as

(12) United States Patent

Spady et al.

(10) Patent No.:           

(45) Date of Patent:       Aug. 24, 2004

COMPACT ROTATING STAGE10/1991 Kato414/936 12/1998 Suzuki et al.414/936

5/2001 White et al.414/935

1/2002 Haraguchi et al.414/936

8/2002 Jourtchenko et al.33/568

8/2002 Kawamatsu et al.700/229

4/2003 Lau et al.414/936

* cited by examiner

(75) Inventors: Blaine R. Spady, Lincoln, NE (US); Dan M. Colban, Tracy, CA (US)

(73) Assignee: Nanometrics Incorporated, Milpitas, CA (US)

Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 Primary Examiner—G. Bradley Bennett

U.S.C. 154(b) by O days.                               (74) Auorney, Agent, or Firm—Silicon Valley Patent Group LIP

                                                                                                 (57)                             ABSTRACT

A compact stage includes a rotary driver and a vertical linear driver that are in the same horizontal plane, which advan-

tageously reduces the height of the device. The stage may include a rotating shaft to which a chuck is mounted. A rotary drive, which may be an annular rotary drive, is coupled to and rotates the rotating shaft. A linear drive is also coupled to the rotating shaft and in one embodiment extends through the center of the annular rotary drive. The linear drive moves the rotating shaft along a vertical axis. The linear drive may be, e.g., a voice coil motor that uses a spring to bias the rotating shaft along the vertical axis.

20 Claims, 7 Drawing Sheets

(21)     Appl. No.: 10/622,385

(22)     Filed:        Jul. 17, 2003

(51)     Int. Cl.7    B65G 49/07

(52)     U.S. Cl.33/569; 414/936

(58) Field of Search33/568, 569; 414/774,

414/935, 936; 269/71

(56)                          References Cited

A * 1/1988 Neuhaus .	269/71
4,770,600 A * 9/1988 Ishikawa .	414/936
4,896,869 A * 1/1990 Takekoshi .	269/71
A * 10/1991 Igari	414/935

U.S. PATENT DOCUMENTS

                                         24,                                                     6,779,278

                                        24, 2004       Sheet      7                     6,779,278

                                           24                                                        779278

                                                    24 2004          Sheet        7                              779278

                                           24                                                        779278

24,                                                        6,779,278

24,                                                        6,779,278

10

 

