JPH0750665B2 - Charged beam drawing device - Google Patents

Description

The present invention relates to a variable dimension beam type charged beam drawing apparatus, and more particularly to a charged beam drawing apparatus with improved lens focusing.

(Prior Art) In recent years, various electron beam drawing apparatuses have been used to form a fine pattern on a sample such as a semiconductor wafer or a mask. Among these apparatuses, an electron beam drawing apparatus of a so-called variable size beam system, which changes a beam size in accordance with a pattern to be drawn, is attracting attention because it satisfies both drawing accuracy and throughput.

FIG. 6 is a schematic configuration diagram showing a conventional variable-dimension beam type electron beam drawing apparatus. In the figure, 10 is an electron gun, 11, ~, 15
Is an electron lens, 16 is the sample surface, 17 is a blanking electrode, 2
Reference numerals 1 and 22 are beam shaping aperture masks, 23 is a beam shaping deflector, 24 is a beam scanning deflector, and 25 is a backscattered electron detector. In this apparatus, the condenser lens 11, 12 illuminates the first aperture mask 21, and the projection lens 13 projects the aperture image of the mask 21 onto the second aperture mask 22. Further, by deflecting the beam by the beam shaping deflector 23, the size and shape of the shaping aperture image combined by the aperture image of the first aperture mask 21 and the aperture of the second aperture mask 22 are changed. Then, this shaping aperture image is projected onto the sample surface 16 by the reduction lens 14 and the objective lens 15. The image P to P ₄ of the electron gun crossover which is the light source is separated from the shaping aperture image to form a so-called Koehler illumination.

By the way, in order to draw an LSI pattern with this type of device, the current density distribution of the electron beam on the sample surface is uniform,
Moreover, it is necessary that the current density of the beam does not change even when the beam size is changed by performing shaping deflection. Therefore,
Prior to drawing, it is necessary to focus the condenser lens and the projection lens so as to satisfy the above two conditions.

Conventionally, this focusing is performed by the following method. That is, the exciting current of the projection lens is slightly changed (about 10 ^{−3 of the} positive focus current), and the exciting current of one condenser lens is first adjusted so that the intensity distribution of the beam becomes the most uniform in each step. Adjustment is performed, and then a certain molding deflection (for example, X dimension is changed from 4 to 2 μm) is performed, the average amount of change in current density before and after that is measured, and the process proceeds to the next step. By repeating this process, the exciting current of the lens is adjusted so as to satisfy the above two conditions.

However, this type of method has the following problems. That is, as is apparent from the above description, since this method is a method in which the measurement is repeated to drive it to the optimum exciting current, the adjustment takes a lot of time. Further, since both the condenser lens and the projection lens are changed, it is necessary to make an adjustment to correct the axis deviation of the beam due to the excitation change of each lens. As described above, in the measurement in which the complicated adjustment is repeatedly performed, the occurrence of an error cannot be avoided as a matter of course, and therefore, the focusing accuracy of the lens is only about 5 × 10 ⁻³ .

(Problems to be Solved by the Invention) As described above, in the conventional apparatus, it takes a lot of time to focus the lens (especially the projection lens) and sufficient accuracy cannot be obtained. Therefore, there is a problem in that the drawing accuracy is reduced due to the defocus of the lens.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a charged beam drawing apparatus capable of highly accurately focusing a lens in a short time and improving drawing accuracy. To provide.

[Structure of the Invention] (Means for Solving Problems) The gist of the present invention is to focus the projection lens.
A forming deflection region is provided so that the penumbra of the second beam forming aperture mask does not occur in the crossover image.

That is, according to the present invention, the aperture image of the first beam shaping aperture mask is projected on the second beam shaping aperture mask by the projection lens, and the second beam shaping aperture mask is projected by the beam shaping deflector. The projection position is changed by, and the shaping aperture image synthesized by the aperture image of the first beam shaping aperture mask and the aperture of the second beam shaping aperture mask is scanned on the sample surface, and the sample surface is scanned. In a charged beam drawing apparatus for drawing a desired pattern on the beam forming aperture mask, a beam detecting aperture mask is provided at a position where the deflection center of the beam forming deflector is to be projected, and the beam at the position where the beam detecting aperture mask is arranged. Means for detecting the center position of the second beam shaping aperture mask is provided. Is obtained as a major at least one direction than the dimension of the tea dimensions aperture image of the first beam shaping aperture mask.

(Operation) In the optical system shown in FIG. 6, if each lens is in a positive focus, the image of the deflection center of the beam shaping deflector is projected at the positions of the crossover images P ₃ and P ₄ . , The crossover images P ₃ and P ₄ do not move even when the shaping deflection is performed. Therefore, focusing of the projection lens should be performed by adjusting the exciting current of the projection lens so that the beam does not move with respect to the shaping deflection at the position where the deflection center is projected at the regular focus.

