US20230040654A1

US20230040654A1 - Polishing pad for wafer polishing device, and apparatus and method for manufacturing same

Info

Publication number: US20230040654A1
Application number: US17/783,059
Authority: US
Inventors: Jin Woo Ahn; Soo Cheon JANG
Original assignee: SK Siltron Co Ltd
Current assignee: SK Siltron Co Ltd
Priority date: 2020-02-05
Filing date: 2020-05-08
Publication date: 2023-02-09
Also published as: KR20210099808A; WO2021157781A1; KR102305796B9; CN115087519A; KR102305796B1; JP2023506029A

Abstract

The present invention provides a method for manufacturing a polishing pad, the method comprising: a step for manufacturing a non-woven pad; a polyurethane impregnation step for impregnating the non-woven pad with polyurethane; and a surface polishing step for polishing the surface of the non-woven pad impregnated with polyurethane, wherein the polyurethane impregnation step and the surface polishing step are performed such that the density ratio between the surface layer and the inside of the polishing pad is uniform.

Description

TECHNICAL FIELD

Embodiments relate to a wafer polishing apparatus, and more particularly to a polishing pad used in a wafer polishing apparatus.

BACKGROUND ART

In general, a single-crystal silicon ingot may be grown and manufactured using a Czochralski method. This method is a method of melting polycrystalline silicon in a crucible in a chamber, soaking a seed crystal, which is a single crystal, in the melted silicon, and slowing raising the seed crystal so as to be grown as a single-crystal silicon ingot (hereinafter referred to as an ingot) having a desired diameter.
A single-crystal silicon wafer manufacturing process includes a single-crystal growth process of forming an ingot using the above method, a slicing process of slicing the ingot to obtain a thin disc-shaped wafer, an edge grinding process of grinding an edge of the wafer obtained through the slicing process in order to prevent fracture or distortion of the wafer, a lapping process of removing damage due to mechanical machining remaining on the wafer in order to improve flatness of the wafer, a polishing process of polishing the wafer, and a cleaning process of removing a polishing agent and foreign matter from the polished wafer.
In the wafer polishing process, thereamong, both surfaces of a wafer may be simultaneously polished using a double side polishing (DSP) apparatus.
FIG. 1 is a perspective view of a general wafer polishing apparatus.
As shown in FIG. 1 , the general wafer polishing apparatus 100 includes an upper surface plate 110, a lower surface plate 120, an upper pad (or upper polishing pad) 130, a lower pad (or lower polishing pad) 140, a carrier 150, a sun gear 160, an internal gear 170, and a central shaft 180.
The upper surface plate 110 and the lower surface plate 120 are disposed so as to be rotatable while facing each other.
The upper pad 130 is disposed under the upper surface plate 110, and the lower pad 140 is disposed above the lower surface plate 120. Inside the upper surface plate 110 and the lower surface plate 120, the upper and lower pads 130 and 140 are disposed so as to face each other in order to polish a wafer W.
Each of the upper surface plate 110 and the lower surface plate 120 may have a disc shape, and each of the upper and lower pads 130 and 140, which are attached to the upper surface plate 110 and the lower surface plate 120, respectively, may also have a disc shape.
The sun gear 160 is installed at an outer circumference of the central shaft 180, and the internal gear 170 is installed at an outer circumference of the lower surface plate 120. The internal gear 170 may be rotated in a direction opposite the rotation direction of the sun gear 160.
The carrier 150 is disposed between the upper pad 130 and the lower pad 140, and may be rotated by rotation of the sun gear 160 and the internal gear 170. In addition, the carrier 150 has an insertion hole, into which the wafer W may be inserted, and a slurry hole, through which slurry may be introduced. The carrier 150 may be formed in the shape of a disc having a screw formed on an outer circumferential surface thereof.
Teeth formed at an outer circumferential surface of the sun gear 160 and teeth formed at an inner circumferential surface of the internal gear 170 are engaged with teeth 152 formed at the outer circumferential surface of the carrier 150. When the upper surface plate 110 and the lower surface plate 120 are rotated about the central shaft 180 by a driving source (not shown), therefore, the carrier 150 performs rotation and revolution.
Although not shown, a plurality of slurry supply holes 190, in which nozzles configured to supply slurry from above the upper surface plate 110 are installed, may be formed through the upper surface plate 110.
In the general wafer polishing apparatus 100 having the above construction, when a wafer W is inserted into and seated in the insertion hole of the carrier 150 installed between the upper surface plate 110 and the lower surface plate 120, friction occurs between the wafer W and the upper and lower pads 130 and 140 attached respectively to the upper surface plate 110 and the lower surface plate 120. At this time, both surfaces of a plurality of the wafers W mounted in the carriers 150 are polished by slurry supplied inwards from above the upper surface plate 110 and the polishing pads 130 and 140 in a batch fashion. That is, polishing of the wafer W due to friction may be performed by rotation of the upper pad 130 of the upper surface plate 110 and the lower pad 140 of the lower surface plate 120 in opposite directions.
However, glazing, in which porous surfaces of the polishing pads 130 and 140 are changed due to frequent friction between the polishing pads 130 and 140 and the wafer W, and surface layers of the polishing pads are closed by the slurry and polishing by-products, occurs. Such grazing reduces coefficients of friction of the polishing pads 130 and 140, whereby wafer polishing quality is deteriorated.

