Chemical deposition reactor and method of forming a thin...

Details Chemical deposition reactor and method of forming a thin... Chemical deposition reactor and method of forming a thin...

2001-02-14

2003-04-01

Lund, Jeffrie R. (Department: 1763)

Coating apparatus

Gas or vapor deposition

With treating means

C118S715000, C118S725000, C118S7230ER

Reexamination Certificate

active

06539891

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a chemical deposition reactor used in a chemical deposition apparatus where reactant materials are supplied discontinuously or sequentially so that the reactant materials are not mixed in gas phases, and more particularly, to a chemical deposition reactor capable of switching rapidly from one process gas to another. The present invention also relates to a method of forming a thin film for use in semiconductor or flat display devices using the above reactor.
BACKGROUND ART
In the manufacture of semiconductor devices, efforts for improving apparatuses and processes have been continued in order to form a high quality thin film on a substrate. Recently, processes for forming a thin film using surface reaction of a semiconductor substrate were proposed. In the processes, thin films are formed by following three methods: Reactant materials are discontinuously supplied to the substrate; a type of thin film is formed by an atomic layer deposition; or reactant materials are sequentially supplied one by one to the substrate. According to the above methods, a film having uniform thickness can be obtained on the whole substrate regardless of the surface roughness of a substrate and impurities in the film can be reduced, resulting in a high quality film.
However, because reactors used in conventional chemical deposition apparatuses are designed to form a thin film using a process where reactant materials are simultaneously supplied into the reactors, the reactors are not optimal for the above three methods.
In a reactor where chemical deposition materials are supplied over a semiconductor substrate, reactant gases usually flow downward over the semiconductor substrate. In this case, a shower head is usually disposed between a reactant gas inlet and the substrate for the uniform flow of the reactant gas over the substrate. However, such a configuration makes the gas flow complex and requires a large size reactor, making rapid switching of reactant gases difficult. Accordingly, the conventional reactor employing a shower head is inadequate for the process where reactant gases are sequentially supplied to the reactor.
On the other hand, in the manufacture of semiconductor or flat display devices, high quality thin films are required. Such thin films may include metal films, insulator films such as metal oxide films, metal nitride films and etc., films for capacitors, interconnects and electrodes, inorganic films used for diffusion prevention, and etc.
These thin films may be formed by a physical vapor deposition, for example a sputtering process. The sputtering process, however, forms thin films with poor step coverage, so a chemical vapor deposition method is usually employed to improve the step coverage.
One of the most common chemical vapor depositions of the prior art is carried out by an apparatus as shown in FIG.
1
A. Referring to
FIG. 1A
, process gases or other reactants
11
,
12
,
13
are supplied into a reactor
1
, respectively, through mass flow controllers
21
,
22
,
23
and valves
30
,
31
,
32
. In this case, a shower head
4
is utilized to obtain uniform flow
5
of the process gases. When a source material is liquid or solid having low equilibrium vapor pressures, a vaporizer
16
is also employed that can heat the source material in a suitable temperature to vaporize and can supply the vaporized source material into the reactor
1
with the carrier gas
13
. When the vaporizer is employed, the initial portion of the source material carried by the carrier gas
13
is exhausted via a bypass valve
33
and an outlet tube
18
due to the fluctuation of flow rate and source material concentration. Then, the bypass valve
33
is shut off and a valve
32
connected to a central supplying tube
17
is opened to supply the carrier gas into the reactor
1
.
The chemical vapor deposition of the prior art performed in this apparatus has the following features: At first, all process gases
11
,
12
,
13
required for the deposition are supplied into the reactor
1
at the same time so that the film is continuously deposited during the process times
11
′,
12
′,
13
′ as in an example shown in FIG.
1
B. At second, the shower head
4
is usually employed to make uniform flow of the process gases on the surface of a substrate.
This method has the following disadvantages: At first, since all process gases exist within the reactor at the same time, the process gases may react in gas phase thereby can deteriorate step coverage of the deposited film and/or produce particles which contaminate the reactor. At second, when using a metal-organic compound as a source material, it is difficult to deposit the film that does not contain carbon impurities. At third, in the case of depositing a multi-component film, all the reactant materials must react simultaneously while the supply of each reactant material is controlled separately by mass flow of the carrier gas, so it is very difficult to control the composition of the deposited film precisely.
To overcome the foregoing problems, a method is proposed in which the process gases are supplied separately as time-divisional pulses rather than supplied continuously.
An example of supplying process gases in this deposition method is shown in FIG.
2
A. Valves in a gas introducing part can be opened or closed so that the process gases can be supplied cyclically as time-divisional pulses into the reactor without being mixed with each other.
Referring to
FIG. 2A
, it can be seen that the process gases
11
,
12
,
13
in FIG. A are supplied in a cycle T
cycle
of
13
′,
12
′,
11
′ and
12
′. A film can be deposited by repeating this cycle. In general, purge gas
12
is supplied between the supply pulses of the reactants
11
and
13
so that the remaining reactants are removed from the reactor before the next reactant is supplied.
Hereinafter, a time-divisional deposition mechanism will be described. Chemical adsorption temperatures of the reactants onto the substrate are generally lower than thermal decomposition temperatures of the reactants. Therefore, when a deposition temperature is maintained higher than the chemical adsorption temperature of the reactant onto the substrate and lower than the thermal decomposition temperature of the reactant, the reactant supplied into the reactor only adsorbs chemically onto the surface of the substrate rather than decomposes. Then, the remaining reactant is exhausted out of the reactor by the purge gas supplied into the reactor. After that, another reactant is introduced into the reactor to react with the reactant adsorbed on the surface, and thus form a film. Because the reactant adsorbed on the substrate cannot form more than one molecular layer, film thickness formed in one supply cycle T
cycle
is constant regardless of amount or time of the supplied reactants. Therefore, as shown in
FIG. 2B
, the deposited film thickness is saturated as the supplying time elapses. In this case, the deposited film thickness is controlled only by the number of the repeated supply cycles.
In the other hand, when the deposition process temperature is no lower than the thermal decomposition temperature of the reactants, the deposited film thickness is proportional to the supply time of the reactants in the supply cycle because the reactants introduced into the reactor decompose continuously to form films on the substrate. In this case, deposited film thickness according to the supply time of the reactants is shown in FIG.
2
C.
However, the foregoing time-divisional deposition has problems as follows:
At first, the reactants used in the deposition process must react readily. Otherwise it is difficult to form a film by time-divisional deposition. In this case, a method is required that facilitate the chemical reaction even at low temperatures.
At second, the exhausting part of the apparatus may be contaminated with particles due to the reactions between the reactants. The gas-introducing part and the reactor may not be contaminat

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