JP2001150336A - Manufacturing method and polishing method for flat plate-shaped substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently manufacture at low cost a flat plate-shaped substrate such as a magnetic disc having one surface to be used. SOLUTION: The flat plate-shaped substrate 1 such as a magnetic disc substrate in which one surface, namely, the front surface 1a is a surface to be processed, is formed, and two substrates 1 are bonded into a substrate pair 3 by facing the other surfaces, namely, back surfaces 1b. Respective front surfaces 1a of two bonded substrates 1 are polished by a double surface polishing device, and two substrates 1 are dried in the bonded state. After specified processing to the surfaces to be processed is finished, two substrates 1 are separated from each other. Therefore, two substrates 1 can be simultaneously manufactured by performing polishing work to the substrates at one time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic disk substrate,
The present invention relates to a method of manufacturing a flat substrate for manufacturing a flat substrate such as a semiconductor wafer and a liquid crystal substrate, and more particularly to a method of manufacturing a flat substrate having a polishing step of polishing a surface of the flat substrate.

[0002]

2. Description of the Related Art A magnetic disk used as a storage medium for a computer is made of aluminum alloy, glass, or the like, and after forming a substrate for a magnetic disk having a through hole in the center, that is, a substrate, is subjected to various surface treatments. It is manufactured through a process. These surface treatment steps include a grinding step, a polishing step, a sputtering step for forming a magnetic film, a plating step, and a cleaning step.

Conventionally, a magnetic disk has generally used a magnetic disk substrate having a magnetic film formed on both sides, but recently, in order to reduce the cost of a magnetic disk drive, a magnetic film is formed on only one side. The development of a magnetic disk drive using the formed magnetic disk has been started.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to enable a flat substrate such as a magnetic disk using only one side to be manufactured efficiently and at low cost.

[0005]

A method of manufacturing a flat substrate according to the present invention is a method of manufacturing a flat substrate by processing one surface to manufacture a flat substrate. Joining the two flat substrates formed on the other surface of each other, simultaneously polishing one surface of each of the two substrates in the joined state, and joining the two substrates in the joined state after the polishing process. And a step of separating the substrate.

A method of manufacturing a flat substrate according to the present invention is a method of manufacturing a flat substrate in which one surface is processed to manufacture a flat substrate. A step of bonding the two substrates on their other surfaces, a step of simultaneously polishing one surface of each of the two substrates in the bonded state, and a step of washing and drying the two substrates in the bonded state; Separating the two substrates in a bonded state after washing and drying.

The method for polishing a flat substrate according to the present invention is a method for polishing a flat substrate in which one surface of a flat substrate is polished.
A step of superimposing two substrates so that the other surfaces thereof face each other, and a step of simultaneously polishing one surface of each of the substrates under a state in which the two substrates are superimposed. It is characterized by.

The method for polishing a flat substrate according to the present invention is a method for polishing a flat substrate in which one surface of a flat substrate is polished, wherein a first surface plate and a second surface plate which are respectively driven to rotate. A plate-like substrate having one surface to be processed is placed between the first layer and the second layer with the other surface facing each other.
Arranging two layers, polishing the one surface of the one-layer substrate by the first platen, and polishing the one surface of the second-layer substrate by the second platen. And simultaneously performing the steps of

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a process diagram showing a method of manufacturing a flat substrate according to an embodiment of the present invention. The magnetic disk is a magnetic disk substrate 1 made of aluminum alloy, glass, or the like. It is manufactured by FIG.
As shown in FIG.
a is a surface to be processed on which various processes such as a polishing process and a magnetic film forming process are performed, and the other surface, that is, the back surface 1b is a non-processed surface on which the magnetic film forming process and the like are not performed.

As shown in FIG. 1B, two substrates 1 are joined by an adhesive 2 with their back surfaces 1b facing each other to form a substrate pair 3, and each substrate 1 has a surface to be processed. 1a faces the opposite side. As shown in FIG. 1 (C), the substrate pair 3 bonded on the back surface 1b is subjected to a polishing process and a cleaning process on each surface 1a, and the surface 1a is mirror-finished. As shown in FIG.

As described above, by simultaneously polishing or cleaning the surfaces of the two substrates 1, the substrates 1 can be manufactured efficiently. Substrate pairs 3 may be left until the formation of the magnetic film by sputtering on the surface of each substrate 1 is finally finished, and the two substrates 1 may be separated after the magnetic film is formed.

