JPH0827173B2 - Pattern detection method - Google Patents

Description

The present invention relates to a pattern detection method, for example, a highly integrated LS.
The present invention relates to a method of detecting a positioning pattern in a mask aligner (exposure device) used for manufacturing.

[Prior Art] Conventionally, for example, in a mask aligner or the like, a method of photoelectrically detecting a linear pattern or the like for alignment on a wafer is known.

However, since a photoresist is coated on the wafer, a large number of interference fringes appear when it is illuminated with single wavelength light. FIG. 7 (A) shows a number of interference fringes a that appear when a linear mark, which is a pattern for alignment, is illuminated with single-wavelength light.

When this is scanned in the direction of the arrow in the figure and converted into an electric signal, a video signal b as shown in FIG. 7 (B) is obtained.

Conventionally, in order to obtain the center from the signal b, an appropriate threshold value c is set in advance and the signal b
It was converted into the binarized signal d shown in FIG. 6C, and the center e of the binarized signal d, that is, the center position of the pattern on the wafer was obtained from this.

[Problems to be solved by the invention]

However, this method cannot be detected when the video signal 1b does not reach the threshold value c as shown in FIG. 7 (D) or when the video signal 2b is not completely symmetrical as shown in FIG. 7 (E). Alternatively, the binarized signal 1d of FIG. 7 (F) was obtained, and 1e of FIG. 7 was detected as the center position, and the correct center position could not be detected.

Further, as shown in FIG. 8A, the threshold value c of the video signal 3b is
When the noise f is present in the vicinity or when the video signal 4d becomes slightly asymmetric due to some defects of the linear pattern itself as shown in FIG. 9 (A), FIG. ) 2
The binarized signal 2d and the binarized signal 3d in FIG. 9 (B) were found, and the correct center position could not be detected.

In order to eliminate these drawbacks of the conventional method, Japanese Patent Publication No. Sho 56-2284 discloses a method in which a video signal is folded from a certain point to obtain the degree of matching between both signals, and the point where the matching degree is the best is obtained as the center position. Is proposed. However, the actually obtained video signals are diverse as shown in FIGS. 10A to 10G due to uneven coating of resist, optical shading, difference in wafer material, etc. For example, it is the same as the video signal 3 in FIG. 3 (A), and the original signal is not so required to have symmetry.

Further, when the linear pattern is viewed at right angles to the length direction, the contrast and the width of the linear pattern appear different as in the pattern 2 shown in FIG. 2 due to the uneven coating of the resist. Therefore, in FIG. 7 (A), the center position to be obtained differs greatly depending on which position the arrow indicating the scanning direction of the pattern is brought to obtain the video signal.

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional technique, to influence noise and asymmetry included in a video signal detected by an image pickup device, variations and distortions of pattern video on the same linear pattern, and sampling. An object of the present invention is to provide a method for accurately determining the center position of a pattern by minimizing the influence of the quantization error due to.

[Means and Actions for Solving Problems] In order to achieve the above object, the present invention provides a two-dimensional video signal within a two-dimensional window of a predetermined size with respect to a video signal obtained by imaging a pattern. The integration is performed in one direction of the coordinates, the evaluation value is sequentially obtained by using the integration signal in the pattern detection window while scanning the integration signal in the pattern detection window, and the outline of the pattern is calculated based on the evaluation signal. It is characterized in that the position is detected, and the center position of the pattern is obtained based on the position of the pattern detection window before and after the rough position and the evaluation value corresponding to the position.

As a result, it is possible to minimize the effects of noise and asymmetry included in the video signal, variations and distortions of the pattern video on the same linear pattern, and the effects of quantization error due to sampling.

In a preferred embodiment of the present invention, the center position of the pattern is obtained by weighted averaging the positions of the detection windows with the corresponding evaluation values. The position of the detection window is obtained from the position in the two-dimensional window and the corresponding integrated signal. Further, a digitized signal is used as the video signal.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a flow chart showing an outline of the processing flow of a method for detecting a mask pattern on a wafer according to an embodiment of the present invention. FIG. 2 is a view in which a window for projection is applied to the alignment mask pattern on the wafer.

In FIG. 2, 1 is a mask pattern image on the wafer where the image signal of the portion is obtained by the image pickup means, 2 is a mask pattern, and 4 is a two-dimensional window. The arrow 11 indicates the x direction and the arrow 12 indicates the y direction.

