Coating apparatus – Gas or vapor deposition
Reexamination Certificate
1998-09-09
2001-01-30
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
Reexamination Certificate
active
06179920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a CVD apparatus for forming a thin film having a high dielectric constant, and more specifically to a CVD apparatus for forming a variety of thin films, in particular a thin dielectric film such as is used in a semiconductor memory, by Chemical Vapor Deposition (CVD) method. The present invention also relates to a method of forming such dielectric thin film using the CVD method.
2. Description of the Background Art
In recent years, there has been a rapid advancement in the integration of semiconductor memory and devices. For instance, device capacity (number of bits) in a dynamic random access memory (DRAM) has quadrupled in three years. This integration aims at achieving the reduction in size of a device, lower power consumption, and lower cost, and so on. Regardless of the improvement in integration, however, a capacitor, being a DRAM component, must be able to accumulate a certain amount of electric charges. Thus, along with the increase in integration of a device, attempts have been made to minimize the thickness of a capacitor dielectric film or to increase the area of a capacitor by making its shape complex.
Nevertheless, it has become difficult to reduce the film thickness of a conventional capacitor with SiO
2
as its main dielectric material. Instead, as a noted alternative measure for increasing storage charge density, the dielectric film material of a capacitor may be replaced with film material having a higher dielectric constant. By using high dielectric constant material, an increase in storage charge density is achieved which is comparable to that obtained by the conventional method of reducing film thickness. Moreover, if a thin film with a high dielectric constant can be used, the film can be of a certain thickness, and the use of a high dielectric constant material may provide advantages with regard to film deposition processes and film reliability.
Most importantly, it is required that such a capacitor dielectric film be a thin film with a high dielectric constant as described above and have small leakage current. The desirable target values for these characteristics, in general, are considered to be approximately 0.5 nm or below for film thickness in SiO
2
equivalent and 2×10
−7
A/cm
2
or below for leakage current density at the voltage application of 1V.
As such, oxide type dielectric films including tantalum oxide, lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), strontium titanate (ST), barium titanate (BT), and barium strontium titanate (Ba, Sr) TiO
3
(hereafter referred to as BST) seem promising. Moreover, several methods have been devised for producing these thin films, and are being put to practical use experimentally.
Generally, to form a thin film on an electrode for a capacitor of a DRAM having minute steps, film deposition employing a CVD method which provides good coverage to surfaces having complex shape is most advantageous in simplifying the process. In a CVD method, organometallic compound containing a given metal is used as the thin film source having a high dielectric constant. By vaporizing the source and spraying the resulting gas onto a substrate, a thin film with a high dielectric constant is formed. It has been a big problem, however, that a CVD source with a stable and good vaporization characteristic does not exist. This is largely due to the unsatisfactory vaporization characteristic, by heating, of the compound of metal and &bgr;-diketon-type dipivaloylmethane (hereinafter referred to as DPM) frequently used as a CVD source.
It was under such circumstances that the applicants proposed in the Japanese Patent Laying-Open No. 7-268634 a CVD source being produced by dissolving a conventional solid material in organic solvent called tetrahydrofuran (THF) and thus having a greatly enhanced vaporization characteristic. Further, a CVD apparatus using liquid source was developed which vaporizes the liquid source and supplies it stably to a reaction chamber. They have also found that this apparatus can be utilized for depositing a high dielectric constant thin film having good surface morphology and electrical characteristics.
Even the use of this CVD apparatus using liquid source, however, has been discovered as not being capable of providing a dielectric film with good stable characteristics that last a long time. Upon examination, it has become apparent that this problem is caused by the very small amount of vaporization residue produced in the vaporization process.
Also, it has been discovered that the vaporizer for making a liquid source proposed by ATM Co. Ltd. in the United States (U.S. Pat. No. 5,204,314) does not provide sufficiently stable film deposition due to the formation of a solid in the portions where the source vaporizes and the consequent blocking of the tubes.
The arrangement of the conventional CVD apparatus using liquid source will be described below.
FIG. 5
is a schematic diagram depicting the representation of a conventional CVD apparatus using liquid source. Here, an example is given in which the BST film is deposited using reactive gas O
2
and the liquid source having solid Ba (DPM)
2
, Sr (DPM)
2
, and TiO (DPM)
2
dissolved in THF. The CVD apparatus includes a source gas supply tube
1
, a reactive gas supply tube
2
, and a reactor
3
. A heating stage
4
is provided in the reactor
3
. A susceptor
5
is provided on the heating stage
4
. The susceptor
5
supports a substrate
6
. A diffusion board
7
is provided in the upper portion of the reactor
3
. Pressure gauges
8
a
,
8
b
are provided in the reactor
3
. An exhaust passage
11
is connected to the reactor
3
. A vacuum valve
9
and a pressure controller
10
are provided somewhere along the exhaust passage
11
. The CVD apparatus also includes a vaporizer
21
, a vaporizer heater
22
, a constant temperature box
23
, a tube heater
24
, and a mixer
25
.
The N
2
gas
13
a
having its amount controlled by a gas flow rate controller
16
flows through a connection tube
26
into the vaporizer
21
. Ba (DPM)
2
/THF in a liquid source vessel
17
is pressurized by the N
2
gas
13
a
through a pressure tube
14
, has its amount controlled by a liquid flow rate controller
15
, and is sent into the vaporizer
21
through the connection tube
26
. Sr (DPM)
2
/THF in a liquid source vessel
18
is pressurized by the N
2
gas
13
a
through a pressure tube
14
, has its amount controlled by a liquid flow rate controller
15
, and is sent into the vaporizer
21
through the connection tube
26
.
TiO (DPM)
2
/THF in a liquid source vessel
19
is pressurized by the N
2
gas
13
a
through a pressure tube
14
, has its amount controlled by a liquid flow rate controller
15
, and is sent into the vaporizer
21
through the connection tube
26
.
THF in a liquid source vessel
20
is pressurized by the N
2
gas
13
a
through a pressure tube
14
, has its amount controlled by a liquid flow rate controller
15
, and is sent into the vaporizer
21
through the connection tube
26
.
Next, the operation will be described.
The N
2
gas
13
having its flow rate regulated by the gas flow rate controller
16
flows through the connection tube
26
. The solution sources in liquid source vessels
17
,
18
,
19
,
20
pressurized by the N
2
gas
13
a
through pressure tubes
14
are provided into the connection tube
26
, and having their amount controlled by the liquid flow rate controllers
15
, are supplied to the vaporizer
21
. Thereafter, the supplied liquid sources run into a large area of the inner wall of the vaporizer
21
heated by the vaporizer heater
22
and instantly vaporize. The vaporized sources inside the vaporizer
21
pass through the source gas supply tube
1
heated by the constant temperature box
23
and the tube heater
24
and are supplied into the reaction chamber
3
a
. The reactive gas
2
b
, on the other hand, passes through the reactive gas supply tube
2
heated by the constant temperature box
23
Horikawa Tsuyoshi
Kawahara Takaaki
Tarutani Masayoshi
Yamamuka Mikio
MacArthur Sylvia R
McDermott & Will & Emery
Mills Gregory
Mitsubishi Denki & Kabushiki Kaisha
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