JP2012145630A - Photomask and exposure method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photomask and an exposure method which allow an exposure pattern with a size equal to or smaller than a wavelength of an exposure light beam to be obtained at low cost and high throughput.SOLUTION: According to one embodiment of the present invention, a photomask 100 includes a substrate and a light-shielding film. The substrate transmits an incident exposure light beam toward a body to be transferred. The light-shielding film is formed on the substrate and shields the exposure light beam. In the light-shielding film, plural square apertures 11, disposed in a lattice shape, are formed.

Description

  The present invention relates to a photomask and an exposure method, and more particularly to a photomask and an exposure method used in an exposure apparatus in a semiconductor manufacturing process.

  In the manufacturing process of a semiconductor element, there is a process for forming a pattern of a semiconductor element on a substrate. In general, a photolithography technique is known as a pattern formation technique for semiconductor elements. In recent years, since the miniaturization of elements has progressed, it is considered that the development of semiconductor elements and their manufacturing techniques will be hindered unless the difficulties resulting from photolithography technology are overcome.

  According to Rayleigh resolution criteria, the minimum width (ie, resolution) that the optical system can discern is proportional to the wavelength (λ) of the light beam and inversely proportional to the numerical aperture. When an exposure light source having a short wavelength or a lens having a large numerical aperture is used, the resolution is theoretically improved and a smaller pattern width can be realized. However, in this case, there arises a problem that the depth of focus becomes small.

  Moreover, as a super-resolution technique (Resolution Enhancement Technology: RET) in the photolithography process, a modified illumination (Off-Axis Illumination: OAI), a phase shift mask (Phase Shift Mask: PSM), and an optical proximity effect correction (Optical Proximity Cryptography: Optical Optix). OPC) is known.

  Optical proximity effect correction (OPC) is a technique that compensates for the effects of light diffraction. If the pattern width is close to the wavelength of the exposure light beam, the exposure light beam may produce a diffraction effect when passing through the mask. As a result, the exposure pattern is distorted by the accumulation of diffracted light. Optical proximity effect correction (OPC) takes into account diffraction effects and compensates for distortion of the exposed pattern. Specifically, the pattern on the mask is corrected so that the accumulated diffracted light matches a predetermined pattern and width.

  Other super-resolution techniques have been proposed (Patent Documents 1 and 2). For example, Patent Document 1 proposes a mask using a photonic crystal. The mask described in Patent Document 1 has a photonic crystal whose exposure wavelength is a photonic band gap in a region that blocks exposure light. As a result, accurate light shielding is possible, and the diffraction effect of the exposure light beam transmitted through the light transmitting portion can be reduced.

  In Patent Document 2, a phase mask is proposed. An exposure light beam having a specific wavelength is incident on the phase mask described in Patent Document 2. A pattern is formed by the zero-order light and the ± first-order light emitted from the phase mask. As a result, a periodic structure using interference of ± first-order light and a uniform structure using zero-order light can be simultaneously produced.

  In recent years, problems in photolithography due to miniaturization of semiconductor elements are not limited to advanced CMOS (Complementary Metal Oxide Semiconductor: CMOS). In the field of semiconductor optical devices applied to optical communication and optical information processing, many proposals have been made to significantly improve characteristics and create new functions by using a periodic structure (photonic crystal structure) with a fine refractive index. . As a technique for producing a photonic crystal structure, for example, a method for producing a two-dimensional or three-dimensional refractive index periodic structure (multidimensional diffraction grating) by electron beam lithography (EB) is shown (Patent Literature). 3).

JP 2009-211072 A JP-A-2005-91702 JP 2000-193811 A

  However, the inventors have found that there are the following problems in the production of a fine structure in a semiconductor optical device. As described above, fine photolithography has problems such as the limit of theoretical resolution, a decrease in process yield, and an increase in cost. In particular, in the field of semiconductor optical devices applied for optical communication and optical information processing, the wafer used and the manufacturing process are different from those of CMOS. For this reason, in the field of semiconductor optical devices, it is impossible to fabricate elements using the most advanced fabrication equipment introduced in advanced CMOS processes. Therefore, a manufacturing apparatus and a manufacturing process that are technically older than those of the advanced CMOS process are generally applied to the manufacturing of the semiconductor optical device.

  The minimum element size in photolithography is determined by the resolution limit of the exposure apparatus. However, the photonic crystal structure applied for optical communication and optical information processing is a periodic structure of fine pores of about 0.1 to 0.4 μm. In order to obtain such a fine structure pattern, for example, an expensive exposure apparatus whose exposure wavelength is about the same as the pattern dimension or shorter than the pattern dimension is required. As such an expensive apparatus, for example, an exposure apparatus using a light source such as KrF (Krypton Fluoride Laser: KrF) or ArF (Argon Fluoride Laser: ArF) used in a leading-edge CMOS process can be cited. Furthermore, a photomask to which super-resolution techniques such as proximity effect correction and phase shift are applied is necessary.

  However, if optical proximity effect correction is applied, the complexity of the photomask increases and the cost of the process increases. Also in the case of the mask described in Patent Document 1, it is expensive to produce a photomask having a fine photonic crystal. That is, in order to apply a super-resolution technique such as a conventional phase shift mask or optical proximity effect correction, an expensive photomask must be manufactured. Further, in the case of the phase mask described in Patent Document 2, the phase mask is expensive. In addition, since the phase mask described in Patent Document 2 uses light interference, there is a problem that only a structure with a constant period depending on the exposure wavelength can be produced. Therefore, the production of the semiconductor optical device using the above-described expensive apparatus or photomask is not realistic in view of the current sales price of the semiconductor optical device.

  On the other hand, in addition to lithography using light, it is conceivable to manufacture a semiconductor optical device using EB lithography. The wavelength of the electron beam is on the order of pm, which is about 1/100000 of the wavelength of light. Therefore, a periodic structure pattern of fine pores of about 0.1 to 0.4 μm can be sufficiently resolved without using an expensive photomask. However, EB lithography has a problem of low throughput because an exposure pattern is directly drawn by an electron beam generated from an electron gun. At present, the throughput of EB lithography is about 3 to 10 wafers / hour for a 200 mm wafer, which is only 1/20 to 1/100 of the throughput of a reduction projection exposure apparatus used in photolithography.

  That is, at present, a low-cost and high-throughput manufacturing method applicable to mass production of fine semiconductor optical devices has not been established.

