JP3695430B2 - Lattice pattern exposure method and exposure apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photoresist exposure method, and more particularly to an exposure method for exposing a lattice pattern to a photoresist using an optical exposure apparatus.
[0002]
[Prior art]
The semiconductor device manufacturing process is roughly divided into film formation, etching, and lithography. Among these, lithography forms an organic film called a photoresist on a substrate, and is usually irradiated with light or X-rays through an exposure mask formed with a light shielding material by an exposure device called a stepper. Or, conversely, the organic film is removed only with a developer by a developer, and the same pattern as the exposure mask or a reduced pattern thereof is formed on the substrate. In addition, there is also a method of forming a pattern by irradiating an organic film on a substrate with an electron beam in the manner of one stroke writing and then developing. Here, the light and X-ray irradiation and the electron beam irradiation are referred to as “exposure”.
[0003]
In some cases, using such a lithography technique, it is desired to form a lattice pattern in which fine patterns such as circles and squares are regularly arranged in a lattice shape on a substrate. There is a two-dimensional periodic structure photonic crystal as an optical element that particularly requires a fine lattice pattern. This is because a submicron circle or square dielectric column is replaced with a square lattice 1 as shown in FIG. 10 or a hexagonal lattice as shown in FIG. 2 or the structure of the honeycomb lattice 3 as shown in FIG. 12, and these lattice-like photoresist patterns are required for the production thereof.
[0004]
In this kind of fine lattice pattern exposure method, it is one of the important elements to form a photoresist pattern as fine as possible with high dimensional accuracy.
[0005]
As a method for forming a lattice pattern of a photoresist, an optical exposure apparatus (here, agreed with “stepper”) using g-line (wavelength 486 nm) or i-line (wavelength 356 nm), which is most often used in the field of manufacturing semiconductor devices, is used. In this case, the exposure is simply performed through an exposure mask having a desired lattice pattern or an enlarged pattern thereof, and the photoresist is directly patterned. When these optical exposure apparatuses are used, the minimum lattice point dimension of the photoresist lattice pattern that can be patterned is “extract” (means that the photoresist is removed after development) or “remains” (the photoresist remains after development). In either case, it is limited by the wavelength of light used. As the wavelength of light used is shorter, a finer lattice pattern can be formed, and a finer lattice pattern can be formed using i-line than g-line. When it is desired to form a finer grating pattern with an i-line stepper, a super-resolution technique such as using a phase shift mask can be used in combination. When it is desired to form a finer lattice pattern by the optical exposure method, a KrF excimer laser exposure machine having a shorter exposure wavelength of 249 nm may be used.
[0006]
However, these optical exposure methods using g-line, i-line, and KrF excimer lasers have a limitation in the minimum size of the lattice points that can be formed by the method of simply transferring the lattice pattern on the exposure mask. It is not sufficient to form a fine lattice pattern for a nick crystal. For both the blank pattern and the remaining pattern, the minimum size of the lattice point that can be actually formed is about 0.7 micron for g-line, about 0.5 micron for i-line, and about 0.45 micron for KrF excimer laser. When the i-line and the phase shift mask are used in combination, a lattice point pattern of about 0.45 microns is obtained as in the case of the KrF excimer laser. A phase shift mask for a KrF excimer laser has many technical difficulties and has not been put into practical use at present. For example, in the case of a photonic crystal having a cylindrical lattice point that forms a hexagonal lattice as shown in FIG. 11, the diameter of the cylinder is about 0.25 to 0.4 microns. It is smaller than the minimum dimension that can be optically exposed.
[0007]
Therefore, for example, as summarized in the special article “Lithography” in “Journal of the Institute of Electronics, Information and Communication Engineers, Vol. 77 No. 11pp1092-1108, November 1994”, X-ray exposure using X-rays and electron beams were used. The use of electron beam exposure is disclosed. In X-ray exposure and electron beam exposure, the X-ray wavelength (about 1 nm) used for exposure and the de Broglie wavelength of the accelerated electron beam are sufficient compared to the wavelengths of g-line, i-line and KrF excimer laser used in light exposure. Since it is small, it has a photoresist lattice pattern consisting of a circle having a minimum diameter of 0.1 microns in the case of X-ray exposure, and a photoresist lattice pattern consisting of a circle having a diameter of 0.1 microns or less in the case of electron beam exposure. It can be formed and has a temporary effect in forming a fine lattice photoresist pattern for a two-dimensional periodic structure photonic crystal.