1		2
COMPACT ROTATING STAGE		tion. A platform is movably coupled to the base, e.g., through linear bearings, and moves along a vertical axis with respect to the base. The annular rotary drive is coupled to
FIELD OF THE INVENTION		one side of the platform, e.g., at an outer portion of the
The present invention relates to a stage used to transport		platform, and the linear drive is coupled to opposing side of the platform, e.g., at an inner portion. The inner portion of
and position substrates for measurement and inspection		the platform may extend through the center of the annular
and/or processing, and in particular to a stage that moves		rotary drive. A rotary bearing may be used to couple the
rotationally and vertically.		platform to the rotating shaft.
BACKGROUND	10	In addition, the stage may include a spring that provides a bias on the rotating shaft along the vertical axis. The linear
Substrates, such as semiconductor wafers or flat panel		drive may be a voice coil motor that can provide a force to
displays, are typically processed in multiple steps. Many of		overcome the spring bias to move the rotating shaft along the
these steps require the measurement and inspection of		vertical axis.
surface characteristics. Surface measurement and inspection	15	In another embodiment of the present invention, a stage
typically are performed using a stage that moves the sub-		includes a rotating shaft to which a chuck is mounted and a
strate so that the entire surface of the substrate can be		means for rotating the rotating shaft. A means for driving the
measured or inspected. In addition, some process steps may		rotating shaft along a vertical axis is also included, where the
be performed on a stage.		means for driving the rotating shaft is on the same horizontal
One type of stage moves in the Cartesian coordinate	20	plane as the means for rotating the rotating shaft. In one
system, i.e., in the X and Y directions, and are commonly		embodiment, the means for driving the rotating shaft
referred to as XY stages. An XY stage can move a substrate		extends through the means for rotating the rotating shaft.
in two independent orthogonal directions, X and Y, to select		In one embodiment, the means for rotating the rotating
an area on a substrate for viewing, imaging, measurement or		shaft is an annular rotary driver. The means for driving the
processing.	25	rotating shaft may be a voice coil motor and in one embodi-
Another type of stage used in the measuring of substrates		ment includes a spring to bias the rotating shaft along the
is a polar coordinate stage, sometimes referred to as an R-0		vertical axis.
stage. R-0 stages move a substrate in a single linear direction		In yet another embodiment of the present invention, a
(R-motion) and also rotate the stage (0-motion). By moving	30	method of moving a stage includes driving a shaft along a
the substrate in the R direction and rotating the substrate,		vertical axis and rotating the shaft about the driver that
any area on the substrate surface may be appropriately		drives the shaft along said vertical axis, such that the shaft
positioned for viewing, imaging, measuring or processing.		and the driver are on the same horizontal plane.
Both types of stages, Cartesian and polar, sometimes		The method may further include driving the shaft and the
include movement in the vertical direction, referred to as the	35	driver along the vertical axis in a horizontal direction.
Z direction.		Further, the method may include biasing the shaft along the
Stages conventionally include separate actuators or		vertical axis, wherein driving the shaft along the vertical axis
motors for each independent direction of motion. The actuators are generally stacked directly or indirectly, over each		comprises applying a force to overcome the bias.
other. Thus, for example, a conventional polar coordinate	40	BRIEF DESCRIPTION OF THE DRAWINGS
stage will place the 0 motor on top of the Z motor.		FIGS. 1 and 2 show perspective views of a compact stage,
Often it is desirable for stages to be as compact as		in accordance with an embodiment of the present invention.
possible, in both the footprint and the height. Limiting the		FIG. 3 shows a top view of one embodiment of a stage in
height ol' a stage is particularly important when the stage is to bc located in a chamber, such as a processing chamber.	45	accordance with the present invention.
While polar coordinate stages arc superior to XY stages in		FIGS. 4A and 4B show cross-sectional views of the stage
terms ol' footprint, the height ol' conventional polar coordi-		of FIG. 3 along lines AA.
natc stages is generally large, due to the above-described		FI(G. 5 shows a cross-sectional view ol' the stage ol' FI(G.
stacking ol' the actuators.		3 along lines 13B.
Thus, what is needed is an improved rotational stage that	50	FI(G. 6 shows a cross-sectional view ol' the Z platform
also moves vertically and has a vertically compact design.		along lines AA in FIG. 3. FIGS. 7A and 7B show a lop view and side view,
SUMMARY		respectively ol' the biasing spring with reinforcing members.
A compact stage, in accordance with the present		FIG. 8 shows a side view ol' onc embodiment ol' a brake
invention, includes a rotary driver and a vertical linear driver		assembly.
Ihal arc in lhc same horizontal plane, which advantageously		FIGS. 9 and         show perspcclivc and l'ronl schematic
reduces lhc heighl ol' lhc device.		views ol' the orientation ol' the rotary drive and the Z drive.
In onc embodiment, a stage in accordance with an		FIG. 11 illustrates a cross-sectional view another embodi-
embodiment ol' the present invention includes a rotating shaft to which a chuck may bc mounted. An annular rotary	60	ment ol' a compact stage.
drive is coupled 10 and rolalcs lhc rolaling shaft. A linear		DESCRIPTION
drive is also coupled 10 lhc rolaling shaft and cxlcnds		FIGS. 1 and 2 show perspcclivc views ol' a compacl slagc
through the center of the annular rotary drive. The linear		1()(), in accordance with an embodiment of the prescnl
drive moves lhc rolaling shaft along a vertical axis.	65	invention. Slagc           is capable ol' linear movcmcnl hori-
The slagc, in accordance Wilh lhc above embodimcnl,		zonlally in lhc R direction and vertically in lhc Z direction.
may include a basc Ihal moves in a linear horizontal direc-		Slagc         is also capable ol' rolaling a chuck         in lhc ()

 

