Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2000-06-07
2001-05-22
Banks, Derris H. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S060000
Reexamination Certificate
active
06234877
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to planarization of a substrate; and more particularly relates to chemical mechanical polishing (CMP) of a semiconductor substrate employing two separate chemical mechanical slurry solutions.
During fabrication of certain semiconductor devices, a metal layer, e.g., tungsten or aluminum may be deposited upon an underlying patterned dielectric layer, e.g., phosphosilicate glass (PSG), borosilicate glass (BSG), borophosphosilicate glass (BPSG) or silicon dioxide (SiO
2
), to form interconnects, for example, within a semiconductor. In forming the interconnects, chemical mechanical polishing of the metal layer removes metal material until reaching the dielectric. Ideally, the polished substrate has a flat surface, leaving metal in voids of the patterned dielectric to serve as interconnect plugs. These interconnects should each have a flat upper surface that is flush with an upper plane defined by the top surfaces of the patterned dielectric layer. When a subsequent metal layer is deposited, the deposited metal electrically connects with ends of the plugs. The interconnect plugs, therefore, provide electrical connections between the upper metal to respective semiconductor regions therebelow.
Available CMP procedures for planarizing a metal layer relative to a patterned dielectric for the formation of an interconnect plug often result in undesirable divits, surface unevenness, or salt residues. Assuming a known planarization procedure employing two separate CMP slurry solutions, it is theorized (pursuant this disclosure), that the addition of a second CMP slurry solution to a polishing procedure while first CMP slurry solution is still present, may alter a pH of the polishing procedure. This change in pH level, in-turn, may effect formation of precipitates, causing the slurry solution to gel and/or provide salt formations.
Furthermore, when injecting different slurry solutions onto a polishing pad at different times during polishing of a semiconductor substrate, the pH of the combined solutions is not precisely controlled; rather, the pH level is in a state of fluctuation as the new slurry solution is dispensed onto the pad and mixed with solutions already on the pad. Thus, the resulting CMP process rate and selectivity are not precisely known. For example, the slurries of certain known CMP processes for polishing tungsten have been found to chemically attack the tungsten layer and create undesirable voids within exposed tungsten plugs, or result in the formation of vias during later process stages. Additionally, if there is a loss of oxide selectivity (for the above described example where the oxide layer serves as the patterned dielectric beneath the tungsten), the lack of oxide selectively may result in complete removal of certain oxide portions so as to expose and damage underlying semiconductor devices beneath the oxide layer-resulting in scrapped material.
SUMMARY OF THE INVENTION
The chemical etch rate of certain materials is strongly dependent on a pH level of the associated slurry solution. Accordingly, the present invention provides new methods for polishing of a substrate, which methods provide greater control of the pH level during the planarization procedures.
During a polishing procedure, a second slurry solution is dispensed onto a polishing pad following use of a first slurry solution, providing a slurry solution transition to alter characteristics of polishing of a semiconductor substrate. The second slurry solution may have a pH that is different from the first solution. Since the polishing pad used for polishing the substrate has a capacity to absorb slurry, a precise switch from one pH to another pH during the polishing of the substrate is not readily available. In accordance with one embodiment of the present invention, a diluting solution is dispensed onto the polishing pad as an intermediate step between the application of respective first and second slurry solutions to the polishing pad. The diluting solution assists neutralization of the polishing pad before the application of the second slurry solution.
In accordance with one aspect of this particular embodiment of the present invention, a substrate is polished using a first slurry solution and a polishing pad. Thereafter, the first slurry solution is substantially removed from the polishing pad using at least one diluting solution. After this step of applying diluting solution to the polishing pad to remove the first slurry solutions, the substrate is further polished using a second slurry solution.
In a preferred aspect of this embodiment of the present invention, the first slurry solution is removed from the polishing pad using (as the diluting solution) a first buffer solution having a pH to the same side of 7 as that of the first slurry solution. Following use of the first buffer solution, a solvent is applied to the polishing pad for neutralizing a pH level. Preferably, the buffer solution and/or solvent are applied to the polishing pad during relative movement of the substrate against the polishing pad and during mechanical conditioning of the polishing pad.
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“Application of Chemical Mechanical Polishing to the Fabrication of VLSI Circuit Interconnections” J. Electrochem. Soc., vol. 138 No. 6, Jun. 1991 pp. 1778-1783.
Kim Sung C.
Koos Daniel A.
Sandhu Gurtej S.
Banks Derris H.
Fields Walter D.
Micro)n Technology, Inc.
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