JP2009216872A - Exposure photomask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of an increase in the cost when an exposure apparatus with a shorter wavelength is used to form a finer pattern than the resolution limit in a process of manufacturing a semiconductor element. <P>SOLUTION: The pattern 4 of an exposure photomask 2 is corrected. A basic pattern 8 being a light-transmitting region where a projection image by an exposure device is formed in the size corresponding to the resolution limit is combined with an auxiliary pattern 10 that shields part of the light-transmitting region against light and divides the residual light-transmitting region into a plurality of partial light-transmitting regions 16. For example, strip-like light-shielding regions 14v, 14h are disposed along the center axes 12v, 12h of the rectangular basic pattern 8, respectively, so as to dispose a cross-shaped auxiliary pattern 10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a photomask for exposure used in a projection exposure apparatus used for manufacturing a semiconductor device or the like.

  As the degree of integration of semiconductor integrated circuits increases, the pattern formed on the semiconductor substrate is miniaturized. Among them, the contact opening pattern is one of the finest and can be designed to have a dimension corresponding to the resolution limit of the exposure apparatus.

Incidentally, the resolution limit R of the exposure apparatus is given by the following equation called the Rayleigh equation.
R = k ₁ · λ / NA (1)

Here, λ is the exposure wavelength, NA is the numerical aperture of the lens, and k ₁ is a proportional coefficient. Of these, λ and NA are determined by the exposure apparatus. In order to reduce R while reducing the decrease in focal depth DOF, a decrease in λ is more advantageous than an increase in NA. Therefore, an exposure apparatus has been developed in which the g-line (λ = 436 nm) to i-line (λ = 365 nm), KrF excimer laser (λ = 248 nm), and the exposure light source have a short wavelength. Incidentally, k ₁ changes not only by the exposure apparatus but also by the resolution performance of the resist material, the controllability of the lithography process, etc., and research and development for increasing the resolution are also in progress in these processes.

Now, in the manufacture of integrated circuits, there is a case where a reduction in the size of the contact opening (for example, down to about 10%) is required to secure a process margin. However, when the original contact opening is designed to have a size corresponding to the resolution limit, the contact opening can be satisfactorily formed even if the contact opening pattern size on the exposure photomask is simply reduced. I can't. In such a case, conventionally, an exposure apparatus having a smaller wavelength λ is used, or the k ₁ factor is reduced by changing the process to meet the demand for size reduction.

A super-resolution technique that enables fine processing beyond the resolution limit has also been proposed and put into practical use. Among them, a phase shift method and an auxiliary pattern method are known as related to a photomask for exposure. The auxiliary pattern method relates to optical proximity effect correction (OPC: Optical Proximity Correction), and an auxiliary pattern less than the size of the main pattern is formed around the main pattern to produce an optical proximity effect (OPE: Optical Proximity Effect). The deformation of the projected image of the main pattern due to is corrected.
JP-A-9-73166

  In general, the shorter the wavelength λ, the more expensive the exposure apparatus. Therefore, when a fine pattern such as a contact opening is formed to be smaller than the resolution limit, there is a problem that the processing cost increases when the wavelength is shortened. Further, when miniaturization is attempted by changing the process, there has been a problem that a significant change of the process is required or it takes time to set the conditions.

  The photomask for exposure according to the present invention is used in a projection exposure apparatus in which a pattern is formed with a light-shielding film on a transparent substrate and has a predetermined resolution limit, and the pattern depends on the projection exposure apparatus. A basic pattern which is a light-transmitting area formed in a size corresponding to the resolution limit, and a part of the light-transmitting area is shielded, and the remaining light-transmitting areas are divided into a plurality of partial light-transmitting areas. A microfabricated pattern synthesized with an auxiliary pattern to be divided into two.

  According to the present invention, it is possible to form a slightly smaller contact opening or the like by changing the pattern of the exposure photomask. As a result, an increase in processing cost due to the shortening of the wavelength of the exposure apparatus can be avoided, and the work load for changing process conditions can be reduced.

  In addition, since the auxiliary pattern is arranged inside the basic pattern, the optical proximity effect with other patterns outside the basic pattern hardly occurs. When designing a mask by OPC in consideration of a pattern arranged outside the basic pattern, a heavy load calculation may be required. On the other hand, according to the present invention, since the layout change for the outer pattern is basically unnecessary, the design change of the exposure photomask can be easily performed.

  Hereinafter, an exposure photomask (hereinafter referred to as a photomask) 2 that is an embodiment of the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings. FIG. 1 is a schematic partial plan view of a photomask 2 according to the first embodiment. FIG. 2 is a schematic partial plan view of a conventional photomask 6 serving as a basis for designing the photomask 2 of FIG.