[0008]
[Problems to be solved by the invention]
Of the conventional lattice pattern exposure methods described above, X-ray exposure newly introduces the problem that it is difficult to produce an X-ray mask used for exposure. The X-ray mask is obtained by forming a pattern with a heavy metal such as Au having a thickness of about 1 micron on a thin film made of Si having a thickness of about 2 microns. Due to its thinness, it is difficult to control the distortion of the pattern, which makes it difficult to manufacture an X-ray mask technically. The production cost of the X-ray mask is naturally much higher than that of the optical exposure mask. A synchrotron radiation source (SOR) is used as a powerful X-ray source. However, since it is an extremely large and expensive light source, an X-ray exposure system is obtained in comparison with an optical exposure apparatus (stepper). Installation is much more difficult. Accordingly, there arises a problem that the manufacturing cost is significantly increased only by exposing a fine lattice pattern using the X-ray exposure technique.
[0009]
On the other hand, although electron beam exposure does not cause a problem in terms of mask production and equipment acquisition like X-ray exposure, it newly introduces a problem that large area exposure cannot be performed. The area that can be exposed by one electron beam scanning using an electron beam is at most about several hundred microns square. If you want to expose an area larger than that, subdivide the area you want to expose into an area of several hundred microns square or less, and move the stage on which the substrate is placed after each small area exposure to expose the next area. This procedure must be repeated to connect the exposure areas. At the joined boundary, the pattern is generally discontinuous due to errors in stage movement accuracy and distortion of the pattern itself. This is fatal for forming a lattice pattern in which regular arrangement of lattice points is important. Therefore, when a lattice pattern is exposed, only a pattern of several hundred microns square or less can be formed. In the case of optical exposure, a lattice pattern having an area of only about 1/1000 to 1/100 can be exposed as compared with a case where a large area of more than a dozen millimeters square can be exposed even with a lattice pattern.
[0010]
Also, electron beam exposure has a drawback that the time required for exposure is much longer than optical exposure in which exposure is performed on the entire surface because the pattern is written with an electron beam like a single stroke. This drastically reduces the manufacturing throughput of the device having the fine lattice pattern, increases the time required for manufacturing the device (TAT: Turn Around Time), and increases the manufacturing cost.
[0011]
In addition, a photoresist for electron beam exposure generally has a drawback that it has lower dry etching resistance than a photoresist for optical exposure.
[0012]
One of the main objects of the present invention is to provide a new method for forming a photoresist lattice pattern having a fine lattice point size that cannot be achieved by a conventional exposure method using a general-purpose optical exposure apparatus. There is to do.
[0013]
Another main object of the present invention is to provide a method for shaping a lattice pattern and a method for consciously introducing lattice defects into the lattice pattern when the above-described new method is used.
[0014]
[Means for Solving the Problems]
The method for exposing a lattice pattern of the present invention is an exposure method in which a lattice pattern is exposed on a photoresist using an optical exposure apparatus, and the lattice pattern is patterned by multiple exposure of at least two different patterns.
[0015]
Multiple patterns of different exposures can be performed, and the lattice pattern can be patterned into a photoresist using the high solubility of the multiple exposure part in the developer or the insolubility of the non-exposed part in the developer. Compared with the exposure method, exposure can be performed at a high speed, and at the same time, fine pattern resolution characteristics reaching the resolution limit of the optical exposure method can be obtained.
[0016]
Each different pattern may be a line and space pattern. The exposure amount of each multiple exposure may be greater than or equal to the critical exposure amount necessary for dissolving the photoresist in the developer.
[0017]
The exposure amount of each time of multiple exposure may be less than the critical exposure amount, and the exposure amount of at least two overlapping exposure portions may be more than the critical exposure amount.
[0018]
The square lattice pattern may be patterned by exposing two line and space patterns at an angle of 90 ° to each other.
[0019]
The hexagonal lattice pattern may be patterned by exposing two line and space patterns at an angle of 60 ° or 30 ° to each other.