FIG. 2 shows the surface 1a of the two substrates 1 bonded together.
FIG. 3 is a side view showing a double-side polishing apparatus for simultaneously polishing the same, FIG. 3 is a cross-sectional view taken along line AA in FIG. 2, and FIG. FIG. 5 is a sectional view taken along line BB in FIG.

As shown in FIGS. 2 and 3, a double-side polishing apparatus 10 includes a base 12 to which a column 11 is fixed, and a processing head 1 mounted on the column 11 so as to be movable in the vertical direction.
And 3. As shown in FIG. 4, a lower surface plate 14 is rotatably incorporated in a horizontal plane in the base 12, and a buff as a lower polishing tool, that is, a polishing pad 15 is annularly formed on an upper surface of the lower surface plate 14. Attached to.

A sun gear 16 having an outer diameter slightly smaller than the inner diameter of the polishing pad 15 is rotatably provided at the center of rotation of the lower stool 14. An annular internal gear 17 having a slightly larger diameter is fixed to the rotary cylinder 18 so as to surround the lower platen 14, and the internal gear 17 is driven to rotate by the rotary cylinder 18.

On the upper surface of the polishing pad 15 of the lower platen 14,
As shown in FIGS. 3 and 4, ten carriers 19 are arranged, and each carrier 19 is arranged.
The external gear portion formed on the outer peripheral portion is meshed with the sun gear 16 and the internal gear 17. Each carrier 1
9, ten circular holding holes 20 for holding the substrate pair 3 as a work are formed by ten. In this double-side polishing apparatus 10, since ten carriers 19 each having ten holding holes 20 are arranged,
At the same time, 100 pairs of substrate pairs 3 can be polished.

However, the number of carriers 19 is not limited to this. For example, any number of carriers 19 can be provided, for example, eight or five. Similarly, the number of holding holes 20 formed in one carrier 19 is ten in the illustrated case, but may be five or eight, and may be an arbitrary number.

As shown in FIG. 2, the processing head 13 has a vertically movable block 21 provided so as to be vertically movable with respect to the column 11, and a support sleeve incorporated in the vertically movable block 21 has a support sleeve as shown in FIG. An upper surface plate drive shaft 23 shown in FIG. 1 is rotatably mounted, and a polishing pad 25 is attached to a lower surface of an upper surface plate 24 connected to the upper surface plate drive shaft 23. In addition, as each polishing pad 15, 25,
It may be attached to the surface of each of the surface plates 14, 24, and by forming a lattice-like groove on the surface of the metal surface plates 14, 24, the surface-side portions of the surface plates 14, 15 are directly formed. A polishing tool may be formed.

In order to transmit the rotation of the upper stool drive shaft 23 to the upper stool 24, a driving body 26 fixed to the lower end of the upper stool drive shaft 23 and a plurality of fixed members fixed to the upper stool 24. A drive plate 29 to which a plurality of support blocks 28 supporting the holder 27 are attached is connected via a universal joint 22.

The upper platen drive shaft 23 is driven to rotate by a motor (not shown) provided on the vertical movement block 21. As shown in FIG. 5, the sun gear 16 is driven to rotate by a sun gear drive shaft 16a, the lower platen 14 is driven to rotate by a hollow lower platen drive shaft 14a, and the internal gear 17 is driven to rotate by a rotary cylinder 18. The drive shafts 16a and 14a and the rotary cylinder 18 are connected to a motor (not shown). Therefore, the sun gear 16 and the internal gear 1 are engaged with each carrier 19 in mesh with the sun gear 16 and the internal gear 17.
When rotated as 7, each carrier 19 revolves around the sun gear 16 while rotating. In this state, when the polishing pad 25 of the upper surface plate 24 is pressed against the polishing pad 15 of the lower surface plate 14 via the substrate pair 3, the substrate pair is moved by the carrier 19 between the upper and lower polishing pads 25, 15 in a horizontal plane. While touching them between them, they move in a horizontal direction while drawing a cycloid curve or trochoid curve. However, the sun gear 16 and the internal gear 17 only need to be in a relatively rotating relationship.
Only the internal gear 17 may be rotated and only the internal gear 17 may be rotated.

