JPH06171967A - Glass substrate cutting device - Google Patents

Abstract

PURPOSE:To improve the efficiency of cutting by inscribing the glass substrate on a substrate holder which moves back and forth between a skiving section and a breaking section with a linear lancing and applying a stress along this lancing, thereby breaking the substrate to a linear shape. CONSTITUTION:The glass substrate A is fixed by means of a vacuum chuck onto a holder 5 of the substrate holder 10. A blade edge 25a mounted to a blade height adjusting plate 24 of the skiving section 20 is brought into contact with the surface of the glass substrate A and is set in the position where the substrate surface can be skived. The substrate holder 10 is moved in this state along the moving path of a forward X direction to inscribe the glass substrate A with the linear lancing by the blade edge 25a. Further, the substrate holder 10 is moved to a right side and is stopped in the position corresponding to the breaking section 30 where the lancing of the glass substrate A is inserted between the recessed part 35a of a receiving plate 35 and the projecting part 38a of a press plate 38. The perpendicular stress in the recessed part 35a direction by the projecting part 38a is added along the lancing to break the glass substrate. The substrate holder 10 is thereafter moved backward to the left side and is returned to its home position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is for cutting a glass substrate, such as a reticle, required as an original plate for reducing projection exposure of a pattern into a predetermined size in order to form a pattern with multiple surfaces on a photomask. The present invention relates to a glass substrate cutting device.

[0002]

2. Description of the Related Art A photomask is used to form a circuit pattern by exposure on a resist on a silicon wafer, and the photomask is provided with circuit patterns with multiple faces.

As a method for forming a circuit pattern with multiple surfaces on a photomask, it is usually 5 times to 1 times on a glass substrate.
Using a reticle (single master for multi-sided reduction exposure) provided with a single circuit pattern enlarged to 0 times the size, it is subjected to repeated reduction projection exposure on a photomask resist by a photo repeater, A method of forming a photomask on which a circuit pattern in which one pattern and the same shape pattern are provided on multiple sides is formed is generally adopted.

At present, the size of the reticle fixing base for setting the reticle on the photo repeater varies depending on the model of the photo repeater.

On the other hand, at the stage of making a reticle (the above-mentioned single original plate), after putting the glass substrate for making the reticle in the storing cassette, the storing cassette is set in an electron beam drawing machine for drawing a single circuit pattern. The glass substrate is set by using the glass substrate, and the glass substrate storage allowable size of the glass substrate storage cassette used at that time is constant regardless of the model of the electron beam drawing machine, and is usually 5 inches × 5.
It is made to set an inch glass substrate.

For example, as a countermeasure to be taken when the glass substrate storage allowable size of the photo-repeater reticle fixing base is smaller than the glass substrate storage allowable size of the glass substrate storage cassette of the electron beam drawing machine, There are three possible methods. (1) Modify the glass substrate storage cassette of the electron beam drawing machine to match the glass substrate fixing allowable size of the reticle fixing base of the photo repeater. (2) Modify the reticle fixing base of the photo repeater,
Adjust to the glass substrate storage allowable size of the glass substrate storage cassette of the electron beam drawing machine. (3) The reticle drawn by the electron beam drawing machine is cut to fit the glass substrate fixing allowable size of the reticle fixing base of the photo repeater.

With respect to (1), however, it requires a considerable amount of cost to modify the glass substrate storage cassette, and the glass substrate storage cassette must be replaced and installed every time the electron beam drawing machine is used, which is a great labor. Therefore, there is a problem that labor is required, and there is a similar problem in (2).

[0008]

As described in (3) above, it is necessary to cut a reticle drawn by an electron beam drawing machine so as to match the size of the reticle fixing base of the photo repeater with the size of the glass substrate storage cassette. On the other hand, it can be considered as a current countermeasure when the size of the reticle fixing base is small, but manually cutting the reticle with a diamond cutter is time-consuming and dangerous from the viewpoint of safety. Is.

In order to solve the above problems, the present invention is to simply and safely automatically cut a glass substrate such as a reticle.

[0010]

DISCLOSURE OF THE INVENTION The present invention is provided with a blade for making a notch in a glass substrate, a skive portion for making a linear notch in the glass substrate, and a stress applied to the notched portion of the glass substrate, A glass substrate, characterized by being composed of a splitting portion for linearly splitting the substrate along the cut portion, and a substrate holder portion for mounting the glass substrate and reciprocating between the skive portion and the splitting portion. It is a cutting device.

