JPH0336298B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a position correction method for an electron beam drawing system.

A conventional method for correcting the position of an electron beam lithography system is to install a Faraday cup with a wire mark for electron beam detection near the top of the movable stage 14, as shown in the plan view of FIG. 3, for example. , D is used to correct the position of the drawn pattern only by detecting and correcting the position. However, in this method, the distance between the position D on the variable stage 14 and the reflecting surface of the reflecting mirror 19 varies from 10 minutes to 30 minutes.
In a normal drawing operation time of about one minute, the amount becomes a non-negligible amount of 0.1 μm or more, and the variation in the position of the substrate 12 placed on the cassette 13 with respect to the position D on the movable stage 14 is also 0.1 μm or more. Since the amount is not negligible, the pattern position accuracy using this method has exceeded 0.2 μm.

In addition, in FIG. 3, C indicates the optical axis position of the electron beam for drawing, and each means 17, 18, 23, 2
4, laser beams 17, 23 and interferometers 18, 24;
This is a well-known length measurement system consisting of:

On the other hand, as a separate conventional position correction method for electron beam writing systems, although not shown, only the position of a reference mark set at a predetermined position on the substrate 12 is changed at time intervals of about 10 to 30 minutes. There is also a method of detecting the amount of variation, feeding back the amount of variation, and correcting the drawing position, but this also allows
The reality is that within the above time range, it is unavoidable that there will be a non-negligible error exceeding at least 0.2 μm.

The problem when attempting to correct the drawing pattern position by measuring these variations is that each variation among the above variation factors cannot be separated in each measurement, and multiple variations included in one measurement. is controlled by mostly independent factors.
Therefore, in order to perform higher-precision correction, one measure is to extremely shorten the measurement time interval, but this reduces the production capacity of the drawing device, so it is not practical in practice. It's inappropriate and doesn't make much sense.

First, an object of the present invention is to provide a mark on the reflecting mirror structure of a laser length measurement system attached to the movable stage in order to measure the position of the movable stage that supports the substrate to be drawn, and to Marks are also provided on the drawing board, and the positions of these two marks are detected by an electron beam at almost constant time intervals and fed back to the control system to correct any fluctuations in the position measured by the laser length measurement system. This provides a method for improving the positional accuracy of a drawn pattern. Furthermore, secondly, by measuring the position near the bottom end of the electron beam optical column with another laser length measurement system and adding correction to the measured position value from the positions of the two marks,
The present invention also provides a method for dramatically improving the positional accuracy of drawn patterns.

The method of the present invention will be explained below using the drawings.

FIG. 1 is a side sectional view conceptually showing the main parts of an electron beam lithography system used in the present invention. 1 is the outer wall of the electron optical lens barrel, 2 is the upper wall of the drawing chamber, 3 is the drawing chamber base plate, 4 is an electron gun consisting of a filament and Wehnelt, 5 is a blanking electrode that controls transmission/blocking of the beam to the electron optical system, 6 is a condenser lens, 7 is a reduction projection lens, 8, 9
11 is a deflection electrode supported by the cylinder 10, and 11 is a backscattered electron detector, which is supported by the cylinder 10. Reference numeral 12 designates a substrate to be drawn, such as a semiconductor substrate or a substrate serving as a photomask for semiconductors, and 13 designates a metal cassette for holding the substrate, which is held on a metal movable stage 14. The movable stage 14 is moved by a motor 15 and a feed screw 16, and the amount of movement is determined by a two-wavelength laser beam 17, an interferometer 18,
The measurement is performed using a well-known length measurement system including a reflecting mirror 19 and the like. A further laser interferometer 21 and a reflector 22 fixed to the tube 10 detect positional variations of the mechanical semi-axes of the electron optical system.

FIG. 2 is a plan view conceptually explaining the position measurement system. When compared with FIG. 1, laser beams 23 and 25 and laser interferometers 24 and 26 are added for one dimension increase. . In other words, the electron beam drawing system shown in FIG. 1 is capable of measuring two-dimensional positional movement. In the electron beam lithography system, the main parts of the electron optical system, stage movement, and its length measurement system mentioned above are all controlled by a computer system, and the stage movement and electron beam blanking are performed according to pattern data prepared in advance.・Drawing is performed by combining deflections.

In FIG. 2, A ₁ is an electron beam detection mark formed on a surface making approximately 90 degrees with the reflection surface of the laser beam reflecting mirror 19, and B ₁ is an electron beam detection mark formed on the surface of the substrate 12 to be drawn. This is a detection mark.
Point C is a position where the optical axis of the electron beam optical system (when the deflection electrode voltages are zero in both two-dimensional directions) intersects the surface of the substrate 12 to be imaged. That is, the positions of the marks A ₁ and B ₁ are determined by the integral value of the Doppler shift of the laser beam for moving those marks to the vicinity of C by the moving operation of the movable stage 14, and by scanning with the electron beam. It is measured as the sum (or difference) of the calculated value of the position of the detected deflection voltage of the mark.