The substrate pair 3 is coated with a polishing liquid. The polishing pads 15 and 25 allow the lapping or polishing of a magnetic disk substrate as a work in the presence of the polishing liquid. Done. Therefore,
When polishing the substrate pair 3, the vertical movement block 21 is used.
Is moved downward to set a predetermined interval between the polishing pad 25 of the upper stool 24 and the polishing pad 15 of the lower stool 14, and the pressing force applied from the upper stool 24 to the substrate pair is adjusted. By rotating both the bases 14 and 24, the sun gear 16 and the internal gear 17 under this condition, a total of 100 pairs of the surfaces 1a and 1a of the substrate 1 can be simultaneously polished.

In the case described above, a pair of substrates 3 is formed by bonding two substrates 1 on the back surface 1b thereof with an adhesive 2, but as shown in FIG.
When the thickness t of the carrier 19 is set to a dimension (t> d) larger than the thickness d of one substrate 1, two holes are formed in the holding holes 20 of each carrier 19 without joining the two substrates 1.
The substrates 1 can be arranged in an overlapping manner. In that case, first, the lower substrate 1 is provided in each holding hole 20.
Are arranged with the surface 1a facing downward, and then the upper substrate 1
On the lower substrate 1 with the surface 1a facing upward. The two substrates 1 forming a pair in an overlapped state are placed in the holding hole 20 so that the front surfaces 1a and 1a face the opposite sides and the back surfaces 1b and 1b face each other. Inside, the first layer of the lower substrate 1 and the second layer of the upper substrate 1 are arranged as two layers.

After the two substrates 1 are stacked in two layers in each holding hole 20, the respective surfaces 1a, 1a are simultaneously polished by the double-side polishing apparatus 10, as described above. As described above, when the two substrates 1 to be paired are polished without being joined, the substrates 1 are separated by the operation of taking out the substrates 1 one by one from each holding hole 20 after the processing. Become.

As a double-side polishing apparatus for simultaneously polishing the surfaces 1a, 1a of the plurality of substrate pairs 3, other than the apparatus using the carrier 19 as described above, for example, Japanese Patent Application Laid-Open No. 3-66025 discloses the apparatus. As shown, a double-side polishing apparatus having an index table provided with a chuck for holding a substrate pair as a work can be used. Also,
Instead of polishing a plurality of substrate pairs 3 at the same time, two pairs of substrates may be simultaneously polished. As such a double-side polishing apparatus, for example, JP-A-6-302567
And those disclosed in JP-A-54-81591 can be used.

Examples of the polishing process of the substrate 1 include a lapping process for adjusting a dimensional error of a work and improving a surface finish state and a polishing process for forming a high mirror surface on the surface of the work. When a polishing pad is used as a polishing tool, polishing, that is, lapping and polishing can be performed, and when a grindstone is used as a polishing tool, grinding can also be performed using the same double-side polishing apparatus.

FIG. 6 is a perspective view showing a cleaning unit assembly 30 as an example of the cleaning / drying apparatus. FIG. 7 is a perspective view showing a cup type scrub cleaning machine arranged in the cleaning unit assembly 30 of FIG. FIG. 8 is a perspective view showing a roll type scrub cleaner disposed in the cleaning unit assembly 30 of FIG.

The cleaning unit assembly 30 uses the substrate pair 3 joined by the adhesive 2 as a work to remove foreign substances such as abrasives attached to the polished surfaces 1a, 1a of the substrate pair 3. Has been applied to wash the first
To four cleaning tanks 31 to 34. Each cleaning tank is a dip tank that transports a plurality of pairs of substrates at a predetermined interval while maintaining the substrates in a vertical state, and exposes the surfaces 1a, 1a to liquid to perform dip cleaning.

In the first cleaning tank 31, cleaning is performed by spraying a cleaning liquid from a nozzle 35 while transporting the substrate to the substrate pair 3 after the polishing process, and the cleaning tank 31 is a shower tank. . In the second cleaning tank 32, the substrate supplied to the second cleaning tank 32 is washed while being transported while the substrate pair is laid, and the cleaning tank 32 is a chemical tank. In the third cleaning tank 33, the cleaning liquid supplied therein is vibrated by an ultrasonic vibrator, and the cleaning liquid is transported while the substrate pair 3 is immersed in the cleaning liquid to perform ultrasonic cleaning. Is an ultrasonic bath. In the fourth cleaning tank 34, the substrate pair is transported and washed with pure water supplied therein, and the cleaning tank 34 is a pure water tank.

