JPH07302741A - Mark position detection method and apparatus for electron beam exposure - Google Patents

Abstract

(57) [Summary] [Purpose] To detect the mark position with a single electron beam scan. Accurate position detection can be performed by eliminating the effects of noise and roughness on the sample. [Structure] Scanning the mark 17 on the sample with an electron beam,
The reflected electrons are detected to obtain a reflected electron signal Y (I) [(b) figure]. Roughness near the mark is observed in the reflected electron signal.
A noise component corresponding to is also included. An autocorrelation calculation is performed on the backscattered electron signal with the width J of the signal component obtained from the alignment mark as a cycle, and an autocorrelation calculation output Z
Obtain (I) [Fig. (C)]. By this calculation, the roughness 18
The noise component due to etc. is sufficiently attenuated. A trigger signal is obtained at a point across the slice level [Fig. (D)], and the midpoint thereof is determined as the center point of the mark.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positioning method and apparatus for accurately drawing a pattern at a desired position on a sample by an electron beam with reference to a positioning mark on the sample. Related to the lithographic technology.

[0002]

2. Description of the Related Art Conventionally, when a pattern is accurately drawn by using an electron beam at a desired position on a sample, the electron beam is scanned so as to cross a reference alignment mark which is arranged on the sample in advance. The position of the alignment mark is obtained from the obtained backscattered electron signal, and a pattern is drawn with an electron beam using the position as a reference. FIG. 5 is a block diagram showing the configuration of a mark position detecting device that has been used conventionally.

As shown in FIG. 5, an electron beam EB obtained from an electron gun and focused by an electron lens is deflected by a deflector 11 and provided on a wafer 16 as shown by an arrow A. Scanning is performed so as to traverse the alignment mark 17. At this time, the backscattered electrons RE generated from the electron beam irradiation position on the sample are detected by the backscattered electron detector 12 provided between the deflector and the sample. The detected backscattered electron signal is amplified by the backscattered electron signal amplifier 13, and the position detection circuit 15 obtains the center position of the alignment mark 17 from the backscattered electron signal.

FIG. 6 is a diagram for explaining a method of obtaining the center position of the alignment mark from the obtained backscattered electron signal in the position detection circuit 15 of FIG. A slice level is set for the obtained reflected electron signal, and a trigger signal is generated at a position where the reflected electron signal crosses this slice level. The two peak positions P1 and P2 in the trigger signal indicate the edge positions at the left and right ends of the alignment mark 17. Therefore, the center position P0 of the alignment mark can be determined by calculating the midpoint between the edge positions P1 and P2 of the two alignment marks [eg Miyauchi et al .; IEEE
E Transactionson Electron Devices ED-17 pp.45
0-457 (1970)].

By the way, in recent years, there has been a tendency for the film thickness of the photoresist to become thicker due to the fact that the multilayer resist method has been adopted in order to cope with the miniaturization of the process. In the detection means, the level of non-stationary noise whose position and intensity change with time becomes relatively high with respect to the level of the reflected electron signal, making it difficult to accurately detect the mark position. In addition, “roughness” occurs and dust adheres to the wafer after undergoing various processes, so that the detection signal is becoming disturbed by these stationary noise sources. There is.

Several improvement plans have been proposed to cope with such a situation. A first improvement plan is to improve the S / N by scanning the same mark a plurality of times and integrating the reflected electron signals in the apparatus shown in FIG. A second improvement plan is proposed in Japanese Patent Laid-Open No. 57-122517, and the mark is scanned a plurality of times as in the first improvement plan. The scanning position is changed little by little.

FIG. 7 is an explanatory view for explaining the second improvement plan, and in this method, as shown in FIG. Scan the line. Here, there is a noise source 18 'such as "roughness" in the mark and in the vicinity thereof, and when scanning the mark edge 17a and the edge portions of these noise sources 18', a mark x in FIG. As shown, the edge portion is detected. When the detection signals are integrated, the result shown in FIG.
As shown in (c), since the signal level at the mark edge 17a becomes higher than the detection levels of other portions, it is possible to easily detect the position of the mark edge 17a by comparing with the threshold value. Become. In the example shown,
The scanning is performed 6 times, but in actuality, the scanning is repeated about 20 times to improve the detection accuracy. According to this method, it becomes possible to remove even information on stationary noise sources that was difficult to remove by the first improvement plan.