[0020]
A honeycomb lattice pattern may be patterned by subjecting a line-and-space pattern having a space pattern having a periodically divided shape to multiple exposure by inclining by 60 ° or 30 °.
[0021]
A lattice pattern including lattice defects may be patterned by multiple exposure of a line and space pattern having a space pattern with a partially divided shape.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0023]
FIG. 1 shows the procedure of one embodiment of the grid pattern exposure method of the present invention, FIG. 2 shows the state in step 1 of the exposure apparatus to which the grid pattern exposure method of FIG. 1 is applied, and FIG. 2 shows the state of the same exposure apparatus in FIG.
[0024]
As shown in FIGS. 1 and 2, the lattice pattern exposure method of the present embodiment first has an exposure having a line-and-space pattern (hereinafter referred to as an L / S pattern) 15 composed of parallel line patterns at equal intervals. First exposure is performed on the photoresist 23 applied on the substrate 18 by using the mask 14 (step S1). Here, the L / S pattern 15 is reduced and projected onto the photoresist 23 in FIG. Next, as shown in FIGS. 1 and 3, using an exposure mask 21 having an L / S pattern 20 that forms an angle θ larger than zero with the line direction of the L / S pattern 15 on the exposure mask 14, a photoresist 23 is used. The second exposure is performed so as to overlap the exposure area 17 (step S2). Thus, the exposure area 22 is finally formed by double exposure. FIG. 4 shows an exposure pattern 7 by the first exposure on the photoresist 23, and FIG. 5 shows an exposure pattern 8 by the second exposure when θ = 90 ° at the same position as the exposure pattern 7 on the photoresist 23. 6 indicates an exposure pattern in which the exposure pattern 7 and the exposure pattern 8 are overlapped.
[0025]
Assuming that the amount of exposure light 6 in the first exposure is E1, and the exposure amount of the exposure light 19 in the second exposure is E2, the portion 10 irradiated with light in both the first exposure and the second exposure in FIG. A portion 11 irradiated with light only in the first exposure, a portion 12 irradiated with light only in the second exposure, and a portion 13 not irradiated with light in both the first exposure and the second exposure. The total exposure amounts of the portion 10 are E1 + E2, the portion 11 is E1, the portion 12 is E2, and the portion 13 is 0. In the case of a positive photoresist, the solubility of the photoresist in the developer has a nonlinear solubility characteristic as shown in FIG. 7 with respect to the exposure amount. Now, assuming that the critical exposure amount necessary for dissolving the photoresist 23 in the developer is E01 from FIG. 7, when E1> E01 and E2> E01, the portion irradiated with light in the first exposure and the second exposure Since all the portions irradiated with light are exposed to an exposure amount exceeding the critical exposure amount E01 necessary for exposure, the photosensitive portion 4 shown by the oblique lines in FIG. A lattice pattern in which the photosensitive portion 5 remains is formed. When the photoresist 23 is a negative type, as shown in FIG. 9, the solubility in a developing solution of a portion irradiated with an exposure dose exceeding the critical exposure dose E02 is drastically lowered. Therefore, if E1> E02 and E2> E02, the non-photosensitive portion 24 shown by hatching in FIG. 8B is dissolved in the developer, and a lattice pattern is formed in which the remaining photosensitive portion 25 remains.
[0026]
When the photoresist 23 is positive and has a relationship of E1 + E2> E01 and E01> E1 and E01> E2, only the portion 10 irradiated with light in both the first exposure and the second exposure is sufficiently exposed. The amount is obtained and exposed. Therefore, the photoresist in the portion 10 of FIG. 6 is dissolved and disappears by development, and a lattice pattern is formed in which the remaining portions 11, 12 and 13 remain. If the photoresist 23 is a negative type, a portion 10 remains and a lattice pattern in which other portions are omitted is formed by development. Note that the values of E1 and E2 may be the same or different.