3		4
direction. Accordingly, stage 100 is sometimes referred to as		coil motor. As shown in FIGS. 4A and 4B, Z drive 156 may
an R-O-Z stage.		include a coil 160 that is mounted to a cap 162, e.g., by bolts
As shown in FIGS. 1 and 2, stage 100 includes a base 110,		or other appropriate mounting mechanism, and the cap 162
which is mostly hidden from view in FIGS. 1 and 2 by a		is mounted to the R block 110, e.g., by bolts or other
cover 111. The base 110 includes R guides 112 and is		appropriate mounting mechanism. A magnet 164 is mounted
coupled to a linear motor 114. Base 110 is moved horizon-		to the Z platform 154, e.g., by bolts 164a shown in FIGS. 3 and 5, or other appropriate mounting mechanism, in the
tally in the R direction by linear motor 114 along R guides		inner portion 154a of Z platform 154. A spring 166 sur-
112. It should be understood that stage 100 is coupled to a		rounds coil 160 and is disposed between the Z platform 154
platform (not shown) with rails that mate with the R guides		and the cap 162. The spring 166 provides an upward bias on
112 and the mating portion for the linear motor 114. In	10	the Z platform 154. By controlling the force produced by the
addition, an R encoder 116 is coupled to the base 110 to		Z drive 156, Z platform 154 may be raised and lowered, e.g.,
detect the relative position of the base 110 with respect to the		the bias of the spring 166 can be used to lower the Z platform
platform. The R encoder 116 may be used in a feedback or		154 by overcoming the bias of the spring 166. The operation
feed forward control system, which is well known in the art.		of a voice coil motor is well known.
Stage         also includes a Z portion 12(), which moves in	15	Reinforcing members 168 extend through cap 162 and arc
a linear vertical direction, i.e., along the vertical Z axis.		used to prevent the spring 166 from buckling. Only one
FIGS. 1 and 2 show the Z portion 120 in raised and lowered		reinforcing member 168 is shown in FIGS. 4A and 4B.
positions, respectively. Within the Z portion 120 is a linear		FIGS. 7A and 7B show a top view and side view, respec-
drive for moving the Z portion 120 in the Z direction, as will		tively of the spring 166 with reinforcing members 168. As
be described in more detail below.	20	can be seen in FIGS. 4A, 4B, and 5, Z platform 154 includes
Also within Z portion 120 is a rotatory drive for rotating		grooves 168a to accommodate reinforcing members 166.
a shaft within the Z portion 120. The shaft is coupled to		Disposed between the R block 110 and Z platform 154 are
chuck 101. By rotating the shaft within the Z portion 120,		linear bearings 170 (shown in FIG. 3), which permit vertical movement of Z platform 154 with respect to the R block 110.
the chuck 101 is rotated in the 0 direction, as illustrated in FIGS. 1 and 2.	25	Four sets of linear bearings 170, i.e., at each corner of Z
FIGS. 1 and 2 show an edge grip chuck 101 mounted on		platform 154, are shown, but some other number of linear bearings 170 may be used if desired. In addition, a brake
stage 100. It should be understood, however, that stage 100		assembly 172 is mounted to R block 110. The brake assem-
is not limited to use with an edge grip chuck, but may be		bly 172 switchably locks against the Z platform 154 to hold
used with any desired chuck.	30	the Z platform 154 at a vertical position, e.g., during an
FIG. 3 shows a top view of stage 100 and FIGS. 4A and		emergency stop. FIG. 8 shows a side view of one embodi-
4B show cross-sectional views of stage 100 along lines AA		ment of the brake assembly 172, which includes an actuator
in FIG. 3. FIG. 5 shows a cross-sectional view of stage 100		174, such as a bistable solenoid, and an arm 175, which is