In the glass substrate cutting device according to the present invention, the skive portion is provided with one or more blades on a path for reciprocating movement of the substrate holder portion, and the positions of the blades are within a horizontal plane. It is a glass substrate cutting device which is variable in a direction perpendicular to the path of the reciprocating movement of the section.

Further, according to the present invention, in the above-mentioned glass substrate cutting device, the folding portions sandwich the cut positions of the glass substrate from above and below, and each of them has a convex portion for applying stress to the cut portion of the glass substrate. This is a glass substrate cutting device in which a pressing plate and a receiving plate having a concave portion are provided, and the positions of the convex portion and the concave portion are variable in a direction perpendicular to the path of the reciprocating movement of the substrate holder in a horizontal plane.

[0013]

1 is a plan view of one embodiment of FIG. 1, a front view of one embodiment of FIG. 2 (a front view as seen from the right side of FIG. 1), and one of FIG. Front view of the embodiment (Fig. 1
According to the front view seen from the right),
As shown in FIG. 1, a substrate holder portion 10 that is linearly movable in the X direction (left and right direction in FIG. 1) along a predetermined guide rail attached to the apparatus body frame F, and an X portion of the holder portion 10. A common base board that can be moved along the directional movement path on one side or both sides along the guide board 14 (or guide rail) on the apparatus body frame F in the direction orthogonal to the X-direction movement path (Y direction). F ₁ is provided, and the skive part 20 and the split part 30 are fixedly supported on the base board F ₁ .

The substrate holder portion 10 includes a glass holder 5 having a vacuum chuck for adsorbing and fixing the glass substrate A, and a holder supporting portion 6 for supporting the holder 5.
The glass substrate A is mounted and fixed on the holder 5 by a vacuum chuck.

As shown in FIG. 2, the skive portion 20 includes a support portion 21 attached to the common base plate F ₁ , an arm 22 attached to the support portion 21, and a vertical slide guide fixed to the support arm 22. 23 and a vertical moving part 24 which is vertically movable (vertical direction with respect to FIG. 1) along the guide 23, and is made downward from the vertical moving part 24 (vertically downward) by a diamond The glass engraving blade (sky blade) 25 is provided on the X-direction moving path side of the substrate holder portion 10. (See Figure 1)

In addition, the skive portion 20 has a common base plate F.
A Y-direction guide board 26 fixed on ₁ is mounted and supported on a support board 27 which is slidable in the Y-direction, whereby the support portion 21 is relatively Y-shaped on the common base plate F _1. Can be appropriately moved in any direction, and after the relative position between the cutting edge of the blade 25a installed on the skive 20 and the side of the split section 30 is adjusted and set to a predetermined position,
The slide movement between the guide board 26 and the support board 27 can be fixed by the set screw 27a.

When the substrate holder unit 10 mounts and fixes the glass substrate A on the glass holder 5 and moves linearly along the X-direction moving path from the left end direction to the right direction in FIG. The cutting edge of the blade 25a of the portion 20 is in contact with the surface of the end portion of the glass substrate A, and a linear notch c is cut into the substrate A.

The folding section 30 includes a supporting portion 31 mounted on the common base board F ₁ , a vertical slide guide rail 32 for guiding the supporting portion 31 in the vertical direction, and a vertical direction along the guide rail 32 ( 1. A support plate 34a attached to a support arm 34 that is integrally attached to the first vertical movement portion 33 is provided with the first vertical movement portion 33 that is adjustable in the vertical direction with respect to FIG. 10 is provided on the side of the moving path in the X direction.

FIG. 2 is a front view of FIG. 1 seen from the left side, and of the skive portions 20 and 20 shown in FIG.
Similarly, among the split parts 30, 30, which face each other on both sides, the split part 30 in the lower right of FIG. 1 is shown in a front view (a front view in which the skive part 20 in the lower left of FIG. 1 and the split part 30 in the upper right are omitted). It is a thing.