[0027]
If θ = 90 °, the photoresist pattern formed by the above method is a square lattice, and the arrangement of lattice points is the same as that of the square lattice 1 in FIG. Needless to say, the angle θ need not be limited to 90 °. For example, assuming that θ = 60 ° and the exposure amount is a positive resist with the conditions of E1 + E2> E01 and E01> E1 and E01> E2, a hexagonal lattice consisting of diamond lattice points (referred to as a triangular lattice) as shown in FIG. There is also. The first exposure pattern 26 and the second exposure pattern 27 form 60 ° with each other, and a double-exposed region in both exposures forms a lattice point 28 of a hexagonal lattice. This is the same as the hexagonal lattice 2 in FIG. In order to perform exposure in an arrangement such as the honeycomb lattice 3 lattice points in FIG. 12, for example, as shown in FIG. 14, when the first exposure pattern 29 and the second exposure pattern 30 are positive resists, E1 + E2> If exposure is performed under the conditions of E01 and E01> E1 and E01> E2, a honeycomb lattice pattern 31 is obtained.
[0028]
It goes without saying that the exposure conditions may be E1> E01 and E2> E01 instead of E1 + E2> E01 and E01> E1 and E01> E2, or a negative photoresist may be used instead of a positive photoresist. Yes. In the latter case, the critical exposure required for dissolution in the developer is E02.
[0029]
The honeycomb lattice 3 can be regarded as a pattern in which lattice points are partially removed from the hexagonal lattice 2. In other words, the honeycomb lattice 3 is a portion of the hexagonal lattice 2 into which a lattice point does not exist, that is, a lattice defect is introduced.
Therefore, the multiple exposure method of the honeycomb lattice pattern shown in FIG. 14 provides a method for introducing lattice defects into the lattice pattern. That is, the line (L) or space (S) of the L / S pattern in the portion where the lattice defect is to be formed is divided at the defect portion. If this method is used, a lattice defect can be introduced into an arbitrary portion of the lattice pattern. A lattice defect in which one lattice point is missing is called a point defect, but a line defect in which point defects are continuously arranged or a lattice defect in which there is no lattice point in a certain region can be formed in the same manner. FIG. 17 shows an example 36 of two superimposed L / S patterns used when introducing an L-shaped lattice defect 37 into a square lattice. Note that “dividing the line” means filling the divided portion with a space, and “dividing the space” means filling the divided portion with a line.
[0030]
By forming a lattice pattern by double exposure divided into two times of the first exposure and the second exposure, the pattern of the exposure mask can be decomposed from the lattice pattern to the L / S pattern. The following advantages arise. That is, a finer lattice pattern can be formed as compared with a case where the lattice pattern is directly transferred to the photoresist once. As shown in FIG. 15 (a), a line AA ′ in the case of exposing a periodic square pattern 32 in which squares having a side of 0.35 microns are arranged with a repetition period of 0.7 microns as shown in FIG. Along the line BB ′ of the L / S pattern 33 in which aperture lines having a width of 0.35 microns are arranged with a repetition period of 0.7 microns as shown in FIG. The light intensity distribution is simultaneously shown in FIG. From FIG. 16, the peak value of the light intensity 35 in the case of the periodic square pattern 32 is about 比 べ smaller than the peak value of the light intensity 34 in the case of the L / S pattern 33, but the trailing is reversed. You can see that it ’s big. As a result, in the case of the periodic square pattern 32, the contrast of the light intensity between the square opening portion and the non-opening portion is almost eliminated, and the pattern is not transferred to the photoresist. On the other hand, in the case of the L / S pattern, the contrast of the light intensity between the opening and the non-opening is large, and the pattern is transferred to the photoresist. The difference between the two results from the shape of the pattern to be transferred. When the pattern size is reduced to about the wavelength, light is also leaked into the non-opening due to light diffraction, and the contrast of the light intensity between the opening and the non-opening begins to decrease. In the case of the L / S pattern 33 in FIG. 15B, the minimum dimension is about the wavelength of light, but only the x direction has a margin in the y direction, but the periodic square pattern 32 in FIG. In the case of, the size is as small as the wavelength in both the x direction and the y direction. That is, if the contrast decrease in the case of the L / S pattern 33 is 1 / k (k> 1), the contrast decrease in the case of the periodic square pattern 32 is 1 / (k × k). For this reason, when a fine lattice pattern is directly transferred to the photoresist, the minimum dimension that can be resolved becomes larger than the wavelength. On the other hand, if the lattice pattern is formed by multiple exposure of the L / S pattern, a lattice pattern of about 0.35 microns can be transferred at the wavelength limit, i.e., i-line, so that a two-dimensional periodic structure photonic crystal can be produced. It becomes possible to transfer a necessary lattice pattern. In the case of the combination of the above pattern size and i line, the value of k is about 2, 1 / k = 0.5, and 1 / (k × k) = 0.25. The availability of an i-line stepper means that a high-speed large-area lattice pattern, which is difficult with electron beam exposure, can be produced, and productivity is dramatically increased. In addition, a photoresist mask for optical exposure that has better dry etching resistance than a photoresist for electron beam exposure can be used.
