JPH011901A - pattern detection device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement of a pattern detection device used in a projection exposure apparatus δ for semiconductor manufacturing, etc.

[Prior Art] As a conventional pattern detection device, there is one shown in FIG. FIG. 5 shows an alignment device as an example of a pattern detection device used in a projection exposure apparatus.

In the figure, 10 is a laser light source, and the laser light LA emitted from the laser light source is reflected by a mirror 12, then expanded to a predetermined beam width by a beam expander 14, and then enters a scanner mirror 16. It looks like this. The scanner mirror 16 has a deflectable configuration, and is configured to vibrate the laser beam LA reflected on the surface of the scanner mirror 16 by driving the scanner mirror 16.

Next, the laser beam LA reflected by the scanner mirror 16 passes through the relay lens 18 and is passed through the beam splitter 20.
after passing through the objective lens 22 and passing through the mirror 24.
It is designed to be reflected by The laser beam LA reflected by the mirror 24 is imaged into a sheet-like spot light by the reticle R, passes through the vicinity of the alignment reticle mark RM formed on the reticle R, and then passes through the projection lens 2.
6, the light is again imaged onto the wafer W as a sheet-like sub-light 1-. Wafer W is stage 2
A wafer mark WM for alignment is placed on the wafer W, and the laser beam LA is designed to irradiate this wafer mark WM. Further, the stage 28 is configured to be movable in the X and Y directions by a drive device 30.

The laser beam LA that irradiated the reticle mark RM and the wafer mark WM is configured to generate detection light (diffraction light, scattered light, etc.) at each mark by the action of the scanner mirror 16 described above, and each detection light The light returns along the same optical path as the incident light and enters the beam splitter 20, and the light transmitted through the beam splitter 20 is received by the detector 32. Then, the detected light is photoelectrically converted by the detector 32, amplified by the amplifier 34 as an alignment signal, and then sent to the alignment signal analysis circuit 36.
It is now output to .

The analysis circuit 36 analyzes the input signal and sends it to a central processing unit (CPU) 38. Then, the central processing unit (CPU) 38 calculates the drive amount of the stage 28 from the input alignment signal, and drives the stage 28 via the drive device 30 to achieve relative alignment between the reticle R and the wafer W. It is supposed to be done.

Next, the overall operation of the above-mentioned prior art will be explained.

First, the laser light LA emitted from the laser light source 10 is transmitted to the mirror 12. Beam expander 14° mirror 16. Relay lens 18. Beam splitter 20. The reticle mark RM formed on the reticle R is irradiated by the respective actions of the optical elements of the objective lens 22 and the mirror 24, and is further imaged onto the wafer W via the projection lens 26. At this time, the stage 28 is driven by the drive device 30 to move the wafer mark WM to the imaging position l of the laser beam LA.

Next, by driving the scanner mirror 16 in the above-described state and vibrating the laser beam LA, the spot of the laser beam LA is scanned by the reticle mark RM and the wafer mark WM, respectively. And the laser beam LA
Detection light such as scattered light generated at each mark by scanning is received by a detector 32, the amount of light is converted into an electrical signal, amplified by an amplifier 34, and then output to an alignment signal analysis circuit 36.

Next, the analysis circuit 36 analyzes the reticle R from the alignment signal.
The amount of positional deviation between the wafer W and the central processing unit (CP) is calculated.
U) At 38, relative alignment between the reticle R and the wafer W is performed by moving the stage 30 based on the deviation.

In the exposure device described above, in order to keep the output of the laser for alignment stable, the laser light LA is always in one state where it is output from the laser light source 10, that is, in a thermally stable state. .

[Problems to be Solved by the Invention] However, lasers not only suffer from thermal stability over time, but also generate noise due to loss of the laser medium and changes in the replenishment state.

Further, the light intensity of the laser light LA output from the laser light source 10 has a property that once noise is generated due to the above-mentioned causes, the noise continues to be generated steadily for a certain period of time.

This noise is 5% of the maximum and minimum width of the laser output.
If it is within this range, it will have little effect on alignment accuracy, but if it exceeds that range, random alignment errors will occur, resulting in the formation of defective chips during the overlay exposure process.

Such defective chips can only be confirmed when the exposed wafer is developed and inspected after processing, so there is a possibility that not only one wafer but the entire lot will be wasted.

The present invention has been made in view of this point, and an object of the present invention is to obtain a pattern detection device that can perform highly accurate alignment.

