US20090149118A1

US20090149118A1 - Silicon Wafer Grinding Apparatus, Retaining Assembly Used for the Same and Silicon Wafer Flatness Correcting Method

Info

Publication number: US20090149118A1
Application number: US12/329,767
Authority: US
Inventors: Do Min Moon
Original assignee: Siltron Inc
Current assignee: SK Siltron Co Ltd
Priority date: 2005-12-20
Filing date: 2008-12-08
Publication date: 2009-06-11
Also published as: US20090142991A1; KR100841094B1; KR20070065780A; CN1986154A

Abstract

A silicon wafer grinding apparatus, a retaining assembly used for the same, and a silicon wafer flatness correcting method are provided.

More particularly, a silicon wafer grinding apparatus, a retaining assembly used for the same, and a silicon wafer flatness correcting method for correcting a wafer flatness in a final grinding process are provided.

The silicon wafer grinding apparatus includes a grinding surface plate having a grinding pad attached thereon; a grinding head arranged opposite to the grinding surface plate and rotated in the same direction as that of the grinding surface plate; a backing film attached at a lower portion of the grinding head for supporting a wafer; and a retainer ring having an inner diameter (a wafer diameter+α) greater than a diameter of the wafer by as much as α and disposed on the backing film.

By forming a diameter or physical properties of a part of the backing film of the wafer retaining assembly, the wafer flatness of the final grinding may be corrected.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. application Ser. No. 11/612,008, which claims priority to and the benefit of Korean Patent Application No. 10-2005-0126460 & 10-2006-0103968 filed in the Korean Intellectual Property Office on Dec. 20, 2005 & Oct. 25, 2006 the entire contents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field
This disclosure relates to a silicon wafer grinding apparatus, a retaining assembly used for the same, and a silicon wafer flatness correcting method.
More particularly, this disclosure relates to a silicon wafer grinding apparatus, a retaining assembly used for the same, and a silicon wafer flatness correcting method for correcting a wafer flatness in a final grinding process.
(b) Description of the Related Art
A semiconductor technology has been developed in a higher integrated process so as to reduce production costs and to improve performance. Accordingly, a silicon wafer requires a more restrictive flatness condition.
Conventionally, manufacturing processes such as lapping, etching, and single surface grinding are performed so as to manufacture a small diameter wafer. However, there is a drawback in that these manufacturing processes satisfy no restrictive flatness conditions.
In order to overcome such a drawback, a large diameter wafer manufacturing method includes a shaping process such as lapping and etching, dual-surface grinding, final grinding, and a cleaning process.
The wafer flatness has been rapidly improved by applying such new processes. However, the wafer flatness is deteriorated in the final grinding after the dual-surface grinding process.
In order to solve such a problem, the structure of a grinding apparatus used in the final grinding has been changed, or various consumables used therewith have been improved. However, sufficient flatness has not yet been obtained.
The above information disclosed in this Background section is only for enhancement of understanding of the background of this disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY OF THIS DISCLOSURE

