JPH03263813A - Apparatus and method for electron-beam lithography - Google Patents

Abstract

PURPOSE:To obtain an optimum irradiation amount in order to obtain an accurate pattern size without executing a trial drawing operation even when a substrate structure or a resist film thickness is different by installing the following: a detector which detects an electron beam radiated from a specimen to be drawn; and a means which controls the irradiation amount by using an output signal of the detector. CONSTITUTION:In an electron-beam lithography apparatus, the following are provided: a detector 7 which radiates an electron beam 2 having a prescribed current value to a specific position on a specimen 5 to be drawn and which detects at least one out of reflected electrons radiated from the specimen 5 to be drawn or secondary electrons; and a means which controls the irradiation amount by using the intensity of a signal detected by the detector 7. For example, said specific position is a region of a target for alignment use on the specimen 5 to be drawn. A signal intensity (S) of reflected electrons at the time when a target pattern is irradiated with the electron beam 2 is measured; the ratio of the (S) to at signal intensity (S0) of reflected electrons of a standard specimen housed in a register 18 is found; an irradiation-time signal from an irradiation-time setting circuit 12 is corrected by using a signal of the ratio S/S0; and the corrected signal is impressed to an irradiation-time control circuit 8.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electron beam lithography apparatus and an electron beam lithography method, and more particularly, to an electron beam lithography apparatus and an electron beam lithography method, and more particularly, to an electron beam lithography apparatus and an electron beam lithography method. The present invention relates to an electron beam lithography apparatus and an electron beam lithography method suitable for determining the irradiation amount.

[Prior Art] Since the electron beam drawing method has a higher resolution than the conventional optical transfer method, it is used as a technique for forming fine patterns on semiconductor wafers in the manufacture of LSIs and the like.

What is important in electron beam lithography is to improve the precision of formed patterns and to increase the throughput in pattern lithography.

Fine pattern drawing is usually performed using an electron beam drawing device. That is, in an electron beam drawing apparatus, an electron beam emitted from an electron gun is focused by an electron lens, deflected by a deflection lens, and irradiated onto a sample to be drawn. At this time,
The drawing pattern data stored in the storage device is subjected to calculations such as lens distortion correction by a computer, and is then applied to the deflection lens by the deflection control circuit. At this time, in order to align the pattern with the pattern already drawn on the sample to be drawn, a backscattered electron detector detects the backscattered electrons when the target pattern provided on the sample to be drawn is irradiated with an electron beam. The above location information is imported into the computer. Position correction is calculated based on this detection information, and feedback is applied to the deflection position through the deflection control circuit. Further, the irradiation amount of the electron beam is controlled based on the irradiation time stored in the irradiation time setting register in advance. As a document related to such an electron beam lithography apparatus, there is, for example, the published patent publication ``JP-A-63-285933J.

Electrons irradiated during electron beam lithography usually pass through an electron beam resist film and enter the substrate. At this time, secondary electrons are generated, or the incident electrons are reflected by the substrate material or the electron beam resist itself and irradiate the electron beam resist again. Therefore, the sensitivity of the electron beam lens l~ changes depending on the type and film thickness of the substrate material or the film thickness of the electron beam resist. Therefore, in order to determine the amount of electron beam irradiation required to obtain the correct pattern dimensions in the conventional electron beam lithography method, it is necessary to test the electron It was necessary to perform line drawing and find the optimal dose conditions.

[Problems to be Solved by the Invention] As mentioned above, in conventional electron beam lithography apparatuses and electron beam lithography methods, in order to correct the irradiation dose due to secondary electrons and reflected electrons, tests are performed using separate samples. Since it was necessary to draw a target, the device had disadvantages in that it was difficult to operate and took a long time.

Therefore, an object of the present invention is to provide an electron beam lithography apparatus and an electron beam lithography system capable of determining the optimum irradiation dose in order to obtain accurate pattern dimensions without performing trial lithography even for different substrate structures or resist film thicknesses. The purpose is to provide a method.

[Means for Solving the Problems] In order to achieve the above object, the electron beam lithography method of the present invention uses an electron beam with a constant current value that does not affect the lithography pattern to be drawn on the target sample. The electron beam is irradiated onto a specific area, the electron beam emitted from the sample to be drawn is detected, and the signal is used to calibrate the amount of electron beam irradiation necessary for drawing.

In addition, in order to carry out the method of the present invention, a conventional electron beam lithography apparatus is equipped with a detector for detecting the electron beam emitted from the sample to be lithography, and a means for controlling the irradiation amount using the output signal of the detector. and configure it.

