Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – Amorphous semiconductor
Reexamination Certificate
1999-09-01
2004-04-06
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
Amorphous semiconductor
C438S784000, C438S788000, C438S478000, C427S569000, C427S585000
Reexamination Certificate
active
06716725
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a plasma processing method and a semiconductor device.
There are plasma processing methods that have been proposed in the prior art through which film formation processing is implemented on a target object such as a semiconductor wafer (hereafter referred to as a “wafer”). In one such method, for instance, after mounting a wafer on a lower electrode provided within an airtight processing chamber, the wafer is heated to a specific temperature. Then, a processing gas such as SiH
4
(silane), TEOS (tetra-ethoxy silane) or the like is introduced into the processing chamber while maintaining the atmosphere within the processing chamber at a specific reduced pressure. Next, high frequency power for plasma generation is applied to an upper electrode facing the lower electrode and high frequency power for biasing is applied to the lower electrode, to generate plasma by dissociating the processing gas. In the next step, a layer insulating film constituted of SiO
2
(silicon dioxide) is formed on the Si (silicon) substrate constituting the wafer, using the plasma.
The adoption of a multilayer wiring structure on an Si substrate achieved by laminating wiring films over a plurality of layers via layer insulating film has become essential to support ultra-fine semiconductor elements of various types formed at the wafer and the ultra-high integration that have been achieved in recent years. In addition, with the design rules for designing semiconductor devices becoming further reduced, the wiring films are positioned in closer proximity to each other and the layer insulating film is becoming even thinner. However, if an SiO
2
film having a dielectric constant of approximately 3.9 is utilized to constitute the layer insulating film, as in the prior art, the capacity between the wirings (incidental capacity) increases and, as a result, the transmission of electrical signals is delayed to result in a reduction in the high-speed operability. Consequently, it is difficult to drive at a low voltage, and moreover, it is difficult to operate at a high clock frequency.
As a solution, a method of lowering the capacity between the wirings by employing a film with a low dielectric constant which has a dielectric constant lower than that of SiO
2
to constitute the layer insulating film has been proposed. The film with a low dielectric constant employed in such a method may be a film constituted of an organic material or a film constituted of an inorganic material. The dielectric constants of a polyimide resin film and a fluorine-containing resin film, either of which may constitute the organic film are 3.0~3.5 and 1.9~2.7 respectively, and are much lower than that of the SiO
2
film. However, organic films do not possess a significant degree of heat resistance due to their poor strength in their molecular structures, and they do not facilitate machining either. In addition, the conformability of organic films to the existing processing methods is poor, which makes it difficult to form various types of elements.
In contrast, an inorganic film such as an SiOF (silicon oxide containing fluorine) film having a dielectric constant of approximately 3.5 has a relatively stable molecular structure, and therefore, unlike the organic films described above, achieves advantages including superior heat resistance, good machinability and good conformability to existing processing methods. In addition, the SiOF film may be processed using an existing film formation apparatus through an existing film formation method by using a mixed gas constituting of, for instance, SiH
4
and SiF
4
for the processing gas. Furthermore, since the dielectric constant of the SiOF film has dependency on the content of the F (fluorine) atoms in the film, the dielectric constant can be reduced by increasing the content of the F atoms.
However, when the F atom content in the SiOF film is increased, the hygroscopicity of the film itself becomes higher in proportion to the increase. According to the observation made by the inventors, this increase in the hygroscopicity may be attributable to the following factor. Namely, the SiO
2
film has a molecular structure expressed as;
with an —OH (hydroxyl group) bond at its trailing end. When F atoms are added into the SiO
2
film at a quantity at which no hygroscopicity manifests, e.g., at 10 mol % ~20 mol %, to set the dielectric constant to approximately 3.5, the —OH is replaced by —F, and the molecular structure expressed as;
is achieved. In addition, if F atoms are added into the SiOF film at a ratio exceeding 20 mol % to further reduce the dielectric constant of the SiOF film, the molecular structure changes to
with the O (oxygen) atom that has been bonded to the two Si atoms replaced by F atoms, thereby destroying the network structure of the SiO
2
film. It is assumed that the resulting series of reactions, whereby a reaction occurs between the Si (—F)
2
bond formed within the SiOF film and H
2
O (water) present in the atmosphere and the like to induce hydrolysis and an Si—OH bond is formed, raises the hygroscopicity of the SiOF film.
In addition, when the SiOF film absorbs moisture, HF (hydrogen fluoride) is created, which corrodes any metal in contact with the layer insulating film, such as that constituting the wiring films, to damage the element. Furthermore, if HF becomes diffused inside the processing chamber, it contaminates the processing chamber and may also cause corrosion of various members and the exhaust system provided inside the processing chamber. Moreover, HF reduces the pH (approximately 9~11) of the slurry used as a polishing agent when flattening the layer insulating film through CMP (chemical mechanical polishing), which results in a reduction in the polishing speed.
A first object of the present invention which has been completed by addressing the problems of the prior art discussed above is to provide a new and improved plasma processing method and a new and improved semiconductor device, which make it possible to form an SiOF film having a low dielectric constant that demonstrates no substantial hygroscopicity.
In addition, in the prior art, if the SiO
2
film is in contact with a metal such as Ti (titanium), the Ti and the O in the SiO
2
become bonded at the interface to result in the formation of a bridge structure such as —Ti—O—Si— and, as a result, a specific bond strength is achieved. However, if F is present in the SiO
2
film during this process, the bond of the —Ti—O—Si— is broken into —Ti—F, H—O—Si and the like, which presents a problem in that the bond with the metal such as that constituting the wiring films in contact with the SiOF film is weakened.
A second object of the present invention which has been completed by addressing the problem of the prior art discussed above is to provide a new and improved plasma processing method and a new and improved semiconductor device, which make it possible to form an SiOB (silicon oxide containing boron) film having a low dielectric constant that achieves a strong bond with the metal material.
SUMMARY OF THE INVENTION
In order to achieve the objects described above, in a first aspect of the present invention, a plasma processing method for implementing film formation processing on a target object placed within a processing chamber by transforming a processing gas introduced into the processing chamber into plasma, that includes a step in which a gas that is constituted of, at least, a gas containing silicon atoms, a gas containing oxygen atoms, a gas containing boron atoms and a gas containing fluorine atoms is introduced as the processing gas into the processing chamber and film constituted of a silicon oxide-type material is formed at the target object by incorporating at least the boron atoms and the fluorine atoms into the molecular structure, is provided.
In this method, by introducing the B atoms into the network structure of the Si—O bond in the SiO
2
film, for instance, a B—O bond network is formed within the network constituted of the Si—O
Finnegan Henderson Farabow Garrett & Dunner LLP
Luu Chuong A
Smith Matthew
Tokyo Electron Limited
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