Phase shift mask and manufacturing method thereof and exposure method using phase shift mask comprising a semitransparent region

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to phase shift masks, and particularly to a structure of a phase shift mask of attenuation type attenuating light intensity, and a method of manufacturing the same. The present invention further relates to an exposure method using the phase shift mask.
2. Description of the Background Art
Recently, high integration and miniaturization of a semiconductor integrated circuit has been remarkably advanced, involving miniaturization of a circuit pattern formed on a semiconductor substrate (hereinafter referred to simply as a wafer).
In particular, a photolithography technique is well known as a basic technique in pattern formation. Although various developments and improvements have been made, miniaturization of a pattern still keeps on advancing, and a demand for enhancement of a pattern resolution has been increasing.
In general, a resolution limit R (nm) in a photolithography technique using a reduction exposure method is described by the following:
R=k.sub.1 .multidot..lambda./(NA) (1)
where .lambda. is a wavelength (nm)of light to be used, NA is a numerical aperture of a lens, and k.sub.1 is a constant which depends on a resist process.
As can be seen from the above expression, in order to enhance the resolution limit, k.sub.1 and .lambda. should be made smaller, and NA should be made larger. That is, the wavelength should be decreased, and NA should be increased, with the constant which depends on a resist process made smaller.
However, improvement of a light source and a lens is technically difficult. In addition, a depth of focus .delta. (.delta.=k.sub.2 .multidot..lambda./(NA).sup.2) of light is made smaller by decreasing the wavelength and increasing NA, which rather leads to deterioration in the resolution.
Description will now be made of a cross section of a mask, an electric field of exposure light on the mask, and light intensity on a wafer in using a conventional photomask, with reference to FIGS. 31A, 31B, 31C.
First, the cross sectional structure of the mask will be described with reference to FIG. 31A. A metal mask pattern 2 of chromium or the like is formed on a glass substrate 1.
Referring to FIG. 31B, an electric field is generated along the mask pattern. Referring to FIG. 31C, however, light beams passing through the mask intensify each other at an overlaid portion of the light beams caused by light diffraction and interference. Consequently, the difference in the light intensity on the wafer becomes smaller, so that the resolution is deteriorated.
A phase shift exposure method with a phase shift mask has been proposed for solving this problem, for example, in Japanese Patent Laying-Open Nos. 57-62052 and 58-173744.
The phase shift exposure method with a phase shift mask disclosed in Japanese Patent Laying-Open No. 58-173744 will now be described with reference to FIGS. 32A, 32B, 32C.
FIG. 32A shows a cross section of the phase shift mask. FIG. 32B shows an electric field on the mask. FIG. 32C shows light intensity on a wafer.
First, referring to FIG. 32A, a phase shifter 6b of a transparent insulation film such as a silicon oxide film is provided at every other aperture portion 6a of a chromium mask pattern 2 formed on a glass substrate 1 to form a phase shift mask.
Referring to FIG. 32B, the electric field of a light beam passing through phase shifter 6b of the phase shift mask is inverted by 180.degree..
Therefore, the light beams transmitted through aperture portion 6a and through phase shifter 6b cancel each other on an overlaid portion thereof caused by a light interference effect. Consequently, as shown in FIG. 32C, the difference in the light intensity on the wafer is sufficient for enhancing the resolution.
Although the aforementioned phase shift mask is very effective for a periodical pattern such as lines and spaces, it cannot be set to an arbitrary pattern because complexity of the pattern causes great difficulty in arrangement of a phase shifter and the like.
As a phase shift mask solving the above problem, a phase shift mask of attenuation type is disclosed, for example, in JJAP Series 5 Proc. of 1991 Intern. Microprocess Conference pp. 3-9 and Japanese Patent Laying-Open No. 4-136854. Description will hereinafter be made of the phase shift mask of attenuation type disclosed in Japanese Patent Laying-Open No. 4-136854.
FIG. 33A is a cross section of the phase shift mask of attenuation type. FIG. 33B shows an electric field on the mask. FIG. 33C shows light intensity on a wafer.
Referring to FIG. 33A, the structure of a phase shift mask 100 includes a quartz substrate 1 transmitting exposure light, and a phase shift pattern 30 having a prescribed exposure pattern including a first light transmit portion 10 formed on a main surface of quartz substrate 1 and having the main surface exposed, and a second light transmit portion 20 converting a phase of transmitted exposure light by 180.degree. with respect to the phase of exposure light transmitted through first light transmit portion 10.
Second light transmit portion 20 has a double layer structure including a chromium layer 2 having the transmittance of 5-40% for exposure light, and a shifter layer 3 converting a phase of exposure light transmitted therethrough by 180.degree. with respect to that of exposure light transmitted through light transmit portion 10.
The electric field on the mask, of exposure light passing through phase shift mask 100 having the above-described structure is as shown in FIG. 33B. The light intensity on the wafer has its phase inverted at an edge of the exposure pattern as shown in FIG. 33C.
The light intensity at an edge of the exposure pattern, therefore, is invariably 0, as shown in the figure, so that the difference in the electric field on light transmit portion 10 and phase shifter portion 20 of the exposure pattern is sufficient for high resolution.
It should be noticed that the transmittance of second light transmit portion 20 for exposure light is set to 5-40% in the above method, for the purpose of adjusting the thickness of the resist film after development thereof by the transmittance, as shown in FIG. 30, so as to adapt the exposure amount appropriately for lithography.
Description will now be made of a method of manufacturing phase shift mask 100. FIGS. 35 to 39 are cross sectional views showing the manufacturing steps according to the cross section of phase shift mask 100 shown in FIG. 33.
Referring to FIG. 35, chromium film 2 having the exposure light transmittance of 5-40% and the thickness of 50-200.ANG., approximately, is formed on glass substrate 1. Thereafter, on chromium film 2 formed is SiO.sub.2 film 3 of a prescribed thickness having the phase of exposure light passing therethrough converted by 180.degree.. An electron beam resist film 5 is formed on SiO.sub.2 film 3.
Referring to FIG. 36, a predetermined portion-of electron beam resist film 5 is exposed to electron beams and developed to form a resist 5 having a desired pattern.
Referring to FIG. 37, with resist film 2 as a mask, the SiO.sub.2 film is etched using a gas of the CHF.sub.3 family. Referring to FIG. 38, chromium film 2 is subjected to wet etching with resist film 5 and SiO.sub.2 film 5 as a mask.
Referring to FIG. 39, phase shift mask 100 is completed by removing resist film 5.
