JPH04302132A - Scanning type projection electron beam exposure system and method - Google Patents

Abstract

PURPOSE:To provide the method capable of attaining especially high throughput in relation to the title exposure system of fine circuit patterns on a resist using electron beams while in this method, the electron beams having the merit of exposing patterns finer than those exposed by an optical system also have the demerit such as the impossibility of increasing the throughput due to the usage of the dotty electron beams. CONSTITUTION:A transmission mask 3 having an opening part of a circuit pattern is scanning-irradiated with space beams so that the transmitted electrons may be projected on a wafer 4 by projection lenses 16, 17. At this time, the focus slippage of the projection lenses 16, 17 out of the scanning position of the space beams 18 is corrected using focus correctors 19, 20. When the scanning step on the whole surface of the transmission mask 3 is finished, the wafer 4 is shifted to expose the next position. This invention can correct the focus slippage as the defect of a projection system by combining the scanning irradiation with the focus correction. Resultantly, the high throughput exceeding 40 wafers to be projected can be actualized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for drawing fine circuit patterns on a resist using an electron beam, and more particularly to a projection type electron beam drawing apparatus aimed at achieving high throughput.

0002

2. Description of the Related Art The formation of microcircuits typified by semiconductor circuits involves: 1) applying a photosensitive agent (resist) to a metal film formed on an insulating plate, a silicon wafer, or a metal film formed on the silicon wafer; 2) irradiate the resist-coated wafer with an optical image of the circuit pattern; 3)
After developing a resist irradiated with an optical image, 4) using the developed resist as a mask, an underlying metal film or the like is etched, and 5) a circuit pattern is formed. The optical image of the circuit pattern projected onto the resist is
It was created by projecting a circuit pattern mask made on a glass plate using an optical lens. The minimum wiring width of a circuit that could be formed by this method using light was approximately 0.5 μm. This limit is due to diffraction aberrations caused by the wavelength of light. Furthermore, electron beams with short wavelengths began to be used to form fine circuits. This method using an electron beam is called an electron beam drawing method, and is a method of drawing a circuit pattern on a resist using a point or rectangular electron beam while controlling the irradiation position using a computer. Since this electron beam lithography method is connected to a computer, it has the advantage that the circuit pattern to be formed can be easily corrected and changed. For this reason, it is often used for drawing custom LSIs that are manufactured in relatively small quantities.

However, the above-mentioned electron beam drawing method is a method of writing circuit patterns one by one using a fine electron beam, and therefore has the disadvantage of poor productivity compared to a method of projecting all at once as an optical image. This productivity is generally compared by an index called throughput, which is the number of wafers that can be written on in one hour. When compared, there was a difference of about one order of magnitude. For this reason, there was a problem in that it was unsuitable for mass-produced LSIs such as memory devices.

[0004] In order to improve this, the Journal of Vacuum Science Technology, B
7(6), November/December, (1989) pp. 1443-1447 (J. Vac. Sci. Tech
nol. B7(6), Nov/Dec 1989,
pp. 1443-1447), it was reported that the projection method was performed using an electron beam in an attempt to improve throughput. FIG. 2 is a diagram explaining the principle of the method. The method reported is that a transmission mask 3 having an opening for a circuit pattern to be projected is placed on a wafer 4 coated with a resist by approximately 0.6 mm.
mm, and while scanning an electron beam onto a transmission mask 3, a shadow picture of the same size is projected.

[0005]

[Problems to be Solved by the Invention] In the above-mentioned conventional method shown in FIG. 2, if the irradiation is tilted by θ degrees as shown by the tilted electron beam 2 in FIG. 2(a), the projected position will be θ×
It shifts by 0.6mm. Even if it is tilted by only 1 milliradian, a positional deviation of 0.6 μm will occur. For this purpose, a vertical electron beam must be scanned across the projection mask with an accuracy of less than 0.1 milliradian. Also,
As shown in the non-parallel irradiation electron beam 6 in FIG. 2(b), α
If the electron beam is irradiated with an aperture angle of For this reason, the aperture angle must also be controlled to 1 milliradian or less. In addition, when drawing very fine circuit patterns of 0.5 μm or less,
Although it is necessary to make a fine transmission mask of the same size, there is a decisive problem in that making this itself is difficult.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an electron lens between a transmission mask and a wafer, and projects an image of the transmission mask onto the wafer using the electron lens. . By installing an electronic lens,
1) It is possible to project onto an accurate position without depending on the irradiation angle or aperture angle of the electrons on the transmission mask. 2) By giving the electron lens a reduction effect, it is possible to draw with an enlarged projection mask, and the transmission mask The production becomes easier.

