Method for forming metal layer using atomic layer deposition

Details Method for forming metal layer using atomic layer deposition Method for forming metal layer using atomic layer deposition

1998-12-15

2001-01-16

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S721000

Reexamination Certificate

active

06174809

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming a metal layer, and more particularly, to a method for forming a metal layer using atomic layer deposition.
2. Description of the Related Art
As the integration of a semiconductor device increases, the design rule is reduced. Thus, the aspect ratio of a contact hole becomes higher, but the junction depth becomes shallower. The junction depth directly depends on a short channel effect of a MOS transistor. That is, a MOS transistor appropriate for a highly-integrated semiconductor device requires a short channel length, and the depth of a source/drain region, i.e., the junction depth, must be shallow to improve the characteristics of the MOS transistor having the short channel. An interconnection technology for connecting the shallow junction to a metal interconnection requires a barrier metal layer. This prevents the metal interconnection from penetrating into the shallow junction, i.e., prevents a junction spiking phenomenon. A titanium nitride (TiN) layer is widely used for the barrier metal layer, and an ohmic layer, e.g., a titanium silicide layer, is interposed between the barrier metal layer and the junction. The titanium silicide layer has a melting point of 1540° C., a resistivity of 13~16 &mgr;U-cm and a barrier height of 0.6eV with respect to an N-type impurity layer, and is widely used for the ohmic layer of the interconnection. The titanium silicide layer used for the ohmic layer is formed by forming a titanium layer on the junction, i.e., a silicon substrate (impurity layer) doped with an impurity, and then annealing to react the titanium layer with the silicon substrate.
As described above, in a conventional method for forming the metal interconnection, an interdielectric layer is formed on an impurity layer, and the interdielectric layer is patterned to form a contact hole exposing a predetermined region of the impurity layer. The ohmic layer, the barrier metal layer and the metal interconnection are formed in sequence on the entire surface of the resultant structure where the contact hole is formed. Here, the ohmic layer can be obtained by forming a titanium layer on the exposed impurity layer and annealing the titanium layer, or forming the titanium silicide layer directly on the impurity layer. The titanium suicide layer must be formed at a temperature low enough to avoid damage to the impurity layer. Thus, there has been proposed a method for forming a titanium silicide layer using plasma-enhanced chemical vapor deposition (PECVD), in “Plasma Enhanced CVD of Blanket TiSi
2
on Oxide Patterned Wafer” by J. Lee et al.,
J. Electrochem. Soc
., vol. 139, No. 4 1992, pp. 1159-1165, and in “Material characterization of plasma-enhanced CVD titanium silicide”, by Alan E. Morgan et al.,
J. Vac. Sci. Technol
. B4(3), 1986, pp. 723-731. However, when the titanium silicide layer is formed on the contact hole having a high aspect ratio in a highly-integrated semiconductor device, the titanium silicide layer shows poor step coverage due to the plasma characteristics. Meanwhile, a method for forming a titanium silicide layer using a low pressure CVD (LPCVD) process at 600 C. or higher has been proposed by V. llderem et al. and G. J. Reynolds et al. (see “Optimized Deposition Parameters for Low pressure CVD titanium silicide”,
J. Electrochem. Soc
., 1988, pp. 2590-2596 and “Selective titanium disilicide by Low Pressure CVD”,
J. Appl. Phys
. 65(8), 1989, pp. 3212-3218). However, when the titanium silicide layer is formed at 600° C. or higher, silicon consumption of the impurity layer contacting the titanium layer is increased, deteriorating junction leakage current characteristics. Thus, it is difficult to adapt the LPCVD titanium silicide layer to be suitable for a highly-integrated semiconductor device requiring a shallow junction.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide a method for forming a metal layer having improved step coverage at 500° C. or lower, using atomic layer deposition.
Accordingly, according to one aspect of the present a sacrificial metal atomic layer is formed on a semiconductor substrate. The sacrificial metal atomic layer reacts with a metal halide gas, thereby removing the sacrificial metal atomic layer and simultaneously forming a metal atomic layer of metal atoms separated from the metal halide gas. The semiconductor substrate is a silicon substrate, and has a predetermined surface region on which a junction doped with an impu is formed, i.e., an impurity layer. Other embodiments include a patterned interdielectric layer having a contact hole exposing a predetermined region of the impurity layer. The sacrificial metal atomic layer and the metal atomic layer are formed in sequence at least once on an initial sacrificial metal atomic layer, which is a sacrificial metal atomic layer initially formed on the semiconductor substrate, to thereby form a metal layer consisting of a plurality of metal atomic layers on the semiconductor substrate. Here, the initial sacrificial metal atomic layer, which is the sacrificial metal atomic layer initially formed on the semiconductor substrate, must be formed such that the entire surface of the exposed impurity layer is completely covered. If the surface of the impurity layer exposed by the contact hole is not completely covered with the initial sacrificial metal atomic layer, the metal halide gas reacts with and damages the impurity layer. Thus, an initial sacrificial metal layer completely covering the entire surface of the impurity layer may be formed prior to forming the initial sacrificial metal atomic layer. At this time, preferably, while the initial sacrificial metal layer is formed, the semiconductor substrate is heated to no more than 500° C., preferably to 300~500° C. The initial sacrificial metal layer is formed of the same material as the sacrificial metal atomic layer. The initial sacrificial metal layer or the sacrificial metal atomic layer is formed by reacting the sacrificial metal source gas with a reducing gas. Here, preferably, H
2
gas or SiH
4
gas is used for the reducing gas.
Meanwhile, the metal halide gas must have a Gibbs free energy lower than that of a composition including a metal atom of the sacrificial metal atomic layer and a halogen atom of the metal halide gas. In other words, the metal atoms of the sacrificial metal atomic layer must be capable of being combined with halogen atoms instead of the combination of the metal atoms of the metal halide with halogen atoms. For instance, in order to form a metal atomic layer formed of titanium on the semiconductor substrate, the metal halide preferably employs TiCl
4
gas, Til
4
gas, TiBr
4
gas or TiF
4
gas. At this time, if the metal halide is TiCl
4
gas, then the sacrificial metal atomic layer is preferably an Al layer, a La layer, a Pr layer, an In layer, a Ce layer, a Nd layer or a Be layer. This is because the Gibbs free energy of TiCl
4
gas is lower than that of Al
2
Cl
6
, LaCl
3
gas, PrCl
3
gas, In
2
Cl
6
gas, CeCl
3
gas, NdCl
3
gas and Be
2
Cl
4
gas. Similarly, if the Til
4
gas is used for the metal halide in order to form a metal atomic layer formed of titanium on the semiconductor substrate, then preferably, the sacrificial metal atomic layer is an Al layer, a Zr layer or a Hf layer. This is because the Gibbs free energy of Til
4
gas is lower than that of Al
2
l
6
gas, Zrl
4
gas and Hfl
4
gas.
Various metal halide gases, e.g., TaCl
5
gas, Tal
5
gas, TaBr
5
gas, TaF
5
gas, HfCl
4
gas, Hfl
4
gas, HfBr
4
gas, HfF
4
gas, ZrCl
4
gas, Zrl
4
gas, ZrBr
4
gas or ZrF
4
gas may be used according to the type of metal atomic layer to be formed on the semiconductor substrate.
As described above, if the metal halide gas is supplied to the surface of the resultant structure where the sacrificial metal atomic layer is formed or where the initial sacrificial metal layer and the initial sacrificial metal atomic layer are formed, then metal atoms in the sacrificial metal ato

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