JPH0582410A - Method for detecting image forming plane - Google Patents

Abstract

PURPOSE:To find the image forming plane of a projection optical system with high accuracy so as to increase the throughput by measuring the light quantity of a pattern projected upon the upper surface of an illuminance detecting unit at three or more points with optical sensors by moving a stage upward and downward and simultaneously detecting the maximum output values of the sensors. CONSTITUTION:An illuminance detecting unit 20 equipped with three or more optical sensors on a sample stage 7 is provided. In addition, three or more rectangular patterns are respectively provided on the upper surface of the unit 20 and the surface of an object 21 to be projected which is provided to the upper surface of the unit 20 through the lens of a projection optical system. The patterns provided on the surface of the object 21 are projected upon the patterns provided on the upper surface of the unit 20 and the projected light quantities are measured at three or more points with the optical sensors by moving the stage 7 upward and downward. Then the focusing plane of the lens of the projection optical system is detected by simultaneously detecting the maximum output values of the optical sensors and the detected plane is used as an image forming plane. Therefore, the image forming plane can be detected with high accuracy in a short time and the throughput can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device for exposing a fine pattern on a semiconductor or the like, or for inspecting the fine pattern, and in particular, for forming a projection optical system when exposing the fine pattern on a semiconductor or the like. The present invention relates to a method for detecting an image plane, which is capable of obtaining an image plane with high accuracy and is suitable for improving throughput.

[0002]

2. Description of the Related Art With the increase in integration of semiconductors, exposure equipment, especially optical equipment, has come to use light with a short wavelength, such as g-line to i-line, and excimer laser light. On the other hand, since a lens with a large numerical aperture (NA) is also used, the depth of focus of the lens becomes shallow, and the wafer surface is accurately aligned with the image plane of the lens as an exposure device. Is needed.

An example of a conventional exposure apparatus will be described with reference to FIG. 9 showing its main structure. In the figure, 1 is a semiconductor wafer as a sample (hereinafter, simply referred to as a wafer), 2 is a circuit pattern drawing mask as a projection target, and 3 is a circuit pattern drawing mask 2 which is movable in X and Y directions while holding the circuit pattern drawing mask 2. A mask stage, 4 is an illumination light source, 5 is a reduction lens interposed between the wafer 1 and a circuit pattern drawing mask 2 which are supported on a pedestal (not shown), and 6 is an alignment pattern provided on the wafer 1. It is a pattern detector for detecting 1a. Reference numeral 7 denotes a stage on which the wafer 1 is placed, and the stepper 7 is configured to be movable in each of X, Y and Z directions. Reference numerals 8a and 8b denote motors for driving the stage 7 in X and Y directions. Reference numerals 9a and 9b denote laser length measuring devices for measuring the position of the stage 7 corresponding to the motors 8a and 8b.
Is an air micrometer for detecting the position of the upper surface of the wafer 1 in the height direction (Z direction). Reference numeral 11 is a stage control system for controlling the motors 8a, 8b and laser length measuring devices 9a, 9b, and 12 is an air micrometer for fetching a Z direction signal of the upper surface of the wafer 1 output from the air micrometer 10 and sending it to the main control system 13. It is a signal processing system.

To perform exposure in the exposure apparatus having the above-described structure, first, the upper surface of the wafer 1 is aligned with the image plane of the reduction lens 5, and then the alignment pattern 1a on the wafer 1 and the circuit pattern drawing mask 2 are provided. The pattern detector 6 detects a deviation from the detected pattern position, and the stage control system 11 moves the stage 7 to detect the alignment pattern 1a so that the detected deviation amount becomes zero. Align the.
Subsequently, the shutter of the illumination light source 4 is opened to perform exposure.