along lines BB in FIG. 3. As shown in FIG. 4A, stage 100		pivotably connected to a lever arm 176. The lever arm 176
includes the base 110, which moves in the R direction, as	35	is rotatably coupled to the R block 110 at the opposite end.
indicated in FIGS. 1 and 2, and thus is sometimes referred		A stop arm 177 is rotatably coupled to the lever arm 176.
to as R block 110. Stage also includes a Z platform 154 that		Guides 177a and 177b are on either side of stop arm 177 and
serves as part of the Z portion 120 (shown in FIGS. 1 and		guide the stop arm 177 to move horizontally when arm 175
2). The Z platform 154 moves vertically relative to the R		moves. The end of the stop arm 177 is grooved. A tang 178
block 110. FIGS. 4A and 4B show the Z platform 154 in	40	on the Z platform 154 is also grooved so that when the stop
raised and lowered positions, respectively. The R block 110		arm 177 is pressed against the tang 178, the grooves mesh
and Z platform 154 may be manufactured from a material,		to prevent any further motion of the Z platform 1154.
such as aluminum or an aluminum alloy, e.g., aluminum		A linear encoder, shown in FIG. 3, is used to detect the
alloy type 7()75 that is annealed prior to the last machining		vertical position of the Z platform 154, e.g., where the scale
operation.	45	is located on the Z platform 154 and the reader
FIG. 6 shows a cross-sectional view of the Z platform 154		is located on the basc 11(). The encoder 18() may bc used in
along lines AA in FI(G. 3. The Z platform 154 includes a		a well known feedback or recd forward control system to
cylindrical inner portion 154"/ and a cylindrical outcr portion		control the position and movement ol' Z platform 154. The
154b. The Z platform 154 is raised at the inner portion 154a,		linear encoder 18() may also bc used to determine the
which provides an inset under the Z platform 154. A linear	50	vertical position of the Z platform 154 on slarl up.
drive, sometimes referred to herein as Z drive 156, is		Alternatively, a secondary encoder 181 may be used to
mounted in the inset inner portion 154, as illustrated in		determine the vertical position on start up. The secondary
FIGS. 4A and 4B. An annular rotary driver, sometimes		encoder 1181, e.g., uses an LED coupled to the Z platform
referred to herein as rotary drive 158, is mounted in the outcr		154 and a photodiode coupled to the basc 110 and deter-
portion 154b ol' the Z platform 154, as illustrated in FIGS.	55	mines approximate distance between the LED and photo-
4A and 4B. The annular rotary drive 158 is, e.g., a brushless		diode based on lhc inlcnsily ol' lhc lighl received by lhc
motor. As can bc scen in FIGS. 4A and 4B, lhc linear drive		photodiode.
extends through the center ol' the annular rotary drive.		Referring back to FIGS. 4A and 4B, the rotary drive 158
Z platform 154 also includes an aperture 155 through		is mounted in the cylindrical outer portion 154b of the Z
which a vacuum or gas may bc provided to a chuck 101. The	60	platform 154. Rotary drive 158 includes a stator 190 and a
path 155b through Z platform 154 to aperture 155 can bc		rotor 194. The stator 190 is mounted to the Z platform 154,
scen in FIG. 5. A scaling bearing is placed in a scaling ring		e.g., using bolls 192, or olhcr approprialc mounting mecha-
155"/ 10 provide a scal bclwccn chuck     and lhc Z platform		nism. The rolor 194 is mounlcd 10 a rolaling shaft 196,
154. A small amount of lubricant may be placed on the chuck		which is rotatably coupled to the Z platform 154 through
in order 10 reduce friction Wilh lhc scaling ring 155a.	65	bearings 198. Thus, lhc Z drive 156 is coupled 10 lhc rolaling
The Z platform 154 is driven in lhc vertical direction		shaft 196 Ihrough lhc Z platform 154 and rotary bearings
using lhc Z drive 156, which in onc embodimcnl is a voice		198.