This disclosure has been made in an effort to provide a silicon wafer grinding apparatus having advantages of overcoming a flatness deterioration of a wafer generated on finally grinding the wafer by improving a retaining assembly without changing a structure of a wafer grinding apparatus.
This disclosure has been made in an effort to provide a wafer flatness correcting method having advantages of correcting wafer flatness on the final grinding of the wafer by using a heterogeneous backing film.
This disclosure has been made in an effort to provide a retaining assembly having advantages of correcting wafer flatness on the final grinding of the wafer by using a heterogeneous backing film.
This disclosure has been made in an effort to provide a heterogeneous backing film assembly used for a retaining assembly having advantages of correcting wafer flatness on the final grinding of the wafer by using a heterogeneous backing film.
This disclosure has been made in an effort to provide a wafer having advantages of providing a flatness of about a wafer margin EE2 mm after the final grinding of the wafer.
An exemplary embodiment of this disclosure provides silicon wafer grinding apparatus.
The silicon wafer grinding apparatus includes a grinding surface plate having a grinding pad attached thereon; a grinding head arranged opposite to the grinding surface plate and rotated in the same direction as that of the grinding surface plate; a backing film attached at a lower portion of the grinding head for supporting a wafer; and a retainer ring having an inner diameter (a wafer diameter+α) greater than a diameter of the wafer by as much as α and disposed on the backing film.
When the backing film is a uniform thickness, the backing film may be formed by a relatively soft material at an edge portion near to the retainer ring.
The edge portion may have a width of about 3 to 5 mm in an inner radial direction from an inner wall of the retainer ring. The edge portion may have a width of less than about 2% of an inner diameter of the retainer ring.
When a backing film surrounded by the retainer ring may be formed of one material, the backing film may have a different thickness at a predetermined portion thereof.
When a backing film surrounded by the retainer ring may be formed of one material, an edge portion of the backing film near the retaining ring is thicker than a center portion further away from the retainer ring.
when a backing film surrounded by the retainer ring may be formed of one material, the backing film include an edge portion having a predetermined width near the retaining ring and at least one land portion having a predetermined height stepped in a radial direction from the edge portion.
The edge portion may have a width of about 3 to 5 mm in an inner radial direction from an inner wall of the retainer ring.
The edge portion may have a width of less than about 2% of an inner diameter of the retainer ring.
When a backing film surrounded by the retainer ring is formed of one material, the backing film may include at least one groove portion along a circumference direction.
The backing film may include an edge portion along a circumference direction and near the inner wall of the retaining ring, and a land portion having a predetermined height surrounded by the groove portion.
The edge portion may have a width of about 3 to 5 mm in an inner radial direction from an inner wall of the retainer ring. The edge portion has a width of less than about 2% of an inner diameter of the retainer ring.
Another embodiment of provides a wafer flatness correcting method.
The wafer flatness correcting method includes marking a center of grinding head;
attaching a first backing film to a grinding head, disposing a retainer ring having an inner diameter (a wafer diameter+α) greater than a diameter of the wafer by as much as α on the first backing film;
disposing a sample wafer in the retainer ring and performing final grinding;
measuring flatness of the finally ground sample wafer;
manufacturing a heterogeneous second backing film according to the measured wafer flatness; and
finally grinding actual wafers.
The manufacturing of a heterogeneous second backing film may include sequentially forming a part of at least one of a foaming layer, a substrate layer, and a pressure sensitive adhesive layer with different materials.
The manufacturing of a heterogeneous second backing film may include sequentially forming a part of at least one of a foaming layer, a substrate layer, and a pressure sensitive adhesive layer to have a different thickness.
The forming the secondary backing film may include removing a portion of the first backing film corresponding to a portion to correct a flatness of the wafer, aligning and attaching the center marking of the secondary backing film to the center of the first backing film.
The forming the secondary backing film may include removing or attaching at least one of the substrate layer of the first backing film and the foaming layer formed on the substrate layer.
Yet another embodiment of this disclosure provides a wafer retaining assembly used so as to correct a flatness of a wafer on finally grinding.
The wafer retaining assembly comprising a circular retainer ring having an inner diameter of the wafer diameter+α and an outer diameter and a backing film including a pressure sensitive adhesive layer attached at a lower portion of the grinding head, a substrate layer formed on the pressure sensitive adhesive layer, a foaming layer formed on the substrate layer, which may be partly attached or detached, and an alignment mark marked at a center thereof.
The backing film may further include a cutting line for detaching at least one of the substrate layer and the foaming layer along a circumference direction.
The backing film may further include a cutting line for detaching all of the substrate layer and the foaming layer along a circumference direction.
The cutting line may be formed at a predetermined interval of at least 3 mm to 5 mm from an inner wall of the retainer ring.
The cutting line may be formed at an external periphery corresponding to 40% of a radius of the backing film.
The backing film includes a groove portion along a circumference direction at a predetermined distance from the center thereof. The groove portion has a width of about 3 to 5 mm from the inner wall of the retainer ring.
At least one of the substrate layer, the foaming layer, and the pressure sensitive adhesive layer may be formed with a different material.
At least one of the substrate layer, the foaming layer, and the pressure sensitive adhesive layer may have a different thickness.
Yet another embodiment provides a wafer having a GBIR in a range of from about 0.2 to about 0.5, an SBIR of less than about 0.3, and an SFQR in a range of from about 0.13 to about 0.18 based on E.E. 2 mm after final grinding.
Yet another embodiment provides A wafer having a GBIR in a range of from about 0.2 to about 0.4, an SBIR in a range of from about 0.15 to about 0.3, and an SFQR in a range of from about 0.1 to about 0.13 based on E.E. 3 mm after final grinding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a silicon wafer grinding apparatus using a retaining assembly according to an exemplary embodiment.

