Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-05-24
2002-07-09
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S653000, C204S298070
Reexamination Certificate
active
06417105
ABSTRACT:
BACKGROUND
Refractory metals and their suicides are widely used in CMOS DRAMs and logic circuits. Silicides offer lower resistivity compared to doped silicon. In addition, silicides also offer higher thermal stability compared to conventional interconnect materials such as aluminum. There are several ways to obtain refractory metal silicide films on the wafer. The most common method to obtain metal silicide is through the salicide process. The salicide process for obtaining titanium silicide film on a wafer is described below:
1. a layer of Ti is deposited on a wafer by sputtering;
2. first rapid thermal anneal (RTA) step: titanium reacts with silicon forming TiSi
2
((C49) phase). This step is done in a nitrogen atmosphere to avoid forming TiSi
2
on the oxide and forms a TiN layer on the titanium;
3. the wafer is removed and selectively etched to the TiN and unreacted Ti;
a. a second RTA step is performed whereby TiSi
2
is transformed from the high resistivity phase (C49) to the low resistivity phase (C54).
The process involves four steps including two high temperature rapid annealing steps. The advantage of RTA versus conventional annealing is that RTA reduces the “thermal budget”, defined as the time the wafer stays in the furnace at high temperature. In general, reducing the thermal budget is desirable.
An alternative way to obtain a silicide film on a wafer would be by depositing a silicide film by sputtering a silicide target. Sputter deposition of silicide film using a silicide target offers the following advantages:
1. eliminates the need for high temperature rapid thermal annealing steps, provided a C54 film can be deposited;
2. reduces silicon consumption from the wafer;
3. eliminates the phase transformation step; and
4. provides an opportunity to deposit an amorphous film.
Aluminides of Ti and Ta are useful barrier materials in the manufacture of integrated circuits. During the manufacture of integrated circuits Ti and Al layers often react to form titanium aluminide during wafer processing. However, formation of titanium aluminide during wafer processing is detrimental to the wafer because it introduces additional stresses in the film and also consumes Ti and Al from interconnect wiring. In order to prevent titanium aluminide formation and consumption of interconnect metal in the wafer during processing, it is desirable to deposit titanium aluminide by sputtering a titanium aluminide target. Depositing a titanium aluminide film eliminates the introduction of stresses associated with formation of titanium aluminide and unnecessary consumption of interconnect metal.
SUMMARY
The invention relates to a method of making enhanced purity stoichiometric and non-stoichiometric articles, such as targets for sputtering and related microelectronics applications, and to such articles, including targets. Stoichiometric articles are defined as single phase microstructure having a chemical composition as predicted by the phase diagram of the constituent elements e.g. TiAl
3
, WSi
2
, TiSi
2
, etc. Non-stoichiometric articles are defined as articles, such as targets, having a composition slightly away from the stoichiometric composition as predicted by the phase diagram of the constituent elements e.g. TiSi
2,4
, WSi2,8, etc. By practicing the invention it is possible to fabricate single phase stoichiometric articles, such as targets and dual-phase non-stoichiometric articles, such as targets, with high densities, higher purity than the starting material, and fine microstructure. Higher purity targets are beneficial for sputtering because they lead to less defects on the silicon wafer thereby increasing yields.
Enhanced purity stoichiometric and non-stoichiometric articles, such as sputtering targets, in accordance with one aspect of the invention which possess a density of 95% or higher of theoretical density and a microstructure not exceeding 20 microns, depending on the chemistry and composition of the article, e.g. target, and its constituent elements.
Enhanced purity articles, such as targets, are defined as having an overall purity (combination of metallic, non-metallic and gaseous components) higher than that of the starting material. The articles may be manufactured by using a combination of reactive sintering, sintering and vacuum hot pressing. It has been found that such a combination can be performed in situ in a vacuum hot press which enables the process to be a one-step process to manufacture stoichiometric and non-stoichiometric, such as sputtering targets starting from elemental powders, i.e. elements in powder form.
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Keller Jeffrey A.
Morales Diana L.
Shah Ritesh P.
Dang Phuc T.
Honeywell International , Inc.
Nelms David
Wells St. John P.S.
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