Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
2000-08-10
2002-07-02
Ghyka, Alexander G. (Department: 2812)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
C438S665000, C438S792000
Reexamination Certificate
active
06413886
ABSTRACT:
BACKGROUND OF THE INVENTION
Filed of the Invention
The invention relates to a method for fabricating a microtechnical structure, in particular a microelectronic structure, in which a filling material is deposited in at least one depression in the structure in an HDP-CVD (High Density Plasma-Chemical Vapor Deposition) process. Depressions such as trenches or holes which are to be filled with a filling material in a later fabrication step are often produced in microtechnical structures. In order to fill the depressions, filling materials are deposited in deposition processes with a pronounced directional characteristic. With the continuously advancing miniaturization of microtechnical structures, it is necessary to fill depressions having larger and larger aspect ratios, that is to say ratios of the depth to the width of the depression.
A known process for depositing filling materials is the HDP-CVD process.
FIG. 1
of the accompanying drawing shows a reactor
1
in which the HDP-CVD process can be carried out. By way of example, a wafer is introduced into a lower chamber
3
of the reactor
1
through an opening
7
and is positioned on a sample table
9
. After the wafer
11
has been positioned on the sample table
9
, the latter is moved vertically upward into the position illustrated in
FIG. 1
, in which the surface of the wafer
11
is arranged approximately at the lower edge of an upper chamber
13
of the reactor
1
. The upper chamber
13
has an approximately rotationally symmetrical dome
15
around which the windings of an electromagnetic coil
17
are passed. A gas inlet
19
is provided on the upper chamber
13
in order to introduce gases that participate in the process into the reactor
1
. A pump
5
serves for evacuating the interior space of the reactor
1
. During the process, the gases introduced through the gas inlet
19
are permanently drawn off again by the pump
5
, so that a continuous gas flow takes place. With regard to the concentration or partial pressures of the gases and their constituents in the interior space of the reactor
1
, an approximately steady state is established during the process.
During the process, an electrical AC voltage having a frequency typically of 400 kHz is applied to the coil
17
(first frequency generator
21
). This leads, in the upper chamber
13
, to the production of a high-density plasma (typically 1×10
11
-1×10
12
ions/cm
3
) in a plasma space
16
. The boundary of the plasma space
16
extends at a distance along the surface of the wafer
11
and the reactor walls. On account of the higher mobility of the electrons in the plasma in comparison with the ions, the plasma is positively charged relative to its surroundings. In this case, the interior of the plasma is virtually free of electrical potential differences. If, on the other hand, ions enter the boundary layer of the plasma, they are accelerated out of the plasma due to electrical field forces. That corresponds to the so-called electrical boundary layer voltage.
In order to be able to control the boundary layer voltage at the boundary layer near the wafer
11
and in order to produce a larger boundary layer voltage there, a second electrical AC voltage is applied between ground potential and the sample table
9
(second frequency generator
23
). The frequency of the second frequency generator
23
is significantly higher than the frequency of the first frequency generator
21
, and is typically more than 10 Mhz. This high frequency has virtually no effect on the ion density of the plasma, so that the plasma density and the boundary layer voltage at the wafer
11
can be set virtually independently of one another.
The above-described reactor
1
and the corresponding HDP-CVD process are exemplary embodiments. HDP-CVD processes can also be performed in a similar manner in other reactors.
When filling depressions having high aspect ratios, care must be taken to ensure that the filling is effected from the bottom of the depression and only a small amount of filling material is deposited on the side walls of the depression. Undesirable voids are otherwise formed. It is known that during the HDP-CVD process, the bombardment of the wafer surface with ions from the plasma leads to removal of the surface material. The removal is markedly dependent on the angle of incidence of the ions on the surface. If the depression to be filled has a bottom running in the horizontal direction and side walls running in the vertical direction and if the boundary layer of the plasma runs parallel to the bottom, then material is removed primarily at the upper edge of the depression. The perpendicularly incident ions densify essentially only the material at the bottom, but drive out hardly any constituents and, on the other hand, owing to the glancing incidence on the side walls, can likewise drive out hardly any material there. In addition to anisotropic removal, it is known that the deposition of material also has a strongly directional component. Specifically, a large amount of material is deposited on areal sections which are oriented perpendicularly to the incident ion flow (bottom), whereas only a small amount of material is deposited on areal regions oriented parallel to the ion flow (side walls). This behavior is taken into account in previous literature models by the assumption of an angle-dependent adhesion coefficient for the depositing molecules (R. Conti et al. (IBM), DUMIC Conference 1999). Since this angle-dependent adhesion coefficient was only introduced empirically, this model cannot, in principle, make any predictions for the filling behavior under different process conditions (exception: ion energy or boundary layer voltage). Accordingly, previous improvements in the filling behavior are mainly based on trial and error.
One parameter which can be set during process control is the ion flow, that is to say the number of ions emerging from the boundary layer of the plasma per unit time. The ion flow depends to a good approximation only on the plasma density. However, the chemical reactions taking place within the plasma are dependent in a sensitive manner on the plasma density. Therefore, the plasma density must be kept within a comparatively small range of values. Otherwise, the quality of the deposited filling material does not satisfy contemporary requirements.
The second well-controllable parameter of the process is the boundary layer voltage, which is directly correlated with the kinetic energy of the individual ions. It is known that the boundary layer voltage should be optimized in such a way that, for a given composition and density of the plasma, on the one hand, a surface that is as planar as possible is produced after the depression has been filled and, on the other hand, effectively no material is removed at the opening edges of the depression, that is to say material removal due to ion bombardment and deposition of filling material approximately balance one another. If effective material removal were permitted, the structure whose depression is to be filled could be damaged.
SUMMARY OF THE INVENTION
The object of the present invention is to specify a method of the type mentioned in the introduction during the performance of which a further well-controllable process parameter is available and, if appropriate, is set. In particular, the intention is for it thus to be possible to fill depressions having large aspect ratios.
The object is achieved by means of methods having the features of claim
1
and of claim
6
. The respective dependent claims relate to developments.
An essential concept of the present invention is that, in the region of the surface of the structure whose depression is to be filled, passivating substances or atomic and/or molecular particles are provided which can passivate the surface of the structure against addition of the filling material and/or of a precursor of the filling material. In this case, the invention is based on the insight that during the deposition of the filling material from the vapor phase, such passi
Kersch Alfred
Schulze-Icking Georg
Ghyka Alexander G.
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Stemer Werner H.
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