Hereinafter, each process will be described in detail with reference to the flowchart of FIG.

First, the video signals in the range of number 1 in FIG. 2 obtained by the image pickup means in step S1 are integrated in the y direction in the two-dimensional window 4, and as shown in number 8 in FIG. 3 (B). The integrated signal P (i) is obtained.

here, Is. In this equation (1), the integrated signal y _j (i) is y
The video signal is as shown by 3 in FIG. 3 (A) when one coordinate j in the direction is determined, and 1 represents the width of integration in the y direction. As a result, random noise included in the video signal is removed, and spike noise is diluted to obtain a clean integrated signal P (i). On this occasion,
The integrated width l in the equation (1) needs to be wide enough to remove noise, but if it is made too large, it is affected by the distortion of the optical image of the alignment pattern caused by uneven coating of the resist, resulting in a large measurement error. The width may be appropriate, so the width should be appropriate.

Next, in step S2, the contrast C is calculated for the integrated signal P (i) by the following equation, and in step S3, signals with the contrast C equal to or less than a threshold K are excluded from measurement.

here, It is defined as the standard deviation, the mean, and the value called cartosis, respectively. Further, n is the range of number 6 in FIG. 3 (B), and 1 to n are the widths of i in the x direction.

Next, a measurement window having a width 7 as shown by number 5 in FIG. 3 (B) is set, and in step S4, the skewness S (j) is shifted while shifting the measurement window in the integrated signal P (i). ).

Skewness S (j) is Is. However, w is the width of the measurement window, P _min is the minimum value of P (i) shown in FIG. 3 (B).
(I, j) is a value normalized by the area by reducing the influence of the offset when obtaining the skewness. Also, M (j) is And the center of gravity in the window 5 is represented by the first moment. Also, Σ (j) is Is the standard deviation within window 5.

FIG. 4 is an example of the skewness signal S thus obtained.

Next, the position of the pattern is obtained based on this skewness signal. First, the maximum value S _max and the minimum value of the skewness signal
S _min is obtained, and K ⁺ and K ⁻ are determined as, for example, K ⁺ = S _max / 2 K ⁻ = S _min / 2 (4).

Next, in step S5, find the point where S crosses zero,
Further, in step S6, a location where S> K ^{+ and} a location where S <K ^{− are} obtained. If each point is represented by 0, +,-, it can be represented by "+ 0-" in the case of the signal of FIG. 4 (a), for example. Similarly, in the cases of FIGS. 7B and 7C, the values are "+ 000-" and "+ 0-0 + 0-", respectively.

Then, in step S7, the symmetry is confirmed. However, the symmetry here means that “0” and “0” and “+” and “−” correspond in order on the left and right, centering on the center “0”. All of the cases shown in FIGS. 4A to 4C are symmetrical.

If, when the result is not as symmetrical as the "+ 0-00-" As shown in Fig. 5, K ^+, K at step S9 ^- changing the value independently of. For example, in the case of FIG. 5, "+"
The number of is 1 and less than the number of "-" is 2 so try lowering the value of K ⁺ a little. By repeating such an operation within a predetermined number of times, as shown in FIG.
It becomes symmetrical with "-0 + 0-".

If symmetry cannot be obtained within a certain number of times,
In step S8, the image in this window is excluded because it has large distortion.

Then, if the symmetry is confirmed, the zero-cross point in the middle can be determined to be near the center of the wafer pattern.

Further, the accurate pattern center position is obtained as follows in step S10. That is, FIG. 4 and FIG.
Since the skewness signal in the figure is actually a digital signal, it is rare that S = 0 at a certain integer i. In most cases, S0 and i at the time of i = k (k is an integer) around the zero cross point. = K + 1 (k is an integer), S0 (composite same order) is obtained. Therefore, the center of gravity before and after the zero-cross point is M ₁ ,
With M ₂ and skewness values S ₁ and S ₂ , the center position M is Ask as. As a result, the quantization error due to the digital image can be removed, and accurate positioning can be performed.

Although the method of obtaining the center position from one window has been described in the above embodiment, as shown in FIG. 6, a plurality of windows 4 can be set for one pattern 2, or a plurality of patterns 2 can be set. It is also possible to obtain a plurality of results for one alignment and prepare a near-true center position from a plurality of results that have not been excluded. The method is, for example, if x ₁ , x ₂ , ..., X _n and n results are obtained, the average and each deviation are obtained, and the absolute value of the deviation exceeds a certain threshold. The same operation is repeated for the remaining ones except the ones. Then, when the absolute values of the deviations of all the remaining results are within the threshold value, the average value thereof is obtained, and it is set as the center position close to the true value.

