JP3458854B2 - Electron beam drawing 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 electron beam drawing apparatus, and more particularly to an electron beam drawing apparatus capable of performing electron beam drawing at high speed and with high accuracy.

[0002]

2. Description of the Related Art An electron beam drawing technique is widely used as one of lithography means. However, the throughput was low and it was not suitable for mass production. Among the current electron beam writing techniques, the variable rectangular beam method is the fastest writing method. In this method, an image of the first mask is formed by irradiating a first mask having a rectangular opening with an electron beam, the image of the first mask is deflected, and the second mask having a rectangular opening is irradiated with the electron beam. The image of the first mask and the rectangular opening on the second mask are overlapped on the second mask, and the overlapping portion of both is irradiated on the sample to perform drawing.

The variable rectangular beam method is very effective when drawing a linear pattern, but it is not an appropriate method when drawing a pattern tilted with respect to the above-described linear pattern. . When drawing a tilted pattern using the variable rectangular beam method, the triangles are formed by dividing the shaded areas into smaller rectangles, so the number of figures increases and the drawing time increases, and the shaded areas There was a problem that the accuracy of was not good.

To solve this problem, the Proceedings of 1989 International Symposium on Micro Process Conference, pages 59 to 63,
It is described that a triangular electron beam is formed by using a key-shaped opening and a hatched portion is drawn.

Further, Japanese Patent Application Laid-Open No. 3-270215 discloses a drawing method and apparatus using a mask having triangular openings formed at four corners.

[0006]

However, in the drawing method using the key-shaped opening, in order to adjust the size and origin of the triangle with high accuracy, it is necessary to use an advanced method such as fitting a current function or using special gold particles. Because the adjustment method was necessary,
There is a problem that it is difficult to form a triangular beam.

Further, in the drawing method using the triangular opening, the point at which the amount of transmitted current is zero is detected, and this point is set as the origin, but the amount of transmitted current is zero because of noise in the detection system. It becomes difficult to accurately detect the point. Furthermore, since the triangular opening is formed apart from the rectangular opening, the amount of movement of the electron beam becomes large. As the amount of deflection increases, the electrons pass off the axis of the lens and deflector,
Astigmatism aberration occurs in the first mask image, and there is a problem that the astigmatism aberration causes a reduction in image resolution and image distortion. Particularly in the formation of the triangular beam, since one side of the first mask is projected in a wafer shape, the influence of the aberration generated in the first mask image directly appears in the drawing accuracy. Therefore, in order to reduce the amount of deflection of the electron beam, the triangular opening is on the axis,
That is, it is necessary to form it in the vicinity of the variable-forming rectangular opening.

An object of the present invention is to provide an electron beam drawing apparatus which can easily adjust a triangular beam and can form a triangular beam for drawing with high accuracy.

[0009]

In order to solve the above problems, the present invention is directed to a first mask having an opening for forming an electron beam pattern, and one for deflecting the electron beam pattern transmitted through the first mask. Alternatively, it comprises a deflecting means composed of a plurality of detectors, and a second mask having a plurality of triangular openings and rectangular openings smaller than the openings of the first mask, and the second mask has the triangular openings. The first mask has at least four different oblique sides, is arranged at a position not overlapping the opening of the first mask, and is arranged around the rectangular opening of the second mask, and the first mask is provided at a diagonal portion thereof. From the structure having an area having no opening larger than the size of the rectangular opening of, and an area having no opening larger than the size of the rectangular opening of the first mask in two adjacent to either of the areas. The above-mentioned deflection means Selects at least one of the triangular apertures or rectangular opening and the triangular opening, characterized by comprising the structure for deflecting the electron beam to be superimposed.

The deflecting means is composed of a single or a plurality of deflectors. The deflector moves the electron beam transmitted through the first mask and selects the opening of the second mask, and transmits the first mask. The overlapping between the electron beam and the opening of the second mask is adjusted.

Further, according to the present invention, a step of irradiating a first mask having an opening with an electron beam to form a first electron beam pattern, and a step of deflecting the first electron beam pattern to a predetermined position, At least one of the openings including a plurality of triangular openings arranged at a position not overlapping the opening of the first mask is selected on the mask, and the first electron beam pattern and the selected opening are overlapped. It is characterized in that a step of forming a second electron beam pattern in combination and a step of drawing the second electron beam pattern on a sample via a transfer lens.

The above problems are solved by the above.

The operation of the present invention will be described with reference to FIGS. FIG. 1 shows an electron gun 7, a first mask 8 having a rectangular opening, a first transfer lens 9, a first figure selection deflector 10, a variable shaping deflector 11, a second figure selection deflector 12,
Second transfer lens 13, second mask 15, second mask 15
The triangular opening 2 formed above, the reduction lens system, and the objective lens system are used. The second mask 15 is formed as shown in FIG.
An electron beam drawing apparatus having an opening as shown in FIG.