 

5		6
The chuck 101 mounts to the rotating shaft 196, e.g., via		a linear drive coupled to said rotating shaft, said linear
bolts 196a. A clamp 202 is mounted on Z platform 154 and		drive moves said rotating shaft along a vertical axis,
the bearing 198 and places a preload on the bearing 198. A		said linear drive extending through the center of said
0 encoder glass 204 is mounted to the rotating shaft 196 by		annular rotary drive.
means of 0 glass hub 206. It is desirable to have a large diameter encoder glass 204. The reader 208 for the 0		2. The stage of claim 1, further comprising:
encoder glass 204 is shown in FIG. 3. The rotary encoder		a base that moves in a linear horizontal direction; and
may be used in a feedback or feed forward loop to control		a platform moveably coupled to said base, said platform
the rotational movement and positioning of the rotating shaft		moving in a linear vertical direction with respect to said
196, and thus, the chuck 101. The operation of a rotary	10	base, said rotating shaft rotatably coupled to said
actuator and a rotary encoder is well known.		platform, said platform having a first side and a second
Thus, as can be seen, the stage 100 in accordance with the present invention has a compact configuration with the		side opposing said first side, wherein said annular
rotary drive 158 encircling the Z drive 156. In other words,		rotary drive is coupled to said first side and said linear
the rotary drive 158 and the Z drive 156 are in approximately		drive is coupled to said second side.
the same horizontal plane. Accordingly, the vertical height	15	3. The stage of claim 2, wherein said first side is the top
of the stage 100 is substantially reduced compared to		side of said platform and said second side is the bottom side
conventional stages.		of said platform.
FIGS. 9 and 10 show perspective and front schematic		4. The stage of claim 2, said platform has an inner section
views of the orientation of the rotary drive 158 and the Z		and an outer section, wherein said annular rotary drive is
drive 156. The Z platform 154, bearings 198, and rotating	20	coupled to said outer section and wherein said inner section
shaft 196, which are disposed between the rotary drive 158		extends through the center of said annular rotary drive.
and the Z drive 156 are not shown in FIGS. 9 and 10. As can		5. The stage of claim 2, further comprising a rotary
be seen, the rotary drive 158 and the Z drive 156 fie within		bearing disposed between said platform and said rotating
the same plane, indicated by dotted lines 199. Because the		shaft; wherein said linear drive is coupled to said rotating
rotary drive 158 and the Z drive 156 lie within the same	25	shaft through said platform and said rotary bearing.
plane, the height of the stage is advantageously minimized.		6. The stage of claim 2, further comprising a linear
It should be understood that the components used with		bearing disposed between said base and said platform.
stage 100 may be varied from what is described herein. For		7. The stage of claim 1, wherein said linear drive is a voice
example, the Z drive 156 may be an actuator other than a	30	coil motor.
voice coil motor, such as a lead screw coupled to another		8. The stage of claim 7, further comprising a spring
rotary motor, or a linear bearing. The rotary drive 158 may		coupled to said rotating shaft, wherein said spring biases
be a brushless "pancake" type motor, or other rotary actuator. FIG. 11, by way of example, illustrates a cross-sectional		said rotating shaft along said vertical axis, wherein said
view a stage 300 that is similar to stage 100, like designated		voice coil motor drives said rotating shaft along said vertical
elements being the same. FIG. 11 shows a Z drive 156	35	axis by overcoming said bias.
coupled to the Z platform, 154, and the Z platform 154,		9. The stage of claim 8, wherein said spring is coupled to
bearings 198, and rotating shaft 196 disposed between the		said annular rotary drive and extends through the center of
rotary drive 302 and the Z platform 154. The rotary drive		said annular rotary drive, said spring biases said annular
302 in FIG. 11 drives the rotation of the rotating shaft 196 using a wheel 204. Thus, as can be seen in FIG. 11, the Z	40	rotary drive along said vertical axis. 10. The stage of claim 1, wherein said linear drive coupled
drive 156 and the rotary drive 302 are within the same plane		to said rotating shaft is a first linear drive, said stage further
206, but the Z drive 156 docs not extend through the center		comprising:
of the rotary drive 3()2. There may be multiple rotary drives		further comprising a second linear drive that is coupled to
3()2 located around the perimeter ol' the Z platform 154.	45	said rotating shaft, said annular rotary drive, and said
In another embodiment, the locations ol' the rotary drive		first linear drive, said second linear drive moves said
and the Z drive may be switched so that the rotary drive		rotating shaft, said annular rotary drive, and said first
rotates the Z stage 154 and Z drive, as opposed to the Z drive		linear drive in a horizontal direction.
lifting the rotary drive.		11. A stage comprising:
The particular components, e.g., motors, bearings, encoders, etc. to bc used arc determined, e.g., based on the	50	a rotating shaft to which a chuck is mounted;
dimensions and accuracy of the desired slagc, and selecting		a means for rotating said rotating shaft; and
such components is well within the abilities ol' those skilled		a means for driving said rotating shaft along a vertical
in lhc arl in lighl ol' lhc prescnl disclosure.		axis, said means for driving said rolaling shaft is on lhc
Although the present invention is illustrated in connection		same horizontal planc as said means for rotating said
with specific embodiments for instructional purposes, the		rotating shaft.
prescnl invention is nol limilcd lhcrclo. Various adaplalions		12. The slagc ol' claim 1 1, wherein said means for driving
and modifications may bc madc without departing from the		said rotating shaft along a vertical axis extends through the
scope of the invention. For example, various embodiments		center of said means for rotating said rotating shaft.
may bc combined to practice the present invention.	60	13. The stage ol' claim 11, wherein said means for rotating
Therefore, the spirit and scope ol' the appended claims		said rotating shaft comprises an annular rotary driver
should nol bc limilcd 10 lhc foregoing description.		coupled 10 said rolaling shaft.
Whal is claimed is:		14. The polar coordinalc ol' claim 13, wherein said annular
1. A stage comprising:		rotary driver comprises a slalor and a rotor, one of which is
a rolaling shaft 10 which a chuck is mounlcd;	65	mounlcd 10 said rolaling shaft and lhc olhcr ol' which is
an annular rotary drive coupled 10 said rolaling shaft, said		coupled 10 said means for driving said rolaling shaft along
rotary drive rolalcs said rolaling shaft; and		a vertical axis.