As shown in FIG. 6, four screw conveyors 40 are rotatably mounted in each of the cleaning tanks, and each substrate pair 3 is provided at four locations in a spiral groove formed in the screw conveyor 40. , And is conveyed continuously from one end to the other end in a state held in a vertical state.

The four cleaning tanks 31 to 34 are arranged in a straight line in a line.
The substrate pair 3 conveyed to the transfer end is lifted and taken out of the cleaning tank, and the taken-out positions are set as scrub cleaning positions 36 to 39, and scrub cleaning is performed at each position by a scrub cleaning machine.

At the scrub cleaning positions 36 and 37, a scrub cleaning machine 41 shown in FIG. 7 is arranged. The scrub cleaning machine 41 has two cup-shaped rotary members which come into contact with the surfaces 1a and 1a of the substrate pair 3. Brushes 42 and 43, an inner peripheral cleaning brush 44 that contacts the inner peripheral surface of the central hole of the substrate pair 3, and an outer peripheral cleaning brush 45 that contacts the outer peripheral surface of the substrate pair. It is designed to be rotationally driven in the direction shown by.

A scrub cleaning machine 46 shown in FIG. 8 is disposed at the scrub cleaning positions 38 and 39. The scrub cleaning machine 46 is composed of two roll-type cleaners which are in contact with the surface of the substrate pair 3 and the inner and outer peripheral surfaces. , And each of the brushes is driven to rotate in a direction indicated by an arrow.

Each scrub cleaning machine is disposed above the transport end of each cleaning tank, and forms one cleaning unit paired with the cleaning tank and the scrub cleaning machine. In the case shown in FIG. 6, one cleaning unit assembly 30 is formed by four cleaning units. However, an arbitrary number of cleaning units may be used in accordance with the type of the substrate pair and the surface treatment process before the cleaning treatment. One cleaning unit assembly 30 can be configured. For example, four or less or four or more cleaning units may constitute one cleaning unit assembly.

FIG. 9 is a plan view showing a cleaning apparatus having a cleaning processing section 51 in which the cleaning unit assembly shown in FIG. 6 is incorporated, and a drying processing section 52 disposed adjacent thereto. FIG. FIG. 11 is a front view of FIG. 9, FIG. 11 is a schematic cross-sectional view along the line CC in FIG. 9, and FIG. 12 is a schematic cross-sectional view along the line DD in FIG.

In the housing 53 of the cleaning section 51,
As shown in FIG. 9, two sets of cleaning unit assemblies 30 are incorporated in parallel with each other, and a cleaning machine that drives scrub cleaning machines 41 and 46 is provided between both cleaning unit assemblies 30. A drive unit 54 is provided. Accordingly, in the cleaning processing section 51, the substrate pair is subjected to the dip cleaning while being transported in the cleaning tank of each cleaning unit assembly 30, and the scrub cleaning is performed for each substrate pair by each scrub cleaning machine. .

As shown in FIG. 10, an air supply unit 55 for blowing out the air cleaned by the filter as shown by the arrow is provided at the upper part of the housing 53. Scrub cleaning is performed in clean air. Done.

FIG. 13 is an enlarged sectional view showing a portion indicated by reference numeral E in FIG. 11, and FIG. 14 is a sectional view taken along line FF in FIG. 11. All the cleaning tanks have substantially the same structure. It has become.

As shown in FIGS. 13 and 14, four screw conveyors 40 are rotatably mounted on the tank main body 56 of each cleaning tank, and the substrate pair 3 carried into the tank main body 56 has a predetermined size. The paper is conveyed in a vertical state from the carry-in end to the carry-out end at intervals.
Each of the screw conveyors 40 has both ends protruding outside of the tank body 56 and is driven to rotate by driving means (not shown) provided outside. Leakage of liquid in 56 is prevented.

As shown in FIG. 10, the tank main body 56 is provided with vertical moving members 57 corresponding to the carry-in end portion and the carry-out end portion. As shown, a support claw 58 for holding the substrate pair 3 is provided. After the substrate pair is placed on the support claws 58 with the vertical moving member 57 at the carry-in end in the ascending limit position, the vertical moving member 57 is moved downward, so that the substrate pair becomes the groove of the four screw conveyors 40. And is carried into the tank body 56. On the other hand, when the vertically moving member 57 at the carry-out end is moved upward, the support claws 58 come into contact with the substrate pair, and the substrate pair is lifted to the upper limit position.