A third improvement plan is Japanese Patent Laid-Open No. 3-104109.
This is proposed in Japanese Patent Publication No. JP-A-2004-115, when scanning the mark with an electron beam, the electron beam is modulated with an amplitude narrower than the scanning range and a period faster than the scanning period while scanning the mark. Then, the change amount of the reflected electrons according to the modulation is obtained, and the mark position is detected based on the change in the change amount at each scanning position.

[0009]

In the above-mentioned first and second improvement plans, since the degree of improvement in the S / N of the detection signal is proportional to the number of scans, the scanning is repeated as many as 20 times. Therefore, there is a problem that it takes a long time to detect the position. Further, the second improvement proposal has a problem that the noise removing capability is reduced when the mark is inclined with respect to the scanning direction of the electron beam. In contrast,
In the third improvement plan, the number of scans is improved to one. However, in the third improvement plan, the apparatus becomes complicated because a new deflector is required for the exposure apparatus, and further,
There was a drawback that the circuit became complicated. Further, although the first and third improvement proposals are effective in removing the non-stationary noise, there is a problem that the effect of suppressing the stationary noise such as "roughness" on the sample is low.

The present invention has been made in consideration of such a point, and an object thereof is to reduce the number of electron beam scans in electron beam exposure and to shorten the detection time as compared with the prior art. , And reduce not only the effects of non-stationary noise components but also the effects of stationary noise components,
This is to enable the center position of the alignment mark to be accurately detected.

[0011]

In order to achieve the above object, according to the present invention, an alignment mark for drawing a pattern on a sample by electron beam exposure using the alignment mark arranged on the sample as a reference. A method of detection, in which the reflected electron signal obtained by scanning the electron beam over the alignment mark is subjected to an autocorrelation calculation using the width of the signal component obtained from the alignment mark as a cycle. There is provided a method characterized by determining a mark position based on a calculation result.

According to the present invention, the electron beam source, the deflection means (11) for scanning the electron beam emitted from the electron beam source on the alignment mark of the sample, and the reflection from the scanned sample A backscattered electron detector (12) for detecting electrons, an autocorrelation calculator (14) for performing an autocorrelation calculation on an output signal of the backscattered electron detector, and a sample based on the calculation result of the autocorrelation calculator There is provided a mark position detection device in electron beam exposure, comprising: a position detection circuit (15) for determining the position of the upper alignment mark.

[0013]

According to the present invention, the autocorrelation calculation is performed on the output signal of the backscattered electron detector for detecting the backscattered electrons from the sample, with the width of the signal component obtained from the alignment mark as a cycle. In general, the width of the reflected electron signal from the stationary noise source as well as the pulse width of the non-stationary noise is sufficiently smaller than the width of the signal component obtained from the alignment mark. Therefore, if the autocorrelation operation is performed with the width of the signal component obtained from the alignment mark as the period, the noise level due to the non-stationary noise and the stationary noise source can be sufficiently reduced, and the (center) of the mark It becomes possible to detect the position accurately. Since the electron beam on the mark needs to be scanned only once, the mark position detection time can be greatly shortened.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. [First Embodiment] FIG. 1 is a block diagram showing the arrangement of the main part of an electron beam exposure apparatus for carrying out the mark position detecting method according to the first embodiment of the present invention. As shown in the figure, the electron beam EB obtained from the electron gun and focused by the electron lens is deflected by the deflector 11, and the wafer 1
Scanning is carried out in the direction of arrow A so as to cross the alignment mark 17 provided on the substrate 6. Here, the length of the portion of the alignment mark 17 which the electron beam EB crosses was 5 μm, the beam diameter of the electron beam was 1 μm, and the scanning distance thereof was 20 μm.

The backscattered electrons RE generated from the electron beam EB irradiation position on the wafer are detected by a backscattered electron detector 12 provided between the deflector and the sample. The detected backscattered electron signal is amplified by the backscattered electron signal amplifier 13, processed by the autocorrelation calculator 14, and then input to the position detection circuit 15. In the position detection circuit 15, the center position of the alignment mark 17 is obtained based on the calculation output of the autocorrelation calculator 14.