  These photomasks 2 and 6 are formed with a light shielding film made of chromium (Cr) or the like on a transparent substrate such as quartz glass. FIG. 1 shows a pattern 4 for forming a contact opening, which is an example of a pattern embodying the present invention, as a part of the pattern, while FIG. 2 shows a conventional pattern for forming a contact opening ( A basic pattern 8) is shown.

  The photomasks 2 and 6 are set in a projection exposure apparatus such as a stepper. The projection exposure apparatus irradiates the photomasks 2 and 6 with light having a wavelength λ from a light source, and forms an image of light transmitted through the photomasks 2 and 6 on an object to be exposed such as a semiconductor substrate by an optical system including lenses. Then, the photoresist applied to the surface of the object to be exposed is exposed.

  By developing after exposure, the photoresist is processed into a pattern corresponding to the exposure pattern. Etching and ion implantation are performed using the patterned photoresist as a mask. For example, the contact opening is formed by etching away an interlayer insulating film or the like using a photoresist as an etching mask. This embodiment corresponds to the case where a positive type photoresist is used, and basically a light-transmitting region of a photomask is provided corresponding to a portion where an opening is formed in the photoresist.

  A conventionally used pattern 8 shown in FIG. 2 is a light-transmitting region where a projection image having a size corresponding to the resolution limit is formed on the photoresist. Usually, the contact opening is designed to be rectangular. Pattern 8 shows a pattern in which vertical and horizontal are substantially equal as an example of a rectangle, that is, a substantially square contact opening is formed. Incidentally, in this case, the length of a rectangular side obtained by projecting the pattern 8 onto the photoresist surface (image surface of the projection exposure apparatus) is designed to be a size corresponding to the resolution limit. Therefore, for example, the size of the side of the rectangle of the pattern 8 formed on the photomask used in the stepper for reducing and projecting to 1/5 has a value corresponding to 5 times the resolution limit.

  A pattern 4 shown in FIG. 1 is obtained by adding an auxiliary pattern 10 in a light transmitting region formed by the basic pattern 8. The auxiliary pattern 10 is strip-shaped light shielding regions 14v and 14h arranged along the central axes 12v and 12h of the basic pattern 8, and the light shielding regions 14v and 14h intersect each other to form a cross shape. The cross-shaped auxiliary pattern 10 shields a part of the light transmitting region of the basic pattern 8 and divides the remaining light transmitting region into four partial light transmitting regions 16-1 to 16-4.

  In FIG. 1, the central axis 12v is a vertical dotted line passing through the midpoints of the upper and lower sides of the basic pattern 8, and the central axis 12h is a horizontal dotted line passing through the midpoints of the left and right sides of the basic pattern 8. .

  The widths (band widths) of the light shielding regions 14v and 14h are set so that the projected images of the partial light transmitting regions 16 adjacent in the horizontal direction or the vertical direction in FIG.

  FIG. 3 is a schematic diagram of the projected image 20 of the pattern 4 that can be formed by the projection exposure apparatus on which the photomask 2 is set. In FIG. 3, for comparison, a pattern 4i obtained by scaling the pattern 4 on the photomask 2 in accordance with the magnification of the projection exposure apparatus and a projection image 22 of the conventional basic pattern 8 are displayed by dotted lines.

  The light intensity in the projection image 20 forms a peak in the region 20 s in each partial light transmission region 16. In FIG. 3, the region 20 m located between the regions 20 s adjacent in the vertical direction or the horizontal direction is a region corresponding to the light shielding region of the pattern 4, but the proximity effect of the light transmitted through the partial light transmitting regions 16 on both sides thereof. Has the light intensity. The light intensity is basically lower than the peaks of the partially light-transmitting regions 16 on both sides, and further becomes weaker as the distance from the straight line L connecting the peak positions increases. Therefore, the contour of the projected image 20 determined based on the light intensity equal to or higher than the threshold Ex that the photoresist is exposed to recedes inward from the projected image 22 in the region 20m.

  FIG. 4 is a conceptual diagram of the light intensity distribution 30 of the projected image 20 along the diagonal line AA of the pattern 4. In the figure, the horizontal axis represents the position along the diagonal, and the vertical axis represents the light intensity. For comparison, the light intensity distribution 32 along the diagonal line AA of the projection image 22 is indicated by a dotted line in FIG. The heights of the peaks 34-1 and 34-2 generated corresponding to the partially light-transmitting regions 16-1 and 16-3 correspond to the light intensity distribution 32 according to the difference in the amount of transmitted light between the pattern 4 and the conventional pattern 8. The light intensity distribution 30 is basically lower than the light intensity distribution 32 as a whole. As a result, the size of the projection image 20 having a light intensity equal to or higher than the threshold value Ex can be smaller than the projection image 22 in the diagonal direction.

