Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Charge transfer device
Reexamination Certificate
2002-01-29
2004-03-30
Lebentritt, Michael S. (Department: 2824)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Charge transfer device
C438S149000, C438S151000, C438S143000, C438S471000, C438S520000
Reexamination Certificate
active
06713323
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device by using a gettering technique, and to a semiconductor device obtained by the manufacturing method. More particularly, the present invention relates to a method of manufacturing a semiconductor device using a crystalline semiconductor film formed by adding a metallic element that catalyzes crystallization of a semiconductor film, and to a semiconductor device obtained by the manufacturing method.
In this specification, “semiconductor device” refers to all devices capable of functioning by using semiconductor characteristics, including all electro-optical devices, semiconductor circuits and electronic devices.
2. Description of the Related Art
Thin film transistors (hereinafter referred to as TFT) are known as a typical semiconductor device using a semiconductor film of a crystalline structure (hereinafter referred to as crystalline semiconductor film). TFT manufacturing techniques attract attention as techniques for forming an integrated circuit on an insulating substrate formed from glass or the like. Projects to put driver circuit-integrated liquid crystal display devices, etc., into practical use are being advanced. Crystalline semiconductor films are being formed by a process based on conventional techniques, i.e., a process in which an amorphous semiconductor film deposited by plasma chemical vapor deposition (plasma CVD) or low-pressure CVD is processed by heat treatment or laser annealing (a technique for crystallizing a semiconductor film by irradiation with laser light).
A crystalline semiconductor film formed in this manner is an aggregate of a multiplicity of crystal grains, and the crystal orientation thereof is random and cannot be controlled. This randomness is a factor which limits characteristics of TFTs. In view of this problem, techniques described below are taken into consideration. Japanese Patent Application Laid-open No. 7-183540 discloses a technique for making a crystalline semiconductor film by adding to a film material a metallic element such as nickel which catalyzes crystallization of a semiconductor film. This technique not only has the effect of reducing the heating temperature necessary for crystallization but also improves orientation of the crystal orientation in one direction. If a TFT is formed by using a crystalline semiconductor film formed by this technique, a reduction in subthreshold factor (S-value) is achieved as well as an improvement in field-effect mobility, thus remarkably improving electrical characteristics.
However, since this technique comprises adding a metallic element capable of catalytic action, it entails a problem in that such a metallic element remains in a crystalline semiconductor film or on the film surface and causes variations in characteristics of devices obtained from the film. For example, the off current in a TFT is increased and variation in off current occurs between the respective devices. That is, a metallic element which catalyzes crystallization becomes a hindrance rather than a necessary material once a crystalline semiconductor is formed.
Gettering using phosphorus is effectively used as a means for removing such a metallic element from a particular portion of a crystalline semiconductor film. For example, it is possible to easily remove such a metallic element from a channel region of a TFT in such a manner that phosphorus is added to a source-drain region of the TFT and heat treatment at 450 to 700° C. is performed.
Phosphorus is implanted into a crystalline semiconductor film by ion doping (a method of implanting ions into a semiconductor by dissociating PH or the like in plasma and by accelerating ions by an electric field, i.e., a method which basically excludes mass separation of ions). The concentration of phosphorus necessary for gettering is 1×10
20
/cm
3
or higher. Addition of phosphorus by ion doping causes amorphization of the crystalline semiconductor film, and recrystallization of the semiconductor film is then performed by annealing. There is a problem of an impediment to the recrystallization due to an increased concentration of phosphorus. Also, addition of phosphorus at a high concentration leads to an increase in the processing time required for doping and, hence, a reduction in throughput of the doping step.
SUMMARY OF THE INVENTION
An object of the present invention is to provide, as a means for solving the above-described problems, a technique for effectively removing from a crystalline semiconductor film a metallic element remaining in the film, which has the effect of catalyzing crystallization of a semiconductor film, and which has been used to obtain the crystalline semiconductor film.
Gettering techniques are ranked as key techniques among techniques for manufacturing integrated circuits by using monocrystal silicon wafers. Gettering is known as a technique in which segregation of a metallic impurity taken into a semiconductor is caused at a gettering site by some energy to reduce the impurity concentration in an active region of a device. Gettering is broadly divided into two kinds: extrinsic gettering and intrinsic gettering. Extrinsic gettering produces a gettering effect by externally causing a strain field or chemical action. Phosphorus gettering by diffusing phosphorus through the back surface of a monocrystal silicon wafer so that the concentration of phosphorus is high falls within this category. Also, the above-mentioned gettering using phosphorus on a crystalline semiconductor film can be regarded as a kind of extrinsic gettering.
On the other hand, intrinsic gettering is known as a technique using a strain field of a lattice defect in a monocrystal silicon wafer which oxygen generated in the wafer concerns. The present invention has been achieved by focusing attention to such intrinsic gettering using a lattice defect or lattice strain. To apply such gettering to a crystalline semiconductor film having a thickness of about 10 to 100 nm, means described below are adopted.
The present invention comprises a process in which a rare gas element is added to a crystalline semiconductor thin film to form a gettering site, and a process for performing heat treatment on the semiconductor thin film. A metal contained in the crystalline semiconductor thin film is moved by the heat treatment to be captured at the gettering site (a region into which ions of the rare gas element have been added), thus removing or reducing the metal in the region of the crystalline semiconductor thin film other than the gettering site. The crystalline semiconductor thin film may be irradiated with strong light instead of undergoing ordinary heat treatment or may be simultaneously processed by ordinary heat treatment and irradiation with strong light.
The present invention is also characterized by placing a gettering site at a sufficient distance from a channel region in a TFT, considering the fact that a strong electric field is liable to concentrate in the vicinity of an end of a gate electrode, i.e., the boundary on the channel region when the TFT is driven.
As a method of adding a rare gas element, ion doping or ion implantation may be used. As a rare gas element used in accordance with the present invention, one of or two or more of He, Ne, Ar, Kr, and Xe may be selected. It is preferable to use Ar as a low-priced gas among these elements. If ion doping is performed, the concentration of one rare gas element contained in a doping gas is set to 30% or higher and, preferably, to 100%. For example, a doping gas having a Kr gas concentration of 30% and an Ar gas concentration of 70% may be used.
According to one aspect of the present invention disclosed in this specification, there is provided a semiconductor device comprising: an insulating film; an electrode; a channel region which overlaps the electrode with the insulating film interposed therebetween; a first impurity region which is adjacent to the channel region and which contains an impurity element i
Hamada Takashi
Murakami Satoshi
Nakamura Osamu
Yamazaki Shunpei
Costellia Jeffrey L.
Lebentritt Michael S.
Luhrs Michael K.
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