In the above conventional technique, however, second light transmit portion 20 has a double layer structure including chromium film 2 for controlling the transmittance and SiO.sub.2 film 3 for controlling the phase difference. This structure, therefore, requires devices and process respectively for formation of a chromium film and an SiO.sub.2 film.
In addition, the chromium film and the SiO.sub.2 film must be etched separately with different etching agents, resulting in numerous steps of the process, and thus leading to higher probabilities of defects and of process errors in the pattern dimension.
Referring to FIG. 40, when a remaining defect (opaque defect) 50 and a pinhole defect (clear defect) 51 should occur in the phase shift mask pattern, repairing methods respectively applicable to a chromium film and an SiO.sub.2 film will be required for repairing the defect. A conventional repairing method, therefore., cannot be employed.
Referring to FIG. 41, according to an exposure method using the above-described phase shift mask 100, the film thickness of a second light transmit portion 20 of phase shift mask 100 is approximately 3050.ANG. to 4200.ANG., which is relatively large. Therefore, as shown in the figure, oblique exposure light out of exposure light from an exposure light source has its phase not reliably converted by 180.degree. even if it transmits through second light transmit portion 20 of phase shift mask 100. Exposure light having a different phase is produced.
SUMMARY OF THE INVENTION
One object of the present invention is to simplify manufacturing process of a phase shift mask, so as to provide a phase shift mask of high quality.
Another object of the present invention is to provide a manufacturing method of a phase shift mask having process simplified.
A still another object of the present invention is to provide an exposure method using a phase shift mask, which can prevent exposure failure and improve the yield in the manufacturing steps of a semiconductor device.
In one aspect of the present invention, the phase shift mask includes a substrate transmitting exposure light, and a phase shift pattern formed on a main surface of the substrate. The phase shift pattern includes a first light transmit portion having the substrate exposed, and a second light transmit portion of a single material having a phase of transmitted exposure light converted by 180.degree. with respect to the phase of exposure light transmitted through the first light transmit portion, and having the transmittance of 5-40%.
The second light transmit portion is preferably formed of a single material selected from the group consisting of an oxide and a nitride oxide of metal, and an oxide and a nitride oxide of metal silicide.
The second light transmit portion is preferably formed of a single material selected from the group consisting of an oxide, a nitride oxide, and a carbide nitride oxide of chromium, and an oxide and a nitride oxide of molybdenum silicide.
The second light transmit portion preferably has the transmittance controlled through oxygen or nitrogen included therein, and the phase difference controlled through the thickness thereof.
In accordance with the present invention, the method of manufacturing a phase shift mask includes the following steps.
A phase shifter film of a prescribed thickness having a phase of transmitted exposure light converted by 180.degree., and having the transmittance of 5-40% is formed on a substrate transmitting exposure light by a sputtering method. A resist film of a prescribed pattern is formed on the phase shifter film.
With the resist film as a mask, the phase shifter film is etched by a dry etching method, so that a first light transmit portion having the substrate exposed and a second light transmit portion formed of the phase shifter film are formed.
The step of forming the phase shifter film preferably includes the step of forming a molybdenum silicide oxide film with a molybdenum silicide target in a mixed gas atmosphere of argon and oxygen.
The mixed gas preferably includes 65-92% argon gas, and an oxygen gas of the remaining percent by volume. The step of forming the phase shifter film preferably includes the step of forming a molybdenum silicide nitride oxide film with a molybdenum silicide target in a mixed gas atmosphere of an argon gas, an oxygen gas and a nitrogen gas.
The mixed gas preferably includes 65-79% argon gas, 8-24% oxygen gas, and 3-20% nitrogen gas by volume.
The step of forming the phase shifter film preferably includes the step of forming a chromium oxide film with a chromium target in a mixed gas atmosphere of argon and oxygen.
The mixed gas includes 36-97% argon gas, and an oxygen gas of the remaining percent by volume.
The step of forming the phase shifter film preferably includes the step of forming a chromium nitride film with a chromium target in a mixed gas atmosphere of argon, oxygen and nitrogen.
The mixed gas preferably includes 48-90% argon gas, 1-39% oxygen, and 6-14% nitrogen by volume.
The step of forming the phase shifter film preferably includes the step of forming a chromium nitride oxide film with a chromium target in a mixed gas atmosphere of argon and nitrogen monoxide.
The mixed gas includes 82-87% argon gas, and nitrogen monoxide of the remaining percent by volume.
The step of forming the phase shifter film preferably includes the step of forming a chromium carbide nitride oxide film with a chromium target in a mixed gas atmosphere of argon, oxygen and methane.
The mixed gas preferably includes 78-88% argon gas, 2-13% oxygen, and 8-10% methane by volume.
The step of forming the phase shift mask preferably includes the step of forming an antistatic film.
The step of forming the antistatic film preferably includes the step of forming a molybdenum film by a sputtering method between the steps of forming the phase shifter film and forming the resist film.
The step of forming the antistatic film preferably includes the step of forming a chromium film by a sputtering method between the steps of forming the phase shifter film and forming the resist film.
The step of etching the phase shifter film is preferably performed by a dry etching method with a mixed gas of carbon fluoride and oxygen.
The step of etching the phase shifter film is preferably performed by a dry etching method with a gas selected from the group consisting of a mixed gas of methylene chloride and oxygen, a mixed gas of chlorine and oxygen, and a chlorine gas.
The step of forming the phase shifter film preferably includes the step of performing heating process at or above 200.degree. C. after forming the phase shifter film by a sputtering method.
As described above, in the phase shift mask and the manufacturing method thereof in accordance with the present invention, the second light transmit portion is formed of a single material film.
In the manufacturing process of the phase shifter, a film of a prescribed single material is formed on a substrate transmitting exposure light by a sputtering method, and thereafter, a second light transmit portion is formed by prescribed etching.
This enables formation of a phase shift portion with a conventional sputtering device, and also enables etching of a phase shifter portion with a single etching agent.
Consequently, the steps of forming a phase shifter film and etching the same are required only once, respectively, in the manufacturing process, so that probabilities of defects and of process errors in the pattern dimension can be reduced, and thus a phase shift mask of high quality can be provided.
In addition, since a second light transmit portion is formed of a single material film, a defective portion can be readily repaired by a conventional method.
The exposure method using the phase shift mask according to the present invention includes the following steps.