In particular, it is effective to use the region of the target for alignment on the sample to be drawn as the specific region. In addition, in order to deal with variations in the characteristics of the detector, the intensity of the signal obtained when the sample to be drawn is irradiated with the electron beam is calibrated using the intensity of the signal obtained when the standard sample is irradiated with the electron beam.

[Function] The reason why the sensitivity of electron beam resist to electron beam changes depending on the substrate material etc. is that the electron beam collides with the atoms that make up the substrate material and the reflected electron beam sensitizes the electron beam resist again. It is in. Most of these reflected electrons are emitted outside the electron beam resist. Therefore, by detecting the amount of emitted electron beams, it is possible to know the amount of reflected electron beams, that is, the amount of change in sensitivity of the electron beam resist due to differences in substrate materials.

If the sensitivity of the backscattered electron detector varies over time, it becomes impossible to determine the correct dose. Therefore, by irradiating an electron beam onto a standard sample whose intensity of backscattered electrons is known in advance and calibrating the sensitivity of the backscattered electron detector, it is possible to always determine the correct irradiation amount.

In addition, when a sample to be drawn is irradiated with an electron beam, the electron beam resist in that area is exposed to light, but if an area for determining the irradiation amount is provided at a specific position on the sample to be drawn, this will not affect the pattern to be drawn. .

【Example] Hereinafter, the present invention will be explained in detail using examples.

FIG. 1 is a schematic diagram of an embodiment of an electron beam lithography apparatus according to the present invention.

An electron beam 2 emitted from an electron gun 1 is focused by multiple stages of electron lenses 3a and 3b, deflected by a deflection lens 4, and irradiated onto a semiconductor wafer 5, which is a sample to be drawn, mounted on a sample stage 14.

Further, the electron beam 2 is turned on and off by a blanking deflector 6. The irradiation time control circuit 8 is a circuit that generates a control signal for the blanking deflector 6, the deflection control circuit 9 is a circuit that generates a control signal for the deflection lens 4, and the detector 7 detects electron beams such as reflected electrons from the semiconductor wafer 5. a detector for detecting the
5 is a means for displacing and jumping the sample stage 14. The computer 11 performs arithmetic processing based on the drawing pattern data stored in the storage device M13, signals from the detector 7, and signals from an operating device (not shown), and controls the irradiation time control circuit 8.
Appropriate signals are provided to the deflection control circuit 9.

In the electron beam drawing apparatus of this embodiment, in particular, the signal obtained from the detector 7 is used not only to determine the position of the sample 5 to be drawn, but also to control the irradiation time.

A part of the reflected electron signal when the electron beam 2 is irradiated onto the target pattern 21 provided for position setting on the drawing sample 5 described in FIG. 2 is used for position calculation, and is used as position information. Used for correction calculations. At the same time, the signal intensity S of reflected electrons when the electron beam 2 irradiates the target pattern is measured, and the standard sample 2 is stored in the register 18.
Find the ratio s/so of the signal strength s0 of the reflected electrons of 3.

Using the signal of this ratio s/so, it is applied to the irradiation time control circuit 8 which does not modify the irradiation time signal from the irradiation time setting circuit 12.

FIG. 2 shows a plan view of the sample stage 14 and the silicon wafer 19 which is the sample 5 to be imaged. The silicon wafer 19 has a circuit pattern area 2 of a plurality of LSI chips, which is a drawing pattern.
0 and a peripheral area where an LSI chip cannot be formed. In this embodiment, a pattern 21 for measuring the reflection of the electron beam is provided in the peripheral area. Furthermore, in case the reflectance differs within the wafer, a pattern 22 for measuring the reflection of the electron beam is provided within each chip in the circuit pattern area 20 of the plurality of LSI chips. As the pattern 21, a target pattern for wafer positioning as explained in FIG. 5 is used. A standard sample 23, which will be explained later, is mounted on the sample stage 140 frame 24.

FIG. 3 shows the flow of one embodiment of the electron beam lithography method according to the present invention.

The drawing sample 5 is mounted on the sample stage 14 and installed in the electron beam drawing apparatus (step 1).

The signal intensity S of the reflected electrons of the standard sample by the standard sample 23 on the sample stage 14. is measured and aligned in the register 18. However, this step may be omitted as long as the data stored in the register 8 does not need to be updated (step 2).

The deflection is controlled so that the irradiation electron beam 2 irradiates the specific pattern 21 or 22 of the drawing sample 5 (step 3).