As shown in FIG. 2, the substrate holder portion 10 has a vertical support shaft 7 for rotatably supporting the holder support portion 6 for supporting the glass holder 5, and a bearing portion 8 for supporting the vertical support shaft 7. The bearing portion 8 is fitted in a notched groove portion 9 formed through the apparatus body frame F along the X-direction movement path of the substrate holder 10 shown in FIG. The bearing portion 8 is mounted and supported on the frame F ₂ .

The X-direction movement drive unit 1 of the substrate holder unit 10
2 will be described. As shown in the front view of FIG. 2, guides and guides are provided at both end edges of the cutout groove 9 on the rear surface of the apparatus body frame F in the longitudinal direction parallel to the X-direction movement path. Guide followers 18, 19 (guide 18
Is equipped with, for example, a rail-shaped guide, and a guide follower 1
The movable frame F ₂ is attached to the 9 lower, whereby the movable frame F ₂ is linearly moved in the X direction along the guide 18.

A nut block 16 is attached and fixed to one side or both sides of the movable frame F _2.
Reference numeral 6 is screwed onto a screw shaft 17 which is driven and rotatable in the apparatus main body frame F side in parallel with the longitudinal direction along the X-direction moving path, and a drive motor (servo motor, pulse motor, etc.) is appropriately used. Then, by rotating the screw shaft 17, the substrate holder portion 10 can be driven and moved along the X-direction movement path by the drive motor.

Further, as shown in FIG. 2, in the substrate holder portion 10, the lower end portion of the vertical support shaft 7 for rotatably supporting the glass holder 5 has a rotating body 11 (gear, sprocket, timing pulley, etc.). ) Is attached and the glass holder 5 is leveled by rotating the rotating body 11 via the power transmission body 11a (gear, endless chain, timing belt, etc.) by the drive source M ₁ (rotary air cylinder, motor, etc.). In the rotation direction, it is rotated at an appropriate angle θ such as every 90 °.

The rotation angle θ is detected by a horizontal rotation shaft 13 rotated by a worm gear 12 meshing with the lower end of the vertical support shaft 7, and a bearing 15 supporting the shaft 13.
A rotary encoder 14 pivotally supported on the shaft 14 is provided, and the rotation angle θ is detected by the rotary encoder 14.

As shown in FIG. 2, the split section 30 includes a support arm 34 on the first vertical moving section 33, and a support plate 34a attached to the support arm 34 and a receiving plate 35 vertically downward. A recess 35b is provided on the lower end surface 35a of the receiving plate 35.

Further, as shown in FIG.
An air cylinder 50 for vertically moving the first vertical moving unit 33 is provided above the first vertical moving unit 33.
The drive unit 50 including a is provided.

The upper stop position of the first vertical moving portion 33 is shown in FIG.
As shown in FIG. 5, a horizontally movable ratchet portion 51 (having a ratchet pawl 51a at its tip end) that performs a reciprocating operation (reciprocating linearly) in the horizontal direction (the lower surface of the ratchet pawl 51a is the first
The upper end position of the first vertical moving portion 33 is provided by contacting the upper surface of the vertical moving portion 33.

The horizontally movable ratchet portion 51 is moved forward and backward in the horizontal direction by the air cylinder 52 as described above. Further, the ratchet pawl 51a is attached to the tip end portion of the horizontal operating rod 52a of the air cylinder 52 via a spring 51b that urges the horizontal operating rod 52a in the horizontal direction.

On the other hand, the bottom stop position of the first vertical moving portion 33 is, for example, as shown in FIG. 2 in the embodiment, the stroke in the extension operation in the vertical compression extension operation of the air cylinder 50a. The stop member, which is set according to the length, may be used to stop the descending operation.
You may set it so that it may intervene under the vertical moving part 33.

Below the first vertical moving portion 33 of the split portion 30, as shown in FIG. 2, a second vertical movable along a vertical guide 32 provided on the supporting portion 31 is movable vertically. A moving portion 36 is provided, a supporting arm 37 parallel to the supporting arm 34 is attached to the vertical moving portion 36, a supporting plate 37a is attached to the supporting arm 37, and the receiving plate 35 is attached upward to the supporting plate 37a. A push plate 38 is attached so as to face with the push plate 38, and the push plate 38 is provided at its upper end portion with a sharp convex portion 38a facing the concave portion 35a at the lower end portion of the receiving plate 35.

