JPH0582416A - Projection exposing device and manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To quickly position a wafer on the optimum image forming plane of a projection optical system with high accuracy by correcting a detection error caused by the surface reflection of a resist film coating the surface of the wafer and reflected light from the surface of the wafer by an oblique incidence AF system with a detected result obtained by an interference AF system. CONSTITUTION:In order to detect the surface of a resist, a Z-stage 3c is moved in the direction in which a wafer W is brought nearer to a second detecting means 6 (interference AF system). Then the stage 3c is stopped at the position where the peak intensity of signal outputs is first detected. Thereafter, a parallel plate 27 is driven to set so that the output of a first detecting means (oblique incidence AF system) can become a prefixed reference signal by driving an X- and Y-stages 3a and 3b under such condition and moving the wafer W to the position immediately below a projection lens PL. Therefore, the wafer can be quickly positioned to the optimum image forming plane of a projection optical system with high accuracy, because the measured value of the first detecting means is corrected with the measured value of the second detecting means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus, for example, a reduction type projection exposure apparatus (stepper) for manufacturing a semiconductor device, and more particularly to a reduction type exposure exposure area of a semiconductor wafer mounted on a wafer stage. The present invention relates to a projection exposure apparatus having an automatic focusing device used for focusing on the focal plane of the projection lens system (projection optical system).

[0002]

2. Description of the Related Art At present, miniaturization of circuit patterns is progressing in accordance with the high integration of VLSI, and accordingly, the reduction type projection lens system of the stepper has higher NA.
Along with this, the allowable progress (depth of focus) of the lens system in the transfer process of the circuit pattern is narrower. Also, the size of the exposed region to be exposed by the projection lens system tends to be increased.

In order to make it possible to transfer a good circuit pattern over the entire exposed area which has been enlarged in size as described above, the exposed area of the wafer must be surely held within the allowable depth of the projection lens system. The whole shot must be positioned. In order to achieve this, it is important to detect the position of the projection lens system on the wafer surface in the optical axis direction with high accuracy and adjust the position of the wafer surface.

As a method of detecting the position of the wafer surface in the stepper, a light beam is incident on the wafer surface from an oblique direction, and the positional deviation of the reflection point of the reflected light from the wafer surface is detected as the positional deviation of the reflected light on the sensor. The detection optical system is used to detect the position of the wafer surface (hereinafter referred to as “oblique incidence AF”), and the reflected light beam (signal light) of the light beam irradiated on the measurement surface (wafer surface) and the measurement surface are independent. A method of detecting position information (distance from a predetermined position, etc.) of the measurement surface by using an interference signal obtained when a reflected light flux (reference light) of a light flux irradiating the reference surface provided on the "Interference AF")) and the like.

[0005]

Among the conventional wafer surface position detecting methods, the oblique incidence AF method has a feature that position detection can be performed at high speed. However, since an optically transparent resist film is generally present on the wafer surface that is the projection target substrate, it may be affected by the surface reflection of the resist film and the interference of the reflected light from the substrate surface (wafer surface). It was

Further, the optical path of the detection light may change depending on the pattern formed on the substrate (wafer). That is, there is a problem that the measured value changes depending on the film thickness of the resist film, the refractive index, the reflectance of the substrate, the shape, and the like. The interference AF method has a problem that the measurement range is narrow.

According to the present invention, by appropriately utilizing both the oblique incidence AF method and the interference AF method, the surface reflection of the resist film coated on the wafer surface and the reflection from the wafer surface (substrate surface) by the oblique incidence AF method are performed. Suitable for manufacturing semiconductor devices that can always position the wafer on the optimum image plane of the projection optical system with high speed and high accuracy by correcting the detection error based on the light based on the detection result obtained by the interference AF method. It aims at providing a simple projection exposure apparatus.

[0008]

A projection exposure apparatus according to the present invention is a projection exposure apparatus for projecting and exposing a pattern on a first object plane onto a second object plane mounted on a movable stage via a projection optical system. Detecting the position of the second object surface in the optical axis direction by irradiating the second object surface with a light beam from an oblique direction and detecting a change in the optical path of the reflected light beam from the second object surface. 1 detection means and the light flux from the light source means is divided into a plurality of light fluxes, one light flux is applied to the exposure area on the second object plane, the signal light reflected by the exposure area, and the other one light flux Is guided to a reference reflection surface, and the interference signal obtained when the reference light reflected by the reference reflection surface is combined with the second light is used.
A second detecting means for detecting the position of the object surface in the optical axis direction, and the first detecting means detects the position of the second object surface based on the detection result obtained by the second detecting means. It is characterized by doing so.