[0031]
When a phase shift mask used for obtaining a resolution higher than the wavelength limit is used in combination with this method, a finer grating pattern can be formed by breaking the wavelength limit. When i-line is used, the size of the lattice point can be up to 0.25 micron square and the repetition period is about 0.5 micron, making it possible to produce a photonic crystal with a finer lattice pattern corresponding to light with a wavelength of 1 micron. Become. Moreover, if patterning for a 1.55 micron wavelength photonic crystal having a repetition period of 0.7 to 0.8 microns is made by using the present invention and a phase shift mask in combination, there is a margin in patterning accuracy. Can do. Note that the phase shift mask is one of super-resolution techniques for obtaining a resolution exceeding the wavelength limit. The present invention can be used in combination with other super-resolution techniques such as annular illumination.
[0032]
In the embodiments described so far, the method of forming a lattice pattern by double exposure has been described, but triple exposure or more may be performed. When triple exposure or more is performed, the shape of the lattice points can be made close to a circle. FIG. 18 shows an example in which a hexagonal lattice pattern is transferred by triple exposure of an L / S pattern. If the L / S pattern 38, the L / S pattern 39, and the L / S pattern 40 are continuously exposed and only the portion 41 that has been triple-exposed using a positive photoresist is set to an exposure intensity that dissolves in the developer. The lattice points can be hexagonal. Selection of whether the photoresist is positive or negative and combinations of various exposure intensity setting conditions, including those described above, are possible. Needless to say, selection, grid point shape selection, for example, square, rhombus, hexagon or the like can be selected.
[0033]
One advantage of forming lattice points in double exposure is that a complete lattice pattern can be formed even if the alignment of the two exposures is slightly shifted. On the other hand, the advantage of grid point formation by multiple exposure of three or more layers is that it is possible to take a large integrated light intensity ratio between a portion subjected to multiple exposure on the photoresist and a portion not so. That is, there is an advantage that the contrast between the light intensity at the lattice point portion and the surrounding light intensity can be doubled by the number of multiple exposures, and a finer lattice point pattern can be resolved.
[0034]
The development process is best performed after multiple exposure, but the development process or baking process may be inserted between multiple exposures.
[0035]
It goes without saying that the present invention is not limited to the above-described embodiments, and can be appropriately changed within the scope of the technical idea of the present invention.
[0036]
【The invention's effect】
As described above, the present invention makes use of the high solubility characteristic of the multiple exposure portion in the developer or the non-exposure property of the non-exposed portion in the developer by multiple exposure of different lattice patterns using light. Since the lattice pattern can be patterned into a photoresist, exposure can be performed at a higher speed than the electron beam exposure method, and at the same time, the fine lattice points can be decomposed into a plurality of L / S patterns to solve the optical exposure method. Fine pattern resolution that reaches the image limit can be obtained, that is, a pattern size of a wavelength that has been impossible in the past, for example, when using i-line, 0.35 microns on a side, or 0.35 microns in diameter The effect that the lattice points can be formed is obtained.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a procedure of a method for exposing a lattice pattern according to the present invention.
FIG. 2 is a schematic perspective view showing a state in step 1 of an exposure apparatus to which the lattice pattern exposure method of FIG. 1 is applied.
3 is a schematic perspective view showing a state in step 2 of the exposure apparatus of FIG. 2. FIG.
4 is a view showing an exposure pattern on a photoresist 23 exposed in the state of FIG. 2; FIG.
5 is a view showing an exposure pattern by exposure when θ = 90 ° at the same position as the exposure pattern 7 on the photoresist 23 in the state of FIG. 3; FIG.
