Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1998-07-09
2001-03-06
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
Reexamination Certificate
active
06197674
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of forming a CVD-Ti film used as, e.g., a contact metal or adhesion, in a semiconductor device and, more particularly, to a CVD-Ti film forming method of forming a Ti film as a barrier layer in a hole of an insulating film which covers a silicon substrate and in which the hole is formed.
In the manufacture of a semiconductor device, to meet recent demands for higher density and higher integration degree, the circuit arrangement more often has a multilayer interconnection structure. In order to make electrical connection between a lower semiconductor device and an upper interconnection layer that are insulated from each other by an insulating film, e.g., an SiO
2
film, interposed between them, a technique that forms a buried portion in a hole, e.g., a contact hole or a via hole, formed in the insulating layer by CVD, thus achieving electrical connection between the upper and lower layers becomes significant.
In the above technique, to fill the contact hole or via hole, generally, Al (aluminum) or W (tungsten), or an alloy containing Al or W as a major component is used. When such a metal or alloy comes into direct contact with the lower Si (silicon) substrate or the Si layer, the metals may undesirably form an alloy in the boundary portion of the lower Si substrate or Si layer due to the absorbing effect of Si or the like. The alloy formed in this manner has a large electric resistance. Such alloying is not preferable in terms of power savings and higher operation speed that are recently demanded of the device.
When W or a W-alloy is used as a buried layer of a contact hole, WF
6
gas used in forming the buried layer enters the Si substrate to degrade the electrical characteristics and the like.
In order to prevent these inconveniences, before formation of a buried layer in a contact hole or via hole, a barrier layer is formed on the inner surface of the hole in advance, and then the buried layer is formed on the barrier layer. As this barrier layer, a layer formed by a Ti (Titanium) film or a two-laminated structure layer consisting of a Ti film and a TiN (titanium nitride) film is generally used.
This barrier layer is commonly formed by physical vapor deposition (PVD). As micropatterning and higher integration of the devices are particularly required recently and the design rule becomes particularly strict, the line width and the hole aperture diameter continue to decrease to result in an increase in aspect ratio. Along with this, the electrical resistance of the PVD film increases, making it difficult to meet the above demands.
For this reason, the Ti film and TiN film that construct the barrier layer are formed by chemical vapor deposition (CVD) which can form a higher-quality film. When forming the Ti film by CVD, TiCl
4
(titanium tetrachloride) and H
2
(hydrogen) are used as the reaction gases. When forming the TiN film, TiCl
4
and NH
3
(ammonia) or MMH (monomethyl hydrazine) are used as the reaction gases.
In recent years, semiconductor devices continue to shrink in feature size and the aspect ratio of a contact hole or via hole formed in an SiO
x
(e.g., SiO
2
) film continues to increase. Therefore, with the conventional TiCl
4
and H
2
gas systems, it is difficult to form a CVD-Ti film in the hole portion with a good step coverage equal to or higher than 100%.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a CVD-Ti film forming method that can form a Ti film in a small hole formed in an insulating film on an Si surface with a good step coverage.
It is another object of the present invention to provide a CVD-Ti forming method that can form a Ti film on both the inner surface of a hole in the insulating film and an Si surface portion exposed from the hole at a high film formation rate and a low temperature.
It is still another object of the present invention to provide a CVD-Ti film forming method that can cope with any one of applications that require a good step coverage and applications that require film formation on both an insulating film and the bottom surface of a hole at a high film formation rate and a low temperature.
In the present invention, when forming a CVD-Ti film in a hole of an insulating film formed on an Si surface of a substrate and having a hole or holes that expose part an parts of the Si surface, Ar gas is used in addition to conventional TiCl
4
gas and H
2
gas, and a plasma of these gases is generated. In plasma generation, Ar gas influences TiCl
4
gas serving as a film formation gas, differently from H
2
gas does. Accordingly, by utilizing the function of Ar gas, a Ti film of a desired state can be formed on the hole.
This will be explained with reference to FIG.
1
. Referring to
FIG. 1
, reference numeral
10
denotes a shower head for introducing a gas into a chamber; and reference symbol W denotes an Si wafer. The right-side system indicates a reaction that takes place when Ar gas does not serve as a reaction gas, and the left-side system indicates a reaction that takes place when Ar gas serve as a reaction gas.
In the right-side system, H ions and/or H radicals decompose TiCl
4
into TiCl
3
+HCl and generate HCl after a TiSi film is formed on the wafer from TiCl
3
(a Ti film is formed on the oxide film). In the left-side system, Ar ions decompose TiCl
4
into TiCl
2
+Cl
2
and TiCl
2
into Ti+Cl
2
. Therefore, components that contribute to film formation increase due to the presence of Ar ions, so the film formation rate can be increased. When the ratio of Ar gas to H
2
gas, the ratio of these gases to TiCl
4
gas, the film formation temperature, the internal chamber pressure, and the power supplied when generating a plasma are adjusted, the film formation rate and the selectivity in film formation can be arbitrarily adjusted.
According to a first aspect of the present invention, these conditions are adjusted such that a Ti film is formed in the hole at high selectivity with respect to the insulating film. More specifically, the film formation rate of the Ti film on the Si surface exposed in the hole is increased sufficiently higher than the film formation rate of the Ti film on the insulating film and on the inner surface of the hole. This decreases the Ti film deposited on the hole entrance and sufficiently increases the Ti film deposited in the hole. In other words, the step coverage can be increased to be equal to or higher than 100%.
In this case, the selectivity can be increased if the following reaction is dominant:
TiCl
4
+2H
2
+Si
2
→TiSi
2
+4HCl
In order to effectively cause this reaction, it is preferable that, as in a second aspect, film formation be performed under such a condition that, when the state of the plasma is measured with plasma spectroscopy, the emission spectra of Ti and Cl
2
substantially do not exist.
Preferably, the substrate temperature is set to 400° C. to 800° C., the supplied power is set to 100 W to 300 W, and the internal chamber pressure is set to 0.5 Torr to 3.0 Torr, and more preferably the ratio of TiCl
4
gas to the sum of H
2
gas and Ar gas is set to 1:100 to 1:300 and the flow rate ratio of H
2
gas to Ar gas is set to 1:1 to 2:1. Then the reaction can be made dominant.
In a third aspect, the ratio of Ar gas to H
2
gas, the ratio of these gases to TiCl
4
gas, the film formation temperature, the internal chamber pressure, and the power supplied when generating a plasma are adjusted, so that a Ti film is formed on the exposed surface of the insulating film and on the Si surface portion in the hole at almost the same film formation rate. In this case, due to the presence of Ar gas, film formation can be done at a high film formation rate and a low temperature, which is suitable for a blanket process.
This film formation is possible if the following reaction is dominant in this case:
TiCl
4
+H
2
→Ti+2Cl
2
+H
2
or
TiCl
4
+H
2
→Ti+Cl
2
+2HCl
Preferably, the substrate temperature is set to 350° C. to 550
Kobayashi Yasuo
Tada Kunihiro
Yoshikawa Hideki
Hoang Quoc
Nelms David
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tokyo Electron Limited
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