JP2840959B2 - Focus setting method for electron beam lithography exposure apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a focus setting method of an electron beam lithography exposure apparatus that draws and exposes a predetermined resist pattern on a substrate by electron beam lithography.
By establishing a method of setting the focus so that it falls within the depth of focus, the aim is to realize an electron beam lithography exposure apparatus that enables excellent resolution and fine processing. A step of obtaining a first focus setting position with a focus setting mark provided on a focus setting mark portion of the substrate, and then an area for forming a pattern on the substrate, that is, a device pattern Calculating an arithmetic mean of the height of the uppermost part and the height of the lowest part of the concavities and convexities in the region; and calculating the position obtained by adding the arithmetic mean to the first focus setting position at the time of electron beam writing exposure. Setting a focus setting position.

[Industrial applications]

The present invention relates to a focus setting method of an electron beam lithography exposure apparatus for writing and exposing a predetermined resist pattern on a substrate by electron beam lithography.

[Conventional technology]

(1) Outline of Electron Beam Writing Exposure Apparatus Since an electron beam writing exposure apparatus can perform high-resolution exposure, it is necessary to draw a resist pattern in, for example, a wafer process in an integrated circuit manufacturing process in which high integration is advanced. It is used as a device.

FIG. 3 is a block diagram for explaining the outline of the electron beam drawing exposure apparatus.

In the electron beam drawing exposure, a predetermined resist pattern is created by directly drawing and exposing an electron beam resist applied to the substrate 6 with an electron beam.

Therefore, the electron beam image exposure apparatus includes an electron lens 2 and an electron lens control unit 9 for focusing the electron beam on the substrate 6, a reflected electron detector 8 for detecting the focusing state of the electron beam, and a focus detection unit. 10. It comprises a deflector 3 for scanning an electron beam to a predetermined position and a scanning control unit 11, and a control unit 12 for controlling the electron lens control unit 9, the focus detection unit 10, and the scanning control unit 11 overall.

That is, the electron beam 4 emitted from the electron gun 1 is focused on the substrate 6 by the electron lens 2 and scanned by the deflector 3.

Therefore, accurately focusing the electron beam 4 focused on the substrate 6 is a defining factor of the resolution in the electron beam writing exposure.

(2) Conventional focus setting method In the conventional focus setting, a focus adjustment mark 7 provided on a substrate 6 by etching or the like is scanned by an electron beam 4, and electrons reflected by the focus adjustment mark 7 at that time are scanned. The focal point of the electron beam 4 is controlled and set so that the backscattered electrons are most captured by the backscattered electron detector 8.

4A and 4B are views for explaining the principle of setting the focus of an electron beam, wherein FIG. 4A is a sectional end view of a focus adjustment mark provided on a substrate, FIG. 4B is a focus adjustment mark waveform taken by reflected electrons, (C) is the first derivative waveform of (b), and (d) is the second derivative waveform of (c).

In FIG. 2A, when the electron beam 4 scans the focus adjustment mark 7 on the substrate 6, electrons are reflected at the step portion of the focus adjustment mark 7.

FIG. 4B shows a waveform captured from the reflected electrons. The focus detection unit performs a second differentiation on the waveform after the first differentiation (FIG. 3C), and obtains the second differentiation shown in the same drawing (d). Obtain the differential waveform. Then, the electronic lens control unit controls the focus so that the four peak points of the secondary differential waveform have the maximum amplitude.

When the flat surface of the substrate formed in the groove of the focus adjustment mark 7 is focused, the spot of the electron beam 4 reflected on the substrate surface becomes the most point-like,
Converge to this point. On the other hand, when out of focus, the spot of the electron beam 4 on the substrate surface becomes large. Since the reflected electrons are generated by scattering at the corners of the grooves of the focus adjustment mark 7, the smaller the spot of the electron beam 4, the larger the amount of electrons hitting the grooves of the focus adjustment mark 7 at one time, Therefore, the amount of the electron beam scattered by the groove of the focus adjustment mark 7 also increases.

In other words, the time when the electron beam 4 hits the flat surface with the largest aperture is the time when the amount of the reflected electrons is the largest, and the beam width 4a of the electron beam 4 at the focus setting position S shown in FIG. It's time to focus.

[Problems to be solved by the invention]

The substrate surface on which the electron beam writing exposure is performed becomes uneven every time patterning is performed, and has a step.

Therefore, it is a condition for performing exposure with good resolution that the uppermost part and the lowermost part of the unevenness are included in the depth of focus of the electron beam.

