JPH0341975B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a figure division method in electron beam exposure, and particularly to a method for creating drawing data from design pattern data for an integrated circuit or the like in pattern formation using an electron beam.

Electron beam exposure has attracted particular attention as a pattern forming technology for semiconductor integrated circuits because the wavelength of electrons is short and is suitable for forming fine patterns, and because electrons have a charge, it is easy to control. It has already begun to be applied to the production of photomasks. As integrated circuits become even larger in the future,
A wide variety of LSIs are required in small quantities, and as an alternative to the conventional process using masks, direct writing technology on wafers using electron beams, which does not require the production of masks, is seen as a promising manufacturing technology. In order to establish direct writing technology using an electron beam, the most important requirement was to improve the productivity of exposure equipment, but an exposure equipment that uses a variable shaped beam was proposed, and the writing speed was significantly improved. The reason is,
In the conventional point beam method, the pattern is filled with points, whereas in the variable shaping beam method, the graphic pattern is divided into rectangles with sides of up to 10 μm, and each rectangle is filled with a surface, so to speak. be. It is important to note here that in the point beam method, the drawing time is determined by the area of the pattern to be filled, whereas in the variable shaped beam method, the drawing time is determined by the number of surfaces to be filled, that is, the number of shots. . In other words, in the variable shaped beam method, even when forming the same pattern, the productivity of the exposure apparatus is improved by changing the method of dividing the pattern and reducing the number of shots.

Now, when forming an integrated circuit pattern by electron beam exposure, the graphic data obtained from the design cannot be used as drawing data for electron beam exposure in its original form. The reason for this is that while design figures are generally described as polygons, electron beam writing data only allows trapezoids at most, and the figure data output in design is expressed only in rectangles. Even so, this is because rectangles overlap each other and result in multiple exposure, which is not suitable for drawing data. Therefore, the design data is subjected to, for example, contouring processing to remove multiple exposures, and then divided into basic figures such as rectangles and trapezoids or drawing unit figures. Here, I would like to touch on basic figures and drawing unit figures.Basic figures are the figures obtained when various patterns are divided into simple patterns such as rectangles and trapezoids, and drawing unit figures are the figures used for drawing. It is a unit figure for pattern creation. In a point beam type exposure apparatus, a basic figure is usually a drawing unit figure. However, in the shaped beam method, since the basic figure generally exceeds the maximum beam size, the basic figure is further divided into figures of less than the maximum beam size to form drawing unit figures. In order to obtain a drawing unit figure using the shaped beam method, there is a method of cutting out the drawing unit figure directly from the contoured figure, but this method tends to damage the repeatability of the drawing unit figure and is not suitable for data compression. For this reason, it is usually divided into basic figures and then divided into drawing unit figures. The following explanation will be based on the latter method.

Conventionally, processing speed has been considered important in the division method into basic figures. An example of the conventional method will be explained using FIG. One contour figure that can be expressed as a collection of rectangles with no slope is represented by P. This contour figure P
Among the sides representing the contour, the side parallel to the X axis is expressed as = (x, x', y). Here, x and x' are the X coordinate values at both ends of the side, x<x', and y is the Y coordinate value of the side. It can be processed and decomposed into basic figures as defined above.

(1) Among the sides of P parallel to the X-axis, choose the one with the maximum y-coordinate value.

Let = (x ₁ , x ₁ ′, y ₁ ).

(2) Among the sides whose projections in the Y-axis direction overlap, choose the one with the largest Y coordinate.

= (x ₂ , x ₂ ′, y ₂ ), (x ₁ , x ₁ ′) ∩ (x ₂ , x ₂ ′) ≠ 0 (3) Draw rectangle L perpendicularly from the side, point A, and point B. The area enclosed by the line and a part or extension of the side. That is, x ₁ ′≦x
A rectangle is a set of points (x, y) that satisfy ≦x ₁ and y ₂ <y<y ₁ .

(4) If L=P, the process is finished; if not, the figure obtained by removing L from P is set as a new P, and the process returns to (1) and the same process is repeated.

