Ion implantation beam monitor

Details Ion implantation beam monitor Ion implantation beam monitor

2001-08-02

2003-11-11

Nguyen, Kiet T. (Department: 2881)

Radiant energy

Irradiation of objects or material

Irradiation of semiconductor devices

C250S398000

Reexamination Certificate

active

06646276

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to an ion implantation beam monitor, in particular for monitoring an ion beam in an ion implanter which implants ions into substrates such as semiconductor wafers.
Semiconductor devices are typically formed from a semiconductor substrate material into which atoms or molecules of selected dopants have been implanted or defused. The dopant particles produce regions in the semiconductor substrate having varying conductivity. By selecting appropriate dopant materials, the majority charge carrier may be locally altered within the substrate.
One preferred technique for adding dopant materials to semiconductor substrates uses ion implantation. This technique minimises the size of the device features created by the dopants within the substrate, reducing the overall size of the semiconductor device itself and increasing operational speed.
The principles of operation of an ion implantation apparatus will be familiar to those skilled in the art. Briefly, a plasma generates positive ions of the selective dopant material in an ion source. The ion source ejects the required positively charged ions, which are accelerated by application of an acceleration potential through a magnetic field. The magnetic field is generated by a mass selection arrangement which deflects the ejected ions around a curved path. The radius of curvature of the flight path of the ions is dependent upon the mass/charge ratio of the individual ions. The exit of the mass selection arrangement has a slit within it so that only ions having a predetermined mass/charge ratio can exit the mass selection arrangement.
Those ions exiting the mass selection arrangement impinge upon a semiconductor substrate to be doped. Typically, this substrate will have previously been patterned with photo resist so that only selected regions are doped. Usually, the ions are decelerated after leaving the mass selection arrangement by a further, adjustable high voltage, to allow the final velocity (and hence, the penetration depth into the wafer) of the ions to be chosen.
Frequently, the cross-sectional area of the ion beam at the substrate is less than that of the substrate. This necessitates scanning of either the substrate relative to a fixed direction ion beam or scanning the ion beam across a fixed substrate. In practice, it is preferable to scan the substrate while maintaining the ion beam in a fixed direction, in a manner described below.
FIGS. 1
a
and
1
b
show a typical substrate holder
10
looking along the lines of ions exiting the slit in the mass selection arrangement. The substrate holder
10
comprises a plurality of substrate supports or paddles
20
, onto which substrates to be doped may be affixed. The substrates supports
20
are spaced equidistantly from a central hub
22
by a plurality of spokes
24
. Located between two of the spokes is a sheet of solid material known as a flag
32
. The purpose of the flag is to allow indexing of the substrates, as will be described in more detail below.
The central hub
22
is connected to a drive
26
by a shaft
28
. The drive
26
, which may for example be an electric motor, drives the shaft
28
such that the hub
22
is caused to move reciprocally in the manner of an inverted pendulum. Referring to
FIG. 1
a,
this motion is indicated by the arrows AA′.
In addition to its reciprocal motion, the hub is also rotated about an axis perpendicular to it, as indicated by the second arrow B in
FIG. 1
a.
Thus, the ion beam, which normally follows a fixed, linear trajectory once it exits the mass selection apparatus, is caused to scan across the plurality of substrates held on the substrate supports
20
by the reciprocating and rotating movement of the substrate holder
10
. The motion of the substrate holder relative to the ion beam creates a series of curvilinear “stripes” across each substrate.
It will be understood that the reciprocal movement of the substrate holder described herein is but one exemplary method of scanning the ion beam relative to the substrates. For example, the substrate holder may be moved linearly in the vertical plane instead, or in a number of other ways.
In order to ensure that each substrate is doped substantially uniformly across its face, it is useful that the ion beam striking the substrates be monitored. If irregularities or drop-outs in the beam occur (due, for example, to sparking in the high voltage supply that accelerates the ions), then the substrate will be doped non-uniformly. One technique used to carry out such monitoring employs a beam stop, arranged downstream of the ion beam. Such a beam stop is also shown schematically in
FIGS. 1
a
and
1
b.
The beam stop
30
includes a Faraday type current detector
40
which may, for example, be a Faraday cup or bucket. The principles of such a device are well-known. Briefly, the centre of the ion beam is directed toward the Faraday type current detector
40
, which absorbs ions from the ion beam impinging upon it. An ion beam current is measured by ancillary circuitry
50
, which calculates the current from the accumulated charge in the Faraday type detector
40
. As the reciprocal movement of the shaft
28
supporting the hub
22
causes the substrate holder
10
to pass between the ion beam and the beam stop, the ion beam is absorbed by the substrates rather than the Faraday type detector, and the beam stop current reduces.
Monitoring of the ion beam current has, in the past, been carried out simply by observing the beam stop current during those periods when the Faraday type detector
40
is completely uncovered, i.e. when the shaft
28
of the substrate holder
10
has swung away from the beam stop
30
, as shown in
FIG. 1
a.
However, in this approach the ion beam drop-outs described above may well be missed, if they occur as the substrate holder moves in front of the Faraday type detector.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved ion implantation beam monitor that alleviates the problems with the prior art.
According to a first aspect of the present invention, there is provided an ion implantation apparatus comprising an ion beam source, a substrate holder downstream of the ion beam source, the substrate holder supporting a plurality of radially spaced substrates, scanning means for scanning the substrates relative to the ion beam, a beam stop, downstream of the substrate holder, for capturing ions in the ion beam not striking the substrate holder, and for generating a beam stop current therefrom, and sampling means, for taking a plurality of samples of the beam stop current which is generated as the ion beam passes between the radially spaced substrates, such that the ion beam current may be monitored over a plurality of discrete time periods.
The gap between substrates is thus used to obtain information about the ion beam continuity. By sampling the beam stop current each time the ion beam passes between two adjacent substrates, for example, information can be obtained on the ion dose received by these two substrates. This in turn can assist in identifying a particular substrate which has not received a correct dose, due to drop-outs in the ion beam, for example.
According to a second aspect of the present invention, there is provided an ion implantation apparatus comprising an ion beam source, a substrate holder, downstream of the ion beam source, scanning means for scanning the substrate holder relative to the ion beam at a predetermined scan rate, a beam stop, downstream of the substrate holder, for capturing ions in the ion beam not striking the substrate holder, and for generating a beam stop current therefrom, timing means, for measuring the time difference between a first time, at which the beam stop current first reduces from a maximum value as the substrate holder passes in front of the ion beam, and a second time, at which the beam stop current first reaches a minimum value as the substrate holder passes in front of the ion beam, and output means for outputting the product of t

Affiliated with

Also associated with

Rating

Ion implantation beam monitor 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 beam monitor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ion implantation beam monitor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3138733