On the other hand, for example, integrated circuits (semiconductor devices) that are becoming more highly integrated
And the like, the step of the unevenness tends to increase. On the other hand, in an electron beam lithography exposure apparatus, a higher NA (numerical aperture) of an electron lens advances to increase the resolution, and the depth of focus tends to decrease. .

Therefore, when exposure is performed on a pattern formed in a previous step on a substrate surface, a problem occurs in that the projections of the pattern protrude outside the depth of focus, and conversely, the resolution is reduced.

FIG. 5 is a diagram for explaining the relationship between the device pattern and the depth of focus, and is a sectional end view of the substrate.

Generally, the focus adjustment marks 7 are provided at several places on the substrate 6 and are provided independently of a region to be patterned.

That is, the focus adjustment mark 7 is
And a pattern 15 exists in a device pattern region 14 for patterning an integrated circuit or the like.

As shown in the figure, the depth of focus ln of the electric beam is determined by the position of the upper end of the step of the focus adjustment mark 7, that is, the surface position of the section e indicated by the arrow in FIG. It is between the + (plus) side margin and the-(minus) side margin in the vertical direction.

Therefore, the pattern 15 in the section b shown by the arrow in FIG.
The upper portion protrudes from the + side margin of the depth of focus, and the resolution is reduced when the electron beam resist applied to the portion is exposed. By the way, sections a, c, d, e indicated by arrows in the figure
Is within the depth of focus ln, and the resolution does not decrease.

The technical problem of the present invention is to solve the above problems in the focus setting of the electron beam lithography exposure apparatus, and to set the focus so that the irregularities of all the patterns in the device pattern area fall within the depth of focus. It is an object of the present invention to realize an electron beam lithography exposure apparatus capable of performing excellent resolution and microfabrication by establishing the above.

[Means for solving the problem]

FIG. 1 is a diagram for explaining the basic principle of the present invention.
FIG. 3B is a sectional end view of the substrate, FIG. 4B is a histogram of a step in the device pattern area, and FIG.

The present invention is a focus setting method for performing correction in consideration of unevenness of a device pattern area to a focus position obtained by a focus adjustment mark.

That is, in an electron beam exposure apparatus that exposes a resist applied to the surface of the substrate 6 with an electron beam, a focus adjusting mark 7 provided on a focus setting mark portion 13 of the substrate 6
To obtain the initial focus setting position S, and then, among the unevenness of the resist layer in the pattern formation region 14 on the substrate 6, the uppermost height Hh and the maximum height Hh based on the initial focus setting position S. A step of obtaining an intermediate height Hn from the lower height HL, and setting the intermediate height Hn to the initial focus setting position S
And setting the position added to the focus position as a focus setting position at the time of electron beam drawing exposure.

[Action]

As shown in FIG. 1C, in the focus setting method of the present invention, an initial focus setting position S is first obtained by using the focus adjustment mark 7. In this case, the initial focus setting position S is the bottom surface of the focus adjustment mark 7 in the figure, but may be the surface of the substrate 6 as shown in FIG. 5, for example. Then
The top height Hh of the unevenness of the resist layer in the pattern formation region 14 based on the obtained initial focus setting position S.
An intermediate height Hn between the height and the lowermost height HL is obtained, and a position obtained by adding the intermediate height Hn to the initial focus setting position S is set as a focus setting position for electron beam drawing exposure.

That is, the focal position at the time of electron beam writing exposure is located exactly at the middle of the unevenness of the device pattern area 14.

The depth of focus ln is between the plus side margin and the minus side margin around the intermediate position.

Therefore, the uppermost and lowermost patterns 15 of the device pattern area 14 can be accommodated within the same depth of focus margin, and the uppermost and lowest parts of the pattern 15 do not protrude outside the depth of focus ln.

 As a result, the resolution at the time of exposure does not decrease.

〔Example〕

 FIG. 2 is a block diagram illustrating an embodiment.

The electron beam lithography exposure apparatus 16 includes an electron beam control system 17 and an electron lens control system 18, and performs electron beam scanning and focus setting. The exposure apparatus 16 sets and controls the focus of the electron beam by the focus setting method described in FIG.

In the present embodiment, a distance measuring device using a laser beam is added to the electron beam writing / exposure device 16, and the unevenness of the device pattern area on the semiconductor wafer 6a is measured.

 Next, the operation will be described.

1) The semiconductor wafer 6a is irradiated with the laser beam from the laser light source 19 via the reflection mirror 20 and the deflection beam splitter 21.