FIG. 2 is a partial cross-sectional view for showing a part ‘B’ of FIG. 1 in detail.

FIG. 3A is a partial cross-sectional view for schematically showing a retaining assembly used for a silicon wafer grinding apparatus according to an exemplary embodiment.

FIG. 3B is a plane view of FIG. 3A.

FIG. 4 is a partial cross-sectional view for schematically showing a retaining assembly used for a silicon wafer grinding apparatus according to another exemplary embodiment.

FIG. 5 is a partial cross-sectional view for schematically showing a retaining assembly used for a silicon wafer grinding apparatus according to yet another exemplary embodiment.

FIG. 6A is a partial cross-sectional view for schematically showing a retaining assembly used for a silicon wafer grinding apparatus according to yet another exemplary embodiment.

FIG. 6B is a plane view of FIG. 6A.

FIG. 7A and FIG. 7B respectively illustrate a graph showing a variance of a thickness along a radial direction of a wafer before and after a convex wafer having a thicker center portion is finally polished according to an exemplary embodiment.

FIGS. 8A and 8B respectively illustrate a diagram showing a variance of a thickness along a radial direction of a wafer before and after a convex wafer having a thicker center portion is finally polished according to an exemplary embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An exemplary embodiment will hereinafter be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic perspective view of a silicon wafer grinding apparatus using a retaining assembly according to an exemplary embodiment, and FIG. 2 is a partial cross-sectional view for showing a part ‘B’ of FIG. 1 in detail.
As shown in FIG. 1 and FIG. 2, according to an exemplary embodiment, a silicon wafer grinding apparatus includes a grinding surface plate 21 on which a grinding pad 22 is attached and rotated, a grinding head 25 arranged opposite to the grinding surface plate 21 and rotated in the same direction as that of the grinding surface plate 21, and a retaining assembly 24 including a retainer ring 28 disposed at a lower portion of the grinding head 25 and for protecting a wafer from being dislodged during the grinding process, and a backing film 24 attached at one side surface of the retainer ring 28 for supporting a wafer 23.
In more detail, as shown in FIG. 2, according to an exemplary embodiment, a backing film 24 may include a foaming layer 241 for detachedly supporting a wafer thereon, a substrate layer 243 for supporting a wafer, a pressure sensitive adhesive layer 245 for attaching the foaming layer 241 and the substrate layer 243 at a lower portion of the grinding head 22, and a release sheet (not shown) that may be attached to the pressure sensitive adhesive layer 245 and be separated therefrom.
When a retainer ring 28 having an inner diameter (a wafer diameter+α) greater than a diameter of the wafer by as much as α is disposed on the backing film 24, the backing film 24 of in the inner diameter of the retainer ring 28 may include a first backing film 24 a and at least one second backing film 24 b having at least one of elasticity, elastic, durability, and thickness different from the same of the first backing film 24.
According to an exemplary embodiment, it is one example that the backing film 24 in the inner diameter of the retainer ring 28 is divided into the first backing film 24 a and the second backing film 24 b, but this is not restrictive. Accordingly, the backing film 24 may further include a third backing film, and the first backing film 24 a may be disposed at a center portion of the wafer and the second backing film 24 b may be disposed at a peripheral portion thereof.
At this time, in order to form the heterogeneous backing film 24, a part of at least one of the foaming layer 241, the substrate layer 243, and the pressure sensitive adhesive layer 245 that are sequentially formed may be differently formed by having at least one different property of matter such as elastic coefficient and durability.
In addition, in the heterogeneous backing film 24, a part of at least one of the foaming layer 241, the substrate layer 243, and the pressure sensitive adhesive layer 245 that are sequentially formed may be differently formed by having different thicknesses.