The alignment between the image plane of the reduction lens 5 and the upper surface of the wafer 1 performed at the time of the exposure is performed by first detecting the upper surface position of the wafer 1 by the air micrometer 10.
The detected upper surface position signal of the wafer 1 is taken into the main control system 13 via the air micrometer signal processing system 12.
Then, the stage control system 11 moves the stage 7 in the Z direction and controls so as to maintain the height of the detected upper surface position of the wafer 1. However, factors such as (1) fluctuations in atmospheric pressure and temperature, (2) temperature change in the pedestal supporting the reduction lens 5, (3) drift of the air micrometer 10, and the like are mainly factors of the image plane of the reduction lens 5. Therefore, the alignment with the upper surface of the wafer 1 is not accurately performed normally only once. At present, a trial exposure is performed using a plurality of wafers 1 and one of them is selected from the development results. Then, the image plane position is obtained, and the height position control of the upper surface of the wafer 1 is performed based on the output value of the air micrometer 10 at the image plane position selected and obtained, and the exposure is performed while the position control is performed. It is supposed to be.

On the other hand, as an exposure apparatus for projecting and exposing a projection object (for example, a reticle) on which a desired pattern is formed onto a surface of an exposure object (for example, a semiconductor wafer), a minute light transmitting portion is formed on a part of the projection object. , By projecting this minute light transmitting portion on the surface of the exposed body and again forming an image of the projection light reflected at the position of the object to be projected through the minute transmitting portion, and detecting the light amount of this passing light. There has been proposed a focus position adjusting method and device (for example, Japanese Patent Laid-Open No. 57-212406) for performing focus position adjustment automatically and in a short time and performing focus position adjustment with high accuracy.

[0007]

The above-mentioned conventional exposure apparatus obtains the in-focus position of the wafer 1 by repeatedly performing the trial exposure, and the height of the upper surface of the wafer 1 based on the output value of the air micrometer 10 at that position. Since the exposure is performed while position control is performed, it takes several tens of minutes for the trial exposure, and it is impossible to correct the drift that occurs in the exposure apparatus and the like in a short time of about several minutes. The decrease in throughput due to exposure has been a problem. In addition, since the depth of focus of the reduction lens 5 has become shallower than in the past, tilt in the exposure area due to waviness or warpage of the surface of the wafer 1 caused by unevenness of the thickness of the wafer 1 becomes a big problem. It was In order to detect the inclination of the surface of the wafer 1, the average height position of the surface of the wafer 1 in the exposure area is not detected by the air micrometer 10, but the height and inclination of the surface of the wafer 1 in the exposure area are detected. It has come to be equipped with a level measuring device for detecting the, and, in order to actually perform the exposure, it is necessary to set the reference value of the height and the inclination in the level measuring device. In order to obtain, the image plane of the reduction lens 5 (focal plane)
There is also a problem that it is necessary to detect the height and inclination of the wafer and accurately align the wafer 1 or another reference plane with the detected image plane position.

In the method of re-passing the reflected projection light through the minute light transmitting portion and the focus adjustment in the apparatus, the amount of light passing through the minute light transmitting portion is detected to find the optimum focusing position. As for the method, the detection of the quantity of the passing light is a method of detecting the maximum quantity of light at each point on the surface of the exposed body, and not a method of simultaneously detecting the maximum quantity of light at a plurality of locations. For this reason, even if the optimum focusing at each focus measurement position on the surface of the exposure object is possible, the height and inclination of the surface of the exposure object in the exposure region cannot be detected, and therefore the image plane is accurately obtained. There was a problem that could not be done.

The present invention has been made in view of the above problems of the prior art.
In particular, in an exposure apparatus for exposing a fine pattern on a semiconductor or the like, an image plane detecting method and apparatus capable of obtaining the image plane of the projection optical system with high accuracy and improving throughput can be provided. The purpose is to

[0010]

In order to achieve the above object, the image plane detecting method of the present invention is to install an illuminance detection unit having photosensors at three or more places on a stage on which a sample is placed, A line-shaped or rectangular-shaped 1 is formed on both of the upper surface of the illuminance detection unit and the surface of the projection target, which is conjugate with the upper surface of the illuminance detection unit, through the lens of the projection optical system.
Alternatively, a plurality of patterns are provided at three or more places, the pattern provided on the surface of the projection target is projected on the pattern provided on the upper surface of the illuminance detection unit, and the light amount of the projected pattern is transferred to the stage. It is moved vertically and measured at three or more points with the optical sensor, the maximum output value of each measured optical sensor is simultaneously detected to detect the focal point of the lens of the projection optical system, and the detected focal plane is formed. This is a method of obtaining the image plane.

