Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2002-02-12
2004-03-09
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06703171
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photomask, a manufacturing method thereof, a patterning method, and a semiconductor device manufacturing method, and particularly a technique effectively applied to the photolithography using ultraviolet radiation, far ultraviolet radiation, vacuum ultraviolet radiation, or the like as a light source.
To manufacture a semiconductor integrated circuit device (LSI: Large Scale Integrated circuit), a lithography technique is used as a method for forming a micropattern on a semiconductor wafer. In the case of the lithography technique, the so-called optical projective exposure method is mainly used which repeatedly transfers a pattern formed on a photomask onto, a semiconductor wafer through a reduction projection optics. A basic configuration of an exposure system is disclosed in Japanese Patent Laid-Open No. 2000-91192.
A resolution R on a semiconductor wafer in the projective exposure method is generally shown by R=k×&lgr;/NA, where k denotes a constant depending on a resist material or a process, &lgr; denotes a wavelength of illumination light, NA denotes a numerical aperture of a projective exposure lens. As seen by the above relational equation, a projective exposure technique using a light source with a shorter wavelength is required as patterns are made more fine. At present, an LSI is manufactured by a projective exposure system using g-line (&lgr;=438 nm) or i-line (&lgr;=365 nm) of a mercury lamp, or a KrF excimer laser beam (&lgr;=248 nm) as a light source. For the purpose of achieving a finer pattern, it is studied to use an ArF excimer laser beam (&lgr;=193 nm) or F
2
excimer laser beam (&lgr;=157 nm) having a shorter wavelength.
A normal photomask has a structure in which a thin film made of chromium or the like is formed as a shading film on a quartz glass transparent for exposure light. This photomask is manufactured by applying a resist onto a substrate in which a chromium film is attached to a quartz plate, exposing it in the form of a desired pattern prepared in advance, further developing it to form a resist pattern, and etching the chromium by using the resist pattern. In the case of this normal photomask, because steps of etching a chromium film and of peeling off the resist are required, it takes a lot of time to manufacture the photomask and the cost thereof increases.
Meanwhile, for example, Japanese Patent Laid-Open No. 5-289307 discloses a photomask using not chromium but a photoresist as a shading film. This is a mask using the fact that a photoresist has a shading characteristic relative to short wavelength rays such as ArF rays or the like. Because this technique makes it possible to fabricate a photomask without including a step of etching chromium, an effect of reducing the mask cost can be expected. Moreover, because there is no step of etching chromium, this technique has an advantage in that a pattern dimension accuracy can be ensured.
SUMMARY OF THE INVENTION
However, the present inventors have found the following problems in a photomask technique (hereafter referred to as a resist shade mask technique) using a photoresist as the above shading film.
That is, as shown in
FIG. 9
, a normal resist material has such a problem that it is impossible to obtain a sufficient shading characteristic against rays having a wavelength larger than 230 nm and therefore to completely function as a shading material. That is, the above resist shade mask technique has such a problem that it is impossible to be applied to KrF excimer laser exposure having a wavelength of 248 nm or i-line exposure having a wavelength of 365 nm.
FIG. 9
shows OD values in the case of a resist using phenolic resin as a base resin, where the OD values mean values represented by −log
10
(Iout/Iin) when it is assumed that incident light is Iin and transmitted light is Iout. Moreover, a transmittance T% is represented by 100×Iout/Iin, OD=−log(T/100). As an OD value increases, the transmittance of light decreases. A resist containing a normal benzene ring has a small OD value in the case of the light having a wavelength larger than 230 nm, similarly to FIG.
9
. That is, a sufficient shading characteristic cannot be obtained from the resist because the resist has a high transmittance.
As a finer pattern is achieved, such problems have become more important because the working accuracy of a mask pattern becomes more stringent and the photomask manufacturing cost is increased due to increase of amounts of pattern data. In general, to manufacture one kind of semiconductor integrated circuit device, increase in the photomask manufacturing cost becomes a very large problem because about 20 to 40 photomasks are used, for example.
Under the above situation, however, it is necessary to make a circuit pattern more fine at present in order to improve a semiconductor device in integration degree and in operation speed, and thereby technical development is progressed so as to shorten the wavelength of exposure light. However, if the wavelength of exposure light is shortened, then a material of the lens is a rare and expensive material such as CaF
2
and illumination damage of an optical member increases, and thereby component life is shortened. Therefore, short-wavelength exposure light becomes expensive.
Moreover, because a KrF excimer laser beam or an i-line is normally used to manufacture a volume zone for a semiconductor device and the like, an adaptive wavelength in the above resist shade mask technique comes to an important problem. According to a study made by the present inventors, it has been found that when the above resist shade mask technique is used without a sufficient consideration, use of the ArF excimer laser exposure is required everywhere, and even if a photomask becomes inexpensive, the total manufacturing cost rather increases. Therefore, to reduce the cost, it is preferable to apply short wavelength exposure only to steps having such merits that performing fineness exceeds rise in cost and to apply the exposure at a comparatively low cost, to other steps.
Moreover, in the period of system LSIs, the requirement for developing and manufacturing small quantity of various types of LSIs in a short period has been raised. To manufacture LSIs as described above, 20 to 40 photomasks are used. Therefore, a photomask-manufacturing TAT (Turn Around Time) is the motive power of the competition power for developing LSIs, Particularly in the case of a system LSI, because the debugging rate of a wiring layer is high, supplying the photomask of this layer in a short time at a low cost is useful for short-term development of and cost reduction in LSIs.
Moreover, in the case of using a resist as a shade band similarly to the above resist shade mask technique, an ArF excimer laser beam having a comparatively high energy is absorbed by an organic resist material. The absorbed light energy excites organic molecules. Some of the light energy is emitted to the outside as fluorescence and phosphorescence and most of the light energy is emitted to the outside as heat energy. At this time, however, some of the energy may cut a chemical bond between organic molecules or cause reactions with other molecules. As a result, there arise such problems that a resist material serving as a shade band deteriorates in accordance with illumination of an ArF excimer laser beam, and finally loses the function of a shade band.
An object of the present invention is to solve the above problems and to provide a technique capable of developing a small quantity of and various kinds of semiconductor devices in a short time and realizing a photomask most suitable to manufacture the devices at a low cost.
An object of the present invention is to provide a technique capable of realizing a photomask having a sufficient shading characteristic even against exposure light having a long wavelength.
An object of the present invention is to provide a technique capable of shortening time required fo
Gotoh Yasuko
Hattori Takashi
Satoh Hidetoshi
Shiraishi Hiroshi
Tanaka Toshihiko
Mattingly Stanger & Malur, P.C.
Rosasco S.
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