Coating processes – Coating by vapor – gas – or smoke
Reexamination Certificate
2001-12-20
2004-07-27
Meeks, Timothy (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
C427S250000, C427S255230, C427S255310, C427S255340, C427S255370, C427S255394
Reexamination Certificate
active
06767581
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a process for the deposition of thin layers by chemical vapor deposition.
In the semiconductor industry, both physical vapor deposition (PVD) and chemical vapor deposition (CVD) processes are used for the deposition of thin layers. Compared to PVD processes, the CVD processes give better edge coverage and greater conformity throughout the coating. CVD processes are therefore used in particular for filling deep trench capacitors or contact holes. The films produced in this way can be either dielectrics (e.g. silicon dioxide, silicon nitride, aluminum oxide, tantalum oxide, etc.) or metals and metal-containing compounds. In particular, layers of transition metals, e.g. tungsten, and of transition metal silicides and nitrides, e.g. WN, WSix, CoSi, TaSi, etc., are deposited.
In CVD processes, the starting materials are introduced into the reactor chamber as gaseous compounds and react on the substrate surface to give the desired end product. The energy necessary for the reaction is introduced in the form of heat by heating the walls, radiation, or susceptor/wafer heating. The typical temperature range for the deposition is from 400° C. to 900° C.
However, there are applications, e.g. filling of structures having extreme aspect ratios or deposition on heat-sensitive layers such as aluminum metalization or organic dielectrics, in which significantly lower temperatures, which are more than 100° C. below the abovementioned customary temperatures, are desirable. Lower temperatures increase edge coverage and conformity and, secondly, the deposition of certain layers without damage to the underlying substrate is made possible for the first time.
Various disadvantages stand in the way of carrying out CVD processes at lower temperatures. Thus, for example, the deposition of certain layers can only be completed above a particular temperature, so that reducing the temperature is not possible at all. In the case of depositions that can be completed in principle, the deposition rate is sometimes reduced so much that the process cannot be completed economically. In other deposition reactions, only the nucleation step (i.e. the covering of the substrate surface with a first layer of the substance to be deposited) is problematical; further deposition can occur at the reduced temperature.
For the reasons mentioned, attempts have been made to develop methods that enable CVD processes to be completed at relatively low temperatures. Such a method of reducing the temperature is the generation of plasma. The ions, free radicals, and excited molecules formed in this way are more reactive than the starting molecules, so that the deposition reactions can occur at lower temperature. However, these plasma enhanced chemical vapor deposition (PECVD) processes frequently result, due to the reactivity and variety of substances formed, in undesirable gas-phase reactions or undesirable secondary reactions which then lead to increased contamination of the layers with extraneous substances.
U.S. Pat. No. 5,637,351 describes a method of increasing the deposition rate in CVD processes. The method adds free-radical formers to the CVD reactor. The patent discloses using organic free-radical formers in the deposition of SiO
2
from a diethylenesilane/oxygen mixture.
There nevertheless continues to be a need for processes that enable the temperature in CVD processes to be decreased while maintaining economically justifiable deposition rates.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a process for the deposition of thin layers by chemical vapor deposition that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that provides a process for the deposition of thin layers by chemical vapor deposition, which can be carried out at temperatures lower than those known from the prior art.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a process for depositing thin layers by chemical vapor deposition. The first step is adding to a gas stream including materials to be deposited an effective amount of nitroxyl radicals of the formula:
R
1
and R
2
are selected from the group including of alkyl, alkenyl, alkynyl, acyl, and aryl radicals. R
1
and R
2
can be identical or different. The alkyl, alkenyl, alkynyl, acyl, and aryl radicals can include heteroatoms.
In accordance with a further object of the invention, the next step is forming from R
1
and R
2
a structure —CR
3
R
4
—CR
5
R
6
—CR
7
R
8
—CR
9
R
10
—CR
11
R
12
—, wherein R
3
, R
4
, R
5
, R
6
, R
7
, R
8
, R
9
, R
10
, R
11
, R
12
can be identical or different and are selected from the group including alkyl, alkenyl, alkynyl, acyl, and aryl radicals with or without heteroatoms.
As stated, in the process of the invention for the deposition of thin layers by chemical vapor deposition, an effective amount of nitroxyl radicals of the formula
is added to the gas stream comprising the materials to be deposited. In this formula, R
1
and R
2
are identical or different alkyl, alkenyl, alkynyl, acyl, or aryl radicals with or without heteroatoms. R
1
and R
2
can also together form a structure —CR
3
R
4
—CR
5
R
6
—CR
7
R
8
—CR
9
R
10
—CR
11
R
12
—, where R
3
, R
4
, R
5
, R
6
, R
7
, R
8
, R
9
, R
10
, R
11
, R
12
are again identical or different alkyl, alkenyl, alkynyl, acyl, or aryl radicals with or without heteroatoms.
In the process of the invention, nitroxyl radicals are added to the gas mixture that is introduced into the reactor chamber. This significantly reduces the deposition temperature compared to conventional CVD processes and the substrate is subjected to considerably less thermal stress. This is particularly advantageous when heat-sensitive layers are already present, e.g. low-k dielectrics based on organic compounds. In addition, a more conformal deposit is achieved. At a given reaction temperature, the addition of the nitroxyl radicals significantly increases the deposition rate or makes the reaction possible for the first time. The nitroxyl radicals differ in their reactivity, so that the deposition reaction can be controlled by appropriate selection of the substances. In addition, attachment of the radicals to the surface can increase the reactivity of the surface, thus allowing deposition on inert or passivated substrates.
Preference is given to embodiments in which R
1
and R
2
form a structure —CR
3
R
4
—CR
5
R
6
—CR
7
R
8
—CR
9
R
10
—CR
11
R
12
—, in which R
3
,R
4
, R
5
, R
6
, R
7
, R
8
, R
9
, R
10
, R
11
, R
12
are identical or different and are each hydrogen, methyl or ethyl. Particular preference is given to R
1
and R
2
forming a structure —CR
3
R
4
—CR
5
R
6
—CR
7
R
8
—CR
9
R
10
—CR
11
R
12
— in which R
3
, R
4
, R
11
, R
12
are each methyl and R
5
, R
6
, R
7
, R
8
, R
9
, R
10
are each hydrogen. The compound defined in this way, viz. 2,2,6,6-tetramethyl-1-piperinyloxy, sublimes without decomposition under reduced pressure and is therefore very well suited to CVD applications.
The process of the invention is preferably employed for the deposition of a dielectric material, in particular for the deposition of silicon dioxide, silicon nitride, aluminum oxide, tantalum oxide, or a mixture thereof.
The process of the invention is also very well suited to the deposition of a metal or a metal alloy, in particular for the deposition of tungsten, cobalt, tantalum, or a mixture thereof.
Good results are likewise obtained in the deposition of metal-containing compounds, in particular the deposition of a metal nitride or a metal silicide, with the deposition of WN, WSi
x
, CoSi, TaSi, or a mixture thereof being found to be very particularly advantageous.
The addition of free nitroxyl radicals is particularly useful when only one precursor gas is utilized, i.e. when only one chemical compound apart from the added nitroxyl radicals is present in the gas stream including the materials to be deposited. The addition of nitroxyl radicals grea
Greenberg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
Meeks Timothy
Stemer Werner H.
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