JPH04342111A - Method and apparatus for projection exposure - Google Patents

Abstract

PURPOSE:To transcribe a circuit pattern in a focused state by a method wherein the displacement from a focal plane of the face of a substrate (a wafer) is detected via a projection optical system. CONSTITUTION:A reticle 1 is irradiated with weak light 17 as compared with exposure light 2 in such a way that the image of the light is formed on the reticle via half mirrors 11, lenses 10 and mirrors 9. Three of more areas which are situated inside an area capable of being exposed through a reducing lens 3 and which are situated inside an area on which a circuit pattern on a wafer 4 is not exposed are irradiated with the weak light 17 as compared with the exposure light 2 at the same wavelength as the exposure light 2 through the reducing lens 3, and the image of the light is formed. Thereby, the displacement amount between a height and a tilt with reference to a focal plane, of a projection optical system, which is changed during an exposure operation can be grasped accurately, and the circuit pattern can be transcribed in a focused state.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a projection exposure apparatus for controlling fine patterns such as semiconductor circuit patterns and display device patterns such as liquid crystal display devices, and more particularly, the present invention relates to a projection exposure apparatus for controlling fine patterns such as semiconductor circuit patterns and display device patterns such as liquid crystal display devices, and in particular, it is capable of exposing the entire exposed area with high resolution. The present invention relates to a projection exposure apparatus equipped with means for detecting the inclination and height of an object.

0002

[Prior art] Exposure of fine patterns of semiconductor integrated circuits;
Alternatively, TFT (Thin Film Transis
(tor) When exposing a drive circuit pattern in a large field of view pattern of a display device typified by a liquid crystal television, it is necessary to expose a pattern that is faithful to the original image and has little variation in line width over the entire exposure area. In particular, in the field of semiconductor integrated circuits, line width patterns of 0.5 μm or less will be developed in the future.
It is necessary to expose the entire surface of an area close to mm, but as the pattern becomes finer, the imaging range (depth of focus) is ±1 μm.
The following is true. For this reason, it is essential to accurately align the photoresist surface on the wafer with the pattern image formation surface. To achieve this, the wafer surface (photoresist surface)
It is necessary to accurately detect the inclination and height of the exposed area.

Conventionally, in the first known example disclosed in Japanese Patent Laid-Open No. 63-7626, a semiconductor laser is focused on the wafer surface from an oblique direction without using a projection lens, and the focused position is determined. The height is detected by detecting the height. Furthermore, in a second known example disclosed in JP-A-63-199420, tilt detection light different from the exposure wavelength is emitted through a projection lens, the reflected light is collected, and the tilt is detected from the focused position. are doing.

0004

Problems to be Solved by the Invention In exposure apparatuses, a problem arises in that when exposure is performed continuously, the projection lens is warmed by the exposure light, causing the focal position to fluctuate. This is a phenomenon that has existed in the past, but the depth of focus of the projection lens has become shallower in order to accommodate the miniaturization of circuit patterns, and a slight drift over time in the focal position of the projection lens, which was not a problem in the past, has become a problem. It has become.

[0005] In such a state, in order to obtain information on the inclination and height within the exposure area, the prior art, in a first known example,
Since the semiconductor laser is focused obliquely onto the wafer surface without passing through the projection lens, it is impossible to detect changes in the focal position due to changes in the temperature of the projection lens. Also,
In the second known example, although the detection light is transmitted through a projection lens, it is different from the exposure light, and due to chromatic aberration, it is not possible to accurately detect changes in the focal position with respect to the exposure light. As described above, both methods have problems in detecting the highly accurate tilt and height control required for exposure of circuit patterns of 0.5 μm or less in exposure equipment that transfers semiconductor circuit patterns. .

An object of the present invention is to provide a projection exposure apparatus that accurately detects the inclination and height of the wafer surface in the exposure area even for a semiconductor wafer, and exposes a high-resolution pattern with little line width variation. There is a particular thing.

[0007]

[Means for Solving the Problems] The above object is to transmit exposure light of the same wavelength as the exposure light by transmitting it through the projection optical system to the area on the substrate (wafer) that can be exposed and where the circuit pattern is not exposed. A method of irradiating and imaging weak light compared to the wafer, and three or more sets of imaging optical systems that reflect the irradiated light on the top surface of the substrate (wafer), pass through the projection optical system again, and return the light in the direction of incidence. By detecting the tilt and height deviation of the substrate surface with respect to the focal plane of the projection optical system, it is possible to align the substrate surface with the focal plane of the projection optical system during exposure.

[0008]

[Operation] That is, by using this means, the substrate (wafer) can be
By always aligning the surfaces, it is possible to transfer the circuit pattern in a focused state, and it is possible to improve the yield of products.

[0009]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 11, the reduction exposure projection apparatus includes an illumination light source, a reduction lens 3 for transferring the pattern of the reticle 1 in a reduced size, a tilting mechanism for adsorbing the wafer 4 and moving it to an exposure position, It mainly consists of a wafer stage 5 consisting of X/Y stages, a pattern detector 6 for detecting an alignment pattern on the wafer, and a main control system 16 for controlling the entire apparatus.

