JPH04136854A - Photomask and production thereof, formation of pattern by using this method and photomask blank - Google Patents

Abstract

PURPOSE:To allow the formation of fine patterns and to lower the generation rate of resolution defects by adopting the constitution to provide a specific phase difference of the light passing translucent regions and light passing transparent regions and specifying the patterns of the transparent regions to prescribed patterns. CONSTITUTION:This mask is provided with the regions 4 translucent to exposing light and the regions 3 transparent thereto and is so constituted that the phase difference of the light respectively passing the regions 4 and the regions 3 is substantially 180 deg.C. The pattern in the regions 3 is specified to the pattern in a single hole, dot, space or line. The transmissivity of the exposing light of the regions 4 is preferably specified to a 1% to 50% range when the transmissivity of the exposing light of the regions 3 is designated as 100%. The thickness (t) of the film 4 is so adjusted as to attain the relation t=lambda/a(n-1) (where lambda is the wavelength of the exposing light; (n) is the refractive index of the translucent film; (a) is the value in a 1.3<=a<=4 range).

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a photomask used in the manufacture of semiconductor devices, etc., particularly a photomask treated to change the phase of illumination light, a method for manufacturing the same, a method for forming a pattern using the same, and a method for manufacturing the photomask. Regarding photomask blanks. [Prior Art] One of the conventional techniques for improving the resolution of an exposure device that transfers a mask pattern is a method of introducing a phase into light transmitted through a mask. For example, in Japanese Patent Publication No. 62-50811, a transparent film that changes the phase is formed on at least one of the light transmitting parts on both sides of the opaque part. According to this method, the resolution can be significantly increased using the same lens as before. Furthermore, in Japanese Patent Laid-Open No. 62-67547, as a means for improving the resolution of a single light transmitting section, light transmitting sections below the resolution limit in which the phase of transmitted light is inverted are provided on both sides of the single light transmitting section. There is. Furthermore, Japanese Patent Application Laid-Open No. 53-5572 proposes a photomask with a phase difference between a light-transmitting part and a semi-transparent part as a stable photomask with a low level of diffraction distortion.

[Problem to be solved by the invention]

In the prior art described in 1., after creating a normal transmission mask, it is necessary to form a transparent film for changing the phase of transmitted light, a so-called phase shifter. . Furthermore, the phase shifters need to be arranged so that the phases of light transmitted through adjacent transmission parts are reversed. Therefore, when arranging a phase shifter in a complex element pattern, it may be difficult to arrange the shifter, and in order to efficiently arrange the chic, trial and error and advanced consideration are required, which requires a lot of effort. It was necessary. In addition, the number of mask manufacturing steps has doubled compared to the conventional method, and the increase in the number of steps has caused major problems such as the occurrence of defects and a decrease in yield. Furthermore, repairing defects in the transparent film requires a lot of effort, which has been a major obstacle to practical application. SUMMARY OF THE INVENTION An object of the present invention is to provide a point mask that can form fine patterns and reduce the incidence of poor resolution. A second object of the present invention is to provide a method for manufacturing the mask. A third object of the present invention is to provide photomask blanks for manufacturing the photomask. A fourth object of the present invention is to provide a pattern forming method using the photomask.

