JPS6246976B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a positioning mark structure that allows accurate position detection by electron beam scanning.

In recent years, as the density of semiconductor integrated circuits has increased, electron beams have been used directly instead of conventional ultraviolet rays to write patterns in order to obtain geometric configurations suitable for desired patterns on semiconductor wafers. Development of ring graphite technology is progressing.

In particular, when the sample to be exposed is a semiconductor wafer coated with photoresist,
In other words, in the case of wafer direct exposure, various patterns are usually formed on the semiconductor wafer corresponding to various processes in semiconductor circuit manufacturing, and the patterns to be exposed are precisely formed on these patterns. It is necessary to expose while aligning.
To meet this requirement, when directly exposing a wafer using an electron beam exposure system, marks are usually placed on the wafer to indicate reference positions, either in advance or simultaneously with pattern formation in the first stage of the semiconductor integrated circuit manufacturing process. A mark is formed, and in the subsequent pattern exposure process, this alignment mark is scanned with an electron beam just before exposure with an electron beam, and the position of the exposure pattern is detected by precisely detecting the position of the alignment mark. is kept within the desired accuracy.
Therefore, the position of the alignment mark can be detected more accurately as the sharpness of the maximum or minimum point of the signal waveform obtained by scanning the alignment mark with an electron beam increases.

Conventionally, the above-mentioned alignment marks have been made using a V-shaped groove formed using an anisotropic etching solution on a silicon substrate whose surface orientation is (100) and whose wall surface is (111), or a silicon substrate whose surface orientation is (111). In most cases, steps formed in a silicon oxide film are used. Therefore, as the various processes in the manufacture of semiconductor integrated circuits are carried out,
Silicon oxide, silicon nitride, polysilicon, etc. are deposited in the V-shaped groove or step, and as a result, the sharpness of the maximum and minimum points of the signal waveform obtained by scanning the alignment mark with an electron beam decreases, and thus There was a problem in that the detection accuracy of the position of the alignment mark decreased.

In order to clarify these drawbacks, the conventional method using a V-shaped groove will be further explained with reference to FIG.

FIG. 1a is a sectional view of a conventional alignment mark using a V-shaped groove, and FIG. 1b is a reflected electron current waveform obtained by scanning the V-shaped groove alignment mark with an electron beam. In Fig. 1a, 11 is a V-shaped groove alignment mark whose surface orientation is (100), 20, 2
1 and 22 indicate the incident position of the incident electron beam, and 3
1 indicates a deposited film of silicon oxide, silicon nitride, polysilicon, or the like. In Figure 1b, 41 is the above V
42 is a signal waveform obtained by electron beam scanning when there is no deposited film 31 such as silicon oxide on the V-shaped groove alignment mark 12, and 42 has the V-shaped groove alignment mark 12; This is a signal waveform obtained by electron beam scanning when a deposited film 31 of silicon oxide or the like is present on top of the deposited film 31.
1 is a setting threshold level used in a positioning method in which the center position between two points where the signal intensity matches the setting threshold level is set as the alignment mark position, as an example of the alignment mark position determination method. . In FIG. 1b, the sharpness of the minimum point of the signal waveform corresponding to the incident position 22 of the incident electron beam is
It is lower than without it. Therefore, the accuracy in determining the position of the two points whose signal intensity matches the set threshold level is reduced, and the accuracy in detecting the position of the alignment mark is therefore reduced. That is, in the case of the conventional V-shaped groove alignment mark,
It can be seen that as the semiconductor integrated circuit is manufactured through various processes, the alignment accuracy deteriorates.

In view of the above-mentioned points, it is an object of the present invention to provide an alignment mark whose position detection accuracy hardly deteriorates even after going through various processes in manufacturing semiconductor integrated circuits when directly exposing a wafer using an electron beam exposure device. , and to improve the sharpness of the maximum and minimum points of the signal waveform obtained by scanning the alignment mark with an electron beam in order to improve alignment accuracy.

A feature of the present invention is that at least two or more V-shaped grooves are formed in a silicon substrate, and the length of the flat part of the convex part between adjacent V-shaped grooves is 4.0 μm or less for electron beam exposure. These are alignment marks.

This invention will be explained below.

FIG. 2a is a sectional view of an embodiment of the alignment mark according to the invention, and FIG. 2b is a reflected electron current signal waveform obtained by scanning the alignment mark according to the invention with an electron beam. 1 in Figure 2 a
11 is a silicon substrate whose plane orientation is (100);
12 is an alignment mark composed of two V-shaped grooves whose wall faces have a (111) orientation formed by anisotropic etching; 151 is a flat convex portion between the two V-shaped grooves; 120 ,121,12
2,123 indicates the incident position of the incident beam, 13
1 indicates a deposited film of silicon oxide, silicon nitride, polysilicon, or the like. In FIG. 2b, 141 is a signal waveform obtained by electron beam scanning when the alignment mark 112 is present and there is no deposited film 131 of silicon oxide or the like on it.
is a signal waveform obtained by electron beam scanning when the alignment mark 112 is present and a deposited film 131 of silicon oxide or the like is present thereon.
In addition, 161 is a setting threshold level used in a positioning method in which the alignment mark position is the center position between two points where the signal strength matches the setting threshold level, as an example of the alignment mark position determination method. be.

