Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2001-05-30
2003-05-06
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S067000, C356S400000
Reexamination Certificate
active
06559924
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an alignment method, alignment apparatus, and profiler suitable for alignment and the like in a semiconductor manufacturing exposure apparatus between a microelectronic circuit pattern, e.g., an IC, LSI, or VLSI, formed on a reticle surface and a wafer, an exposure apparatus, semiconductor device manufacturing method, and semiconductor manufacturing factory using the alignment method, alignment apparatus, and profiler, and an exposure apparatus maintenance method.
Most exposure apparatuses currently used are called steppers or scanners. In this specification, the steppers and scanners are not discriminated, but are also described as “exposure apparatuses” for descriptive convenience unless they need to be specifically discriminated.
BACKGROUND OF THE INVENTION
As integrated circuits shrink in feature size and increase in integration degree, a semiconductor manufacturing projection exposure apparatus must be able to project and expose a circuit pattern on a reticle surface onto a wafer surface with a higher resolution. For this purpose, in consideration of the fact that the projecting resolution of a circuit pattern depends on the numerical aperture (NA) of a projection optical unit and the exposure wavelength, studies have been made on an exposure method in which the exposure wavelength is fixed and the NA of the projection optical unit is increased, and an exposure method in which the exposure wavelength is decreased, an i-line is preferred over a g-line and an excimer laser oscillation wavelength is preferred over the i-line wavelength, and 248- and 193-nm wavelengths, and moreover 157-nm wavelength are used as the laser oscillation wavelength. A projection exposure apparatus using a 193-nm exposure wavelength is already commercially available.
As the circuit patterns shrink in feature size, a demand for high-precision alignment between a wafer and a reticle on which an electronic circuit pattern is formed has also arisen. When aligning a reticle and wafer with each other, light (exposure light) that photosensitizes a resist applied on the wafer surface and light (to be referred to as “non-exposure light” hereinafter) that does not photo-sensitize the resist, e.g., light with a wavelength of 633-nm, which is the oscillation wavelength of an He—Ne laser, are often used. Conventionally, the alignment wavelength practically employed is mostly that of the non-exposure light, because it is not easily influenced by a semiconductor manufacturing process. More specifically, since a resist to be photosensitized by exposure light is absorbed by the exposure light, the exposure light is transmitted through the resist with a low transmittance, and sometimes the exposure light is not transmitted at all. When the exposure light is used for alignment, while it passes through the resist, is reflected by an alignment mark, and passes through the resist again, it sometimes becomes very weak to be used as an alignment signal. When the exposure light interferes with light reflected by the resist surface, interference fringes are formed on the detected image, leading to degradation in precision. This is because the light is reflected by the resist surface with a reflectance of approximately 4%, and light transmitted through the resist twice also has an intensity of the same level as this, forming interference fringes with a high visibility (brightness contrast).
In view of this, in Japanese Patent Laid-Open Nos. 63-32303, 2-130908, and the like, the present applicant has also proposed an alignment apparatus using non-exposure light that is transmitted through a resist with a high transmittance. Such an apparatus is already commercially available so its effect has been confirmed. This method is a so-called non-exposure light TTL Offaxis method, in which chromatic aberration in non-exposure light of a projection optical unit for transferring and projecting a reticle pattern onto a wafer is corrected in the wavelength width as an alignment optical unit. As described in the above references, most of the currently employed alignment methods are a method of forming an optical image of an alignment mark on a wafer on an image sensing element such as a CCD camera, and image-processing an electrical signal from the image sensing element, thereby detecting the wafer position. With this method, light is not attenuated even after it is transmitted through the resist twice. Thus, even if monochromatic light is used as the non-exposure light, the interference fringes formed by interference with the light reflected by the resist surface have a low visibility (brightness contrast). In the references, since monochromatic light is not used but light with a correction wavelength width of, e.g., 70 nm or more in half width, is used, the interference fringes are suppressed to a level that does not pose any problem.
As a method of eliminating a process error called WIS (Wafer Induced Shift) as one of alignment errors, the present applicant has proposed a system called offset analyzer. As an example of WIS, the shape of the alignment mark and the shape of a resist on the alignment mark become asymmetric due to a process error. In a planarizing process in a modern metal CMP (Chemical Mechanical Polishing) step and the like, the structure of the alignment mark often becomes asymmetric. This produces a rotation error as shown in
FIG. 5
or a magnification error as shown in
FIG. 6
in global alignment, leading to a serious problem as a decrease in precision.
In order to eliminate degradation in precision which is caused when an alignment mark shape becomes asymmetric due to the process, in the offset analyzer, before a wafer position necessary for alignment of a wafer and reticle relative to each other is to be performed with a non-exposure light TTL offaxis alignment detection system with a highly stable base line, the surface shapes of a plurality of identical marks on the wafer which are used for alignment are measured, outside an exposure apparatus with an alignment apparatus, with a profiler (stereoscopic measurement unit) such as an AFM (Atomic Force Microscope) before and after resist coating. An offset, with which the three-dimensional relative positional relationship between the mark shapes before resist coating and those after resist coating matches with a signal from the detection system of the alignment apparatus, is calculated. Then, the wafer and reticle are aligned with each other by using the calculated offset. In this manner, a system for measuring the surface shapes of the marks before and after resist coating outside an alignment apparatus (exposure apparatus) with a profiler such as AFM, and calculating an offset with which the three-dimensional relative positional relationship between the respective mark shapes matches with a signal from the detection system of the alignment apparatus, is called an offset analyzer.
FIG. 3
shows data obtained when actual alignment marks are measured with the AFM. These data are indicated as signals displayed to correspond to respective alignment marks AM in FIG.
3
. These data are those obtained after resist coating. The structures of the alignment marks AM are those called metal CMP as shown in FIG.
4
. As is seen from
FIG. 3
, regarding the surface shapes of the alignment marks AM at shots on the left, right, and center of the wafer W, although the surface shape of the alignment mark AM of the shot at the center is symmetrical, the surface shape of each of the left and right shots is asymmetric with the asymmetry being reversed between the left and right shots. This is WIS. Even when such WIS occurs, with an offset analyzer, a highly stable alignment method can be implemented at high precision with less base line fluctuation.
A profiler used in the offset analyzer may be an AFM, a probe type profiler, or an optical non-contact type profiler. Any profiler poses no problem as far as it satisfies the specifications.
Since the resist is transparent to a wavelength used by the optical profiler, it is difficult
Ina Hideki
Matsumoto Takahiro
Sentoku Koichi
Adams Russell
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Kim Peter B.
LandOfFree
Alignment method, alignment apparatus, profiler, exposure... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Alignment method, alignment apparatus, profiler, exposure..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Alignment method, alignment apparatus, profiler, exposure... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3028893