Semiconductor device manufacturing: process – Masking
Reexamination Certificate
2002-01-15
2004-03-09
Whitehead, Jr., Carl (Department: 2813)
Semiconductor device manufacturing: process
Masking
C430S311000
Reexamination Certificate
active
06703328
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for manufacturing a semiconductor device and, more particularly, to a technique which is effectively applied to a lithography technique in the steps of manufacturing a semiconductor device.
BACKGROUND OF THE INVENTION
In manufacturing semiconductor devices including an LSI (LARGE SCALE INTEGRATED CIRCUIT) or the like, a lithography technique is used as a method of forming a micropattern on a semiconductor wafer. As this lithography technique, a so-called optical projection exposure method in which patterns formed on photo masks are repeatedly transferred onto a semiconductor wafer through a reduction projection optical system is the mainstream. A basic configuration of an aligner is disclosed in, e.g., Japanese Patent Application Laid-Open No. 2000-91192.
A resolution R on the semiconductor wafer in the projection exposure method is generally expressed by R=k×&lgr;/NA. In this equation, reference symbol k denotes a constant depending on a resist material or a process, reference symbol &lgr; denotes the wavelength of illumination light, and reference symbol NA is the numerical aperture of a projection exposure lens. As is apparent from this relational equation, with an advance of micropatterning, a projection exposure technique source having a shorter wavelength is necessary. At the present, an LSI is manufactured by a projection aligner using a g-ray (&lgr;=438 nm), an i-ray (&lgr;=365 nm) of a mercury lamp, or a KrF excimer laser (&lgr;=248 nm) as an illumination light source. In order to realize further micropatterning, the employment of an ArF excimer laser (&lgr;=193 nm) or an F
2
excimer laser (&lgr;=157 nm) having a shorter wavelength has been examined. However, in general, the costs and maintenance cost of the aligner and the processes increase as the wavelength becomes short. For this reason, a plurality of exposure light sources are combined to each other to manufacture a semiconductor device. As a typical example, a semiconductor device is manufactured in such a manner that an i-ray and a KrF excimer laser are selectively used depending on the steps of manufacturing the semiconductor device.
A general photo mask has a structure in which a thin film made of chromium or the like is formed as a shield film on a quartz glass plate which can transmit exposure light. Such a photo mask is manufactured in the following manner. That is, a resist is coated on a quartz glass plate obtained by forming a chromium film on a quartz plate, the resultant quartz glass plate is exposed in the shape of a prepared desired pattern and developed to form a resist pattern, and chromium is etched by using the resist pattern as an etching mask.
On the other hand, for example, in Japanese Patent Application Laid-Open No. 5-289307, a photo mask in which a resist is used as a shield film in place of a chromium film. This is a photo mask using the fact that the photoresist has a low transparency with respect to short-wavelength light such as ArF light.
Incidentally, a machining precision of a mask pattern on a photo mask has become severer with the advance of micropatterning in manufacturing a semiconductor device. At the same time, the problem of an increase in cost for manufacturing a photo mask with an increase in the amount of pattern data has become conspicuous. In general, since 20 to 40 photo masks are used to manufacture one type of semiconductor device, the increase in cost for manufacturing a photo mask is a considerably serious problem. In addition, in a system LSI, it is demanded to rapidly supply customized products in line with the demands of customers. In order to accede to the demand, necessity to prepare a photo mask having a desired pattern in a short TAT has increased. Furthermore, since production cycles of not only LSIs but also other semiconductor devices become short, a TAT for developing LSIs is strongly required to be short. Also in this sense, necessity of preparing a photo mask having a desired pattern for a short TAT has been increased. In particular, a debug rate of a wiring layer is high in a system LSI. For this reason, to supply the mask of this layer in a short period of time at low cost is useful to develop an LSI in a short period of time and to reduce the costs.
A photo mask disclosed in Japanese Patent Application Laid-Open No. 5-289307 can be manufactured without the step of etching chromium. For this reason, the effect of a reduction in mask cost can be expected. In addition, since the manufacturing steps do not include the process of etching chromium, it is also advantageous for assuring the precision of pattern dimensions. Also, since the photo mask can be manufactured without the step of etching chromium, a TAT for manufacturing a photo mask is short.
However, the inventors of this invention found that a photo mask technique using the resist as a shield material had the following problems.
Specifically, in Japanese Patent Application Laid-Open No. 5-289307, a technique in which a pattern is transferred onto a semiconductor wafer by using a photo mask having a shield pattern constituted of a resist film is disclosed. However, any pattern monitoring technique on a photo mask such as an alignment monitoring technique for a photo mask or a discriminator monitoring technique is not disclosed, and a description which suggests the pattern monitoring technique is not made therein.
When a semiconductor device is manufactured as described above, a large number of photo masks usually 20 to 40 photo masks are required, and alignment must be performed. Therefore, alignment mark monitoring for aligning patterns formed of the photo masks is required. Since a large number of photo masks are used, mask management using discrimination codes of the photo masks such as the names, lot numbers, or bar codes of the photo masks is required. In general, light having a wavelength longer than 240 nm such as halogen light, red diode light, or a helium-neon (He—Ne) laser beam is used to monitor photo mask alignment marks and discriminators. However, according to the examination result obtained by the inventors of this invention, as shown in
FIG. 14
, it was found out that a general resist material was unable to obtain sufficient shield properties for light having a wavelength longer than 230 nm and did not sufficiently function as a shield material. For this reason, when alignment marks or discriminators are formed of resists, shielding properties and light-absorbing properties are so insufficient that discrimination, recognition, or monitoring is made difficult.
Specifically, in the technique in the gazette which discloses a photo mask using the resist as a shield material, alignment mark monitoring and discriminator monitoring on a photo mask are not considered at all. For this reason, patterns obtained by different photo masks are offset from each other, and it is impossible to discriminate the photo masks, resulting that the photo masks can not be easily managed. No consideration is given to these problems, in particular, to the problem of the mask discrimination, in the gazette which discloses the photo mask using the resist as a shield material.
FIG. 14
shows an OD value of the resist obtained when using a phenol resin as a base resin. The OD value is a value expressed by −LOG 10 (I OUT/I IN) when incident light and transmitted light are represented by I IN and I OUT, respectively. Since a transmittance T% is expressed by 100×I OUT/I IN, OD is expressed by −LOG (T/100) is satisfied. As the OD value increases, the transmittance of light decreases. In this case, for the sake of descriptive convenience, the film thickness of the resist is set to be 1 &mgr;m. When the resist is used as the photo mask, the film thickness is generally set to be 0.5 &mgr;m or less so as to prevent the film thickness of the resist from adversely affecting transfer characteristics. When the film thickness is 0.5 &mgr;m, the OD value is ½. In a resist c
Hattori Takashi
Tanaka Toshihiko
Dolan Jennifer M
Jr. Carl Whitehead
Miles & Stockbridge P.C.
Renesas Technology Corporation
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