JP2004101868A - Photomask manufacturing method - Google Patents

Abstract

In a resist mask, a slight resist scum remaining on a glass substrate serves as a light shielding material to cause a transfer defect. Therefore, it is an object of the present invention to establish a method for manufacturing a resist mask (photomask) without resist scum.
In order to solve the problem of the resist mask, after a resist pattern is formed on a transparent substrate, VUV light is irradiated in an environment where oxygen exists near the resist pattern. This method solves the above problem.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a photomask used in lithography. In particular, the present invention relates to a method of manufacturing a photomask using a resist having low cost and a short production TAT (Turn Around Time) as a mask material with less scum and less mask defects.
[0002]
[Prior art]
In manufacturing a semiconductor integrated circuit device, a lithography technique is used as a method of transferring a fine pattern onto a semiconductor wafer. In lithography, a projection exposure apparatus is mainly used. A pattern of a photomask mounted on the projection exposure apparatus is transferred onto a semiconductor wafer to form a device pattern.
[0003]
An ordinary photomask is manufactured by processing a metal light-shielding material such as chromium (Cr) formed on a transparent quartz substrate or an inorganic film dimming material such as MoSi, ZrSiO, or SiN. That is, an ordinary photomask is configured such that a light-shielding film or a light-reducing film made of a metal such as chromium or an inorganic film is formed in a desired shape on a quartz substrate. These films are usually formed by a sputtering method. The processing of the light shielding film is, for example, as follows. After applying an electron beam sensitive resist on the light shielding film, a desired pattern is drawn on the electron beam sensitive resist by an electron beam drawing apparatus. Subsequently, after a resist pattern having a desired shape is formed by development, the light-shielding film is processed by dry etching or wet etching using the resist pattern as a mask. Thereafter, after removing the resist, washing or the like is performed to form a light-shielding pattern of a desired shape on the transparent quartz substrate. The same applies to the case of a darkening film.
[0004]
In recent years, competition for the development of LSIs has progressed, and the need for accelerating device debugging has necessitated a large number of photomasks, and the necessity for producing photomasks at low cost has increased. Further, the necessity of manufacturing a photomask in a short manufacturing period (TAT) has also increased.
In particular, the demand is increasing because of the demand for small-quantity and various kinds of system LSIs.
[0005]
A so-called resist mask method in which a light-shielding film is formed of a resist film has been disclosed for the purpose of simplifying the manufacturing process of a photomask and reducing costs (for example, see Patent Document 1). This method utilizes the property that ordinary electron beam-sensitive resists or light-sensitive resists shield vacuum ultraviolet light (VUV light) having a wavelength of about 200 nm or less. According to this method, the step of etching the light-shielding film and the step of removing the resist become unnecessary, so that the cost of the photomask can be reduced and the TAT can be reduced by simplifying the steps.
This method can be used not only for VUV light but also for lithography using DUV light, for example, a KrF excimer laser having a wavelength of 248 nm, by using a light-absorbing resist as a mask material.
[0006]
[Patent Document 1]
JP-A-5-2189307
[Problems to be solved by the invention]
In the above-described resist mask, there is a problem that the resist used as the mask material strongly absorbs the exposure light, so that if the resist remains as a scum on the glass surface, a transfer defect occurs.
[0008]
FIG. 4 shows a typical electron beam (EB) sensitive resist resin. As can be seen from FIG. 5 which shows the spectral absorption characteristics of this resin, the absorption coefficient of ArF excimer laser light having a wavelength of 193 nm is 20 / μm or more. Exhibit extremely strong light absorption. For this reason, especially in ArF excimer lithography using light having a wavelength of 193 nm, if a resist having a thickness of 5 nm remains between pattern lines, pattern dimension abnormality occurs. Inspection of a residue having a thickness of 5 nm is difficult in ordinary inspection. Moreover, the asher used as a scum removal method with a normal Cr mask or the like performs vacuum evacuation and the like, so particles are easily generated, and there is a problem that it is difficult to use a resist mask which cannot perform hard cleaning such as brush cleaning. . For this reason, the resist mask is originally advantageous in terms of cost and TAT, but there is a problem that the yield is reduced due to the problem of scum and the above advantages cannot be enjoyed.