6 is a view showing an exposure pattern in which the exposure pattern 7 of FIG. 4 and the exposure pattern 8 of FIG. 5 are overlapped.
FIG. 7 is a graph showing the solubility-exposure amount characteristics of a positive photoresist.
8A is a view showing a photoresist 23 after development in one state of the exposure amount of the first exposure and the exposure amount of the second exposure, and FIG. 8B is a view after development in a state different from FIG. 8A. It is a figure which shows the photoresist 23 of.
FIG. 9 is a graph showing the solubility-exposure amount characteristics of a negative photoresist.
FIG. 10 is a schematic diagram showing a square lattice.
FIG. 11 is a schematic diagram showing a hexagonal lattice.
FIG. 12 is a schematic diagram showing a honeycomb lattice.
FIG. 13 is a schematic diagram for explaining a hexagonal lattice multiple exposure method.
FIG. 14 is a schematic diagram illustrating a method for exposing a honeycomb lattice.
15A is a schematic diagram of an example of a periodic square pattern, and FIG. 15B is a schematic diagram of an example of an L / S pattern.
FIG. 16 is a graph illustrating a difference between the present invention and a conventional method.
FIG. 17 is a diagram showing an example of two superimposed L / S patterns used when introducing L-type lattice defects into a square lattice.
FIG. 18 is a diagram illustrating an example in which a hexagonal lattice pattern is transferred by triple exposure of an L / S pattern.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Square lattice 2 Hexagonal lattice 3 Honeycomb lattice 4, 25 Photosensitive part 5, 24 Non-photosensitive part 6, 19 Exposure light 7, 8, 9 Exposure pattern 10, 11, 12, 13, 41 Part 14, 21 Exposure mask 15, 20, 33 L / S pattern 16 Reduction optical lens 17, 22 Exposure region 18 Substrate 23 Photoresist 26, 29 First exposure pattern 27, 30 Second exposure pattern 28 Grid point 31 of hexagonal lattice 31 Grid point of honeycomb lattice 32 Periodic square pattern 34 L / S pattern light intensity 35 Periodic square pattern light intensity 36 Two L / S patterns 37 L-shaped lattice defects 38, 39, 40 L / S pattern

Claims (5)

An exposure method for a lattice pattern in which a lattice pattern is exposed to a photoresist by multiple exposures three times or more using an optical exposure apparatus, and different line and space patterns are necessary for dissolving a positive photoresist in a developer. The exposure is performed with less than the critical exposure amount, the exposure amount in the overlapped exposure portion of 3 times or more is set to the critical exposure amount or more, and a line and space pattern having a partially divided shape is subjected to multiple exposure to form a lattice. A method of exposing a lattice pattern , comprising patterning a lattice pattern including a defect . An exposure method of a lattice pattern in which a lattice pattern is exposed to a photoresist by multiple exposures three times or more using an optical exposure apparatus, and different line and space patterns are made insoluble in a negative photoresist. The exposure is less than the required critical exposure, the exposure at the overlapped exposure part of 3 times or more is set to the critical exposure or more, and the line and space pattern having a partially divided shape is subjected to multiple exposure. A method for exposing a lattice pattern, comprising patterning a lattice pattern including lattice defects .   In an exposure method of exposing a lattice pattern to a photoresist using an optical exposure apparatus, when the lattice pattern is patterned by multiple exposures of three or more different line and space patterns, the periodically divided shapes are formed. A lattice pattern exposure method comprising patterning a pattern by multiple exposure of a line and space pattern having a tilt of 60 ° or 30 °.   In an exposure method in which a grating pattern is exposed on a photoresist using an optical exposure apparatus, when the grating pattern is patterned by multiple multiple exposures of different line and space patterns, a partially divided shape is formed. A lattice pattern exposure method comprising patterning a lattice pattern including lattice defects by multiple exposure of a line and space pattern.   In an exposure apparatus that exposes a grating pattern on a photoresist using an optical exposure apparatus, when the grating pattern is patterned by multiple exposures of three or more different line and space patterns, a partially divided shape is formed. An exposure apparatus for a lattice pattern, characterized by patterning a lattice pattern including lattice defects by multiple exposure of a line-and-space pattern.

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