On the side of the second vertical moving portion 36, the second
Driving unit 4 including air cylinder 41 for vertically moving vertically moving unit 36 along vertical guide 32.
Equipped with 0. The upper stop position and the lower stop position of the second vertical movement unit 36 by the drive unit 40 can be set by adjusting the stroke length of the air cylinder 41 and the installation height of the air cylinder 41.

The folding section 30 applies a stress from above and below to the linear notch c cut at the end of the glass substrate A by the movement of the substrate holder section 10 in the X direction,
The glass substrate A is linearly broken along the portion of the notch c.

Next, the folding operation of the glass substrate A by the folding section 30 will be described with reference to FIGS. 1 and 2. In FIG. 2, the ratchet pawl 51a of the horizontal ratchet portion 51 is moved to the first vertical position by the air cylinder 52. The moving unit 33 is moved to a horizontal retracted position laterally from the upper surface, and the air cylinder 50 stops the first vertical moving unit 33 at the upper stop position. The air cylinder 41 causes the second vertical moving unit 3 to move.
6 with the bottom resting position, first the sharp protrusion 3
The glass substrate A is provided between the pressing plate 38 provided with 8a and the receiving plate 35, which is on the upper side of the pressing plate 38 and faces the stationary plate with a distance larger than the thickness of the glass substrate A. The substrate holder unit 10 is fed by the movement operation along the X-direction movement path.

Then, the air cylinder 52 is operated to cause the ratchet pawl 51a to project to the upper surface of the first vertical moving portion 33, and the tip end portion of the ratchet pawl 51a is brought into contact with the vertical side surface of the first vertical moving portion 33. Let

Then, the air cylinder 50a is operated to lower the first vertical moving portion 33 to lower the receiving plate 35 to the lower position (the lower position of the receiving plate 35 is the lower position of the lower surface of the receiving plate 35). The height at the position is set to be equal to the height of the upper surface of the glass substrate A).

When the receiving plate 35 descends to the lower stop position, the ratchet pawl 51a is laterally projected horizontally from the upper surface of the first vertical moving portion 33 by the urging force of the spring 51b to be in the lower stop position. The upward movement of the first vertical movement unit 33 is locked.

Then, the air cylinder 41 is operated to vertically raise the second vertical moving portion 36 to push up the pressing plate 38 toward the receiving plate 38, and the convex portion 38a cuts the straight line from the lower surface of the glass substrate A. When the glass substrate A is pressed along c, the glass substrate A is cut into the cutout c at this time, and the concave portion 35a of the receiving plate 35 and the convex portion 38a of the pressing plate 38 which is pressed toward the central portion of the concave portion 35a. Break stress is applied by and, and the glass substrate A is cut along the notch c.

Next, based on the plan view of FIG. 1, the movement adjusting unit 60 for adjusting the positions of the skive portion 20 and the split portion 21 in the Y direction (the direction orthogonal to the X-direction moving path) will be described below. .

The skive 20 and bend-breaking section 21 are connected by a common base plate F _1, the common base plate F ₁ can be moved and adjusted in the Y direction by movement adjusting portion 60.

The movement adjusting section 60 is a device main body frame F.
Shaft 6 rotatably supported on the bearing portion 61 on the side
2. An adjusting handle 63 such as an adjusting lever for rotating the screw shaft 62, and a nut block 64 screwed to the screw shaft 62 and mounted and supported on the common base board F ₁ side.

By rotating the adjusting handle 63 in any one direction, the screw shaft 62 rotates, and the common base board F ₁ mounting and supporting the nut block 64 is moved forward and backward along the guide G ₁ in the Y direction. It is what makes me.

Since the skive part 20 and the split part 21 can be moved in the Y direction at the same time, the positions of the receiving plate 35 and the pressing plate 36 with respect to the blade 25a always correspond to each other as shown in the plan view of FIG. On the line.

By turning the adjustment handle 63 of the movement adjusting section 60, the blade 25a on the common base board F ₁ is moved, and the blade 25a is moved to the straight portion of the glass substrate A to be cut.
The position of can be set. The skive section 20
As shown in the side view of FIG. 2, the blade height that is slidable in the vertical direction with respect to the support plate 23 so that the blade height of the blade 25a can be set slightly lower than the upper surface height of the glass substrate A. Height adjusting screw 24 rotatably supported by a bearing 23a attached to the upper side of the supporting plate 23.
The blade height adjusting unit 25 is formed by screwing b onto the adjusting plate 24.