First, a resist film is applied onto a pattern formation layer. Then, the resist film is exposed using a phase shift mask having a phase shift pattern having a first light transmit portion formed on a substrate transmitting exposure light having the substrate exposed, and a second light transmit portion of a single material having a phase of transmitted exposure light converted by 180.degree. with respect to the phase of exposure light transmitted through the first light transmit portion, and having the transmittance of 5-40%.
As a result, it is possible to form a thin second light transmit portion of the thickness of approximately 1500.ANG. to 2000.ANG., and to convert the phase of oblique exposure light by 180.degree.. Therefore, exposure light has its phase uniformed after transmitting through the second light transmit portion of the phase shift mask, making it possible to prevent occurrent of exposure failure. Consequently, the yield can be improved in the manufacturing steps of a semiconductor device.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view of a phase shift mask in a first embodiment according to the present invention.
FIG. 2A is a cross sectional view of a phase shift mask according to the present invention. FIG. 2B is a schematic diagram showing an electric field of exposure light on the mask. FIG. 2C is a schematic diagram showing light intensity on a wafer.
FIGS. 3 to 6 are cross sectional views showing the first to fourth steps of the manufacturing method of the phase shift mask in the first embodiment according to the present invention.
FIG. 7 is a schematic diagram showing the structure of a DC magnetron sputtering apparatus.
FIG. 8 is a graph showing the relation of n value, k value and a film thickness in using a krF laser.
FIG. 9 is a graph showing the relation of n value, k value and a film thickness in using an i-line.
FIG. 10 is a graph showing the relation of n value, k value and a film thickness in using a g-line.
FIG. 11 is a plot showing case by case a flow ratio of a mixed gas in formation of the phase shifter film in the first embodiment.
FIGS. 12 to 15 are cross sectional views showing the first to fourth steps of the manufacturing method of a phase shift mask in a second embodiment according to the present invention.
FIG. 16 is a graph showing the relation of n value, k value and a film thickness in using an i-line.
FIG. 17 is a graph showing the relation of n value, k value and a film thickness in using a g-line.
FIG. 18 is a first diagram plotting case by case a flow ratio of a mixed gas in formation of the phase shifter film in the second embodiment.
FIG. 19 is a second diagram plotting case by case a flow ratio of a mixed gas in formation of the phase shifter film in the second embodiment.
FIG. 20 is a third diagram plotting case by case a flow ratio of a mixed gas in formation of the phase shifter film in the second embodiment.
FIGS. 21 to 25 are cross sectional views showing the first to fifth steps of the manufacturing method of a phase shift mask in a third embodiment according to the present invention.
FIG. 26 is a cross sectional view showing a defect repairing method of a phase shift mask according to the present invention.
FIG. 27 is a schematic diagram showing a state of an exposure method using the phase shift mask according to the present invention.
FIG. 28 is a graph showing the relationship between focus offset and contact hole size in the exposure method using the phase shift mask according to the present invention.
FIG. 29 is a graph showing the relationship between focus offset and contact hole size in the exposure method using a photomask in a conventional technique.
FIG. 30 is a graph showing a comparison of the relationship between coherence and depth of focus of the exposure method using the phase shift mask according to the present invention with that of the exposure method using a phase shift mask in a conventional technique.
FIG. 31A is a cross sectional view of a photomask in a conventional technique. FIG. 31B is a schematic diagram showing an electric field of exposure light on the mask. FIG. 31C is a schematic diagram showing light intensity on a wafer.
FIG. 32A is a cross sectional view of a phase shift mask in a conventional technique. FIG. 32B is a schematic diagram showing an electric field of exposure light on the mask. FIG. 32C is a schematic diagram showing light intensity on a wafer.
FIG. 33A is a cross sectional view of a phase shift mask in a conventional technique. FIG. 33B is a schematic diagram showing an electric field of exposure light on the mask. FIG. 33C is a schematic diagram showing light intensity on a wafer.
FIG. 34 is a graph showing the relation between a transmittance of exposure light and a thickness of a resist film.
FIGS. 35 to 39 are cross sectional views showing the first to fifth steps of a manufacturing method of a phase shift mask in a conventional technique.
FIG. 40 is a cross sectional view showing a problem of the phase shift mask in the conventional technique.
FIG. 41 is a diagram showing a problem of the exposure method using a phase shift mask in a conventional technique.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first embodiment in accordance with the present invention will hereinafter be described.
First, description will be made of the structure of phase shift mask in this embodiment with reference to FIG. 1. A phase shift mask 200 includes a quartz substrate 1 transmitting exposure light, and a phase shift pattern 30 formed on a main surface of quartz substrate 1. Phase shift pattern 30 includes a first light transmit portion 10 having quartz substrate i exposed, and a second light transmit portion 4 of a single material having a phase of transmitted exposure light converted by 180.degree. with respect to the phase of exposure light transmitted through first light transmit portion 10, and having the transmittance of 5-40%.
Description will be made of an electric field of exposure light passing therethrough on phase shift mask 200 of the above structure, and light intensity on a wafer with reference to FIGS. 2A, 2B, 2C.
FIG. 2A is a cross sectional view of phase shift mask 200 described above. Referring to FIG. 2B, since the electric field on the mask is inverted at an edge of a exposure pattern, the electric field at the edge portion of the exposure pattern is invariably zero. Accordingly, as shown in FIG. 2C, the difference in the electric field on the wafer at light transmit portion 10 and at phase shift portion 4 of the exposure pattern is sufficient for obtaining higher resolution.
It should be noticed that the transmittance of second light transmit portion 4 is set to 5-40% for the purpose of adjusting the thickness of a resist film after development to adapt appropriately the exposure amount for lithography.
Description will now be made of a manufacturing method of phase shift mask 200 in a second embodiment, employing a molybdenum silicide oxide film or a molybdenum silicide nitride oxide film as a phase shifter film.
FIGS. 3 to 6 are cross sectional views showing the manufacturing process of phase shift mask 200 shown in FIG. 1.
Referring to FIG. 3, on a quartz substrate 1 formed is a phase shifter film 4 of a molybdenum silicide oxide film or a molybdenum silicide nitride oxide film by a sputtering method.
Thereafter, in order to stabilize the transmittance of phase shifter film 4, heating process is performed at or above 200.degree. C. using a clean oven or the like.
Consequently, fluctuation of the transmittance (0.5-1.0%) conventionally caused by heating process such as resist application process (approximately 180.degree. C.) in formation of a phase shifter film can be prevented.
