Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-02-25
2002-02-12
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C250S492210
Reexamination Certificate
active
06346352
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of repairing and writing a reticle or photomask or any light transmittable substrate. More particularly, it relates to a method of using short duration laser ablation to repair bump and divot defects on a light transmittable substrate.
2. Description of Related Art
The use of lithographic technology in transferring patterns from photomasks to semiconductor substrates in the fabrication of semiconductor devices, such as integrated circuits, has been highly developed and widely used. Reticles, or photomasks, are used with a variety of radiation sources, both visible and ultraviolet, as well as x-rays and electron beams.
Typically, the substrates of a reticle or photomask comprise a transparent material which allows light to pass through preferably at greater than 98% transmittance. Suitable substrate materials include soda lime glass, quartz (lightly doped and undoped), and sapphire. A metal or other light blocking or opaque material is then blanket deposited on the transparent substrate to be patterned and etched to a desired integrated circuit pattern. One type of photomask, a phase shift mask, which may or may not include an opaque material deposited thereon, utilizes etched portions of the quartz substrate itself to form the pattern. Wherein the phase shift mask has a patterned metal layer thereover, etching the quartz also provides a means for attenuating the pattern at the edges to provide higher resolution during photolithography.
In order to prepare the quartz substrate for fabrication of the photomask, the substrate is first planarized to provide a smooth surface within acceptable process parameters. However, planarization according to known means in the art such as plasma etching or chemical mechanical polishing will still leave defects. Generally, bump defects occur when the planarization process does not provide sufficient planarization in a localized area on the substrate surface. Bump defects, if left uncorrected on the substrate surface, alter the phase shift of the substrate. It may also adversely affect the quality of the pattern when the metal layer is deposited thereover since the metal deposited over the bump defect may be semi-transparent. Substrates with bump defects must be scrapped leading to waste and high manufacturing costs. Thus, it would be desirable to provide a means of localized repair for the quartz substrate, and in general, for any transparent substrate.
After planarization of the substrate, the metal or light blocking material is blanket deposited, patterned and etched to the desired integrated circuit pattern. Typically, a photoresist is used to pattern the light blocking material. Etching by means of chemical etching may result in divot defects when over-etching occurs and a portion of the substrate is also removed. Divot defects would alter the phase shift of the photomask reducing the clarity of the projected integrated circuit pattern onto a semiconductor wafer. Given the tight constraints on line width in the current generation and the next generation of semiconductor devices, divot and other defects on the photomasks cannot be tolerated in photolithographic techniques.
The prior art addresses the repair of opaque and clear defects resulting from either too much metal on the substrate, e.g., chrome bridges, or too little metal on the substrate, e.g., pinholes, but does not address repairing the transparent substrate. U.S. Pat. No. 5,035,787 to Parker discloses a method of repairing opaque and clear defects using a focused ion beam (FIB). Opaque defects are sputter etched with minimum mask damage while clear defects are filled in directly from the beam using a source which is compatible with the mask material. However, no mention is made of repairing the substrate, only defects caused by the patterning and etching of the metal layer is addressed.
U.S. Pat. No. 5,382,484 to Hosono describes a method of removing a bump defect in a phase shift mask by coating the bump with a correction film formed by a deposition gas and the FIB, and etching back the film and bump with a focused ion beam using a gallium source. Divots are filled with a spin-on-glass film and etched back with an FIB. Gallium stains and residue from the correction are then removed with an Nd:YAG laser having a wavelength of 532 nm. This technique, although addressing the need for repair of defects on the transparent substrate, utilizes sputter etching with the FIB which can lead to damaged areas printing onto wafers in some circumstances.
U.S. Pat. No. 5,405,721 to Pierrat repairs quartz with a gallium source FIB and removing the gallium stains with wet etching. The problem lies in being able to etch the same depth from the substrate, the top shifting layer and the bottom shifting layer of the phase shift mask to compensate for the phase shift.
U.S. Pat. No. 5,439,763 to Shimase et al. corrects defects in the phase shifter portions of photomasks by using an etch stop layer under the phase shifter comprising Al
2
O
3
during FIB planarization using a reactive gas to planarize the defect down to the etch stop layer. This method requires that an additional layer be added to the photomask which may effect the transmittance of the photomask.
U.S. Pat. No. 5,882,823 to Neary, assigned to the assignee of the present invention, discloses a two-step FIB repair process wherein the FIB is used to core out a quartz bump defect leaving a thin wall of quartz which is removed using an isotropic hydrofluoric acid etch. FIB at an angle may also be used to remove the remaining walls and for removing attached metal defects. However, the wet etch is performed over the entire photomask and is not conducive to localized repairs.
Thus, there remains a need for localized repair of the transparent, particularly quartz, substrate in the fabrication of reticles and photomasks.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method of localized repair of the transparent substrate used in reticles and photomasks which would correct bump and divot defects.
It is another object of the present invention to provide a method of localized repair of quartz substrates used in reticles and photomasks.
A further object of the invention is to provide a method of repairing bump defects on transparent substrates used in reticles and photomasks.
It is yet another object of the present invention to provide a method of repairing divot defects on transparent substrates used in reticles and photomasks.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a method of correcting a bump defect on a phase shift mask comprising the steps of: implanting a light absorbing material into the bump defect; and irradiating the light absorbing material implanted into the bump defect until substantially all of the light absorbing material is removed.
Preferably, the step of implanting a light absorbing material comprises implanting a light absorbing material selected from the group consisting of gallium, boron, phosphorus, arsenic, antimony and combinations thereof. Most preferably, the step of implanting a light absorbing material comprises implanting gallium ions into the bump defect.
Preferably, the step of irradiating the light absorbing material comprises irradiating the light absorbing material with a laser operating at femtosecond and/or attosecond pulses.
In a second aspect, the present invention is directed to a method of correcting a defect in a substrate comprising the steps of: providing a light transmittable substrate, the substrate having one or more bump defects; implanting light absorbing ions into a bump defect on the substrate to form a stained bump; laser ablating the staine
Hayden Dennis M.
Neary Timothy E.
Ross John N.
DeLio & Peterson LLC
International Business Machines - Corporation
Kotulak Richard M.
Peterson Peter W.
Rosasco S.
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