By rotating the knob 24a of the screw 24b to move the blade height adjusting plate 24 in the vertical direction, the relative height of the blade 25a with respect to the upper surface of the glass substrate A can be set. The position is set such that the blade tip of the blade 25a can contact the surface of the glass substrate A and skive.

With the blade 25a in contact with the surface of the glass substrate A, the X-direction movement drive unit 1 is driven to move the substrate holder unit 10 from the left end in the drawing to the right in the forward X-direction movement path. When the glass substrate A is moved along, the linear cut c is first cut in the glass substrate A by the blade 25a of the skive portion 20.

Subsequently, the substrate holder portion 10 is further moved rightward along the X-direction movement path, and the glass substrate A is moved to a position corresponding to the split portion 30. It should be noted that the reciprocal movement distance along the X-direction movement path due to the start movement of the substrate holder 10, the movement stop, the return movement start, and the movement stop are the X
This is performed by current control and pulse control of a drive control motor such as a servo motor or a pulse motor that drives and rotates the screw shaft 17 of the directional movement drive unit 1.

FIG. 3A shows a cut c in the glass substrate A.
FIG. 6B is a partially enlarged front view of the embodiment in which the state of being fed between the concave portion 35a of the receiving plate 35 and the convex portion 38a of the pressing plate 38 is explained, and the glass in which the linear cut c is cut. After the substrate A moves between the receiving plate 35 and the pressing plate 38, the air cylinder 40 is driven to push up the pressing plate 38, and the glass substrate A is interposed between the receiving plate 35 and the pressing plate 38, and the respective concave portions thereof. The portion of the notch c is made to correspond to the position where the protrusion 35a and the protrusion 38a face each other, and is sandwiched.

Subsequently, as shown in FIG. 3B, the push plate 3
When the glass substrate A is sandwiched between the receiving plate 35 and the ratchet pawl 51a (stop member) by slightly pushing up 8
And the upward movement is stopped, and the protrusion 38 of the push plate 38 is stopped.
a is a concave portion 3 of the cut c portion of the glass substrate A from below.
Notch c of glass substrate A to push up in the direction of 5a
A vertical stress is applied to the portion in the direction of the concave portion 35a by the convex portion 38a, and the glass substrate A can be broken along the notch c portion. The glass cut end portion after folding is collected in the lower collection box 70.

After cutting the glass substrate A in the X direction by the mechanism as described above, the second vertical moving portion 36 is lowered by the air cylinder 41 to return the push plate 38 to the original height, while the air cylinder 52 is used. The ratchet pawl 51a of the horizontal ratchet portion 51 is connected to the first vertical moving portion 3
3 Move to a horizontal retracted position laterally from the upper surface and make it stationary, and then use the air cylinder 50a to move the first vertical moving portion 33
To raise the receiving plate 35 to the original height.

Then, the X-direction movement drive unit 1 is driven,
The substrate holder portion 10 is moved back toward the left end of the drawing in FIG. 1 and returned to its original position.

Subsequently, the glass holder 5 is rotated in the rotation angle θ direction to move the glass holder 5 to, for example, θ =
It is possible to rotate 90 °, and after that, by skiving in the Y direction of the glass substrate A in the skive portion 20 by the mechanism described above to cut the notch c, and then in the folding portion 30, crease cutting can be performed.

The skive section 20 is used for the return movement.
The blade edge of the blade 25a and the cut edge portion of the glass substrate A can be returned to the original position without substantially contacting each other, but during cutting when the suction fixing by the glass holder 5 is incomplete. In consideration of the case where a slight movement of the glass substrate A occurs, a micromotor for rotating a screw shaft 24b for raising and lowering the slide plate 24 of the blade height adjusting unit 25 shown in FIG. The height of the blade 25a is adjusted by the normal rotation and the reverse rotation of the blade 25a, or the lowering operation of the blade 25a during the forward movement of the substrate holder unit 10 and the upward operation during the backward movement of the substrate holder unit 10 are automatically performed. Good. In addition, as shown in FIG. 1, the place where the glass plate A is sandwiched between the receiving plate 35 and the pressing plate 38 of the splitting part 30 in the present invention may be only on one end side of the cut c of the glass substrate A, as shown in FIG. As shown in FIG. 4, the glass substrate A may be sandwiched over the entire length of the notch c.