The present invention provides a method of irradiating and image-forming light of the same wavelength as the exposure light onto the wafer surface through a projection optical system immediately before or during exposure, and a method of irradiating and imaging the wafer surface with light having the same wavelength as the exposure light. Detects the substrate (wafer) through the projection optical system
By providing a method for detecting defocus amounts at three or more points on the surface, the height and inclination of the substrate (wafer) surface can be controlled to match the focal plane of the projection optical system.

An embodiment of a method of detecting defocus of the substrate in a reduction exposure apparatus and adjusting the height and inclination of the substrate surface to the focal plane of the projection optical system will be described with reference to FIGS. 1 to 8.

First, as shown in FIG. 1, an exposure apparatus irradiates a reticle 1 with exposure light 2 and transfers a pattern on the reticle 1 onto a wafer 4 through a reduction lens 3. As shown in FIG. The exposure light 2 is blocked by a blade 8 provided on the reticle 1 so as not to expose areas other than the circuit pattern portion on the reticle 1. Therefore, the exposure light 2 irradiated onto the wafer 4 has an exposure area 19 shown in FIG.
The circular exposure area 18 is a region where the area where the circuit pattern is drawn is projected, and the region where the exposure light 2 is irradiated onto the wafer when the blade 8 does not block the light is the circular exposure possible area 18.

Therefore, as shown in FIG. 1 (however, FIG. 1 shows only two sets of focus detection systems, there are three or more sets). Between the blade 8 and the reticle 1, a mirror 9, a condensing lens 10, A sensor 13 detects the amount of shift of the top surface of the wafer 4 with respect to the focal plane of the projection optical system using a focus detection optical system composed of half mirrors 11 and 12 and sensor sections 13 and 14.
, 14, and input into the main control unit 16 via the signal processing unit 15, the focus detection position and the tilt stage 40
The driving amount of the thick electric element 43 is calculated based on the proportional law from the positional relationship with the driving point of the thick electric element 43, and based on that data, the tilt stage 4
0 piezoelectric element 43 is driven to control the inclination. Furthermore, the motor 44 is driven to control the Z stage 41. In this way, it is possible to align the upper surface of the wafer 4 with the focal plane of the reduction lens 3. Here, a method for detecting the amount of deviation of the surface of the wafer 4 with respect to the focal plane of the projection optical system will be described.

Light 17, which is weaker than exposure light, is irradiated via the half mirror 11, lens 10, and mirror 9 so as to form an image on the reticle 1. The light irradiated and imaged on the reticle 1 passes through the reduction lens 3 and is within the exposure range 18, and
Light having the same wavelength as the exposure light 2 and weaker than the exposure light 2 is passed through the reduction lens 3 to areas 21 (areas 20 shown in FIG. 2) where the circuit pattern on the wafer is not exposed, at three or more locations (areas 20 shown in FIG. 2). (showing three locations) is irradiated and imaged. Since regions 19 and 20 shown in FIG. 2 are adjacent to each other, there is no significant difference in height on the wafer surface. In addition, as shown in FIG. 10, the resist coated on the wafer 4 shows no change in film thickness after development at areas where the exposure light amount is small, and the film thickness after development changes rapidly after a certain exposure light amount is exceeded. decreases to Furthermore, as shown in FIG. 10, the amount of exposure light actually used for transferring the circuit pattern is about three times the amount of light that causes the film thickness to change rapidly. Therefore, even if focus detection is performed using the area to be exposed next with a light amount of about 1/30 or less of the exposure light amount used for circuit pattern transfer, the focus detection can be performed without affecting the exposure state. Furthermore, the reflected light of the irradiation light 17 on the wafer passes through the reduction lens 3 again to the upper mirror 9 and the half mirror 11.
, 12 and enter the sensor sections 13 and 14. A method for detecting defocus from this reflected light will be described in detail using FIGS. 3 and 4.

FIG. 3 shows the optical path of the reflected light in FIG. 1 in an easy-to-understand manner. The sensor parts 13 and 14 are composed of a sensor 35 and a pinhole 36. When the wafer 4 is on the focal plane of the reduction lens 3, the focal position of the reflected light detection system is at position 38 in FIG. Sensor part 1
4 is placed. Here, when the wafer 4 changes in the vertical direction, the sensor outputs 31 and 32 change according to the principle shown in FIG.
By changing the focal position in the Z direction, the peak value of the light intensity distribution of the reflected light projected onto the sensor surface becomes lower and the tail becomes wider. Therefore, the amount of light passing through the pinhole 36 decreases as the focus shifts. ), the result is as shown in FIGS. 4(a) and 4(b), and the difference signal 33 is as shown in FIG. 4(c). Same figure (
Within the range 34 in the Z direction shown in c), the focal direction deviation amount Z
Since the relationship between the difference signal 33 and the difference signal 33 is proportional, it is possible to determine the amount of deviation of the surface of the wafer 4 from the focal position of the reduction lens 3 from the difference signal 33.