The above method was described as a method of focusing on the side with the maximum Y coordinate value and projecting it downward, but it is also possible to reverse the idea of up and down and project from the bottom to the top,
The same is true if we consider it as a left-right projection. Here, we will take up the above-mentioned top-to-bottom projection, and hereinafter this division method will be referred to as a conventional division method and compared with the present invention.

There are other conventional methods for dividing outline figures into basic figures, but either method has problems in pattern formation. First of all, when a variable shaping beam is used, the number of shots increases significantly and productivity decreases, and when a point beam is used, the beam position is susceptible to fluctuations, so-called beam drift, resulting in pattern distortion. Quality tends to deteriorate. Second, when shaped beams are used, pattern quality deteriorates at the joints of each shot because beams of various sizes are mixed.

The first problem will be explained using FIGS. 2A to 2C. This pattern actually exists in the gate pattern of 64K-bit MOS memory, has a width of approximately 2 μm, a length of over 2 mm, and is repeated over 100 times on one chip. When the above-mentioned division method is applied to the contour figure of FIG. 2A, the contour figure 2B is obtained. In the point beam method, this figure becomes the drawing unit figure, but if you draw it twice as an extremely thin and adjacent figure like this, it will be affected by beam drift, and the patterns will tend to separate at the contact area between the two patterns. Pattern quality tends to deteriorate. In the variable shaping beam method, the figure shown in FIG. 2C, which is obtained by further dividing the figure shown in FIG. 2B by the maximum dimension of the beam used, becomes the figure of the drawing unit, but in this case, the number of shots increases.

Next, the second problem will be explained using FIGS. 3A to 3C. As is already known, due to space charge effects, the shaping beam edge droop is proportional to the beam current. Figure 3A shows the drooping of this beam edge. Here, the vertical axis represents the current density of the shaped beam, and the horizontal axis represents the beam dimensions. Since the current density of the beam is constant, as the beam size increases, the beam current increases and the width of the beam edge dip becomes larger. That is, in FIG. 3A, the droop widths S ₁ and S ₂ satisfy S ₂ >S ₁ . FIG. 3B shows a case where beams with the same beam size are connected, and FIG. 3C shows a case where beams with different beam sizes are connected. In FIGS. 3B and 3C, the vertical and horizontal axes are the same as in FIG. 3A. If the beam dimensions are the same, the overall current density, that is, the charge distribution, will be flat as shown in Figure 3B, as shown by the dotted line, but if the beam dimensions are different, it will be flat as shown in Figure 3C. As shown by the dotted line, the charge distribution becomes non-uniform. This bias in charge distribution becomes more noticeable when the beam dimensions differ greatly, and the pattern becomes more likely to be interrupted, resulting in a deterioration in pattern quality. Therefore, in pattern formation, it is not desirable to connect shots with greatly different beam currents, and the use of beams with extremely large or small beam currents must be avoided. For these reasons, it is necessary to set the upper and lower limits of the beam area to be used, but although it is easy to set the upper limit of the area, it is extremely difficult to specify the lower limit of the beam area to be used for a variety of LSI patterns. It is difficult and no special treatment has been applied until now.

An object of the present invention is to provide a graphic division method that solves the second problem mentioned above.

In order to achieve the above object, the present invention provides that, when a figure pattern to be formed is divided into basic figures consisting of rectangles, in the figure dividing step, a first contoured figure pattern or a newly generated figure pattern is created by the division. a step of determining whether or not there is a short side smaller than the allowable minimum value ε of the side length of the shaped beam among the sides of the contour of the figure pattern; and the minimum allowable value ε from the extension line of the short side.
Search to see if there is an edge other than the short side in the distant area, and if there is an edge other than the short side, use the division path up to the point where that edge starts to exist, and if it does not exist, A process of dividing a figure by using a line up to a point where it intersects with a side other than the short side as a dividing route, and when a line other than the extension line of the short side is used as a dividing route, the minimum allowable value ε is calculated from the dividing route. Search to see if there is an edge of the figure to be divided within a distant area, and if the edge exists, use the division path up to the point where the edge begins to exist, and if it does not exist, search for edges other than the edge. This method includes the step of dividing the figure by forming a dividing path up to the point where the edges intersect.

