JPH01283831A - Charged beam exposing method - Google Patents

Abstract

PURPOSE:To accurately focus a beam to all exposure areas so as to enable formation of precise patterns by setting current of coil for focus adjustment, for each exposure area, to such a current value that the focus meets at the exposure area. CONSTITUTION:Since reflected electrons or secondary electrons go out of the surface of a substrate 2 even if there is a photosensitive film on a substrate 2, if the convergent point of a beam 1 accords with the surface of the substrate 2 as shown in b1, the peak value (p) of a differential waveform becomes maximum, and if the convergent point slides upward or downward as shown in b2 or b3, the peak value (p) becomes small according to its slide. Therefore, if defining the peak value (p) in current values I1-I5 as P1-P5, and taking the current value in X axis (abscissa) and the peak value (p) in Y axis (ordinate), and approximating both relations with quadratic curve Y=a(x-b)<2>+c and seeking a current value at a point that the maximum point of the quadratic curve, i.e., the peak value becomes maximum, that current value becomes current value Im. Hereby, it becomes possible to focus beams to all exposure areas and to form precise patterns.

Description

[Detailed Description of the Invention] [Summary] Using a charged beam exposure apparatus that focuses exposure using a focused charged beam by adjusting the current of a focusing coil, a plurality of exposure orders π distributed on the surface of a substrate to be exposed are used. Regarding the method of exposing the exposed area, in order to ensure that all exposed areas are well focused, multiple positions are set on the surface of the exposed substrate outside the exposed area, and the exposed area is exposed at those positions. The current value of the focus adjustment coil when the surface is in focus is determined for each position, and by interpolation from the above positions surrounding the exposure area to the center of the exposure area, the exposure area is brought into focus from the above current value at the position. The current value that matches the current value is determined for each exposure area, and the current value of the focus adjustment coil is adjusted to that current value to expose the corresponding exposure area. The value is determined using a mark with a step, beam scanning by switching the current value, a peak value of a differential waveform of reflected or secondary electron intensity, and a quadratic curve approximating the peak value.

[Industrial application field]

The present invention relates to a charged beam exposure method, and more particularly, to a charged beam exposure method that uses a charged beam exposure apparatus that focuses exposure using a focused charged beam by adjusting the current of a focusing coil to produce a plurality of exposed beams distributed on the surface of a substrate to be exposed. Relating to a method of exposing an area.

The above-mentioned charged beam exposure uses an electron beam or an ion beam as a focused charged beam, and is suitable for forming fine patterns on semiconductor devices and photomasks used in their manufacture. As patterns become finer, more attention has to be paid to focusing.

[Conventional technology]

FIG. 3 is an explanatory diagram of a charged beam exposure apparatus, (a) is a side view of an example of a charged beam optical system, (b1) to (b3)
(c) is a side view showing out-of-focus, and (c) is a configuration diagram of main parts related to focusing of the device.

In the same figure, the side view of (a) shows an example of a charged beam optical system, in which a charged beam 1 emitted from a charged beam source S is focused by an aperture A1 focusing lens, and is focused by the action of a deflection electrode E, etc. It is deflected to irradiate and expose the surface of the substrate 2 to be exposed.

At that time, if the focal point of the beam 1 matches the surface of the substrate 2 as shown in (b1), the exposure will be in focus, but (b
2) As shown in (b3), if the surface of the substrate 2 shifts upward or downward, out-of-focus occurs. In that case, it is necessary to correct and focus the beam 1 as shown by the broken line.

Therefore, as shown in (a), the charged beam optical system is provided with a focusing coil 3, and as shown in (c), the apparatus has two reference planes 5a at different heights on the sample stage. 5
b, an optical measuring device 6 such as a laser interferometer capable of measuring the heights of the reference planes 5a and 5b and the surface height of the substrate 2 on the sample stage, and a current in the coil 3 based on the signal from the measuring device 6. A configurable current control circuit is provided.

Note that, in many cases, this current control circuit also has a function of correcting the current of the coil 3 to correct out of focus caused by deflection of the beam l.

Further, 4 in (a) is an electron detector that detects reflected or secondary electrons emitted when the substrate 2 is irradiated with the beam 1, and is used for positioning the substrate 2 in the surface direction.

Focusing on the substrate 2 is performed using the signals obtained when the measuring device 6 measures the heights of the reference planes 5a and 5b and the reference planes 5a and 5b.
The correlation between the two is determined from the current value of the coil 3 when focusing on point b, and the height is measured for each exposure area on the surface of the substrate 2 with the measuring device 6, and from the signal, the height is determined for each exposure area. This is done by setting the current value of the coil 3.

(Thus, the exposure is focused for each exposure area, and no problem occurs even if the exposure area is shifted vertically due to warpage of the substrate 2 or the like.