  The present invention has been made in view of the above circumstances, and provides a photomask and an exposure method that can obtain an exposure pattern having a size equal to or smaller than the wavelength of the exposure light beam at low cost and high throughput. Objective.

  A photomask which is one embodiment of the present invention includes a substrate through which incident exposure light is transmitted toward a transfer target, and a light-shielding film which is formed on the substrate and shields the exposure light. The film is formed with a plurality of positive n (n is an integer of 3 or more) rectangular openings arranged in a lattice pattern.

  A photomask which is one embodiment of the present invention transmits a first light-transmitting portion having a convex m-gon shape (m is an integer of 3 or more), which transmits an exposure light beam with a predetermined transmissivity or more, and the exposure light beam. It is adjacent to the first light-shielding part in the same plane as the surface on which the first light-shielding part is disposed, and the shape is a convex n-gon (n is an integer of 3 or more). A second light-transmitting portion; and a light-shielding portion that is in contact with an outer periphery of the first light-transmitting portion and an outer periphery of the second light-transmitting portion and shields the exposure light beam by a predetermined light-shielding rate, A first side of the convex m-gon that includes the apex of the convex m-gon that is closest to the two translucent parts, and a first side of the convex n-gon that includes the apex of the convex n-gon that is closest to the first translucent part. The first side and the second side are not opposed to each other when the two sides are not parallel, or when the first side and the second side are parallel The length of the longest side of the convex m-gon is the first opening diameter when m is equal to 3, and the longest diagonal of the convex m-gon is the first opening diameter when m is 4 or more. When the second opening diameter is the length of the longest side of the convex n-gonal shape when the second opening diameter is equal to 3, and the longest diagonal length of the convex n-gonal shape when n is 4 or more. The shorter length of the aperture diameter of 1 and the diameter of the second aperture is equal to or less than the length obtained by dividing the wavelength of the exposure light beam by the reduction magnification of the reduction exposure apparatus that generates the exposure light beam. .

  An exposure method according to one embodiment of the present invention includes: a first translucent part having a convex m-gon shape (m is an integer of 3 or more) that transmits an exposure light beam with a predetermined transmissivity or more; and the exposure light beam. Adjacent to the first light-shielding part in the same plane as the first light-shielding part that transmits the light more than the light transmittance, and the shape is a convex n-gon (n is an integer of 3 or more) A second light-transmitting portion, and a light-shielding portion that is in contact with the outer periphery of the first light-transmitting portion and the outer periphery of the second light-transmitting portion and shields the exposure light beam by a predetermined light-shielding rate, The first side of the convex m-gon that includes the apex of the convex m-gon that is closest to the second light-transmitting part, and the convex n-gon that includes the apex of the convex n-angle that is closest to the first light-transmitting part The second side is not parallel, or when the first side and the second side are parallel, the first side and the second side are not opposed to each other. In the photomask, when m is equal to 3, the length of the longest side of the convex m-gon is the first opening diameter, and when m is 4 or more, the length of the longest diagonal line of the convex m-gon is When n is equal to 3, the length of the longest side of the convex n-gon is the second opening diameter when the length of the longest diagonal of the convex n-gon is the second opening diameter. Irradiating the exposure light beam having a wavelength longer than a length obtained by multiplying the shorter length of the first opening diameter and the second opening diameter by the reduction magnification of the reduction exposure apparatus that generates the exposure light beam To do.

  ADVANTAGE OF THE INVENTION According to this invention, the photomask and exposure method which can obtain the exposure pattern of the magnitude | size below the wavelength of an exposure light beam at low cost and high throughput can be provided.

It is principal part sectional drawing of the general semiconductor exposure apparatus 600 for demonstrating the outline | summary of the exposure process using a photomask. 6 is an enlarged top view of a main part of a photomask 400 according to Comparative Example 1. FIG. It is a figure which shows the light intensity distribution on the to-be-transferred body of the exposure light beam which permeate | transmitted the opening part in the III-III cross section of FIG. FIG. 4 is a light intensity distribution diagram on an object to be transferred of an exposure light beam transmitted through an opening in the IV-IV cross section of FIG. 2. It is a figure which shows the calculation result of the two-dimensional light intensity distribution on a to-be-transferred object at the time of using the photomask 400 concerning the comparative example 1. FIG. 2 is an enlarged top view of a main part of the photomask 100 according to the first embodiment. FIG. 2 is a top view further enlarging a main part of the photomask 100 according to the first embodiment. It is a figure which shows the calculation result of the two-dimensional light intensity distribution on a to-be-transferred object in case an opening part is a regular hexagon. FIG. 6 is an enlarged top view of a main part of a photomask 200 according to a second embodiment. 10 is an enlarged top view of a main part of a photomask 500 according to Comparative Example 2. FIG. It is a light intensity distribution figure which shows the light-blocking rate t dependence of the light intensity distribution which the single opening part at the time of using the photomask 500 concerning the comparative example 2 uses. FIG. 6 is an enlarged top view of a main part of a photomask 300 according to a third embodiment. It is a figure which shows the example of the adjacent typical opening part. It is a figure which shows the example of the adjacent typical opening part.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted as necessary.

  First, an outline of an exposure process using a photomask will be described as preparation for understanding the present invention. FIG. 1 is a cross-sectional view of a main part of a general semiconductor exposure apparatus 600 for explaining an outline of an exposure process using a photomask. As general semiconductor exposure apparatuses, reduction projection exposure apparatuses such as steppers and scanners are widely used. The reduction projection exposure apparatus forms an exposure pattern by reducing and projecting a pattern drawn on a photomask onto a transfer target. The semiconductor substrate 1 is held on a stage (not shown) in the semiconductor exposure apparatus. For example, the semiconductor substrate 1 is made of a material such as Si, SiGe, InP, or GaAs.

  As shown in FIG. 1, a dielectric film 2 is formed on the semiconductor substrate 1. A photoresist film 3 is formed on the dielectric film 2. The photoresist film 3 is formed by, for example, spin coating. However, the method for forming the photoresist film 3 is not limited to spin coating.

  A photomask 10 is fixed above the photoresist film 3 by, for example, a mask holder (not shown). In the photomask 10, a light shielding film 5 is formed on a transmissive substrate 4. The transmissive substrate 4 is a substrate that transmits the exposure light beam 6 and is generally made of glass or synthetic quartz. The light shielding film 5 is a film that shields the exposure light beam 6 and is generally made of chromium.

