Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-06-18
2001-01-30
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C216S012000, C430S966000, C378S208000
Reexamination Certificate
active
06180292
ABSTRACT:
FIELD OF INVENTION
The invention relates to pattern replication using x-rays and in particular to an X-ray mask mounted device called a pellicle, which serves to provide a large pattern area, a wide choice of materials and greater precision in manufacturing.
BACKGROUND OF THE INVENTION AND RELATION TO THE PRIOR ART
The manufacturing of semiconductor integrated circuit devices is dependent upon the accurate replication of generated patterns onto the surface of a device substrate. This is usually accomplished by the production of a computer generated pattern into a chromium layer on a quartz substrate, and the pattern is then transferred via optical lithography. The replication operation is effected using a variety of processes, such as subtractive, for example etching; additive, for example deposition; and, by using such material modification techniques as oxidation, and ion implantation.
Heretofore in the art, optical lithography, which is a projection printing technique has been employed in the replication process. In optical lithography the mask is located some distance from the wafer to be exposed and a four or five times reduction between the mask image and the wafer image can be involved, which simplifies both the lithography and mask production and in turn provides tolerance of defects.
As the art is progressing, the desire for greater density is making the use of X-ray replication directly on the wafer very attractive. The considerations in using X-ray replication however are quite formidable. The X-ray technique involves proximity replication so that the X-ray mask images are made the same size as the final images on the wafer. Because of the one-to-one relationship of the image on an X-ray mask and the image formed on the wafer, any position errors in building the X-ray mask are replicated one for one onto the wafer. Thus, the position accuracy requirements for the fabrication of X-ray masks are very difficult to achieve and, as a result, X-ray masks are expensive to fabricate. In use, particles unavoidably settle on masks. The ability, previously available in optical lithography, of keeping settled particles outside of the depth of focus window in the replication, so that the particle is highly de-focused and does not print, is no longer available in the X-ray proximity replication. In some situations a particle that has settled on a mask can absorb X-ray photons and must be removed. A major source of a settling particle problem comes from the effect of the X-ray energy on the resist material that form the desired patterns. When the x-ray resist is irradiated, organic material is released from the resist. Because X-ray lithography is a proximity printing process, this material will travel the short distance between the mask and the wafer and then land on the x-ray mask. In particular, this material is prone to bonding to the x-ray mask absorber pattern. In a short time, this organic material begins to attenuate the x-rays resulting in longer exposure times, dimensional control problems, and pattern defects. This accumulation of contamination would ordinarily necessitate cleaning of the x-ray mask. However, due to the expense and fragility of the x-ray masks, and the risk involved with cleaning them, this is not considered to be a reasonable solution.
It is therefore important to protect the relatively delicate and not easily cleaned X-ray masks from contaminants and mechanical damage due to scratches and the like without introducing mechanical stresses that may affect the placement accuracy.
There has been some activity in the art directed to this problem in U.S. Pat. No. 5,793,836 in which a protective structure is described which provides a membrane that would lie between the mask and the wafer to assist in protecting the mask from contamination.
As progress with membranes advances needs are being encountered for larger pattern areas, greater precision in processing and availability of a wider range of materials.
SUMMARY OF THE INVENTION
In the invention, larger area X-ray masks, a wider range of X-ray mask membrane and mounting materials and greater precision in manufacture is achieved through the use of a membrane and rigid spacer type of pellicle mounting structure in which a precise thickness bulk etchable spacer material that is responsive to protection with an etch response conversion resist is employed together with a membrane material that is susceptible to vapor deposition processes. The arrangement permits etching operations to selectively remove portions of the bulk spacer and to be able to employ the finely controllable deposition processes for positioning the ultra thin membrane. The technique permits wider ranges of membrane materials, the selective protection for spacer shaping and the removal, by the low stress process of etching, of the unused bulk spacer material.
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Acosta Raul Edmundo
Angelopoulos Marie
Cordes Steven Allen
International Business Machines - Corporation
Mohamedulla Saleha R.
Morris Daniel P.
Riddles Alvin J.
Young Christopher G.
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