[0009]
[Means for Solving the Problems]
In order to solve the problem of the resist mask, after forming a resist pattern on a transparent substrate, VUV light is irradiated in an environment where oxygen exists near the resist pattern. This method solves the above problem. Further, when VUV light is irradiated from the glass surface side opposite to the surface on which the resist pattern is formed, further improvement in cleaning efficiency and reduction in pattern dimensional change can be obtained.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Before describing the present invention in detail, the meanings of terms in the present application will be described as follows.
1. The terms “darkening area”, “darkening film”, and “darkening pattern” indicate that the exposure light applied to the area has an optical characteristic of transmitting less than 25%. Generally, less than 15% is used. The terms “light-shielding region”, “light-shielding film”, and “light-shielding pattern” indicate that the region has an optical property of transmitting less than 2% of exposure light applied to the region. Generally, less than 1% is used. On the other hand, the terms “transparent” and “transparent film” indicate that they have an optical property of transmitting 60% or more of the exposure light applied to the area. Generally, 90% or more is used.
2. “Photoresist pattern” refers to a film pattern obtained by patterning a photosensitive organic film by a photolithographic technique.
Note that this pattern includes a simple resist film having no opening in the relevant portion. The photosensitive beam source includes, in addition to light, an electron beam, an X-ray, and a charged particle beam. Photosensitive organic films include those containing inorganic substances such as Si, in addition to those composed only of organic substances.
[0011]
(Embodiment 1)
FIG. 1 shows a photomask manufacturing process of the present invention. First, as shown in FIG. 1A, an electron beam sensitive resist 11 is applied and formed on a glass substrate 10. The electron beam sensitive resist used here is a phenol resin-based chemically amplified resist shown in FIG. 4, but is not limited thereto. Any photoresist that has sensitivity to a drawing line described below and has a dimming property with respect to exposure light when performing lithography may be used.
Here, since a photomask used for ArF lithography is manufactured, as shown in FIG. 5, this novolak resin-based chemically amplified resist has obtained sufficient dimming property with respect to ArF excimer laser light having a wavelength of 193 nm. In the case of manufacturing a photomask for KrF lithography, a photoresist capable of sufficiently absorbing a KrF excimer laser beam having a wavelength of 248 nm by mixing a light absorbing agent such as anthracenemethanol or binding to a resin may be used.
[0012]
Next, a desired circuit pattern is drawn by the electron beam 13 as shown in FIG. Although the case where an electron beam is used as a drawing method is described here, a laser having a wavelength of 365 nm or 248 nm may be used instead of the electron beam.
However, in that case, it is necessary to use a photoresist responsive to the laser beam as the resist 11. Thereafter, development was performed to form a resist pattern 14 on the quartz glass substrate 10 as shown in FIG. At this time, resist scum (foreign matter) was formed on the glass substrate (15) and on the resist (16). The film thickness was not constant because it was indefinite, but it was a scum having a film thickness of 10 nm on average.
Here, since the scum 16 on the resist pattern 14 is originally a black defect on the place to be shielded from light, there is no adverse effect on the pattern transfer, but the scum 15 on the glass becomes a black defect. FIG. 6 shows the effect of scum on transfer. This is a case where a 130 nm line and space pattern is formed using ArF lithography with a lens numerical aperture NA of 0.7. 4 shows an optical image when the focus is changed. The set value of the focus is 0, 0.1, 0.2, 0.25 μm. As the defocus increases, the amplitude of the optical image decreases.