First Exemplary Embodiment

FIG. 3A is a partial cross-sectional view for schematically showing a retaining assembly used for a silicon wafer grinding apparatus according to an exemplary embodiment, and FIG. 3B is a plane view of FIG. 3A.
As shown in FIG. 3A and FIG. 3B, when a backing film 32 has a constant thickness, the center of a grinding head 25 is arrayed on the center of the backing film 32 which is attached thereon, the backing film 32 is formed by heterogeneously forming a center portion 32 a and an edge portion 32 b disposed apart from the center portion 32 a so as to polish an edge portion of the wafer within the retainer ring 28 having an inner diameter (a wafer diameter+α) that is greater than a diameter of the wafer by as much as α. At this time, the center portion 32 a and edge portion 32 b may be formed of different materials having at least one different property of matter such as elastic coefficient and durability.
Since the retainer ring 28 has an inner diameter (a wafer diameter+α) that is greater than a diameter of the wafer by as much as α, it is easy for the wafer to be attached to or detached from the retainer ring 28.
At this time, the backing film 32 may be heterogeneously formed by changing the number or size of foaming apertures at a predetermined portion of the foaming layer 241 therein.
Particularly, since the edge of the wafer is relatively more polished due to centrifugal force of the grinding head 25 at the final grinding process, and accordingly the flatness of the wafer is deteriorated, the edge portion 32 b near the retainer ring 28 (hereinafter referred to as “edge portion” because the edge portion polishes an edge portion of a wafer even though it substantially corresponds to an external periphery portion of the backing film 32) may be formed by a relatively soft material.
In addition, considering wafer flatness after the final grinding process, it is preferable that the edge portion 32 b has a width of about 3 to 5 mm (measured along a radial direction of the wafer) from an inner wall of the retainer ring 28.
That is, it is preferable that the edge portion 32 b has a width of less than about 2% (measured along a radial direction of the wafer) from an inner wall of the retainer ring 28 (e.g., since a 12 inch wafer has a diameter of 300 mm, a ratio of the edge width of 3 to 5 mm to the inner diameter 300 mm+α of the retaining ring is expressed as a percentage).
By forming the edge portion 32 b in this manner, a margin of the wafer may be increased and the edge portion after the final grinding process may have a standard flatness.

Second Exemplary Embodiment

FIG. 4 is a partial cross-sectional view for schematically showing a retaining assembly used for a silicon wafer grinding apparatus according to another exemplary embodiment.
As shown in FIG. 4, when a backing film 42 surrounded by the retainer ring 28 is formed of the same material, the backing film 42 may have a different thickness at a predetermined portion thereof.
According to an exemplary embodiment, the backing film 42 may include an edge portion 42 a near the inner wall of the retaining ring 28 and a land portion 42 b at a center portion further away from the retainer ring 28 in comparison with the edge portion 42 a.
It is preferable that the edge portion 42 a has a width of from about 3 to about 5 mm (measured along a radial direction of the wafer) from the inner wall of the retainer ring 28, and the land portion 42 b may include at least one stepped land portion having different heights in a radial direction.
That is, it is preferable that the edge portion 42 a has a width of less than about 2% (measured along a radial direction of the wafer) to an inner diameter of the retainer ring 28 considering standard deterioration of wafer flatness after the final grinding process.
In the present exemplary embodiment, the edge portion 42 a is disposed along a circumference direction at an edge portion of the backing film 42, but this is not restrictive. Accordingly, the edge portion 42 a may be disposed at a center portion of the backing film 42 and at least one portion of the backing film 42 may be formed thicker than the other portion.

