Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Utility Patent
1998-06-23
2001-01-02
Everhart, Caridad (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S660000, C438S680000, C427S314000, C427S372200
Utility Patent
active
06169032
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a CVD film formation method for forming a metal film such as a Ti (titanium) film or a TiN (titanium nitride) film on a semiconductor substrate placed in a raw-material gas atmosphere.
2. Discussion of the Background
A semiconductor device is generally constructed by forming a circuit device on a semiconductor substrate made of silicon (hereinafter, referred to as a “semiconductor wafer”), forming a contact hole for connecting the circuit device to a metal wiring or a via hole for connecting the metal wirings to each other via an interlevel dielectric film, and burying these holes with a buried layer made of metal.
Prior to the formation of the buried layer, a barrier layer is formed in order to prevent impurities and silicon from being diffused. The barrier layer is formed at least on the interlevel dielectric film of the wall of the contact hole and on the terminal surface of the circuit element (serving as a connecting surface) and usually consists of two-layer metallic thin films such as a Ti film and a TiN film.
Up to now, the barrier layer of this type has been formed by a physical vapor deposition (PVD) method. However, with increasing demands for miniaturization and high integration of the device, the design rule thereof has become strict. In other words, wiring and holes have to be reduced in width and aperture and formed with a high aspect ratio.
Therefore, it has been difficult to form the barrier layer made of a Ti film or a TiN film on the bottom of holes by the conventionally-used PVD method.
In place of the PVD method, a CVD (Chemical Vapor Deposition) method has been employed for forming an appropriate barrier layer and the buried layer.
For example, in the case where the Ti film is formed by using the CVD method, use is made of a raw material gas mixture containing TiCl
4
(titanium tetrachloride) gas and H
2
(hydrogen) gas. In the case where the TiN film is formed, use is made of a raw material gas mixture containing TiCl
4
gas and either NH
3
(ammonia) gas or MMH (monomethylhydrazine) gas.
However, the film-formation process employing a conventional CVD method includes rapid heating and cooling steps of a semiconductor wafer. Consequently, high stress is applied to the film, with the result that crystal defect and distortion of the semiconductor wafer due to the stress take place after the film formation.
When the semiconductor wafer is distorted, cracks occur in the film. The center portion and the peripheral portion of the semiconductor wafer are not brought into the same focus in a light exposure device in a photolithographic step. When the cracks are formed in the formed film, a conductive failure takes place. In addition, the exposed underlying film due to the cracks is etched in the etching step.
BRIEF SUMMARY of THE INVENTION
An object of the present invention is to provide a CVD film-formation method free from cracks by preventing crystal defect and distortion of an object to be processed (a semiconductor wafer) while minimizing stress to be applied to the film formed on a semiconductor wafer.
To attain the objects of the present invention, there is provided a method of forming a thin film on an object to be processed placed in a reduced process chamber, by chemical Vapor Deposition (CVD), comprising the steps of:
introducing arbitrarily chosen gases into the process chamber having an object to be processed loaded therein before a raw material gas is introduced, to set an inner pressure to a film-formation pressure determined in accordance with film-formation conditions;
introducing the raw material gas for use in film formation into the process chamber;
performing the film formation for a predetermined time determined in accordance with the film-formation conditions; and
terminating only a raw material gas supply, followed by terminating a supply of the arbitrarily chosen gases while flow rates thereof are gradually reduced, after completion of film formation process, thereby preventing a rapid pressure change of the process chamber and preventing a rapid temperature change of the semiconductor substrate due to the rapid pressure change.
The present invention also provides a method of forming a thin film on an object to be processed placed in a reduced process chamber by CVD (Chemical Vapor Deposition) while heating the object to be processed mounted on a susceptor by a heater housed in the susceptor, which comprises the steps of:
loading the object to be processed into the process chamber;
placing an object to be processed near the susceptor to heat the object to be processed with heat radiation from the heater for an appropriate time before the object to be processed is directly heated;
mounting the object to be processed onto the susceptor and heating the object to be processed by the heater;
forming a film on the object to be processed by CVD;
moving the object to be processed away from the heater and placing the object to be processed near the heater for an appropriate time to reduce the temperature of the object to be processed; and
unloading the object to be processed from the process chamber, thereby preventing a rapid temperature change of the object to be processed.
According to the present invention described in the foregoing, to load the object to be processed (the semiconductor wafer) into the process chamber from the transfer chamber, the supporting pins are first moved up and the semiconductor substrate is mounted thereon. While the supporting pins are maintained as they are, the semiconductor wafer is heated with heat radiation from the heater housed in the susceptor. After the temperature of the semiconductor wafer is thus increased to some extent, the semiconductor wafer is mounted on the susceptor and then heated until the temperature reaches a film-formation temperature determined in accordance with film-formation conditions. In this manner, it is possible to prevent rapid temperature change of the semiconductor wafer. To unload the semiconductor substrate from the process chamber after completion of the film-formation process, the supporting pins are first moved up to keep the semiconductor wafer away from the susceptor. In this way, direct heating of the semiconductor wafer by the heater is stopped. After the temperature of the semiconductor wafer decreases to some degree, the semiconductor wafer is unloaded and moved into the transfer chamber having a low temperature atmosphere. It is therefore possible to prevent a rapid temperature change of the semiconductor wafer in the cooling step.
To initiate the film formation on the semiconductor wafer, arbitrarily chosen gases are introduced into the process chamber, thereby adjusting the pressure to a film-formation pressure determined in accordance with the film formation conditions before the raw material gas is introduced. It is therefore possible to suppress a rapid pressure change accompanying the rapid temperature change in the process chamber. After the film-formation process is completed, only the supply of the raw material gas is terminated, and the supply of the other gases is gradually terminated. In this manner, it is possible to suppress a rapid pressure change accompanying the temperature change in the process chamber.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: 5574247 (1996-11-01), Nishitani et al.
patent: 6080444 (2000-06-01), Shimizu et al.
Hatano Tatsuo
Murakami Seishi
Everhart Caridad
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tokyo Electron Limited
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