Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-03-29
2001-04-10
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S296000
Reexamination Certificate
active
06214496
ABSTRACT:
BACKGROUND
1. Technical Field
This disclosure relates to semiconductor fabrication tools and more particularly, to an improved system and method for generating patterns on reticles used in semiconductor fabrication processes.
2. Description of the Related Art
Semiconductor fabrication processes typically include photolithographic processing to pattern areas of a surface of a semiconductor device. The semiconductor fabrication process typically includes applying a photoresist material to the surface of the semiconductor device. The photoresist is patterned by exposing the photoresist to light, typically ultraviolet light, to crosslink the resist material (negative resist). This cross linking prevents a reaction with a developer which develops away areas of the photoresist which were not crosslinked by the exposure to the UV light. Other types of photoresists have chains broken by exposure (positive resist) to ultraviolet light.
Photoresists are patterned using a photomask. The photomask functions as a shield to prevent light form passing through it in predetermined areas during photolithography. The photomask typically provides a black or highly absorbent layer of material, usually chromium or a chromium alloy, patterned in accordance with the patterning design to be projected onto the photoresist. The absorbent layer is formed on a substrate, which may include a glass or quartz material. Other techniques are used which may include electrons and electron beam masks, scattering masks and/or stencil masks, for example, scattering with angular limitation in projection electron beam lithography (SCALPEL).
With decreasing feature sizes of semiconductor components, masks are increasingly more difficult to fabricate and inspect. It is known that advanced semiconductor processing is very sensitive to image quality provided by masks. The defect fabrication capability for reticles is limited to a certain minimum feature size. This minimum feature size typically depends on the process and fabrication tools used to provide the pattern on the reticle.
Reticles may be written by laser pattern generators or electron beam pattern generators. Since reticles typically include a multitude of features below a micron in size. Fabrication is performed using automated devices. Referring to
FIG. 1
, a reticle fabrication device
10
is shown. Device
10
includes a stage
14
for positioning a mask or reticle
16
to be fabricated. An energy source
18
provides a laser beam or an electron beam for writing a pattern on mask
16
with a predetermined intensity of light or electrons. Mask
16
is preferably guided by stage
14
according to a computer generated image of the pattern to be written on mask
16
.
Both laser and electron beam pattern generators have the capability for complex reticle patterns, including those with narrow geometries, dense optical proximity correction (OPC) and phase shift masks (PSM). OPC helps compensate for lost light to ensure that the precise patterns are formed on a semiconductor wafer. For example, without OPC, a rectangle can end up looking like an oval on the wafer because light tends to round on the edges. OPC corrects this by adding tiny serifs (lines) to the corner to ensure that the corners are not rounded or moving a feature edge so wafer features are sized more accurately. Phase shift masks alter the phase of light passing through the photomask, and permit improved depth of focus and resolution on the wafer. Phase-shift helps reduce distortion on line resolution of wafer surface irregularities.
Although laser pattern generator provide higher reticle throughput, lower cost and better placement accuracy, laser pattern generators produce large corner rounding. Referring to
FIG. 2
, a circular laser/electron beam spot
30
is shown for writing a pattern on for a reticle on a mask blank
32
. Mask blank
32
includes a resist layer
33
formed on a blank mask
32
. A pattern
34
is formed by exposing portions of resist to light or electrons. The pattern is created by applying laser/electron spot
30
thereon to expose resist
33
. Typically, blank mask
32
includes an energy absorbent material, such as, chromium, molybdenum or their alloys, or metal oxides on a glass or quartz substrate. After exposure resist
33
is developed and exposed portions of energy absorbent material on blank mask
32
is etched away. As laser/electron spot
30
approaches a corner
38
, resist
33
cannot be exposed in corner
38
as a result of the geometry of laser/electron spot
30
. This is referred to as corner rounding. The large corner radius is related to the beam diameter as approximately equal to 1.17×beam diameter for laser beams. State of the art tools are capable of corner rounding as low as 300 nm.
Conventional solutions to large corner rounding include employing serifs, hammerheads and other types of add-on structures. The addition of these structures adds to the complexity of the reticle pattern, increases data volume for storing the reticle design and makes the reticle pattern more difficult to inspect due to the add-on features.
Therefore, a need exists for a system and method which reduces corner rounding in reticle fabrication processes. A further need exists for a system and method which reduces the need for add-on structures in reticle fabrication processes.
SUMMARY OF THE INVENTION
A method for fabricating mask patterns in accordance with the present invention includes the steps of providing a mask blank for patterning, propagating an energy beam having an elliptical cross-sectional shape onto the mask blank, the elliptical cross-sectional shape having an elongated axis and edges at opposite ends of the elongated axis and positioning the mask blank to write a pattern on the mask blank wherein the positioning includes employing the edges of the elliptical cross-sectional shape of the energy beam to write corners of the pattern.
Another method for fabricating mask patterns for processing semiconductor devices comprising the steps of providing a mask blank to be patterned, providing a design data set for a pattern to be written on the mask blank, propagating an energy beam having an elliptical cross-sectional shape onto the mask blank, the elliptical cross-sectional shape having an elongated axis and edges at opposite ends of the elongated axis and translating and rotating the mask blank according to the design data set to write a pattern on the mask blank wherein the rotating includes employing the edges of the elliptical cross-sectional shape of the energy beam to write corners of the pattern.
In alternate methods, the step of positioning may include the steps of mounting the mask blank on a positioner for positioning the mask blank. The step of propagating a energy beam may include the step of shaping the beam using a lens system. The step of propagating an energy beam may include the step of propagating an ultraviolet laser beam. The step of propagating an energy beam may include the step of propagating an electron beam. The step of positioning the mask blank preferably includes the step of writing corners by positioning the elongated axis of the energy beam at an angle that bisects an angle formed by adjacent sides of the corners.
A system for fabricating mask patterns in accordance with the present invention includes an energy source for providing an elliptical cross-sectional shape onto a mask blank, the elliptical cross-sectional shape having an elongated axis and edges at opposite ends of the elongated axis and a positioner for positioning the mask blank to write a pattern on the mask blank such that the edges of the elliptical cross-sectional shape of an energy beam are employed to write corners of the pattern.
In alternate embodiments, the system may further include a processor for providing control signals to the positioner for positioning the mask blank. The processor preferably includes a memory storage device, the memory storage device including a data set for providing digital data representing the pattern to the processor for producing the co
Besenbock Wolfgang
Carpio Enio Luiz
Braden Stanton C.
Huff Mark F.
Infineon Technologies North America Corp.
Mohamedulla Saleha R.
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