JP3247700B2 - Scanning projection electron beam drawing apparatus and method - Google Patents

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 a fine circuit pattern on a resist by using an electron beam, and more particularly to a projection type electron beam drawing apparatus for achieving high throughput.

[0002]

2. Description of the Related Art A fine circuit represented by a semiconductor circuit is formed by: 1) a photosensitive agent (resist) on a metal film formed on an insulating plate, a silicon wafer or a metal film formed on the silicon wafer; (Hereinafter, a wafer coated with a resist will be described as a representative). 2) The wafer coated with the resist is irradiated with an optical image of a circuit pattern.
After developing a resist irradiated with an optical image, 4) etching a metal film or the like as a base using the developed resist as a mask, and 5) forming a circuit pattern. The optical image of the circuit pattern projected on the resist
It was created by projecting a circuit pattern mask made on a glass plate with an optical lens. The minimum wiring width of a circuit that can be formed by this method using light was about 0.5 μm. This limit is due to diffraction aberration caused by the wavelength of light. In order to further form a fine circuit, an electron beam having a short wavelength has been used. 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 while controlling the irradiation position of a point or rectangular electron beam using a computer. Since this electron beam drawing method is connected to a computer, there is an advantage that a circuit pattern to be formed can be easily corrected and changed. For this reason, it is often used for drawing a custom LSI whose production number is relatively small.

However, the above-described electron beam drawing method has a disadvantage that productivity is lower than that of a method of projecting as a collective optical image because a method of writing a circuit pattern one by one with a fine electron beam. This productivity is generally compared with an index called the throughput of how many wafers can be drawn in one hour, but the throughput of the electron beam lithography method described above is several sheets, In comparison, there was about an order of magnitude difference. For this reason, LSIs that are mass-produced like memory devices
Had the problem of being unsuitable.

[0004] In order to improve this, Journal of Vacuum Science Technology, B7
(6), November / December, (1989) pp. 1443-1444 (J. Vac. Sci. Technol. B7 (6), Nov / Dec.
1989, pp.1443-1447) reported that the projection method was performed with an electron beam to improve the throughput.
FIG. 2 is a diagram for explaining the principle of the method. The method reported is that a transmission mask 3 having an opening of a circuit pattern to be projected is placed about 0.6 mm above a resist-coated wafer 4.
, And projects a shadow image of the same magnification while scanning the electron beam onto the transmission mask 3.

[0005]

In the above-described conventional method shown in FIG. 2, if the irradiation is performed at an angle of θ degrees as shown by the inclined electron beam 2 in FIG.
It is shifted by 0.6 mm. Even if the inclination is only 1 milliradian, a displacement of 0.6 μm occurs. For this reason, a vertical electron beam must be scanned on the projection mask with an accuracy of less than 0.1 milliradian. FIG.
As shown by the non-parallel irradiation electron beam 6 in (b), when irradiation is performed with an aperture angle of α, the irradiation electron beam is reduced and projected, and a defect occurs in pattern connection between the scanning irradiation electron beams. For this reason, the aperture angle must be controlled to 1 milliradian or less. Further, when a very fine circuit pattern of 0.5 μm or less is to be drawn, a fine transmission mask of the same size must be made, but it is decisive that it is difficult to manufacture this. I have a problem.

[0006]

According to the present invention, an electronic lens is provided between a transmission mask and a wafer in order to solve the above-mentioned problem, and an image of the transmission mask is projected onto the wafer using the electron lens. . By providing an electronic lens,
1) The projection can be performed at an accurate position without depending on the irradiation angle and the opening angle of the electrons on the transmission mask. 2) The electron lens can be drawn with an enlarged projection mask by having a reduction effect, and the transmission mask can be obtained. Is easy to manufacture.

[0007]

The operation of the present invention will be described with reference to FIG. In the present invention, as described above, the projection electron lens 8 is placed between the transmission mask 3 and the wafer 4 coated with the photosensitive agent, and the electron transmitted while scanning the irradiation electron beam 7 on the transmission mask 3 is used as the projection electron lens. At 8 the light is projected onto the wafer. Since the projection electron lens 8 is provided, even if the irradiation electron beam 7 is inclined like the oblique 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 used. Since the electron beam 4 is located at the rear focal point of the electron lens 8, all the electrons emitted from the point P reach the point Q on the wafer 4 coated with the photosensitive agent. Does not move the point to be projected. If the projection electron lens 8 is used as a reduction, the circuit pattern of the transmission mask 3 can be reduced and projected, so that it is sufficient to make an enlarged transmission mask, which facilitates mask production.