  As described above, the pattern 4 of the photomask 2 according to the embodiment can form a projection image 20 having a shape corresponding to the basic pattern 8 and slightly smaller than the projection image 22 formed by the basic pattern 8. it can. By using an etching mask formed by patterning a photoresist with the projected image 20, it is possible to form a contact opening having a smaller shape than when the projected image 22 corresponding to the resolution limit is used. .

  As shown in FIG. 3, the central portion of the projection image 20, that is, the region 20 w corresponding to the intersection of the light shielding regions 14 v and 14 h is far from each region 20 s corresponding to the peak position of the light intensity. At 20w, the light intensity can be minimal. Therefore, the light intensity in the region 20w becomes less than the threshold value Ex, and the photoresist in the region may not be dissolved during development. However, even in that case, the photoresist in the minute region 20w can be peeled off and removed when the surrounding photoresist is dissolved and removed.

  On the other hand, in this regard, a photomask 40 having another pattern can be used instead of the pattern 4. FIG. 5 is a schematic partial plan view of a photomask 40 according to the second embodiment of the present invention. The photomask 40 has another pattern 42 for forming a contact opening in place of the pattern 4. In FIG. 5, the same components as those in the first embodiment are denoted by the same reference numerals. The auxiliary pattern 44 arranged in the basic pattern 8 in the pattern 42 is other than the intersecting portion of the band-shaped light shielding regions 14v and 14h along the central axes 12v and 12h described above, and the intersecting portion is a translucent region. (Partially transparent region 16-5). According to this configuration, it is possible to increase the light intensity at the center of the projected image 20 to the threshold value Ex or higher and dissolve and remove the photoresist at that portion by development.

  Incidentally, in the pattern 42, the five partial light-transmitting regions 16-1 to 16-5 are formed by the auxiliary pattern 44. The auxiliary pattern can be arranged so that more partially light-transmitting regions are formed. For example, when a rectangular piece constituting the basic pattern 8 has a size larger than the resolution limit, the auxiliary pattern is arranged so that three or more partial light-transmitting regions are formed in the direction along the side. May be.

  The exposure photomask according to the present invention is applied regardless of whether or not the object to be exposed is a semiconductor substrate. For example, the exposure photomask is used for producing a circuit substrate such as a liquid crystal panel. You can also

It is a typical partial top view of the photomask for exposure which concerns on the 1st Embodiment of this invention. It is a typical partial top view of the conventional photomask for exposure. It is a schematic diagram of the projection image of the pattern of the photomask for exposure of 1st Embodiment formed of the projection exposure apparatus. It is a conceptual diagram of the light intensity distribution of the projection image along the diagonal line AA of the pattern of the photomask for exposure of 1st Embodiment. It is a typical partial top view of the photomask for exposure which is the 2nd Embodiment of this invention.

Explanation of symbols

  2,40 photomasks, 4,42 patterns, 8 basic patterns, 10,44 auxiliary patterns, 14v, 14h light shielding area, 16 partial light shielding areas, 20, 22 projection images.

Claims (4)

In a photomask for exposure used in a projection exposure apparatus in which a pattern is formed with a light shielding film on a transparent substrate and has a predetermined resolution limit,
The pattern includes a basic pattern, which is a translucent area in which a projection image by the projection exposure apparatus is formed in a size corresponding to the resolution limit, and a part of the translucent area is shielded and the remaining translucent area. A photomask for exposure, comprising a microfabricated pattern obtained by synthesizing an auxiliary pattern for dividing a light region into a plurality of partially light-transmitting regions. In the photomask for exposure according to claim 1,
The photomask for exposure according to claim 1, wherein the auxiliary pattern is formed so as to produce a light proximity effect between the partially transparent regions adjacent to each other. In the photomask for exposure according to claim 1 or 2,
The basic pattern is a rectangle whose size along the first side and the second side orthogonal to each other is a size corresponding to the resolution limit in the projection image,
The auxiliary pattern is disposed along a first central axis that passes through a midpoint of each of the first side and its opposite side, and a second central axis that passes through a midpoint of each of the second side and its opposite side. Be a cross-shaped pattern,
A photomask for exposure. In the photomask for exposure according to claim 3,
Of the band-like region along the first central axis and the band-like region along the second central axis, the portions other than the intersection of the two belt-like regions are used as the auxiliary pattern, and the intersection is a light-transmitting region. The photomask for exposure characterized by these.

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