JP4542724B2 - Autofocus device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic focusing apparatus for a semiconductor exposure apparatus used in a photolithography process in a semiconductor manufacturing process.
[0002]
[Prior art]
The focus adjustment in the conventional semiconductor exposure apparatus is performed by actually exposing and developing a semiconductor wafer using a tilted mask for focus adjustment, obtaining a focused position (best focus), and based on this, the mask is adjusted. The optimum position was determined. Alternatively, the mask is fixed, the semiconductor wafer side is tilted, and actual exposure / development is performed to determine the in-focus position, and the optimum position of the semiconductor wafer is determined.
[0003]
[Problems to be solved by the invention]
However, in the conventional focus adjustment method in the semiconductor exposure apparatus, time and man-hours are required to determine the optimum position of the mask and the semiconductor wafer. In addition, when the optical system changes with time, there is a problem that it is impossible to detect or correct a focus shift.
[0004]
The present invention solves the problems of the prior art and provides an automatic focusing device for a semiconductor exposure apparatus that can automatically focus.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a first invention of the present invention is an auto-focus device, in which an image of a pattern irradiated on the surface of a semiconductor wafer mounted on a wafer stage is photographed, and a corresponding pattern is photographed. A plurality of pattern photographing means for outputting electric signals, a plurality of stage adjusting means for adjusting the position of the wafer stage in accordance with a control signal, and the electric signals output from the plurality of pattern photographing means each have a maximum peak value. As described above, the control unit is provided with a focus control unit that gives the control signal to the plurality of stage adjusting units and controls the pattern so that the surface of the semiconductor wafer on the wafer stage is focused.
[0006]
In the second invention, the stage adjusting means in the first invention is constituted by a bellows or a piezoelectric element.
[0007]
According to the present invention, since the automatic focusing apparatus is configured as described above, the following operation is performed.
[0008]
When a pattern is irradiated onto the surface of the semiconductor wafer mounted on the wafer stage, the pattern is photographed by a plurality of pattern photographing means. An electrical signal corresponding to each photographed pattern is output from the pattern photographing means and is provided to the focus control means. In the focus control means, control signals for the plurality of stage adjustment means are generated so that the electric signals output from the pattern photographing means each have the maximum peak value. Each stage adjustment means adjusts the position of the wafer stage in accordance with a control signal given from the focus control means. As a result, the control is finally performed so that the pattern is focused on the surface of the semiconductor wafer on the wafer stage.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1A and 1B are configuration diagrams of an autofocus device showing an embodiment of the present invention.
This automatic focusing apparatus is used by being incorporated in a semiconductor exposure apparatus, and controls its position so that the exposure pattern is focused on the surface of the semiconductor wafer.
[0010]
As shown in FIG. 1A, the automatic focusing apparatus has a wafer stage 11 on which a semiconductor wafer 1 to be exposed is mounted. The wafer stage 11 is attached to the gantry 13 via a plurality of stage adjusting means (for example, bellows) 12. The bellows 12 is a thin tube having a smooth mountain-shaped continuous cross section, and can be freely expanded and contracted within a certain range by controlling the air pressure in the tube by the air pressure AIR.
[0011]
On the other hand, a plurality of pattern photographing means (for example, a video camera) 14 is provided above the wafer stage 11. As shown in FIG. 1B, the video camera 14 is arranged so as to photograph an alignment mark M for position adjustment in a pattern irradiated to the semiconductor wafer 1 through an optical system (not shown). The video camera 14 is composed of a CCD (Charge Coupled Device) or the like, which decomposes and reads the captured image of the alignment mark M into pixels, converts the luminance for each pixel into an electric signal SIG, and sequentially outputs it.
[0012]
The output side of the video camera 14 is connected to a focus control means (for example, control unit) 15. The control unit 15 controls the air pressure AIR given to each bellows 12 so that the electric signal SIG output from each video camera 14 has the maximum peak value. The control unit 15 includes, for example, a microprocessor and an air compressor controlled by the microprocessor.
[0013]
In this autofocus device, it is necessary to adjust the installation position of each video camera 14 at the beginning of installation. In this adjustment, first, the semiconductor wafer 1 is tilted, the pattern of the mask for adjustment is exposed and developed, and a focused position is obtained. Next, the bellows 12 is adjusted so that the entire semiconductor wafer 1 is in focus. Furthermore, the alignment mark M is irradiated onto the semiconductor wafer 1 in this state, and the position and focus of each video camera 14 are adjusted so that the electric signal SIG output from each video camera 14 has the maximum peak value. After the adjustment, each video camera 14 is fixed.
