Coating apparatus – Gas or vapor deposition
Reexamination Certificate
1999-07-08
2002-07-09
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
Reexamination Certificate
active
06416584
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to manufacturing of a semiconductor device, and more particularly, forming of a thin film such as a dielectric film in a capacitor.
2. Description of the Related Art
The capacitance (C) of a capacitor is proportional to the area (A) of the capacitor's electrodes and a dielectric constant (&egr;) of a dielectric material between the electrodes, and inversely proportional to distance (d) between the electrodes, as shown in the following equation.
C &agr;&egr;(A/d)
Thus, increasing the area (A) of electrodes, using a dielectric film having a high dielectric constant, or decreasing the distance between the electrodes can increase the capacitance (C) of the capacitor.
As semiconductor devices become more highly integrated, the areas available for capacitor formation within semiconductor devices become smaller. Accordingly, techniques have been developed for increasing the capacitance of capacitors formed in small areas. One technique uses three-dimensional electrodes to increase the area (A) of the electrodes, but the three-dimensional electrodes are subject to structural restrictions. Use of a dielectric film having a high dielectric constant (&egr;) can increase the capacitance (C) of a capacitor and permit high semiconductor integration. In addition, a thinner dielectric film reduces the distance (d) between electrodes and produces higher capacitance of a capacitor, but reducing the distance (d) between the electrodes often has the drawback of increasing the leakage current of the capacitor.
Recently, tantalum oxides, such as a tantalum pentoxide (Ta
2
O
5
) having a high dielectric constant (&egr;), have been tried as dielectric films for capacitors. However, with a tantalum pentoxide film, leakage current can be large when the film is thin. A problem with tantalum pentoxide is non-uniform film deposition, and oxygen and carbon impurities often allow the leakage current through weak portions of the tantalum pentoxide film. To solve the leakage problem, several methods have been suggested. Among the suggested methods is a dry-oxygen (dry-O
2
) annealing, and a low temperature ultraviolet-ozone (UV-O
3
) annealing at 500° C. or less followed by a dry-oxygen annealing, IEEE Transactions on Electron Devices, Vol. 38, No. 3, March 1991, entitled “UV-O
3
and Dry-O
2
; Two-Step Annealed Chemical Vapor Deposited Ta
2
O
5
Films for Storage Dielectrics of 64-MB DRAM's”, by Shinriki and Masayuki Nakata, which is hereby incorporated by reference in its entirety, discloses the latter method. In the known methods, formation and UV-O
3
annealing of the tantalum oxide film are respectively performed in separate chambers shown in
FIGS. 1 and 2
.
Referring to
FIG. 1
, a chamber
8
for forming a tantalum oxide film includes a shower head
10
in an upper portion of chamber
8
. Shower head
10
receives pentaethoxytantalum as a source gas for the tantalum oxide film from a supply line
12
and oxygen (O
2
) as a reaction gas from a second gas supply line
14
. A first valve
12
a
and a second valve
14
a
are in the first and second gas supply lines
12
and
14
, respectively. A susceptor
16
is on the floor of the chamber
8
for mounting of a wafer
18
. A pumping line
20
connects to the bottom of the chamber
8
, and a pump
22
attaches to the pumping line
20
. After forming the tantalum oxide film, wafer
18
becomes a wafer
23
, which is transferred to an annealing chamber
9
(FIG.
2
). In annealing chamber
9
, a UV-O
3
annealing is performed on the tantalum oxide film.
Referring to
FIG. 2
, UV-O annealing chamber
9
includes a quartz window
11
on the ceiling thereof. A UV lamp housing
13
includes a UV lamp
15
for generating UV rays that pass through quartz window
11
into chamber
9
. A shower head
17
below quartz window
11
is also made of quartz to uniformly pass UV rays into chamber
9
. Shower head
17
supplies a gas mixture containing oxygen (O
2
) and ozone (O
3
) gases that form an oxide film with a uniform thickness. Shower head
17
connects to an ozonizer
19
installed outside chamber
9
. A susceptor
21
is on the floor of chamber
9
and below shower head
17
, and wafer
23
having the tantalum oxide film is on susceptor
21
. An ozone decomposer
25
connects to a bottom of chamber
9
via a pumping line
27
, and a pump
29
connects to ozone decomposer
25
.
As described above, the conventional method forms a tantalum oxide film and uses a separate chamber for a UV-annealing to remove defects from the tantalum oxide film.
SUMMARY OF THE INVENTION
In accordance with an embodiment of the present invention, an apparatus for forming a dielectric film on a semiconductor substrate includes a shower head on in a reaction chamber, and a mounting stand in the reaction chamber, below the shower head. The semiconductor substrate is loaded on the mounting stand. A first gas line for supplying a source gas for depositing the dielectric film and a second gas supply line for supplying a reaction gas for depositing the dielectric film and an annealing gas, typically ozone, for annealing the dielectric film connect to the shower head.
When the dielectric film is a composite dielectric film, the first gas supply line may include several lines, which supply respective source gases for the layers of the composite dielectric film. An ozonizer connects to the second gas supply line in parallel. The second gas supply line can include respective gas supply lines for supplying the reaction gas and the annealing gas.
A supply line for an inert gas such as nitrogen (N
2
) or argon (Ar) gas may connect to the second gas supply line for purging the reaction chamber and the second gas supply line. The inert gas supply line and the second gas supply line can respectively include mass flow controllers (MFCs). An ozone decomposer connects to the reaction chamber via a pumping line between the ozone decomposer and the bottom of the reaction chamber. A pump connects to the ozone decomposer.
The apparatus may further include a second pumping line, which bypasses the ozone decomposer, to protect the ozone decomposer from contamination caused by gas discharged during deposition of a dielectric film. The ozone decomposer connects to the ozonizer via an ozone purifying line, and a control valve on the pumping line directs the gas flow from the reaction chamber to the second pumping line or the ozone decomposer.
According to another embodiment of the present invention, a reaction chamber includes five (first through fifth) semiconductor substrate mounting stands. Each of the second through fifth semiconductor substrate mounting stands faces respective shower heads. The chamber also includes a gas spraying means capable of forming air curtains of an inert gas around the shower heads.
According to an aspect of the invention a method for forming a dielectric film includes (a) depositing a dielectric film on a semiconductor substrate, (b) annealing the dielectric film at a temperature lower than a crystallization temperature of the film, and (c) annealing the dielectric film at a temperature higher than the crystallization temperature. When a tantalum oxide dielectric film is formed, the tantalum oxide film is first annealed at approximately 450° C. in an ozone or oxygen atmosphere and then annealed in a dry-oxygen or wet-oxygen atmosphere.
The steps (a) and (b) or the steps (a), (b), and (c) can be performed in situ in an apparatus. In particular, a reaction chamber including a shower head for source and annealing gases and a susceptor for heating the semiconductor substrate can perform steps (a) and (b). A first gas supply line that supplies a source gas for forming the dielectric film and a second gas supply line that supplies a reaction gas for forming the dielectric film and an annealing gas connect to the shower head. A second dielectric film may be further formed on the dielectric film and then annealed in situ in the same chamber. In the step (b), the semiconductor substrate can be ann
Hyung Yong-woo
Park Young-wook
Won Seok-jun
Heid David W.
MacArthur Sylviar
Mills Gregory
Samsung Electronics Co,. Ltd.
Skjerven Morrill LLP
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