Regarding the mark A ₁ , the factors that cause the value measured in this way to vary within a certain time interval are the amount δ ₁ by which the mark changes with respect to the reflecting surface of the reflecting mirror 19, and the electron beam optical system. There is a variation amount δ _c of the position C of the optical axis due to mechanical causes and a variation amount ε based on electrical causes. Regarding mark B ₁ , the above-mentioned fluctuation amounts δ _c and ε of the position C point of the optical axis of the electron beam optical system, and the fluctuation amount δ ₂ of point B ₁ with respect to the reflecting surface of the reflecting mirror 19 are obtained. There is. Also, regarding the distance between the mark A ₁ and mark B ₁ above, therefore,
Both the fluctuation amounts of δ ₁ and δ ₂ are related to each other.

Strictly improve the instrumentation of electron beam lithography equipment (approximately 1/10
By controlling the temperature (to around 0°C), the relative expansion and contraction of the drawing chamber upper wall 2 and the base plate 3 of the apparatus shown in FIG. Amount of variation in the above mark A ₁ that occurs over a period of 30 minutes or less δ _c
can be expected to be suppressed to about 0.1 μm. Also, within this period of time, the amount of fluctuation ε is also
It is expected that it can be suppressed to about 0.1 μm. It is almost impossible to control fluctuations due to temperature factors in the movable stage 14 due to the movement and fluctuations in the metal cassette 13 due to temperature factors from outside the drawing room, and the cassette 13 is held on the movable stage 14. It must be assumed that the fulcrum changes every time the cassette 13 is replaced. Therefore, the amount of variation δ ₂ of the mark B ₁ can normally be about 0.1 μm or more. Looking at the amount of variation δ ₁ in the position of the mark A ₁ attached to the reflector structure, since the reflector 19 is usually made of hard glass, this amount of variation δ ₁ is so small that it can be ignored. be.

To summarize the above, in the present invention, an electron beam detection mark A ₁ is attached to the reflecting mirror structure of a laser length measurement system, and the distance between the mark B ₁ on the drawing target substrate 12 and the mark A ₁ is measured, Since the position of the substrate 12 with respect to the mark A ₁ is corrected at approximately constant time intervals within about 10 to 30 minutes, the temperature of the outer wall of the electron beam lithography system is controlled quite strictly as described above. The variation in position is only controlled by the amount of variation (δ _p +ε) in the electron beam optical system. Therefore, according to the method of the invention,
Pattern position accuracy of 0.2 μm or less can be obtained.

The second method of the present invention is to provide, in addition to the stage length measurement system, a length measurement system for detecting positional fluctuations near the bottom end of the electron beam column, as shown in FIGS. 1 and 2. be. This is done by a reflecting mirror 22 and interferometers 21 and 26 attached to the barrel 10 at the lowest end of the lens barrel, and the variable element δ _c or an amount correlated thereto is detected. What remains of the amount of variation in mark A ₁ is δ ₁ , which is negligibly small, and ε, which is normally impossible to measure. Therefore, only in this way ε
can be clearly measured and corrected. mark
The measurement and correction of the position of mark B ₁ with respect to A ₁ is as described above. Therefore, according to the second method of the present invention, even if the outer wall temperature of the drawing device is loosely controlled to about 0.1°C to 0.2°C, the drawing pattern position accuracy can be maintained at about 0.1 μm or less. .

In applying the present invention, instead of forming the mark _A1 on the reflecting mirror 19 directly on the surface that makes 90 degrees with the reflecting surface of the reflecting mirror 19, the mark A1 is vacuum-deposited on another thin glass plate. For example, a cruciform or L shape is formed on a chromium-gold double conductive layer by
A small mark substrate 27 on which a letter-shaped engraved mark is formed.
The most practical method is to attach it to the side of the reflecting mirror 19. In addition, such a small mark substrate 27 is made by forming a cross-shaped or L-shaped mark with a depth of about 1 μm on a plate with a low expansion coefficient such as silicon by photo-etching, and similarly pasting this mark on the side surface of the reflecting mirror 19. It's okay. Furthermore, as shown in FIG. 2, these small mark substrates 27 may be extended so as to cover part of the surface of the movable stage 14, and the mark _A2 may be provided on this extended portion. In this way, the amount of movement of the movable stage 14 to detect the mark _A1 is small, and thereby the distance between the laser interferometers 18 and 21 and the distance between 24 and 26 can be widened. There is a practical constructional convenience in that it can be taken. Note that if the small mark substrate 27 is a non-conductive substrate, a conductive layer is provided to connect the conductive layer and the structure of the metal stage 14 or the reflecting mirror 19, as shown in FIG. 2, in order to allow current to flow out. Line 28 is required.