Subsequently, an electron beam resist film 5 (EP-810S (registered trademark) manufactured by Nihon Zeon) of approximately 5000.ANG. in thickness is formed on phase shifter film 4. Since the molybdenum silicide oxide film or molybdenum silicide nitride oxide film does not have conductivity, an antistatic film 6 (Espacer 100 (registered trademark) manufactured by Showa Denko) of approximately 100.ANG. is formed thereon for prevention of being charged in irradiation of electron beams.
Referring to FIG. 4, electron beam resist film 5 is irradiated with electron beams, and thereafter, antistatic film 6 is washed away with water. Resist film 5 having a prescribed resist pattern is then formed by development of resist film 5.
Referring to FIG. 5, phase shifter film 4 is etched with resist film 5 as a mask. At this time, an RF ion etching apparatus of horizontal flat plate type is employed, which performs etching for approximately eleven minutes under the conditions of the electrode-substrate distance of 60 mm, the operating pressure of 0.3 Torr, and the flow rates of reaction gases CF.sub.4 and O.sub.2 of 95 sccm and 5 sccm, respectively.
Referring to FIG. 6, resist 5 is removed. Through these steps, the phase shift mask in accordance with the present embodiment is completed.
Formation of the phase shifter film utilizing the above-described sputtering method will hereinafter be described in detail. To have the transmittance for exposure light within the range of 5-40%, and to convert a phase of exposure light by 180.degree. are the requirements for a phase shift film.
As a film satisfying these conditions, therefore, a film made of a molybdenum silicide nitride oxide was employed in the present embodiment.
Description will be made of a sputtering apparatus for forming the aforementioned film with reference to FIG. 7.
FIG. 7 is a schematic diagram showing the structure of a DC magnetron sputtering apparatus 500.
DC magnetron sputtering apparatus 500 includes a vacuum vessel 506 provided with a magnetron cathode 509 including a target 507 and a magnet 508 therein.
An anode 510 is provided opposed to and spaced by a predetermined distance from target 507, on the opposite surface of which from target 507 provided is a quartz substrate 1 of 2.3 mm in thickness and 127 mm square, for example.
An exhaust pipe 512 and a gas feed pipe 513 are provided at predetermined positions of vacuum vessel 506. In formation of a film, molybdenum silicide is used as a target, and the temperature of quartz substrate 1 is held at 60.degree.-150.degree. C. by a heater and a temperature controller, not shown.
Under these conditions, argon as a sputter gas and a mixed gas of oxygen and nitrogen as a reaction gas are introduced from gas feed pipe 513 at a prescribed rate, the pressure in vacuum vessel 506 is held at a prescribed value, and a direct current voltage is applied between electrodes.
In this embodiment, phase shifter films of a molybdenum silicide oxide and of a molybdenum silicide nitride oxide were formed in various conditions.
Table 1 shows the pressure in vacuum vessel 506, the deposition rate and the film material in each of the cases in which various flow ratios of the mixed gas are set. A phase shifter film of a molybdenum silicide nitride oxide is to be formed in Cases M-1 to M-7, M-14, and M-15, while a phase shifter film of a molybdenum silicide oxide is to be formed in Cases M-8 to M-13, M-16, and M-17.
Tables 2-4 are graphs showing the transmittance, the n value and the k value in an optical constant (n-i.multidot.k), and the film thickness d.sub.s for converting a phase of exposure light by 180.degree., in the cases employing a krF laser (.lambda.=248 nm), an i-line (.lambda.=365 nm) and a g-line (.lambda.=436 nm) as exposure light, respectively.
In Tables 2-4, the film thickness d.sub.s can be obtained from the following:
d.sub.s =.lambda./2(n-1) (2)
where .lambda. is a wavelength of exposure light, and n is a value in the optical constant.
TABLE 1______________________________________gas flow ratio depositi% pressure .times. 10.sup.-3 on rate filmcase Ar O.sub.2 N.sub.2 Torr .ANG./min material______________________________________M-1 72.6 23.8 3.6 2.0 709 MoSiM-2 77.1 18.3 4.6 2.0 645 nitrideM-3 72.1 8.6 19.3 2.0 600 oxideM-4 68.6 7.9 23.5 2.1 525 filmM-5 61.4 7.0 31.6 2.1 486M-6 57.4 13.1 29.5 2.2 522M-7 65.4 17.8 16.8 2.0 578M-8 79.5 20.5 0 2.0 635 MoSiM-9 73.3 26.7 0 2.0 600 oxideM-10 78.8 21.2 0 2.6 225 filmM-11 81.1 18.9 0 2.6 632M-12 82.3 17.7 0 2.6 650M-13 83.5 16.5 0 2.6 754M-14 73.4 14.9 11.7 3.0 702 MoSiM-15 79.0 16.8 4.2 2.8 750 nitride oxide filmM-16 76.0 24.0 0 2.6 830 MoSiM-17 92.0 8.0 0 5.5 487 oxide film______________________________________
TABLE 2______________________________________krF laser (wavelength 248 nm) ##STR1## ##STR2## ##STR3##case % n k .ANG.______________________________________M-1 5.22 1.195 0.409 1355M-2 3.59 1.860 0.437 1442M-3 2.92 1.986 0.530 1258M-4 0.69 2.14 0.868 1088M-5 0.74 2.09 0.821 1137M-6 1.8 1.922 0.569 1345M-7 2.6 1.963 0.538 1288M-8 7.0 1.79 0.318 1570M-9 4.6 1.68 0.322 1824M-10 10.2 1.730 0.251 1700M-11 5.0 1.76 0.350 1630M-12 6.13 1.91 0.384 1360M-13 5.51 1.90 0.394 1380M-14 3.52 2.054 0.5325 1176M-15 3.03 2.111 0.5855 1116M-16 4.39 1.804 0.3844 1541M-17 6.88 1.842 0.3409 1472______________________________________
TABLE 3______________________________________i-line (wavelength 365 nm) ##STR4## ##STR5## ##STR6##case % n k .ANG.______________________________________M-1 11.6 1.874 0.280 2088M-2 11.5 1.950 0.304 1921M-3 8.82 2.11 0.397 1644M-4 2.9 2.318 0.697 1382M-5 4.15 2.344 0.626 1362M-6 3.5 2.01 0.511 1807M-7 4.53 1.88 0.414 2074M-8 44.5 2.11 0.118 1644M-9 78.6 1.85 0.0169 2147M-10 73.8 1.77 0.020 2370M-11 18.7 1.91 0.222 2005M-12 12.2 1.81 0.254 2250M-13 17.9 1.98 0.245 1860M-14 8.55 2.068 0.389 1709M-15 8.71 2.189 0.420 1535M-16 9.39 1.707 0.2536 2581M-17 16.5 1.833 0.2207 2192______________________________________
TABLE 4______________________________________g-line (wavelength 436 nm) ##STR7## ##STR8## ##STR9##case % n k .ANG.______________________________________M-1 12.0 1.786 0.249 2774M-2 16.4 2.006 0.265 2167M-3 11.7 2.148 0.358 1900M-4 3.9 2.346 0.644 1620M-5 3.4 2.121 0.572 1945M-6 4.4 1.860 0.410 2535M-7 8.8 2.018 0.367 2141M-8 46.3 2.197 0.114 1821M-9 83.0 1.795 0.0069 2742M-10 78.0 1.733 0.0123 2974M-11 22.2 1.901 0.195 2420M-12 21.1 1.982 0.220 2220M-13 13.3 1.702 0.213 3105M-14 13.0 2.124 0.3325 1940M-15 11.9 2.185 0.3653 1840M-16 17.9 1.886 0.222 2460M-17 18.2 1.775 1.1934 2812______________________________________
FIGS. 8 to 10 are graphs of data shown in Table 2 to respectively, in which the horizontal axis indicates the n value in the optical constant, the left vertical axis indicates the k value in the optical constant, and the right vertical axis indicates the film thickness d.sub.s.