The intensity S of reflected electrons from the specific pattern 21 or 22 is measured. When the pattern 21 is a target pattern for positioning, the signal from the detector 7 during positioning is used (step 4).

The intensity S of the reflected electrons and the intensity S stored in the register 18. The intensity ratio s/sI of reflected electrons is determined from (step 5).

The information on the resist sensitivity of the register 17 is expressed as the above intensity ratio s/
s, and correct the irradiation time (Step 6).

Using the corrected irradiation time, the irradiation time control circuit 8 controls the blanking deflection circuit 6 to perform drawing (step 7).

Next, details of the intensity ratio s/s o will be explained. FIG. 4(a) shows a schematic cross-sectional structure of a wafer. A tungsten film 26 having a thickness of d (μm) is deposited on the silicon substrate 25 . On top of this, an electron beam resist 27 having a thickness of 1 μm was spin-coated.

Drawing was performed on the silicon wafer using a variable shaped beam type electron beam drawing device with an acceleration voltage of 30 KV. FIG. 4(b) shows the results of examining changes in the sensitivity of the electron beam resist by varying the thickness of the tungsten 26 on the silicon substrate 25. The sensitivity ratio is shown in the figure, assuming that the sensitivity is 1.0 when d=o, that is, when the substrate is made of only silicon. As is clear from the figure, the sensitivity increases when the tungsten thickness reaches 0.3 μm, but there is no change when the thickness is greater than that.

Further, the reflected electron beam intensity when the pattern 21 for reflection measurement shown in FIG. 2 is irradiated with an electron beam is similarly shown in FIG. 4(c) as a function of the tungsten film thickness. The figure shows relative values, with the strength of the silicon substrate 25 being 1.0.

Compared to the change in sensitivity of the electron beam resist shown in FIG. 4(b), the dependence of the reflected electron beam intensity on the tungsten film thickness is greater, but shows a similar tendency. From these results, a relationship as shown in FIG. 4(d) can be obtained as the relationship between the reflected electron beam intensity ratio and the resist sensitivity ratio.

In this embodiment, the relationship shown in FIG. 4(d) is approximated by the following equation.

R=ao+a1S+a2S2+a3S3+-(1) where R is the sensitivity ratio of the electron beam resist to the standard sample (silicon Si), S is the intensity ratio of the reflected electron beam to the standard sample, and avr ale a2T aff+... is a coefficient. These coefficients take approximately the same value even if the type of material deposited on the silicon substrate changes.

However, when the substrate material is different or when the acceleration voltage of the electron beam lithography apparatus is changed, it is necessary to use different coefficients.

As is clear from FIG. 4(cl), since the reflected electron beam intensity ratio and the resist sensitivity ratio have a nearly linear relationship, equation (1) poses no problem in practice if up to the first-order coefficients are taken into consideration.

In this example, R=0.75+0.255 (2) can be used.

FIG. 5 shows the target pattern 21 used for positioning in the electron beam lithography of the silicon LSI pattern of this embodiment shown in FIG.

FIG. 5(a) is a plan view of the structure, and FIG. 5(b) is a cross-sectional view of the structure. Silicon substrate 28 as target pattern 21
A groove 29 having a depth of about 1 micron is formed in the groove. A tungsten silicide film 30 having a thickness of 0.3 microns is deposited on the silicon substrate 28 as a material to be processed. Further, an electron beam resist 31 having a thickness of 2 microns is spin-coated thereon. Electron beam A-A for alignment
Irradiate the positions 'B-B', c-c', and D-D'.

The backscattered electron signal obtained at the position A-A' is shown in Figure 5 (c
). Normally, only the position of the signal is used, but in this embodiment, the signal strength S obtained in a flat area is used. Signal strength S when a silicon substrate is irradiated with an electron beam. The ratio S = s/s.

In this example, S=1.6. Substituting this into the third equation, R=1. , ], 5. 1/R=
Since it is 0°87, it is 87° compared to the case of a silicon substrate.
It was found that it is sufficient to give an irradiation dose of %.

FIG. 6 is a diagram illustrating the standard sample 33 in FIG. 2. In general, the backscattered electron detector 7 is constantly irradiated with electron beams and therefore tends to be susceptible to changes over time. Therefore, in this embodiment, a pattern 3 made of heavy metals such as gold, platinum, tungsten, molybdenum, tantalum, etc. is used as a standard sample 23 on a silicon substrate 32 as shown in FIG.
3 was used. Figure 6(a) is a plan view, and Figure 6(b) is a
) is the EE' cross section. When this pattern is scanned with an electron beam whose shape and current value have been calibrated, a signal as shown in FIG. 3(c) is obtained. The signal strength s0 is due to reflected electrons from silicon, and the signal strength S is due to reflected electrons from a heavy metal (tungsten in this embodiment). Since the temporal fluctuation of the backscattered electron detector 7 is mainly due to the offset term and gain term, the S obtained in Fig. 6(c)
. and SQ as the coefficient a in equation (1). and a□ can be calibrated. Of course, if the variation in the gain term is small, calibration can be performed using only the signal obtained when silicon is irradiated with an electron beam.