DISCLOSURE

Technical Problem

Embodiments provide a polishing pad for wafer polishing apparatuses capable of preventing glazing during a wafer polishing process, thereby improving flatness of a wafer, and an apparatus and method for manufacturing the same.

Technical Solution

An embodiment provides a polishing pad manufacturing method including a step of manufacturing non-woven fabric, a polyurethane impregnation step of impregnating the non-woven fabric with polyurethane, and a surface finishing step of finishing the surface of the non-woven fabric impregnated with the polyurethane, wherein the polyurethane impregnation step and the surface finishing step are performed such that a density ratio of a surface layer to the interior of a polishing pad is uniform.
The polyurethane impregnation step may include a pretreatment step of pretreating the non-woven fabric, a first drying step of removing moisture from the non-woven fabric, an impregnation step of impregnating the non-woven fabric with polyurethane, a second drying step of drying the polyurethane contained in the non-woven fabric by impregnation, and a pressing process of pressing the non-woven fabric impregnated with the polyurethane.
In the impregnation step, a polyurethane impregnation process may be performed at least twice.
The impregnation step may include a first impregnation process of impregnating the non-woven fabric with hydrophilic polyurethane and a second impregnation process of impregnating the non-woven fabric with hydrophobic polyurethane.
In the surface finishing step, buffing may be performed such that a density ratio of a porous layer containing the polyurethane to a porous layer containing no polyurethane in the surface layer of the polishing pad is 1:1.
The non-woven fabric may have a thickness of 4 mm to 6 mm, and the thickness of the non-woven fabric removed by the buffing may be 2.5 mm to 3.5 mm.
The polishing pad may have an overall density of 0.44 to 0.55 g/cm³.
Another embodiment provides an apparatus for manufacturing a polishing pad for wafer polishing apparatuses, the apparatus including a non-woven fabric manufacturing unit configured to manufacture non-woven fabric, a polyurethane impregnation unit configured to impregnate the non-woven fabric with polyurethane, and a surface finishing unit configured to finish the surface of the non-woven fabric impregnated with the polyurethane, wherein the polyurethane impregnation unit includes a first polyurethane water tank configured to receive hydrophilic polyurethane and a second polyurethane water tank configured to receive hydrophobic polyurethane for impregnation.
The surface finishing unit may perform buffing such that a density ratio of a porous layer containing the polyurethane to a porous layer containing no polyurethane in the surface layer of the polishing pad is 1:1.
The non-woven fabric may have a thickness of 4 mm to 6 mm, and the thickness of the non-woven fabric removed by the buffing may be 2.5 mm to 3.5 mm.
A further embodiment provides a polishing pad for wafer polishing apparatuses manufactured using the manufacturing method or apparatus