[0008]

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 the Wehnelt 10 and accelerated by the anode 11.
The accelerated electron beam irradiates the shaped aperture 12 as an accelerated electron beam 21. Typical accelerated electron beam 21
Has an energy of 20 kV to 50 kV. Forming draw 1
An electron beam is formed by forming a square electron beam through a square aperture having a size of, for example, about 0.1 mm to 1 mm on one side. The size of the area electron beam 18 is determined according to the fineness of a circuit pattern to be drawn.
The smaller the drawing of the circuit pattern, the smaller the opening size of the forming aperture 12. This is because the finer the circuit pattern, the cooler
To lower resolution and uniformity of irradiation current density
This is because the demands on them become stricter. Although a square has been described as an example here, it goes without saying that a square other than a square may be used. The electron beam formed by the shaping aperture 12 is projected while scanning on the transmission mask 3 using the first irradiation lens 13 and the second irradiation lens 14. The image of the opening of the transmission mask 3 at the portion irradiated with the 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 the first projection lens 16 and the second projection lens 17 have a tandem configuration in which the focal length is the same. At this time, the directions of the exciting magnetic fields of the first projection lens 16 and the second projection lens 17 are reversed so that the rotation of the projected image does not occur.

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

When the entire surface of the transmission mask 3 is irradiated with electrons,
Projection can be achieved with a single irradiation, but this is difficult for the following reasons. That is, since the projection lens has image plane distortion, the focal plane of the projected image does not become flat, and the image is more blurred around the projected image. Therefore, the size of the area electron beam is limited to a range where image blur does not matter, and projection is performed while correcting the focus. For this focus correction, the first projection lens 16 and the second projection lens 1
7, a first focus corrector 20 and a second focus corrector 1
9 are provided. This focus compensator has a structure in which a conductor cylinder is placed in a lens magnetic field. When, for example, a positive potential is applied to the cylinder, the acceleration voltage (energy) of electrons passing through the cylinder increases. As a result, the lens action by the lens magnetic field is weakened and the focal length is lengthened. Conversely, when a negative potential is applied, the intensity increases and the focal length decreases. That is, the focus correctors 19 and 2 are changed according to the electron irradiation position on the transmission mask 3.
0 is applied to correct the field curvature aberration of the more projection lens to vary the potential. This correction is made by table control. That is, a correction table corresponding to the position of the irradiation electron beam is provided, and a voltage is applied to the corrector using the correction data stored in this table. In the case of the same magnification projection, the same voltage is applied to the first focus corrector and the second focus corrector. After projecting and drawing the chip pattern on the wafer in this way, a stage (not shown) on which the wafer 18 is mounted
Is moved to perform the projection drawing at the next position. Focus compensator
Causes magnification change and rotation of the projected image due to focus correction
You. The effect of the two-stage focus correction described above is obtained between the two correctors.
The effect can be offset. This is the mask projection
This is extremely important in the Ip drawing apparatus. Although only the focus is corrected in the description, it is also possible to divide the focus corrector into eight and add a voltage for astigmatism correction to the focus correction voltage.

The position to be projected and drawn on the wafer 4 is determined by the following method. 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 depends on the size of the circuit. 1 μm square opening 2 around chip pattern 23
Reference numeral 2 denotes an opening for projecting and drawing at a predetermined position on the wafer 18. FIG. 5 is a plan view of the wafer 18.
A position 25 for drawing a circuit pattern on the wafer 18
Are provided in advance. Drawing is performed on the alignment mark 26 at a drawing position 25 indicated by a dotted line.

The electron beam transmitted through the 1 μm square opening 22 is scanned on the alignment mark 26 provided on the wafer 4 to match the position of the 1 μm opening 22 with the alignment mark 26. The alignment mark 22 is, for example, a cross-shaped groove as shown in FIG. 6, and the relative position between the electron beam and the alignment mark is detected by scanning a 1 μm square electron beam as shown by the arrow in the figure. The detected shift amount 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 minute deviation amount can be adjusted by the projection deflector 24. Since a plurality of alignment marks 26 are provided around the position to be projected, a rotational displacement can also be detected. This rotational deviation is 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 such as the letter A in FIG. 7A may be generated. In this case, the pattern is divided into two patterns as shown in FIGS. The division may be two or more. Further, depending on the size of the circuit pattern, it is also possible to draw in four parts as shown in FIGS. 8A to 8D.

Although the distortion of the projection lens is considerably reduced by the tandem structure, a problem arises when a fine chip pattern is drawn. In view of this, the distortion of the projection lens is taken into consideration, and the transmission mask 3 that is distorted in advance so that the distortion is corrected as a projection result is created. For the information on the distortion, a transmission mask 3 having a mesh-shaped opening is created and projected and drawn,
It can be easily obtained by measuring in advance.

