Radiant energy – Inspection of solids or liquids by charged particles
Reexamination Certificate
2000-10-13
2003-02-18
Anderson, Bruce (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
C356S237300, C356S237400, C356S237500, C356S335000, C356S336000
Reexamination Certificate
active
06521889
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates to a dust particle inspection apparatus and a device manufacturing method using the same. The present invention is suitably usable for inspection of the state of presence/absence a foreign substance such as a dust particle (presence/absence of or the size of such particle) or the height of such dust particle (magnitude in a direction of a normal to a surface where the particle is adhered to), upon a substrate such as a mask, for example, having a circuit pattern formed thereon, particularly in the field of the manufacture of devices such as semiconductor devices (e.g., IC or LSI), CCDS, liquid crystal panels or magnetic heads, for example. Thus, the present invention is suitably applicable to the manufacture of high-precision devices such as described above.
Particularly, the present invention provides specific advantageous effects when the same is applied to a semiconductor exposure method called a “Proximity X-ray Lithography” (hereinafter, “PXL”) wherein an X-ray beam of a wavelength 7-10 angstroms emitted from an electron accumulation ring (synchrotron radiation unit) is used as a light source and wherein a pattern of a mask is transferred to a wafer at a unit magnification while the mask and the wafer are dispose d opposed to each other with a gap of a few tens microns maintained therebetween.
Generally, in IC manufacturing processes, a circuit pattern formed on a substrate such as a mask is transferred to a wafer, being coated with a resist, by use of an exposure apparatus. If in this procedure there is a foreign substance such as a dust particle upon the surface of the substrate, such particle is also transferred in the transfer process to decrease the yield of the IC or LSI production.
In the conventional PXL procedure, a mask is disposed opposed to a wafer with a gap (clearance) of 10-30 microns kept therebetween, and the mask pattern is transferred to the wafer through Fresnel diffraction.
As regards exposure apparatuses of PXL type, an exposure apparatus having a largest exposure range of 52 mm square has currently been proposed. The largest exposure range of 52 mm square means that, even in the unit-magnification exposure, for a wafer of a size of 4 inches or larger, the whole surface of the wafer can not be exposed through a single exposure operation.
In the PXL exposure process, the whole surface of a wafer is exposed while the wafer is moved sequentially as in a repetition reduction exposure apparatus, called a “stepper”. Thus, in this respect, an exposure apparatus of PXL type may be called as a “unit magnification X-ray stepper”.
As regards the resolution, a result of 100 nm or less, or a result of 20 nm or less based on the alignment result, has been reported. Also, it is recognized that the PXL has a potential for an exposure process for devices of 1 gigabit or more. One special feature of the PXL is an X-ray mask.
Conventional X-ray mask manufacturing processes will now be explained, with reference to FIG.
5
and the like. Here, as regards the thicknesses of a mask, a wafer and a film thereon, for better understanding, they are illustrated in proportions different from practical proportions.
In the manufacture of a PXL mask, as shown in
FIG. 5
, a silicon (Si) wafer
30
is prepared as a substrate. Then, as shown in
FIG. 6
, a SiC film
31
of a thickness of 2-3 microns, called a membrane, is formed on the Si wafer
30
.
When the SiC film
31
is produced on the Si wafer
30
, practically the film is formed on the top and bottom faces of the substrate as well as the side face thereof. Since, however, the bottom face and the side face do not provide a function, in FIG.
6
and later, the films formed there are not illustrated.
Subsequently, as shown in
FIG. 7
, the surface of the SiC film
31
is flattened by polishing, whereby a SiC film
32
is provided. Then, as shown in
FIG. 8
, an ITO film or SiO
2
film
33
is produced as an etching stopper and also for better affinity with an X-ray absorptive layer. Thereafter, as shown in
FIG. 9
, a material having a relatively high X-ray absorptivity such as W, Ta or Ta
4
B, for example, is applied with a thickness 0.3-0.5 micron, as an X-ray absorptive material
34
. Then, as shown in
FIG. 10
, through various processes such as resist application, desired patterning with an electron beam patterning apparatus, development, etching, and resist separation, a pattern is defined by the X-ray absorbing material
34
.
Subsequently, as shown in
FIG. 11
, a portion of the Si wafer
30
at a side thereof remote from the pattern is removed by back etching, such that X-rays can transmit through the Si wafer portion
35
corresponding to the exposure range. Finally, as shown in
FIG. 12
, the peripheral portion of the Si wafer
30
is mounted on a frame
36
, by which an X-ray mask is accomplished.
It is well known that, in order to minimize the patterning error, an additional procedure may be performed after the step of
FIG. 10
, so that, as shown
FIG. 13
, the Si wafer
30
is mounted on a frame
36
and then, as shown in
FIG. 14
, the portion of the Si wafer
30
corresponding to the exposure range is back etched to enable transmission of X-rays therethrough. Thereafter, as shown in FIG.
15
and like
FIG. 12
, various processes such as resist application, desired patterning with an electron beam patterning apparatus, development, etching, and resist separation may be performed so that a pattern is defined by the X-ray absorbing material
34
.
However, if the patterning process is performed after the frame
36
is mounted to the Si wafer
30
, there may arise a problem that the Si wafer
30
and the frame
36
are detached from each other due to heat. In consideration of it, in many cases, the X-ray mask is produced by taking processes such as shown in
FIGS. 5-12
.
As regards the frame, it may be called as a “support ring”. As for the material thereof, Pyrex or SiC is used. For mounting it to the membrane, an anodic bonding process or an adhesive agent is used.
A proposal has been made to use an integral type frame
37
(
FIG. 15
) wherein the frame
36
of
FIG. 13
is made of the same material as the Si wafer
30
, that is, to make the Si wafer substrate
30
and the frame
36
as a unit.
There is a problem peculiar to the PXL. That is, when a dust particle of a size larger than the exposure gap between a mask and a wafer is sandwiched between the mask (particularly, a SiC membrane) and the wafer, the SiC portion of the mask may be destroyed.
Seemingly, if the exposure gap is 10 microns, there is no possibility that a dust particle larger than 10 microns is present between a wafer and a mask. This is particularly so because a good yield rate is regarded absolutely important in the semiconductor manufacture. However, this is not correct. Particularly, if a dust particle is attached to a peripheral portion outside the effective area of a wafer or mask, a problem peculiar to the PXL arises.
As regards such dust particle adhered to the peripheral portion of a mask or wafer, it has not raised a critical problem since the current semiconductor manufacturing procedure uses, in most cases, an exposure apparatus called “optical exposure apparatus” wherein a pattern of a mask is projected and printed on a wafer through a projection optical system. In such optical exposure apparatus, there is a distance of 1 cm or more between the wafer and the projection optical system of the exposure apparatus. Further, the peripheral portion of a wafer is not used for the IC production. Therefore, as regards a dust particle at the wafer peripheral portion, no inspection process is currently performed.
However, according to the observation of the wafer peripheral portion made by the inventors of the subject application, in many cases there were large dust particles at the wafer peripheral portion. It has been found that, even in the semiconductor manufacture wherein a good yield rate is regarded absolutely important, in many cases there are large dust particles at the wafe
Ina Hideki
Itoga Kenji
Anderson Bruce
Hashmi Zia R.
LandOfFree
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