Above the carry-out ends of the first and second cleaning tanks 31 and 32, a scrub cleaner 41 is provided for scrub-cleaning the substrate pair lifted by the vertically moving member 57. As shown in FIGS. 13 and 14, an arm 61 having one cup-shaped rotating brush 42 of the scrub cleaning machine 41 is rotatably mounted on a washing machine driving section 54, and the other cup-shaped rotating brush 43 is connected to the arm 61. The arm 62 is also pivotally mounted on the washer driving unit 54. Further, an arm (not shown) having the inner peripheral surface cleaning brush 44 and the outer peripheral surface cleaning brush 45 shown in FIG.

Above the carry-out ends of the third and fourth cleaning tanks 33 and 34, a scrub cleaner 46 for scrubbing the substrate pair raised by the vertically moving member 57 is provided. As shown in FIG. 9, shafts 63 and 64 provided with respective roll-type rotary brushes 47 and 48 of the scrub cleaner 46 are provided in a washer driving unit 54, and the respective shafts 63 and 64 are It is movable toward and away from each other.

As shown in FIG. 14, in order to transfer the substrate pair scrubbed by the scrub cleaning machine 41 above the carry-out end of the first cleaning tank 31 to above the carry-in end of the second cleaning tank, as shown in FIG. A work transfer device 65 is provided between the two cleaning tanks 31 and 32. The work transfer device 65 has a slide block 67 which is reciprocally movable along a guide rail 66, and a pivot shaft 68 rotatably mounted on the slide block 67 within a range of 180 degrees includes a substrate pair 3
Is held. Therefore, after the slug-cleaned substrate pair is supported on the holding claws 69 and the holding claws 69 are turned 180 degrees, the substrate pairs 3 are transferred above the carry-in end of the second cleaning tank 32.

As shown in FIG. 9, between the respective cleaning tanks, the carry-in end of the first cleaning tank 31, and the fourth cleaning tank 34.
The work transfer machines 65 shown in FIG. However, the work transfer device 65 provided at the unloading end of the fourth cleaning tank 34 is unloaded to the drying processing unit 52 when the holding claws 69 rotate 90 degrees.

In the housing 71 of the drying section 52,
As shown in FIG. 9, a dryer driving unit 72 is provided so as to be continuous with the cleaning unit driving unit 54, and two drying units 72 are provided on both sides of the drying unit driving unit 72 so as to correspond to the two cleaning unit assemblies 30.
Each is provided with a spin dryer 73. Each of the spin dryers 73 has a finger for gripping the substrate pair 3 at the outer peripheral portion thereof, and removes moisture attached to the substrate pair by rotating the substrate pair.

The cleaning section 51 is provided above the housing 71.
An air supply unit 55 is provided in the same manner as described above. In the housing 71, the substrate pairs carried out from the respective cleaning unit assemblies 30 are immediately loaded into the spin dryer 73, and the dried substrate pairs are transported. For this purpose, a dryer driving section 72 is provided, and two transport heads 74 are arranged on both sides of the dryer drive section 72. Each transport head 74 is mounted on a guide rail 75 so as to be movable in the horizontal direction, and the transport head 74 is It is movable toward and away from the spin dryer 73.

Therefore, the substrate pair cleaned by the cleaning processing unit 51 can be transported to the drying processing unit 52 and immediately spin-dried, so that foreign matter and the like adhere between the cleaning processing and the drying processing. Can be prevented,
The degree of cleaning of the substrate pair can be increased. Moreover, there is no need to submerge and store the cleaned substrate pair in a container to which pure water has been supplied, so that there is no need for an installation space for the container.

Although the illustrated cleaning apparatus has two sets of cleaning unit assemblies 30, only one set of cleaning unit assemblies 30 may be incorporated in the housing 53. Although the scrub cleaner has a mixture of a cup type and a roll type, all may be a scrub cleaner having a cup type rotary brush or a scrub cleaner having a roll type rotary brush. A washing machine may be used. The dip tanks for dip cleaning the substrate pairs are combined in the order of a shower tank, a chemical solution tank, an ultrasonic tank, and a pure water tank, but the order of these combinations can be changed as appropriate, and the number of tanks can be freely set. It can be used in combination with other types of dep tanks as appropriate. The continuous transfer of the substrate pair in each cleaning tank is performed by a walking beam in which a member provided with a hook or a finger for holding the substrate pair is moved to the cleaning tank or the upper part of the cleaning tank instead of the screw conveyor 40. You may make it perform by a conveyer of a formula.

