Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-03-01
2001-07-03
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S328000, C257S335000
Reexamination Certificate
active
06255693
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for implanting ions during semiconductor manufacturing by using programmable waveforms.
BACKGROUND OF THE INVENTION
Semiconductor integrated circuits (ICs) are typically manufactured using a series of deposition, implantation, and annealing steps to form desired regions and junctions within a semiconductor wafer. Implantation is premised on the theory of implanting different elements in a wafer using different energy levels, doses, and angles to achieve the optimum dopant concentration and junction depth in a wafer. An implant dose is determined by the beam current applied to ionize the elements to be implanted, implant time, and beam diameter. A higher beam current ionizes more particles, resulting in a higher implant dose concentration. Implant depth is controlled by varying the implant energy and/or angle. To achieve deeper junctions, higher energy levels and/or angles that allow channeling are used. Channeling is the phenomenon whereby implanted ions travel easily through specific crystallographic orientations.
As IC technology advances, multiple ion implants are becoming more prevalant to allow detailed engineering of doping profiles, which optimizes transistor and other IC device performance. Currently, to perform such multiple implants, implantation equipment stops the implantation beam current after each particular energy and dose. This is done either with or without removing the wafers from the chamber. The implant dose, energy, and/or angle are then changed prior to restarting the next implantation. This unduly burdens the manufacturing process due to the added overhead and cost associated with such downtime.
As a result of such high costs associated with changing implant dose, energy, and/or angles, device designers are forced to use fewer implants. Instead, they must use more DT (i.e., a combination of time spent in a furnace and the temperature at which the furnace is set). DT is needed to merge implants together by diffusing implanted ions through the wafer, a process which ideally is performed by using multiple implants to create such profiles.
It is undesirable to rely so heavily on DT to obtain desired impurity profiles. DT degrades steep implant profiles that are often crucial in ICs. A conventional doping profile is shown in
FIG. 1A
, resulting from three separate implants. The number of dopants, N, is plotted versus the depth, X, in a wafer.
FIG. 1B
, shows the effects of a 1,050 to 1,150 degrees Celsius DT for two hours used to obtain a final doping profile. As ICs are scaled down, steep implant profiles are even more critical to optimized device performance because there is less area within which to obtain desired dopant density variations necessary for proper device performance. As can be seen from
FIG. 1B
, previous techniques of forming doping profiles do not result in steep, sharply defined profiles. Furthermore, DT often results in significant lateral spread of the implanted dopants, undesirably decreasing achievable integrated circuit (IC) density.
Another problem with relying so heavily on DT is that it reduces valuable thermal budget required for many process steps needed for forming ICs. The thermal budget for a particular device is the amount of time and temperature that the device can withstand before device performance is degraded. Many process steps reduce the remaining thermal budget. It is thus critical to conserve thermal budget when possible.
There is a need for a technique for implanting semiconductor wafers which allows for efficient multiple implants. There is a need to decrease the amount of overhead and cost associated with changing implantation energy, dose, and/or angle between such implants. It is further desirable to decrease the amount of DT, which is currently used and needed, for forming doping profiles in semiconductor wafers. A technique for forming steeper, sharply defined doping profiles is needed in order to keep pace with performance standards required of ever shrinking device geometries in today's ICs.
SUMMARY OF THE INVENTION
The present invention teaches a method and apparatus for performing multiple implantations in a semiconductor wafer. An implanter is used, which allows for setting of variable waveforms, corresponding to energy, beam current, and angle, used for implantation. A ramping voltage is used to vary the energy level of the ions during a single implant step. A ramping beam current source provides a variable density of ions. Furthermore, a programmable motor is mechanically connected to a wafer table, which allows for automatic programmed tilting of a substrate being implanted on the wafer table.
An implanter with the capability of using variable waveforms for the energy, beam current, and angle gives device designers a big advantage. Using the implanter and method of the invention, detailed or well defined doping profiles are created using only a single implant, which previously required multiple implants to create. Such detail includes the ability to provide sharp transitions in doping density. By creating the doping profile using a single implant, the amount of DT (i.e., a combination of time spent in a furnace and the temperature at which the furnace is set) needed to produce the optimum profile is minimized and, in some cases, eliminated. The amount of overhead and cost associated with producing optimum doping profiles is also minimized using the invention due to the ability to create the optimum doping profiles in a single implant.
In one embodiment, during an implant, the energy levels of the ions are ramped at least twice to form detailed doping profiles. During such implant, the energy levels are ramped by applying a voltage to the acceleration tube and ramping it at approximately 75 to 160 keV/s, decreasing the ramp rate for a time, and then ramping it again at between approximately 300 to 2,500 keV/s to obtain an ending voltage of approximate 200 keV to 1 MeV prior to turning off the voltage.
REFERENCES:
patent: 3697827 (1972-10-01), Simon
patent: 3778626 (1973-12-01), Robertson
patent: 3897274 (1975-07-01), Stehlin et al.
patent: 4258077 (1981-03-01), Mori et al.
patent: 4410801 (1983-10-01), Sakurai et al.
patent: 4745287 (1988-05-01), Turner
patent: 4772976 (1988-09-01), Otomo et al.
patent: 5091655 (1992-02-01), Dykstra et al.
patent: 5126575 (1992-06-01), White
patent: 5136171 (1992-08-01), Leung et al.
patent: 5155369 (1992-10-01), Current
patent: 5160846 (1992-11-01), Ray
patent: 5177366 (1993-01-01), King et al.
patent: 5365098 (1994-11-01), Miyamoto et al.
patent: 5373164 (1994-12-01), Benveniste
patent: 5389793 (1995-02-01), Aitken et al.
patent: 5432352 (1995-07-01), vanBavel
patent: 5460989 (1995-10-01), Wake
patent: 5510648 (1996-04-01), Davies et al.
patent: 5641969 (1997-06-01), Cooke et al.
patent: 5648277 (1997-07-01), Zhang et al.
patent: 5759901 (1998-06-01), Loh et al.
patent: 5963801 (1999-10-01), Aronowitz et al.
patent: 2-305468 (1990-12-01), None
Ryssel, H., et al.,Ion Implantation, John Wiley & Sons Pub., 138-9, 148-9, 158-9, (1986).
Wolf, S., “Ion Implantation for VLSI”,Silicon Processing for the VLSI Era, vol. 1, Lattice Press, Sunset Beach CA, 309, (1986).
Prall Kirk
Reinberg Alan R.
Meier Stephen D.
Micro)n Technology, Inc.
Schwegman Lundberg Woessner & Kluth P.A.
LandOfFree
Ion implantation with programmable energy, angle, and beam... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ion implantation with programmable energy, angle, and beam..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ion implantation with programmable energy, angle, and beam... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2499721