The transmittance T is also shown in FIG. 8 to 10.
Referring to FIG. 8 showing the cases of exposure light of the krF laser, it can be seen that the transmittance T within the range of 5-40% required for a phase shifter film is obtained in M-1, M-8, M-10 to M-13, and M-17.
Referring to FIG. 9 showing the cases of exposure light of the i-line, the transmittance T within the range of 5-40% required for a phase shift mask is obtained in M-1 to M-3, M-8, and M-11 to M-17.
Referring to FIG. 10 showing the cases of exposure light of the g-line, it can be seen that the transmittance T within the range of 5-40% required for a phase shifter film is obtained in M-1 to M-3, M-7, and M-11 to M-17.
As a result, the films formed in M-1 to M-3, M-7, M-8, and M-11 to M-17 can be employed as a phase shifter film.
FIG. 11 is a graph showing the above cases with respect to gas flow ratios. In the graph shown in FIG. 11, respective rates of argon, oxygen and nitrogen in Cases M-1 to M-17 are described.
In this graph, a point of a mixed gas in each case is plotted, wherein the base of the triangle indicates the flow ratio (%) of argon, the left oblique side thereof indicates the flow ratio (%) of oxygen, and the right oblique side thereof indicates the flow ratio (%) of nitrogen. In accordance with the result shown in FIGS. 8 to 10, a case the film of which is applicable as a phase shifter film is indicated by a circle, while a case the film of which is not applicable to a phase shifter film is indicated by a cross.
As can be seen from the graph in FIG. 11, a mixed gas for forming a molybdenum silicide oxide film applicable as a phase shifter film includes 76-92% argon and 18-24% oxygen by volume.
A mixed gas for forming a molybdenum silicide nitride oxide film applicable as a phase shifter film includes 65-79% argon, 8-24% oxygen, and 3-20% nitrogen by volume.
The upper limit of oxygen is set to 35%, because the rate occupied by oxygen of 50% or more will cause deposition of an oxide on an electrode in the sputtering apparatus, thereby preventing sputtering. It is thus defined by the restriction of the apparatus.
As described above, in the phase shift mask in accordance with the present invention, a second light transmit portion is constituted only of a molybdenum silicide oxide film or a molybdenum silicide nitride oxide film having the transmittance of 4-50%.
In the manufacturing process thereof, a molybdenum silicide oxide or a molybdenum silicide nitride oxide is formed to a prescribed film thickness by a sputtering method, and thereafter, a prescribed etching is performed, whereby the second light transmit portion is formed.
Consequently, a phase shifter film can be formed with a conventional sputtering apparatus, and additionally, probabilities of defects and errors in a pattern dimension can be reduced because etching process is required only once.
Description will hereinafter be made of a method of manufacturing phase shift mask 200 in accordance with a third embodiment, where either of a chromium oxide film, a chromium nitride oxide film, and a chromium carbide nitride oxide film is employed as a phase shifter film.
FIGS. 12 to 15 are cross sectional views showing the manufacturing steps of phase shift mask 200 shown in FIG. 1.
Referring to FIG. 12, phase shifter film 4 of a chromium oxide film, a chromium nitride oxide film, or a chromium carbide nitride oxide is formed on quartz substrate 1 by a sputtering method.
In order to stabilize the transmittance of phase shifter film 4, heating process is performed at approximately 200.degree. C. or more with a clean oven or the like.
This prevents fluctuation of the transmittance (0.51-1.0%) caused by conventional heating processing (approximately 180.degree. C.) in resist application process after phase shifter film formation.
Subsequently, a resist film 5 of approximately 5000.ANG. in thickness is formed on phase shifter film 4.
Referring to FIG. 13, resist film 5 is irradiated with an i-line and developed so as to have a prescribed resist pattern.
Referring to FIG. 14, phase shifter film 4 is etched with resist film 5 as a mask. At this time, an RF ion etching apparatus of horizontal flat plate type is employed, in which etching is performed for approximately four minutes under the conditions of the electrodesubstrate distance of 100 mm, the operating pressure of 0.3 Torr, the flow rates of reaction gases CH.sub.2 Cl.sub.2 and O.sub.2 of 25 sccm and 75 sccm, respectively. The phase shift mask in accordance with the present embodiment is thus completed.
Detailed description will now be made of formation of the phase shift mask utilizing the sputtering method described above. To have the transmittance within the range of 5-40% for exposure light, and to convert of a phase of exposure light by 180.degree. are the requirements for a phase shifter film.
As a film satisfying these conditions, therefore, a film made of a chromium oxide, a chromium nitride oxide, or a chromium carbide oxide nitride is employed in the present embodiment.
The structure of the sputtering apparatus for forming the above phase shifter film is the same as that shown in FIG. 7, and the description thereof is not repeated.
In the present embodiment, phase shift masks of a chromium oxide film, a chromium nitride oxide film, and a chromium carbide nitride oxide film were formed in various cases.
Table 5 shows the pressure in vacuum vessel 506, the deposition rate and the film material in each of the cases in which various flow ratios of a mixed gas are set. A phase shifter film of a chromium oxide is to be formed in Cases C-1 to C-13, a phase shifter film of a chromium nitride oxide is to be formed in Cases C-14 to C-26, and a phase shifter film of a chromium carbide nitride oxide is to be formed in Cases C-27 to C-30.