Further, in the semiconductor device manufacturing method of the present invention, a light beam is radiated onto the wafer surface from an oblique direction, and a change in the optical path of a light beam reflected from the wafer surface is detected, whereby the optical axis of the wafer surface is detected. First to detect the position in the direction
The light flux from the detection means and the light source means is divided into a plurality of light fluxes, and one light flux is applied to the exposure area on the wafer surface,
Using the interference signal obtained when the signal light reflected in the exposure area and the other one light flux are guided to the reference reflection surface and the reference light reflected by the reference reflection surface is combined, Second detection means for detecting the position in the optical axis direction, and after detecting the position of the wafer surface by the detection means based on the detection result obtained by the second detection means, The semiconductor device is manufactured by projecting and exposing the pattern onto the wafer surface through a projection optical system.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view of essential parts of a first embodiment of the present invention, and FIGS. 2 and 3 are explanatory views of a part of FIG.

In FIG. 1, PL is a reduction type projection lens system (projection optical system), and its optical axis is indicated by AX1 in the figure. The projection lens system PL reduces the circuit pattern of the reticle R by a factor of, for example, 1/5, and projects it to form a circuit pattern image on its focal plane. The optical axis AX1 is parallel to the z-axis direction in the figure. W is a wafer whose surface is coated with a resist, and has a large number of exposed regions (shots) in which the same patterns are formed in the previous exposure step.

Reference numeral 3 is a wafer stage on which a wafer is placed. The wafer W is adsorbed and fixed to a wafer chuck (not shown) of the Z stage 3c of the wafer stage 3. The wafer stage 3 includes an X stage 3a that moves in the x-axis direction, a Y stage 3b that moves in the y-axis direction, and a Z stage 3c that rotates by a motor 10 around an axis parallel to the z-axis direction and the x, y, and z-axis directions. It consists of and. Also x,
The y and z axes are set to be orthogonal to each other. Therefore, by driving the wafer stage 3, the position of the surface of the wafer W is adjusted in the optical axis AX1 direction of the projection lens system PL and the direction along the plane orthogonal to the optical axis AX1,
Furthermore, the tilt with respect to the focal plane, that is, the circuit pattern image is also adjusted.

The X stage 3a and the Y stage 3b detect position information by a laser interference device (not shown) and adjust the position. Reference numeral 7 is a reflector, which has a thin pattern formed on the surface thereof and is placed on a part of the outside of the wafer W on the surface of the Z stage 3c. A light projector 4 irradiates the spot light in the vicinity of the optical axis AX1 of the projection optical system PL on the surface of the wafer W. A light receiver 5 receives the reflected light from the surface of the wafer W in the light flux from the light projector 4, and obtains position information of the wafer W in the Z direction (optical axis AX1 direction) from the light receiving position. When a two-divided sensor or PSD is used as the light receiver 5, the surface of the wafer W is set so as to coincide with the focal plane of the projection optical system PL when the differential output from the sensor becomes zero. Such an output value will be called a reference signal here.

The light projector 4 and the light receiver 5 are arranged on the optical axis A of the wafer W.
It constitutes one element of the first detection means of the oblique incidence AF method for detecting the position (image plane position) information of the surface of the wafer W with respect to the position in the X1 direction, that is, the focal plane of the projection optical system PL.

Reference numeral 6 is a second detecting section utilizing interference, which is arranged near the projection optical system PL. As will be described later, the second detection unit 6 obtains the interference obtained when the reflected light (signal light) from the wafer W surface and the reflected light (reference light) from the reference reflecting surface provided independently of the wafer W are combined. An interference AF method is used in which the position of the second detection unit 6 on the wafer W surface in the optical axis AX2 direction is detected using a signal.

Reference numeral 8 denotes a signal processing unit which obtains position information of the wafer W in the optical axis AX2 direction using the interference signal obtained by the second detection unit 6. The second detection unit 6 and the signal processing unit 8 constitute one element of the interference AF type second detection means for detecting the position of the wafer W in the optical axis AX2 direction. A control circuit 9 drives the motor 10 based on signals from the signal processing unit 8 and the light receiver 5 to control the position of the Z stage 3c in the Z direction.

FIG. 2 is an explanatory view showing the structure of the first detecting means of the oblique incidence AF system of FIG. In the figure, the projector 4
Is a light emitting diode 21, a condenser lens 22, a diaphragm 23,
It is composed of the first imaging lens 24. Light emitting diode 2
The light flux from No. 1 is condensed by the condenser lens 22, and the diaphragm 23
Is illuminating. Then, the image of the diaphragm 23 is formed on the wafer W by the first image forming lens 24, so that the spot light is irradiated onto the surface of the wafer W.