7		8
15. The polar coordinate of stage of claim 11, wherein		18. A method of moving a stage, said method comprising:
said means for driving said rotating shaft along a vertical		driving a shaft along a vertical axis; and
axis comprises a voice coil motor coupled to said means for		rotating said shaft about the driver that drives said shaft
rotating said rotating shaft.		along said vertical axis, such that said shaft and driver
16. The stage of claim 15, wherein said voice coil motor	5	are on the same horizontal plane.
comprises a magnet and a coil one of which is mounted to		19. The method of claim 18, further comprising driving
a platform, said platform is coupled to said means for		said shaft and said driver that drives said shaft along said vertical axis in a horizontal direction.
rotating and is rotatably coupled to said rotating shaft, said		20. The method of claim 18, further comprising, biasing

platform extends through the center of said means for

10 said shaft along said vertical axis and wherein driving said rotating said rotating shaft.      shaft along said vertical axis comprises applying a force to

 

17. The stage of claim 16, wherein said means for driving overcome said bias. said rotating shaft further comprises a spring for biasing said rotating shaft along a vertical axis.

 

BACKGROUND OF THE INVENTION	5	Stops that limit the rotation of the theta-axis rotor to less
In the manufacture of many devices, the need exists to lift		than one revolution, home sensors and limit switches to
and rotate the part, for example, in the manufacture of		constrain the vertical movement, and rotation of the theta-
semiconductor devices. A semiconductor wafer is a thin,		axis rotor are optional features.
circular slice of pure silicon on which semiconductors are built. The largest wafer in current use is about 300 mm (12	10	BRIEF DESCRIPTION OF THE DRAWINGS
inches) in diameter. Many individual semiconductor devices		Further features and other objects and advantages will
or "chips" can be fabricated on each wafer, depending on the		become apparent from the following detailed description
chip and wafer size.		made with reference to the drawings in which:
For inspection, test or fabrication, a wafer is mounted on	15	FIG. 1 is a plan view of a direct drive vertical lift and
a rotating stage that must be capable of orienting the wafer		rotation stage according to the present invention; and
at precise angular positions about an axis perpendicular to		FIG. 2 is an elevation view in section taken along line
the wafer surface. The stage must be rapidly rotated from one position to another. Such stages must also be adjustable		11—11 in FIG. 1.
in the vertical direction, although only about 10 mm or less	20	DESCRIPTION OF THE PREFERRED
of vertical adjustment is needed.		EMBODIMENT
In the past, stages as above described have required		Referring now to FIG. 1, a magnet shield 11 surrounds
complex mechanical components, such as worm gears, lead		theta-axis rotor assembly 10 upon which a wafer is held
screws, and separate motors, all of which can be a source of		during inspection. fiese elements rotate about an axis (the
positioning errors. Moreover, these mechanical components	25	theta-axis) which is perpendicular to the top surface of the
resulted in a bulky apparatus having an undesirably large		rotor assembly. Surrounding the rotor assembly is a theta-
footprint. Other direct drive technologies, such as piezoelec-		axis housing assembly 20 which has a central opening in
tric drives, have limited travel range and require additional		which the theta-axis rotor is journaled by bearing.
mechanical elements to extend their travel range.		The theta-axis housing assembly 20 moves vertically up
SUMMARY OF THE INVENTION	30	and down carrying the theta-axis rotor assembly. The vertical motion of the theta-axis housing assembly is guided by
