Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
2002-04-22
2004-09-28
Norton, Nadine G. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S714000, C438S717000, C438S719000, C438S725000
Reexamination Certificate
active
06797634
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to a method of conditioning an etching chamber and a method of processing semiconductor substrates that form semiconductor devices, including the conditioning of the etching chamber. This invention is particularly advantageously utilized in etching of multi-layered structure comprising an organic bottom anti-reflective coating (BARC) and a conductive material layer in the same etching chamber.
2. Description of Related Art
Formation of fine patterns with high dimensional controllability and high selectivity is required to increase the density of semiconductor integrated circuits. The fine patterns are usually formed by selectively etching a material film over a surface of a semiconductor substrate (e.g., a wafer) using fine photo-resist patterns as a mask. Recently, deep UV (DUV) light such as KrF or ArF excimer laser light is used to form the resist patterns. In photolithography, using DUV light, a BARC layer functioning as an anti-reflection layer is widely used.
In a process using the BARC, a BARC layer is formed between the resist film and the material film to be etched. After the resist pattern is formed by photolithography, the BARC layer is patterned using the resist pattern as a mask. Plasma etching using an etching gas atmosphere containing oxygen as a primary etching species forms the BARC pattern. Then, the material layer is patterned using stacked mask of the resist and the BARC patterns.
When forming gate electrodes of transistors, the material film may be a polysilicon film on a thin gate dielectric film formed on a surface of the semiconductor substrate. A bulk of the polysilicon film may be etched using a chlorine-based etching gas atmosphere (main etching gas atmosphere), such as Cl
2
/HBr/O
2
or Cl
2
/O
2
. After the bulk of the polysilicon film is etched, the polysilicon film is over-etched using another etching gas atmosphere (over-etching gas atmosphere) in order to remove residues of the polysilicon film. The over-etching is made by, for example, HBr/O
2
. The over-etching gas atmosphere provides a high etching rate ratio (selectivity) over the underling gate dielectric film. Therefore, the residue of the polysilicon film can be removed without significantly etching the gate dielectric film.
In the etching for forming gate electrodes, a high-density plasma etching apparatus, such as ECR (Electron Cyclotron Resonance) plasma etching apparatus or ICP (Inductive Coupled Plasma) etching apparatus, is used. Usually, a plurality of wafers that forms a lot, which are housed in one or more cassettes, are transferred to an etching apparatus. Each of the wafers housed in the cassette is processed one by one by the etching apparatus with a same condition.
When the plurality of wafers is successively processed, by-products formed during the etching are deposited and accumulated on the inner wall of an etching chamber of the apparatus. The accumulation of the by-product forms particles that cause pattern defects. The accumulated by-product releases gasses to the etching gas atmosphere that disturb the etching process. Therefore, the accumulated by-product is removed by plasma cleaning. The etching chamber is subjected to the plasma cleaning after processing, for example, all the wafers in a lot, all the wafers housed in a cassette, or a certain number of wafers.
A fluorine-based gas, such as SF
6
or NF
3
, is used for the plasma cleaning. After the plasma cleaning, fluorine-containing species remains in the etching chamber. The residual fluorine-containing species release fluorine into the etching gas atmosphere used for etching polysilicon layer. The fluorine released into the etching gas atmosphere decreases the selectivity to the underlying gate dielectric layer.
A dummy etching is conducted using a dummy wafer and a dummy etching gas atmosphere having a composition similar to, or the same as, the main etching gas atmosphere used for etching the polysilicon layer, e.g., Cl
2
/HBr/O
2
. The residual fluorine content in the etching chamber is reduced. After these pretreatment steps, the first wafer is processed.
In the actual process, the top BARC film is etched with an oxygen-based etching gas atmosphere, such as Cl
2
/O
2
or Cl
2
/O
2
/Ar. A bulk of the polysilicon layer is etched using a chlorine-based etching gas atmosphere, such as Cl
2
/HBr/O
2
. The polysilicon layer is over-etched to remove residue of the polysilicon using another etching gas atmosphere containing oxygen, such as HBr/O
2
. In the etching of the BARC layer and the polysilicon layer, optical emission from the plasma is monitored to automatically detect the completion, that is, the end point, of the etching.
Thus, according to related etching methods, after a cleaning using a fluorine-containing gas atmosphere, and a dummy etching using a Cl
2
/HBr/O
2
gas atmosphere, a plurality of wafers having the BARC layer is successively etched.
However, this inventor has found as a result of various experiments and studies that according to this related method, the size of the etched pattern changes during the successive processing of the wafers. That is, the size in the first wafer is the largest among those of the processed wafers and the sizes in the subsequently processed wafers gradually decrease and reach to a substantially constant value. Thus, a first problem is that the pattern size varies in the short term. Secondly, the inventor has also found that as the pattern size tends to gradually increase according to the number of processed wafers, long-term variation of the pattern size also becomes a problem.
SUMMARY OF THE INVENTION
Accordingly, it is a first object of this invention to provide a method for preventing the pattern size variation in the short term.
Methods of conditioning an etching chamber for processing a semiconductor substrate, and methods of processing a plurality of semiconductor substrates for forming semiconductor devices are performed in accordance with the first object of this invention. The substrate comprises: a conductive material layer on a surface of the substrate; a BARC layer stacked over the conductive material layer; and a mask pattern formed over the BARC layer.
According to an aspect of this invention, the processing of the semiconductor substrate comprises: etching the BARC layer using a first etching gas atmosphere containing oxygen; and etching the conductive material layer using a second etching gas atmosphere. The method of conditioning, before processing the semiconductor substrate, comprises: conducting a dummy run in the etching chamber using a dummy run gas atmosphere containing at least one of chlorine and bromine; and conditioning the etching chamber after conducting the dummy run using a conditioning gas atmosphere containing oxygen.
According to another aspect of this invention, the method of conditioning, before processing the semiconductor substrate, comprises: conducting a dummy run in the etching chamber using a dummy run gas atmosphere to increase an effective amount of oxygen radical scavenging species in the etching chamber; and conditioning the etching chamber after conducting the dummy run using a conditioning gas atmosphere to adjust the effective amount of oxygen radical scavenging species in the etching chamber.
According to another aspect of this invention, the method of a plurality of semiconductor substrates for forming semiconductor devices comprises: a. introducing one of the plurality of semiconductor substrates in an etching chamber; b. etching the organic material layer using a first etching atmosphere containing oxygen; c. etching the conducting material layer using a second etching gas atmosphere; and repeating steps a through c until all of the plurality of semiconductor substrates are processed. The method of processing further comprises a method of conditioning, before processing the plurality of semiconductor substrates, comprising: conducting a dummy run in the etching chamber using a dummy run gas atmosphere containing at least one of chlorine and
Kawasaki Microelectronics Inc.
Norton Nadine G.
Oliff & Berridg,e PLC
Tran Binh X.
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