The light receiver 5 comprises a second image forming lens 25, a position detecting sensor 26, and a rotatable parallel plane plate 27. The image of the diaphragm 23, which is the spot light reflected by the wafer W, is imaged on the position detection sensor 26 by the second imaging lens 25 through the rotatable parallel plane plate 27. The position detecting sensor 26 detects the image forming position of the light beam (wafer W
Signal in the Z direction) is output. That is, the position information of the wafer W in the Z direction is obtained from the incident position information of the light flux on the position detection sensor 26.

FIG. 3 is a schematic view of a main part of the second detector 6 of FIG. In the figure, the light flux from the white light source means L is collimated by the collimator lens CL1 and split into two light fluxes of reflected light and transmitted light by the beam splitter BS. Of these, the reflected light LR is guided onto the surface of the wafer W, and the signal light reflected by the wafer W returns to the original optical path and enters the beam splitter BS. Further, the transmitted light LT is incident on the reference reflection surface M, the reference light reflected by the reference reflection surface M returns to the original optical path, and is incident on the beam splitter BS.

Then, the beam splitter BS combines the signal light and the reference light and causes them to interfere with each other, and the interference signal is detected by the detector D. The interference signal from the detector D is input to the signal processing unit 8. The signal processing unit 8 processes the interference signal to obtain position information of the wafer W surface in the optical axis AX2 direction.

In this embodiment, as shown in FIG. 6, the objective lens OL1 is arranged between the beam splitter BS and the wafer W, and the beam splitter BS and the reference plane M are arranged.
An objective lens OL2 similar to the objective lens OL1 may be disposed between and to cause the condensed light flux to enter each surface.

FIG. 4 shows the position Δ of the wafer W when the test surface (wafer surface) W is moved in the direction of the optical axis AX2 in the configuration shown in FIG. 3 and the intensity I of the signal output obtained from the detector D at that time. (Δ) is a graph. In the figure, the place where the intensity I (Δ) becomes maximum is L → BS → W → BS in FIG.
It is detected that the optical path lengths of the route of → D and the route of L → BS → M → BS → D match. FIG. 5 shows the intensity I (Δ) of the signal output with respect to the positional change Δ of the surface W to be inspected when the light source means L is completely monochromatic light in the configuration shown in FIG. In this case, the intensity I (Δ) becomes a sinusoidal signal with respect to the change of the position Δ.

As described above, when the light source means L is a monochromatic light, a signal having a sine shape is generated only when the optical path lengths coincide with each other as the band width of the light wavelength region gradually increases as shown in FIG. The signal changes to have a strong peak. Therefore, in this embodiment, a day color light source is used as the light source means L, and the detector D detects the signal peak to detect the position of the surface to be inspected (wafer surface).

Next, a method of detecting the position of the wafer W in the optical axis AX1 direction in the projection exposure apparatus of FIG. 1 will be described.

In the present embodiment, the detection result obtained by the first detection means is corrected based on the detection result by the second detection means, and the wafer W is set at a predetermined position in the optical axis AX1 direction.

First, the optical axis AX1 is provided just below the projection lens PL.
The stage 3 so that the reflector 7 is positioned below
Move in y direction. Then, the Z stage 3 is moved so that the optimum image forming surface of the projection lens PL and the surface of the reflecting plate 7 coincide with each other.
Drive in the direction. As a method of detecting the optimum image plane of the projection lens PL, for example, a thin pattern is formed on the reflection plate 7. Then, this pattern is illuminated by reflection or transmission to form a pattern image by the projection optical system PL, and the contrast of the pattern image is observed by a solid-state image sensor arranged at a position conjugate with the reticle R with respect to the projection lens PL. Various TTL focus detection methods such as a detection method can be applied.

Next, the reflection plate 7 is moved by the X, Y stages 3a and 3b directly below the second detector 6 of the interference AF system (optical axis A).
X2 downward). At this time, the mirror M in FIG. 3 is moved toward or away from the beam splitter BS, and the intensity I (Δ) of the signal output from the photodetector D is moved.
The mirror M is fixed at the position where is maximized.

After that, the wafer W coated with the resist is moved to a position just below the second detector 6 (below the optical axis AX2) which is an interference AF system to drive the Z stage 3c to drive the second detector 6 (interference AF system). ), The position of the resist-coated wafer W in the Z direction is detected. At this time, two peaks of the signal output intensity I (Δ) may be detected, but these peaks are the results of detecting the resist surface and the wafer (substrate) surface, respectively.

In this embodiment, the resist surface is detected, and the Z stage 3c is moved in the direction in which the Z stage 3c is moved closer to the second detection section (interference AF method) and the position away from the wafer W, and the intensity of the signal output is first. The Z stage 3c is stopped at the position where the peak of I (Δ) is detected. Next, in this state, the X and Y stages 3a and 3b are driven to move the wafer W to a position immediately below the projection lens PL (below the optical axis AX1) to move the first detection means (oblique incidence AF method).
The parallel plate 27 so that the output of is a predetermined reference signal.
Drive and set.

