Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
1998-09-29
2001-10-02
Chaudhari, Chandra (Department: 2813)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S440000, C438S655000, C438S656000, C438S657000
Reexamination Certificate
active
06297113
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally related to a method of manufacturing a semiconductor device and a semiconductor device manufactured thereby, and more particularly, to a semiconductor device manufacturing method wherein a well is formed in a semiconductor substrate by high-energy ion implantation.
2. Description of the Background Art
A semiconductor manufacturing method—by which, a well is formed by high-energy ion implantation after an isolating oxide film for separating element regions has been formed—is described in, e.g., (1) Japanese Patent Application Laid-open No. 6-252354 and (2) Japanese Patent Application Laid-open No. 5-74729. More specifically, reference (1) discloses a method comprising the steps of forming an isolating oxide film; forming a resist mask having an opening on a silicon nitride film used for forming the isolating oxide film as well as on the isolating oxide film, by omission of formation of a thermal oxide film commonly called a pad film; and forming a well by implanting ions through the opening. Reference (2) discloses a method comprising the steps of: forming a doped polysilicon cover film in place of a pad oxide film; implanting ions into a substrate through an opening formed in a resist mask; and subjecting the substrate to heat treatment for 6 hrs. at 1200° C., thus forming a well.
The pad film plays a role in preventing introduction of undesirable impurities into a substrate from a resist mask or from outside the substrate at the time of ion implantation or heat treatment following the ion implantation. When high-energy ions pass through the pad oxide film, there occurs a knock-on phenomenon in which oxygen atoms are knocked on from the oxide film. Because of this phenomenon, there arises a problem of electrical properties of an element formed on a well being deteriorated by excessive oxygen atoms mixed into the surface of the substrate or by crystalline imperfections in a monocrystalline area within the substrate.
According to the technique described in reference (1), it is necessary to change implantation energy several times in a stepped manner in order to form a uniform well. Further, since the technique uses a silicon nitride film which is as thick as 100 nm, a great noncontiguous region arises along a boundary area between the silicon nitride film and the isolating oxide film. For this reason, the technique is not suitable for formation of a well of a microminiature LSI. Further, the reference does not at all describe knocked-on oxygen atoms. The technique described in reference (2) is intended to solve the problem stemming from the pad oxide film, through use of the cover film. However, the technique suffers a drawback of a substrate being subjected to heat treatment for a long period of time at high temperature.
Recent LSI chips are made compact and have their structure further complicated. For this reason, there exists a strong demand for both a reduction in thermal load on a semiconductor device throughout the entire manufacturing process and an improvement in reliability of the device so as to ensure a longer life of the device.
The present invention has been conceived to solve the aforementioned problems, and a first object of the present invention is to provide a semiconductor device manufacturing method which enables a considerable reduction in the amount of oxygen atoms included in a gate oxide film formed on a well or a considerable reduction in the degree of crystalline imperfection.
A second object of the present invention is to provide a semiconductor device manufacturing method which enables a recovery or improvement in the life of a gate oxide film of an element formed on a well through heat treatment at a comparatively low temperature.
A third object of the present invention is to provide an optimum combination of transistor structural parameters, conditions for ion implantation, and conditions for heat treatment, which is required for achievement of a recovery or improvement in the life of a gate oxide film.
SUMMARY OF THE INVENTION
The above objects of the present invention are achieved by a semiconductor device manufacturing method (first method). The method includes an element region formation step of forming an element region by separating the surface of a semiconductor substrate through use of an isolating oxide film. The method also includes a pad film formation step of forming a pad film on the surface of the element region. The method further includes a first well formation step of forming a resist mask having an opening in a first given region on the pad film and on the isolating oxide film, removing the pad film from the inside of the opening, forming a well in the semiconductor substrate by implantation of ions of the first conductivity type into the opening, and removing the resist mask. Moreover, the method includes a dielectric film formation step of forming a dielectric film for use as a gate dielectric film on the surface of the well by means of thermal oxidation.
The above objects of the present invention are also achieved by the semiconductor device manufacturing method wherein a second well formation step is provided between the pad film formation step and the dielectric film formation step (second method). The step comprises formation of a resist mask having an opening in a second given region on the pad film and the isolating oxide film, removal of the pad film from the inside of the opening, formation of a well in the semiconductor substrate by implantation of ions of the second conductivity type into the opening, and removal of the resist mask.
The above objects of the present invention are also achieved by the semiconductor device manufacturing method wherein a third well formation step is provided between the pad film formation step and the dielectric film formation step (third method). The step comprises formation of a resist mask having an opening in a second given region on the pad film and the isolating oxide film, formation of a well in the semiconductor substrate still having the pad film formed thereon by implantation of ions of the second conductivity type into the opening, and removal of the resist mask.
The above objects of the present invention are also achieved by the semiconductor device manufacturing method wherein a sacrificial oxide film step is provided between the first well formation step and the dielectric film formation step (fourth method). The step comprises formation of a sacrificial oxide film through thermal oxidation on the surface of the well from which the pad film is removed and removal of the sacrificial oxide film.
The above objects of the present invention are also achieved by a semiconductor device manufacturing method (fifth method). The method includes an element region formation step of forming an element region by separating the surface of a semiconductor substrate through use of an isolating oxide film. The method also include a pad film formation step of forming a pad film on the surface of the element region. The method further includes a fourth well formation step of forming a resist mask having an opening in a first given region on the pad film and on the isolating oxide film, forming a well in the semiconductor substrate still having the pad film formed thereon by implantation of ions of the first conductivity type into the opening, and removing the resist mask. The method further includes an annealing step of annealing the surface of the well having the pad film still formed thereon in a nitrogen atmospheric furnace or a rapid thermal annealing furnace and of removing the pad film. Moreover, the method includes a dielectric film formation step of forming a dielectric film for use as a gate dielectric film on the surface of the well by means of thermal oxidation.
The above objects of the present invention are also achieved by the semiconductor device manufacturing method wherein a fifth well formation step is provided between the pad film formation step and the annealing step (sixth method). The step
Chaudhari Chandra
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
Schillinger Laura M
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