It is an object of the present invention to provide a vertical		linear bearings 30, 31, 32, and 33. The linear bearings
lift and rotation stage without worm gears, lead screws, or		precisely guide the theta-axis housing in its vertical motion
separate drive motors.	35	(along the z-axis) and restrain rotation of the housing. The
It is a further object of the present invention to provide a		linear bearings may comprise recirculating linear ball bear-
small footprint vertical lift and rotation stage.		ings coupled with precision ground shafts or any other type
Briefly, according to the present invention, a direct drive		of linear bearings, such as linear motion guides, cross roller
vertical lift and rotation stage comprises an annular z-axis		bearings, linear ball bearings, and many other types.
housing having a central opening and a z-axis rotor assem-	40	The terms "z-axis" and "theta-axis" are commonly used
bly journaled by a bearing assembly within the central		terms in the motion control art. The z-axis is the generally
opening of the z-axis housing. The z-axis rotor assembly has		vertical axis and the theta-axis is an axis of rotation. In the
a threaded upper end. A first brushless permanent magnet		embodiment being described, these two axes are at least
motor is positioned between the z-axis housing and the		parallel and may even be collinear.
z-axis rotor. An annular theta-axis housing has a central	45	Referring now to FIG. 2, the base of the lift and rotation
opening. The theta-axis housing has threads that engage the		stage is an annular z-axis housing assembly 40 with a central
threads on the z-axis rotor. Linear bearings between the		opening. A z-axis rotor assembly 50 is journaled by bearing
z-axis housing and the theta-axis housing prevent relative		48 in the central opening of the z-axis housing assembly 40.
rotation. A theta-axis rotor assembly is journaled by a		Various precision bearings, including preloaded, may be
bearing assembly within the central opening of the theta-axis	50	used. A brushless permanent magnet motor comprises arma-
housing. A second brushless permanent magnet motor is		ture winding 42 and a winding support steel ring or lami-
positioned between the theta-axis housing and the theta-axis		nation stack 43 fixed in the z-axis housing by mounting
rotor. A linear position sensor detects vertical movement		flange 45 and permanent magnets 52 mounted in the z-axis
between the theta-axis housing and the z-axis housing and a		rotor assembly. The magnets have North and South poles
rotary sensor detects rotating movement between the theta-	55	aligned in the radial direction and alternating in the circum-
axis rotor assembly and the theta-axis housing. The action of		ferential direction. Preferably, there is an even number of
the first permanent magnet motor raises and lowers the		magnets spaced around the circumference of the z-axis rotor
theta-axis rotor assembly and the action of the second		assembly and an even number of armature coils spaced
permanent magnet motor rotates the theta-axis rotor assem-		around the z-axis housing assembly. In a most preferred
bly.	60	embodiment, the coils are in three groups each energized by
In one embodiment, the permanent magnet motors com-		one of three phases.
prise armature windings secured to the housing assemblies,		The linear bearings 30, 31, 32, and 33 are all fixed relative
rare earth permanent magnets secured to the rotor		to the z-axis housing 40 and theta-axis housing 20.
assemblies, and magnetic metal lamination stacks or steel		The z-axis rotor has threads 55 on the upper end thereof
ring support the armature windings.	65	that engage threads 25 on the theta-axis housing. Rotation of
The type of the position sensors employed will depend on		the z-axis rotor 50 causes a vertical movement in the
the motion performance requirement, speed, resolution,		theta-axis housing which is prevented from rotating by the

