Measuring and testing – Surface and cutting edge testing – Roughness
Reexamination Certificate
1999-01-19
2001-08-14
Noland, Thomas P. (Department: 2856)
Measuring and testing
Surface and cutting edge testing
Roughness
Reexamination Certificate
active
06272907
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to that area of metrologic technology concerned with measuring a surface's topology, and, more particularly, to profilometry, and to atomic force microscopy (“AFM), also sometimes referred to as scanning force microscopy (“SFM”).
2. Description of the Prior Art
Recently, the field of surface profilometry has expanded greatly. In addition to advances in classical profilometry, the nascent fields of tunneling force microscopy and AFM have greatly enlarged the interest, scope and capability of profilometric technology.
Classical profilometry scans a surface along orthogonal X-axis and Y-axis directions using a diamond tipped stylus while measuring the stylus' vertical (Z-axis) displacement. In many commercial instruments, the stylus is connected to a linear variable differential transformer (“LVDT”) sensor, or to a capacitive plate, for sensing the stylus' vertical displacement. Typically, the stylus includes an elongated bar that is secured with a pair of coaxial pivots, while the other end of the stylus is coupled to the Z-axis displacement sensing mechanism, e.g. either a capacitor's plate for a capacitive sensor, or a ferromagnetic plunger of the LVDT sensor.
Very sensitive flexure pivot assemblies are commonly used for supporting the stylus used for classical profilometry. The components of such a flexure pivot assembly are small, delicate, require precision assembly, and therefore are expensive to manufacture. In addition, machining such stylus assemblies from discrete components tends to make them comparatively large, and the sensing elements to which they couple are also relatively large. Therefore, profilometer heads including the stylus are, in general, larger than desirable. Consequently, profilometer heads generally respond slowly to vertical displacements, and the scanning speed at which profilometers operate is limited by the inertia of the profilometer's head. Hence, improving profilometer performance while concurrently reducing their manufacturing cost and contact force makes gentler, smaller, lighter, faster and less expensive profiling heads very desirable.
The more recently developing field of AFM for measuring a surface's topography generally uses a very light, micromachined, bendable cantilever probe having a sharp tip for sensing a surface's topology at atomic dimensions. However, systems for detecting minute vertical displacement of an AFM's sensing probe, e.g. optical-beam-deflection or optical interferometry, are, in general, much larger than the cantilever itself. Consequently, it is generally difficult to move an AFM's head assembly as swiftly as desired for high speed scanning. Traditionally, AFM systems circumvented this problem by holding the sensing head assembly stationary while moving the sample along orthogonal X and Y axes. Although such a system may move small samples easily during AFM scanning, it is generally unsuited for use on large samples, such as semiconductor wafers or magnetic recording disks measuring several inches in diameter.
Accordingly, not only does AFM necessarily require a physically small AFM sensing probe, but advancing AFM technology and performance also makes a correspondingly small, light weight, and compact sensor for detecting AFM probe Z-axis displacement desirable. Integration of a compact vertical displacement sensor into an AFM probe would yield a small, light weight, and compact AFM head having a low mass. Such a low mass AFM probe would permit very high speed scanning along orthogonal X-axis and Y-axis directions by a small and compact X-axis and Y-axis drives.
Referring now to
FIG. 1
, depicted there is a prior art AFM or profilometer system referred to by the general reference character
20
. The system
20
includes a XY axes drive
22
upon which rests a sample
24
. The XY axes drive
22
scans the sample
24
laterally with respect to a sensing head
26
along a X-axis
32
and a Y-axis
34
that are orthogonal to each other, or along any other arbitrary axes obtained by compound motion along the X-axis
32
and the Y-axis
34
. In the instance of an AFM, to provide rapid movement along the axes
32
and
34
the XY axes drive
22
may be provided by a piezo electric tube having
4
quadrant electrodes. As the XY axes drive
22
moves the sample
24
laterally, a probe tip or stylus
36
lightly contacts an upper surface
38
of the sample
24
while moving up and down vertically parallel to a Z-axis
42
in response to the topology of the upper surface
38
. In the illustration of
FIG. 1
, the probe tip or stylus
36
is secured to a distal end of an elongated cantilever arm
44
extending outward from the sensing head
26
. The sensing head
26
, which may if necessary be servoed up and down parallel to the Z-axis
42
, senses vertical deflection of the probe tip or stylus
36
by the topology of the sample's upper surface
38
. A signal transmitted from the sensing head
26
to some type of signal processing device permits recording and/or displaying the topology of the upper surface
38
as detected by the system
20
.
AFM applications of systems such as of the system
20
experience substantial cross coupling among movements along the mutually perpendicular axes
32
,
34
, and
42
. Consequently, movement of the sample
24
with respect to the AFM sensing head
26
, and frequently even the measurement of such movement, are insufficiently precise for metrologic applications. Consequently, at present AFM performance may be adequate for imaging, but not for metrology. The mass of the sample
24
itself (such as an 8 inch diameter semiconductor wafer) impedes high speed, precise movement of the sample
24
. Therefore, scanning a massive sample
24
swiftly requires holding the sample
24
fixed while scanning the sensing head
26
.
FIG. 2
depicts an alternative embodiment, prior art AFM or profilometer system. Those elements depicted in
FIG. 2
that are common to the AFM or profilometer system depicted in
FIG. 1
carry the same reference numeral distinguished by a prime (′) designation. In the system
20
′ depicted in
FIG. 2
, the sample
24
′ rests on a base plate
48
which also supports a XY stage
52
. In scanning the sample
241
using the system
20
′, the XY stage
52
moves the sensing head
26
′ carrying the cantilever arm
44
′ parallel to the orthogonal X-axis
32
′ and Y-axis
34
′, or along any other arbitrary axes obtained by compound motion along the X-axis
32
′ and the Y-axis
34
′.
E. Clayton Teague, et al., in a technical article entitled “Para-flex Stage for Microtopographic Mapping” published the January 1988, issue of the Review of Scientific Instruments, vol. 59 at pp. 67-73 (“the Teague et al. article”), reports development of a monolithic, Para-flex XY stage
52
, that the article describes as being machined out of metal. The embodiments of the monolithic plate of such an XY stage
52
is depicted both in
FIGS. 3
a
and
3
b
. The XY stage
52
depicted in both FIGs. includes an outer base
62
that is fixed with respect to the system
20
′. The outer base
62
is coupled to and supports a Y-axis stage
64
by means of four stage suspensions
66
. Each of the stage suspensions
66
consists of an intermediate bar
68
, one end of which is coupled to the outer base
62
by a flexure
72
, and another, distal end of the intermediate bar
68
is coupled to the Y-axis stage
64
by a second symmetrical flexure
72
. Similar to the coupling of the outer base
62
to the Y-axis stage
64
, the Y-axis stage
64
is coupled to and supports a X-axis stage
74
by means of four stage suspensions
66
that are identical to the stage suspensions
66
which couple the outer base
62
to the Y-axis stage
64
. The stage suspensions
66
coupling the outer base
62
to the Y-axis stage
64
and the stage suspensions
66
coupling the Y-axis stage
64
to the X-axis stage
74
are or
Neukermans Armand P.
Slater Timothy G.
Noland Thomas P.
Schreiber Esq. D. E.
Xros, Inc.
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