Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
2001-04-02
2003-10-21
Mai, Huy (Department: 2873)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
C356S237500, C356S612000, C250S559400
Reexamination Certificate
active
06636303
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a foreign substance inspecting method and apparatus suitably used in lithography (e.g., in Proximity X-ray Lithography: to be referred to as PXL hereinafter) with which a mask pattern is exposed and transferred with a one-to-one exposure onto a wafer arranged close to the mask by using, as a light source, X-rays with a wavelength of 7 Å to 10 Å and output from an electron storage ring (to be referred to as an SR hereinafter) serving as a synchrotron radiator, and an exposure apparatus using this inspecting method.
More particularly, the present invention relates to a foreign substance inspecting method and apparatus which cope with the problem of a foreign substance specific to PXL exposure with which exposure is performed by separating a mask and wafer from each other by a very small distance of several tens of &mgr;m or the like, and an exposure apparatus using this inspecting method.
BACKGROUND OF THE INVENTION
PXL is a micropattern exposure technique with which a mask is set to oppose a wafer at a gap of 10 &mgr;m to 30 &mgr;m and a pattern on the mask is transferred to the wafer by Fresnel diffraction.
As a PXL type exposure apparatus, currently, one with a maximum exposure range of 52 mm square is expected to be manufactured. As this exposure apparatus performs one-to-one exposure with the maximum exposure range of 52 mm square, if exposure is to be performed on a wafer with a size of 4 inches or more, the entire surface of the wafer cannot be exposed by one exposure operation. For this reason, exposure is performed while sequentially moving the wafer so that the entire surface of the wafer is exposed, as with a repetitive stepper for an optical exposure apparatus. Hence, a PXL exposure apparatus is sometimes called a one-to-one exposure X-ray stepper.
The characteristic feature of the PXL exposure apparatus resides in its high resolution. With a high resolution of 100 nm or less and alignment of 20 nm or less having already been reported, the PXL exposure apparatus may become a leading exposure method for a 1-GDRAM or RAMs with capacities larger than that. One of the special items of the PXL is an X-ray mask. A conventional manufacturing process for an X-ray mask will be described with reference to
FIGS. 9
to
19
. Note that in
FIGS. 9
to
19
, for descriptive convenience, the thicknesses of the films are illustrated with a proportion different from that of actual films.
In fabrication of the X-ray mask, first, as shown in
FIG. 9
, a Si wafer
30
is prepared as a substrate and, as shown in
FIG. 10
, a SiC film
31
called a membrane and with a thickness of 2 &mgr;m to 3 &mgr;m is formed on it. When forming the SiC film
31
on the Si wafer
30
, SiC films are formed on the upper and lower surfaces and side surfaces of the wafer. As the SiC films on the lower surface and side surfaces of the wafer are not related to the function of the mask, they are omitted in FIG.
10
and so on.
In
FIG. 11
, the SiC surface is polished to form a planar SiC film
32
, and an ITO film or SiO
2
film
33
is formed, as shown in FIG.
12
. In the step of
FIG. 13
, an X-ray absorber
34
, e.g., W, Ta, or Ta
4
B, having a relatively high X-ray absorption performance is formed to a thickness of 0.3 &mgr;m to 0.5 &mgr;m. In
FIG. 13
, preparation of the substrate is completed.
In the step of
FIG. 14
, a resist is applied to the substrate, and a desired pattern is drawn on the substrate with an electron beam drawing unit. Then, the substrate is subjected to development, etching, and resist removal, thereby forming a pattern. When the pattern is formed, the opposite side to the pattern portion is etched back so X-rays can be transmitted through a Si portion
35
within the exposure range. Finally, in
FIG. 16
, the substrate is mounted on a frame
36
, thus completing an X-ray mask.
In order to decrease drawing errors, the frame
36
in the state shown in
FIG. 13
may be mounted as shown in
FIG. 17
, and Si in the portion
31
within the exposure range may be etched back, so X-rays can be transmitted through this portion. After that, a resist is applied to the substrate, and a desired pattern is drawn on the substrate with an electron beam drawing unit. Then, the substrate is subjected to development, etching, and resist removal, thereby forming a pattern. The X-ray mask shown in
FIG. 19
is thus completed. It is known that this method has a high precision since the substrate is finally mounted on the frame.
In fact, however, if the substrate is subjected to the drawing process after it is mounted on the frame, the mount may be peeled due to heat. Therefore, conventionally, the X-ray mask is usually formed with the steps of
FIGS. 9
to
16
. The frame
36
is sometimes called a support ring, and is made of, e.g., Pyrex or SiC. To mount the membrane, anodic bonding or an adhesive is used. Another method is also proposed in which, as shown in
FIG. 17
, the frame is also made of Si to form an integral frame
37
, and an Si wafer substrate and the frame are formed integrally.
In the PXL exposure apparatus, since a membrane with a thickness of 2 &mgr;m to 3 &mgr;m is used as a mask, it has a specific problem in that a foreign substance with a size equal to or larger than the exposure gap is sandwiched between the wafer and mask (particularly, a SiC membrane) to come into contact with them, thereby fracturing the SiC portion of the mask.
Assuming that a typical exposure gap is 10 &mgr;m, the existence of a foreign substance with a size equal to or larger than 10 &mgr;m between the wafer and mask may seem nonsensical in semiconductor manufacture where the idea of high yield prevails. This size, however, cannot be ignored as the size of a foreign substance occurring on the periphery of a wafer.
Most exposure apparatuses used in present semiconductor manufacture are optical exposure apparatuses, and a foreign substance attaching to the periphery of a wafer does not pose an issue. In an optical exposure apparatus, since the distance between the wafer and the projection optical system of the exposure apparatus is at least 1 cm, the problem of the contact of a foreign substance does not arise, and the situation is completely different from that of the PXL exposure apparatus. Furthermore, since the periphery of the wafer is not used for formation of ICs, an inspection for a foreign substance on the periphery of the wafer is not conventionally performed.
The present inventors performed observation of the peripheries of various types of wafers. It has become apparent that many large-sized foreign substances are present on the periphery of a wafer even in the semiconductor manufacture where the idea of high yield prevails. However, due to the reason described above, a foreign substance on the periphery of a wafer does not pose a serious issue in the conventional optical exposure apparatus. Even in the optical exposure apparatus, a foreign substance can move from the periphery of a wafer and shift onto the wafer pattern, thus causing a problem. As a countermeasure for this, inspection is performed by using a wafer foreign substance inspecting apparatus for detecting a foreign substance on a patterned wafer, so that a decrease in yield is prevented.
Still, in the PXL exposure apparatus, unlike in the optical exposure apparatus, a foreign substance on the periphery of a wafer can cause fracture of a mask. This is a serious problem.
FIGS. 20
to
22
are views for explaining a phenomenon that occurs when a mask
1
is exposed at a predetermined gap with a foreign substance
13
attaching to the periphery of a wafer
2
. In
FIG. 21
, after the wafer moves, when a portion near the periphery of the wafer is exposed, a force acts on the foreign substance
13
attaching to the wafer
2
. In the state of
FIG. 21
, since the foreign substance
13
is in contact with that portion of the mask
1
where the Si portion is not etched back, it does not fracture the mask
1
.
After the shot shown in
FIG. 21
is exposed, when the wafer
2
is
Ina Hideki
Matsumoto Takahiro
Sentoku Koichi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Mai Huy
LandOfFree
Foreign substance inspecting method and apparatus, which... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Foreign substance inspecting method and apparatus, which..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Foreign substance inspecting method and apparatus, which... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3137558