JPS60741A - Exposure by electron beam - Google Patents

Abstract

PURPOSE:To prevent the lowering of pattern precision by a method wherein an irregularity on a sample is scanned plural times while the intensity of the objective current of an electron optical system for exposure is changed, the height of the sample is measured on the basis of the contribution of the contrasts of reflected electronic signal waveforms and the measured height is added to the drawing conditions. CONSTITUTION:In case a smaple 1 having a protrusion 2 is scanned with an electron beam 3 and a pattern is drawn, a reflected electron detector is provided, the focal length of the electron beam 3 is made to change little by little according to changing the intensity of the objective current of an electron optical system for exposure and the sample 1 is scanned in such a way that the electron beam 3 transverses the protrusion 2. The distribution curve of contrast is obtained from the objective current and the contrast value at the sacnning time, thereby finding the objective current at the time when the contrast becomes maximum. By applying the relation between the objective current at the time of the previously found maximum contrast and the length of the sample 1, the height of the sample 1 is decided and the result is made to feedback to the drawing conditions such as the adjustment of deflecting voltage, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electron beam exposure method, and particularly to a method for preventing a decrease in pattern accuracy due to a change in the height of a sample relative to an electron optical system. It is.

[Prior art]

If the height of the sample changes with respect to the electron optical system, the scanning length on the sample when the electron beam is deflected by a predetermined angle will change, and the focus will shift, which will affect the precision of the pattern drawn on the sample. descend. For this reason, conventionally, an optical system that uses light to detect the height of the sample is provided separately from the electron optical system for exposure, and the detected value is fed back to the electron optical system to compensate for changes in the height of the sample. There is something like this. However, this method of detecting height using light requires the provision of an insulator such as glass, which is essential to the optical system, near the electron optical system, and this is charged by the electron beam.
This causes positional drift or astigmatism of the electron beam, and requires a light optical system in addition to the electron optical system, making the device complex and expensive. There are still some methods in which the height of the sample is determined by detecting the distance between two fixed points on the sample from the deflection angle of the electron beam using an electron optical system for exposure without using a light optical system. However, this method has the disadvantage that it is difficult to measure the height with high precision.

[Purpose of the invention]

The present invention uses an electron optical system for exposure without using a light optical system to measure the height of a sample with higher precision, thereby minimizing the decrease in pattern accuracy due to changes in the height of the sample. It is something whose purpose is to do something.

[Structure of the invention]

To achieve this object, the present invention scans the irregularities on the sample with an electron beam multiple times by changing the objective lens current of the electron optical system for exposure, and determines the shape of the sample from the contrast distribution of the reflected electron signal waveform obtained at that time. The present invention is an electron beam exposure method in which the height is measured and the measurement results are fed to the drawing conditions such as deflection voltage adjustment for drawing.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 4. As shown in FIG. 1, a ridge-shaped protrusion (or a groove may be used) 2 is provided on the surface of a sample 1, and a backscattered electron detector (not shown) is connected to the protrusion 2 to detect backscattered electrons as shown by A and B. A signal waveform is obtained.

The differences between the maximum and minimum values of these reflected electron signal waveforms A and H are called contrasts Ca and Cb, and this contrast value indicates that the electron beam 3 passing through the protrusion 2 is focused more accurately. Ql shows a large value.

Therefore, the focal length of the electron beam 3 is changed little by little by changing the objective lens current of an exposure electron optical system (not shown), and each time the electron beam 3 is scanned across the protrusion 2, and the contrast value at that time and the objective lens current are 3, a contrast distribution curve as shown by C1 in FIG. 3 is given. From this contrast distribution curve C1, an objective lens current 401 is obtained when the electron beam 3 is most accurately focused on the protrusion 2, that is, when the contrast is at its maximum value. In order to calculate the objective lens current 401 when the contrast reaches its maximum value, determine the threshold level as shown by the symbol S in FIG. The lens current AI, 42, is preferably obtained from the following formula.

1st night As the sample 1 approaches the objective lens, the code C appears in the third movement.
As indicated by 2, the objective lens current p moves to the right in FIG.
o1 and ((oz corresponds to the height of sample 1.

Therefore, if the relationship between the objective lens current when the contrast is maximum and the height of the sample at that time is established in advance using a known sample as shown in FIG. 4, the objective lens current 4o1 and The height of sample 1 at that time can be measured from lo2.

The height of the sample 1 can be measured with high accuracy because the rate of change in the objective lens current with respect to the change in height can be taken to be sufficiently large relative to the control unit of the current.

This measurement result is fed back to the drawing conditions such as deflection voltage adjustment and objective lens current, thereby compensating for the height deviation of the sample l and drawing is performed.

[Effects of the Invention] As described above, according to the present invention, the height of the sample can be measured with higher precision using an electron optical system for exposure without using a light optical system. The deterioration in pattern accuracy due to height changes can be suppressed to a smaller extent, and the apparatus does not become complicated or expensive.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway enlarged view showing an example of the relationship between an electron beam and an example of unevenness provided on the surface of a sample for carrying out the present invention, and FIG.
The figure shows the reflected electron signal waveform when the protrusion is scanned with an electron beam, Figure 3 shows the contrast distribution of the reflected electron signal waveform as the objective lens current changes, and Figure 4 shows the contrast distribution of the reflected electron signal waveform as the objective lens current changes. FIG. 6 is a diagram showing the relationship between the objective lens current and the sample height at the maximum. , 1... Sample, 2... Protrusion, 3... Electron beam, A, B
...Reflected electron signal waveform. Ca, Cb...Contrast, C1, C2...Contrast distribution curve, S. Sletsonjord level. Applicant: Toshiba Machinery Co., Ltd.

Claims (1)

[Claims] The height of the sample is measured by changing the objective lens current of the electron optical system for exposure and scanning the unevenness on the sample with an electron beam multiple times, from the contrast distribution of the reflected electron signal waveform obtained at that time.
An electron beam exposure method characterized by feeding back the measurement results to writing conditions such as deflection voltage adjustment.