Next, the method of detecting the center position of the alignment mark according to the present invention will be described with reference to FIG. 2A to 2D are explanatory views showing a method of detecting the center position according to the present invention. Here, as shown in FIG. 2A, it is assumed that a roughness 18 on the sample has occurred near the alignment mark 17. In that case, the reflected electron signal Y
As shown in FIG. 2B, (I) has a waveform having a stationary noise component at that location.

Next, the width of the signal component generated from the mark portion with respect to the reflected electron signal Y (I) is calculated as the correlation calculation width J.
As a result, the autocorrelation calculation shown in the equation (1) is performed. Z (I) = ΣY (J) × Y (I + J) (1) (However, the range of Σ, that is, the change range of J is from J1 to J
(Up to 2) At this time, the correlation calculation width J is set to 6 μm which is the width of the signal component generated from the mark portion. By this autocorrelation calculation, a signal having a cycle shorter than the correlation calculation width J is removed or sufficiently attenuated. FIG. 2C is a waveform diagram of the autocorrelation calculation output Z (I) obtained by this calculation result. Next, at the point where this autocorrelation calculation output Z (I) crosses the slice level, a trigger signal is generated as shown in FIG. The center position of the mark can be obtained by obtaining

Since it has become possible to accurately detect the alignment mark in this way, the conventional 20%
It has become possible to reduce the misalignment of the drawing pattern due to the position measurement error of the alignment mark that has occurred to about 3%.

Further, unlike the conventional method, it is not necessary to perform a large number of scans and signal integrations in order to improve the S / N, and it is possible to accurately detect the mark center position with one electron beam scan. , The detection time can be greatly shortened. For example, the detection time was shortened to 1/20 as compared with the conventional case where electron beam scanning and signal integration were performed 20 times in order to improve the S / N.

As a result, the conventional example (first and second improvement plans)
However, the drawing time of 197 seconds is required for each 6-inch wafer, and the mark detection time is about 30 seconds, but the method of the present invention reduces the position detection time of the alignment mark. Since it is possible to reduce the time by 28 seconds, it is possible to reduce the processing time per wafer to 169 seconds. Therefore, the number of wafers drawn per hour could be increased from about 18 in the conventional case to about 21.

[Second Embodiment] FIG. 3 is a block diagram showing the arrangement of the main part of an electron beam exposure apparatus for carrying out the mark position detecting method according to the second embodiment of the present invention. Figure 3
In the above, since the same reference numerals are given to the same parts as those in FIG. 1, duplicate description will be omitted. Also,
Also in the case of this embodiment, the length of the portion of the alignment mark 17 which the electron beam EB crosses is 5 μm, the beam diameter of the electron beam is 1 μm, and its scanning distance is 20 μm.

In the present embodiment, the output signal of the backscattered electron signal amplifier 13 is subjected to a first-order differential operation in the differentiating circuit 19, and the operation result is input to the autocorrelation operator 14. FIG. 4 is a signal waveform diagram for explaining the mark position detecting method according to the present embodiment. As shown in FIG. 4A, when the roughness 18 on the sample is generated in the vicinity of the alignment mark 17, the primary differential signal Y ′ (I) of the reflected electron signal Y (I) is changed to that of FIG. ), The waveform has a stationary noise component. Next, with respect to the first-order differential signal Y '(I), the autocorrelation calculation shown in the equation (1)' is performed with the width of the signal component generated from the mark portion as the correlation calculation width J. At this time, the correlation calculation width J is set to 6 μm, which is the width of the signal component generated from the mark portion. Z ′ (I) = ΣY ′ (J) × Y ′ (I + J) (1) ′

By this autocorrelation calculation, signals having a cycle shorter than the correlation calculation width J are removed or sufficiently attenuated. The waveform of the autocorrelation calculation output Z '(I) obtained at this time is shown in FIG. 4 (c). Therefore, the center position of the mark can be obtained from the autocorrelation calculation output Z '(I) by measuring the distance between the peaks of the signal in the same manner as the conventional method. Here, the distance between the peaks of the measured signals was 5 μm, and thus the mark width was 5 μm.