[Means for Solving the Problems] A pattern detection device according to the present invention includes a light receiving means for receiving all or a part of illumination light from a light source; a detection means for detecting; a comparison means for comparing the information on the detected light amount fluctuation with predetermined reference information; and a comparison means for comparing the information on the detected light amount fluctuation with predetermined reference information: based on the result of the comparison, the accuracy of the light information generated from the pattern (for example, the recognition accuracy of the pattern, The technical point is to include an output means for determining alignment accuracy, etc.) and outputting a predetermined output.

[Operation] Receives all or part of the illumination light from the light source, detects the light amount fluctuation of the illumination light based on the information, and compares the information of the detected light amount fluctuation with predetermined reference information to perform the work. Since various outputs such as interrupting the exposure can be generated, highly accurate pattern detection can be performed, and miss shots can be prevented during exposure operation.

[Example bN] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a projection exposure apparatus according to an embodiment of the invention. Note that since the optical system for alignment is almost the same as that of the prior art described above, details of the similar parts will be omitted.

First, the overall configuration of the embodiment will be explained. In the figure, the laser light LA emitted from the laser light source ]0 is
Most of the laser beam LA is reflected by the half mirror 40, and the reflected laser beam LA is imaged on the reticle R and the wafer W by the actions of optical elements similar to those in the prior art. Detection light from the reticle mark RM and wafer mark WM is received by a detector 32.

The amount of detection light received by the detector 32 is converted into an electrical signal, which is further amplified by an amplifier 34. The signal output from the amplifier 34 is input to the alignment signal analysis circuit 36 to determine the amount of positional deviation between the reticle R and the wafer W, and the information is sent to the central processing unit (CPU).
42.

On the other hand, a part of the laser beam LA transmitted through the half mirror 40 is received by a noise detector 44, and the noise detector 44 is configured to convert the amount of the received light into an electrical signal. This noise signal is then output to a laser noise analysis circuit 46, which obtains predetermined noise information and outputs the information to a central processing unit (CPU) 42. central processing unit (CP)
U) At 42, it is determined whether alignment is possible based on the information from the laser noise analysis circuit 46, and if the result exceeds a predetermined amount of noise components, a warning is issued by the display 48 or the warning lamp 50, If the noise component is less than a predetermined value, alignment is performed based on information from the alignment signal analysis circuit 36.

The display device 48 outputs a warning message using a CRT (not shown), and also has an input function using a keyboard or the like (not shown). The configuration is such that the reference noise component amount can be changed arbitrarily. The display 48 can also be used to measure the output of the laser, adjust the output, and adjust noise, and can also be used to monitor the lifespan of the laser and the replacement time.

Next, the structure and operation of the laser noise analysis circuit 46 will be explained with reference to FIGS. 2 and 3. FIG. 2 is a block diagram showing the configuration of the laser noise analysis circuit 46,
Fig. 3 shows a of Fig. 2.

The relationship between voltage and time at points b and c is shown.

In the figure, 52 is a current-voltage converter that converts a signal from the current manually inputted from the noise detector 44 into a voltage, and the output from the current-voltage converter 52 is shown in FIG. 3(A).
The signal is converted into a DC component only signal by the low-pass filter 54, and is outputted to the attenuator 56 as an average output within a certain time. Attenuator 56
In this case, the average output of the laser inputted from the low-pass filter 54 is attenuated to a predetermined value, and then outputted to the comparator 64. The attenuation rate of the attenuator 56 is set to a constant value so that laser noise can be detected at a constant rate even when the average output of the laser changes over time.

On the other hand, in the peak hold circuit 58, the laminar voltage converter 5
The bottom hold circuit 60 uses the maximum value of the noise component of the signal input from the second circuit 60 as the minimum value of the same noise component.
As shown in Figure (B), the peak hold circuit 58
The differential amplifier 62 outputs the outputs from the bottom halt circuit 60 and the comparator (
comparator) 64. The peak hold circuit 58 and the bottom hold circuit 60 are configured to attenuate the output over time so as not to respond to changes in laser noise.

In the comparator 64, the attenuator 5
6 and the differential amplifier 62, that is, the average output of the noise component and the absolute value of the amplitude of the same noise component, and the result of the magnitude is output as a signal.