[Problem to be solved by the invention]

However, in the above exposure method, since the current value of the coil 3 for focusing is determined via the reference planes 5a, 5b and the measuring device 6, it is indirect and tends to include errors. Since it is an optical method, there is a problem in that the presence of a photoresist film (resist film) on the substrate 2 causes a mistake in that it is performed at a different height from the surface of the substrate 2. This makes it difficult to form accurate patterns when patterns become even finer in semiconductor devices and the like.

Therefore, the present invention provides a method for exposing a plurality of exposure areas distributed on the surface of a substrate to be exposed using a charged beam exposure apparatus that focuses exposure by a focused charged beam by adjusting the current of a focusing coil. , the aim is to ensure that all exposure areas are well focused directly by the beam without having to measure the height of the substrate surface with an optical measuring device.

[Means to solve the problem]

The above purpose is to set a plurality of positions on the surface of the exposed substrate outside the exposure area, and to calculate the current value of the focus adjustment coil for each position when the surface of the exposed substrate is focused at that position.
By interpolating from the above positions surrounding the exposure area to the center of the exposure area, the current value at which the exposure area is focused is determined for each exposure area from the above current value at the position, and the current value is applied to the focus adjustment coil. This problem is solved by the charged beam exposure method of the present invention, in which currents are combined to expose a corresponding exposure area.

According to the present invention, the current value of the focus adjustment coil when the focus is adjusted at the set position is determined by providing a stepped mark at that position, and changing the current value of the focus adjustment coil multiple times at appropriate intervals. Each time the mark is scanned with the beam, the peak value of the differential waveform of the intensity of reflection or secondary electrons generated during scanning is determined for each scan, and a quadratic curve of the current value versus current value approximates the peak value. It is desirable to find the current value at the point where the peak value according to the curve is maximum.

[For production]

According to the method of the present invention, the current of the focus adjustment coil is set for each exposure area to a current value that brings the image into focus in that exposure area.

Further, since the current value when the current value is focused at the set position, which is the basis of the setting, is determined by irradiation with the exposure beam, it is straightforward, and errors are reduced compared to the conventional case.

In this way, all exposure areas can be well focused. This makes it possible to form accurate patterns even when patterns become even finer in semiconductor devices and the like.

〔Example〕

Embodiments of the charged beam exposure method according to the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a plan view illustrating an embodiment, and FIG. 2 is a diagram illustrating the determination of a current value that focuses on a mark.

The exposure method of the present invention uses the exposure apparatus explained in FIG. It differs from the conventional method in that it is determined by a direct method using scanning of the beam 1.

Generally, since the deflection range of the charged beam 1 in the exposure apparatus is smaller than the width of one chip of a semiconductor device,
In the exposure, the deflection ranges are arranged on the substrate 2 by moving the substrate 2, so that the exposure range covers one chip or even a plurality of chips.

Therefore, the exposure area may be set to an appropriate size area, such as capturing it as one deflection range or capturing it as one chip, depending on the fluctuation situation of the surface height of the substrate 2 on the sample stage. .

The current value updated for each exposure area of the coil 3 is
Find it as follows.

That is, as shown in FIG. 1(a), a plurality of positions are set on the surface of the substrate 2 outside the exposure area 7, and marks 8 with steps are provided at the positions. The mark 8 may be provided, for example, near the outside of the four corners of the chip, and the mark 8 may be, for example, a depression or protrusion of 3 to 10 μm square and about 1 μm deep. Therefore, it is also possible to use the alignment mark provided for alignment in the plane direction of the substrate 2 as the mark 8.

The substrate 2 is placed on a sample stage so as to be exposed, and the current value of the coil 3 when the mark 8 is in focus is determined for each mark 8 as will be described later with reference to FIG.

The current value of the coil 3 when exposing an arbitrary exposure area 7 is determined by the marks 88 to 8d around the exposure area 7 (marks 88 to 8d in FIG. 1(a)) as shown in FIG. 1(b). It is determined by interpolation from the above-mentioned current value determined in step 8).

To explain this part more specifically, for example, it is as follows. In FIG. 1(b), assuming that the marks 88 to 8d are arranged in a rectangular shape, the coordinates of the mark 8a with the mark 8d as the origin are (xo, 0), and the coordinates of the mark 8c are (0,
, Yo), the coordinates of the center of the exposure area 7 are (X, Y), and the current values when the marks 88 to 8d are focused are Ia to Id, then the exposure area 7 is exposed. The current value ■ of the coil 3 when
X (Yo Y) +IbX Y+Ic (XO-
X) ) /Xo Y.

is required. If the exposure area 7 is surrounded by three or more marks 8 corresponding to the marks 88 to 8d, the same can be obtained by applying the interpolation method.

This current value I allows the exposure region 7 to be well focused.