Although the embodiments of the present invention have been described above, it is clear that the present invention is not limited to the above embodiments. For example, the standard sample 23 does not need to be specially provided, and a component made of silicon with a gold pattern formed thereon, which is provided for electron beam irradiation correction, can be used.

[Effects of the Invention] As explained above, according to the present invention, the optimum electron beam irradiation amount can be automatically determined based on the reflected electron beam intensity from the sample to be drawn, which not only improves dimensional accuracy but also improves dimensional accuracy. There is no need to perform trial drawing, and throughput is also improved.

[Brief explanation of drawings]

FIG. 1 is a schematic structural diagram of one embodiment of an electron beam lithography apparatus according to the present invention, FIG. 2 is a plan view of the sample stage and lithography sample shown in FIG. 1, and FIG. 3 is a diagram of an electron beam lithography method according to the present invention. Figure 4 shows the cross-sectional structure of the silicon wafer used in this example, and the relationship between the reflected electron beam intensity ratio and the resist sensitivity ratio. Figure 5 (a,), ( b) and (c)
6(a), (b), and (c) are respectively a plan view and a cross-sectional view showing the structure of a target for alignment, and a diagram showing a reflected electron beam signal obtained when scanning an electron beam.
These are a plan view and a cross-sectional view showing a pattern for calibrating the relational expression between the backscattered electron beam intensity ratio and the resist sensitivity ratio, and a diagram showing a backscattered electron beam signal obtained when scanning the electron beam. DESCRIPTION OF SYMBOLS 1... Electron gun, 2... Electron beam, 3a, 3b... Electron lens, 4... Deflection lens, 5... Sample to be drawn, 6...
Blanking deflector, 7... Backscattered electron detector, 8...
- Irradiation time control circuit, 9...Deflection control circuit, 1o...
Backscattered electron signal processing circuit, 11... Control computer, 12... Irradiation time setting circuit, 13... External storage device, 14... Sample stand, 15... Sample stand mailing section, 16
...Sample stage translation control circuit, 17...Regist sensitivity register. 18... Standard strength register, 19... Silicon wafer, 20... LSI circuit pattern, 21.22...
Pattern for measuring amount of backscattered electrons, 23... Standard sample,
24...Frame, 25.28.32...Silicon substrate,
26.33...Tungsten film, 27.31...
Electron beam resist, 29... Groove provided for positioning, 30... Tungsten silicide film.

Claims (1)

[Claims] 1. In an electron beam lithography system, an electron beam having a predetermined current value is irradiated onto a specific position on a sample to be drawn, and reflected electrons or secondary electrons emitted from the sample to be drawn are generated. An electron beam lithography apparatus comprising: a detector for detecting at least one of the above; and means for controlling the irradiation amount using the intensity of the signal detected by the detector. 2. In claim 1, a means for mounting a standard sample as a standard on a part of the sample stage on which the sample to be drawn is mounted, and controlling the irradiation amount using the intensity of the signal detected by the detector. An electron beam lithography apparatus having means for calibrating the intensity of a signal detected by the detector using the intensity of a signal obtained when the standard sample is irradiated with an electron beam. 3. When determining the amount of irradiation to be applied to the sample to be drawn in an electron beam lithography system, an electron beam with a predetermined current value is irradiated to a specific position on the sample to be drawn prior to lithography, and the electron beam is emitted from the sample to be drawn. An electron beam lithography method that detects at least one of reflected electrons or secondary electrons and controls the irradiation amount using the intensity of the detected signal. 4. In the electron beam drawing method according to claim 3, the intensity of the signal obtained when the sample to be drawn is irradiated with the electron beam is calibrated by the intensity of the signal obtained when the standard sample is irradiated with the electron beam. An electron beam drawing method characterized by: 5. The electron beam lithography method according to claim 3, wherein the specific position is a region of a target for positioning on the sample to be lithographically drawn. 6. The electron beam lithography method according to claim 3, wherein the signal for determining the irradiation amount is a signal obtained when the target is irradiated for alignment.