Tables 6 to 8 are graphs showing the transmittance, the n value and the k value in the optical constant (n-i.multidot.k), and the film thickness d.sub.s for converting a phase of exposure light by 180.degree. in the cases employing a krF laser (.lambda.=248 nm), an i-line (.lambda.=365 nm) and a g-line (.lambda.=436 nm), respectively.
In Tables 6 to 8, the film thickness d.sub.s can be obtained from the following:
d.sub.s =.lambda./2(n=1) (2)
where .lambda. is a wavelength of exposure light, and n is a value in the optical constant.
TABLE 5______________________________________ pres-gas flow ratio sure .times. depositi film% 10.sup.-3 on rate ma-case Ar O.sub.2 N.sub.2 NO CH.sub.4 Torr .ANG./min terial______________________________________C-1 71.4 28.6 0 0 0 3.0 259 CrC-2 92.3 7.7 0 0 0 3.9 850 oxideC-3 90.0 10.0 0 0 0 3.0 900 filmC-4 85.0 15.0 0 0 0 2.0 941C-5 85.5 14.5 0 0 0 6.1 796C-6 89.3 10.7 0 0 0 8.0 828C-7 92.7 7.3 0 0 0 4.0 758C-8 96.6 3.4 0 0 0 4.0 448C-9 94.8 5.2 0 0 0 8.1 733C-10 93.1 6.9 0 0 0 6.1 791C-11 90.2 9.81 0 0 0 4.0 824C-12 90.1 9.93 0 0 0 4.1 787C-13 95.1 4.92 0 0 0 8.2 659C-14 54.1 32.4 13.5 0 0 1.5 110 CrC-15 48.8 39.0 12.2 0 0 1.5 108 nitrideC-16 87.2 6.4 6.4 0 0 4.1 592 oxideC-17 82.9 4.9 12.2 0 0 4.2 523 filmC-18 90.0 1.3 8.7 0 0 4.1 756C-19 76.0 0 0 24.0 0 2.0 600C-20 83.0 0 0 17.0 0 3.2 620C-21 75.5 0 0 24.5 0 2.3 570C-22 86.0 0 0 14.0 0 4.2 550C-23 86.5 0 0 13.5 0 4.1 580C-24 82.4 0 0 17.6 0 3.2 520C-25 86.2 0 0 13.8 0 4.2 129C-26 87.1 0 0 12.9 0 4.1 675C-27 85.2 5.3 0 0 9.5 4.0 471 CrC-28 82.9 7.9 0 0 9.2 3.0 513 carbideC-29 78.3 13.0 0 0 8.7 2.0 642 nitrideC-30 87.9 2.3 0 0 9.8 8.1 399 oxide film______________________________________
TABLE 6______________________________________krF laser (wavelength 248 nm) ##STR10## ##STR11## ##STR12##case % n k .ANG.______________________________________C-1 8.9 2.782 0.5696 696C-13 3.50 2.538 0.7448 806.2C-25 3.80 7.565 0.7347 792______________________________________
TABLE 7______________________________________i-line (wavelength 365 nm) ##STR13## ##STR14## ##STR15##case % n k .ANG.______________________________________C-1 31.7 2.23 0.187 1484C-2 8.95 2.529 0.5108 1194C-3 6.08 2.355 0.5495 1347C-4 6.52 2.481 0.5749 1212C-5 5.81 2.258 0.5252 1451C-6 5.64 2.272 0.5364 1435C-7 6.18 2.275 0.5186 1432C-8 6.22 2.225 0.5000 1490C-9 12.9 2.513 0.4171 1238C-10 8.52 2.296 1.4603 1408C-11 6.63 2.238 0.4922 1474C-12 7.23 2.299 0.8949 1405C-13 11.3 2.579 0.4634 1159C-14 9.79 2.44 0.468 1267C-15 10.0 2.50 0.476 1217C-16 5.35 2.527 0.6365 1195C-17 4.65 2.494 0.6588 1222C-18 8.78 2.632 0.5399 1118C-19 0.199 2.142 1.098 1599C-20 0.543 2.283 1.089 1250C-21 1.42 2.316 0.8407 1387C-22 1.60 2.346 0.8336 1100C-23 0.102 2.290 1.3672 1415C-24 1.38 2.413 0.9021 1100C-25 12.1 2.471 0.4257 1241C-26 1.80 2.505 0.8904 1213C-27 6.18 2.530 0.6010 1196C-28 5.06 2.283 0.5625 1422C-29 3.47 2.440 0.7066 1267C-30 8.65 2.413 0.4894 1291______________________________________
TABLE 8______________________________________g-line (wavelength 436 nm) ##STR16## ##STR17## ##STR18##case % n k .ANG.______________________________________C-2 19.58 2.660 0.3262 1313C-3 14.2 2.365 0.3689 1597C-4 11.1 2.285 0.4029 1696C-5 17.3 2.595 0.3495 1411C-6 16.1 2.538 0.3669 1417C-7 19.73 2.629 0.3220 1338C-8 21.9 2.630 0.2936 1537C-9 27.1 2.590 0.2343 1371C-10 25.3 2.900 0.2514 1147C-11 21.2 2.539 0.297 1416C-12 20.8 2.617 0.3062 1348C-13 21.4 2.676 0.2760 1301C-16 14.4 2.786 0.4263 1221C-17 12.5 2.732 0.4621 1258C-18 9.94 2.053 0.3587 2070C-19 1.93 2.607 0.925 1356C-21 2.84 2.706 0.8715 1270C-22 6.13 2.706 0.6562 1280C-23 3.60 2.631 0.7820 1320C-24 5.02 2.748 0.7250 1250C-26 3.98 2.630 0.7475 1337C-27 1.29 1.731 0.4952 2982C-28 14.5 2.482 0.3834 1471C-29 5.50 2.335 0.5641 1633C-30 18.8 2.580 0.3304 1380______________________________________
FIGS. 16 and 17 are graphs; of data shown in Tables 7 and 8. The horizontal axis indicates the n value in the optical constant, the left vertical axis indicates the k value in the optical constant, and the right vertical axis indicates the film thickness d.sub.s.
The transmittance T is also shown in FIGS. 16 and 17.
Referring to FIG. 16 showing the case of exposure light of the i-line, it can be seen that the transmittance T within the range of 5-40% required for a phase shift mask is obtained in C-1 to C-16, C-18, C-25, C-27, C-28, and C-30.