[0007]

[Operation] The operation of the present invention will be explained using FIG. In the present invention, as already mentioned, the projection electron lens 8 is placed between the transmission mask 3 and the wafer 4 coated with a photosensitive agent, and while the irradiation electron beam 7 is scanned over the transmission mask 3, the transmitted electrons are projected onto the projection electron lens. 8, the image is projected onto the wafer. By installing the projection electron lens 8, even if the irradiation electron beam 7 is tilted like the tilted irradiation electron 2 shown in the figure, the transmission mask 3 is placed at the front focus of the projection electron lens 8, and the wafer coated with the photosensitive agent is 4 is placed at the back focus of the electron lens 8, all the electrons emitted from point P reach point Q on the wafer 4 coated with a photosensitizer. The projected point does not move. If the projection electron lens 8 is used as a reduction lens, the circuit pattern on the transmission mask 3 can be reduced and projected, so that mask production becomes easier by simply making an enlarged transmission mask.

[0008]

Embodiment FIG. 3 shows a specific embodiment of the present invention. Electrons are emitted from the electron source 9. The emitted electrons are current-controlled by Wehnelt 10 and accelerated by anode 11. The accelerated electron beam irradiates the shaping aperture 12 as an accelerated electron beam 21. Typical accelerated electron beam 21
The energy of is 20kV to 50kV. Forming aperture 1
For example, one side is 0.1 mm to 1 mm.
The electron beam is shaped by a square aperture of approximately the same size as the one shown in FIG. The size of the area electron beam 18 is selected depending on the fineness of the circuit pattern to be drawn. The finer the circuit pattern is drawn, the smaller the aperture size of the forming aperture 12 is made. Also, here we used a square as an example, but
Of course, shapes other than squares are also fine. Forming aperture 1
The electron beam formed in step 2 is passed through the first irradiation lens 13 and the second
Projection is performed while scanning the transmission mask 3 using the irradiation lens 14. An image of the aperture of the transmission mask 3 in the portion irradiated with electrons is projected onto the wafer 18 using the first projection lens 16 and the second projection lens 17. In this embodiment, the magnification of the projection lens is the same, and a tandem configuration in which the first projection lens 16 and the second projection lens 17 have the same focal length is designed to reduce distortion of the projected image. Further, at this time, the directions of the excitation magnetic fields of the first projection lens 16 and the second projection lens 17 are set in opposite directions to prevent rotation of the projected image.

The transmission mask 3 has a size (chip size) constituting one LSI circuit, and is about 5 mm to 20 mm. Since the irradiated electron beam is 1 mm square or less, the irradiated electron beam is scanned over the entire surface of the transmission mask 3 by the scanning deflection plate 15 placed between the first irradiation lens 13 and the second irradiation lens 14, and the entire surface of the transmission mask is is projected onto the wafer 18. The scanning deflection plate 15 is also placed at the center (focal position) of the first irradiation lens and the second irradiation lens 14 of the tandem structure. Therefore, even if the electron beam is deflected, the transmission mask 3 can be irradiated almost vertically without being tilted.