Advantageous Effects

A polishing pad for wafer polishing apparatuses according to an embodiment and an apparatus and method for manufacturing the same have an effect in that density of polyurethane provided on a surface layer of the polishing pad by impregnation is equalized, whereby it is possible to prevent glazing during a wafer polishing process, and therefore it is possible to improve flatness of a wafer.
In addition, the polishing pad according to the embodiment has an effect in that high roughness of the surface layer of the polishing pad is maintained, whereby it is possible to inhibit a conventional phenomenon in which a removal rate is reduced due to an increase in pad use time, and therefore the lifespan of the polishing pad is increased.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a general wafer polishing apparatus.
FIG. 2 is a schematic view showing the construction of a wafer polishing pad manufacturing apparatus according to an embodiment.
FIG. 3 is a flowchart showing a wafer polishing pad manufacturing method according to an embodiment.
FIGS. 4 and 5 are process charts showing a process of manufacturing a polishing pad according to the manufacturing method of FIG. 3 .
FIGS. 6A and 6B are sectional views of a polish pad containing polyurethane before buffing and after buffing.
FIG. 7 is a graph showing densities of a polishing pad according to an example and a polishing pad according to a comparative example based on the thickness thereof.
FIG. 8 is CT images showing the fault states of the polishing pads of FIG. 7 at a thickness of 100 μm.

