Method of forming a thin film

Details Method of forming a thin film Method of forming a thin film

2000-12-06

2003-11-11

Meeks, Timothy (Department: 1762)

Coating processes

Direct application of electrical, magnetic, wave, or...

Plasma

C427S578000, C427S255280, C427S252000, C117S088000, C117S092000, C117S093000, C117S102000, C117S103000

Reexamination Certificate

active

06645574

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a deposition method of thin films required for manufacturing semiconductor devices, flat panel devices, and etc.
BACKGROUND ART
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
5
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. 1A
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 contaminated with the particles due to the reactions of the reactants because the reactants are separated by the purge gas. In the other hand, the exhausting part may be easily contaminated with particles because the reactants mix and react with each other at exhaust.
At third, it is required to supply inert purge gas between the reactant supply pulses to prevent gas-phase reactions in the gas-introducing part and the reactor, so the gas-supply cycle is complex, the time for a supply cycle is longer than absolutely necessary, and thus the deposition is slow.
A method is disclosed in the U.S. Pat. No. 5,916,365 in which a film is formed by repeating a gas-supply cycle, i.e., supplying first reactant gas into a reactor, exhausting remaining reactant gas within the reactor by a vacuum pump, supplying second reactant gas which is activated by passing through a radical generator using an RF power or other means, and exhausting remaining reactant gas by the vacuum pump.
The exhaust rate of the vacuum pump decreases as the pressure decreases, so it takes long time to exhaust the remaining reactant gases from the reactor with the vacuum pump. Therefore, in this method, it is difficult to have high growth rate of the film per unit time when it desired to exhaust the remaining reactant gases completely. When the exhausting time is too short, the reactant gases remain in the reactor so that the two reactant gases mix and react in gas phase. Furthermore, in the method of the U.S. Pat. No. 5,916,365, it is difficult to maintain stable plasma in the reactor because the supply and exhaust of the reactant gases cause wide pressure variation in the reactor.
DISCLOSURE OF INVENTION
Therefore, it is an object of the present invention to provide a method which can form a thin film effectively even if reactants do not react readily in a time-divisional source supply chemical vapor deposition method.
It is another object of the present invention to provide a method which can minimize supply time of a purge gas in a gas-supplying cycle to reduce cycle time in a time-divisional source supply chemical vapor deposition.
I

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