[0011]

With the image plane detection method and the apparatus having the above-mentioned configuration, when the pattern provided on the surface of the projection target is projected on the pattern provided on the upper surface of the illuminance detection unit, the projected pattern is obtained. The amount of light is measured at three or more places by moving the stage up and down by the optical sensor. Then, the measured maximum output value of each optical sensor is detected at the same time, and the focal plane of the lens of the projection optical system, that is, the imaging plane is obtained in a short time and with high accuracy, and at the same time, the throughput is improved. be able to. The upper surface of the illuminance detection unit is made to coincide with the detected in-focus plane, and the height and the inclination of the upper surface of the illuminance detection unit in the matched state are measured by a level measurement device to determine the reference of the level measurement device. The value can be obtained, and the stage is moved to match the obtained reference value of the level measuring device so that the surface of the sample (wafer) in the exposure area coincides with each other to perform highly accurate focusing and perform sequential exposure. be able to.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an explanatory view of the structure of an image plane detector, FIG. 2 is an explanatory view of line pattern alignment, and FIG. 3 is Z.
FIG. 4 is a diagram showing a relationship between a direction level and a light sensor output for detecting a light amount, FIG. 4 is a diagram showing an example of a pattern provided on a circuit pattern drawing mask and an illuminance detection unit, and FIG. 5 is a plurality of planar focal positions. It is a figure explaining the method of calculating | requiring an imaging plane from.

In FIG. 1, the wafer 1 is adsorbed and placed on a chuck. Stage 7 is an XY stage,
It is composed of a Z stage and a tilt stage. As shown in FIG. 4, the imaging plane detection unit 20 has an upper surface formed with at least three first detection patterns 20a formed by one or a plurality (group) of linear or rectangular transparent portions, At least three photoelectric conversion elements (sensors) are arranged on the back surface of the upper surface corresponding to the positions of the first detection patterns 20a formed on the upper surface. Then, the height of the light receiving surface of the sensor of the image plane detection unit 20 and the average height of the surface of the wafer 1 are made to coincide with each other, and the image plane detection unit 20 and the chuck are mounted on the stage 7. There is. Reference numeral 8a is an X-axis drive source that drives the X stage, and 8b is a Y-axis drive source that drives the Y stage. Although not shown, there are a Z-axis drive source for finely moving the Z stage up and down, and a tilt drive source for tilting the tilt stage. The Z-axis drive source includes a Z-axis displacement detector that detects the displacement of the Z stage in the Z-axis direction with high accuracy, and the tilt drive source also detects the tilt amount of the tilt stage with high accuracy. Is provided. Reference numeral 9a is an X-axis laser length measuring device that measures the displacement of the X stage, and 9b is a Y-axis laser length measuring device that measures the displacement of the Y stage. Reference numeral 3 denotes a mask stage on which the mask 21 is placed, which is used to align the mask 21 with a reference position for exposure projection. 4 is an exposure illumination light source, a shutter,
1 shows an exposure illumination optical system composed of condenser red and the like. Reference numeral 5 denotes a reduction projection lens that performs reduction projection exposure of the circuit pattern formed on the mask 21 onto an exposure area on the wafer 1. A detector 6 detects an alignment pattern provided on the wafer 1. A level measuring device for detecting the height and inclination in the exposure area on the wafer 1 and the height and inclination of the upper surface of the image plane detection unit 20 is specifically, for example, PCT Application No. 702643/90 (April 20.1990).
It is configured by providing two pairs of the light emitter 22 and the light receiver 23 as described in FIG.