The electron beam emitted from the electron gun 7 is applied to the first mask 8 to form a first mask image 3. As shown in FIG. 3, the first mask image 3 and the second mask are superposed on each other by selecting at least one of the triangular openings 2 of the second mask 15 arranged in positions having four different oblique directions. The first figure selection deflector 10 is adjusted so that the first mask image 3 is moved by the variable shaping deflector 11 so that one acute angle of the selected triangular opening 14 is always used, so that the superimposition can be performed. Adjustment can be done easily,
Moreover, the electron beam with which the wafer 22 is irradiated can be formed into a triangular pattern having an arbitrary size.

The direction of the hypotenuse of the present invention is shown in FIG.
As shown in (b), it is the direction indicated by a perpendicular arrow 201 drawn from the arbitrary point on the hypotenuse to the open side of the triangle.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) An embodiment of the present invention will be described with reference to FIG. A rectangular opening 1 for variable shaping is provided in the center of the second mask, and a triangular opening 2 having an acute angle of 45 degrees is arranged around the rectangular opening 1. The triangular opening 2 faces in four directions and enables drawing of various 45-degree diagonal lines. A collective graphic opening 26 for drawing memory cells is arranged on the outer circumference of the triangular opening 2. The maximum length of each opening is 125 μm. The reduction ratio of the optical system is 1/25, which is 5 μm on the wafer. The triangular opening 2 and the collective graphic opening 26 are smaller than the first mask image 3, and each opening is illuminated with the first mask image 3 at once.

FIG. 5 shows an electron optical system. By the first transfer lens 9 and the second transfer lens 13, the first mask image 3 is changed to the second mask image 3.
The first mask image 3 is moved by a plurality of deflectors formed on the mask 15 and between the two lenses. The selection of the triangle is performed by the two-stage variable shaping deflectors 24 and 25 for forming the variable shaped beam.

Since the collective graphic opening 26 on the outer periphery is used in a place where there are many repetitive patterns, even if it takes some time to select a graphic, the throughput is hardly affected. However, in the case of the triangular opening portion 2, it is highly likely that the opening portion is frequently changed to a rectangular shape or a triangle having a different orientation, and therefore high-speed selection is required. Therefore, in this embodiment, the triangular opening 2
Is selected by the two-stage variable shaping deflectors 24 and 25. The two-stage variable shaping deflectors 24, 2
No. 5 has a maximum output of 20 V and a settling time of 100 nsec.

The size of the triangle is determined by deflecting the first mask image 3 in one X or Y direction as shown in FIG. In addition,
The one direction described here includes an error in a range in which only one side of the first mask image 3 contributes to the beam shape determination. That is, the size is changed while always using one acute angle of the triangular opening 2. As a result, the origin 4 of each triangle
(Represented by a large point) is immovable, and the adjustment of superposition is easy, so that the size of the triangle can be arbitrarily changed. Further, since the origin 4 is determined by the processing coordinates of the mask, the rotation amount of the optical system, and the reduction rate, no extra adjustment is required. In the present embodiment, the deflection for controlling the size of the triangle also has a two-stage variable shaping deflector 24, 2.
Do in 5.

In general, the variable shaping deflector has a short deflection distance, but since it is capable of high-speed deflection, it is possible to switch between a rectangle and a triangle at high speed, and is suitable for drawing a pattern with many oblique lines at a predetermined angle. . By using two variable shaping deflectors and optimizing the interlocking ratio of the two deflectors, it is possible to minimize the off-axis that occurs when the electron beam is largely deflected. Further, by using the deflector with 8 poles, highly accurate drawing can be performed.

For the deflection of the first mask image 3 using the two-stage variable shaping deflector, the data for selecting the figure and the data for adjusting the size of the triangle are separately input and the respective deflectors are controlled. By doing so, the deflection of the first mask image 3 is performed. In order to adjust the size with the deflection sensitivity of the triangular beam, complicated processing is required. Therefore, in the present embodiment, the deflection sensitivity of the rectangular opening 1 is used. By changing the deflection voltage on the rectangular aperture and finding the absolute value of overlap depending on the distance of the midpoint of each beam profile,
The deflection sensitivity can be known. By disposing the triangular opening portion 2 in the vicinity of the rectangular opening portion 1, it is possible to ignore the distortion of the second or higher order of the deflection on the triangular opening portion 2.

Therefore, the deflection sensitivity calibration using the rectangular opening 1 can be applied to the calibration of the triangular beam. As a result, the relationship between the change in the deflection voltage and the change in the magnitude can be obtained.