  That is, the exposure light beam 6 passes through the opening 7 which is a portion where the light shielding film 5 is not formed, and reaches the photoresist film 3. Further, the exposure light beam 6 is blocked by the light shielding portion 8 which is a portion where the light shielding film 5 is formed. Therefore, the exposure light beam 6 does not reach the photoresist film 3 below the light shielding portion 8. Thereby, the exposure light beam 6 transmitted through the opening 7 is irradiated to the photoresist film 3 as a bright and dark pattern. Thus, an exposure pattern corresponding to the photomask 10 is formed on the developed photoresist film 3.

  Strictly speaking, it is not necessary for the opening 7 to transmit all of the exposure light beam 6, and it is sufficient to transmit an exposure light beam in an amount larger than that for exposing the photoresist film 3. That is, if the amount of light to which the photoresist film 3 is exposed is defined as “photosensitive threshold Ith” and the ratio of the amount of transmitted light to the amount of exposure light 6 is defined as “transmittance”, the transmittance of the opening 7 is , Ith may be equal to or greater than the value obtained by dividing the exposure light beam 6 amount.

  Strictly speaking, it is not necessary for the light-shielding portion 5 to shield all of the exposure light beam 6, and it may be transmitted as long as the exposure light beam is smaller than the photosensitive threshold value Ith. That is, if the ratio of the amount of exposure light beam that is shielded against the amount of exposure light beam 6 is defined as “light shielding rate”, the light shielding rate of the opening 7 is smaller than the value obtained by dividing Ith by the amount of exposure light beam 6. Any value is acceptable.

  FIG. 1 is a schematic diagram of a semiconductor exposure apparatus. Accordingly, the semiconductor exposure apparatus 600 shown in FIG. 1 is shown with a dimensional ratio different from that of an actual semiconductor exposure apparatus. Further, for simplification of the drawing, in FIG. 1, a condenser lens and a projection lens through which the exposure light beam 6 passes are omitted.

Comparative Example 1
Next, as a preparation for understanding the technical effect of the photomask according to the embodiment of the present invention, a photomask 400 according to Comparative Example 1 will be described. FIG. 2 is an enlarged top view of the main part of the photomask 400. As shown in FIG. 2, the photomask 400 has circular openings 41 formed in a triangular lattice shape. The light shielding portion 42 covers the space between the openings 41. The opening 41 corresponds to the opening 7 shown in FIG. 1, and the light shielding part 42 corresponds to the light shielding part 8 shown in FIG. Since the cross-sectional configuration of the photomask 400 is the same as that of the general photomask 10, description thereof is omitted.

In the photomask 400, the openings 41 are arranged in a triangular lattice as an example of the lattice-like arrangement. Thereby, the opening part 41 comprises the typical photonic crystal structure pattern. Hereinafter, the diameter of the opening 41 and _{d 4,} the period between the opening 41 and _{a 4.} Thereafter, unless otherwise specified, the dimension display on the photomask in the top view shows the actual dimension on the photomask. In addition, the dimension display concerning a to-be-transferred body (photoresist film 3 on the semiconductor substrate 1 of FIG. 1) shows the value which multiplied the reduction projection magnification of the semiconductor exposure apparatus to the dimension in a photomask.

In the photomask 400, when the opening size (diameter d ₄ ) of the opening 41 is reduced to the vicinity of the wavelength λ of the exposure light beam, the diffraction effect of the exposure light beam is increased. Here, the effective focal length from the photomask 400 to the transfer target (for example, the photoresist film 3 in FIG. 1) is R. Also, r is the distance from the optical axis of the exposure light beam on the transfer object. In this case, the light intensity distribution I (r) formed on the transfer medium by the exposure light beam transmitted through one circular opening 41 is expressed by the following equations (1) and (2).

In the equation (1), _{J 1} represents a first type primary Bessel function.

The light intensity distribution I (r) represented by the equation (1) is generally called an Airy disk, and the light intensity distribution spreads on concentric circles. The distance r ₀ from the optical axis of the first zero point of the light intensity, which indicates a measure of this spread, is expressed by the following formula (3).

From Expression (3), when the diameter d ₄ of the opening 41 is not sufficiently large with respect to the wavelength λ of the exposure light beam, the opening diameter (of the opening 41 of the light intensity distribution I (r) on the transfer target is determined. The spread with respect to the diameter d ₄ ) becomes significant. FIG. 3 is a view showing the light intensity distribution on the resist of the exposure light beam transmitted through the opening in the III-III cross section of FIG. In this calculation, the wavelength λ of the exposure light beam is 365 nm (exposure wavelength of the i-line of the mercury lamp), the reduction magnification of the reduction projection exposure apparatus is 1/5, and the diameter d ₄ is 1.0, 1.25, 1 It was changed to 5 μm. As shown in Expression (3), it can be seen that the light on the transfer medium spreads when the diameter of the opening is reduced. Hereinafter, unless otherwise specified, calculation results are shown using the same exposure light wavelength and reduction magnification as those described above.

The actual light intensity distribution on the transferred object is a superposition of exposure light beams transmitted through the plurality of openings 41. Therefore, the actual light intensity distribution _Itotal on the transfer target is expressed by the following equations (4) and (5).

Here, the calculation result of the light intensity distribution of the exposure light beam on the transfer medium is shown. FIG. 4 is a light intensity distribution diagram on the resist of the exposure light beam transmitted through the opening in the IV-IV cross section of FIG. That is, FIG. 4 shows the light intensity distribution on the resist due to the superposition of the exposure light beams transmitted through the three openings. In this calculation, the diameter d ₄ was constant at 1.2 μm, and the period a _{4 of the} triangular lattice was changed to 2.0, 2.5, 3.0, and 3.5 μm. As shown in FIG. 4, as the cycle a ₄ decreases, i.e. as the distance between adjacent openings becomes smaller, the contrast difference of the light intensity at the opening shielding part is reduced by the influence of the interference, no longer resolved You can see that

Next, FIG. 5 is a diagram illustrating a calculation result of a two-dimensional light intensity distribution on the transfer target when the photomask 400 is used. Incidentally, in this calculation, and the period _{a 4} of a triangular lattice and 2.1 .mu.m. Under these conditions, the light intensity distribution was calculated when the diameter d ₄ of the opening 41 was 1.2 μm and 1.4 μm.

