Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – Insulated gate formation
Reexamination Certificate
1998-11-30
2001-11-20
Wilczewski, Mary (Department: 2822)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
Insulated gate formation
C134S002000, C438S906000
Reexamination Certificate
active
06319801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method of cleaning a substrate having a patterned metal layer formed thereon and in particular to a cleaning method and a cleaning solution for removing metallic contaminants adhering to the substrate on which a metal layer has been formed by fine and high-density patterning.
2. Description of the Related Art
In recent years, as devices are becoming denser, substrates having thin-film multilayered structure, such as a semiconductor substrate, a liquid crystal substrate, a printed substrate for electronic devices and a substrate having magnetic materials, are subjected to fine processing of the multilayered films.
In particular, semiconductor devices become highly dense and gate electrodes thereof are made fine. For this, low-resistant suicide materials (WSix, TiSix) or metal materials such as tungsten (W) etc., or multilayered structure having TiN, WN sandwiched between W or WSix film or TiSix film came to be used as a gate electrode material.
FIG. 1
shows the schematic structure of a thin-film transistor. After a gate oxide film (SiO
2
)
2
is formed on a Si (silicon) substrate
1
, a film of metal is deposited on the gate oxide film
2
. The film of metal is finely patterned by dry etching to form a gate electrode
3
. Thereafter, a source region
4
and a drain region
5
are formed in the substrate
1
by ion implantation.
In these steps, metallic contaminants
6
such as Fe. Al etc. are generated from the dry etching apparatus and the ion implanter and adhere to the surface of the gate oxide film
2
. The metallic contaminants
6
on the gate oxide film
2
diffuse into the Si substrate
1
through the gate oxide film
2
in a subsequent thermal treatment step. This causes leak current to occur readily in the channel region under the gate electrode
3
, or to reduce the maximum permissible voltage between the source region and the drain region, resulting in deterioration in the reliability of the device.
Accordingly, it is necessary to remove the metallic contaminants
6
from the surface of the gate oxide film
2
, and after dry etching of the film of metal on the gate oxide film
2
and after ion implantation, a cleaning treatment using an acidic cleaning solution is applied so that the metallic contaminants
6
developed during these steps are removed from the surface of the gate oxide film
2
.
Usually, In the semiconductor process using a Si substrate, SPM (sulfuric acid-hydrogen peroxide mixture) or HPM (hydrochloric acid-hydrogen peroxide-water mixture) is mainly used as a cleaning solution for removing metallic contaminants.
Liquid crystals and printed substrates are rarely cleaned with an acidic cleaning solution and are cleaned with an organic solution such as IPA (isopropyl alcohol).
However, the conventional acidic cleaning solutions (SPM, HPM) used for removal of metallic contaminants have the problem of their possible etching of materials constituting the gate electrode
3
.
In particular, TiN and W among metal wiring materials used as low-resistance gate are easily etched with these acidic solutions, so these cannot be used for cleaning treatment.
As shown in
FIG. 2A
, for example, the gate electrode
3
is a DRAM gate electrode composed of multilayered films such that a poly-sillcon layer
7
is formed on the gate oxide film
2
and a silicide (Tiix) layer
8
and a nitride film (TiN)
9
are sequentially deposited on the poly-silicon layer
7
. If the cleaning solution SPM or HPM is used for removal of metallic contaminants developed after dry etching or after ion implantation, then the side wall of the nitride film (TiN)
8
is etched as shown in
FIG. 2B
, so the multilayered structure cannot be maintained and the gate electrode and the wiring may be removed.
Further, when DHF (fluoric acid-aqueous system-water mixture) effective for removal of metals is used as the cleaning solution, the silicide layer (TiSix)
9
is greatly etched and the gate oxide film (SiO
2
)
2
is also etched, so DHF cannot be used.
As described above, as the integration of semiconductor devices advances, the width of the gate electrode is also made fine, so the amount of material etched by treatment with the conventional acidic cleaning solution cannot be neglected, and there was need for a cleaning solution capable of removing metal contamination without etching low-resistance metal materials.
SUMMARY OF THE INVENTION
The present invention was made in view of these circumstances, and the object of the invention is to provide a cleaning method for removal of metallic contaminants from the surface of a substrate without etching any patterned metal material formed thereon in the treatment of cleaning the substrate, as well as the cleaning solution used in this method.
According to the present invention, an aqueous solution having a chelating action with metals such as iron (Fe), aluminum (Al) etc., is used as a cleaning solution for removal of metallic contaminants. More specifically, a carboxylic acid having a chelating action may by used as the cleaning solution. That is, the cleaning solution may be composed of an aqueous solution containing one of water-soluble carboxylic acid such as acetic acid, formic acid, citric acid, oxalic acid etc., ammonium carboxylate, and carboxylic acid having amino group. A chelating agent may be added to the carboxylic acid having a chelating action so as to enhance the chelating action with metals.
The cleaning method according to the present invention is comprised of the step of removing metallic contaminants from the surface of a substrate having a patterned metal layer formed thereon with the cleaning solution.
The material constituting the patterned metal layer is Ti (titanium), W (tungsten), Co (cobalt), Ni (nickel) or Ta (tantalum), or a compound consisting of each of these transition metals with Si (silicon), N (nitrogen) or O (oxygen), so that metallic contaminants can be removed certainly without etching the patterned metal layer.
For example, in the case where a gate oxide film is formed on a semiconductor substrate and then a gate electrode is formed thereon, the carboxylic acid and amino group added to the cleaning solution form a complex by chelating action with metals such as Fe, Al etc., so that the metallic contaminants attached to the gate oxide film can be removed.
The metallic contaminants In this case are often chemically or physically adsorbed onto the surface oxide film in the form of metal oxides or metal atoms. According to the present invention, the adsorbed metallic contaminants can be easily captured and removed by chelating action.
On the other hand, the metal material of the gate electrode makes strong intermetallic bonding, so there is no or less possibility that this bonding is cleaved and removed by the chelating action of the cleaning solution. Accordingly, even if the cleaning solution according to the invention is used for cleaning treatment, the portion of the gate electrode is hardly etched.
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Aoki Hidemitsu
Wake Tomoko
NEC Corporation
Wilczewski Mary
Young & Thompson
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