As described above, according to the present invention, a minimum permissible value ε of the side length of the shaped beam is set, and the beam is divided so as not to generate a drawing unit figure having a shorter side than this, so the lower limit of the area of the beam is set. As a result, the bias in the charge distribution due to large differences in beam dimensions is avoided, and the quality of the drawn pattern is improved.

Next, the present invention will be explained based on examples.

In order to explain the embodiments of the present invention in an easy-to-understand manner, it is assumed that the graphic pattern of the integrated circuit is composed of a collection of rectangles with no slope. If there is a figure that includes diagonal lines such as a tilted rectangle,
Although additional processing is required in addition to the embodiments of the present invention shown below, the present invention is still applicable. The electron beam exposure apparatus will be described below as one of a variable shaping beam type, which is particularly effective in achieving the effects obtained by the present invention.

Before describing the embodiments of the present invention in detail, an outline of the embodiments will be described below.

(1) Determine whether there is a short side among the sides of the contoured shape where the length of one side of the shaped beam is smaller than the allowable minimum value ε, and if it exists, divide the line extending that short side. By dividing the shape as a route, there will be no short side smaller than ε in the contour of the divided figure (corresponding to FIG. 4).

(2) In the case of (1), new ε is added to the outline of the new figure generated by one division.
If a short side of less than
).

(3) In the case of (1), in order to avoid the division resulting in a figure with a width less than ε, search for the existence of an edge from the division route to an area ε away, and if it exists, search for the edge. The division path is defined as the point where the line begins to exist, and does not extend beyond that point (corresponding to D in Figure 4).

(4) Classify the figures divided by (1) to (3) into two types.

Type: When the projection in the direction (downward) of the top edge parallel to the X axis overlaps with edges other than the top edge (corresponding to Figure 5A).

Type: When the projection of the top edge parallel to the X axis in the Y direction (downward) touches the edge parallel to the X axis (the fifth
(corresponds to Figure B).

(5) The shape of the mold and mold is further determined by the length of the top side w, the length of the top side of the forming beam l, and the dividing path.
Classification is performed based on the magnitude relationship between the length l _cx of C _x and the length l _cy of the dividing path _Cy (corresponding to FIGS. 6 and 10).

(6) Divide the figure classified in (5) using the conventional dividing method.

(7) In the division of (6), divide using the conventional division method,
When this is further divided into drawing unit figures, the number of divisions will increase and the figures (which are known in advance) will be classified into undesirable classifications using a different division route than the conventional method (C _y for types, C for types). _x )
(type: corresponds to Figure 7b).

(8) In the division in (6), for those divided using the conventional division method (C _x for the mold, C _y for the mold), the result of division is a figure with a width less than ε. In order to avoid this, it is searched to see if an edge exists up to a region ε away from the division route, and if it exists, the division route is set up to the point where that edge begins to exist, and it is not extended any further (9th
(corresponding to Figure and Figure 12).

(9) Repeat steps (4) to (8) to divide all shapes into basic shapes.

(10) Divide the basic figure into drawing unit figures.

The above is an outline of the embodiment of the figure division method of the present invention, and the present invention is used in the steps (1), (2), (3), and (8) above.

Next, embodiments of the present invention will be described in more detail.

First, a description will be given of processing when a short side with a length less than ε exists among the sides of the outline of a graphic pattern. Fourth
An example is shown in Figure A. The length indicated by ε in the figure is
This is the minimum allowable length of one side of the shaped beam. The value of ε varies depending on the maximum beam size, beam current density, etc., but for example, ε=0.5 μm is considered. The broken line indicates a dividing path according to the conventional dividing method, and if this is followed, a basic figure with a short side whose side length is less than ε will be generated. In this way, in the case of a figure that has a short side with a length less than ε among the sides representing the outline, if this figure is divided into basic figures as it is, it is likely to produce basic figures with sides whose side length is less than ε. . Therefore, in the present invention, if there is a short side with a length less than ε, the short side is extended and used as a dividing path, and the original figure is divided in advance. An example is shown in FIG. 4B. Here, the broken line is the dividing route when the present invention is implemented. Two cases need to be considered when extending the short side to form a dividing path. One is the case where, as shown in FIG. 4C, as a result of division by extending the short sides, a step called ABCD, which includes the short sides of ε or less, appears in the cut figure. In this case, simply extend the newly generated short side BC and use CE as the next cutting path. The other case is as shown in FIG. 4D, where a peninsular shape ACDE whose width is less than ε is produced as a result of division by extending the short side. In this kind of division, one side is ε
It is desirable to avoid this because it will not be possible to form a batten unless a beam with a diameter smaller than Therefore, when extending a division route, we search for the existence of a pattern boundary including neighboring regions that are ε away from the route. up to the point where it starts. In the example shown in FIG. 4D, ABE becomes a new dividing route. The handling of the newly generated BE level difference less than ε is the same as in the case of FIG. 4C, as described above.