  In FIG. 5, the white portion indicates that the light intensity is high, and the black portion indicates that the light intensity is low. Further, an equal light intensity line indicated by a white line indicates a photosensitive threshold value Ith of the photoresist film. That is, the photoresist film in a region (inside the white line in FIG. 5) where the light intensity is higher than the photosensitive threshold value Ith is exposed to form an exposure pattern.

When the diameter d ₄ of the opening 41 is small (d ₄ = 1.2 μm), light diffraction becomes significant, and interference occurs between the adjacent openings 41. In this case, the openings 41 arranged at the vertices of the equilateral triangle form concentric Airy disks represented by the formula (1). Therefore, the diffracted light of the exposure light beam is superimposed in the same phase at a point equidistant from each of the three openings 41 arranged at the apex of the equilateral triangle on the transfer object. In addition, the diffracted light from the two openings 41 is overlapped at the same phase even at a point equidistant from the two openings 41 on the transfer target. As a result, a region having a high light intensity and a region having a low light intensity are periodically formed on the transfer medium between the openings 41, leading to a decrease in contrast. As a result, as shown in FIGS. 4 and 5, a circular exposure pattern cannot be resolved due to a decrease in contrast of light intensity.

On the other hand, when the diameter d ₄ of the opening 41 is large (d ₄ = 1.4 μm), light diffraction becomes small, and interference between adjacent openings 41 is suppressed. As a result, a circular exposure pattern can be resolved as shown in FIG. However, it results in increasing the diameter d ₄ of the opening 41, the exposure pattern is also increased. For this reason, it becomes impossible to form a fine exposure pattern required for producing a photonic crystal.

Embodiment 1
Next, the photomask 100 according to the first embodiment of the present invention will be described. In order to avoid the phenomenon in the photomask 400 described above and obtain a photonic crystal structure, it is necessary to reduce the spread due to the diffraction effect of the exposure light beam that has passed through the opening. Therefore, in photomask 100 according to the present embodiment, the shape of the opening is not a circle but a regular polygon. Hereinafter, the configuration of the photomask 100 according to this embodiment will be specifically described.

FIG. 6 is an enlarged top view of the main part of the photomask 100 according to the first embodiment. As shown in FIG. 6, the photomask 100 has square openings 11 formed in a lattice pattern. The light shielding portion 12 covers the space between the openings 11. In FIG. 6, the openings 11 are arranged in a triangular lattice shape as an example of the lattice-like arrangement. Thereby, the opening part 11 comprises the typical photonic crystal structure pattern. Hereinafter, the length of a diagonal line of the opening 11 and d _1, the period between the opening 11 and a _1. Other configurations are the same as those of the photomask 400 according to the comparative example 1, and thus the description thereof is omitted.

  FIG. 7 is an enlarged top view of the main part of the photomask 100 according to the first embodiment. In FIG. 7, in order to identify the adjacent openings, the adjacent openings are denoted by reference numerals 111, 112, and 113, respectively. In FIG. 7, reference signs A to R are attached to indicate positions on the photomask 100. Reference signs A to D denote apexes of the opening 111, respectively. Reference signs E to H denote apexes of the opening 112, respectively. Reference numerals K to N denote apexes of the opening 113, respectively. Reference numerals I, J, and O to R denote end points of line segments, respectively. Further, in FIG. 7, the hatching of the light shielding portion 12 is omitted in order to clearly display the code.

  As shown in FIG. 7, the shapes of the openings 111 to 113 are square. Therefore, in the same row (vertical row in FIG. 7), the transfer target is equidistant from the ends of two adjacent openings, that is, the side AD of the opening 111 and the side FG of the opening 112. On the upper line segment IJ, the light wave of the exposure light beam is superimposed in the same phase. Thereby, the light intensity distribution becomes stronger on the line segment IJ on the transfer target.

  However, the points on the transfer target between different rows are equidistant from the side NM of the adjacent opening 113 and the side AB of the opening 111, and the length of the line segment in which the light waves of the exposure light are overlapped in the same phase Is shorter than the length of the side AB and the side NM. The line segment OP in FIG. 7 is a line segment having the same distance from the side AB and the side NM. At this time, the part of the line OP which is equidistant from the side AB and the side NM and where the light waves of the exposure light beam are overlapped in the same phase is only the line segment QR. Regarding the other points on the line segment OQ and the line segment RP, although the distances from the side AB and the side NM are equal, the light wave of the exposure light beam is overlapped in the same phase, that is, on the side AB and the side NM. There is no section. Therefore, the phase uniformity of the light waves of the exposure light beams that are superimposed is relaxed. Therefore, the influence of the light wave interference of the exposure light beam can be suppressed at a point on the transfer medium between the openings 11 in the adjacent different rows.

  As described above, each side of the openings 111 to 113 is parallel to the side of the adjacent opening, but some of the sides are not completely opposed to the side of the adjacent opening. As a result, the influence of interference is less than in the case where the sides of the adjacent openings are all parallel and opposed. Therefore, the influence of interference can be suppressed as compared with the case where the shape of the opening is circular.

  As is clear from the above description, each side of the opening 11 in FIG. 6 may not completely face the side of the adjacent opening. Furthermore, each side of the opening 11 may not be parallel to all the sides of the adjacent opening. In short, the influence of interference is suppressed as the length of the portion where each side of the opening 11 and each side of the adjacent opening are opposed or the length of the parallel portion is shorter.

  Therefore, according to the photomask 100, it is possible to prevent a decrease in contrast on the transfer target and to obtain a spot-like exposure pattern having a diameter smaller than the wavelength of the exposure light beam. That is, according to the photomask 100, a photonic crystal structure pattern constituted by a spot pattern having a diameter smaller than the wavelength of the exposure light beam can be obtained.

In the photomask 100, the influence of diffracted light between adjacent openings on the transfer target can be reduced. In other words, an exposure pattern having a dimension equal to or smaller than the wavelength λ of the exposure light beam can be obtained using the diffraction effect between adjacent openings under the condition that the diffraction effect due to the aperture transmission appears. Therefore, in order for the diffraction effect to appear, the length d ₁ of the diagonal line of the opening 11 is equal to or less than the value obtained by dividing the wavelength λ of the exposure light beam by the reduction magnification M (0 <M <1) of the reduction projection exposure apparatus. It is necessary to be.