As shown in FIG. 4, the mask 21 has one or a plurality of positions corresponding to the positions of the first detection patterns 20a passing through the reduction projection lens 5 in at least three places on the periphery of the circuit pattern. The second detection pattern 21a formed of the (group) line-shaped or rectangular opaque portion is formed.

Reference numeral 11 denotes a stage control system, which is a main control system 1
3 and the displacement amount of the X stage measured by the X-axis laser length measuring device 9a, and Y measured by the Y-axis laser length measuring device 9b.
An XY stage, which constitutes the stage 7, based on the displacement amount of the stage, the displacement amount of the Z stage detected by the Z axis displacement detector, and the tilt amount of the tilt stage detected by the tilt amount detector, It controls each of the stage and the tilt stage. Also, the stage control system 11
Is the displacement amount of the X stage measured by the X-axis laser length measuring device 9a, the displacement amount of the Y stage measured by the Y-axis laser length measuring device 9b, the displacement amount of the Z stage detected by the Z-axis displacement, and the tilt. The tilt amount of the tilt stage detected by the amount detector is transmitted to the main control system 13. 24 is a signal processing system of the level measuring device, which is a light receiving device 23 of the level measuring device.
The height and inclination of the surface of each exposure area of the wafer from the apparatus reference plane shown in FIG. Signal processing system 2 of this level measuring instrument
For example, PCT Application N
o.702643 / 90 (April 20.1990). Reference numeral 25 denotes a signal processing system of the imaging plane detection unit, which converts a video signal detected by each of the three photoelectric conversion elements (sensors) provided in the imaging plane detection unit 20 into a digital signal and outputs the digital signal. It is a thing. The main control system 13 sends a drive signal for opening and closing the shutter of the exposure illumination optical system, and the reduction projection lens 5 for the pattern formed on the mask.
In order to obtain the image forming plane (shown by 29 in FIG. 5) by X, the X stage and the Y stage are moved to control a command signal for aligning the center of the image forming plane detection unit 20 with the optical axis of the reduction projection lens 5. The deviation amount is calculated based on the image digital signal transmitted to the system 11 and detected by the signal processing system 25 of the imaging plane detection unit between the first detection pattern 20a and the second detection pattern 21a. A command signal is transmitted to the stage control system 11 so as to eliminate the displacement amount, and then a command to slightly move the Z stage up and down with the X stage and the Y stage stationary is transmitted to the stage control system 11 to transmit the X stage and the Y stage. At least three second detection patterns detected by the signal processing system 25 of the image plane detection unit by slightly moving the Z stage up and down with the stage stationary. Calculating the imaging point position Z _1, Z _2, Z ₃ on the basis of the displacement of the peak M _1, M _2, high precision of the Z stage showing the M ₃ of 1a detection digital signal, the calculated imaging Point positions Z ₁ , Z ₂ , Z ₃ and arrangement coordinates (X ₁ , Y ₁ ) (X ₂ , Y ₂ ) of three photoelectric conversion elements (sensors)
(X ₃ , Y ₃ ) and image plane 2 with respect to device reference plane 28
9 is calculated, and the stage control system 11 is operated to drive the Z stage and the tilt stage so that the plane formed by the light receiving surfaces of the sensors of the image plane detection unit 20 matches the calculated image plane 29. To command. Then, the main control system 13 is a plane in which the planes formed by the light receiving surfaces of the respective sensors of the image plane detecting unit 20 are aligned with the calculated image plane 29 with the X stage and the Y stage stationary. After matching, the height and inclination of the upper surface of the image plane detection unit 20 are measured with a level measuring device,
The height and inclination of the upper surface of the imaging plane detection unit 20 calculated from the signal processing system 24 of the level measuring device are measured by the level measuring device for each exposure region of the wafer before the actual exposure. The height and inclination of the standard. In addition,
In order to accurately align the image plane and the upper surface of the image plane detection unit 20, the pattern provided on the upper surface of the detection unit 20 needs to be formed on the upper surface of the plate with chrome or the like.

