Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
2000-01-05
2003-02-11
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S003000, C134S006000, C134S026000, C134S028000, C134S029000, C134S034000
Reexamination Certificate
active
06517636
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods for wet processing semiconductor substrates. More particularly, this invention relates to methods for reducing particle contamination of semiconductor substrates during wet processing.
BACKGROUND OF THE INVENTION
Wet processing of semiconductor substrates, such as wafers, flat panels, and other electronic component precursors is used extensively during the manufacture of integrated circuits. Preferably, wet processing is carried out to prepare the semiconductor substrates for processing steps such as diffusion, ion implantation, epitaxial growth, chemical vapor deposition, and hemispherical silicon grain growth, or combinations thereof. During wet processing, the semiconductor substrates are contacted with a series of processing solutions. The processing solutions may be used, for example, to etch, to remove photoresist, to clean, or to rinse the semiconductor substrates. See, e.g., U.S. Pat. Nos. 4,577,650; 4,740,249; 4,738,272; 4,856,544; 4,633,893; 4,778,532; 4,917,123; and EP 0 233 184, assigned to a common assignee, and Burkman et al.,
Wet Chemical Processes
-
Aqueous Cleaning Processes,
pg 111-151 in Handbook of Semiconductor Wafer Cleaning Technology (edited by Werner Kern, Published by Noyes Publication Parkridge, N.J. 1993), the disclosures of which are herein incorporated by reference in their entirety.
There are various types of systems available for wet processing. For example, the semiconductor substrates may be processed in a single vessel system closed to the environment (such as a Full-Flow™ system supplied by CFMT Technologies), a single vessel system open to the environment, or a multiple open bath system (e.g., wet bench) having a plurality of baths open to the atmosphere.
Following processing, the semiconductor substrates are typically dried. Drying of the semiconductor substrates can be done using various methods, with the goal being to ensure that there is no contamination created during the drying process. Methods of drying include evaporation, centrifugal force in a spin-rinser-dryer, steam or chemical drying of wafers, including the method and apparatus disclosed in, for example, U.S. Pat. No. 4,778,532.
A frequent problem encountered during wet processing is contamination of the semiconductor substrates with particles made of materials such as Si
3
N
4
, Si, SiO
2
, resist residue, hair, linen, dust, dirt and other solid contaminants. Particle contamination of the semiconductor substrates is undesirable as it can cause device defects in the semiconductor substrates, reducing overall manufacturing yields. Thus, much effort has focused on understanding the mechanism of particle deposition onto semiconductor substrates during wet processing so that it can be minimized.
Particles are deposited onto semiconductor substrates during wet processing through various mechanisms. For example, an article by Riley et al., entitled
Investigating Liquid
-
Based Particle Deposition and The Effects of Double
-
Layer Interactions Using Hydrophobic Silicon Wafers,
Microcontamination, December 1990, p. 20-24, discloses that the primary mechanism of particle deposition onto a silicon wafer immersed in a liquid is effected by the interaction of the particle with the wafer surface. For example, negatively charged particles were found to primarily deposit onto a negatively charged wafer during withdrawal of the wafer through the gas-liquid interface of the solution. In this case, the negatively charged particles were deposited onto the wafer via a thin film of liquid that covers the wafer on withdrawal. In contrast, for positively charged particles, the majority of particles deposited on the negatively charged wafer surface while the wafer was fully immersed in the solution via a bulk deposition mechanism. Thus, in the case of positively charged particles, it was recommended to minimize wafer contact time in the bath, and for negatively charged particles, an additional rinsing step was recommended to remove particles adhering to the surfaces of the wafers after removal of the wafers from the solutions.
Further studies have been conducted related to particle deposition mechanisms resulting in alternative solutions. For example, in an article by T. Kezuka, et al., entitled
The Behavior of Particles in Liquid Chemicals and Their Deposition Control onto Silicon Wafers,
17
th
Symposium on ULSI Cleaning Technology, Feb. 5 to Feb. 6, 1993, JA (NOKYO)-Hall, Tokyo, Japan (“Kezuka”), it was reported that certain surfactants could be added to a hydrofluoric acid containing solution to prevent polystyrene latex particles from being deposited onto the silicon wafers while the silicon wafers were fully immersed in the hydrofluoric acid containing solution. Anionic surfactants were found to be particularly useful in preventing bulk deposition of polystyrene latex particles onto silicon wafers. This effect was hypothesized to be impart due to the zeta potentials of the particles and silicon wafer surfaces.
U.S. Pat. No. 5,656,097 to Olesen et. al., (hereinafter “Olesen”) discloses an alternative solution for reducing particle contamination during wet processing. In Olesen, semiconductor wafers are processed in an open vessel in a particular sequence of cycles. The method includes filling the vessel with one or more dilute cleaning solutions, completely “dumping” the cleaning solutions after cleaning, and rinsing the wafers after one or more of the cleanings by filling the tank with rinsing water and spraying the walls of the tank and wafers with the rinsing water while the tank is being filled. Megasonics are also used in certain cycles to inhibit particle deposition. Olesen discloses that low concentrations of surfactants may be used in the cleaning solutions.
Despite these proposed solutions for reducing particle contamination during wet processing, particle contamination is still a problem that can be further improved. The present invention seeks to provide other methods of reducing particle contamination during wet processing. Particularly, it has been found that contact of semiconductor substrates with a gas-liquid interface during wet processing can be a significant source of particle contamination. This particle contamination is especially problematic when contacting the semiconductor substrates with a gas-liquid interface during immersion in a processing solution (including a rinsing solution).
One possible solution is to minimize the exposure of the semiconductor substrates to gas-liquid interfaces during wet processing. However, in traditional multiple open bath systems (e.g., wet bench systems), where the semiconductor substrates are moved in and out of numerous baths containing processing solutions, the semiconductor substrates must be exposed to multiple gas-liquid interfaces.
Single vessel systems, if designed appropriately, can eliminate the exposure to multiple gas-liquid interfaces encountered in multiple open bath systems. However, even in a single vessel system, the semiconductor substrates must still be exposed to at least one gas-liquid interface (usually when the vessel is initially filled). This initial gas-liquid interface that the semiconductor substrates are exposed to can cause particle contamination that is difficult to remove in subsequent processing steps.
The present invention provides methods for reducing particle contamination in both single vessel and multiple bath systems where the semiconductor substrates are exposed to at least one gas-liquid interface during immersion. Particularly, the methods of the present invention reduce particle contamination during the wet processing by including, among other features, the use of a surfactant when the semiconductor wafers are contacted with gas-liquid interfaces during immersion.
SUMMARY OF THE INVENTION
The present invention provides methods for reducing particle contamination of semiconductor substrates during wet processing. In one embodiment, the method includes initially immersing and contacting the semiconductor substrates with an initial liqui
CFMT, Inc.
Gulakowski Randy
Kornakov M.
Woodcock & Washburn LLP
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