Electron filter for current implanter

Details Electron filter for current implanter Electron filter for current implanter

2002-08-13

2004-05-11

Lee, John R. (Department: 2881)

Radiant energy

Irradiation of objects or material

Irradiation of semiconductor devices

C250S398000, C250S290000

Reexamination Certificate

active

06734447

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to process chambers for processing substrates in the fabrication of semiconductor integrated circuits. More particularly, the present invention relates to an electron filter for removing dissociated electrons from a process chamber, particularly an ion implantation chamber for semiconductors.
BACKGROUND OF THE INVENTION
Generally, the process for manufacturing integrated circuits on a silicon wafer substrate typically involves deposition of a thin dielectric or conductive film on the wafer using oxidation or any of a variety of chemical vapor deposition processes; formation of a circuit pattern on a layer of photoresist material by photolithography; placing a photoresist mask layer corresponding to the circuit pattern on the wafer; etching of the circuit pattern in the conductive layer on the wafer; and stripping of the photoresist mask layer from the wafer. Each of these steps, particularly the photoresist stripping step, provides abundant opportunity for organic, metal and other potential circuit-contaminating particles to accumulate on the wafer surface.
In the semiconductor fabrication industry, minimization of particle contamination on semiconductor wafers increases in importance as the integrated circuit devices on the wafers decrease in size. With the reduced size of the devices, a contaminant having a particular size occupies a relatively larger percentage of the available space for circuit elements on the wafer as compared to wafers containing the larger devices of the past. Moreover, the presence of particles in the integrated circuits compromises the functional integrity of the devices in the finished electronic product. Currently, mini-environment based IC manufacturing facilities are equipped to control airborne particles much smaller than 1.0 &mgr;m, as surface contamination continues to be of high priority to semiconductor manufacturers. To achieve an ultra-clean wafer surface, particles must be removed from the wafer, and particle-removing methods are therefore of utmost importance in the fabrication of semiconductors.
Ion implantation is a processing step commonly used in the fabrication of the integrated circuits on the wafer. Ion implantation is a form of doping, in which a substance is embedded into the crystal structure of the semiconductor substrate to modify the electronic properties of the substrate. Ion implantation is a physical process which involves driving high-energy ions into the substrate using a high-voltage ion bombardment. The process usually follows the photolithography step in the fabrication of the circuits on the wafer.
The ion implantation process is carried out in an ion implanter, which generates positively-charged dopant ions in a source material. A mass analyzer separates the ions from the source material to form a beam of the dopant ions, which is accelerated to a high velocity by a voltage field. The kinetic energy attained by the accelerated ions enables the ions to collide with and become embedded in the silicon crystal structure of the, substrate. Finally, the doped silicon substrate is subjected to a thermal anneal step to activate the dopant ions.
A typical conventional ion implantation chamber is generally indicated by reference numeral
10
in FIG.
1
and includes a chamber wall
12
that is provided with a chamber bottom
13
and defines a chamber interior
14
. A chamber lid
16
may be provided for closing the chamber interior
14
. A scan wheel
18
, having a rotatable hub
19
from which extend multiple spoke arms
20
, is mounted in the chamber interior
14
. A wafer holder
21
is mounted on the extending end of each spoke arm
20
. In application, a wafer
22
is mounted on the bottom surface of each wafer holder
21
for the implantation of ions in the wafer
22
, as shown in FIG.
2
. An ion beam generating system
24
, disposed beneath the chamber bottom
13
, generates and emits an ion beam
25
upwardly through an elongated slot
15
provided in the chamber bottom
13
adjacent to the scan wheel
18
. Accordingly, as the scan wheel
18
rotates typically at a speed of about 900 r.p.m., as indicated in
FIG. 1
, the wafers
22
mounted on the bottom surfaces of the respective wafer holders
21
are passed over the slot
15
, such that the ion beam
25
strikes the surface of the wafer
22
and implants ions from the ion beam
25
into the material layer or layers (not shown) on the wafer
22
. A cryo pump
27
is operated to draw process gases and other residual chemicals from the chamber interior
14
, through a pump opening
28
in the chamber bottom
13
.
The ion implantation process heretofore described is carried out under high-vacuum conditions in the chamber interior
18
. These conditions produce dissociated electrons, which adhere to the surface of the wafer
22
during and after the process and are a major source of particle contamination. The resulting particle contamination adversely affects the yield of devices having features with sizes less than 0.13 &mgr;m on the wafer
22
.
Accordingly, an object of the present invention is to provide an electron filter for a process chamber used in the processing of substrates.
Another object of the present invention is to provide an electron filter for preventing or minimizing particle contamination of a substrate during or after an ion implantation process.
Still another object of the present invention is to provide an electron filter for trapping electrons during an ion implantation process.
Another object of the present invention is to provide an electron filter which contributes to a clean, reduced-particle environment inside a process chamber.
Yet another object of the present invention is to provide an electron filter which enhances the yield of devices on a substrate.
A still further object of the present invention is to provide an electron filter which is positively charged to facilitate trapping electrons during an ion implantation process.
Yet another object of the present invention is to provide an electron filter which may be used in conjunction with a cryo pump to remove dissociated electrons from the surfaces of substrates and trap the electrons to prevent or reduce particle contamination of the substrates.
Another object of the present invention is to provide a method of removing electrons from substrates or a process chamber in which substrates are processed in order to prevent or at least reduce particle contamination of the substrates.
Still another object of the present invention is to provide an ion implantation chamber which is equipped with an electron filter for the removal of electrons from substrates processed in the chamber or from the chamber interior.
SUMMARY OF THE INVENTION
In accordance with these and other objects and advantages, the present invention comprises an electron filter for trapping dissociated electrons in a substrate processing chamber. The electron filter typically includes at least one filter element which is connected to a voltage source for applying a positive voltage to the filter element. During an ion implantation process, dissociated electrons are drawn from the interior of the chamber and trapped in the filter element to prevent or reduce contamination of the substrates.
In a typical embodiment, the electron filter is mounted directly above a pump opening in the chamber bottom and electrons are trapped in the filter as a cryo pump evacuates particulate contaminants from the chamber. The electron filter may include upper and lower or upper, middle and lower filter elements separated from each other with spacers. In a typical embodiment, the filter element or elements typically have mesh openings less than about 1 mm wide.


REFERENCES:
patent: 5289010 (1994-02-01), Shohet
patent: 5374456 (1994-12-01), Matossian et al.
patent: 5942039 (1999-08-01), Kholodenko et al.
patent: 6038018 (2000-03-01), Yamazaki et al.
patent: 6101971 (2000-08-01), Denholm et al.
patent: 6132564 (2000-10-01), Licata

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