If the entire surface of the transmission mask 3 is irradiated with electrons,
Although it is possible to perform projection with one irradiation, this is difficult for the following reasons. That is, because the projection lens has field distortion, the focal plane of the projected image does not become flat, and the image becomes blurred toward the periphery of the projected image. For this reason, the size of the area electron beam is limited to a range where image blurring does not become a problem, and the beam is projected while correcting the focus. For this focus correction, the first projection lens 16 and the second projection lens 17
a first focus corrector 20 and a second focus corrector 19 respectively within the
is provided. This focus corrector has a structure in which a conductive cylinder is placed within the lens magnetic field. For example, when a positive potential is applied to this cylinder, the acceleration voltage (energy) of electrons passing through the cylinder
becomes higher. As a result, the lens action by the lens magnetic field becomes weaker and the focal length becomes longer. Conversely, when a negative potential is applied, it becomes stronger and the focal length becomes shorter. That is, the field distortion of the projection lens is corrected by changing the potentials applied to the focus correctors 19 and 20 depending on the position of electron irradiation on the transmission mask 3. This correction is done by table control. That is, it has a correction table corresponding to the position of the irradiated electron beam, and applies a voltage to the corrector using the correction data stored in this table. In the case of same-magnification projection, the same voltage is applied to the first focus corrector and the second focus corrector. After the chip pattern is projected and drawn on the wafer in this manner, the stage (not shown) on which the wafer 18 is placed is moved to perform projection drawing at the next position. Although only the focus is corrected in the explanation, it is also possible to divide the focus corrector into eight parts and add a voltage for astigmatism correction to the focus correction voltage.

The position to be projected onto the wafer 4 is determined by the method described below. FIG. 4 shows an example of an opening pattern of the transmission mask 3. A 10 mm square chip pattern 23 made of single crystal silicon is formed as an opening. This size varies depending on the scale of the circuit. A 1 μm square aperture 22 around the chip pattern 23 is an aperture for projection drawing onto a predetermined position on the wafer 18. FIG. 5 is a plan view of the wafer 18. On the wafer 18 there is a position 25 where a circuit pattern is drawn.
An alignment mark 26 for determining the position is provided in advance. This alignment mark 26 is drawn at a drawing position 25 indicated by a dotted line.

The electron beam transmitted through the 1 μm square aperture 22 is scanned over the alignment mark 26 provided on the wafer 4, so that the 1 μm aperture 22 and the alignment mark 26 are aligned. The alignment mark 22 is, for example, a cross-shaped groove as shown in FIG. 6, and the relative position of the electron beam and the alignment mark is detected by scanning the groove with a 1 μm square electron beam in the direction of the arrow in the figure. The detected amount of deviation is matched by mechanically moving the stage or the transmission mask 3. Scanning of the electron beam transmitted through the 1 μm square aperture 22 onto the alignment mark 26 is performed by a projection deflector 24 provided at the center of the projection lenses 16 and 17. Further, the projection deflector 24 can also be used to adjust minute amounts of deviation. Since a plurality of alignment marks 26 are provided around the position to be projected, rotational deviation can also be detected. This rotational deviation is also adjusted by rotating the stage or the transmission mask 3.

The circuit pattern formed on the transmission mask 3 has a complicated structure. Therefore, an isolated pattern like the letter A shown in FIG. 7(a) may occur. In this case, the pattern is divided into two patterns as shown in FIGS. 7(b) and 7(c), and both are drawn in an overlapping manner. The division may be two or more. Furthermore, depending on the size of the circuit pattern, it is also possible to draw the circuit pattern separately into four parts as shown in FIGS. 8(a) to 8(d).

Although the distortion of the projection lens can be considerably reduced by using a tandem structure, it becomes a problem when drawing a fine chip pattern. Therefore, in consideration of the distortion of the projection lens, a distorted transmission mask 3 is created in advance so that the distortion is corrected as a projection result. Information on distortion is obtained by creating a transmission mask 3 with mesh-like openings and projecting it.
It can be easily obtained by measuring in advance.

Although the embodiments described above are examples of the same size, reduction is also possible, and reduction projection is particularly effective. FIG. 9 shows an example in which projection is reduced to 1/2. In order to reduce distortion of the projected image, a tandem structure was used here as well. The focal length of the first reduction projection lens 26 is twice the focal length of the second reduction projection lens 27. Transmission mask 25 for reduction that is twice the size of the chip to be drawn
is placed at the front focal position of the first reduction projection lens 26. On the other hand, the wafer 18 is placed at the focal position of the second reduction projection lens 27. The operations of the focus correctors 19, 20 and the projection deflector 24 are similar to those in the previous embodiment.