2) The laser beam reflected from the semiconductor wafer 6a is detected by the photo detector 22.

3) From the output signal of the photodetector 22, the signal detection unit 23
Outputs the distance measurement result.

4) The histogram processing unit 24 performs a histogram process on the distance measurement result in the above 3).

5) The lens correction value calculation unit 25 calculates an arithmetic mean value between the maximum value and the minimum value from the result of the histogram processing in 4), and outputs a focus correction signal corresponding to the arithmetic mean value to the electron beam writing / exposure device 16. To the electronic lens control system 18.

6) The electronic lens control system 18 sets the focus by adding the position corresponding to the focus correction signal of 5) to the focus position obtained from the focus adjustment mark on the semiconductor wafer 6a.

As described above, the focal position at the time of drawing exposure can be corrected and set to the middle point of the unevenness in the device pattern area.

In general, the height difference between the uppermost portion and the lowermost portion of the unevenness of the pattern area is equal to or less than the depth of focus margin. However, as the NA of the electron lens is increased, the depth of focus margin is becoming smaller and smaller. The method of the present invention, in which equal depth of focus margins are obtained at the uppermost part and the lowermost part of the section, is excellent in that it enables extremely flexible and highly accurate focus setting corresponding to the device pattern.

Therefore, by focusing on the middle point of the irregularities, the top or bottom of the irregularities does not exceed the depth of focus margin, and stable exposure can always be performed.

〔The invention's effect〕

As described above, according to the focus setting method of the present invention, the height of the uppermost part of the unevenness of the resist layer in the pattern formation region 14 is determined with reference to the initial focus setting position S obtained using the focus adjustment mark 7. An intermediate height Hn between Hh and the lowermost height HL was obtained, and a position obtained by adding the intermediate height Hn to the initial focus setting position S was set as a focus setting position at the time of electron beam drawing exposure. The focus can be set at an intermediate point between the uppermost portion and the lowermost portion of the device pattern area to be exposed by the exposure.

Therefore, the pattern in the device pattern area does not protrude beyond the depth of focus, and exposure with extremely high resolution can be performed on the pattern.

As a result, it is possible to realize an electron beam lithography exposure apparatus capable of performing excellent resolution and fine processing even on a substrate having large surface irregularities.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view for explaining the basic principle of the present invention. FIG. 1 (a) is a sectional end view of a substrate, FIG. 1 (b) is a histogram of steps in a device pattern area, and FIG. FIG. 2 is a block diagram illustrating an embodiment, FIG. 3 is a block diagram illustrating an outline of an electron beam exposure apparatus, and FIG. 4 is an electron beam. Is a diagram for explaining the focus setting principle of
(A) is an end view of a cut portion of the focus adjustment mark provided on the substrate, (b) is a focus adjustment mark waveform taken by backscattered electrons, (c) is a first derivative waveform of (b), and (d) is Fig. 5 is a diagram for explaining the relationship between the device pattern and the depth of focus, and is a sectional end view of the substrate. In the figure, 1 is an electron gun, 2 is an electron lens, 3 is a deflector, 4 is an electron beam, 4a is a beam width, 5 is a stage, 6
Is a substrate, 6a is a semiconductor wafer, 7 is a focus adjustment mark, 8
Is a backscattered electron detector, 9 is an electron lens control unit, 10 is a focus detection unit, 11 is a scan control unit, 12 is a control unit, 13 is a focus setting mark unit, 14 is a device pattern area, 15 is a pattern, and 16 is an electron. Beam drawing exposure apparatus, 17 is an electron beam control system, 18 is an electron lens control system, 19 is a laser light source, 20 is a reflection mirror,
21 is a polarizing beam splitter, 22 is a photodetector, 23
Denotes a signal detection unit, 24 denotes a histogram processing unit, and 25 denotes a lens correction value calculation unit.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/027 G03F 7/20 504 G03F 7/20 521

Claims (1)

(57) [Claims] An electron beam exposure apparatus for exposing a resist applied on the surface of a substrate (6) by an electron beam, wherein a focus adjusting mark (7) provided on a focus setting mark portion (13) of the substrate (6) is used. Calculating the initial focus setting position (S) using the initial focus setting position (S) among the irregularities of the resist layer in the pattern formation region (14) on the substrate (6). A step of obtaining an intermediate height (Hn) between an upper height (Hh) and a lowermost height (HL); and adding the intermediate height (Hn) to the initial focus setting position (S). Setting a position as a focus setting position at the time of electron beam writing exposure.