sd

(12) United States Patent

Botos

US006700249B1

(10) Patent No.:        US Bl

(45) Date of Patent:          Mar. 2, 2004

 

(54) DIRECT DRIVE VERTICAL LIFT AND ROTATION STAGE

(75) Inventor: Stephen J. Botos, Pittsburgh, PA (US)

(73) Assignee: Aerotech, Inc., Pittsburgh, PA (US)

 Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 28 days.

(21)     Appl. No.: 10/299,888

(22)     Filed:       Nov. 19, 2002

(51)      Int. Cl.⁷      H02K 16/00

(52)      U.S. Cl.  310/80; 310/12; 310/68 B;

310/112

(58) Field of Search  310/68 B, 154.33,

310/112, 12, 80; 318/135; 414/935, 936; 74/25

(56)                        References Cited

U.S. PATENT DOCUMENTS

4,504,753 A * 3/1985 Koch310/75 R 4,521,707 A * 6/1985 Baker .310/80

 

A * 6/1988 Suzuki et al. 310/114 6,075,325 6/2000 Kouno et al.315/307

 

            6,184,631                                          2/2001 Noma et al.315/224

 

            6,355,999                       3/2002 Kichiji et al.310/112

4/2002 Wakabayashi et al.74/490.03

            6,486,574                                           11/2002 Botos et al.310/12

 

    2001/0035698                            11/2001 Nakatsuka et al.310/318

FOREIGN PATENT DOCUMENTS

	2001-85759	* 3/2001	HOIL/41/107
	2001-258206	*	H02K/16/OO

* cited by examiner

Primary Examiner—Burton Mullins

(74) Attorney, Agent, or Firm—Webb Ziesenheim Logsdon Orkin & Hanson, P.C.

(57)                              ABSTRACT

A direct drive vertical lift and rotation stage comprises an annular z-axis housing having a central opening, a z-axis rotor assembly journaled within the central opening of the z-axis housing, a motor between the z-axis housing and the z-axis rotor, an annular theta-axis housing having a central opening, a theta-axis rotor assembly journaled within the central opening of the theta-axis housing, and a motor between the theta-axis housing and the theta-axis rotor.

9 Claims, 2 Drawing Sheets

 

        20         29        23      22             12 24 25                       16      17      10        1 1                  26              28

 

          40          45          43                    52                       55                    48        50

U.S. Patent                        Mar. 2, 2004          Sheet 1 of 2            US  Bl

 

U.S. Patent                       Mar. 2 , 2004           Sheet 2 Of 2                US 6, 700,249 Bl

 

US 6,700,249 Bl

1		2
DIRECT DRIVE VERTICAL LIFT AND		accuracy, acceleration, etc. Position sensors, for example,
ROTATION STAGE		may include incremental or absolute encoders of the magnetic or optical type. Position sensors may also comprise resolvers and related multipole devices.
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.