Next, the origin of superposition of the first mask image 3 and the triangular aperture 2 (the starting point of the deflection voltage and the size of the triangle) is determined. The origin of the two superpositions can be obtained by extrapolation from the above-mentioned deflection sensitivity and the origin of the superposition of the first mask image 3 and the rectangular image. However, in the extrapolation, another point is added to increase the error of the deflection sensitivity calibration. A calibration method is desired. FIG. 6 shows the calibration method. By the two-stage variable shaping deflectors 24 and 25,
The transmission current was measured while changing the size of the triangle. In the figure, the maximum value of the current (where the increase in the current stops) is where the first mask image 3 and one side of the triangular opening 2 completely match. It is possible to use the zero current as a reference, but the maximum value has a steeper change, and accurate adjustment is possible. The increasing part of the current is a quadratic function,
The maximum value is obtained by performing fitting as shown in FIG. 7 after the maximum value with a zero-order function. Since the size of the triangle at this time can be uniquely obtained from the size of the aperture and the reduction ratio of the electron optical system, the size of the triangular beam can be adjusted thereafter according to the previously obtained deflection sensitivity.

As a result of the above adjustment, 64 is formed on a 6-inch wafer.
As a result of drawing the wiring pattern of the MDRAM, it was possible to significantly reduce the number of shots to 10 shots only by the variable shaping, 10 shots using the collective figure irradiation method, and 3 × 10 shots by using the triangular beam. Also, the roughness of the diagonal lines was improved to 0.03 μm, which is 1/3 of the conventional value of 0.1 μm. This can contribute to improving the productivity and yield of semiconductor production.

(Embodiment 2) This embodiment uses an electron optical system similar to that of Embodiment 1, but the arrangement of the triangular openings 2 of the second mask 15 is different. FIG. 8 shows the second mask 15 of this embodiment.
Shows the arrangement of. In this embodiment, the triangular openings 2 having different angles are also provided on the second outer circumference. The inner circumference has a triangular opening of 45 degrees, four triangles of 30 degrees on the upper side and four triangles of 60 degrees on the lower side. All triangles have a shield in one direction that is larger than the first mask image to prevent leakage beams when changing the size of the triangle. The triangle was selected by the figure selection deflector, which enabled large-angle deflection.
The maximum output of the deflector is 200 V, and the settling time is 10 μsec.
Is. However, the variable shaping deflector 11 was used for adjusting the size of the triangle.

An example of deflection by the variable shaping deflector 11 will be described with reference to FIG. The triangle size calibration data 32 and the triangle selection deflection data 33 are separately input from the control computer 34 and added to form a deflection signal, and the analog amplifier 35 inputs the deflection signal to the variable shaping deflector 11. One mask image 3 is deflected. The size of the triangle was adjusted by using the relationship between the deflector voltage and the transmission current. FIG. 10 shows the first derivative waveform of the transmission current. As shown in FIG. 11, the zero-order waveform and the first-order differential waveform are fitted with a quadratic function and a linear function, respectively, so that the sensitivity of deflection and the origin can be obtained. The first-order differential waveform has a steeper waveform and is suitable for fitting. However, when there is a lot of noise, the accuracy is decreased. The result of obtaining the adjustment accuracy from the drawing result. 0.03 μm in the 0th-order waveform and 0.
A dimensional accuracy of 02 μm was obtained.

In this embodiment, the triangular openings having the angles of 30 degrees, 45 degrees and 60 degrees are used, but the present invention is not limited to this, and the triangular openings having an arbitrary angle may be used.

Example 3 In this example, the same optical system as in Example 1 was used, but the method of adjusting the size of the triangular opening 1 was changed. Adjustment can be facilitated if the shape of the triangular beam can be directly measured. As shown in FIG. 12, a linear mark having a width formed of tungsten 29 is formed on the silicon 30. A so-called beam profile can be obtained by scanning the above with a triangular beam 27 and performing first-order differentiation. FIG. 13 shows the beam profile. The size of the triangle can be obtained by fitting the triangular beam profile with the width and height of the triangle. Further, by differentiating the beam profile, a steep profile appears at both ends of the beam. The size can be known by finding the center of each from the intersections of the determined levels as shown in the figure. With this method, the size can be obtained at a higher speed than the fitting shown in FIG. The adjustment accuracy according to this example was 0.02 μm.

[0029]

As described above, according to the present invention, it becomes easy to form and adjust a triangular beam in an electron beam drawing apparatus, which can contribute to speeding up of the apparatus.

[Brief description of drawings]

FIG. 1 is a diagram showing an electron optical system of the present invention.

