Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – By reaction with substrate
Reexamination Certificate
2001-05-01
2003-07-29
Cuneo, Kamand (Department: 2829)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
By reaction with substrate
C438S773000
Reexamination Certificate
active
06599845
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an oxidation method of oxidizing surfaces of workpieces, such as semiconductor wafers, and an oxidation system.
BACKGROUND ART
Generally, a semiconductor wafer, such as a silicon substrate, is subjected to various processes including a film forming process, an etching process, an oxidation process, a diffusion process and a modification process when fabricating a semiconductor integrated circuit. For example, the oxidation process among those processes is used for oxidizing a surface of a single-crystal silicon film or a polysilicon film and for oxidizing a metal film. The oxidation process is used mainly for forming gate oxide films and insulating films for capacitors.
Oxidation methods are classified by pressure into atmospheric pressure oxidation methods that are carried out in an atmospheric atmosphere and vacuum oxidation methods that are carried out in a vacuum atmosphere. Oxidation methods are classified by oxidizing gas into wet oxidation methods including a wet oxidation method disclosed in, for example, JP-A No. Hei 3-140453, that use steam generated by burning hydrogen in an oxygen atmosphere in an external combustor, and dry oxidation methods including a dry oxidation method disclosed in, for example, JP-A No. Sho 57-1232 that supply only ozone or oxygen into a processing vessel.
In view of quality and characteristics including dielectric strength, corrosion resistance and reliability, an insulating film formed by a dry oxidation process is superior to that formed by a wet oxidation process. In view of deposition rate and uniformity, generally, an oxide film (insulating film) formed by an atmospheric oxidation process is satisfactory in oxidation rate but the same is not satisfactory in the intrafilm thickness uniformity of an oxide layer formed on the surface of the wafer. On the other hand, an oxide film formed by a vacuum oxidation process is satisfactory in the intrafilm thickness uniformity of the oxide layer but the same is not satisfactory in oxidation rate.
Design rules that have been hitherto applied to designing semiconductor integrated circuits have not been very severe the aforesaid various oxidation methods have been selectively used taking into consideration purposes of oxide films, process conditions and equipment costs. However, line width and film thickness have been progressively decreased and severer design rules have been applied to designing semiconductor integrated circuits in recent years, and design rules requires higher film characteristics and higher intrafilm thickness uniformity of films. The conventional oxidation methods are unable to meet such requirements satisfactorily.
A wet oxidation system disclosed in, for example, JP-A No. Hei 4-18727 supplies H
2
gas and O
2
gas individually into a lower region in a vertical quartz processing vessel, burns the H
2
gas in a combustion space defined in a quartz cap to produce steam, makes the steam flow upward along a row of wafers to accomplish an oxidation process.
Since this prior art oxidation system burns H
2
gas in the combustion space, a lower end region in the processing vessel has a high steam concentration, the steam is consumed as the same flows upward and an upper end region in the processing vessel has an excessively low steam concentration. Accordingly, the thickness of an oxide film formed on the surface of the wafer is greatly dependent on the position where the wafer is held for the oxidation process and, in some cases, the intrafilm thickness uniformity of the oxide film is deteriorated.
Another oxidation system disclosed in, for example, JP-A No. Sho 57-1232 arranges a plurality of wafers in a horizontal batch-processing reaction tube, supplies O
2
gas or supplies O
2
gas and H
2
gas simultaneously through one of the opposite ends of the reaction tube into the reaction tube., and forms an oxide film in a vacuum atmosphere.
However, since this prior art oxidation system forms a film in an atmosphere of a relatively high pressure by a hydrogen burning oxidation method, steam is a principal element of reaction, an upper region with respect to the flowing direction of gases in the processing vessel and a lower region in the processing vessel differ excessively from each other in steam concentration and hence it is possible that the intrafilm thickness uniformity of the oxide film is deteriorated.
A third oxidation system disclosed in, for example, U.S. Pat. No. 6,037,273 supplies O
2
gas and H
2
gas into the processing chamber of a wafer-fed processing vessel provided with a lamp heating device, makes the O
2
gas and the H
2
gas interact in the vicinity of the surface of a semiconductor wafer placed in the processing chamber to produce steam, and forms an oxide film by oxidizing the surface of the wafer with the steam.
However, this oxidation system supplies O
2
gas and H
2
gas through gas inlets spaced a short distance in the range of 20 to 30 mm from the wafer into the processing chamber, makes the O
2
gas and the H
2
gas interact in the vicinity of the surface of the semiconductor wafer to produce steam, and forms the oxide film in an atmosphere of a relatively high process pressure. Thus, it is possible that the intrafilm thickness uniformity of the film is deteriorated.
DISCLOSURE OF THE INVENTION
The present invention has been made to solve the aforesaid problems effectively. Accordingly, it is an object of the present invention to provide an oxidation method and an oxidation system capable of improving the intrafilm thickness uniformity of the oxide film and the interfilm thickness uniformity of oxide films and the characteristics of oxide films, maintaining oxidation rate on a relatively high level.
According to the present invention, an oxidation method of oxidizing surfaces of workpieces heated at a predetermined temperature in a vacuum atmosphere created within a processing vessel comprises the steps of: producing active hydroxyl species and active oxygen species; and oxidizing the surfaces of the workpieces by the active hydroxyl and the active oxygen species.
In the oxidation method according to the present invention, an oxidative gas and a reductive gas are supplied into the processing vessel by separate gas supply systems, respectively, in the step of producing active hydroxyl and active oxygen species.
In the oxidation method according to the present invention, the processing vessel has a predetermined length, the workpieces are arrange at predetermined pitches in a processing region in the processing vessel, an oxidative gas and a reductive gas are supplied into the processing vessel so as to flow from one end of opposite ends of the processing vessel toward the other end of the processing vessel in the step of producing active hydroxyl and active oxygen species.
In the oxidation method according to the present invention, parts of the processing vessel through which the oxidative gas and the reductive gas are supplied into the processing vessel are positioned a predetermined distance apart from the processing region of the workpieces in the processing vessel.
In the oxidation method according to the present invention, the predetermined distance is determined such that the oxidative gas and the reductive gas do not affect adversely temperature distribution in the processing region of the workpieces and the oxidative gas and the reductive gas supplied into the processing vessel can be satisfactorily mixed.
The separation of the parts of the processing vessel through which the oxidative gas and the reductive gas are supplied into the processing vessel from the processing region by the predetermined distance prevents the oxidative gas and the reductive gas from adversely affecting temperature distribution in the processing region in which the workpieces are processed and enables the satisfactory mixing of the oxidative gas and the reductive gas.
In the oxidation method according to the present invention, the predetermined distance is about 100 mm or above.
In the oxidation method according to the present
Hasebe Kazuhide
Sato Shoichi
Umezawa Kota
Cuneo Kamand
Sarkar Asok Kumar
Smith , Gambrell & Russell, LLP
Tokyo Electron Limited
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