[0013]
This is an optical image in the case where a slight amount of resist remains only between the patterns indicated by G in FIG. FIG. 6B shows the case where the scum is absent, FIG. 6C shows the case where the resist has a thickness of 2.5 nm, and FIG. 6D shows the case where the resist has a thickness of 5 nm. Even a small amount of resist remains between the lines, causing a sharp decrease in light intensity, causing dimensional changes and a source of poor resolution.
[0014]
Next, as shown in FIG. 1D, the surface on which the resist pattern was formed was irradiated with VUV light 18 to remove scum. At this time, at least the atmosphere on the surface side was an environment in which oxygen was present. Here, the atmosphere was used, but if the oxygen concentration is further increased, the rate of scum removal is increased, and a TAT shortening effect is obtained. As the VUV light, light having a wavelength of 200 nm or less can be used. However, when a Xe ₂ excimer lamp light having a peak wavelength of 172 nm is used, the ozone generation efficiency having an ashing effect is high, and sufficient for breaking the chemical bond of the resist. Since it has photon energy, scum can be removed efficiently. Furthermore, since the excimer lamp is continuous light, it is easy to handle and inexpensive, and the lamp is easy to maintain. In addition to the Xe ₂ excimer lamp light, a Kr ₂ excimer lamp light having a peak wavelength of 146 nm is also effective. Since the Kr ₂ excimer lamp light has a higher photon energy than that of the Xe ₂ excimer lamp, it is effective for removing scum of a photoresist having a high benzene ring content and a strong bond. Since the Xe ₂ excimer lamp absorbs less light due to oxygen than the Kr ₂ excimer lamp light, the light attenuation in an atmosphere environment is small and the scum can be efficiently removed from a normal resist.
[0015]
Since scum removal processing can be performed in an air environment, adhesion of particles due to vacuum evacuation such as asher is small, and sample replacement is easy.
However, since ozone is generated, it is necessary to exhaust the gas or to treat it in, for example, a box so that ozone does not leak.
[0016]
(Embodiment 2)
FIG. 2 shows an outline of the scum removing method used in the second embodiment. The photomask 1 including the quartz glass substrate 10 and the resist pattern 14 manufactured in the same steps as in the first embodiment up to the step shown in FIG. 1C is placed on the scum removing device 2 as shown in FIG. The scum removing device 2 includes a VUV lamp 21, a housing 20, and a window member 24 made of quartz glass. The interior of the scum removal device 23 surrounded by the housing 20 and the window material 24 was filled with an inert gas so that the VUV lamp light was not attenuated.
Here, it is desirable to reduce oxygen and water vapor having a high absorption rate of VUV light as much as possible. Here, nitrogen is used as the inert gas, but other gases having low VUV light absorption may be used. A vacuum may be used, but if the vacuum is applied, the cooling efficiency of the VUV lamp decreases. In this case, it is necessary to take measures against the heat of the lamp, for example, by cooling with water. The quartz glass substrate 10 was placed in contact with the window material 24 so that the VUV lamp light 22 was irradiated through the window material 24 and the quartz glass substrate 10. The outside of the scum removing device and the vicinity 25 of the resist pattern were in an environment where oxygen was present. Although it may be in an atmospheric environment, harmful ozone is generated by irradiating oxygen. Therefore, it is desirable to enclose this system with an enclosure 26 and purge the oxygen inlet to increase the oxygen concentration. VUV light was supplied to oxygen from oxygen 27 and exhausted from an exhaust port 28.
Here, a Xe ₂ excimer lamp was used as the VUV lamp.