Although the embodiment described above is an example of the same magnification, it is possible to reduce the size, and in particular, the reduction projection is effective. FIG. 9 shows an embodiment in which the projection is reduced to half. In order to reduce the distortion of the projected image, a tandem structure was used here.
The focal length of the first reduction projection lens 26 is twice the focal length of the second reduction projection lens 27. A reduction transmission mask 25 having a size twice as large as a chip size to be drawn.
Is located at the front focal position of the first reduction projection lens 26. On the other hand, the wafer 18 is located at the focal position of the second reduction projection lens 27. The operations of the focus correctors 19 and 20 and the projection deflector 24 are the same as in the above-described embodiment.

[0016]

The electron beam lithography apparatus which has been practically used is one in which a dot or a rectangular electron beam is sequentially drawn. When a large-scale LSI is used, the throughput is as low as one sheet.
It was not practical. The present invention allows for 20 to 40 images per hour since it only projects. The opening of the transmission mask can be easily drawn by a conventional electron beam drawing apparatus. Even if one hour is required for the transmission mask 3, 100 masks can be easily drawn from this one mask, so that there is no substantial decrease in throughput. The main effect of the present invention is that it is possible to drastically improve a drawing process which has been conventionally inefficient.

[Brief description of the drawings]

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

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

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

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

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

FIG. 6 is a diagram illustrating an example of an alignment mark.

FIG. 7 is a diagram illustrating an example of division of a pattern of a transmission mask.

FIG. 8 is a diagram illustrating an example of separating a pattern of a transmission mask.

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

[Explanation of symbols]

Reference numeral 3: transmission mask, 4: wafer, 9: electron source, 10: Wehnelt, 11: anode, 12: forming aperture, 13:
1st irradiation lens, 14 ... 2nd irradiation lens, 15 ... scanning deflection plate, 16 ... 1st projection lens, 17 ... 2nd projection lens,
18 area electron beam, 19 first focus corrector, 20
Second focus corrector, 21: accelerating electron beam, 24: projection deflecting plate.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-53-144680 (JP, A) JP-A-2-121251 (JP, A) JP-A-61-147525 (JP, A) JP-A-62 281246 (JP, A) JP-A-60-44952 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/027

Claims (6)

(57) [Claims] A mask having an electron beam passage opening; a first electron lens for projecting an area electron beam passing through the mask onto an electron photosensitive material; and a projection image distortion of the first electron lens. A second electron lens for reducing the size, a first focus corrector disposed in a lens magnetic field of the first electronic lens, and a second focus lens disposed in a lens magnetic field of the second electronic lens. A scanning projection electron beam lithography apparatus comprising a focus corrector. 2. The scanning projection electron beam lithography apparatus according to claim 1, wherein each of said first focus corrector and said second focus corrector comprises a cylindrical conductor. 3. An electron source, a mask having an opening pattern for passing an electron beam from the electron source, and an electron lens for projecting an area electron beam passing through the mask onto an electron-sensitive material. Wherein the pattern shape of the aperture pattern is previously distorted in order to correct distortion of a projected image projected on the electro-sensitive material by the electron lens. apparatus. 4. A surface on a mask having an electron beam passing aperture.
While irradiating the product electron beam while scanning, the electron beam
Using an electron lens, the area electron beam that has passed through the passage opening
Projected onto the electro-sensitive material, and projected onto the electro-sensitive material.
Scanning projection electron beam writing to form a desired projection image pattern
In the apparatus, before irradiating while scanning on the mask
The area of the electron beam is formed on the electro-sensitive material.
Should be according to the fineness of detail of the desired projected image pattern
Characterized in that means for changing are further added.
Scanning electron beam lithography system. 5. A mask having an electron beam passage opening, a first electron lens for projecting an area electron beam passing through the mask onto an electron-sensitive material on a wafer, and a projection of the first electron lens. A second electron lens for reducing image distortion, a first cylindrical conductor disposed in a lens magnetic field of the first electron lens, and a second cylindrical lens disposed in a lens magnetic field of the second electron lens; Using a scanning projection electron beam lithography system having a second cylindrical conductor, the same focus correction voltage is applied to the first cylindrical conductor and the second cylindrical conductor. And forming a projected image of the electron beam passage opening on the electro-sensitive material to perform drawing. 6. The first focus corrector or the second focus.
In addition to the focus correction voltage applied to it,
The astigmatism correction voltage is superimposed and applied.
The scanning projection electron beam writing apparatus according to claim 1.