On the other hand, too small diagonal length d ₁ of the opening 11, together with the diffraction effect becomes too pronounced, which could lead to decrease in illuminance of the exposure light beam, the exposure pattern can not be obtained. When the diagonal length d ₁ is equal to or less than the wavelength of the exposure light beam, propagating components of the exposure light beam is unable transmission. Therefore, it is necessary that the length d ₁ of the diagonal line of the opening 11 is not less than the wavelength λ of the exposure light beam.

From the above, in the present embodiment, the condition of the diagonal length d ₁ with which the effect of the present invention is obtained is expressed by the following equation (6).

Further, when the formula (6) is rewritten, the wavelength λ is expressed by the following formula (7).

That is, in the present embodiment, there is no lower limit to the wavelength, and it is possible to use an exposure light beam having a length obtained by multiplying the diagonal length d ₁ of the opening 11 by the reduction factor M.

  Moreover, in this Embodiment, although the shape of the opening part is made into the square, the shape of an opening part is not limited to this. That is, the shape of the opening can be any positive n (n is an integer of 3 or more) square (that is, a regular polygon) including a square. As an example, a case of a regular hexagon is shown. FIG. 8 is a diagram illustrating a calculation result of a two-dimensional light intensity distribution on the transfer target when the opening is a regular hexagon. In this calculation, the period a of the triangular lattice is 2.1 μm, the length d of the diagonal line of the opening is 1.2 μm, and the same conditions as those in the left diagram of FIG. That is, in the case of a circle, the pattern was not formed by interference when the diameter of the opening was 1.2 μm, but by making the shape of the opening a regular hexagon, the influence of interference was suppressed, and the pattern was It can be seen that it is formed.

Hereinafter, the length of the longest diagonal line of the regular n-gon is defined as the maximum diameter of the opening. In the photomask 100, the diagonal length d ₁ of the opening 11 corresponds to the maximum diameter of the opening.

  In addition, the photomask according to this embodiment can be manufactured only by changing the pattern arrangement of the opening and the light shielding portion by a normal photomask manufacturing method. That is, a photonic crystal can be manufactured without requiring an expensive mask such as a phase shift mask, an expensive apparatus such as an electron beam irradiation apparatus or an exposure apparatus applied to a leading edge process. Accordingly, it is possible to produce a photonic crystal by an inexpensive and technically simple process.

  Furthermore, since the photomask according to this embodiment has a regular n-square shape including a square shape, the photomask is easier to manufacture than when the aperture shape is circular. In general, a pattern on a photomask is drawn using an electron beam drawing apparatus, a laser drawing apparatus, or the like. Therefore, when the pattern shape is a shape with many straight lines such as a regular n-gon, the drawing grid can be enlarged. Thereby, the photomask according to this embodiment can be manufactured in a shorter time and at a lower cost.

Embodiment 2
Next, Embodiment 2 of the present invention will be described by showing a specific configuration example. FIG. 9 is an enlarged top view of a main part of the photomask 200 according to the second embodiment. The photomask 200 differs from the photomask 100 according to the first embodiment in the shape and arrangement of the openings. The photomask 200 has a regular hexagonal opening 21 that is one of regular polygons. The light shielding part 22 covers the space between the openings 21, and hereinafter, the length of the longest diagonal line of the openings 21 is d ₂ and the period between the openings 21 is a ₂ . Since the other structure of the photomask 200 is the same as that of the photomask 100, description thereof is omitted.

  In the photomask 200, one opening 21 and the opening 21 adjacent to the one opening 21 and arranged on the vertex of the regular hexagonal center have different rotation angles. In FIG. 9, the openings 21_0 to 21_6 have different rotation angles. In the photomask 300, a group of seven openings having different rotation angles corresponding to the openings 21_0 to 21_6 is arranged in a honeycomb shape.

In FIG. 9, when the reference rotation angle is Δθ, the rotation angle θ _m of the opening 21_m (m is an integer of 0 or more and 6 or less) is expressed by the following equation (8).

In the photomask 200, the rotation angles of adjacent openings are different. Therefore, it is necessary that openings having a rotation angle of m × Δθ do not overlap each other even if m is an integer and the openings are translated. Since the positive n (n is an integer of 3 or more) square has a rotational symmetry of 360 ° / n, the condition that openings having different rotation angles do not overlap each other is expressed by the following formula (9).

  In FIG. 9, the reference rotation angle Δθ is 5 °. In addition, an example in which the rotation angle of the peripheral opening 21 increases counterclockwise with respect to the central opening 21_0 has been described. However, the configuration of FIG. 9 is merely an example, and the method of selecting the integer m is not limited to this. Further, the rotation angle of the opening 21 may be increased clockwise, and the openings 21_0 to 21_6 may be randomly arranged on the center and apex of the regular hexagon.

  According to the photomask 200, as compared with the photomask 100, the transfer from the end of the opening is also performed on the transfer target body between two adjacent openings 21 in the same row (vertical row in FIG. 9). The distance is different. Accordingly, it is possible to suppress the influence of the light wave interference of the exposure light beam between the two adjacent openings 21 in the same row (vertical row in FIG. 9). In addition, the distance from the end of each opening 21 is also random between the openings 21 in different rows adjacent to each other, and the phase of the light wave of the exposure light beam superimposed on the transfer body is more relaxed. Is done. Therefore, it is possible to further suppress the influence of the interference of the light wave of the exposure light beam between the adjacent openings 21 in different rows.

  As a result, according to the photomask 200, not only the same action and effect as the photomask 100 are exhibited, but also a contrast reduction on the transfer object is further prevented, and a spot image having a diameter smaller than the wavelength of the exposure light beam, It can be obtained more easily. That is, according to the photomask 200, a photonic crystal structure pattern composed of spots having a diameter smaller than the wavelength of the exposure light beam can be obtained more easily.