Third Exemplary Embodiment

FIG. 5 is a partial cross-sectional view for schematically showing a retaining assembly used for a silicon wafer grinding apparatus according to yet another exemplary embodiment.
As shown in FIG. 5, when a backing film 52 surrounded by the retainer ring 28 is formed of one material, the backing film 52 may have at least one groove portion 52 a along a circumference direction thereof.
According to an exemplary embodiment, the backing film 52 may include a groove portion 52 a along a circumference direction and near to the inner wall of the retaining ring 28, and a land portion 52 b having a predetermined height surrounded by the groove portion 52 a.
The groove portion 52 a is entirely formed along a thickness direction of the backing film 52, but this is not restrictive. The groove portion 52 a may be formed only to the foaming layer or may be formed through the foaming layer to the substrate layer.
It is preferable that the groove portion 52 a has a width of about 3 to 5 mm (measured along a radial direction of the wafer) from the inner wall of the retainer ring.
That is, it is preferable that the groove portion 52 a has a width of less than about 2% (measured along a radial direction of the wafer) to an inner diameter of the retainer ring 28 considering a deterioration of a wafer flatness of after the final grinding process.
It is preferable that the groove portion 52 a is formed at an edge portion of the backing film 52. However, the groove portion 52 a may be formed at a center portion of the backing film 52.
Now, correcting wafer flatness using a final grinding apparatus is schematically described.
According to an exemplary embodiment, 20 numbered sample wafers are firstly prepared, grinding pads 22 are attached to a grinding plate 21, and a slurry 27 is supplied from a nozzle 26 to the grinding pad 22.
A wafer 23 is then disposed on the grinding pad 22 and the grinding plate 21 is rotated in the same direction as that of the grinding pad 22 while the wafer 23 is delicately pressed by the grinding head 25, and thus, a surface of the wafer 23 is ground.
The wafer 23 is processed by a shaping process such as lapping and etching, dual-surface grinding, final grinding, and a cleaning process.
Particularly, according to an exemplary embodiment of the present invention, before the final grinding process, the sample wafers are ground, the thickness of the ground wafers are measured, and then a portion of the wafer to be corrected (hereinafter referred to as “correctable portion” is determined.
When the wafer is cut from an ingot, the wafer generally has a convex center portion. Accordingly, the center portion thereof may be further ground using a retaining assembly shown in FIG. 5.
The retaining assembly shown in FIG. 5 may be purchased having the release sheet that is capable of being attached to or detached from a pressure sensitive adhesive layer 31 shown in FIG. 3A, FIG. 4 and FIG. 5, may be separated by the release sheet, and may be attached on a bottom surface of the grinding head 25 using the pressure sensitive adhesive layer 31.
At this time, each center of the grinding head 25 and the backing film 52 is marked and aligned, and then the retainer ring 28 having an inner diameter (a wafer diameter+α) that is greater than a diameter of the wafer by as much as α is disposed on the backing film 52. Finally, the competed retaining assembly grinds a wafer.
In this exemplary embodiment, the backing film is heterogeneously formed by having a groove portion 52 a of a width of 3 mm to 5 mm along a circumference portion from an inner wall of the retainer ring 28 as shown in FIG. 5, and the wafer is actually ground using the heterogeneous backing film formed in this manner.
Table 1 shows a total thickness variance (GBIR) for the flatness of the whole area, a site back ideal focal plane range (SBIR) for the flatness of the local area, and a reference plane-site front least square focal plane range (SFQR) for providing a reference on patterning with respect to the wafers of before/after the final grinding using a conventional single backing film and using a heterogeneous backing film according to an exemplary embodiment. At this time, the heterogeneous backing film is formed by circumferentially forming a groove portion 52 a having a width of about 3 to 5 mm (measured along a radial direction of the wafer) from the inner wall of the retainer ring.
