Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2001-03-07
2001-12-04
Hail, III, Joseph J. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S527000
Reexamination Certificate
active
06325702
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to semiconductor manufacture, and more particularly to polishing a substrate assembly surface using a chemical-mechanical -polishing (CMP) pad.
BACKGROUND OF THE INVENTION
In microchip fabrication, integrated circuits are formed on a substrate assembly. By substrate assembly, it is meant to include a bare wafer, as well as a wafer having one or more layers of material formed on it. Such layers are patterned to produce devices (e.g., transistors, diodes, capacitors, interconnects, etc.) for integrated circuits. In forming these devices, the one or more patterned layers can result in topographies of various heights.
In patterning layers on a wafer or patterning trenches in a wafer, lithography is used to transfer an image on a mask to a surface of the substrate assembly. Lithography (“microlithography” or “photolithography”) has resolution limits based in part on depth of focus requirements. These limits become more critical as geometries are diminished Thus, to have a target surface area of a substrate assembly in focus for lithographic patterning, it is necessary that the target surface area be sufficiently planar for the lithography employed. However, topographies of various heights make planarity problematic. One approach to obtaining sufficient planarity is using a chemical-mechanical -polishing (CMP) process. CMP may be used to remove unwanted material, and more particularly, may be employed to planarize a surface area of a substrate assembly. In removing unwanted material, it is important to remove as little wanted material as possible. Thus, chemical solutions used in CMP are often formulated to be more selective to remove one material over another, and thus the solution's chemical composition is directed at removing different materials at different rates. One such solution, Rodel ILD1300 made by Rodel, Inc. of Newark, Del., has a four to one (4:1) selectivity of boro-phospho-silicate glass (BPSG) to a doped silicon oxide formed from tetraethyl orthosilicate (TEOS) [hereinafter the doped silicon oxide formed from TEOS is referred to as “TEOS”]. Rodel ILD1300 also has a twelve to one (12:1) selectivity of BPSG to nitride. Conventionally, improvements in CMP selectivity between silicon nitride and BPSG/TEOS, polysilicon and BPSG/TEOS, or tungsten and titanium nitride have been made by changing chemical composition of the solution, such as by varying pH for selectivity to nitride or varying oxidants for selectivity to metal.
In addition to chemical reactions, CMP also includes a mechanical component for removing material. Mechanical removal for CMP is generally described by Preston's equation:
R
CMP
=K
CMP
v
P
(1)
where R
CMP
is the mechanical removal rate, P is the pressure, v is the relative velocity between a porous polishing pad and a substrate assembly surface, and K
CMP
is a constant proportional to the coefficient of friction between the pad and the substrate assembly surface. Conventionally, P is 20,685 to 55,160 Pa (3 to 8 pounds per square inch (psi)) and n is 0.333 to 1.667 rev/s (20 to 100 rpms). K
CMP
depends on the material(s) being removed.
As direct contact between the pad and the substrate assembly surface reduces removal rate owing to an absence of CMP solution, porous pads with continuous grooves in concentric ellipses have been made. By porous, it is meant that CMP solution particles may be absorbed within pad material. Such intrinsically porous pads allow for transport of CMP solution particles across raised portions of pads with continuous grooves. Pitch of such grooves or channels is conventionally 0.1 to 2 mm wide. Notably, this approach is directed at removing materials more readily, and not directed at selectively removing a material as between materials.
A non-porous pad is described in U.S. Pat. No. 5,489,233 to Cook, et al. In Cook et al., a pad is formed out of a solid uniform polymer sheet The polymer sheet has no intrinsic ability to absorb CMP solution particles. Such non-porous pads are formed with channels of varying configurations (macro-textured). The raised portions or contact portions of such non-porous pads are roughened (micro-textured) to allow transport of slurry particulate from channel to channel. Notably, such pads may be impregnated with microelements to provide such micro-texturing, as described in U.S. Pat. No. 5,578,362 to Reinhardt, et al.
In Cook et al., it is suggested that polishing rates may be adjusted by changing the pattern and density of the applied micro-texture and macro-texture. However, Cook et al. does not show or describe tailoring selectivity to particular materials. Accordingly, it would be desirable to have a methodology for CMP pad manufacturing which allows a target selectivity to be programmed into a CMP pad for a desired application.
SUMMARY OF THE INVENTION
The present invention provides enhanced selectivity in a CMP process by providing a special purpose CMP pad. Such a CMP pad includes at least one predetermined duty cycle of non-contact portions (those surfaces directed toward but not contacting a substrate assembly surface during polishing) to contact portions (those surfaces directed toward and contacting a substrate assembly surface during polishing). Such a CMP pad is formed at least in part from a material that intrinsically is non-porous with respect to a CMP solution particulate to be employed with use of the pad. Furthermore, such a CMP pad may be configured to transport CUP solution particulate across its contact portions. Such a CMP pad alters relative removal rates of materials without altering CMP solution chemical composition.
A duty cycle in accordance with the present invention is provided by configuring a CMP pad with a recessed portion or a raised portion, such as by a recess or an island, to provide a non-contact portion and a contact portion, respectively. A duty cycle or spatial frequency for an arrangement or pattern of islands or recesses is selected to enhance selectivity as between materials to be polished. Accordingly, such a CMP pad may be programmed with a target selectivity by configuring it with a predetermined duty cycle.
CMP pads in accordance with the present invention are to provide improved selectivity over CMP chemical selectivities alone. Such pads may be used to remove one dielectric in the presence of another dielectric, such as one silicon oxide, doped or undoped, in the presence of another siliconoxide, doped or undoped.
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patent
Hail III Joseph J.
Micro)n Technology, Inc.
Ojini Anthony
Schwegman Lundberg Woessner & Kluth P.A.
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