According to the above operation, the measured value of the first detecting means (oblique incidence AF method) is corrected by the second detecting means (interference AF method), and thus the first detecting means optimizes the projection lens PL. It is possible to accurately detect the deviation of the resist surface from the image plane position and match them.

When the parallel plate 27 is not used, the resist surface is aligned with the focal plane of the projection lens PL by using the second detecting means, and then the surface is detected by the first detecting means, and the position is determined as the reference position. The reference position is referred to when another resist surface position is detected by the second detecting means.

In this embodiment, the optimum image plane position of the projection lens PL is set to the optimum position for projection exposure, for example, d / n when the optimum position for projection exposure is the substrate surface (wafer surface). (D is the resist film thickness, n
Is the refractive index of the resist), and d / 2n in the case of the intermediate between the resist surface and the substrate surface (wafer surface), the optical distance from the resist surface to the optimum position for projection exposure x / n (x is the substrate surface To the optimum position for projection exposure, and n is the refractive index of the medium in which x is located) is preferably added as an offset value to the first detection means.

[0033]

According to the present invention, as described above, the oblique incidence AF
By appropriately using both the AF method and the interference AF method, the interference AF method can be used to detect the surface reflection of the resist film applied on the wafer surface by the oblique incidence AF method and the detection error due to the reflected light from the wafer surface (substrate surface). By performing correction based on the obtained detection result, it is possible to achieve a projection exposure apparatus suitable for semiconductor device manufacturing, which can always position the wafer on the optimum image plane of the projection optical system at high speed and with high accuracy. ..

In particular, according to the present invention, the disadvantage of the oblique incidence AF method in which it is unclear which position in the resist film applied to the wafer surface is detected is the disadvantage of the interference AF method capable of accurately detecting the position of the substrate surface. By correcting based on the result,
It is possible to achieve a projection exposure apparatus that can always set the optimum image forming plane of the projection optical system to an optimum position at high speed and with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory view of a part of FIG.

FIG. 3 is an explanatory view of a part of FIG.

FIG. 4 is an explanatory diagram of an output signal from the detection unit in FIG.

5 is an explanatory diagram of an output signal from the detection unit in FIG. 3 when monochromatic light is used as a light source.

FIG. 6 is an explanatory view of another embodiment of FIG.

[Explanation of symbols]

 PL Projection optical system R Reticle W Wafer 3 Stage 4 Emitter 5 Light receiver 6 Second detector 7 Reflector 8 Signal processor 9 Control circuit 10 Motor L White light source CL1, CL2 Collimator lens BS Beam splitter M Mirror (reference plane) OL1, OL2 Objective lens D Detector 21 Light emitting diode 22 Condensing lens 23 Aperture 24 First imaging lens 25 Second imaging lens 26 Position detection sensor 27 Parallel plane plate

Claims (2)

[Claims] 1. A projection exposure apparatus for projecting and exposing a pattern on a first object plane onto a second object plane mounted on a movable stage via a projection optical system, wherein a light flux is obliquely directed onto the second object plane. And a plurality of light fluxes from the light source means and a first detection means for detecting the position of the second object plane in the optical axis direction by detecting a change in the optical path of the reflected light flux from the second object plane. Of the light beam, and one light beam is applied to the exposure area on the second object surface, and the signal light reflected by the exposure area and another light beam are guided to the reference reflection surface, and the reference reflection surface is reflected. Second detection means for detecting the position of the second object surface in the optical axis direction by using an interference signal obtained when the reference light reflected by the surface is combined. The position of the second object plane is detected by the first detection means based on the obtained detection result. A projection exposure apparatus characterized by the above. 2. A first detection for detecting the position of the wafer surface in the optical axis direction by irradiating the wafer surface with a light beam from an oblique direction and detecting a change in the optical path of a reflected light beam from the wafer surface. Means and the light flux from the light source means is divided into a plurality of light fluxes, one light flux is applied to the exposure area on the wafer surface, and the signal light reflected by the exposure area and the other one light flux are used as reference reflection surfaces. A second detecting means for detecting the position of the wafer surface in the optical axis direction by using an interference signal obtained by combining the reference light reflected by the reference reflecting surface with the reference light. After detecting the position of the wafer surface by the detection means based on the detection result obtained by the second detection means, the pattern on the reticle surface is projected and exposed on the wafer surface through the projection optical system to obtain a semiconductor device. Is characterized in that Semiconductor device manufacturing method.