Comparative Example 2
Next, as a preparation for understanding the technical effect of the photomask according to the third embodiment of the present invention described later, a photomask according to comparative example 2 will be described. FIG. 10 is an enlarged top view of the main part of the photomask 500 according to Comparative Example 2. As shown in FIG. 10, the photomask 500 has circular openings 51 formed in a lattice shape. A light shielding plate 53 having a concentric shape (similar shape) with the opening 51 is formed in the opening 51. The light shielding part 52 covers the space between the openings 51. Thereby, the opening 51 and the light shielding plate 53 constitute a ring-shaped band-shaped opening 54. That is, the exposure light beam reaches the transfer target through the strip-shaped opening 54. The light shielding plate 53 is formed of the same material as the light shielding portion 52, for example. Hereinafter, the diameter of the opening 51 is d ₅₁ , the diameter of the light shielding plate is d ₅₃ , and the period between the openings 51 is a ₅ . Since the other structure of the photomask 500 is the same as that of the photomask 400 according to Comparative Example 1, description thereof is omitted.

  Although the shape of the opening of the photomask 500 according to Comparative Example 2 is circular, the shape of the opening is not limited to this. That is, the shape of the opening may not be a perfect circle but an ellipse. The shape of the opening can be any positive n (n is an integer of 3 or more) square.

In the photomask 500, the size of the band-shaped opening 54 varies depending on the size of the light shielding plate 53. Here, a light shielding rate t by the light shielding plate 53 is defined. The light shielding rate t is expressed by the following formula (10) by the ratio of the area of the opening 51 and the area of the light shielding plate 53.

Light intensity distribution I on the transfer of the time (r), using the first type primary Bessel function _{J 1,} represented by the following formula (11) and (12).

Here, the calculation result of the light intensity distribution of the exposure light beam on the transfer object when the photomask 500 is used is shown. In this calculation, the wavelength λ of the exposure light beam is 365 nm (exposure wavelength of i-line of the mercury lamp), the reduction magnification of the reduction projection exposure apparatus is 1/5, the period a _{5 of the} triangular lattice is 2.1 μm, and the aperture The light intensity distribution was calculated with the diameter d ₅₁ of ₅₁ being 1.4 μm.

  FIG. 11 is a light intensity distribution diagram showing the dependency of the light intensity distribution formed by a single opening when the photomask 500 is used on the light blocking rate t. FIG. 11 shows the cases where the light blocking ratio t is 0, 0.25, 0.5, and 0.75. In FIG. 11, a white part indicates that the light intensity is high, and a black part indicates that the light intensity is low. Further, an equal light intensity line indicated by a white line indicates a photosensitive threshold value Ith of the photoresist film. That is, an exposure pattern is formed by exposing the photoresist film in a region where the light intensity is higher than the photosensitive threshold value Ith (the inner portion of the white line in FIG. 11).

  When the photomask 500 is used, as shown in FIG. 11, when the opening 51 is not shielded from light (light shielding rate t = 0, that is, when the opening 51 is a simple circular opening), the photoresist film is The diameter of the exposed circular area is maximized. On the other hand, as the light shielding ratio t increases, the diameter of the circular region where the photoresist film is exposed decreases. That is, by increasing the light shielding rate, that is, by increasing the size of the light shielding plate, it is possible to effectively reduce the diameter of the circular region where the photoresist film is exposed even if the diameter of the opening 51 is the same. Therefore, according to the photomask 500, it is possible to reduce the size of the exposure pattern formed by a single opening by providing a similar light shielding plate in the opening.

  If the reduction magnification of the reduction projection exposure apparatus used for exposure is 1/5, the diameter of the opening 51 of 1.4 μm corresponds to 380 nm on the photoresist film 3. That is, when there is no light shielding plate, an exposure pattern having a diameter of 380 nm or less cannot be formed. However, as described above, according to the photomask 500, since the size of the exposure pattern can be reduced by the light shielding plate, an exposure pattern having a diameter of the exposure wavelength (365 nm) or less can be obtained. Thereby, according to the photomask 500, it is possible to obtain an exposure pattern having a size equal to or smaller than the exposure wavelength.

Embodiment 3
Next, a photomask according to the third embodiment of the present invention will be described. FIG. 12 is an enlarged top view of the main part of the photomask 300 according to the third embodiment. In the photomask 300, a light shielding plate 33 concentric with and similar to the opening 31 (regular hexagon) is formed inside the opening 31 having a regular hexagon. The light shielding portion 32 covers the space between the openings 31. Hereinafter, the length of the longest diagonal line of the opening portion 31 is d ₃₁ , the length of the longest diagonal line of the light shielding plate 33 is d ₃₃ , and the space between the openings 31. the period and _{a 3.} Thereby, the opening 31 and the light shielding plate 33 constitute a ring-shaped band-shaped opening 34. That is, the exposure light beam reaches the transfer target through the strip opening 34. Since the other structure of the photomask 300 is the same as that of the photomask 200 according to the second embodiment, the description thereof is omitted.

  The photomask 300 has a light shielding plate 33 inside the opening 31. Therefore, the photomask 300 not only has the same operation and effect as the photomask 200, but also can reduce the size of the exposure pattern formed by a single opening. Therefore, according to the photomask 300, an exposure pattern having a size smaller than the wavelength of the exposure light beam can be obtained more easily. That is, according to the photomask 300, a photonic crystal structure pattern composed of a spot pattern having a diameter smaller than the wavelength of the exposure light beam can be obtained more easily.

  Incidentally, in the present embodiment, when it is desired to increase the illuminance of the exposure light beam on the transfer object, the light shielding rate t may be set in the range of 0.25 to 0.50 as shown in FIG. . In addition, when it is desired to narrow the region exposed to the photoresist film on the transferred material as much as possible, the light shielding rate t may be set in the range of 0.50 to 0.75 as shown in FIG.

Other Embodiments The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention. For example, in the above-described embodiment, a pattern for forming a periodic photonic crystal structure is shown. However, the pattern formed by the photomask of the present invention is not limited to this example. For example, it is effective when patterning a large area such as an image sensor or a liquid crystal panel at low cost and high throughput in addition to a general electronic circuit.

  The cross-sectional configuration and material of the photomask in the above embodiment are merely examples, and the configuration and material of the photomask are not limited thereto.

Although the wavelength of the exposure light beam in the above-described embodiment is 365 nm, this is merely an example. That is, exposure light beams having other wavelengths such as g-line or h-line of a mercury lamp or laser light by excimer laser (for example, ArF, KrF, or F ₂ ) can be used. Although the reduction ratio is 1/5, it is merely an example, and other reduction ratios can be applied. Generally, the lower the reduction magnification, the higher the resolution.

  In the above-described embodiment, the triangular lattice has been described as an example of the arrangement of the openings. However, other lattice arrangements such as a square lattice can be applied.