In Fig. 2, the reflector 19, which is an element of the laser length measurement system, is arranged so that only one mirror is required for the two-dimensional direction.
Although it is shaped like a letter, it may be divided into two parts. In that case, a mark must be added to each reflector. These marks corresponding to A ₁ or A ₂ are 2 in any case.
You may add more than one. In this case, it is also possible to measure the inclination of the reflecting mirror 19 in the horizontal plane over time by measuring two or more marks, and to correct errors in position measurement due to this inclination. This is usually 2
This is a secondary correction, and caution should be taken when the amount is large.

The mark B ₁ on the substrate 12 to be drawn is the same as that of the substrate 1.
In the case where 2 is a so-called hard mask substrate in which a thin film of chromium or chromium and chromium oxide is deposited on a glass plate, a cross-shaped or L-shaped mark is provided directly on the mask substrate in advance by photo-etching or other method. For example, it has been confirmed that mark detection using backscattered electrons is possible, and there is no need to form marks using other heavy metal films. Also, mark
As described with respect to A ₂ , the small mark substrate 29 provided with another mark B ₂ can be temporarily pressed against the substrate 12 and used in place of the mark B ₁ .

If the substrate 12 to be drawn is a semiconductor wafer, the mark _B1 may be formed directly on the substrate in advance by photoetching or other method.

Two or more of each mark B ₁ or B ₂ may be provided. Furthermore, by detecting these relative fluctuation amounts, it is possible to find out the rotational fluctuation amount of the board.
This makes it possible to recognize instability in the holding between the substrate 12 and the cassette 13 or between the cassette 13 and the movable stage 14.

The horizontal plane of the electron beam detection mark described above may be designed to be within the focal depth of the electron beam and within the same plane as the substrate 12 to be drawn, but only the surface of a specific mark is higher than the surface of the substrate to be drawn. Even if the focus is shifted within a certain distance, it is possible to detect marks using an electron beam if the focus is automatically adjusted.

The shape of the electron beam was not mentioned in the explanation, but whether it is a spot beam, a fixed rectangular beam, or a variable area beam, the beam shape and
Since the dimensions are controlled in the system, there is no problem in applying the method of the invention in any beam shape.

As explained in detail above, according to the present invention,
In an electron beam lithography system, it is possible to improve the lithography position accuracy and bring about industrial significance.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional conceptual diagram showing the main parts of an electron beam lithography system used in the method of one embodiment of the present invention, Fig. 2 is a conceptual plan view showing the position measurement system of the same equipment, and Fig. 3 is a conventional example. FIG. 2 is a conceptual plan view of the device shown in FIG. 1, 2, 3... Electron beam lithography device wall, 12
...Substrate to be drawn, 13...Metal cassette, 14
...Metal stage, 16...Feed screw, 17,
20, 23, 25...2 wavelength laser beam, 1
8, 21, 24, 26... Interferometer, 19, 22...
... Reflector, 27, 29 ... Small board for mark, A ₁ ,
A ₂ , B ₁ , B ₂ ...Electron beam detection mark, C...
...Electron beam optical system optical axis position, D...Faraday cup position.

Claims (1)

[Scope of Claims] 1. In order to measure the position of a movable stage that supports a substrate to be drawn, at least one electron beam is applied to a two-dimensional laser length measuring system reflecting mirror structure mounted on the movable stage. A detection mark, and at least one electron beam detection mark are provided on the substrate to be drawn, and the positions of these electron beam detection marks are changed at arbitrary approximately constant time intervals to the electron beam. A method for correcting a position of an electron beam drawing system, comprising: detecting the position using the laser length measurement system, and correcting a change in position measured by the laser length measurement system. 2. Claim 1, characterized in that a small mark substrate provided with at least one electron beam detection mark is fixed to the side surface of a reflecting mirror structure for a two-dimensional laser length measurement system. The method for correcting the position of the electron beam lithography system described above. 3. Position correction of an electron beam drawing system according to claim 1, characterized in that a small mark substrate provided with at least one electron beam detection mark is temporarily fixed to a substrate to be drawn. Method. 4 2 in the reflector structure for the 2-dimensional laser length measurement system
Two electron beam detection marks are provided on the substrate to be drawn, and the former corrects fluctuations in the perpendicularity of the two-dimensional laser length measurement system, and the latter 2. A method for correcting the position of an electron beam drawing system according to claim 1, wherein the mechanical stability of the substrate to be drawn and a cassette holding the substrate are monitored. 5. At least one electron beam detection mark on a reflecting mirror structure of a first two-dimensional laser length measurement system attached to the movable stage for measuring the position of the movable stage that supports the substrate to be drawn. , at least one mark for detecting an electron beam is provided on each of the substrates to be drawn, and a reflecting mirror is attached to the tube portion for the electron optical axis of the electron beam, so that the tube portion for the optical beam axis is provided with a reflecting mirror. A second two-dimensional laser length measuring system for measuring the position is provided, and the position of each of the electron beam detection marks is detected by the electron beam at arbitrary approximately constant time intervals, and each of the first and second laser A method for correcting the position of an electron beam writing system, characterized by correcting variations in position measured by a length measuring system.