[Means for Solving the Problems] The above objects include (1) a transparent substrate having at least a region that is semitransparent to exposure light and a region that is transparent; The structure is such that the phase difference of the light passing through each transparent area is substantially 180°, and the pattern of the transparent area is a pattern of a single hole, trough, space, or line. A photomask with (2
) In the photomask according to item 1 above, the transmittance of the exposure light in the semi-transparent area is 10% higher than the transmittance of the exposure light in the transparent area.
(3) A mask having an opaque area, a semi-transparent area, and a transparent area on a transparent substrate. The phase difference between the light passing through the translucent area and the transparent area is substantially 180°, and the pattern of the transparent area is a single hole, dot, space, or (4) In the photomask described in 3 above, the transmittance of the exposure light in the semi-transparent area is 100% of the transmittance of the exposure light in the transparent area. This is achieved by a photomask characterized in that it is in the range of 1% to 50%. The second purpose is to (5) form a semitransparent layer containing at least 1N of a film that is semitransparent to exposure light on a transparent substrate, and remove a desired portion of the semitransparent layer. (6) The method for producing a Hol-mask according to (6)
forming an etching stopper layer on the transparent substrate;
A step of forming a semitransparent layer including at least one layer of a film that is semitransparent to exposure light on the etching stopper layer, and a step of removing a desired portion of the semitransparent layer to form a desired pattern in the semitransparent layer. (7) forming a semi-transparent film on a transparent substrate; removing the semi-transparent film in a desired pattern; and exposing the exposed film. 3. The method according to item 1 or 2 above, which comprises a step of removing the transparent substrate to a desired depth.
- Achieved by a method of manufacturing a mask. - The purpose of item 3 described in (8) is to have a semi-transparent layer on a transparent substrate including at least one layer of a Y transparent film, and the semi-transparent layer has a transmittance of 1% for exposure light. The film thickness of the film constituting the semi-transparent layer is Σ ((nl-1) d, ):φλ u=1 (where d+ and nl are 1 The thickness and refractive index of the th film, m is the number of films constituting the semi-transparent layer,
A photomask blank characterized in that λ is the wavelength of the light, and φ is a value in the range of ]/4≦φ≦3/4. A photomask blank characterized in that the layer is a composite film further including at least IM of a transparent film, (10) In the photomask blank described in l or 9, there is a conductive layer between the transparent substrate and the semitransparent layer. A photomask blank characterized by being provided with a transparent film, (]-1-) In the photomask blank described in J2, 9 or 10, the transparent film formed on - is made of Cr having a thickness of 40 nm or less. This is achieved by using photomask blanks that are characterized by a film of The fourth purpose is to (12) prepare a sample having a thin film of a photosensitive material on a substrate, and expose the sample to light of a desired wavelength through the photomask according to any one of 1 to 4 above. This is achieved by a pattern forming method characterized by a step of irradiating the photosensitive material with a photosensitive material, and developing the sample to form a pattern of the photosensitive material. The semitransparent layer in (5), (6), (8), (9), and (1, 0) above refers to a composite film that has at least one layer of a semitransparent film, and further includes a transparent film. It may be. That is, this semitransparent layer as a whole is semitransparent, and a phase difference may be generated between it and the transparent region. [Operation] Since the phase of the light passing through the semi-transparent film is reversed with respect to the light passing through the light transmitting portion, the phase is reversed at the boundary, and the light intensity at the boundary approaches O. As a result, the ratio of the intensity of light passing through the light-transmitting portion to the intensity of light at the pattern boundary becomes relatively large, and a light intensity distribution with a higher ratio of I/last than the conventional method can be obtained. This will be explained using drawings. First, the conventional method is
This will be explained using figures. FIG. 2(a) shows a cross-sectional view of a conventional photomask, where 1 is a glass substrate and 2 is a Cr light shielding film.
It is a membrane. The amplitude distribution of the light passing through the light transmission section 3 is
As shown in Figure (b), they have the same reference numerals. When this light is projected onto a wafer through a lens, the distribution of light intensity spreads to just below the light shielding part, as shown in FIG. 2(c). Therefore, it has been difficult to form fine patterns using conventional methods. In contrast, the present invention will be explained with reference to FIG. Figure 1 (a
) is a sectional view of an example of the mask of the present invention. 1 is a glass substrate, and 4 is a semi-transparent film. The film thickness t of the semi-transparent film 4 is: λ/a(n-1) (where λ is the wavelength of the exposure light, T) is the refractive index of the semi-transparent film, and a is 1.3≦a≦4. Adjust so that the relationship is within the range of values). The amplitude distribution of the light transmitted through this mask is as shown in FIG. It is reversed and has a negative sign. When this light is projected onto the wafer 2 through a lens, the phase is reversed at the boundary between the light transmitting part 3 and the semi-transparent film 4, as shown in FIG.
Directly below that, the light intensity becomes approximately O. Therefore, the spread of the light intensity distribution is suppressed, and a fine pattern with high contrast can be formed. [Example] The present invention will be explained in detail below. (Example 1) A mask having the structure shown in FIG. 1 was manufactured as a first example mask of the present invention. . FIG. 1(a) shows a cross-sectional view of the photomask. 1 is a glass substrate, and 4 is a semi-transparent film. The thickness of the semi-transparent film 4 is t=λ/a(n-1) (where λ is the wavelength of the exposure light, n is the refractive index of the semi-transparent film,
The relationship was adjusted so that a was in the range of 1.3≦a≦4. The exposure wavelength is the J-line of a mercury lamp (365
nm) was used. Here, the semi-transparent film 4 was made of coated glass to which a light absorbing agent was added. Since the refractive index of this glass with respect to exposure light was approximately 1.45, the film thickness of the coated glass was approximately 420 nm. Further, at this time, the amount of the light absorbing agent added was adjusted so that the transmittance of exposure light was 15%. Note that the transmittance setting above depends on the sensitivity of the resist used,