However, when the forming deflection is performed, the second
The aperture mask aperture (second aperture) and the first aperture mask aperture image (first aperture image) overlap with each other, and the overlapping manner changes depending on the deflection amount and direction. On the other hand, when you need focus,
That is, when the condenser lens is deviated from the normal focus, the crossover image P ₂ is deviated from the deflection center of the beam forming deflector, and similarly the crossover images P ₃ and P ₄ are also deflected by the deflector. It is off the center image position. That is, the Koehler illumination condition for completely separating the crossover image and the shaping aperture image to form an image is not satisfied. If the shaping deflection is performed in this state, the penumbra of the second aperture is generated in the crossover image, and therefore the beam moves even if the projection lens is in focus, so that the excitation current is adjusted so that the beam does not move. Was impossible to adjust. This is the reason why the conventional complicated focusing has been used.

Therefore, in the present invention, in order to focus the projection lens, the shaping deflection region is provided so that the penumbra of the second aperture does not occur in the crossover image, and the conventional problem is solved. Since the penumbra of the second aperture does not occur in the crossover image in the deflection area that is not in contact with the second aperture, the projection lens can be focused with high accuracy by changing the deflection amount in this area. Becomes

(Examples) The details of the present invention will be described below with reference to illustrated examples.

FIG. 1 is a schematic configuration diagram showing an electron beam drawing apparatus according to an embodiment of the present invention. In the figure, 10 is an electron gun, and the electron beam emitted from this electron gun 10 is a condenser lens.
11,12, projection lens 13, reduction lens 14 and objective lens 15
It is irradiated onto the sample surface 16 via. Condenser lens 1
The reference numerals 1 and 12 focus the electron beam emitted from the electron gun 10 to illuminate the first beam shaping aperture mask 21.

The aperture image (first aperture image) 21 a of the first aperture mask 21 is projected by the projection lens 13 onto the second beam shaping aperture mask 22. A beam shaping deflector 23 is arranged between the first aperture mask 21 and the projection lens 13. By deflecting the beam by the deflector 23, the position of the first aperture image 21a on the second aperture mask 22 changes, and the apertures of the first aperture image 21a and the second aperture mask 22 (second aperture). The size of the shaping aperture image changes due to the combination with 22a. Then, the shaping aperture image is formed on the sample surface 16 by the reduction lens 14 and the objective lens 15.

A blanking electrode 17 for turning the beam on and off is arranged between the electron gun 10 and the condenser lens 11. Further, a beam scanning deflector 24 is arranged between the reduction lens 14 and the objective lens 15. The deflector 24 scans the shaping aperture image on the sample surface 16. Further, an electron detector 25 for detecting backscattered electrons from the sample surface 16 is arranged between the objective lens 15 and the sample surface 16.

The positions of the crossover images have a relationship as shown in FIG. That is, the crossover image P ₂ is formed at the deflection center of the beam forming deflector 23, and the crossover image P ₄ is further formed at the center of the objective lens 15.

The configuration up to this point is the same as that of the conventional apparatus, and the difference of this embodiment from this is that a beam detection aperture mask 31, a beam detection deflector 32, and a backscattered electron detector 33 are newly provided. That is, the beam detection aperture mask 31 is arranged at a position where the deflection center of the beam shaping deflector 23 is projected. Below the second aperture mask 22, a beam detection deflector 32 for scanning the beam on the beam detection aperture mask 31 is arranged. Furthermore, above the beam detection aperture mask 31, a backscattered electron detector 33 for detecting backscattered electrons from the aperture mask 31 is arranged.

The relationship between the second aperture image and the first aperture image is as shown in FIG. That is, the second aperture 22a
Is a 40 μm × 70 μm rectangle, and the first aperture image 21a
Is a rectangle of 60 μm × 30 μm. Therefore, it is possible to perform the deflection of a = 70−30 = 40 μm by the beam forming deflector 23 without contacting the second aperture 22a.

Next, a lens focusing method in the present apparatus having the above configuration will be described with reference to FIG.

First, when the beam is deflected by the beam shaping deflector 23 as shown in b.c. when the focus of the projection lens 13 is deviated, the center of the beam in the beam detecting aperture mask 31 is B.c.
Move like C. This amount of movement is Δ. Amount of movement Δ
The beam detecting deflector 32 scans the beam on the beam detecting aperture mask 31, and the reflected electrons at this time are detected by the electron detector 33.
The coordinates of the aperture center position of the aperture mask 31 on the deflection coordinates of 32 are detected and calculated from the amount of change. That is, the center position of the beam on the beam detection aperture mask 31 is detected, and the movement amount of the beam center position is obtained.

As described above, the deflection by the beam shaping deflector 23 is changed to the second deflection.
If the beam is not in contact with the aperture 22a, the second
Since the penumbra of the aperture 22a does not appear in the beam intensity distribution at the position of the aperture mask 31, high detection accuracy can be obtained.

At this time, the relationship between the movement amount Δ and the exciting current I of the projection lens 13 is approximately represented by the following equation.

Δ = k · θ · (I−I ₀ ) where θ is the deflection angle, k is a constant, and I ₀ is the current value at the positive focus. By measuring Δ with respect to I and obtaining I ₀ with Δ = 0 by the least square method, focusing can be performed with about 20 times the accuracy of the conventional example.

