Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
2001-04-12
2002-09-10
Lebentritt, Michael S. (Department: 2824)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
C438S761000, C438S763000, C438S778000
Reexamination Certificate
active
06448191
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to methods of forming high dielectric constant thin films, and more specifically to a method of forming a high dielectric constant thin film used for a semiconductor memory or the like. The present invention also relates to a method of manufacturing a semiconductor device provided with such high dielectric constant thin film.
2. Description of the Background Art
Recently, semiconductor memories or devices have been increasingly reduced in size. In a dynamic random access memory (a DRAM), for example, the number of bits has quadrupled in three years. Such rapid reduction in size is intended for high integration degree of the device, reduction in power consumption and cost, or the like. However, even if the integration degree increases, a capacitor of the DRAM must be provided with a prescribed capacitance. Therefore, a thickness of a film of a capacitor material must be reduced. With SiO
2
which has conventionally been used, it is difficult to reduce the thickness of the film. If the material provided with higher dielectric constant is employed, a sufficient capacitance would be ensured as in the case of the reduction in the thickness of the film. Thus, many studies have been done for utilizing a high dielectric constant material for the memory device.
The most important requirement for the capacitor material is that it is a thin film having the above mentioned high dielectric constant and small leakage current. Namely, as long as the high dielectric constant material is used, a thickness of the film must be as small as possible and the leakage current must be a minimum value. Generally, it is preferable that the thickness of the film is at most 0.5 nm of an equivalent SiO
2
thickness and a leakage current density when 1V is applied is at most 2×10
−
7
A/cm
2
. In the case of the thin film formed on an electrode for a capacitor of the DRAM having a step portion, the film must be formed by CVD (Chemical Vapor Deposition) providing high conformity even in the case of a complicated shape. However, there is no such material for CVD that has stable and sufficient vaporization property. This is because a &bgr;-diketone type dipivaloylmethanate (hereinafter abbreviated as DPM) compound, which is often used as the material for CVD, is not provided with sufficient vaporization property by heating.
In this context, the present inventor has found that the effect of the vaporization property dramatically increases when a conventional solid material is dissolved in an organic solvent of tetrahydrofuran (hereinafter abbreviated as THF), and proposed that the material should be used for CVD (Japanese Patent Laying-Open No.5-299365). However, it has been found that a good result cannot necessarily be obtained even when the material is used for formation of a dielectric film using a CVD apparatus for a liquid material which has conventionally been used for forming an SiO
2
film. Then, the present inventor has developed a CVD apparatus for a liquid material capable of sufficiently vaporizing the liquid material and stably supplying it for a reaction chamber (Japanese Patent Laying-Open No. 6-310444 and No. 7-94426). However, even when the dielectric film is formed by the CVD apparatus for vaporizing the solution, stable and sufficient film property (including electrical property) is not necessarily obtained.
FIG. 5
is a schematic illustration showing a CVD apparatus for forming a high dielectric constant thin film which has been disclosed in Japanese Patent Laying-Open No. 9-219497.
Referring to
FIG. 5
, a solution
14
in which a solid of Ba (DPM)
2
is dissolved in a solvent of THF (the solution is hereinafter abbreviated as Ba (DPM)
2
/THF), Sr (DPM)
2
/THF
15
and Ti (t-BuO)
2
(DPM)
2
/THF
16
are fed to a vaporizer
23
through liquid mass flow controllers
19
and air valves
22
. THF
17
is fed to vaporizer
23
through liquid mass flow controllers
19
and air valves
21
. N
2
carrier gas
18
is fed to vaporizer
23
through gas flow controller
20
and air valve
21
. Vaporizer
23
is provided above a reaction chamber
32
. A susceptor
30
with a heater
31
is provided in reaction chamber
32
. A substrate
29
is placed on susceptor
30
. A gas nozzle
28
is provided on a ceiling of reaction chamber
32
. The material gas which has been fed to vaporizer
23
is mixed with O
2
gas
33
in a mixer
27
, and supplied for reaction chamber
32
through gas nozzle
28
. A vent is denoted by a reference numeral
26
, and air valves on the sides of vent and reaction chamber are respectively denoted by
24
and
25
. A pressure controller
34
is provided below reaction chamber
32
.
Now, a method of manufacturing a high dielectric constant thin film using a conventional CVD apparatus for forming the high dielectric constant thin film will be described.
Referring to
FIG. 5
, a mixture of Ba (DPM)
2
/THF
14
, Sr (DPM)
2
THF
15
, Ti (t-BuO)
2
(DPM)
2
/THF
16
, THF
17
and N
2
carrier gas
18
are fed to vent
26
from vaporizer
23
, so that a flow of the mixture of the gas and liquid is obtained. O
2
gas
33
is supplied for reaction chamber
32
and pressure controller
34
is adjusted, so that a pressure in reaction chamber
32
is set at a desired level (for example at 5 Torr). Air valve for vent
24
is closed and, at the same time, air valve for reaction chamber
25
is opened. Thus, the mixture of gas and liquid is supplied for reaction chamber
32
, and a film of (Ba, Sr) TiO
3
(hereinafter abbreviated as a BST thin film) of Stoichiometric is formed on substrate
29
.
FIG. 6
is a cross sectional view showing a semiconductor device thus formed. Referring to
FIG. 6
, a poly-Si plug
4
is formed in a silicon substrate
2
. A barrier metal
3
is formed on poly-Si plug
4
. An Ru storage node
1
is formed on barrier metal
3
. A BST thin film
35
including TiO (DPM)
2
is formed to cover Ru storage node
1
. When thicknesses
6
and
7
of BST thin film
35
formed on Ru storage node
1
are respectively d
max
and d
min
, a distance
8
between adjacent Ru storage nodes
1
,
1
is W (~0.13 &mgr;m) and a height
9
of Ru storage node
1
is D (~0.36 &mgr;m), a coverage d
min
/d
max
is at most 50% for an aspect ratio D/W (at least 3).
The conventional method of manufacturing the high dielectric constant thin film has been performed as described above.
However, in the case of the DRAM of 4-Gbit class or the like, aspect ratio D/W is at least 3 for the semiconductor device having a step portion as shown in FIG.
6
. Even on the step portion, a conformal coverage (at least 80%) must be ensured. However, when TiO (DPM)
2
is used as a Ti material, the coverage is at most about 50% for aspect ratio D/W of at least 3, whereby sufficient coverage is not obtained. As a result, it is difficult to form an upper electrode (a cell plate) on the BST thin film.
SUMMARY OF THE INVENTION
The present invention is made to solve the aforementioned problem. An object of the present invention is to provide a method of manufacturing a high dielectric constant thin film ensuring sufficient coverage.
Another object of the present invention is to provide a method of forming a high dielectric constant thin film which has been improved to ensure a sufficient capacitance as in the case of a reduction in a thickness of the film.
Another object of the present invention is to provide a method of forming a high dielectric constant thin film which has been improved to reduce a material used and a cost.
Another object of the present invention is to provide a method of forming a high dielectric constant thin film which has been improved to make the formation of the high dielectric constant thin film considerably stable for a long period of time.
Still another object of the present invention is to provide a method of manufacturing a semiconductor device provided with a high dielectric constant BST thin film having a conformal coverage.
In a method of forming a high dielectric constant thin
Horikawa Tsuyoshi
Kawahara Takaaki
Matsuno Shigeru
Sato Takehiko
Tarutani Masayoshi
Lebentritt Michael S.
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
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