It is necessary to decide taking photosensitivity characteristics into consideration, and although it is not limited to 15%, it is preferably 1% or more in order to obtain the effects of the present invention. Further, the upper limit of the transmittance is desirably about 50% in consideration of variations in practical processes, but the effect can be obtained even if the transmittance is higher than this. More effective is a range of 5 to 30%. The pattern of transparent areas formed a single hole, dot, space or line pattern, respectively. Further, in order to obtain the effects of the present invention, it is desirable that the thickness t of the semitransparent film is in the range of 1.3≦a≦4 in t-λ/a(n-1). Even outside this range, the effect of improving contrast 1 to last can be obtained, albeit slightly. In addition, the material of the semi-transparent film 4 is not limited to coated glass, but may also be an organic film or an inorganic film, etc. The desired transmittance can be obtained, and the phase of the transmitted light is almost reversed to the phase of the light passing through the light transmitting part 3. If possible, any material can be used. Furthermore, although the semitransparent film 4 is composed of a single film in the above embodiment, the structure of the mask is not limited to this. By using this photo mask, the light intensity of the transmitted light becomes almost O just below the boundary between the light transmitting part 3 and the semi-transparent film 4, as shown in FIG. 1(c). The spread of the light intensity distribution was suppressed, and a fine pattern with high contrast could be formed. (Example 2) In the second example, as shown in FIG. 3, the structure of the semi-transparent layer was a multilayer film. A thin Cr film 6 and a coated glass film 7 were deposited on a glass substrate 1, and a desired pattern portion was removed. In this case, the transmittance was adjusted to 1% with the thin Cr film 6, and the phase difference with the transparent portion was adjusted with the coated glass film 7. The transmittance of the thin Cr film for exposure light may be in the range of 1 to 50%. The thickness of the coated glass film 7 may be approximately the same as the thickness limit of the semi-transparent film 4 shown in the first embodiment, but in order to set a phase difference of 180° with higher precision, a thin Cr film may be used. 6
We also took into account the phase shift of the light passing through. That is, in this embodiment, the semitransparent layer consists of a thin Cr film 6 and a coated glass film 7, and the thickness of the thin Cr film 6 is such that the transmittance is 1.
%, and the thickness of the coated glass film 7 is Σ ((n+ 1) d+) = φλ (where d+ and n are the thickness and refractive index of the fifth film constituting the semi-transparent layer, m is the number of films constituting the semi-transparent layer, which is 2 in this example, λ is the wavelength of the exposure light, and φ is 1/4≦φ
≦3/4). With this structure, the same effects as in Example 1 were obtained. (Example 3) In the third example, as shown in FIG.
A thin Cr film 6 was formed thereon, this thin Cr film 6 was removed in a desired pattern, and then the glass substrate was etched to a desired depth. It is preferable that the thickness of the thin Cr film is 40 nm or less, and the transmittance of the exposure light is adjusted in the range of 1 to 50% as shown in the first embodiment. In this example, it was set to 1%. The etching depth is the same as the thickness limit of the coated glass film shown in the second embodiment.
In order to set a phase difference of 18o° with high precision, thin Cr
It was determined in consideration of the phase shift of light transmitted through the film 6. Furthermore, if it is difficult to control the etching depth of the glass substrate 1, a structure as shown in FIG. 5 may be used. A transparent etching stopper 8 made of TTO is provided on a glass substrate J, a transparent film 9 is placed on top of the etching stopper 8, and a thin Cr film 6 is placed on top of the transparent etching stopper 8.
This is provided. The same effects as in Example 1 were obtained with the structures shown in FIGS. 4 and 5. (Embodiment 4) The fourth embodiment has a structure in which the problem with the knee of the first embodiment is addressed. Coated glass is used for the semitransparent film 4 in FIG. 1, but this material and the glass substrate 1 are made of almost the same material. When processing by dry etching using a similar gas, sufficient selectivity cannot be obtained. Therefore, sophisticated etching control is required. In contrast, in this embodiment, as shown in FIG. 6, an etching stopper 8 is disposed between the glass substrate 1 and the semi-transparent layer 4. Although a silicon nitride film is used here, it is not limited to this. Furthermore, if there is no conductive material on the glass substrate, a charge amplification phenomenon will occur during pattern formation with an electron beam, resulting in problems such as pattern misalignment.
It is also effective to use a conductive film such as a TTO film. When preventing charge-up by other methods, there is no need to use a conductive film. The thickness of the semi-transparent film 4 was the same as described above. As described above, the mask structure of the present invention needs to be adjusted so that the phases of light passing through the light-transmitting part and the semi-transparent part are reversed. It is also effective to combine the structure of the present invention with a normal mask or a conventional phase shift type mask within the same substrate. In other words, when the alignment marks used to align the positions of the exposure equipment and the mask and the detection window patterns used to align the positions of the mask and wafer were formed using a normal light-shielding film, the results were better than when using a semi-transparent film. A high SN ratio was obtained for the detection signal. Further, the effect of the present invention is effective in forming a hole pattern, and a hole pattern with a diameter of 0.4 μm can be formed using an optical system, which conventionally had a limit of forming a hole pattern with a diameter of 0.5 μm. Furthermore, it was confirmed that resolution deterioration due to focal position shift was also small. Furthermore, when the photomask of the present invention shown in each of the above-mentioned Examples was used to form an electrode wiring conduction hole of a semiconductor element, a conduction hole that was 0.1 μm smaller than the conventional one could be formed. Furthermore, as the depth of focus increased, the incidence of poor resolution was also significantly improved. Furthermore, it goes without saying that the effects of the present invention do not depend on the exposure wavelength. In the above embodiment, the exposure wavelength is one line (365 nm
), but the wavelength is not limited to this. g-line (
Similar results were obtained with KrF excimer laser light, ArF excimer laser light, etc. [Effects of the Invention] According to the present invention, a finer pattern can be formed than in the conventional transmission type mask. Furthermore, the process for creating a photomask is almost the same as that for a conventional transmission type mask, and the process is significantly simplified compared to that for a conventional phase shift mask. Furthermore, as a result of fabricating a semiconductor device using the photomask of the present invention, it was possible to achieve a finer specific hepatane pattern and to reduce the device area compared to the conventional mask. Furthermore, as the depth of focus improved, the incidence of poor resolution was also significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a photomask according to an embodiment of the present invention, an amplitude distribution diagram of transmitted light, and a light intensity diagram. FIG. 2 is a cross-sectional view of a conventional photomask, a diagram of amplitude distribution of transmitted light, and a diagram of light intensity. 3, 4, 5, and 6 are cross-sectional views of other embodiments of the present invention. 1... Glass substrate 2... Cr film 3 - Light transmitting part 4 - Semi-transparent film 6 - Thin Cr film 7
Coated glass film 8...Etching stopper 9...Transparent pattern