US 6,700,249 Bl

3		4
linear bearings 30, 31, 32, and 33. The vertical motion is		a z-axis rotor assembly journaled by a bearing assembly
measured by an incremental encoder comprised of a scale 26		within the central opening of the z-axis housing, said
mounted on the theta-axis housing and an encoder reader 28		z-axis rotor assembly having a threaded upper end;
mounted relative to the z-axis housing.		a first brushless permanent magnet motor between the
Incremental encoders are commonly used measurement	5	z-axis housing and the z-axis rotor;
transducers. Optical incremental encoders pass light from a		an annular theta-axis housing having a central opening,
lamp or light-emitting diode at a grating attached to the axis		said theta-axis housing having threads that engage the
to be measured. The grating normally has two tracks offset		threads on the z-axis rotor;
90 signal degrees apart with respect to each other (in		linear bearings between the z-axis housing and the theta-
quadrature). A single marker on a third track serves as a home marker (in the case of a rotary encoder, a once-per-	10	axis housing to prevent relative rotation thereof;
revolution marker). The light reflected from the grating		a theta-axis rotor assembly journaled by a bearing assem-
continues through a reticule or mask which, together with		bly within the central opening of the theta-axis housing;
the grating, acts as a shutter. The shuttered light falling on		a second brushless permanent magnet motor between the
a detector results in the generation of electrical signals.	15	theta-axis housing and the theta-axis rotor;
These signals are amplified and output as two amplified		a linear motion sensor for detecting vertical movement
sinusoids or square waves in quadrature and are output on		between the theta-axis housing and the z-axis housing;
two separate channels as signals SIN and COS. With simple		and
incremental encoders, the position is measured by counting		a rotary motion sensor for detecting rotating movement
the zero crossings (sinusoidal) or edges (square waves) of	20	between the theta-axis rotor assembly and the theta-
both channels. Where greater precision is required, the		axis housing such that the action of the first permanent
amplified sinusoidal signals (SIN and COS) are sent to an		magnet motor raises and lowers the theta-axis rotor
encoder multiplier where the intermediate positions are		assembly and the action of the second permanent
resolved at spaced time intervals.		magnet motor rotates the theta-axis rotor assembly.
An encoder multiplier uses the SIN and COS signals to	25	2. The direct drive vertical lift and rotation stage accord-
resolve many positions within one grating period (scribe		ing to claim 1, wherein the permanent magnet motors
lines). The multiplier, for example, is able to produce up to		comprise armature windings secured to the housing assem-
65,000 transitions within one grating period as opposed to		blies and rare earth permanent magnets secured to the rotor
the four by a simple incremental encoder. See, for example,		assemblies.
U.S. Pat. No. 6,356,219.	30	3. The direct drive vertical lift and rotation stage accord-
Feedback from the incremental encoder is used to control		ing to claim 2, wherein the armature windings are supported
the currents applied to each phase in the armature winding		by lamination stacks or steel ring.
to precisely position the theta-axis housing in the vertical		4. The direct drive vertical lift and rotation stage accord-
direction.	35	ing to claim 3, wherein the incremental rotary encoder for
Referring again to FIG. 2, a brushless permanent magnet motor comprises an armature winding 22 and lamination		rotating movement between the theta-axis rotor assembly and the theta-axis housing comprises an encoder scale
stack or steel ring 23 fixed in the z-axis housing by mounting		mounted on the theta-axis rotor and an encoder reader
flange 29 and permanent magnets 12 mounted in the theta-		mounted on the theta-axis housing.
axis rotor assembly. The magnets have North and South	40	5. The direct drive vertical lift and rotation stage accord-
poles aligned in the radial direction and alternating in the		ing to claim 3, wherein the incremental linear encoder for
circumferential direction. Preferably, there is an even num-		detecting vertical movement between the theta-axis housing
ber of magnets spaced around the circumference of the		and the z-axis housing comprises an encoder scale mounted
theta-axis rotor assembly and an event number of armature		on the theta-axis housing and an encoder reader mounted
coils spaced around the theta-axis assembly.	45	relative to the z-axis housing. 6. The direct drive vertical lift and rotation stage accord-
In a most preferred embodiment, the coils are in groups of		ing to claim 3, wherein stops limit the rotation of the
three, each energized by one of three phases. Each phase is		theta-axis rotor to less than one revolution.
individually energizable. The vertical motion is measured by		7. The direct drive vertical lift and rotation stage accord-
an incremental encoder comprised of a scale 26 mounted on		ing to claim 3, further comprising home sensors and limit
the theta-axis housing and an encoder reader 28 mounted	50	switches to constrain the vertical movement and rotation of
relative to the z-axis housing.		the theta-axis rotor.
Having thus defined the invention in the detail and		8. The direct drive vertical lift and rotation stage accord-
particularity required by the Patent Laws, what is desired		ing to claim 3, wherein the armature windings are two or
protected by Letters Patent are set forth in the following		three phase windings.
claims.	55	9. The direct drive vertical lift and rotation stage accord-
The invention claimed is:		ing to claim 3, wherein the vertical and rotary positions are
1. A direct drive vertical lift and rotation stage comprising: an annular z-axis housing having a central opening;		precisely controlled by feedback from motion sensors.