Alignment system and alignment method in exposure apparatus

Details Alignment system and alignment method in exposure apparatus Alignment system and alignment method in exposure apparatus

2001-05-30

2002-12-10

Adams, Russell (Department: 2851)

Photocopying

Projection printing and copying cameras

Step and repeat

C355S055000, C355S067000, C355S072000, C355S075000, C355S077000, C356S399000, C356S400000, C356S401000, C356S389000, C356S389000, C250S548000, C250S492200, C250S492220, C430S005000, C430S022000

Reexamination Certificate

active

06493065

ABSTRACT:

FIELD OF THE INVENTION AND RELATED ART
This invention relates generally to an alignment system and an alignment method. More particularly, the invention concerns an alignment system and an alignment method for use in a semiconductor manufacturing exposure apparatus, for performing a relative positioning (alignment) of a fine electronic circuit pattern (such as an IC, an LSI or a VLSI) formed on the surface of a reticle (first object) and a wafer (second object).
Currently used exposure apparatuses are mainly those called a stepper and those called a scanner. In this specification, however, for convenience, all of them are simply referred to as “exposure apparatus”, except in cases where they should be distinguished.
In another aspect, the invention is directed to a method for optimum use of an exposure apparatus, which is based on data communication between a place where the exposure apparatus is present (such as a semiconductor factory) and a place remote therefrom (e.g., a vendor such as a manufacturing apparatus maker or a consultation company), through an internet.
In order to meet further decreases in size and further increases in density of an integrated circuit, projection exposure apparatuses for manufacture of semiconductor devices are required to have an ability of projecting a circuit pattern of a reticle and printing it upon the surface of a wafer, with a high resolving power. Since the projection resolution of a circuit pattern depends on the numerical aperture (NA) of a projection optical system and the exposure wavelength (the wavelength used for the exposure), various exposure methods have been attempted such as, for example, an exposure method in which the NA of a projection optical system is enlarged while the exposure wavelength is fixed, and an exposure method in which the exposure wavelength is shortened such as, for example, from g-line to i-line, from i-line to an excimer laser emission wavelength, or, even in the excimer laser emission wavelength, to 248 nm, 193 nm and to 157 nm. As regards the exposure wavelength of 193 nm, commercial products are already available-
On the other hand, due to decreases in size of circuit patterns, there is a requirement for high precision alignment of a reticle (having an electronic circuit pattern) and a wafer. Alignment errors may be generally categorized into an apparatus factor and a process factor. Recently, errors attributable to any apparatus factor are well corrected, as much as possible. As regards errors attributable to any process factor, called WIS (Wafer Induced Shift), an alignment detecting system which can meet this has been proposed by the same assignee of the subject application, as an offset analyzer system.
First, as an example of WIS, due to a process error factor, the shape of an alignment mark or the shape of a resist on that mark becomes asymmetric. During a flattening process in a recently introduced metal CMP (Chemical Mechanical Polishing) process, for example, the structure of an alignment mark frequently becomes asymmetric. This causes, in a global alignment process, a rotational error (
FIG. 1A
) or a magnification error (
FIG. 1B
) which directly leads to a deteriorated precision. Here,
FIG. 1A
illustrates a case where rotational errors are produced in a global alignment process.
FIG. 1B
shows a case where magnification errors are produced in a global alignment process. Straight lines in these drawings depict the direction and amount of the errors produced.
In an offset analyzer such as mentioned above, for relative alignment of a wafer and a reticle, the position of the wafer is detected by use of an alignment system of a non-exposure light TTL off-axis system having a stable baseline. Prior to this detection, as regards plural but the same marks formed on the wafer for use in the alignment process, the surface shape thereof before and after resist application is measured (at calibration, for example), outside the alignment system (exposure apparatus) and by use of a profiler (solid shape measuring device) such as an AFM (Atomic Force Microscope), for example. Then, an offset, when the three-dimensional relative positional relationship between the resist and the wafer mark is harmonized with a signal of a detecting system of the alignment system, is calculated. The alignment operation is made by using the calculated value. Through the procedure described above, degradation of precision due to the produced symmetry in the alignment mark shape can be avoided.
This is the system called an offset analyzer, in which, outside the alignment system (exposure apparatus), the surface shape is measured before and after resist application, by using a profiler such as an AFM, and in which an offset, as the three-dimensional relative positional relationship between the resist and the wafer mark is harmonized with the signal of a detecting system of the alignment system, is calculated.
FIG. 1C
shows the results of measurement of actual alignment marks, made by use of an AFM. Signals are those after resist application. The structure of the alignment marks is such as called a metal CMP, as shown in FIG.
1
D.
FIG. 1D
illustrates the structure of an alignment mark, called a metal CMP. It is seen from
FIG. 1C
that, as regards the shape of a resist upon alignment marks at left and right side shots as well as an alignment mark at a central shot, the surface shape at the central shot is symmetric whereas the surface shape at the left and right side shots is asymmetric. Also, it is seen that the asymmetry is inverted, between the left and right side shots. This is what called WIS. The WIS can be met by use of an offset analyzer, and high precision and a stable alignment method with a small baseline change can be accomplished.
Referring to
FIGS. 1E and 1F
, an already proposed offset analyzer will be explained.
FIG. 1E
is a schematic view for explaining the flow of a wafer and information where an offset analyzer is provided.
FIG. 1F
shows the structure of the offset analyzer.
Here, as described hereinbefore, a stepper, a scanner, an aligner or the like is called an exposure apparatus. An alignment detecting system is called an alignment scope. A system in which the surface shape is measured before and after resist application, outside an alignment system (exposure apparatus) and by use of a profiler and in which an offset as the three-dimensional relative positional relationship between the resist and the wafer is harmonized with the signal of a detection system of the alignment system, is called an offset analyzer.
Referring to
FIG. 1E
, the flow of a wafer and information will be described first.
In this example, as shown at step
2
in
FIG. 1E
, a wafer
31
is conveyed to an offset analyzer
32
before a resist is applied thereto. The shape (surface shape) of an alignment mark on the wafer
31
is measured by using a profiler.
Then, at step
3
in
FIG. 1E
, the wafer
31
is conveyed to a coater
33
for resist application, and a resist is applied to the wafer.
Then, at step
4
in
FIG. 1E
, the wafer
31
is conveyed again to the offset analyzer
32
, and the surface shape of the resist on the alignment mark is measured by using the profiler.
Subsequently, a signal for the alignment mark on the wafer
31
is detected by use of a detecting system installed in the offset analyzer
32
and being similar to an alignment scope of the exposure apparatus.
Then, by use of a signal simulator of the offset analyzer
32
, an offset is calculated. For this offset calculation, a three-dimensional relative positional relationship between the resist and the wafer mark should be harmonized. Specifically, while changing the three-dimensional relative positional relationship between the resist and the wafer mark, the relationship with which the result of the signal simulator is registered with the alignment mark signal, is taken as the three-dimensional relative positional relationship between the resist and the wafer mark. By using the relative positional relationship at that time, an alignment signal is

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