  As is clear from the above description, in the opening of the present invention, the arrangement of the sides of the adjacent openings only needs to satisfy a predetermined condition, and the shape of the opening itself is not particularly limited. That is, the shape of the opening is not limited to a regular n-gon, and may be a polygon with different side lengths. However, the polygon is preferably a convex polygon. In the case of a general convex polygon, the length of the longest diagonal line may be the maximum diameter of the opening.

  And about the arrangement | positioning of the edge | side of an opening part, the edge | sides of an adjacent opening part should not be parallel. Or even if the edge | sides of an adjacent opening part are parallel, even if a part of one side does not oppose the other party's edge | side. In the present invention, “sides oppose” means that a perpendicular line can be drawn from a point on a certain side to the other side. Therefore, “a part of one side does not face the other side” means that a certain side includes a point where a perpendicular cannot be drawn to the other side.

  An example of a typical adjacent opening satisfying the above conditions is shown. 13 and 14 are diagrams showing examples of typical adjacent openings. Reference signs A to E in FIG. 13 indicate apexes of the opening 61, and reference signs F to H indicate apexes of the opening 62, respectively. Reference signs A to E in FIG. 14 indicate apexes of the opening 71, and reference signs F to I indicate apexes of the opening 72, respectively. 4 indicates a point facing the vertex J on the side ED, and K indicates a point facing the vertex E on the side FG. 7, 13 and 14, alphabets are used as symbols, but it goes without saying that the same alphabets in FIGS. 7, 13 and 14 indicate different points.

  For example, as shown in FIG. 13, for the adjacent openings 61 and 62, the side DE of the opening 61 and the side GF of the opening 62 need not be parallel.

  Alternatively, as shown in FIG. 14, for the adjacent openings 71 and 72, even if the side DE of the opening 71 and the side GF of the opening 72 are parallel, the side DE or the entire side GF faces the other. In other words, it is only necessary that the part where the side DE and the side GF face each other is a part. In the example illustrated in FIG. 14, for the side DE, the line segment DJ does not face the side GF, and for the side GF, the line segment KF does not face the side DE. If the sides of the adjacent openings are arranged in the above positional relationship, the effect of the present invention can be obtained although there is a difference in size.

  As described above, in order to obtain the effect of the present invention, the length of the diagonal line of the opening must be equal to or smaller than the value obtained by dividing the wavelength λ of the exposure light beam by the reduction magnification M of the reduction projection exposure apparatus. It is. When the shape of the opening is a general convex polygon, it is necessary that the length of the longest diagonal line is equal to or less than the value obtained by dividing the wavelength λ of the exposure light beam by the reduction magnification M of the reduction projection exposure apparatus.

  Further, in the case of a convex polygon having a different shape of the opening, first, the length of the longest diagonal (longest diagonal) is obtained for each convex polygon. When the lengths of the longest diagonal lines of the polygons are compared, it is necessary that the shortest longest diagonal line length is equal to or less than the value obtained by dividing the wavelength λ of the exposure light beam by the reduction magnification M of the reduction projection exposure apparatus. is there. When the shape of the opening is a triangle, it is necessary that the length of the longest side is equal to or less than the value obtained by dividing the wavelength λ of the exposure light beam by the reduction magnification M of the reduction projection exposure apparatus.

  A part or all of the above embodiment can be described as in the following supplementary notes, but is not limited thereto.

  (Additional remark 1) It is provided with the board | substrate which the incident exposure light beam permeate | transmits toward a to-be-transferred body, and the light shielding film which shielded the said exposure light beam formed on the said board | substrate, A photomask in which a plurality of positive n (n is an integer of 3 or more) rectangular openings are formed.

  (Supplementary note 2) The supplementary note 1, wherein a maximum diameter of the opening is not less than a wavelength λ of an exposure apparatus that performs exposure using the photomask and not more than a value obtained by dividing the wavelength λ by a reduction magnification. Photo mask.

  (Supplementary Note 3) One of the plurality of openings, and the other opening adjacent to the one opening are arranged at different rotation angles, respectively. 2. The photomask according to 2.

  (Supplementary note 4) The photomask according to supplementary note 3, wherein the plurality of openings are arranged in a triangular lattice pattern.

  (Supplementary Note 5) The first opening of the plurality of openings and the six openings adjacent to the first opening are arranged at different rotation angles, respectively. 4. The photomask according to 4.

  (Appendix 6) The six openings are composed of second to seventh openings arranged at the apexes of which the centers are regular hexagons, and the rotation angles of the first to seventh openings are: The photomask according to appendix 5, wherein the photomask increases in this order at a predetermined angular pitch.

  (Supplementary note 7) The photomask according to supplementary note 6, wherein the second to seventh openings are arranged clockwise or counterclockwise in this order.

  (Appendix 8) The photomask according to appendix 6 or 7, wherein the plurality of openings are configured by arranging a group of the first to seventh openings in a honeycomb shape. .

  (Supplementary Note 9) A light shielding plate that is concentric with and similar to each of the plurality of openings, and is formed inside each of the plurality of openings, and each of the plurality of openings and the light shielding plate The photomask according to any one of appendices 1 to 8, wherein the exposure light beam is incident on the substrate through a band-shaped opening formed by the step (1).

  (Additional remark 10) The value which remove | divided the area of the said light shielding board by the area of the said opening part is 0.25 or more and 0.75 or less, The photo as described in any one of Additional remark 1 thru | or 9 characterized by the above-mentioned. mask.

  (Supplementary Note 11) A first translucent part having a convex m-gon shape (m is an integer of 3 or more) that transmits the exposure light beam at a predetermined transmissivity or higher, and the exposure light beam is transmitted at the transmissivity or higher. A second light-transmitting portion that is adjacent to the first light-shielding portion in the same plane as the surface on which the first light-shielding portion is disposed and has a convex n-gon (n is an integer of 3 or more). A light shielding portion that is in contact with an outer periphery of the first light transmitting portion and an outer periphery of the second light transmitting portion and shields the exposure light beam at a predetermined light shielding ratio or more. A first side of the convex m-gon that includes the vertex of the convex m-gon that is close to the second side of the convex n-gon that includes a vertex of the convex n-gon that is closest to the first light-transmitting portion is parallel to the first side. Or when the first side and the second side are parallel, the first side and the second side include portions that do not face each other, and m is equal to 3. Is the length of the longest side of the convex m-gon, the length of the longest diagonal line of the convex m-gon is the first opening diameter when m is 4 or more, and the convexity when n is equal to 3. When the length of the longest side of the n-gon is the second opening diameter when n is 4 or more and the length of the longest diagonal line of the convex n-gon is the second opening diameter, The photomask having a shorter length of the opening diameter of 2 is equal to or less than a length obtained by dividing the wavelength of the exposure light beam by the reduction magnification of a reduction exposure apparatus that generates the exposure light beam.