Furthermore, the configuration of the laser noise analysis circuit 46 is as follows:
In addition to what is shown in the figure, something like the one shown in Figure 4 may be considered. This has a configuration in which the attenuator 56 shown in FIG. 2 is omitted, and an A/D converter 66 and a microprocessor 68 are added in place of the comparator 64. That is, the average laser output from the unattenuated low-pass filter 54 and the absolute value of the amplitude of the noise component obtained by the differential amplifier 62 are each output to the A/D converter 66, and both human power signals are respectively output. The signal is converted into a direct current, and the microprocessor 68 calculates the ratio of noise to the average output of the laser, and is particularly effective when higher precision is required.

Next, the overall operation of the above embodiment will be explained.

First, the laser light LA is output from the laser light source 10, and is irradiated onto the reticle mark RM as a spot light. Then, by driving the stage 28, the wafer mark WM is moved to the imaging position of the laser beam LA that irradiates the wafer W via the projection lens 26. Here, noise during laser oscillation (slight fluctuations in light intensity) is constantly detected by the noise detector 44, converted into an electrical signal, and transmitted to the laser noise analysis circuit 46. Note that the detection of the noise component by the noise detector 44 is not performed during the first print of exposure, but is performed during the exposure that requires the alignment operation after the second print.

Next, the scanner mirror 16 is driven and the laser beam LA is
vibrate the reticle mark RM and wafer mark WM.
The spots of the laser beam LA are each scanned.

The detection light (scattered light) generated by this is detected by the detector 3.
2, and transmits the optical information as position information of each mark to an alignment signal analysis circuit 36 via an amplifier 34.

Next, in the central processing unit (CPU) 42, based on the information manually input from the laser noise analysis circuit 46, when the ratio of the laser noise component exceeds a predetermined value, the warning lamp 50 is turned on and the display 48 shows the warning lamp 50. This message is displayed to prompt the operator to take action. Alternatively, it is also possible to interrupt the exposure according to the content of the work manually performed in advance. On the other hand, when the ratio of noise components is less than a predetermined value, normal alignment is performed based on data input from the alignment signal analysis circuit 36.

According to the actual example above, the output of the laser beam LA is 9
Noise components are always detected, and when the noise component exceeds a reference value, the operator is warned by the display 48 and warning lamp 50, so even if noise occurs in the laser light source 10, exposure can be interrupted, etc. This treatment has the effect of preventing misalignment shots.

Furthermore, if the data when the noise level from the laser light source 10 is equal to or higher than the reference value is stored sequentially for each alignment exposure operation in correspondence with the step-and-repeat exposure map (shot arrangement on the wafer), This method has the advantage that missed shots at each shot position can be predicted after processing one wafer. In addition, the representative position M on the wafer
Even if step-and-repeat exposure is performed after measuring the alignment marks for shots in advance and precisely measuring the shot arrangement on the wafer, make sure that the noise level is below the reference value during sample alignment (mark detection). It is recommended to measure the mark position using

Note that the laser detection by the noise detector 44 in the above embodiment can also be performed using laser leaking from the periphery of the laser light source 10.

Furthermore, the present invention is not limited to alignment systems such as exposure apparatuses shown in the above embodiments, but is also applicable to pattern detection systems using laser light, etc., such as pattern line width measuring devices, foreign object inspection devices, defect inspection devices, etc. It can also be widely used.

Note that the same reference numerals in each figure indicate the same or corresponding parts.

[Effects of the Invention] As described above, according to the present invention, since fluctuations in the amount of illumination light are detected, pattern detection can be performed with high accuracy. Furthermore, since fluctuations in the amount of illumination light for pattern detection are detected, errors during pattern detection can be predicted, and there is also the effect that misshots during exposure can be prevented by the operator's judgment.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 and FIG.
3 is an explanatory diagram showing the operation of the embodiment, and FIG. 5 is a block diagram showing an example of the prior art. "Explanation of symbols of main parts"

Claims (1)

[Claims] (1) A light source for irradiating illumination light onto a pattern formed on an object, and a first detection means for detecting light information generated from the pattern by the irradiation, and based on the detected information. A device for detecting the pattern by using a light receiving means for receiving all or a part of the illumination light from the light source; a second detecting means for detecting a variation in the amount of the illumination light based on information from the light receiving means; ; comparison means for comparing the detected light amount fluctuation information with predetermined reference information;
A pattern detection device comprising: output means for determining the accuracy of the information detected by the first detection means based on the comparison result and outputting a predetermined output.