Claims (1)

[Claims] 1. On a transparent substrate, there is at least a region that is semitransparent to exposure light and a region that is transparent, and light that passes through the semitransparent region and the transparent region, respectively. The phase difference is essentially 1
1. A photomask having a configuration of 80°, and characterized in that the pattern of the transparent area is a pattern of a single hole, dot, space, or line. 2. In the photomask according to claim 1, the transmittance of the exposure light in the semi-transparent region is in the range of 1% to 50% when the transmittance of the exposure light in the transparent region is 100%. A photomask featuring 3. On a transparent substrate, an opaque area and a semi-transparent area,
The transparent area has a configuration in which the phase difference of light passing through the translucent area and the transparent area is substantially 180°, and the pattern of the transparent area is a single hole. ,
A photomask characterized by a pattern of dots, spaces or lines. 4. In the photomask according to claim 3, the transmittance of the exposure light in the semi-transparent region is in the range of 1% to 50%, when the transmittance of the exposure light in the transparent region is 100%. A photomask featuring 5. Forming a semi-transparent layer containing at least one film that is semi-transparent to exposure light on a transparent substrate, and removing a desired portion of the semi-transparent layer to form a desired pattern on the semi-transparent layer. 3. The method of manufacturing a photomask according to claim 1, further comprising the steps of: 6. Forming an etching stopper layer on the transparent substrate; forming a semitransparent layer containing at least one film that is semitransparent to exposure light on the etching stopper layer; and forming a desired portion of the semitransparent layer. 3. The method of manufacturing a photomask according to claim 1, further comprising the step of removing the semi-transparent layer to form a desired pattern. 7. A claim characterized by comprising the steps of forming a semi-transparent film on a transparent substrate, removing the semi-transparent film in a desired pattern, and removing the exposed transparent substrate to a desired depth. Item 2. A method for manufacturing a photomask according to item 1 or 2. 8. A semi-transparent layer including at least one layer of a semi-transparent film is provided on a transparent substrate, and the semi-transparent layer has a transmittance of 1% to 50% for exposure light, and The film thickness of the film constituting the semi-transparent layer is ▲Mathematical formula, chemical formula, table, etc.▼ (However, d_i and n_i are the thickness and refractive index of the i-th film constituting the semi-transparent layer, m is the translucent A photomask blank characterized by satisfying the following relationship: the number of films constituting a layer, λ is the wavelength of exposure light, and φ is a value in the range of 1/4≦φ≦3/4. 9. The photomask blank according to claim 8, wherein the semitransparent layer is a composite film further including at least one layer of a transparent film. 10. The photomask blank according to claim 8 or 9, characterized in that a conductive thin film is provided between the transparent substrate and the semi-transparent layer. 11. The photomask blank according to claim 8, 9 or 10, wherein the semi-transparent film is made of carbon having a thickness of 40 nm or less.
A photomask blank characterized by being a film made of r. 12. A step of preparing a sample having a thin film of a photosensitive material on a substrate, and a step of irradiating the sample with light of a desired wavelength through the photomask according to any one of claims 1 to 4. A pattern forming method comprising developing a sample to form a pattern of the photosensitive material.