In FIG. 2b, the incident position 122 of the incident beam
The sharpness of the minimum point corresponding to is lower when the deposited film 131 is present than when the deposited film 131 is not present. On the other hand, the sharpness of the maximum point corresponding to the incident position 123 of the incident beam is almost the same with or without the deposited film 131. This is because the deposited film 131 is thickly deposited on the concave portions of the alignment mark 112, and thinly deposited or hardly deposited on the convex portions. 13
1, and as a result, the sharpness of the minimum point of the signal waveform corresponding to the concave portion of the alignment mark 112 decreases. On the other hand, when the deposited film 131 is present, the reflected electron efficiency of the convex portion is almost unchanged compared to when the deposited film 131 is present, and as a result, the sharpness of the maximum point of the signal waveform corresponding to the convex portion of the alignment mark 112 is remains almost unchanged. Therefore, the accuracy of positioning the two points whose signal strength matches the set threshold level 161 hardly decreases, and the accuracy of detecting the position of the alignment mark hardly decreases.

As described above, compared to the conventional case where one V-shaped groove is used as an alignment mark, when two adjacent V-shaped grooves according to the present invention are used as an alignment mark, it is easier to process the semiconductor integrated circuit manufacturing process. It can be seen that the decrease in position detection accuracy that occurs as the value increases becomes almost negligible.

Further, the signal magnitude or the sharpness of the signal waveform at the maximum point of the signal waveform corresponding to the convex portion of the alignment mark 112 is determined by the length of the convex flat portion 151 between the two V-shaped grooves of the alignment mark 112. f and V
It varies depending on the depth d of the shaped groove. This point will be explained with reference to FIG.

FIG. 3a shows how the reflected electron intensity I changes depending on the depth d of the V-shaped groove and the length f of the convex flat part 151 when the incident electron beam is incident on the incident position 123 in FIG. The curve 21
1, 212, 213, 214, and 215, the length f of the convex flat portion 151 is 1.5 μm and 2.0 μm, respectively.
2.5 μm, 3.0 μm, and 4.0 μm, and for comparison, a curve 216 is shown for the case where the incident electron beam is incident on the incident position 121 in FIG. 2. The reflected electron intensity I increases as the depth d of the V-shaped groove increases, but d≧1.5
In the range of μm, it is almost constant and increases as the length f of the flat part becomes smaller, but f
Almost the same changes are shown in the range of ≦2.0 μm. Furthermore, in order to facilitate the design of a signal processing system for position detection, the intensity of reflected electrons when incident on the incident position 123 is greater than the intensity of reflected electrons when incident on the incident position 121 in FIG. It is necessary that f≦
It turns out that 4.0 μm is sufficient.

Next, FIG. 3b shows the sharpness of the maximum point of the reflected electron current waveform when the incident electron beam enters the incident position 123 in FIG.
It shows how the shape changes depending on the depth d of the groove and the length f of the flat part of the convex part 151, and the curves 221, 222, 223, 224, and 225 respectively correspond to the length f of the flat part of the convex part. is 1.5μm, 2.0μm, 2.5
The cases of μm, 3.0 μm, and 4.0 μm are shown. As can be seen, the sharpness of the maximum point of the reflected electron current waveform increases as the depth d of the V-shaped groove increases, but it remains almost constant in the range of d 1.5 μm, and the sharpness of the maximum point of the reflected electron current waveform increases as the depth d of the V-shaped groove increases, but it remains almost constant in the range of d 1.5 μm, and the sharpness of the maximum point of the reflected electron current waveform increases as the depth d of the V-shaped groove increases. As f becomes smaller, it becomes larger, but it tends to be saturated in the range of f2.0 μm.

According to Fig. 3 a and b, two adjacent V-shaped grooves are used as alignment marks as described above, and the length f of the flat part of the convex part between two adjacent V-shaped grooves is set to f≦4.0 μm. A signal for highly accurate position detection can be obtained by setting the range to .

Here, it will be stated that the above range does not depend on the exposure conditions, that is, the accelerating voltage and current of incident electrons for exposure, the type and thickness of the resist, the type, sensitivity and arrangement of the backscattered electron detector.

Regarding the accelerating voltage and current of incident electrons for exposure,
An accelerating voltage of 15 to 20 KV is normally used, and in this voltage range, the distance that incident electrons are scattered in the substrate and travel laterally from the incident position is approximately 2 μm on one side. This value faithfully reflects the behavior of incident electrons, and examines whether the incident electrons repeatedly collide and scatter with sample constituent atoms in the sample, lose energy and stop, or jump out from the sample surface again and become backscattered electrons. This has also been confirmed by calculations using the Monte Carlo method.

