Semiconductor device manufacturing: process – Introduction of conductivity modifying dopant into...
Reexamination Certificate
1998-12-03
2001-02-20
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Introduction of conductivity modifying dopant into...
C438S302000, C438S303000
Reexamination Certificate
active
06191012
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates generally, to a method for forming a doped region in a semiconductor device, and more particularly, to a method for forming a shallow doped junction using ion implantation.
2. Description of the Prior Art
As the demand for high performance semiconductor devices increases, device manufacturers continually redesign semiconductor devices, such as integrated circuits, to have smaller and smaller dimensions. Of the many different device components used in an integrated circuit, the dimension of the gate electrode in a metal-oxide semiconductor (MOS) device is the benchmark dimension by which all other device components are measured. Typically, state of the art MOS devices have gate dimensions in the range of about 0.1 to 0.25 microns.
As gate dimensions are scaled to smaller and smaller values, a concomitant requirement for a reduction in the junction depth of transistor components such as source and drain regions, exists. In addition to requiring a small junction depth, state of the art MOS transistors also require extremely high surface doping concentrations in the source and drain regions. Typically, many doped regions are formed in a semiconductor substrate in the vicinity of the substrate surface. Dopant atoms of either n-type or p-type are typically incorporated into the silicon substrate using both thermal diffusion and ion implantation.
Ion implantation is a physical process in which dopant atoms are ionized, accelerated to a velocity high enough to penetrate the surface of a silicon substrate, focused into a narrow ion beam, and scanned as a beam across the surface of a semiconductor substrate. Dopant ions impacting the surface of the substrate enter the substrate and come to rest below the substrate surface. The depth of penetration into the semiconductor substrate depends upon the particular species and the ion implantation energy. Ion implantation is used in most doping operations in the fabrication of submicron dimension integrated circuit devices. State of the art ion implantation processes can be carried out to form doped regions of precise doping concentration and implantation depth. Doping by means of thermal diffusion is a chemical process typically used to dope thin film layers that do not require the formation of well-defined doped regions.
Typically, source and drain regions in MOS transistors are formed by ion implantation techniques, and in the case of an n-type transistor, dopants such as phosphorus, arsenic, and antimony are commonly used. Modem ion implantation systems analyze an ion beam that has been extracted from an ion source. The extraction efficiency varies depending upon the particular source material and the particular dopant species to be implanted. For common n-type dopants the maximum beam currents are obtained from singly charged individual ions.
To operate an ion implantation system efficiently, and at low cost, a maximum beam current is necessary to maintain a high throughput. Accordingly, the formation of n-type source and drain regions is most commonly carried out using singly-charged, single n-type ions. Since the ion implantation depth, for a given species, varies directly with the ion implantation energy, a very low implantation energy must be used to form a shallow junction in the substrate. The ion implantation system must be operated at very low voltages to obtain the low implantation energy necessary to form a shallow doped region. However, both ion beam extraction efficiency and dose measurement can be adversely affected at low voltage operation. Additionally, at low voltages, beam stability is reduced and spot size control becomes more difficult. Accordingly, a need existed for a method of forming a shallow, highly-doped region in a semiconductor substrate, while maintaining optimal ion implantation operating conditions.
SUMMARY OF THE INVENTION
In practicing the invention there is provided a method for forming a shallow junction in a semiconductor device, which in one embodiment, includes the implantation of an antimony dimer into a silicon substrate. A shallow doped region having a dopant concentration of about 1.0E17 to at least the solid solubility of antimony in silicon (1.0E20 atoms/cm
3
) is obtained with a junction depth ranging from about 5 to 80 nanometers. The inventive process enables high efficiency operation of an ion implantation system, while improving the overall throughput of the ion implantation system. By creating shallow doped junctions with an antimony dimer, the effective energy of the implantation is one-half of that for a single antimony ion. Because the effective implantation energy is one-half that of the single ionic species, the ion implantation system can be operated at relatively high energy levels. Additionally, the implantation of antimony dimer imparts two antimony atoms for each implanted ion. As a result, the dose necessary to produce a highly-doped region can be obtained at twice the rate realized from a single antimony ion.
The inventive process includes the steps of providing a substrate having a predefined implant region; providing an ion beam of substantially pure antimony dimer; and implanting the antimony dimer into the predefined implant region. The foregoing process can be advantageously employed to form a variety of device structures and integrated circuit device, such as source drain extension regions, implanted resistors, bipolar emitter regions, and the like.
REFERENCES:
patent: 5893743 (1999-04-01), Gomi et al.
patent: 6008098 (1999-12-01), Pramanick et al.
patent: 6022771 (2000-02-01), Ma et al.
patent: 6025242 (2000-02-01), Ma et al.
Buynoski Matthew S.
Ng Che-Hoo
Advanced Micro Devices
Brinks Hofer Gilson & Lione
Le Dung A
Nelms David
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