BEST MODE

Hereinafter, embodiments will be clearly disclosed through the description of the embodiments with reference to the accompanying drawings. In the following description of the embodiments, it will be understood that, when an element, such as a layer (film), a region, a pattern, or a structure, is referred to as being “on” or “under” another element, such as a substrate, a layer (film), a region, a pad, or a pattern, it can be “directly” on or under another element or can be “indirectly” formed such that an intervening element is also present. Terms such as “on” or “under” are described on the basis of the drawings.
In the drawings, the size of each element is exaggerated, omitted, or schematically illustrated for convenience of description and clarity. In addition, the size of each element does not entirely reflect the actual size thereof. In addition, the same reference numerals denote the same elements throughout the description of the drawings. Hereinafter, embodiments will be described with reference to the accompanying drawings.
FIG. 2 is a schematic view showing the construction of a wafer polishing pad manufacturing apparatus according to an embodiment, FIG. 3 is a flowchart showing a wafer polishing pad manufacturing method according to an embodiment, FIGS. 4 and 5 are process charts showing a process of manufacturing a polishing pad according to the manufacturing method of FIG. 3 , and FIG. 6 is a sectional view of a polish pad containing polyurethane before buffing (a) and after buffing (b).
As shown in FIG. 2 , the wafer polishing pad manufacturing apparatus according to the embodiment may include a non-woven fabric manufacturing unit 1, a polyurethane impregnation unit 2, a surface finishing unit 3, and a tape pasting and cutting unit 4.
Here, each of the units 1, 2, 3, and 4 may be a combination of a series of devices, and each of the units 1, 2, 3, and 4 may constitute a single connected manufacture route.
The non-woven fabric manufacturing unit 1 includes a series of devices configured to manufacture non-woven fabric, which is a main material used in the polishing pad. For example, as shown in FIG. 4 , the non-woven fabric manufacturing unit 1 may include a supply unit 10 configured to supply a bundle of fibers C, a pressing unit 20 configured to press the bundle of fibers C, and a bonding unit 30 and a punching unit 40 configured to perform a needle punching process.
The polyurethane impregnation unit 2 includes a series of devices configured to impregnate the non-woven fabric with polyurethane in order to coat the non-woven fabric with polyurethane. For example, as shown in FIG. 4 , the polyurethane impregnation unit 2 may include a pretreatment water tank 50, a first drying unit 60, a first polyurethane water tank 70, a second polyurethane water tank 80, a second drying unit 100, and a pressing roller 110.
The surface finishing unit 3 includes a series of devices configured to remove a surface layer portion from the non-woven fabric impregnated with polyurethane. For example, as shown in FIG. 5 , the surface finishing unit 3 may include sandpaper 120 for buffing.
The tape pasting and cutting unit 4 includes a series of devices configured to paste a double-sided tape T to one surface of the buffed polishing pad and to cut the polishing pad in the form of a circular pad.
For example, as shown in FIG. 5 , the tape pasting and cutting unit 4 may include a cutter unit 130, a tape pasting unit 140, a pressing unit 150, a shape cutting unit 160, and a package inspection unit 170.
Hereinafter, a polishing pad manufacturing method using the wafer polishing pad manufacturing apparatus according to the embodiment including the above construction will be described in detail.
As shown in FIG. 3 , a polishing pad for wafer polishing apparatuses (hereinafter referred to as a polishing pad) according to an embodiment may be manufactured using a polishing pad manufacturing method including a non-woven fabric manufacturing step (S100), a polyurethane impregnation step (S200), a surface finishing step (S300), a tape pasting and cutting step (S400), and a polishing pad mounting step (S500).
1) Non-Woven Fabric Manufacturing Step (S100)
The polishing pad according to this embodiment starts to be manufactured in the form of a pad while the non-woven fabric manufacturing step is performed. The non-woven fabric is fabric that is not woven using a loom. Since fibers are directly combined in the form of fabric, the non-woven fabric is also called bonded fabric. Here, polyester, viscose rayon, nylon, polypropylene, cotton, hemp, wool, asbestos, glass fibers, or acetate may be selected as the fibers.
The non-woven fabric is manufactured using a dry-laid non-woven fabric manufacturing method, which does not use water, or a wet-laid non-woven fabric manufacturing method, which uses water. In the non-woven fabric manufacturing step (S100) according to this embodiment, the dry-laid non-woven fabric manufacturing method may be used.
More specifically, in the non-woven fabric manufacturing step (S100), i) the supply unit 10 supplies a bundle of fibers C to the pressing unit 20, ii) the pressing unit 20 presses the supplied bundle of fibers C into a web (fibers that are thinly spread) W, and iii) the bonding unit 30 and the punching unit 40 punch the web (W) fibers using a needle to manufacture non-woven fabric F, as shown in FIG. 4 (1). The polyurethane impregnation step (S200) is performed to provide the manufactured non-woven fabric F with physical properties necessary for the polishing pad Pad.
2) Polyurethane Impregnation Step (S200)
The polyurethane impregnation step (S200) includes a process of soaking the non-woven fabric F manufactured in step 1) (S100) in the polyurethane water tank 70 so as to be impregnated with polyurethane for a predetermined time. A plurality of pores, i.e. a porous layer, is present not only at the surface of the non-woven fabric F but also in the interior of the non-woven fabric F. Polyurethane PU may permeate the porous layer of the non-woven fabric F to provide physical properties necessary for the polishing pad Pad.
