance value is exceeded, it is determined that “foreign matter is present”, and then the situation at the same point of the same shot on the previous wafer is confirmed.
As a result, when the previous wafer is within the tolerance, it is determined that the foreign matter is attached or the flaw is generated only on the wafer being processed, that is, it is temporary, and the exposure process is continued. When the same result as that of the previous wafer is generated, it is determined that “wafer chuck attached foreign matter is present”, that is, it is determined that the same result is continuously obtained, and an alarm is generated or the apparatus is stopped. As a result, the exposure process can be interrupted to remove the foreign matter adhering to the wafer chuck, so that the yield reduction due to the poor resolution due to the foreign matter adhering to the wafer chuck can be prevented at an early stage.

The effects of the present invention will be described below.

(1) The autofocus mechanism is provided with a plurality of measurement points other than the center of the shot, and focus monitoring is performed at all the measurement points to compare the focus difference between consecutive shots and the same shot of consecutive wafers to obtain the tolerance. By connecting the focus difference determination device, it is possible to check if there is a focus difference at the same position in succession on multiple wafers. It can be determined whether there is a focus difference.

Further, by correcting the inclination of the XY stage, it is possible to eliminate variations between devices, reduce tolerance, and improve detection accuracy.

(2) By setting the measurement points of the focus adjustment mechanism to four corners in one shot range and one point in the center of the shot, the tilt direction of the wafer and the gap between the wafer and the wafer chuck are generated. It is possible to accurately detect the location of the foreign matter.

(3) Since the focus difference determination device detects and corrects the tilt amount of the XY stage from the values of a plurality of consecutive shots on the same wafer, variations between devices are eliminated, tolerance is reduced, and detection accuracy is reduced. Can be improved.

Although the present invention has been concretely described based on the embodiments by the present inventor, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say. For example, in the above embodiment, the early detection of the foreign matter attached to the wafer chuck was described, but since the foreign matter or the scratch attached to the back surface of the wafer can also be detected, the attached position of the foreign matter or the scratch can be detected by storing the attached position of the foreign matter or the scratch. You can investigate trends. As a result, it is possible to trace the source of the foreign matter or the scratch, so that it is possible to detect the foreign matter or the scratch early and take an early countermeasure.

Further, a function for removing the detected foreign matter adhering to the wafer chuck, for example, a foreign matter suction means (not shown)
Is linked with the focus difference determination device,
When it is determined that "there is foreign matter attached to the wafer chuck", the exposure process is automatically interrupted, and the foreign matter suction means can remove the foreign matter attached to the wafer chuck. Therefore, the present invention makes it possible to rapidly and automatically perform the steps from the detection of foreign matter adhering to the wafer chuck to the removal thereof in the exposure process which requires particularly high accuracy.

[0026]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

That is, by performing focus monitoring at a plurality of points within a shot, it is possible to detect a resolution defect due to a small foreign substance. Furthermore, the foreign matter on the wafer chuck can be detected without erroneous detection by the flow chart for determining the foreign matter on the wafer chuck.

[0028]

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of an optical system of a reduction projection exposure apparatus which is an embodiment of the present invention.

2A is a top view of an autofocus mechanism of the present invention, and FIG. 2B is a cross-sectional view.

FIG. 3 is a model at the time of 5-point focus measurement in a shot according to the present invention.

FIG. 4 is a flowchart of a foreign matter adhered on a wafer chuck according to the present invention.

5A is a top view of a conventional autofocus mechanism, and FIG. 5B is a sectional view.

[Explanation of symbols]

1 ... Stepper, 2 ... Illumination optical system, 3 ... Projection optical system, 4 ... Mercury lamp, 5 ... Elliptical mirror, 6 ... Integrator, 7 ... Condenser lens, 8 ... Reticle, 9 ... Reduction projection lens, 10 ... Auto focus mechanism, 11 ... Wafer, 12 ... XY table, 12
a ... Wafer chuck, 13 ... Focus difference determination device, 14, 14a, 14b, 14c, 14d, 14e ...
... Light emitting elements, 15, 15a, 15b, 15c, 15d,
15e ... Light receiving element, 16 ... Focus detection light, 1
7, 17a, 17b, 17c, 17d, 17e ... Measuring point, 18 ... Light emitting element, 19 ... Light receiving element, 20 ... Focus detection light, 21 ... Shot center measuring point,

Claims (3)

[Claims] 1. An illumination system for exposing a photoresist coated on a wafer to light, a projection system for reducing a pattern formed on a reticle and projecting it onto the wafer, and an XY.
An exposure apparatus comprising a wafer chuck provided on a table for adsorbing and fixing a wafer, and an autofocus mechanism for automatically adjusting a focus by providing a measurement point at a shot center, wherein the autofocus mechanism includes: A plurality of measurement points other than the shot center are provided, focus monitoring is performed for all measurement points, and a focus difference determination device that determines the tolerance by comparing the focus differences between consecutive shots and the same shot of consecutive wafers is connected. An exposure apparatus characterized by the above. 2. The exposure apparatus according to claim 1, wherein the measurement points are set at four corners of the shot range and one point at the center of the shot. 3. The focus difference determination device detects and corrects the tilt amount of the XY stage from the values of a plurality of consecutive shots on the same wafer.
Or the exposure apparatus according to 2.