In this case, by setting the width of the signal component generated from the mark portion as the correlation calculation width J, the noise component that is constantly generated due to the roughness on the sample near the mark is the autocorrelation calculation output Z '( In I), the mark position was removed, and therefore accurate mark position detection was possible without this influence. Further, unlike the conventional method, it is not necessary to perform a large number of scannings and signal integrations in order to improve the S / N, and it is possible to accurately detect the mark width with a single electron beam scanning. It has become possible to significantly reduce

The preferred embodiment has been described above.
The present invention is not limited to these examples, and various modifications can be made without departing from the scope of the present invention. For example, the width of the alignment mark, the scanning distance of the electron beam, and the beam diameter of the electron beam described in the embodiments can be appropriately changed. Further, the autocorrelation calculation width is not limited to the width used in the present embodiment, but may be any width as long as the signal component obtained from the mark to be detected, and may be an appropriate width according to the size of the mark used. Values can be used.

[0026]

As described above, according to the present invention, an autocorrelation calculation is performed on the reflected electron signal obtained by scanning the alignment mark, and the mark position is detected based on the calculation result. Therefore, according to the present invention, accurate position detection can be performed by scanning the electron beam once, and the position detection time can be greatly shortened. Further, by performing the autocorrelation calculation, it is possible to sufficiently suppress the stationary noise component such as the roughness on the sample, so that the accurate position detection can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of an electron beam exposure apparatus for explaining a first embodiment of the present invention.

FIG. 2 is a signal waveform diagram for explaining the operation of the first embodiment of the present invention.

FIG. 3 is a block diagram of an electron beam exposure apparatus for explaining a second embodiment of the present invention.

FIG. 4 is a signal waveform diagram for explaining the operation of the second embodiment of the present invention.

FIG. 5 is a block diagram of an electron beam exposure apparatus for explaining a conventional example.

FIG. 6 is a signal waveform diagram for explaining the operation of the conventional example.

FIG. 7 is an explanatory diagram for explaining another conventional example.

[Explanation of symbols]

 11 deflector 12 backscattered electron detector 13 backscattered electron signal amplifier 14 autocorrelation calculator 15 position detection circuit 16 wafer 17 alignment mark 18 roughening on sample 19 differentiating circuit EB electron beam RE backscattered electron

Claims (4)

[Claims] 1. A method for detecting an alignment mark when a pattern is drawn on the sample by electron beam exposure with reference to the alignment mark arranged on the sample, wherein the alignment mark is scanned with an electron beam. The reflected electron signal obtained by performing autocorrelation calculation with the approximate value of the width of the signal component obtained from the alignment mark as the period, and determining the mark position based on the obtained calculation result. Mark position detection method in electron beam exposure. 2. A method of detecting an alignment mark when a pattern is drawn on the sample by electron beam exposure with reference to the alignment mark arranged on the sample, wherein the electron beam scans the alignment mark. The backscattered electron signal obtained by the above is subjected to a differential calculation process, and the obtained first differential signal is subjected to an autocorrelation calculation using the approximate value of the width of the signal component obtained from the alignment mark as a cycle. A mark position detecting method in electron beam exposure, characterized in that the mark position is determined based on the obtained autocorrelation calculation result. 3. An electron beam source, deflection means for controlling the electron beam emitted from the electron beam source so as to scan the alignment mark of the sample, and reflection for detecting backscattered electrons from the scanned sample. An electron detector, an autocorrelation calculation circuit that performs an autocorrelation calculation on the output signal of the backscattered electron detector, and a position that determines the position of the alignment mark on the sample based on the calculation result of the autocorrelation calculation circuit. A detection circuit, and a mark position detection device for electron beam exposure. 4. An electron beam source, a deflection means for controlling the electron beam emitted from the electron beam source to scan an alignment mark of a sample, and a reflection unit for detecting reflected electrons from the scanned sample. An electron detector, a differentiation circuit that performs a differentiation operation on the output signal of the backscattered electron detector, and an autocorrelation calculation circuit that performs an autocorrelation operation on the output signal of the differentiation circuit,
A position detecting circuit for determining the position of the alignment mark on the sample based on the calculation result of the autocorrelation calculating circuit, and a mark position detecting apparatus in electron beam exposure.