Note that if a peninsular pattern with a width less than ε exists in the first place, the beam size for forming this pattern must also be less than ε. Also, in the case of the pattern shown in Fig. 4E, unless multiple exposure is allowed,
No matter what division path is chosen, a basic figure with one side less than ε is required.

As a result of the above processing, there is no short side with a length less than ε among the sides of the contour figure, except in unavoidable cases as shown in FIG. 4E. I will explain.

First, graphic patterns are classified into two types. Representative patterns of these two types are shown in FIGS. 5A and 5B. Here, w is the length of the top edge, C _x ,
C _y indicates candidates for dividing routes in each pattern. Focusing on the top edge parallel to _the X axis = ₍ x ₁ , The projection is first on the other side parallel to the X axis and x = x ₁ or x
The case of contact at =x ₁ ′ is a type. That is,
As shown in Figure 5A, the projection of side AB is first
When they overlap at CD, it is a mold, and when they first come into contact with side EF, as shown in FIG. 5B, it is a mold. On the other hand, as shown in Figure 5C,
If it applies to both types, it will be classified as type. In this way, all graphic patterns can definitely be classified into one of the types.

First, a method of dividing a type graphic pattern will be explained.

The dividing path is either C _x or C _y in FIG. 5A. FIG. 6 shows the classification of patterns according to the magnitude relationship of the length w of the uppermost side, the length l of the maximum side of the shaped beam, the length l _cx of the dividing path C _x , and the length l _cy of the dividing path _Cy . w, l _cy was compared with l, and l _cx was compared with l _cy ×n. l _cx may be compared with l, but in order to make the pattern shape dependence more pronounced, n of l _cy
(n is an integer, for example, n=2).

In the conventional division method, C _x is used as the division path, but among the various patterns shown in FIG. 6, the number of shots increases and the division becomes undesirable in case (3).
FIG. 7A shows the state of division using the conventional method using drawing unit figures. In such a case, that is, when w≧l, l _cx ≧nl _cy , and l _cy <l, division is performed using the C _y path of the present invention.

A divided embodiment of the invention is shown in FIG. 6B. Compared to the conventional division method, the effect of reducing the number of shots is obvious.

Now, when C _y is used as a dividing path, edges with length less than ε cannot occur, but when C _x is used as a dividing path, care must be taken to ensure that edges less than ε occur. . The case where C _x is a divided path will be explained using FIG. 8.

In the same figure, w, C _x and C _y are already in Figure 5A,
As shown in B. Here, the dashed-dotted line m at a distance p below the dividing path C _x is
This shows that a graphic pattern always exists up to that point. As shown in Figure 8A, if p≧ε, there is a sufficiently large figure pattern below the division path C _x , so there will be no problem with the remaining figure patterns below when dividing by C _x . . However, as shown in FIG. 8B, when p<ε, a drawing unit figure whose side length is less than ε is generated in the figure pattern below C _x , so division at C _x is inappropriate as it is.

Therefore, when extending the division route, we search for the existence of a pattern boundary, including the region ε away from the route below, and if a pattern boundary exists, the extension of the division route is performed until the pattern boundary is new in the vicinity. up to the point where it begins to exist.

For example, in the pattern shown in Figure 9, the dividing route is set to point D.
Instead of extending from to G to point H, we will divide it into a rectangle with one side of .

Next, a method of dividing a graphic pattern of the type shown in FIG. 5B will be explained.