The illustrated washing device and drying device are merely examples, and these devices are not limited to the above-mentioned types, and various types can be used.

The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the scope of the invention.

For example, in the illustrated embodiment, the present invention is applied to manufacture a hard disk by treating the surface 1a of a magnetic disk substrate, but the present invention is applied to manufacture a semiconductor device and a liquid crystal. The invention can be applied. 2. Description of the Related Art Semiconductor devices are manufactured through various surface treatment steps on the surface of a single-crystal flat semiconductor wafer such as silicon, that is, a semiconductor substrate. The liquid crystal substrate is manufactured through various surface treatment steps on the surface of a flat glass substrate. The present invention can be applied to a manufacturing method including a step of polishing the surface of the semiconductor substrate or the liquid crystal substrate.

[0051]

According to the present invention, the surfaces of two flat disk substrates such as magnetic disk substrates are simultaneously polished and the substrates are separated after the processing, so that only one surface is polished. A flat substrate to be processed can be efficiently manufactured at low cost. In addition to the polishing process, the two substrates are simultaneously cleaned and dried, whereby a flat substrate can be efficiently manufactured.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method of manufacturing a flat substrate according to an embodiment of the present invention.

FIG. 2 is a side view showing an example of a double-side polishing apparatus for simultaneously polishing the surface of a substrate.

FIG. 3 is a sectional view taken along line AA in FIG. 2;

FIG. 4 is a perspective view showing a lower platen incorporated in a base of the double-side polishing apparatus.

FIG. 5 is a sectional view taken along line BB in FIG. 2;

FIG. 6 is a perspective view showing a cleaning unit assembly as an example of a cleaning device for simultaneously cleaning the surface of a substrate.

FIG. 7 is a perspective view showing a cup type scrub cleaner disposed in the cleaning unit assembly shown in FIG. 6;

FIG. 8 is a perspective view showing a roll type scrub cleaner disposed in the cleaning unit assembly shown in FIG. 6;

FIG. 9 is a plan view showing a cleaning apparatus having a cleaning processing unit in which the cleaning unit assembly shown in FIG. 6 is incorporated and a drying processing unit arranged next to the cleaning processing unit.

FIG. 10 is a front view of FIG. 9;

FIG. 11 is a schematic sectional view taken along line CC in FIG. 9;

FIG. 12 is a schematic sectional view taken along line DD in FIG. 9;

FIG. 13 is a cross-sectional view showing an enlarged portion indicated by reference numeral E in FIG.

FIG. 14 is a sectional view taken along line FF in FIG. 13;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate (magnetic disk substrate) 1a Surface (one surface) 1b Back surface (other surface) 2 Adhesive 3 Substrate pair 10 Double-side polishing device 30 Cleaning unit 41, 46 Scrub cleaner 51 Cleaning processing part 52 Drying processing part 73 Spin dryer

Claims (4)

[Claims] 1. A method of manufacturing a flat substrate, wherein one surface is processed to manufacture a flat substrate, wherein two flat substrates each having one surface to be processed are treated on the other surface. A step of bonding two substrates in a bonded state simultaneously, a step of simultaneously polishing one surface of each of the two substrates in a bonded state, and a step of separating the two substrates in a bonded state after polishing. Substrate manufacturing method. 2. A method of manufacturing a flat substrate, wherein one surface is processed to manufacture a flat substrate, wherein two flat substrates having one surface to be processed are respectively processed to the other surface. Bonding two substrates in a bonded state simultaneously; polishing one surface of each of the two substrates in a bonded state; cleaning and drying the two substrates in a bonded state; and cleaning and drying the two substrates. And a step of separating the substrate. 3. A method for polishing a flat substrate, wherein one surface of the flat substrate is polished, wherein the other two surfaces of the two flat substrates are opposed to each other. And a step of simultaneously polishing one surface of each of the substrates in a state where the two substrates are superimposed on each other. . 4. A method for polishing a flat substrate, wherein one surface of the flat substrate is polished, wherein one surface of each of the first surface plate and the second surface plate, each of which is driven to rotate, is provided. Disposing a flat-plate-shaped substrate, which has become a surface to be processed, in two layers, a first layer and a second layer, with the other surfaces facing each other; and A method for polishing a flat substrate, comprising: simultaneously performing polishing of one surface and polishing of one surface of the substrate of the second layer by the second platen.