[0016]

[Effects of the Invention] The electron beam lithography equipment that has been put into practical use so far draws sequentially with point or rectangular electron beams, and when it comes to large-scale LSIs, the throughput is low at about one piece.
It wasn't practical. Since the present invention only projects images, it is possible to print 20 to 40 images per hour. The openings of this transmission mask can be easily created using a conventional electron beam lithography system. Even if this transmission mask 3 requires one hour, 100 images can be easily drawn from this one mask, so there is no substantial reduction in throughput. The main effect of the present invention is that the drawing process, which has conventionally been inefficient, can be dramatically improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a conventional drawing method.

FIG. 2 is a diagram illustrating the basic configuration of the present invention.

FIG. 3 is a diagram showing an embodiment of the present invention.

FIG. 4 is a diagram showing an example of a transmission mask.

FIG. 5 is a diagram showing the relationship between alignment mark positions on a wafer and positions to be drawn.

FIG. 6 is a diagram showing an example of alignment marks.

FIG. 7 is a diagram showing an example of dividing a pattern of a transmission mask.

FIG. 8 is a diagram showing an example of separating patterns of a transmission mask.

FIG. 9 is an example of a projection lens that performs reduction projection.

[Explanation of symbols]

3... Transmission mask, 4... Wafer, 9... Electron source, 10... Wehnelt, 11... Anode, 12... Shaping aperture, 13...
First irradiation lens, 14... Second irradiation lens, 15... Scanning deflection plate, 16... First projection lens, 17... Second projection lens,
18...area electron beam, 19...first focus corrector, 20...
Second focus corrector, 21... accelerated electron beam, 24... projection deflection plate.

Claims (12)

[Claims] [Claim 1] A scanning projection system characterized by scanning an area electron beam through a transmission mask having a specific aperture pattern, and projecting the transmitted electron beam onto a material sensitive to electrons using an electron lens. Electron beam lithography equipment. Claim 2: The number of electron lenses for projecting transmitted electron beams is one.
2. The scanning projection electron beam lithography apparatus according to claim 1, wherein the scanning projection electron beam lithography apparatus has a magnification of 1:1. Claim 3: There is one electron lens for projecting the transmitted electron beam.
2. The scanning projection electron beam lithography apparatus according to claim 1, wherein the reduction is less than or equal to . 4. The scanning projection electron beam lithography apparatus according to claim 1, further comprising a deflector for deflecting the electron beam and a focus corrector in the electron lens for projection. 5. A scanning projection electron beam lithography apparatus according to claim 1, wherein the electron lens for projecting is composed of a two-stage electron lens. 6. The projection electron lens is composed of two stages, a transmission mask is placed at the front focal position of the first projection electron lens, and a transmission mask is placed at the front focal position of the first projection electron lens.
6. The scanning projection electron beam lithography apparatus according to claim 5, characterized in that it has a tandem optical configuration in which a resist is placed at the back focal position of the projection electron lens. 7. The scanning projection electron beam lithography apparatus according to claim 5, wherein the magnetic field directions of the projection electron lenses configured in two stages are opposite to each other. 8. The scanning projection electron beam lithography apparatus according to claim 1, wherein a target specific pattern is drawn by superimposing and projecting images of a plurality of transmission masks. 9. Scanning characterized in that the target specific pattern is divided into a plurality of sections, and the target specific pattern is projected by sequentially lining up and projecting a plurality of divided transmission masks. Shape projection electron beam drawing method. 10. A minute circular or rectangular opening is provided on the outer periphery of the specific opening pattern, and an alignment mark made on the resist or the bottom surface of the resist is detected and projected using an electron beam transmitted through the mark. The device according to claim 1, characterized in that the device confirms the correct position. 11. A scanning projection electron beam lithography method, wherein the shape of the specific aperture pattern is a pattern distorted in advance so as to correct distortion of a projection lens. Claim 12: Claim 1 for pattern formation of an LSI circuit.
An LSI device created using the scanning projection electron drawing apparatus described above.