Polyurethane PU is a compound generated as the result of combination between polyol and isocyanate. That is, polyurethane is a polymer compound having urethane repeatedly combined in a polymer chain. There are epoxy, polyester, and phenol as this compound.
As shown in FIG. 4 (2), the polyurethane impregnation step (S200) may include i) a pretreatment process, ii) a first drying process, iii) an impregnation process, iv) a second drying process, and v) a pressing process.
The pretreatment and drying processes are performed before polyurethane (PU) impregnation such that the polyurethane (PU) impregnation process is smoothly performed. The pretreatment process may include a process of soaking the non-woven fabric F in the pretreatment water tank 50, in which a cleaning solution or a chemical is contained. The non-woven fabric F manufactured in step 1) (S100) may be moved into the pretreatment water tank 50 by rollers R. After the pretreatment process, the non-woven fabric F may be moved to the first drying process by rollers R.
The first drying process may be a process of removing moisture from the non-woven fabric F soaked in the cleaning solution or the chemical. For example, the first drying process may be performed through the first drying unit 60, which is capable of evaporating the cleaning solution or the chemical using a heater or a fan.
The impregnation process is a process of soaking the non-woven fabric F in the polyurethane water tank 70, in which polyurethane PU is contained. Polyurethane PU is manufactured by mixing two or more kinds of liquid, and properties thereof are determined depending on the kind of isocyanate and polyol, which are reactants. Long combinations contained in polyol assist in forming a soft elastic polymer, and huge-amount combinations assist in forming a hard polymer. When a length corresponding to an intermediate between two combinations is maintained, high elasticity with moderate stiffness may be achieved. That is, when polyurethane PU is manufactured, a ratio between a soft segment and a hard segment, which are components thereof, may be adjusted to acquire elasticity and softness suitable for use. When the percentage of the soft segment is higher, lower hardness and higher elasticity are achieved.
In the polyurethane (PU) impregnation process, conditions may be controlled to change the mass, volume, and thickness of polyurethane PU contained in the non-woven fabric F. Here, the conditions may be impregnation time, concentration of polyurethane PU, the number of impregnations, and the movement speed of the non-woven fabric F.
In this embodiment, density of polyurethane (PU) at the surface and in the interior of the polishing pad Pad may be equalized, whereby it is possible to improve air-permeability, and therefore it is possible to remedy glazing. To this end, at least one of the following equalization conditions may be included in the polyurethane impregnation process.
First, in the polyurethane impregnation process, the non-woven fabric F containing polyurethane PU may be primarily soaked in the second polyurethane water tank 80. That is, the polyurethane impregnation process may be performed at least twice. In addition, the non-woven fabric F containing polyurethane PU may be further soaked in a third polyurethane water tank 90 or a cleaning tank 90 so as to be further impregnated with polyurethane or to be cleaned, as needed.
Here, polyurethane in the first polyurethane water tank 70 and the second polyurethane water tank 80 may be hydrophobic. That is, polyurethane may not combine with water.
In addition, the first polyurethane water tank 70 may be filled with hydrophilic polyurethane, and the second polyurethane water tank 80 may be filled with hydrophobic polyurethane. When polyurethane in the first polyurethane water tank 70 is hydrophilic, polyurethane may more smoothly move from the surface to the interior of the non-woven fabric F when the non-woven fabric is impregnated with polyurethane, than hydrophobic polyurethane.
Second, the non-woven fabric that is impregnated with polyurethane may be manufactured so as to be thick. For example, the polyurethane impregnation step (S200) may be performed on non-woven fabric having a thickness of 5 mm manufactured in the non-woven fabric manufacturing step (S100) (conventional non-woven fabric has a thickness of 2.3 mm). In the surface finishing step (S300), a description of which will follow, therefore, a buffing thickness may be increased by 2.7 mm more than the conventional non-woven fabric.
That is, in the embodiment, the non-woven fabric may have a thickness of 4 mm to 6 mm, and the thickness of the non-woven fabric that is removed at the time of buffing may be 2.5 mm to 3.5 mm.
Subsequently, the second drying process may be performed. For example, the second drying process may be performed through the second drying unit 100, which is capable of drying polyurethane using a heater or a fan.
Subsequently, the non-woven fabric UF containing polyurethane PU passes through the pressing roller 110 so as to be pressed such that polyurethane PU deeply permeates even the interior of the non-woven fabric UF.
3) Surface Finishing Step (S300)
After the polyurethane impregnation step (S200), the surface finishing step (S300) is performed on the non-woven fabric UF. In the surface finishing step (S300), the non-woven fabric UF is sanded or buffed using sandpaper in order to remove foreign matter from the surface and the bottom of the non-woven fabric UF. Also, in the surface finishing step (S300), the thickness of the polishing pad and the surface porosity of the polishing pad may be adjusted.