The dividing path is either C _x or C _y in FIG. 5B. As in the case of molds, the classification of various patterns is shown in FIG.

w, l, _lcy , and n are as already shown in the explanation of FIG. In the figure pattern of the type _{, the} length of _the division path C _x in the Just think about it.

In the conventional division method, C _y is used as the division path, but among the various patterns shown in FIG. 10, the number of shots increases and the division becomes undesirable in case (4). That is, in the case of w<l, l _cy ≧nw, the present invention divides along the dividing path C _x .

In patterns other than (4) in Fig. 10, that is, patterns (1), (2), and (3), C _y is the dividing path, but
Similar to the mold, the minimum allowable length ε for one side
It is necessary to perform a division that does not produce edges less than . An example to which the present invention is applied will be explained using FIG. 11. w, C _x , C _y , p, and m are as shown in FIG.

As shown in FIG. 11A, if p≧ε, there is a sufficiently large figure to the right of the division path C _y , so
When dividing by C _y , there will be no problem with the remaining figure pattern on the right. As shown in Fig. 11B, when p<ε, the figure pattern on the right side of C _y does not produce a figure whose side length is less than ε, so the pattern boundary is searched including the area ε away from the dividing route, and the dividing Determine the route. FIG. 12A shows a case where the pattern shown in FIG. 11 is divided according to the present invention. The shaded part is the figure to be cut out. Special examples of molds are shown in Figures 12B and C. Here, if the Y value of the side that touches the projection of side AB in the Y-axis direction is equal on the left and right, for example, as shown in Figure 12B, if w≧l, then
Divide by C _y ', and if w<l, as shown in FIG. 12C, divide by C _x .

A comparison of division between the embodiment to which the present invention has been applied and the conventional method described above is shown in FIGS. 13A and 13B.

In the division shown in FIG. 13B according to the conventional method, there are many drawing unit figures with small sides, but in the division shown in FIG. 13A according to the embodiment to which the present invention is applied, there are almost no drawing unit figures with small sides. I can see that you haven't.

As described above, when pattern formation is performed using a variable shaped beam according to the figure division method in electron beam exposure according to the present invention, the beam area used can be made uniform and pattern quality can be improved.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the conventional figure division method, Figure 2A
~C is an explanatory diagram of the problems of the conventional division method, Figure 2D
3 is a diagram showing an example of pattern division according to the present invention.
Figures A to C are diagrams showing the sagging width of the beam edge.
Figures A to E, Figures 5 A to C, Figures 7 A and B, Figures 8 A and B, Figure 9, Figures 11 A and B, and Figure 12 A
-C are pattern diagrams for explaining the division method of the present invention based on various forms of patterns, Fig. 6, Fig. 1
Figure 0 is a diagram for explaining the application of the present invention, Figure 13
Figures A and B are plot diagrams for comparison with conventionally used division methods. P...Contour figure, L...Rectangle, _S1 , _S2 ...Dip width, ε...Minimum allowable width, w...Length of the top side,
l... Length of the maximum side of the shaped beam, C _x , C _y ...
Division path, l _cx , l _cy ... Division length, p... distance, m
...distance p below the dividing path C _x or outside C _y
A location far away.

Claims (1)

[Claims] 1. In a figure dividing method in electron beam exposure in which a figure pattern to be formed is divided into basic figures consisting of rectangles when forming a pattern using an electron beam, an initial outlined figure pattern or a step of determining whether or not there is a short side smaller than an allowable minimum value ε of the side length of the formed beam among the sides of the contour of the figure pattern newly generated by the division; If so, extend the short side and calculate the minimum allowable value ε from the extension line of the short side.
Search to see if there is an edge other than the short side in the distant area, and if there is an edge other than the short side, use the division path up to the point where that edge starts to exist, and if it does not exist, A process of dividing a figure by using a line up to a point where it intersects with a side other than the short side as a dividing route, and when a line other than the extension line of the short side is used as a dividing route, the minimum allowable value ε is calculated from the dividing route. Search to see if there is an edge of the figure to be divided within a distant area, and if the edge exists, use the division path up to the point where the edge begins to exist, and if it does not exist, search for edges other than the edge. A method for dividing a figure in electron beam exposure, comprising the step of dividing the figure by forming a dividing path up to a point where the edges intersect.