Etching a substrate: processes – Gas phase etching of substrate
Reexamination Certificate
1999-10-29
2002-12-17
Mills, Gregory (Department: 1763)
Etching a substrate: processes
Gas phase etching of substrate
C216S006000, C134S001100, C438S003000, C438S742000
Reexamination Certificate
active
06495054
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an etching method of etching an oxide containing alkaline-earth metals as constituent elements, a chemical vapor growth apparatus for forming an oxide film containing alkaline-earth metals as constituent elements, and a cleaning method of the apparatus.
New materials that have not been conventionally used are beginning to be used in new semiconductor devices represented by very-large-scale semiconductor integrated circuits. So, chemical vapor deposition is beginning to be demanded to deposit thin films of these new materials. One of these new materials is barium strontium titanate ((Ba,Sr)TiO
3
):BST) which is a high-dielectric constant material used in a charge storage film (capacitive film) of a DRAM.
In the semiconductor device fabrication processes, dry etching superior in micro fabrication properties is widely used. However, alkali-earth metals such as Sr and Ba constructing the above material are not etched because the vapor pressure of a compound formed by a conventional etching gas is low.
Meanwhile, the semiconductor device fabrication processes extensively employ the formation of thin films by chemical vapor deposition (CVD) having high step coverage and capable of depositing in large areas. When a thin film is deposited by this CVD, a deposit sticks not only to a substrate for deposition but also to a reaction chamber exposed to a deposition gas or to jigs installed in the chamber. This deposit peels off owing to stress or mechanical stimulus, and the peeled dust particles fall on the substrate during deposition or during transfer of the substrate, thereby causing particle contamination of the formed thin film. Therefore, it is necessary to clean and remove the deposit, other than the objective deposit, sticking to the interior of the apparatus.
This cleaning method is desirably performed without disassembling the apparatus in order to raise the throughput. As this method of cleaning without disassembling the apparatus, a cleaning gas for changing the deposit into a substance having high vapor pressure is supplied into the apparatus to remove the deposit.
Unfortunately, alkaline-earth metals such as Sr and Ba constructing the aforementioned material cannot be removed because the vapor pressure of the compound formed by this conventional cleaning method is low.
A thin film containing alkaline-earth metals cannot be dry-etched and a chemical vapor deposition apparatus for depositing a thin film containing alkaline-earth metals cannot be cleaned with gas for the same reason: none of conventional etching gases and cleaning gases can form an alkaline-earth metal compound having high vapor pressure.
It is narrowly possible to etch a thin film containing alkaline-earth metals such as Ba and Sr by using chlorine trifluoride (ClF
3
) gas. However, a high temperature of 800° C. or more is necessary for the etching, and yet the etching rate of Ba and Sr is lower than that of Ti.
Additionally, under severe conditions in which ClF
3
is used at high temperatures, the corrosiveness of ClF
3
increases. The most serious problem is that SiO
2
is also etched when ClF
3
is used at high temperatures. SiO
2
is frequently used as interlayer dielectrics and a surface protective film in semiconductor devices. These SiO
2
-based films already formed are destroyed when a thin film containing alkaline-earth metals is dry-etched.
Also, a reaction chamber of a chemical vapor deposition apparatus is often made of quartz, and most jigs such as a substrate holder and a gas supply nozzle installed in the reaction chamber are made of quartz. Therefore, when a chemical vapor deposition apparatus for depositing a thin film containing alkaline-earth metals is cleaned by using a gas such as ClF
3
, quartz is eroded especially at high temperatures, resulting in destruction of the apparatus.
As described above, when a gas containing a halogen such as fluorine is used as an etching gas or a cleaning gas, no alkaline-earth metal compound having high vapor pressure is formed. Consequently, etching or cleaning takes a long time and hence is difficult to perform.
Also, when a fluorine-containing gas is used to etch or clean a chemical vapor growth apparatus, SiO
2
is corroded, and this destroys an interlayer insulating film or the apparatus.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an etching method capable of easily etching an oxide of an alkaline-earth metal.
It is another object of the present invention to provide an etching method which does not etch SiO
2
-containing layers in a semiconductor device, or an etching method which etches a thin film containing an oxide film of an alkaline-earth metal without etching quartz members of a chemical vapor growth apparatus, and to provide a chemical vapor growth apparatus, and a cleaning method of the chemical vapor growth apparatus.
To achieve the above objects, an etching method of the present invention comprises the steps of preparing an oxide layer containing at least one type of alkaline-earth metal; and etching the oxide layer containing at least one type of alkaline-earth metal by using, as an etching gas, either a halogen gas other than fluorine gas, or a gas containing at least one material selected from the group consisting of an interhalogen compound consisting of halogen elements other than fluorine, and a halogen hydride consisting of a halogen element other than fluorine and hydrogen.
The step of etching the oxide layer desirably includes a step of etching in an ambient at not less than 500° C.
The step of etching the oxide layer desirably includes a step of etching the oxide layer while changing an etching temperature.
The step of etching the oxide layer may includes:
a first etching step having a first etching condition; and
a second etching step having a second etching condition, and
the etching temperature in the first etching step is different from the etching temperature in the second etching step.
The second etching step is preferably successively performed after the first etching step, and the etching temperature in the first etching step is lower than the etching temperature in the second etching step.
The etching method may further comprise a step of repeating a plurality of times the step of successively performing the first and the second step.
The step of etching the oxide layer above-mentioned preferably includes a step of etching using chlorine gas as the etching gas.
The step of etching the oxide layer preferably includes a step of using a gas activated by plasma excitation as the etching gas.
The oxide layer above-mentioned is preferably a (Ba,Sr)TiO
3
layer.
Chlorides, bromides, and iodides of alkaline-earth metals have relatively high vapor pressures. So, a thin film containing an alkaline-earth metal can be etched by using chlorine, bromine, or iodine. Also, since F highly corrosive for SiO
2
is not contained, SiO
2
portions used in a semiconductor device or in a film formation apparatus are not damaged. Therefore, dry etching using chlorine, bromine, and iodine gases can be effectively used as a cleaning means of a film formation apparatus. Additionally, the etching temperature can be lowered when active halogen radicals are formed by activating a halogen.
Particularly chlorides of alkaline-earth metals have relatively high vapor pressures, so alkaline-earth metals contained in a thin film can be etched at a high temperature of 700° C. or more. However, in the temperature range of 700° C. or more within which alkaline-earth metals can be etched, chlorides of metals such as titanium and tantalum evaporate and at the same time redeposit by thermal decomposition. This makes etching difficult to perform. A thin film containing a plurality of metals including alkaline-earth metals can be dry-etched by dividing the dry etching step into: a step of preferentially dry-etching metals whose chlorides thermally decompose to redeposit at high temperatures, and a step of preferentially dry-etching the alkaline-earth metals.
Also, by
Eguchi Kazuhiro
Hieda Katsuhiko
Kiyotoshi Masahiro
Okumura Katsuya
Yamazaki Soichi
Alejandro Luz
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Mills Gregory
LandOfFree
Etching method and cleaning method of chemical vapor growth... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Etching method and cleaning method of chemical vapor growth..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Etching method and cleaning method of chemical vapor growth... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2980243