As shown in FIG. 6(a), the polyurethane (PU) impregnation density of the polishing pad Pad is high at a surface layer portion of the polishing pad and is gradually lowered toward the interior of the polishing pad. Due to high polyurethane (PU) density at the surface of the polishing pad Pad, therefore, slurry introduced into the surface of the polishing pad Pad at the time of wafer polishing is not moved to the interior of the polishing pad. As a result, glazing occurs in the state in which the slurry is adhered to the surface of the polishing pad.
In order to solve this problem, in the surface finishing step (S300), pores P in the surface layer may be further exposed by removing a part of the surface through buffing using the sandpaper 120, as shown in FIGS. 5 (3) and 6(b). Consequently, a ratio of the part of the surface layer portion of the polishing pad Pad impregnated with polyurethane PU to the interior of the polishing pad impregnated with no polyurethane may be increased, whereby the slurry may be moved to the interior of the polishing pad Pad, and therefore the slurry may not be adhered to the surface of the polishing pad.
The overall density of the polishing pad Pad may be 0.44 to 0.55 g/cm³, the compression rate of the polishing pad Pad may be 1.9 to 2.0%, and the hardness of the polishing pad Pad may be 88 Asker C. That is, even though the polyurethane (PU) impregnation density in the surface layer portion of the polishing pad Pad is adjusted, fundamental physical properties necessary for the polishing pad Pad may be satisfied.
4) Tape Pasting and Cutting Step (S400)
The tape pasting and cutting step (S400) is a step of attaching a double-sided tape T to one surface of the polishing pad UF impregnated with polyurethane PU and cutting the polishing pad in the form of a circular pad.
More specifically, in the tape pasting and cutting step (S400), as shown in FIG. 5 (4), i) the cutter unit 130 cuts the polishing pad UF impregnated with polyurethane PU to a predetermined length, ii) the tape pasting unit 140 pastes a double-sided tape T to one surface of the polishing pad UF (PSA prepasting), iii) the pressing unit 150 presses the double-sided tape T (PAS pasting, Press), iv) the shape cutting unit 160 cuts the polishing pad UF having the double-sided tape T pasted thereto by pressing into a predetermined shape (e.g. a circular shape having the size of a surface plate), and v) the package inspection unit 170 inspects a product and packages the product (inspection, shipping).
5) Polishing Pad Mounting Step (S500)
One surface of the double-sided tape T of the polishing pad UF packaged in the fourth step (S400) is attached to a surface plate of a wafer polishing apparatus, and a wafer polishing process is performed using slurry.
FIG. 7 is a graph showing densities of a polishing pad according to an example and a polishing pad according to a comparative example based on the thickness thereof.
As shown in FIG. 7 , it can be seen that the polishing pad according to the example, which was manufactured so as to have a uniform polyurethane impregnation rate using the above manufacturing apparatus and method, has an average density value irrespective of the thickness of the polishing pad (from the top to the bottom). In contrast, the polishing pad according to the comparative example has a high density at surface layer portions constituting the top and the bottom.
In the conventional polishing pad (comparative example), slurry introduced into the surface of the pad is not moved to the interior of the pad during the polishing process due to high density of the surface thereof, whereby glazing occurs in the state in which the slurry is adhered to the surface of the polishing pad.
In the polishing pad according to the example, density at the surface and the interior of the pad is uniform, and therefore mobility of the slurry to the interior of the polishing pad may be improved.
FIG. 8 is CT images showing the fault states of the polishing pads of FIG. 7 at a thickness of 100 μm.
It was observed that glazing occurring at the polishing pad according to the comparative example was formed from the surface to the interior of the polishing pad by a depth of 300 μm. That is, the layer thickness of glazing may be formed from the front of the polishing pad to a depth of 300 μm.
As shown in FIG. 8 , it can be seen from the photographed 100 μm thickness layers of the example and the comparative example that the comparative example has a larger whiter spot (glazing area).
In the polishing pad according to the example, density at the surface and the interior of the pad is uniform, whereby slurry is smoothly introduced into the interior of the pad, and therefore the glazing area is controlled from the surface layer of the pad to a depth of 100 μm.
In the polishing pad for wafer polishing apparatuses according to the embodiment and the method of manufacturing the same, the density of polyurethane exposed from the surface of the polishing pad is equalized, whereby it is possible to prevent glazing during the wafer polishing process, and therefore it is possible to improve flatness of the wafer.
Also, in the polishing pad according to the embodiment, high roughness of the surface layer of the pad is maintained, whereby it is possible to inhibit a conventional phenomenon in which a removal rate is reduced due to an increase in pad use time. That is, the lifespan of the polishing pad may be increased.
The features, structures, and effects described in the above embodiments are included in at least one embodiment, but are not limited to only one embodiment. Furthermore, features, structures, and effects illustrated in each embodiment may be combined or modified in other embodiments by those skilled in the art to which the embodiments pertain. Therefore, it is to be understood that such combinations and modifications fall within the scope of the present disclosure.