[0017]
FIG. 3 shows the light intensity distribution of the VUV irradiation light at this time. A, B, C and D in the figure correspond to the positions of A, B, C and D shown in FIG. Since the point A located in the lamp box is filled with the inert gas, the attenuation of the light intensity is very small. From the point B to the point C, the attenuation of the Xe ₂ excimer lamp light having a peak wavelength of 172 nm is small because the light is in the quartz glass. At point D outside the glass surface, the light intensity is rapidly attenuated due to the presence of a large amount of oxygen. Although the light intensity is abruptly attenuated, the scum that becomes a transfer defect is scum attached to the glass substrate, and the intensity is strong and the scum can be efficiently removed. Sufficient VUV light is intensively applied to the scum attached to the glass in an environment having a sufficiently high oxygen concentration, so that a large amount of ozone and VUV light are concentrated on the glass surface, and the scum removal efficiency is high. Since the VUV light becomes weaker toward the upper surface of the resist pattern, deformation and deterioration of the resist pattern due to VUV light irradiation are small. The Xe ₂ excimer lamp light is transmitted through the fused silica glass, has high ozone generation efficiency, and has high photon energy, so that it is suitable for removing scum. In addition, Xe ₂ excimer lamp light is easy to handle as continuous light, and the cost is low.
[0018]
The VUV light is not limited to the Xe ₂ excimer lamp light, but needs to be light having a wavelength that transmits through the mask substrate 10 and the window material 24. The shorter the wavelength, the higher the photon energy and the easier it is to decompose organic matter, but the light must be of a wavelength that transmits these window materials. For example, a Kr ₂ excimer lamp having a shorter peak wavelength of 146 nm is not suitable because it is absorbed by a quartz glass substrate.
[0019]
【The invention's effect】
According to the present application, a resist mask without scum can be easily manufactured. Since it is scumless, the occurrence of transfer defects is reduced. In addition, since scum is not required, scum inspection can be omitted, and from this viewpoint, cost can be reduced and manufacturing TAT can be improved. That is, it usually takes eight hours to inspect a slight scum, but there is also an effect of reducing the time.
[Brief description of the drawings]
FIG. 1 is a process diagram showing a photomask manufacturing process of the present invention.
FIG. 2 is an explanatory diagram showing a second manufacturing process of the photomask of the present invention.
FIG. 3 is a characteristic diagram showing light intensity characteristics of VUV irradiation light.
FIG. 4 is a molecular formula showing a material structure of a typical electron beam sensitive resist.
FIG. 5 is a characteristic diagram showing a spectral absorption characteristic of a typical electron beam sensitive resist.
FIG. 6 is a characteristic diagram showing an optical image distribution of pattern transfer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photomask, 2 ... Scum removal apparatus, 10 ... Quartz glass, 11 ... Resist, 13 ... Electron beam, 14 ... Resist pattern, 15 ... Scum, 16 ... Scum, 17 ... Oxygen presence atmosphere, 18 ... VUV light, 20 ... Housing, 21 ... VUV lamp, 22 ... VUV light, 23 ... Inert gas atmosphere, 24 ... Window material (glass), 25 ... Oxygen present atmosphere, 26 ... Box, 27 ... Oxygen introduction port, 28 ... Exhaust port.

Claims (7)

In a method for manufacturing a photomask using a resist pattern as a light-shielding portion,
Exposing one main surface side of the transparent substrate on which the resist pattern is formed to an atmosphere containing oxygen,
A method for manufacturing a photomask, comprising irradiating light from the other main surface side of the transparent substrate so as to transmit through the transparent substrate. The method according to claim 1, wherein the light irradiation uses a vacuum ultraviolet light source provided in a gas that is cut off from the atmosphere containing oxygen and has a low absorptivity of the vacuum ultraviolet light. Photomask manufacturing method. The method according to claim 1, wherein the light is vacuum ultraviolet light. The method according to claim 3, wherein an Xe ₂ excimer lamp is used for the irradiation with the vacuum ultraviolet light. 2. The method according to claim 1, wherein the atmosphere is air. 3. The method according to claim 2, wherein nitrogen is used as the gas having a low vacuum ultraviolet light absorption rate. In a method for manufacturing a photomask using a resist pattern as a light-shielding portion,
A method for manufacturing a photomask, comprising irradiating VUV light in an environment where oxygen is present after forming the resist pattern on a transparent substrate.

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