Coating processes – Coating by vapor – gas – or smoke
Reexamination Certificate
1999-11-04
2002-11-05
Meeks, Timothy (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
C118S715000
Reexamination Certificate
active
06475563
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a chemical vapor deposition method and apparatus for forming various deposited films such as metal films, semiconductor films and insulating films used in memory devices such as semiconductor devices and optical magnetic disks or in flat panel display devices. More particularly it relates to a chemical vapor deposition method and apparatus making use of a liquid starting material.
2. Related Background Art
Deposited films formed by chemical vapor deposition method (CVD method) using appropriate apparatus therefore (CVD apparatus) can be roughly grouped into metal films, semiconductor films and insulating films.
In the case of semiconductor films, a film forming method capable of obtaining uniform films with fewer faults is desired. As for insulating films, uniform films are also desired and a film forming method that can achieve excellent coating properties on step portions is desired. This is because most insulating films are used to insulate wirings from each other in an integrated circuit (IC) or to protect its uneven surface.
In the case of metal films, a film forming method that can achieve excellent uniformity and coating performance on step portions is also desired as in the case of the insulating films. This is because the metal films are mostly used in wiring materials for ICS. In such instances the coating properties on step portions at the holes thereof are required so that upper and lower wirings can be connected via openings called contact holes or through holes.
FIG. 1
diagrammatically illustrates the prior art CVD apparatus used for a prior art CVD method.
In
FIG. 1
, reference numeral
403
denotes a reaction chamber formed of quartz or the like, provided with substrate holders
410
that are disposed in plurality to Support thereon a corresponding number of substrates
409
on which films are to be formed. Reference numeral
408
denotes an exhaust pipe, which is connected to a main pump
404
comprised of a mechanical booster pump and an auxiliary pump
405
comprised of a rotary pump. The pumps are used to evacuate the inside of the reaction chamber
403
.
As for a gas feeding system, a bomb (bubbler)
402
having a bubbling mechanism that bubbles a liquid starting material, a gas pipe
406
through which carrier gas for the bubbling is fed, a valve
401
, and a gas pipe
407
through which vaporized starting materials are fed into the reaction chamber
403
are provide.
Such a conventional CVD apparatus can be used so long as routine film formation is carried out, but it is sometimes unsuitable provide fine structure or to form large area films as recently demanded. In other words, conventional apparatus are poor multi-purpose uses i.e., adaptability to any CVD methods. This problem will be discussed below by giving an example.
Recently, as materials for the wiring of highly integrated semiconductor devices called VLSI or ULSI, aluminum films formed not by sputtering but by CVD have attracted notice. In particular, in CVD methods making use of an organic compound comprising an organoaluminum compound, it is reported that conditions for deposition differ greatly between an insulator and a conductor. Hence, selective deposition can be made where aluminum is deposited only on the conductor or a semiconductor. This selective deposition of aluminum is very useful when fine integrated circuits are fabricated. In particular, when the ratio of depth to diameter (aspect ratio) of a hole is more than 1, the selective deposition can provide aluminum wiring that can not be realized by sputtering which is a substitute technique. In sputtering, disconnection occurs when the hole has a large aspect ratio. The reason therefore will be explained below with reference to
FIGS. 2A
to
2
C. In
FIGS. 2A and 2B
, reference numeral
201
denotes a monocrystalline silicon substrate;
202
, an insulating film such as silicon dioxide film; and
203
, a wiring material such as aluminum.
FIG. 2A
illustrates how the wiring is formed when the hole has a small aspect ratio, and
FIG. 2B
how the wiring is formed when the hole has a large aspect ratio of 1 or more.
In sputtering, a hollow
204
or a void
205
is formed. On the other hand, in selective deposition by CVD, the hole is completely filled with aluminum
303
as shown in
FIG. 2C
, and there is a very low probability of disconnection.
In
FIG. 3
, reference numeral
301
denotes a silicon substrate;
302
, an insulating film such as silicon dioxide film;
303
, a metallic material such as aluminum deposited by CVD; and
304
, wiring of aluminum deposited by sputtering or CVD.
Thus, in the case when the wiring of a fine semiconductor device is fabricated using the CVD apparatus shown in
FIG. 1
, a carrier gas CGS such as hydrogen, whose pressure is reduced by means of a reducing valve
401
, is fed to the bubbler
402
. Most of material gases that enable the selective deposition of aluminum are liquid at room temperature, as exemplified by dimethylaluminum hydride (DMAH) and triisobutylaluminum (TIBA). For this reason, the bubbling, i.e. the step of generating bubbles in the bubbler
402
is carried out, so that a mixed gas comprised of the carrier gas and saturated vapor of organoaluminum compound such as DMAH is fed into the reaction chamber. The mixed gas is thermally decomposed on the heated semiconductor substrates
409
, and aluminum is deposited on the substrate as a result of its surface reaction with the substrates.
Unreacted gas in the reaction chamber
403
is exhausted outside by means of the main pump
404
and auxiliary pump
405
.
However, difficulties have been encountered in scaling-up an experimental CVD apparatus that has stably achieved selective deposition to a mass-production CVD apparatus.
This results in an increase in faults not only in the case of the metal films but also in the case of the semiconductor films, and results in a lowering of step portion coating properties in the case of the insulating films.
According to a finding made by the present inventors, the poor general-purpose properties are caused by the constitution of the conventional CVD apparatus, as follows:
First, the mixing ratio of the starting material liquid compound and other gas can only be very poorly controlled.
Second, a temperature change in the vicinity of the bubbler causes a change in the mixing ratio of the compound.
Third, residual gases in the bubbler cause a change in the mixing ratio of the compounds.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a chemical vapor deposition method and apparatus that can stably good quality deposited films even if there are changes in environmental conditions or changes in operational parameters.
Another object of the present invention is to provide a chemical vapor deposition method and apparatus that has excellent operability and mass-productivity and reduces production cost.
Still another object of the present invention is to provide a chemical vapor deposition method and apparatus that can form deposited films that are uniform over a wide area, cause less unwanted faults and can be formed in good step portion coating properties.
The present invention provides an apparatus for forming a gaseous starting material from a liquid starting material and feeding the gaseous starting material into a reaction chamber of the CVD apparatus comprising;
a container that holds the liquid starting material, pressure reducing means for reducing the pressure inside the container, and heating means for heating the liquid starting material held in the container; the liquid starting material being boiled, and a CVD method making use of the apparatus.
The present invention also provides an apparatus for feeding a starting gas into a reaction chamber with starting gas feeding means and depositing a thin film on a substrate placed in the reaction chamber, wherein;
the starting gas feeding means comprises a heating apparatus comprising a heating member having a plurality of through-holes t
Hayakawa Yukihiro
Kataoka Yuzo
Kawasumi Yasushi
Makino Kenji
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Meeks Timothy
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