As described above, according to this embodiment, the beam detection aperture mask 31, the beam detection deflector 32, and the backscattered electron detector 33 are provided.
And the size of the second aperture 22a is set to be large in one direction according to the size of the first aperture image 21a, the beam on the beam detection aperture mask 31 in the deflection region not in contact with the second aperture 22a. It is possible to detect the center position of and the movement amount thereof. Therefore, the projection lens 13 can be focused with high accuracy without generating the penumbra of the second aperture 22a in the crossover image. Furthermore, condenser lens 1
Since the above adjustment can be performed independently of the focusing of 1 and 12, the focusing of the projection lens 13 can be completed easily and in a short time. Therefore, the drawing accuracy can be improved and the drawing throughput can be improved.

The present invention is not limited to the above embodiment. For example, the aperture shape of the second beam shaping aperture mask is not limited to the rectangular shape, but may be a polygonal shape (five sides or more) as shown in FIG. Also,
The second aperture 22a may be formed by two openings. That is, the first aperture is provided so that the beam does not contact the second aperture 22a when the beam is deflected to b, and the beam does not contact the second aperture 22a when the beam is deflected to c. It suffices that the second opening be provided in the first opening, and the region between the first opening and the second opening need not be opened. In short, the second
It suffices that the size of the aperture 22a is larger than that of the first aperture image 21a in at least one direction.

Further, as a means for detecting the beam position at the position where the aperture mask for beam detection is arranged, as shown in FIG. 5 (a), the aperture mask 31 is divided into four, and the current flowing into each of the aperture masks 31a, ... It is also possible to obtain the beam position by detecting it. in this case,
The beam detecting deflector and the backscattered electron detector are not required. Further, as shown in FIG. 5 (b), the aperture masks 31a, 31d, and 31d, which are divided into four parts, may be partially overlapped with each other except at the central portion to eliminate the gap between the masks. Further, a Faraday cup may be provided on the sample surface, and instead of detecting the reflected electrons, an electron beam that has passed through the beam detection aperture mask may be detected.

Further, it is also possible to apply to an ion beam drawing apparatus of a variable size beam system using an ion beam instead of an electron beam. In addition, various modifications can be made without departing from the scope of the present invention.

[Advantages of the Invention] As described in detail above, according to the present invention, focusing of the projection lens can be performed with high accuracy and in a short time. Therefore, it is possible to prevent deterioration of drawing accuracy due to defocusing of the lens and the like, and it is possible to improve drawing accuracy.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an electron beam drawing apparatus according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing a relationship between a second aperture and a first aperture image used in the apparatus, and a third diagram.
FIG. 4 is a schematic diagram for explaining the operation of the above-mentioned device, and FIGS. 4 and 5 are for explaining modified examples, respectively.
FIG. 5 is a schematic view showing the relationship between the second aperture image and the first aperture image, FIG. 5 is a plan view showing an aperture mask for beam detection, and FIG. 6 is a schematic configuration diagram showing a conventional device. 10 …… electron gun, 11, 12 …… condenser lens, 13 …… projection lens, 14 …… reduction lens, 15 …… objective lens, 16…
... sample surface, 17 ... blanking electrode, 21 ... first beam forming aperture mask, 22 ... second beam forming aperture mask, 23 ... beam forming deflector, 24 ...
Beam scanning deflectors, 31, 31a, ..., 31d ... Beam detection aperture masks, 32 ... Beam detection deflectors, 33 ...
Backscattered electron detector.

Claims (4)

[Claims] 1. An aperture image of a first beam shaping aperture mask is projected onto a second beam shaping aperture mask by a projection lens, and a second beam shaping aperture mask is projected by a beam shaping deflector. The projection position is changed by, and the shaping aperture image synthesized by the aperture image of the first beam shaping aperture mask and the aperture of the second beam shaping aperture mask is scanned on the sample surface, and the sample surface is scanned. In a charged beam drawing apparatus for drawing a desired pattern on the beam detecting aperture mask provided at a position where the deflection center of the beam forming deflector is to be projected, and a position for arranging the beam detecting aperture mask. Means for detecting the center position of the beam, and the second beam shaping aperture mask Charged particle beam drawing apparatus characterized by aperture dimension is larger in at least one direction than the size of the aperture image of the first beam shaping aperture mask. 2. A beam detecting deflector for scanning the beam on the beam detecting aperture mask, and an electron for detecting reflected electrons from the aperture mask, as means for detecting the center position of the beam. The charged particle beam drawing apparatus according to claim 1, further comprising a detector. 3. A beam detecting deflector for scanning a beam on the beam detecting aperture mask, and a beam detecting deflector for detecting an electron beam passing through the aperture mask, as means for detecting the center position of the beam. Claim 1 characterized in that a Faraday cup is provided.
Charged beam drawing apparatus according to the item. 4. The beam detecting aperture mask is divided into a plurality of means as means for detecting the center position of the beam, and the inflow current is detected for each of the divided aperture masks. Charged beam drawing apparatus according to item 1.