Referring to FIG. 17 showing the case of exposure light of the g-line, it can be seen that the transmittance T within the range of 5-40% required for a phase shift mask is obtained in Cases C-2 to C-13, C-16 to C-18, C-22, C-24, and C-28 to C-30.
As a result, the films formed in Cases C-1 to C-18, C-22, C-24, C-25, and C-27 to C-30 can be employed as a phase shifter film.
FIGS. 18 to 20 are graphs showing the above cases based on the relation of gas flow ratios in mixed gases Ar+O.sub.2, Ar+O.sub.2 +N.sub.2, Ar+NO, and Ar+O.sub.2 +CH.sub.4, respectively.
The graph of FIG. 18 shows the rates of argon, oxygen and nitrogen in Cases C-1 to C-18.
In this graph, a point of a mixed gas in each case is plotted, wherein the base of the triangle indicates the flow ratio (%) of argon, the left oblique side of the triangle indicates the flow ratio (%) of oxygen, and the. right oblique side of the triangle indicates the flow ratio (%) of nitrogen.
In accordance with the result in FIGS. 16 and 17, a case the film of which is applicable as a phase shifter film is indicated by a circle, while a case the film of which is not applicable as a phase shifter film is indicated by a cross.
As can be seen from the graph of FIG. 18, a mixed gas for forming a chromium oxide film applicable as a phase shifter film includes 36-97% argon and 3-64% oxygen by volume.
A mixed gas for forming a chromium nitride oxide film applicable as a phase shifter film includes 48-90% argon, 1-39% oxygen, and 6-14% nitrogen by volume.
The upper limit of oxygen is set to 39%, because the rate occupied by oxygen of 50% or more will cause deposition of an oxide on an electrode in the sputtering apparatus, thereby preventing sputtering. It is thus defined by the restriction of the apparatus.
FIG. 19 is a graph showing the rates of argon and NO in Cases C-19 to C-26. In accordance with the results in FIGS. 16 and 17, a case the film of which is applicable as a phase shift mask is indicated by a circle, while a case the film of which is not applicable as a phase shifter mask is indicated by a cross.
FIG. 20 is a graph showing the rates of argon, oxygen and methane in Cases C-27 to C-30.
In the graph, a point of a mixed gas in each case is plotted, wherein the base of the triangle indicates the flow ratio (%) of argon, the left oblique side thereof indicates the flow ratio (%) of oxygen, and the light oblique side thereof indicates the flow ratio (%) of methane.
In accordance with the result in FIGS. 16 and 17, a case the film of which is applicable as a phase shifter film is indicated by a circle, while a case the film of which is not applicable as a phase shifter film is indicated by a cross.
As can be seen from the graphs in FIGS. 19 and 20, a mixed gas for forming a chromium nitride oxide film applicable as a phase shifter film includes 82-87%.argon, and 13-18% nitrogen monoxide by volume.
A mixed gas for forming a chromium carbide nitride oxide film applicable as a phase shifter film includes 78-88% argon, 2-13% oxygen, and 8-10% methane by volume.
As described above, in the phase shift mask in accordance with the present embodiment, a second light transmit portion is constituted only of a film of a chromium oxide, a chromium nitride oxide, or a chromium carbide nitride oxide, having the transmittance of 4-50%.
In the manufacturing process thereof, a film of a chromium oxide, a chromium nitride oxide, or a chromium carbide nitride oxide is formed to a prescribed film thickness by a sputtering method, and thereafter, a prescribed etching is performed, so that the second light transmit portion is formed.
Consequently, a phase shifter film can be formed with a conventional sputtering apparatus, and probabilities of defects and errors in a pattern dimension can be reduced since etching process is required only once.
Although an oxide and a nitride oxide of molybdenum silicide, and an oxide, a nitride oxide, and a carbide nitride oxide of chromium are used as the second light transmit portion in the second and third embodiments, it is not limited to them, and an oxide and a nitride of metal, and an oxide and a nitride oxide of metal silicide may be used.
Description will now be made of a fourth embodiment in accordance with the present invention. In the present embodiment, an antistatic metal film is formed for prevention of being charged in irradiation of electron beams or laser beams on a phase shifter film in the manufacturing process thereof.
The manufacturing process of the phase shifter film will be described with reference to FIGS. 21 to 25.
FIGS. 21 to 25 are cross sectional views corresponding to the cross sectional structure of the phase shift mask shown in FIG. 1.
Referring to the figures, as in the second and third embodiments, phase shifter film 4 is formed on quartz substrate, which is made of a molybdenum silicide oxide film, a molybdenum silicide nitride oxide film, a chromium oxide film, a chromium nitride oxide film, or a chromium carbide nitride oxide film.
Thereafter, an antistatic film 6 of approximately 100-500.ANG. in thickness is formed on phase shifter film 4. When the film material of the phase shifter film belongs to the Mo family, a molybdenum film is to be formed as antistatic film 6. When it belongs to the Cr family, a chromium film is to be formed as antistatic film.
This is because phase shifter film 4 of a molybdenum silicide oxide, a molybdenum silicide nitride oxide, a chromium oxide, a chromium nitride oxide, or a chromium carbide nitride oxide, formed in the aforementioned method does not have conductivity.
With regard to Cases C-1 to C-3 described in connection with the third embodiment, since a chromium oxide film formed in the above cases has conductivity, the antistatic film is not required.
Subsequently, an electron beam resist film of approximately 5000.ANG. in thickness is formed on antistatic film 6.
Referring to FIG. 22, resist film 5 having a desired resist pattern is formed by exposing to electron beams and developing a prescribed portion of electron beam resist film 5.
Referring to FIG. 23, sequential dry etching of antistatic film 6 and phase shifter film 4 is performed using a CF.sub.4 +O.sub.2 gas, with electron beam resist film 5 as a mask when antistatic film 6 belongs to the Mo family.
Referring to FIG. 24, resist film 5 is removed using O.sub.2 plasma or the like. Referring to FIG. 25, antistatic film 6 is removed by etching with etching liquid (a mixture of ammonium ceric nitrate and perchloric acid) or the like.
The phase shift mask is thus completed.
Referring to FIG. 23 again, when antistatic film 6 belongs to the Cr family, sequential dry etching of antistatic film 6 and phase shifter film 4 is performed with a CH.sub.2 Cl.sub.2 +O.sub.2 gas, a Cl.sub.2 +O.sub.2 gas, or Cl.sub.2 gas, with electron beam resist film 5 as a mask.