[0053]

The glass substrate cutting device of the present invention comprises a skive portion provided with a blade for making a notch in the glass substrate, a folding portion for breaking along the notch, and a glass substrate placed and fixed to the skive portion. Since it is composed of a horizontally rotatable substrate holder part that linearly reciprocates between the split part and the split part, the surface of the glass substrate or the front and back surfaces can be It is possible to cut a straight cut on both sides.

Further, since the position of the blade of the skive portion can be changed in the direction perpendicular to the path of the reciprocating movement of the substrate holder portion in the horizontal plane, a linear cut for cutting the glass substrate into a desired size is appropriately made. Can be carved into position.

Further, since the split portion is provided with the pressing plate having the convex portion and the receiving plate having the concave portion, the glass substrate is sandwiched by the pressing plate and the receiving plate, and the convex portion is slightly on the concave side. By pressing on, the glass substrate can be broken along the notches.

[0056]

The glass substrate cutting device of the present invention can automatically and simply cut a glass substrate such as a reticle by automatically cutting and breaking the glass substrate surface without manual work. There is an effect such that the glass substrate can be efficiently cut into a size that matches the glass substrate storage allowable size in the glass substrate storage cassette of the electron beam drawing machine.

[Brief description of drawings]

FIG. 1 is a plan view of an embodiment of a glass substrate cutting device of the present invention.

FIG. 2 is a front view of an embodiment of the glass substrate cutting device of the present invention.

3 (a) and 3 (b) are front views for explaining a glass substrate breaking operation by a folding part in an embodiment of the glass substrate cutting device of the present invention.

FIG. 4 is a plan view for explaining another example of the folding section in one embodiment of the glass substrate cutting device of the present invention.

[Explanation of Codes] 1 ... X-direction movement drive unit 5 ... Glass holder 6 ... Supporting unit 7 ... Vertical support shaft 8 ... Bearing unit 9 ... Notch groove unit 10 ... Substrate holder unit 11 ... Rotating body 12 ... Worm gear 13 ... Rotating shaft 14 … Rotary encoder 15… Bearing 16… Nut block 17… Gear shaft 18… Guide 19
... Guide follower 20 ... Skive part 21 ... Support part 22 ... Support arm
23 ... Support plate 24 ... Slide plate 25 ... Blade height adjusting part 25a ... Skive blade 26 ... Guide 27 ... Slide board 30 ... Folding part 31 ... Support part 32 ... Guide rail 3
3 ... 1st vertical moving part 34 ... Support arm 35 ... Receiving plate 36 ... 2nd vertical moving part 37 ... Support arm 38 ... Push plate 38a ... Convex part 40 ... Drive part 41 ... Air cylinder 50 ... Drive part 50a ... Air cylinder 51 ... Horizontal ratchet part 51a ... Ratchet claw 51b ... Spring 52 ... Air cylinder 52a ... Operating rod 60 ... Movement adjusting part 61 ... Bearing part 62 ... Screw shaft 63 ... Adjusting handle 64 ... Nut block 70 ... Recovery box A ... Glass substrate c … Cut F… Machine body frame F ₁ … Common base board F ₂ … Movable frame G ₁ … Guide X… X direction movement path

Claims (3)

[Claims] 1. A skive part for making a cut in a glass substrate, a skive part for making a straight cut in the glass substrate, and a stress is applied to the cut part of the glass substrate to straighten the glass substrate along the cut part. 1. A glass substrate cutting device, comprising: a splitting portion that is split into pieces and a substrate holder portion that mounts a glass substrate and reciprocates between the skive portion and the splitting portion. 2. The skive part is provided with one or more blades on the reciprocating path of the substrate holder part, and the position of these blades is perpendicular to the reciprocating path of the substrate holder part in a horizontal plane. The glass substrate cutting device according to claim 1, wherein the glass substrate cutting device is variable. 3. The folding part sandwiches the cut position of the glass substrate from above and below, and is provided with a pressing plate having a convex part for applying stress to the cut part of the glass substrate and a receiving plate having a concave part. The glass substrate cutting device according to claim 1 or 2, wherein the positions of the convex portion and the concave portion are variable in a direction perpendicular to the path of the reciprocating movement of the substrate holder portion within a horizontal plane.