[0017] In order to detect the amount of defocus as described above,
■ There is a method of detecting the wafer surface immediately before exposure and aligning the wafer surface with the focal point position of the reduction lens 3, and ■ A method of constantly detecting the focal point position during exposure and always aligning the wafer surface with the focal point position of the reducing lens 3. be. Here, each processing method will be explained using FIGS. 5 to 8.

(2) During exposure, as the exposure light 2 enters the reduction lens 3, the position of the focal plane of the reduction lens 3 changes as shown in FIG. Therefore, by performing focus detection at the same time as the alignment operation and immediately before exposure, the in-focus position of the reduction lens can be detected and the focus shift during exposure can be suppressed to within the focus displacement during exposure. Furthermore, a flowchart of this process is shown in FIG. First, after the stage 42 is moved in the X and Y directions, alignment and simultaneous focus detection/driving amount calculation/tilt/Z stage drive are performed, and after alignment and focusing are completed, exposure begins. After the exposure of one field is completed, if the exposure of all fields on the wafer is not yet completed, this process is repeated by moving the stage 42 in the X and Y directions again.

(2) During exposure, as the exposure light 2 enters the reduction lens 3, the position of the focal plane of the reduction lens changes as shown in FIG. Therefore, after the alignment operation is completed, the in-focus position of the reduction lens 3 can be detected, and defocus can be suppressed during exposure. Furthermore, the flow of this process is shown in FIG. First, the stage 42 is moved in the XY directions, and after alignment is completed, focus detection/driving amount calculation/
Focusing is performed by tilt/Z stage drive. After the exposure of one field is completed, if the exposure of all fields on the wafer is not completed, the stage 42 is moved again in the XY direction.
This process is repeated by moving in the direction.

In this way, by reducing the amount of deviation between the wafer surface and the focal plane of the reduction lens 3 immediately before exposure, the size and shape of the pattern to be transferred onto the wafer can be accurately determined, thereby increasing the product yield. It becomes possible to improve.

[0021]

[Effects of the Invention] In an exposure apparatus, by detecting the deviation of the substrate (wafer) surface from the focal plane through the projection optical system, the amount of deviation in height and inclination of the projection optical system with respect to the focal plane that changes during exposure can be detected. Since it is possible to accurately detect the pattern, it is possible to transfer the circuit pattern in a focused state, and it is possible to improve the yield of products.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an embodiment of the present invention;

[Fig. 2] An explanatory diagram showing the relationship between the exposure area and the focus detection area on the wafer,

FIG. 3 is a diagram explaining the principle of an embodiment of focus detection,

FIG. 4 is a focus detection signal characteristic diagram used in an embodiment of the present invention;

[Fig. 5] Timing chart showing the relationship between exposure sequence and focusing,

FIG. 6 is a flowchart of processing of an embodiment of focus detection;

[
Figure 7: Timing chart showing the relationship between exposure sequence and focusing;

FIG. 8 is a flowchart of processing of an embodiment of focus detection;

[
FIG. 9: Diagram explaining the principle of focus detection,

[Fig. 10] Characteristic diagram of resist sensitivity and focus detection light,

[Figure 1
1] Configuration diagram of an exposure apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Reticle, 2... Exposure light, 3... Reduction lens, 4... Wafer, 5... Wafer stage 6... Pattern detector, 8... Blade, 9... Mirror, 10... Lens, 11, 12... Half mirror, 13, 14 ...Sensor section, 15...Signal processing section, 1
6... Main control unit, 17... Focus detection illumination light, 18... Exposure possible area, 19... Exposure area, 20... Non-exposed area, 21... Focus detection light irradiation area, 31, 32... Sensor output, 33... Difference signal , 34... Focus detection range of differential signal, 35... Sensor, 36... Pinhole, 37... ND filter, 38... Reflected light detection system focal position, 40... Tilt stage, 41... Z stage, 42... X/Y stage, 43
... Thick electric element, 44... Motor.

Claims (2)

[Claims] 1. A projection method in which a circuit pattern formed on a reticle is exposed onto a substrate by a projection optical system, comprising:
The projection optical system irradiates and images light, which has the same wavelength as the exposure light and is weaker than the exposure light, on three or more areas on the substrate within the exposure area and where the circuit pattern is not exposed, and forms an image of the irradiation. Detecting reflected light from the substrate surface through the projection optical system, and detecting defocus amounts at three or more points on the substrate surface to align the substrate surface with respect to the focal plane of the projection optical system. A projection exposure method characterized by: 2. A projection device that exposes a circuit pattern formed on a reticle onto a substrate using a projection optical system, comprising:
Means for irradiating and image-forming light having the same wavelength as the exposure light and weaker than the exposure light onto the substrate surface through the projection optical system at three or more areas within the exposure possible range and where the circuit pattern is not exposed. and a means for detecting reflected light of the irradiated light from the substrate surface through the projection optical system and measuring defocus amounts at three or more points on the substrate surface, the substrate being determined by the defocus amount detecting means. A projection exposure apparatus comprising means for adjusting the inclination of the substrate surface with respect to the focal plane of the projection optical system based on the amount of defocus of the surface.