INDUSTRIAL APPLICABILITY

Embodiments are applicable to a polishing pad for wafer polishing apparatuses and an apparatus and method for manufacturing the wafer polishing pad.

Claims

1. A method of manufacturing a polishing pad for wafer polishing apparatuses, the method comprising:

a step of manufacturing non-woven fabric;

a polyurethane impregnation step of impregnating the non-woven fabric with polyurethane; and

a surface finishing step of finishing a surface of the non-woven fabric impregnated with the polyurethane, wherein

the polyurethane impregnation step and the surface finishing step are performed such that a density ratio of a surface layer to an interior of a polishing pad is uniform.

2. The method according to claim 1, wherein the polyurethane impregnation step comprises:

a pretreatment step of pretreating the non-woven fabric;

a first drying step of removing moisture from the non-woven fabric;

an impregnation step of impregnating the non-woven fabric with polyurethane;

a second drying step of drying the polyurethane contained in the non-woven fabric by impregnation; and

a pressing process of pressing the non-woven fabric impregnated with the polyurethane.

3. The method according to claim 2, wherein, in the impregnation step, a polyurethane impregnation process is performed at least twice.

4. The method according to claim 3, wherein the impregnation step comprises:

a first impregnation process of impregnating the non-woven fabric with hydrophilic polyurethane; and

a second impregnation process of impregnating the non-woven fabric with hydrophobic polyurethane.

5. The method according to claim 4, wherein buffing is performed such that a density ratio of a porous layer containing the polyurethane to a porous layer containing no polyurethane in the surface layer of the polishing pad is 1:1.

6. The method according to claim 5, wherein

the non-woven fabric has a thickness of 4 mm to 6 mm, and

a thickness of the non-woven fabric removed by the buffing is 2.5 mm to 3.5 mm.

7. The method according to claim 6, wherein the polishing pad has an overall density of 0.44 to 0.55 g/cm³.

8. An apparatus for manufacturing a polishing pad for wafer polishing apparatuses, the apparatus comprising:

a non-woven fabric manufacturing unit configured to manufacture non-woven fabric;

a polyurethane impregnation unit configured to impregnate the non-woven fabric with polyurethane; and

a surface finishing unit configured to finish a surface of the non-woven fabric impregnated with the polyurethane, wherein

the polyurethane impregnation unit comprises:

a first polyurethane water tank configured to receive hydrophilic polyurethane; and

a second polyurethane water tank configured to receive hydrophobic polyurethane for impregnation.

9. The apparatus according to claim 8, wherein the surface finishing unit performs buffing such that a density ratio of a porous layer containing the polyurethane to a porous layer containing no polyurethane in the surface layer of the polishing pad is 1:1.

10. The apparatus according to claim 9, wherein

the non-woven fabric has a thickness of 4 mm to 6 mm, and

a thickness of the non-woven fabric removed by the buffing is 2.5 mm to 3.5 mm.