  (Supplementary Note 12) A first translucent portion that transmits exposure light more than a predetermined transmissivity and has a convex m-gon shape (m is an integer of 3 or more), and transmits the exposure light more than translucency. The second light-transmitting light is adjacent to the first light-shielding portion in the same plane as the surface on which the first light-shielding portion is disposed, and has a convex n-gonal shape (n is an integer of 3 or more). And a light shielding part that contacts the outer periphery of the first light transmitting part and the outer periphery of the second light transmitting part and shields the exposure light beam by a predetermined light shielding rate or more, A first side of the convex m-gon that includes the apex of the convex m-gon that is closest to the first translucent part, and a second side of the convex n-gon that includes the apex of the convex n-gon that is closest to the first translucent part. When the first side and the second side are not parallel or when the first side and the second side are parallel, the photomask includes a portion where the first side and the second side do not face each other, Is equal to 3, the length of the longest side of the convex m-gon is the first opening diameter, and the length of the longest diagonal line of the convex m-gon is the first opening diameter. If the length of the longest side of the convex n-gon is the second opening diameter when n is 4 or more, the length of the longest diagonal line of the convex n-gon is the second opening diameter. An exposure method of irradiating the exposure light beam having a wavelength longer than a length obtained by multiplying a shorter length of the part diameter and the second opening diameter by a reduction magnification of the reduction exposure apparatus that generates the exposure light beam.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Dielectric film 3 Photoresist film 4 Transparent substrate 5 Light-shielding film 6 Exposure light beam 7, 11, 21, 21_0-21_6, 31, 41, 51, 61, 62, 71, 72, 111-113 Opening 8, 12, 22, 32, 42, 52 Light-shielding part 34, 54 Band-shaped opening 10, 100, 200, 300, 400, 500 Photomask 600 Semiconductor exposure apparatus

Claims (10)

A substrate through which the incident exposure light beam is transmitted toward the transfer object;
A light shielding film formed on the substrate for shielding the exposure light beam,
The light shielding film is formed with a plurality of positive n (n is an integer of 3 or more) rectangular openings arranged in a lattice pattern.
Photo mask. The maximum diameter of the opening is equal to or greater than a wavelength λ of an exposure apparatus that performs exposure using the photomask, and is equal to or less than a value obtained by dividing the wavelength λ by a reduction magnification.
The photomask according to claim 1. One opening of the plurality of openings and another opening adjacent to the one opening are arranged at different rotation angles, respectively.
The photomask according to claim 1 or 2. The plurality of openings are arranged in a triangular lattice shape,
The photomask according to claim 3. The first opening of the plurality of openings and the six openings adjacent to the first opening are arranged at different rotation angles, respectively.
The photomask according to claim 4. The six openings are composed of second to seventh openings arranged at the vertices of a regular hexagon at the center,
The rotation angles of the first to seventh openings are increased in this order at a predetermined angular pitch.
The photomask according to claim 5. The second to seventh openings are arranged in this order, clockwise or counterclockwise,
The photomask according to claim 6. The plurality of openings are configured by arranging a group of the first to seventh openings in a honeycomb shape,
The photomask according to claim 6 or 7. A first translucent part having a convex m-gon shape (m is an integer of 3 or more), which transmits exposure light more than a predetermined transmissivity;
Adjacent to the first light-shielding portion in the same plane as the surface on which the first light-shielding portion is disposed, which transmits the exposure light beam at the light transmittance or more. The second translucent part),
A light-shielding portion that is in contact with an outer periphery of the first light-transmitting portion and an outer periphery of the second light-transmitting portion and shields the exposure light beam by a predetermined light-shielding rate,
The first side of the convex m-gon that includes the apex of the convex m-gon that is closest to the second light-transmitting part, and the convex n-gon that includes the apex of the convex n-angle that is closest to the first light-transmitting part The second side is not parallel, or when the first side and the second side are parallel, the first side and the second side include portions that do not face each other,
When m is equal to 3, the length of the longest side of the convex m-gon is the first opening diameter, and when m is 4 or more, the length of the longest diagonal line of the convex m-gon is the first opening diameter. When the length of the longest side of the convex n-gon is the second opening diameter, the length of the longest diagonal line of the convex n-gon is the second opening diameter. The shorter length of the opening diameter and the second opening diameter is equal to or shorter than the length obtained by dividing the wavelength of the exposure light beam by the reduction magnification of the reduction exposure apparatus that generates the exposure light beam.
Photo mask. A first translucent part having a convex m-gon shape (m is an integer of 3 or more) that transmits exposure light more than a predetermined transmissivity, and the first light transmitting part that transmits the exposure light more than the transmissivity. A second light-transmitting part adjacent to the first light-shielding part and having a convex n-gon shape (n is an integer of 3 or more), A light-shielding portion that is in contact with an outer periphery of the first light-transmitting portion and an outer periphery of the second light-transmitting portion and shields the exposure light beam by a predetermined light-shielding rate or more, and is closest to the second light-transmitting portion. The first side of the convex m-gon that includes the vertex of the convex m-gon and the second side of the convex n-gon that includes the vertex of the convex n-gon that is closest to the first light transmission part are not parallel, or When the first side and the second side are parallel to each other, the photomask includes a portion where the first side and the second side do not face each other.
When m is equal to 3, the length of the longest side of the convex m-gon is the first opening diameter, and when m is 4 or more, the length of the longest diagonal line of the convex m-gon is the first opening diameter. When the length of the longest side of the convex n-gon is the second opening diameter, the length of the longest diagonal line of the convex n-gon is the second opening diameter. Irradiating the exposure light beam having a wavelength equal to or longer than a length obtained by multiplying a shorter length of the opening diameter and the second opening diameter by a reduction magnification of the reduction exposure apparatus that generates the exposure light beam;
Exposure method.