Referring to FIG. 24, resist film 5 is removed using O.sub.2 plasma or the like. Referring to FIG. 25, antistatic film 6 is removed by etching with sulfuric acid.
The phase shift mask is thus completed.
Although an antistatic film of molybdenum is formed in the case of a phase shift mask belonging to the Mo family, and an antistatic film of chromium is formed in the case of a phase shift mask belonging to the Cr family in etching of the phase shift mask, the present invention is not to limited to this, and the same effects can be obtained by using an antistatic film of Mo for a phase shift mask belonging to the Cr family, or using an antistatic film belonging to the Cr family for a phase shifter film belonging to the Mo family.
As described above, providing a molybdenum film in the manufacturing process of the phase shift mask, an antistatic effect in irradiation of light beams can be obtained. This also serves as a light reflecting film for a position detector of optical type.
Although a molybdenum film or a chromium film is used as an antistatic film in the fourth embodiment, the same effects can be obtained by using a film of W, Ta, Ti, Si, Al or the like, or alloys thereof.
Description will be now made of methods of detecting a defect and repairing the same, when a remaining defect (an opaque defect) 50 or a pin hole defect (a clear defect) 51 occurs on the phase shift mask formed in the first to third embodiments, as shown in FIG. 26.
First, utilizing a light transmit type defect detection apparatus (manufactured by KLA, 239HR type), the presence of a defect in a manufactured phase shift mask is checked by comparing chips.
In this defect detection apparatus, the check is carried out with light emitted from a mercury lamp.
As a result, a remaining defect in which the phase shifter film remains on the pattern to be etched, and a pin hole defect in which the phase shifter film to be left is eliminated because of a pin hole or a lacked shape are detected.
These defects are then repaired. The remaining defect is repaired by a laser blow repair apparatus with a YAG laser, as in a conventional photomask.
Another method of removing the remaining defect is to perform assist-etching by FIB with a gas for sputter etching.
The pin hole defect is repaired by burying the pin hole defect portion through deposition of a carbon film 52 by FIB assist deposition method, as in a conventional photomask.
A good phase shift mask can thus be obtained without carbon film 52 being peeled off even when the repaired phase shift mask is washed.
Description will now be made of an exposure method using the above-described phase shift mask.
When the phase shift mask is used, a phase shifter film is formed with the thickness of approximately 1500.ANG. to 2000.ANG. as shown in film thickness dimension (ds) of Table 2 to Table 4 and Table 6 to Table 8. Since the phase shifter film is formed with the thickness approximately half of that of a conventional phase shifter film, it is possible to convert oblique exposure light included in exposure light by 180.degree. as shown in FIG. 27.
As a result, as shown in FIG. 28, when a contact hole of 0.4 .mu.m is to be opened, for example, it is possible to allow focus tolerance of 1.2 .mu.m. In the case of a conventional photomask, as shown in FIG. 29, when a contact hole of 0.4 .mu.m was to be opened, focus offset of only 0.6 .mu.m was allowed.
In an exposure apparatus having coherence of 0.3 to 0.7 favorably 0.5-0.6, as shown in FIG. 30, it is possible to substantially improve depth of focus as compared to the case of the conventional photomask.
FIGS. 28 and 29 show the relationship between contact hole size and focus tolerance in the case where a reduction and projection exposure apparatus having a reduction ratio of 5:1 is used. However, it is possible to obtain similar effects with a reduction and projection exposure apparatus having a reduction ratio of 4:1 or 3:1, or projection exposure apparatus having a reduction ratio of 1:1. It is possible to obtain similar effects not only with a projection exposure apparatus but also with a contact exposure apparatus and a proximity exposure apparatus.
In addition, it is possible to obtain similar effects that a krF laser (.lambda.=248 nm), an i-line (.lambda.=365 nm) and a g-line (.lambda.=436 nm) is using as exposure light.
As described above, according to the exposure method using the phase shift mask in this embodiment, since it is possible to prevent occurrence of exposure failure, it is possible to improve the yield in the manufacturing steps of a semiconductor device. The exposure method can be effectively used in the manufacturing steps of a semiconductor device such as a DRAM of 4M, 16M, 64M, 256M, an SRAM, a flash memory, an ASIC (Application Specific Integrated Circuit), a microcomputer, and GaAs. Furthermore, the exposure method can be well used in the manufacturing steps of a unitary semiconductor element and a liquid crystal display.
In the phase shift mask in accordance with the present invention, a second light transmit portion is made only of a single material film.
Additionally, in the manufacturing process of the phase shift film, the second light transmit portion is formed by forming a prescribed phase shifter film on a substrate transmitting exposure light by a sputtering method, and thereafter, performing a prescribed etching.
This enables formation of a phase shifter film at a single step with a conventional sputtering apparatus. Moreover, since etching process is required only once, probabilities of defects and errors in the pattern dimension will be decreased, so that a phase shift mask high quality can be provided.
Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Number	Date	Country
4-335523(P)	Nov 1992	JPX
5-91445(P)	Apr 1993	JPX
5-285327(P)	Nov 1993	JPX

Number	Name	Date
4359490	Lehrer	Nov 1982
4661426	Matsuda et al.	Apr 1987
4678714	Watakabe	Jul 1987
4717625	Watakabe et al.	Jan 1988
4722878	Watakabe et al.	Feb 1988
4738907	Shigetomi et al.	Apr 1988
4783371	Watakabe et al.	Nov 1988
4792461	Watakabe et al.	Dec 1988
4873163	Watakabe et al.	Oct 1989
4957834	Matsuda et al.	Sep 1990
5286581	Lee	Feb 1994

Number	Date	Country
0507487A2	Oct 1992	EPX
0528687A1	Feb 1993	EPX
57-62052	Feb 1982	JPX
58-173744	Mar 1983	JPX
4-136854	May 1992	JPX
5-2261A	Jan 1993	JPX
5-2259A	Jan 1993	JPX
5-127361	May 1993	JPX
5-181257A	Jul 1993	JPX

Phase shift mask and manufacturing method thereof and exposure method using phase shift mask comprising a semitransparent region

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Entry
"Imaging Characteristics of Multi-Phase-Shifting and Halftone Phase-Shifting Masks," JJAP Series 5 Proc. of 1991 Intern. Microprocess Conference, pp. 3-9, 1991.
"Si-N Attenuated Phase Shift Layer for Phase Shift Mask Application," IBM Technical Disclosure Bulletin, pp. 440-441, vol. 35, No. 3, Aug. 1992.