Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2001-01-12
2003-04-29
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S146000, C438S680000, C438S785000
Reexamination Certificate
active
06555421
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing a semiconductor device, and more particularly, it relates to such, a method and apparatus for manufacturing thin films of a uniform thickness on a substrate.
2. Description of the Related Art
When thin films are formed on a substrate, a film-forming apparatus of the sheet-feed type is used as one example.
An explanation will be made of the case in which a tantalum oxide thin film (Ta
2
O
5
film) is formed on a substrate as a concrete example. Generally, the tantalum oxide thin film is formed by means of a CVD method.
FIG. 11
is a schematic view showing one example of such conventional semiconductor manufacturing apparatuses for forming thin films of tantalum oxide on a substrate. As a raw material for the tantalum oxide thin film, pentaethoxy tantalum in a liquid state is used, and it is accommodated in a tank
21
which is disposed in a thermostatic chamber
22
. The temperature of the tank
21
is controlled at a constant temperature such as, for example, 35° C. by means of the thermostatic chamber
22
. An N2 gas supplied to the tank
21
from an N2 supply piping
28
pressurizes the interior of the tank
21
, so that the pentaethoxy tantalum, which is contained therein as a liquid raw material, is pushed out to a raw material supply piping
29
. The pentaethoxy tantalum in the form of a liquid taw material as described above is supplied from the raw material supply piping
29
to an evaporator
23
, and an N2 carrier gas is also supplied to the evaporator
23
from the N2 supply piping
28
. A film-forming gas evaporated by the evaporator
23
is introduced through the supply piping
24
into a reaction chamber
25
together with the above-mentioned N2 carrier gas. Simultaneous with this, oxygen is introduced into the reaction chamber
25
from an oxygen tank (not shown), so that the pentaethoxy tantalum is thermally decomposed in the reaction chamber
25
to form a tantalum oxide thin film on a substrate. After the formation of the tantalum oxide thin film, the atmosphere in the reaction chanter
25
is exhausted by a discharge pump
26
through an exhaust piping
27
.
In the prior art, to form a tantalum oxide thin film on a substrate uniformly, there have been proposed various configurations of the reaction chamber
25
, introduction and exhaust recipes for the film-forming gas, etc.
For example, Japanese Patent Application Laid-Open No. 7-94419 discloses a semiconductor processing apparatus which is constructed as follows. A flat reaction tube is provided in a heating space defined by a pair of parallel plate heaters with a substrate to be treated being disposed in the heating space. The reaction tube is provided at it opposite ends with a gas feed port and a gas exhaust port. The direction of flow of the film-forming gas can be switched over during an film-forming operation.
FIG. 12
illustrates the reaction chamber of the semiconductor processing apparatus as described in the above-mentioned Japanese Patent Laid-Open No. 7-94419. In this figure, an unillustrated substrate is horizontally disposed substantially in the center of the interior of the reaction tube
31
, and gas feed ports
32
,
33
and gas exhaust ports
34
,
35
are provided at opposite ends of the reaction tube
31
, the gas feed ports
32
,
33
being disposed in an opposed relation with respect to the gas exhaust ports
34
,
35
, respectively, with the substrate being interposed therebetween. For example, a gas supplied from the gas feed port
32
passes through the reaction tube
31
substantially in parallel with the substrate to be exhausted from the gas exhaust port
35
, as indicated by an arrow
36
in
FIG. 12
, thus forming a first thin film on the substrate. Subsequently, the direction of flow of the film-forming gas is reversed, that is, the film-forming gas is supplied from the gas feed port
33
to the reaction tube
31
, passing the surface of the substrate as indicated at an arrow
37
, and exhausted from the gas exhaust port
34
, thereby forming a second thin film on the substrate. Such a method of supplying a film-forming gas while alternately changing the direction of flow thereof is generally called a flip-flop method. The reason for adopting the flip-flop method is to counterbalance or offset an inclination that the thin film tends to have in the direction of flow of the film-forming gas, by reversing the flow of the film-forming gas.
Concretely, in cases where the film-forming gas is caused to flow in one direction from an upstream side to a downstream side along a surface of the substrate
11
so as to form a thin film thereon, as indicated at arrows
41
in
FIG. 13
, the thickness of the thin film thus formed tends to be thicker in a direction from the upstream to the downstream side, as illustrated in FIG.
14
. The reason for this phenomenon is considered as follows. That is, generally, the internal pressure of the reaction chamber or reaction tube
31
is as low as 25 Pa or so and the flow rate or speed of the film-firming gas is high, so that the film-forming gas, being not heated until it enters the reaction chamber, has a tendency that it is activated hardly at the upstream side but easily at the downstream side. Accordingly, in the prior art, the flip-flop method is used to provide a thin film on the substrate
11
substantially in parallel to a surface thereof, as illustrated in
FIG. 16
, by causing the film-forming gas to flow from the upstream side to the downstream side in parallel with the surface of the substrate
11
as indicated at arrows
41
in
FIG. 15
, and then causing the film-forming gas to flow in a reverse direction from the downstream to the upstream side as indicated at arrows
42
to thereby offset the inclination in the thickness of the thin film. As illustrated in
FIG. 16
, on a first layer
51
in the form of a thin film on a substrate
11
obtained by causing a film-forming gas to flow from an upstream to a downstream side as indicated at an arrow
41
, there is formed a second layer
51
in the form of a thin film by causing a film-forming gas to flow from the downstream to the upstream side as depicted at an arrow
42
, and hence it is intended to provide the formation of thin films which are substantially in parallel to a surface of the substrate
11
as a whole.
However, there is a problem in that in actuality, the use of the conventional film-forming method as referred to above could not provide a good result of thin film formation as illustrated in FIG.
16
.
FIG. 17
illustrates a cross section of thin films obtained by the above-mentioned Prior art technology. As is clear from this figure, the formation of thin films in parallel to a surface of a substrate
11
is not achieved although on a first layer
51
′ in the form of a thin film that is formed by causing a film-forming gas to flow in a direction from an upstream to a downstream side as indicated at an arrow
41
, there is provided a second layer
52
′ in the form of a thin film that is obtained by causing the film-forming gas in a reverse direction from the downstream to the upstream side as indicated at an arrow
42
.
The reason for this is that upon forming the thin films, the first layer
51
′ is influenced by the surface condition of the substrate
11
which is a base or backing layer for the formation of the first layer
51
″, so that an inclination in the thickness of the first layer
51
′ becomes remarkable, whereas the second layer
52
′ has a backing layer in the form of the first layer
51
′ which is of the same material as that of the second layer
52
″, thus providing a tendency not to create a thickness inclination. Therefore, the distribution of thickness of the thin films or layers is greatly influenced by the arrangement or condition of the first layer
51
″, so if the inclination of the first layer
51
′ is great, even the use of the flip-flop method could not achieve a uni
Matsuyama Naoko
Sasaki Sinya
Elms Richard
Hitachi Kokusai Electric Inc.
Luu Pho M.
McGinn & Gibb PLLC
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