Regarding the behavior of the electron beam incident on the substrate, the results of Monte Carlo calculations for aluminum, which has almost the same electron scattering ability as silicon, which is the constituent material of the substrate of the present invention, were reported by K. Murata in J. Appl.
It is reported in detail in Phys.Vol.45, No.9 (1974) pp4110-4117, and Fig. 4(a) on p4113 of the same paper
When the incident electron energy is 20KV, the distance that an electron beam incident perpendicularly to the substrate travels in the lateral direction is approximately 2.0
It is shown that it is μm.

Therefore, when considering reflected electrons on both sides of the incident position as in the present invention, the value on one side is twice the value, that is, f
The effect of the present invention is exhibited within the range of ≦4.0 μm. Furthermore, the magnitude of the current only determines the magnitude of the obtained signal level and does not change the signal waveform itself.

Regarding the type and thickness of the resist, electron beam resists are generally made of light elements such as hydrogen and carbon, and the degree of scattering of incident electrons is very small compared to silicon substrates. The type and thickness of the resist are not factors that change the signal waveform itself.

Regarding the type, sensitivity, and placement of the backscattered electron detector, these are requirements that determine the energy range or scattering direction range of the scattered backscattered electrons. has no special energy dependence or scattering direction dependence. This is because the scattering phenomenon of electrons in the sample is essentially a random phenomenon, and therefore the increase or decrease in the number of reflected electrons due to the unevenness of the sample surface does not vary greatly depending on the reflected electron energy or scattering direction.

As described above, it is clear that the range of f≦4.0 μm according to the present invention does not depend on the exposure conditions.

In the above explanation, we did not discuss in detail the energy of incident electrons, that is, the accelerating voltage, but
The above explanation similarly applies within the range of acceleration voltages used in ordinary electron beam exposure apparatuses, that is, the range of acceleration voltages of 10 to 20 KV.
Moreover, although the case where the number of V-shaped grooves is 2 has been described as an example, the same applies to the case where the number of V-shaped grooves is 3 or more. Furthermore, it goes without saying that any crystal that can form the V-shaped groove in the same manner as in the case of a silicon substrate with a plane orientation of (100) can be similarly applied.

As explained in detail above, the present invention is applicable to direct exposure of a wafer using an electron beam exposure apparatus, in which two or more silicon substrates having a wall orientation of (111) are attached to a silicon substrate with a (100) orientation. Using alignment marks that form V-shaped grooves and set the length of the flat part of the convex part between adjacent V-shaped grooves to be 4.0 μm or less, find the maximum point corresponding to the center of the flat part of the backscattered electron current waveform. By using this for position detection, the position detection accuracy does not deteriorate even after the semiconductor integrated circuit manufacturing process. Therefore, the accuracy of microfabrication technology such as LSI manufacturing using electron beam exposure equipment improves, and Highly integrated, higher performance LSI
It has the advantage of being easy to manufacture.

[Brief explanation of the drawing]

Figure 1a is a cross-sectional view of a conventional alignment mark using a V-shaped groove, and Figure 1b is a reflected electron current obtained by passing an electron beam through the V-shaped groove alignment mark in Figure 1a. It is a signal waveform. FIG. 2a is a sectional view of an embodiment of the alignment mark according to the present invention, and FIG. 2b is a reflected electron current signal waveform obtained by scanning the alignment mark according to FIG. 2a with an electron beam. Figure 3a shows the depth d of the V-shaped groove and the length f of the flat part of the convex part of the reflected electron intensity I when the incident electron beam enters the incident position 123 in Figure 2.
FIG. 3b shows the sharpness of the maximum point of the reflected electron current waveform when the incident electron beam enters the incident position 123 in FIG. FIG. 3 is a diagram showing the dependence of the value width δ on the V-shaped groove depth d and the length f of the flat portion of the convex portion. In the figure, 11 and 111 are silicon substrates whose surface orientation is (100), 12 and 112 are V-shaped grooves whose wall surfaces are oriented (111), and 20, 21, 22, 12
0, 121, 122, 123 are the incident positions of the incident electron beams, 31, 131 are deposited films such as silicon oxide films, 41, 141 are signal waveforms when there is no deposited film, and 42, 142 are when there is a deposited film. signal waveform, 151 is the flat part of the convex part between the V-shaped grooves, 61,
161 is a set threshold level for determining the alignment mark position, 211, 212, 21
3, 214, and 215 have the length of the flat part of the convex part of 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, and 4.0 μm, respectively.
216 is the reflected electron intensity when the electron beam enters the incident position 123, and 216 is the reflected electron intensity when the incident electron beam enters the incident position 121.
221, 222, 223, 224, and 225 have a convex flat part length of 1.5 μm, 2.0 μm, and 2.5 μm, respectively.
The sharpness of the maximum point of the reflected electron current waveform when the electron beam is incident on the incident position 123 is evaluated in terms of half-width when the electron beam is 3.0 μm, 4.0 μm.

Claims (1)

[Claims] 1. An alignment mark for electron beam exposure in which at least two or more V-shaped grooves are formed on a silicon substrate, and the length of the flat part of the convex part between adjacent V-shaped grooves is 4.0 μm or less.