By the above method, the result obtained from the locally deteriorated part is excluded, only the highly reliable result is left, and the results are averaged, so that more accurate alignment can be performed.

Further, in the above-described embodiment, the case of detecting the linear pattern in the y direction has been described, but the linear pattern in the x direction can be detected in the same manner by exchanging the x and y directions.

Further, the alignment pattern can be applied to a straight line, a cross, a quadrangle, a circle, or the like, and any pattern center position can be obtained by the same method in the x and y directions.

[Effects of the Invention] As described above, according to the present invention, integration is performed in the x or y direction within a two-dimensional window and the pattern detection window is shifted within the integrated signal while integrating within the detection window. The evaluation value is obtained using a signal, the approximate position of the pattern is obtained based on the evaluation value signal, and precision is obtained based on the position of the pattern detection window before and after the approximate position and the evaluation value corresponding to the position. By determining the pattern center position, the effect of noise, shading,
It became possible to detect the pattern position with high accuracy without being affected by the difference in the brightness of the background, the difference in the appearance of interference fringes, and the unevenness of the resist. Further, by applying it to a mask aligner or the like, it becomes possible to perform precise alignment of alignment marks on the wafer.

[Brief description of drawings]

FIG. 1 is a flowchart showing a processing flow of a method for detecting a pattern for alignment on a wafer according to an embodiment of the present invention, and FIG. 2 is a diagram in which a window for projection is applied to a pattern for alignment, FIG. 3 (A) is a diagram showing a video signal waveform, FIG. 3 (B) is a diagram showing an integrated signal accumulated in a window, and FIGS. 4 and 5 are diagrams showing skewness signals. FIG. 6 is a view showing that a plurality of windows are set in a plurality of wafer patterns, FIG. 7 (A) is a view showing a positioning pattern coated with photoresist, and FIG. 7 (B). FIG. 7 is a diagram showing a video signal waveform, FIG. 7 (C) is a diagram showing a binarized signal waveform binarized by a predetermined threshold which is a conventional method, and FIG. 7 (D) is a threshold level. Figure 7 (E) showing a smaller video signal waveform is asymmetric FIG. 7 (F) shows a binarized signal waveform obtained by binarizing the video signal shown in FIG. 7 (E) by a threshold value, and FIG. 8 (A) shows FIG. 8B is a diagram showing a video signal waveform having noise, FIG. 8B is a diagram showing a binarized signal waveform obtained by binarizing the video signal shown in FIG. FIG. 9A is a diagram showing an asymmetrical video signal waveform detected by an error in an alignment pattern, and FIG. 9B is a binary image obtained by binarizing the video signal shown in FIG. FIGS. 10A to 10G are diagrams showing various signal waveforms, and FIGS. 10A to 10G are diagrams showing various video signal waveforms.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location G06T 7/60 H01L 21/027 21/68 F H01L 21/30 502 M (72) Inventor Hiroshi Terui 53 Imaiue-cho, Nakahara-ku, Kawasaki-shi, Kanagawa Canon Inc. Kosugi Plant (56) References JP-A-63-106503 (JP, A) JP-A-53-69063 (JP, A)

Claims (3)

[Claims] 1. A two-dimensional window of a predetermined size is provided for a video signal obtained by imaging a pattern by an imaging means,
In the two-dimensional window, video signals are integrated with respect to one direction of two-dimensional coordinates, and a pattern detection window is set for the integrated signal,
While scanning the integrated signal with the pattern detection window, an evaluation value is sequentially obtained using the integrated signal in the pattern detection window, and a rough position of the pattern is detected based on the evaluation value signal. A pattern detection method, characterized in that a center position of the pattern is obtained based on a position of the pattern detection window before and after the position and the evaluation value corresponding to the position. 2. The pattern detecting method according to claim 1, wherein the center position of the pattern is obtained by weighted averaging the positions of the detection windows with the corresponding evaluation values. 3. The pattern detecting method according to claim 2, wherein the position of the detection window is obtained from the position in the two-dimensional window and the corresponding integrated signal.