FIG. 2 is a view showing the arrangement of openings according to the present invention and the direction of the hypotenuse of a triangle.

FIG. 3 is a diagram showing deflection of a first mask image.

FIG. 4 is a diagram showing the arrangement of openings according to the first embodiment.

FIG. 5 is a diagram showing an electron optical system according to an example.

FIG. 6 is a diagram showing a waveform of a transmission current.

FIG. 7 is a diagram showing a method of adjusting the maximum size by a transmission current.

FIG. 8 is a diagram showing the arrangement of openings according to the second embodiment.

FIG. 9 is a diagram showing addition of data.

FIG. 10 is a diagram showing an observation state of a triangular beam profile of Example 2.

FIG. 11 is a diagram showing fitting of a differential waveform according to the second embodiment.

FIG. 12 is a diagram showing a third embodiment.

FIG. 13 is a diagram showing an observation state of a triangular beam profile of Example 3.

FIG. 14 is a diagram showing fitting of a differential waveform according to the third embodiment.

[Explanation of symbols]

1 ... Rectangular opening, 2 ... Triangular opening, 3 ... First mask image, 4 ... Triangle origin, 6 ... First mask image moving region,
7 ... Electron gun, 8 ... First mask, 9 ... First transfer lens, 1
0 ... 1st figure selection deflector, 11 ... Variable shaping deflector, 12
... second figure selection deflector, 13 ... second transfer lens, 15 ...
Second mask, 16 ... First reduction lens, 17 ... Second reduction lens, 18 ... First objective lens, 19 ... Second objective lens,
20 ... Objective deflector, 22 ... Wafer, 23 ... Rectangular origin,
24 ... 1st variable shaping deflector, 25 ... 2nd variable shaping deflector, 26 ... Collective figure aperture, 27 ... Triangular beam, 29 ...
Tungsten, 30 ... Silicon, 32 ... Triangle size calibration data, 33 ... Triangle selection deflection data, 34 ... Control computer, 35 ... Analog amplifier, 40 ... Deflection direction, 41 ...
Deflection direction, 42 ... Linear mark having a width, 201 ... Vertical arrow indicating the hypotenuse direction.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiro Kawasaki 882 Ichimo, Hitachinaka-shi, Ibaraki Hitachi Ltd. Measuring Instruments Division (72) Inventor Tokuro Saito 1-280 Higashi Renegoku, Kokubunji, Tokyo Hitachi, Ltd. Central Research Laboratory (56) Reference JP 2002-33265 (JP, A) JP 2001-23878 (JP, A) JP 59-169131 (JP, A) JP 55-26620 (JP, A) JP 10-163088 (JP, A) JP 6-120126 (JP, A) JP 6-69112 (JP, A) JP 6-5500 (JP, A) JP 5-304083 (JP, A) JP 5-90140 (JP, A) JP 5-90139 (JP, A) JP 4-128844 (JP, A) JP 4-53221 (JP, A) Kaihei 3-270215 (JP, A) (58) Survey Field (Int.Cl. ^7, DB name) H01L 21/027 H01J 37/305

Claims (3)

(57) [Claims] 1. A step of irradiating a first mask having an opening for forming an electron beam pattern, a plurality of rectangular openings and at least four directions and provided in the vicinity of the rectangular opening. A triangle opening and a non-opening area are provided at diagonal portions of the rectangular opening, and two adjacent openings on one side of the diagonal portion of the opening are larger than the first mask image. Irradiating a second mask having a non-existing region with the first mask image formed by the rectangular opening and the first mask by a variable shaping deflector, and calibrating the deflection sensitivity of the variable shaping deflector in advance. A step of selecting the first mask image by the calibrated variable shaping deflector by selecting one of the plurality of triangular apertures and selecting a predetermined size, and superimposing it. A beam is applied to the sample through a reduction lens That process and an electron beam lithography method for characterized by using an electron beam pattern beam with. 2. The electron beam drawing method according to claim 1, wherein the step of calibrating the deflection sensitivity of the variable shaping deflector is performed by using the rectangular aperture. 3. A step of irradiating a first mask having an opening for forming an electron beam pattern, a rectangular opening, and at least four directions, and the first mask being in the vicinity of the rectangular opening. A plurality of triangular openings provided so that the deflection distortion of the first mask image formed by the mask does not exceed a negligible moving area, and a collective figure opening arranged on the outer periphery of the triangular openings. An area without an opening is provided in a diagonal portion of the rectangular opening, and two areas adjacent to one of the diagonal portions of the opening are provided with an opening-free area larger than the first mask image. The first mask using a second mask
And a step of irradiating the second mask with a mask image, the electron beam having passed through the second mask is passed through a transfer lens, and the sample is irradiated with the electron beam for exposure.