Semiconductor device manufacturing: process – Chemical etching – Altering etchability of substrate region by compositional or...
Reexamination Certificate
1999-06-03
2001-09-25
Dang, Trung (Department: 2823)
Semiconductor device manufacturing: process
Chemical etching
Altering etchability of substrate region by compositional or...
C438S692000, C438S424000, C438S435000, C438S437000
Reexamination Certificate
active
06294473
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the polishing of substrates and is particularly advantageous in the manufacture of semiconductor devices or the like. More specifically, the present invention is directed to a semiconductor device (or a precursor to a semiconductor device) layer comprising modified silicon dioxide, whereby the layer polishes at a much lower removal rate than unmodified silicon dioxide.
DISCUSSION OF THE PRIOR ART
During semiconductor device manufacture, one or more layers comprising silicon dioxide are polished or planarized, typically by a chemical-mechanical polishing (“CMP”) process. This process will hereafter be referred to as “oxide CMP.”
Oxide CMP has been problematic. Whereas other CMP processes tend to begin with one material and then stop at the interface to a second material, oxide CMP is a “blind” process, because it generally begins and ends with silicon dioxide at the surface. Generally speaking, no obvious interface is ever reached to indicate an end point.
As a result, oxide CMP is often conducted for a predetermined amount of time, and the surface profile is then measured. If the oxide layer has not been sufficiently thinned and/or the desired degree of planarity has not been obtained, then the silicon dioxide substrate must be re-polished. If the substrate is too thin, then the semiconductor device must be reworked or scrapped. Such a process can be expensive and inefficient.
In shallow trench isolation (“STI”), silicon nitride is typically used as a stop layer and as a means to provide end point detection. For other semiconductor device manufacturing steps involving a silicon dioxide containing substrate (other than STI), a silicon nitride layer is very difficult, typically impossible, to be successfully integrated into the total semiconductor process.
A need therefore exists to provide an oxide CMP process capable of efficiently and effectively indicating when a desired amount of silicon dioxide has been removed and/or when a desired degree of planarization has been obtained.
SUMMARY OF THE INVENTION
The present invention is directed to a method for polishing a silicon dioxide substrate during the manufacture of a semiconductor device or semiconductor device precursor. The method includes the step of hydrophobically modifying a substrate comprising silicon dioxide.
In a preferred embodiment, the oxide CMP processes of the present invention comprise at least the following steps. First, a base layer comprising silicon dioxide is created on a semiconductor device (or a semiconductor device precursor). The silicon dioxide can be deposited in a hydrophobic state, such as by altering the mix of the source gases that feed a CVD (chemical vapor deposit) reactor. In one embodiment, the feed gases are modified to decrease the amount of oxygen radical available for CVD (such as by replacing at least a portion of the O
2
with N
2
O), thereby increasing (at least at the surface) the ratio of hydrophobic moieties (such as siloxane moieties) to hydrophilic moieties, (such as silanol moieties), relative to conventional CVD of silicon dioxide.
Alternatively, conventional hydrophilic silicon dioxide can be deposited by conventional means, such as by CVD, and the surface of the silicon dioxide can later be hydrophobically modified. In either event, the silicon dioxide, at least at the surface, is hydrophobically modified, thereby causing a surface layer of the silicon dioxide to be less hydrophilic (the modified silicon dioxide is sufficiently less hydrophilic to decrease the average rate of polishing by at least 10%, more preferably by at least 25%, yet more preferably by at least 50% and yet more preferably up to 100%, relative to the average rate of polishing of conventional, hydrophilic silicon dioxide).
Hydrophobicity can be quantified according to the contact angle of a drop of water on the surface of a substrate (See, FIG.
6
). For the silicon dioxide substrates of the present invention, hydrophobic modification preferably increases the contact angle by at least 5 degrees, more preferably at least 10 degrees and yet more preferably at least 25 degrees. Conventional (hydrophilic) silicon dioxide provides a contact angle of less than about 80 degrees. Preferred hydrophobically modified silicon dioxide of the present invention provide a contact angle of greater than 90 degrees.
In a second step, a top layer, preferably comprising silicon dioxide, is created over the layer comprising hydrophobically modified silicon dioxide, whereby the layer comprising modified silicon dioxide is bonded between the top layer and the base layer. In a third step, the top layer is then polished until at least a portion of the layer comprising modified silicon dioxide is exposed to the polishing interface (the layer comprising modified silicon dioxide acts as a “stop layer” or an “endpoint detection” layer).
Optionally, the exposed portion of the layer comprising modified silicon dioxide is thereafter chemically treated to thereby increase the modified silicon dioxide layer's hydrophobicity, preferably to its original unmodified state.
The hydrophobically modified silicon dioxide of the present invention can be used as a stop layer or an end-point detection layer and can be used as a substitute for conventional stop layers or end-point detection layers otherwise used in silicon dioxide polishing. The hydrophobically modified silicon dioxide of the present invention also provides the option of a stop layer or end-point detection layer where none was previously possible, due to manufacturing constraints.
The hydrophobically modified silicon dioxide of the present invention is particularly advantageous where the hydrophobic modification can be reversed, thereby allowing the stop layer or end-point detection layer to be activated and/or inactivated, as desired. Furthermore, the hydrophobically modified silicon dioxide of the present invention can be advantageous relative to many conventional stop layers or end-point detection layers, because the present invention does not require the introduction of a completely new layer, such as silicon nitride, the presence of which can be more problematic than a hydrophobically modified silicon dioxide. The hydrophobically modified silicon dioxide of the present invention removes many of the constraints and much of the complexity typical of convention stop layers or end-point detection layers with respect to the polishing of silicon dioxide.
REFERENCES:
patent: 5576247 (1996-11-01), Yano et al.
patent: 5626924 (1997-05-01), Ishikawa
patent: 5855804 (1999-01-01), Walker
patent: 5950101 (1999-09-01), Yano et al.
“Chemical Etch Rate of Plasma-Enhanced Chemical Vapor Deposited SiO2 Films”, Besser and Louris, J. Electrochem. Soc., vol. 144, No. 8, Aug. 1997.
“The Use of Hydrophobic AEROSIL® in the Coatings Industry”, Technical Bulletin Pigments, Degussa, Frankfurt, Germany, 4thedition, May 1993.
Benson Kenneth A.
Dang Trung
Kaeding Konrad
Kita Gerald K.
Rodel Holdings Inc.
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