Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1999-03-24
2001-05-15
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S009000
Reexamination Certificate
active
06232234
ABSTRACT:
FILED OF THE INVENTION
The present invention relates to a semiconductor process, and in particular, to a method of reducing the amount of residual particles in a chamber after a film-forming reaction by using a low power plasma-activated reaction under vacuum conditions.
BACKGROUND OF THE INVENTION
With the rapid development of integrated circuit technologies, there has been a continuous drive to reduce the size of these circuits. Thus, semiconductor technologies have strived to increase the integrated circuit density on a chip. As the semiconductors are miniaturized and features become more closely spaced, the tolerance of process conditions become more critical because minute defects will cause circuits on these wafers to fail.
Chemical vapor deposition or physical vapor deposition are both popular methods of forming layers or “films” on a wafer. These techniques, and others, utilize reaction gases applied by a recipe for forming layers on the wafers. For example, low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), or high density plasma chemical vapor deposition (HDPCVD) also need reaction gases to deposit a particular type of layer, for instance a silicon nitride layer. The reaction gases for forming the silicon nitride layer are SiH
4
, NH
3
, N
2
, N
2
O or SiH
2
Cl
2
, NH
3
, N
2
, and N
2
O. Further, a borophosphorsilicated glass (BPSG) layer can be formed by low-pressure chemical vapor deposition using tetraethylorthosilicate (TEOS) as a reactant. A silicon dioxide layer can be formed by a chemical vapor deposition process, using TEOS as a source at a temperature between about 650 to 750 degrees centigrade, at a pressure of about 1 to 10 torr. Other techniques used in semiconductor processing also generally require the presence of some gas in a chamber for certain purposes. For example, some thermal annealing processes utilize nitrogen gas. In addition, various carrier gases are utilized in a variety of reactions.
It is a particular issue, however, that residual reaction gases typically remain in the reaction chamber after the film-forming reactions have been completed. The pressure of residual reaction gases causes the the formation of particles in the film, which are referred to as in-film paticulates, due to continued reaction in the gas phase. These in-film particulates are increasingly problematic as semiconductor film patterns (line widths) are being reduced in size and lead to an increasing percentage of defective devices.
Typically, the reaction gases will be pumped out of (evacuated from) the chamber after a semiconductor process and this should reduce the potential number of particulates formed. Particularly, it is known that the in-film particle number can be reduced by pumping out residual gases in gaslines and from the reaction chamber after processing. However, it is also the case that some of the residual gas used in the film forming reaction will remain in the chamber and gas lines after the processing has been completed. It is also known that the residual gases in the reaction chamber itself are much more critical in affecting in-film particle numbers because the reaction chamber has a much higher temperature than anywhere else in the equipment and the chemical reaction rates usually increase with temperature. Thus, increasing the pumping speed after the process has been completed to evacuate the chamber more quickly is the usual method to remove residual gases and thereby minimize particulate formation. However, it is only somewhat effective. Further reduction in the in-film particle number is desired as line widths continue to decrease in order to reduce losses due to defects. This cannot currently be achieved by known techniques. What is required is a method to reduce the incidence of in-film particles and thereby improve semiconductor productivity.
SUMMARY OF THE INVENTION
The present invention generally provides a method and apparatus to reduce the incidence of in-film particles on semiconductor devices and thereby reduce the proportion of defective devices produced.
The invention is applicable in processes for forming thin films for integrated circuit fabrication using techniques involving chemical reagent gases. In such processes, a residue of chemicals will remain in the reaction chamber after the desired film-forming reaction. After film-forming is completed, then according to the invention, a short period of lowered power plasma-activated process is imposed in the presence of reaction gases, while simultaneously pumping to evacuate the reaction chamber, to remove residual chemical compound and thereby reduce the in-film particle number. The method of the invention includes flowing a carrier gas, such as one containing helium and nitrogen gases and reaction gases, such as NH
3
or O
2
or N
2
O into the chamber. Power to the plasma generator is slowly reduced to between about 5 to 50% of the power used for film forming, and preferably to between about 10 to about 20%, to promote reaction of any residual chemical compound in the chamber with the reaction gases. The chamber is also simultaneously and preferably continuously evacuated by pumping to remove the reacted residual chemical compound to prevent or minimize particle deposition.
The reduced power plasma can be achieved by several techniques including increasing gap spacing at a constant power or gradient power. Alternatively, it can be obtained by maintaining the same spacing as in the main film-forming process but with a smaller power source. In accordance with the invention, in-film particulates are reducd.
REFERENCES:
patent: 5854138 (1998-12-01), Roth et al.
Chen Hung-Chuan
Lin Yuh-Min
Su Shih-Chieh
Yao Liang-Gi
Applied Materials Inc.
Christensen O'Connor Johnson & Kindness PLLC
Hoang Quoc
Nelms David
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