Further, the operation of the above configuration will be specifically described. First, based on the command from the main control system 13,
The stage control system 11 moves the X stage and the Y stage in the X and Y directions to align the center of the image plane detection unit 20 with the optical axis of the reduction projection lens 5. Then, based on a command from the main control system 13, the shutter of the exposure illumination system 4 is opened, and the three second detection patterns 21a provided around the mask 21 are connected through the reduction projection lens 5 as shown in FIG. Reduction projection is performed on the upper surface of the image plane detection unit 20. Even if the relative positional relationship between the mask 21 and the reduction projection lens 5 slightly changes,
Even if the magnification or the like changes due to changes with time or environmental changes such as temperature, the same image plane as in the actual exposure state is formed on the upper surface of the image plane detection unit 20.

By the way, as shown in FIG.
When the second detection pattern 21a has a line shape, the slit image 2 reduced and projected on the upper surface of the image plane detection unit 20 is obtained.
6 and the transparent linear pattern 27 of the first detection pattern 20a formed on the upper surface of the image plane detection unit 20 that receives the light 6 do not coincide with each other and are deviated from each other, so that the main control system 13 , The displacement is calculated based on each image signal detected from each photoelectric conversion element (sensor), and the X stage and the Y stage are finely moved via the stage control system 11 so as to eliminate this displacement. Match both as shown in b).

Next, with the X stage and the Y stage fixed, the main control system 13 is operated by the stage control system 11
Command to move the Z stage up and down,
While slightly moving the stage in the vertical direction, the photoelectric conversion elements (sensors) in the imaging plane detection unit 20 and the imaging of the second detection pattern 21a obtained through the first detection pattern 20a are detected and detected. A signal is taken in via the signal processing system 25. The main control system 13 is the table control system 1
The relationship between the Z direction position obtained through 1 and the output value of the signal detected by each sensor forms a mountain curve as shown in FIG. 3, and the point M showing the maximum output value is easily detected. To be done. Position Z in the Z direction showing the detected maximum output value
Is the image forming position of the second detection pattern formed on the mask 21 by the reduction lens 5 at the position (X, Y) where the sensor is installed.

That is, the main control 13 includes three second detections detected from the respective sensors installed corresponding to the positions of the first detection pattern 20a through the signal processing system 25 of the image plane detection unit. Based on the displacement of the high-precision Z stage indicating the peaks M ₁ , M ₂ and M ₃ of the detected digital signal (shown in FIG. 5B) of the working pattern 21a, the device reference plane 2
The image forming point positions Z ₁ , Z ₂ , Z ₃ with respect to 8 are calculated, and the calculated image forming point positions Z ₁ , Z ₂ , Z ₃ and the arrangement coordinates (X _{1 of the} three photoelectric conversion elements (sensors) , Y ₁ ) (X ₂ , Y ₂ )
(X ₃ , Y ₃ ) and image plane 2 with respect to device reference plane 28
Calculate 9. Then, the main control system 13 issues a command to the stage control system 11 so that the upper surface of the imaging plane detection unit 20 matches the calculated imaging plane 29, and the stage control system 11 switches the Z stage and the tilt stage. The plane formed by the light receiving surfaces of the respective sensors of the image plane detection unit 20 under drive control is matched with the calculated image plane 29.

At this time, the image formation plane may be calculated in the same manner as the case of calculating the image formation plane 29 and it may be confirmed that the two coincide.

Then, the main control system 13 matches the plane formed by the light receiving surfaces of the respective sensors of the image plane detection unit 20 with the calculated image plane 29 with the X stage and the Y stage fixed. After that, the height and inclination of the upper surface of the image plane detection unit 20 are measured with a level measuring device,
Before actually exposing the height and inclination of the upper surface of the imaging plane detection unit 20 calculated from the signal processing system 24 of the level measuring device, for each exposure region of the wafer for each exposure region of the wafer measured by the level measuring device. Use as a standard for height and inclination. The pattern provided on the upper surface of the detection unit 20 needs to be formed on the upper surface of the plate with chrome or the like.