By the way, when the focus is on the position of mark 8, the coil 3
The current value Im is determined as shown in FIG. In the figure, (a) is a plan view of mark 8, (b1) to (b3)
) is a diagram showing the relationship between the beam 1 scanning the mark 8 and the differential waveform of reflected or secondary electron intensity, and (c) is a diagram showing a method for determining the current value 1 m.

First, five levels of current values 1 to I5 are set at appropriate intervals around the point that is thought to be the current value Is, and the current of the coil 3 is set to the current value 1. ~ ■ 5, scan the mark 8 with the beam 1 as shown in Fig. 2 (a), and collect the reflected or secondary electrons generated during scanning with the electron detector 4 (Fig. 3 (a)
) is detected and the differential waveform of its intensity is determined.

In this case, even if there is an angry light film on the substrate 2, the reflected or secondary electrons will be emitted from the surface of the substrate 2.
As shown in 1), if the focal point of beam 1 coincides with the surface of substrate 2, the peak value p of the differential waveform becomes maximum, and (b2)
As shown in (b3), when the focal point shifts upward or downward, the peak value p decreases in accordance with the shift. Generally, it is rare that the peak value p becomes maximum at any of the current values (1) to (5).

Therefore, the peak value p at current values 11 to 15 is defined as p, ~
p, the current value is taken on the X axis (horizontal axis) and the peak value p is taken on the Y axis (vertical axis), and the relationship between the two is approximated by a quadratic curve Y = a (X - b) + c, and the If we find the current value at the maximum point of the quadratic curve (the point where Y is maximum), that is, the point where the peak value p is maximum, we get:
The current value becomes the current value -. FIG. 2(c) shows this situation.

Since the current value Is obtained in this way is obtained by irradiating the beam 1 to that position, the conventional method of determining the current value by measuring the height of that position with the measuring device 6 is not possible. In comparison, the method of determination is more direct and there are fewer errors.

In this way, the current value of the coil 3 when exposing the exposure area 7 is determined so that each exposure area 7 is accurately focused, so that all the exposure areas 7 are well focused.

However, this method has the advantage that the cost of the exposure apparatus can be reduced because the measuring device 6 is not required.

〔Effect of the invention〕

As described above, according to the configuration of the present invention, a plurality of exposed light beams distributed on the surface of a substrate to be exposed are distributed using a charged beam exposure apparatus that performs focusing of exposure by a focused charged charged beam by adjusting the current of a focusing coil. In the method of exposing a region, it is now possible to directly obtain the set current value of the focus adjustment coil using a beam to ensure that all exposed regions are well focused, making it possible to improve pattern alignment in semiconductor devices, etc. This has the effect of making it possible to form a precise pattern even if further miniaturization progresses.

[Brief explanation of the drawing]

Fig. 1 is a plan view for explaining the embodiment, Fig. 2 is an explanatory view for determining the current value that brings the mark G into focus, (a) is a plan view of the mark, and (b1) to (b3)
is a diagram showing the relationship between the beam scanning the mark and the differential waveform of reflected or secondary electron intensity, (c) is a diagram showing the interpolation method for determining the current value of 1 m, and Figure 3 is an explanatory diagram of the charged beam exposure device. Figure (a)
are side views of an example of a charged beam optical system, (b1) to (b3)
) is a side view showing defocus, and (c) is a configuration diagram of the main parts related to focusing of the device. In the figure, 1 is a charged beam, 2 is a substrate to be exposed, 3 is a focus adjustment coil, 4 is an electron detector, 7 is an exposure area, 8.8a to 8d are marks, I, ~■u, ■... are 3 The current value of ps p+ to p5 is the peak value of the differential waveform. rb) Prefecture 1 Tsui 2 Ward Cha 3 X

Claims (1)

[Scope of Claims] 1) When exposing a plurality of exposure areas distributed on the surface of a substrate to be exposed using a charged beam exposure device that focuses exposure by a focused charged beam by adjusting the current of a focusing coil. , Set multiple positions on the exposed substrate surface outside the exposed area, calculate the current value of the focus adjustment coil for each position when the exposed substrate surface is in focus at that position, and then By interpolation from the position surrounding the exposure area, the current value at which the exposure area is focused is determined for each exposure area from the current value at the position, and the current of the focus adjustment coil is adjusted to that current value. A charged beam exposure method characterized by exposing a corresponding exposure area. 2) The current value of the focus adjustment coil when the focus is achieved at the above set position is determined by setting a mark with a step at that position.
The current value of the focus adjustment coil is switched multiple times at appropriate intervals, and the mark is scanned with the beam each time, and the peak value of the differential waveform of the intensity of reflections or secondary electrons generated during scanning is determined for each scan. 2. The charged beam exposure method according to claim 1, wherein the current value is determined by determining a quadratic curve of the current value versus the current value that approximates the peak value, and determining the current value at the point where the peak value of the curve is the maximum.