[0014]
2A to 2C are explanatory views showing the operation of the autofocus device of FIG. The operation of FIG. 1 will be described below with reference to FIGS. 2 (a) to 2 (c).
First, a semiconductor wafer 1 to be exposed is mounted on a wafer stage 11 and a circuit pattern is irradiated onto the semiconductor wafer 1 through an optical system (not shown).
[0015]
Next, the video camera 14 starts monitoring the alignment mark M on the semiconductor wafer 1. The electric signal SIG output from each video camera 14 is given to the control unit 15. The electric signal SIG varies depending on the state of the alignment mark M irradiated on the surface of the semiconductor wafer 1.
[0016]
As shown in FIG. 2A, when the focus is achieved and the alignment mark M is accurately irradiated on the surface of the semiconductor wafer 1, the electric signal SIGa output from the video camera 14 has a maximum peak value. Is shown.
[0017]
On the other hand, as shown in FIGS. 2B and 2C, when the focus is shifted forward or backward of the surface of the semiconductor wafer 1, the peak values of the electrical signals SIGa and SIGc output from the video camera 14 become small. .
[0018]
The control unit 15 increases / decreases the air pressure AIR given to each bellows 12 in a predetermined order, and expands / contracts these bellows 12 so that the electric signals SIG output from the respective video cameras 14 all show the maximum peak value. .
Thus, the circuit pattern can be focused on the entire surface of the semiconductor wafer 1.
[0019]
As described above, the automatic focusing apparatus according to the present embodiment includes the plurality of video cameras 14 that capture the alignment mark M and the bellows 12 so that the electric signal SIG output from these video cameras 14 exhibits the maximum peak value. A control unit 15 for adjusting the position of the semiconductor wafer 1 is provided. Thereby, the focus can be automatically adjusted in the semiconductor exposure apparatus.
[0020]
In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. Examples of this modification include the following.
[0021]
(A) The bellows 12 may be controlled by the pressure of nitrogen gas or the like in addition to air.
(B) Although the bellows 12 is used to adjust the position of the semiconductor wafer 1, a piezoelectric element such as a piezo element can be used instead of the bellows. A piezo element is an element whose thickness changes due to crystal distortion when a voltage is applied to a semiconductor crystal. In the case of a piezo element, there is a certain relationship between the applied voltage and the displacement caused thereby. Therefore, once the position adjustment is performed, there is an advantage that the position of the control signal at that time can be stored and the position can be immediately adjusted to a predetermined position from the second time.
[0022]
(C) Although the video camera 14 is used to photograph the alignment mark M, the present invention is applicable as long as the output signal of the photographed image can be obtained as an electrical signal, such as a digital camera.
[0023]
(D) Although the video camera 14 is set to shoot the alignment mark M, the video camera 14 may shoot another circuit pattern to adjust the focus.
[0024]
【The invention's effect】
As described above in detail, according to the first invention, a plurality of pattern photographing means for photographing a pattern on the surface of a semiconductor wafer and outputting an electrical signal, and a control signal for the position of the wafer stage on which the semiconductor wafer is mounted. And a focus control means for giving a control signal to each stage adjustment means so that an electric signal output from each pattern photographing means shows a maximum peak value. Thereby, the pattern can be automatically focused on the surface of the semiconductor wafer on the wafer stage.
[0025]
According to the second invention, the stage adjusting means in the first invention is constituted by a bellows or a piezoelectric element. Thereby, the position of the stage can be adjusted with a small size and high accuracy. In particular, in the case of a piezoelectric element, since there is a certain relationship between the voltage and displacement of the control signal, it is possible to immediately adjust to a predetermined position by storing the value of the control signal. effective.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an autofocus device showing an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing an operation of the autofocus device in FIG. 1;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Semiconductor wafer 11 Wafer stage 12 Bellows 13 Base 14 Video camera 15 Control part M Alignment mark

Claims (2)

A plurality of pattern photographing means for photographing a pattern irradiated on the surface of the semiconductor wafer mounted on the wafer stage and outputting an electrical signal corresponding to the photographed pattern;
A plurality of stage adjusting means for adjusting the position of the wafer stage according to a control signal;
The control signal is given to the plurality of stage adjusting means so that the electrical signals output from the plurality of pattern photographing means respectively show maximum peak values, and the focus of the pattern is focused on the surface of the semiconductor wafer on the wafer stage. Focus control means for controlling to fit,
An autofocus device characterized by comprising. 2. The automatic focusing apparatus according to claim 1, wherein the stage adjusting means is constituted by a bellows or a piezoelectric element.

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