As described above, it is possible to calculate the reference plane (imaging plane) of the wafer surface, which is measured and measured by the level measuring device during the actual exposure.

The size of the second detection pattern 21a formed on the mask 21 is the circuit pattern size (1 μm).
From the following), it is necessary to make finer.

Next, the main control system 13 sends a designation signal to the stage control system 11 to step and repeat the X stage and the Y stage in order to shift to the exposure process, and raises the surface of the wafer 1 for each exposure region. And the inclination are measured by a level measuring device and a signal processing system of the level measuring device, and the measured height and inclination are matched with the reference plane, so that the surface of the wafer for each exposure region has a circuit formed on a mask. It becomes an image plane by the reduction projection lens of the pattern.
In order to print a high-definition circuit pattern of μm or less,
Even if the exposure wavelength becomes a short wavelength like i-line and excimer laser light, and the focal depth of the reduction lens projection 5 becomes shallow,
A high-definition circuit pattern can be reliably printed.

That is, the focusing drift of the reduction projection optical system can be corrected with high accuracy, and the time required for the correction can be shortened. As a result, the exposure wavelength is i-line and excimer laser light. As described above, in the reduction projection exposure apparatus in which the wavelength has a short wavelength and the margin of the depth of focus is extremely small, it is possible to stop the conventional trial exposure, so that it is possible to significantly improve the throughput.

[0026]

Since the present invention is constructed as described above, it is possible to accurately measure the focusing plane of the lens of the projection optical system by measuring three or more focal points at the same time, and By directly detecting the in-focus position with the optical sensor of the illuminance detection unit, the image formation plane can be detected with high accuracy and in a short time, so it becomes possible to obtain the reference value of the level measuring device, and the conventional test exposure. The focus detection due to can be stopped, and the throughput can be greatly improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a configuration of an imaging plane detecting device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of line pattern matching.

FIG. 3 is a diagram showing a relationship between a Z direction level and an output of a light sensor for detecting a light amount.

FIG. 4 is a diagram showing an example of patterns provided on a circuit pattern drawing mask and an illuminance detection unit.

FIG. 5 is an explanatory diagram of a method of obtaining an image formation plane from a plurality of planar focus positions.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Wafer (sample), 2, 21 ... Circuit pattern drawing mask (projection object), 5 ... Reduction lens, 7 ... Stage, 11 ... Stage control system, 20 ... Illuminance detection unit, 20a, 21a ... Pattern, 25 ... Optical sensor signal processing system, 29 ... Image plane.

Claims (2)

[Claims] 1. An apparatus for projecting an image on a sample surface via a projection system, wherein an illuminance detection unit having three or more optical sensors is installed on a stage on which a sample is placed, and an upper surface of the illuminance detection unit. And providing one or a plurality of linear or rectangular pattern groups at three or more locations on both the flat upper surface of the illuminance detection unit and the surface of the conjugate object through the lens of the projection optical system, The pattern provided on the surface of the projection target is projected on the pattern provided on the upper surface of the illuminance detection unit, and the light amount of the projected pattern is moved up and down the stage, and the light sensor is provided at three or more places. The measured output value of each optical sensor is measured at the same time, and the point having the maximum output value is obtained as the in-focus point. The inclination and height of the sample surface are determined from the in-focus points of three or more points, respectively. Ask Image plane detecting method characterized by obtaining a reference value of the output device. 2. Similar to claim 1, the in-focus position is detected at three or more measurement points, and the sensor output simultaneously reaches the maximum value at three or more points where the in-focus position is detected based on the result. Tilt the upper surface of the detection unit and
Move in the height direction, make the upper surface of the detection unit coincide with the focusing surface of the lens of the projection optical system, measure the tilt and height of the sample surface as the origin of the detector, and measure this surface. A detector that determines the tilt and height of the sample surface by using the focal plane reference value as the reference plane and creating the same plane as the focal plane based on the result of detecting the focal plane of the projection system. A method for detecting an image plane, which is characterized by obtaining a reference value of.