Generally, a wafer maker has effected that the specification of the wafer margin has a 2 mm E.E. (Edge Exclusion). However, since the wafer flatness is exceeded at a periphery portion thereof, the specification of the wafer margin often exceeds the standard value at a periphery portion thereof.
In order to achieve the standard value, the wafer flatness is measured based on 2 mm E.E. or 3 mm E.E. (Edge Exclusion) using a probe of 2 mm or 3 mm diameter.
As shown in Table 1, it may be known that the GBIR has a smaller value such as 0.567, 0.440, and 0.294 as the groove portion 52 a has a smaller width, when the wafer is finally ground using the retaining assembly having a heterogeneous backing film 52, which is formed by circumferentially forming a groove portion 52 a having a width of from about 3 to about 5 mm (measured along a radial direction of the wafer) from the inner wall of the retainer ring, particularly based on the standard 2 mm E.E.
In addition, based on the standard 2 mm E.E., it may be known that the SBIR has a smaller value such as 0.331, 0.296, and 0.181, and the SFQR has a smaller value such as 0.183, 0.159, and 0.134 as the groove portion 52 a has a smaller width.
That is, according to an exemplary embodiment, after the final grinding process, a wafer may have a GBIR in a range of from about 0.2 to about 0.5, an SBIR being less than about 0.3, and an SFQR being less than about 0.18 based on the standard 2 mm E.E.
According to another exemplary embodiment of the present invention, after the final grinding process, a wafer may have a GBIR in a range of from about 0.2 to about 0.4, an SBIR ranging from about 0.15 to about 0.3, and an SFQR about 0.1 to about 0.13 based on the standard E.E. 3 mm.
In order that a client may select the retainer assembly with such a standard value, the retainer assembly may be purchased having a release sheet 11 as shown in FIG. 6A.
Meanwhile, a backing film 12 may include a secondary backing film by sequentially forming at least one of a substrate layer 123 and a foaming layer 125 on a pressure sensitive adhesive layer 121 with a different material.
In addition, the backing film 12 may include a secondary backing film by sequentially forming at least one of the substrate layer 123 and the foaming layer 125 on the pressure sensitive adhesive layer 121 to have a different thickness.
At this time, the secondary backing film 12 may be formed by removing a first backing film at a portion of the backing film corresponding to the correctable portion of the wafer, or by aligning and attaching a second backing film at a portion of the backing film corresponding to the correctable portion of the wafer.
At this time, a part of at least one of the substrate layer 123 and the foaming layer 125 sequentially formed on the pressure sensitive adhesive layer 121 may be removed.
In addition, a part of at least one of the substrate layer 123 and the foaming layer 125 sequentially formed on the pressure sensitive adhesive layer 121 may be additionally attached.
As shown in FIG. 6B, the retainer assembly may include a circular retainer ring 13 having an inner diameter of the wafer diameter+α, an outer diameter and the backing film 24 including a pressure sensitive adhesive layer 121 attached at a lower portion of the grinding head, a substrate layer 123 formed on the pressure sensitive adhesive layer 121, a foaming layer 125 formed on the substrate layer 123, which may be partly attached or detached, and an alignment mark 15 marked at a center thereof.
At this time, the backing film 12 may further include a cutting line 17 for detaching at least one of the substrate layer 123 and the foaming layer 125 along a circumference direction.
The cutting line 17 may be formed at a predetermined interval of at least 3 mm to 5 mm from an inner wall of the retainer ring 13 toward the alignment mark 15.
Particularly, the cutting line 17 may be formed at an external periphery corresponding to 40% of a radius R of the backing film.
The backing film 12 may include a groove portion along a circumference direction at a predetermined distance from the center thereof.
It is preferable that the groove portion has a width of about 3 to 5 mm (measured along a radial direction of the wafer) from the inner wall of the retainer ring.
That is, it is preferable that the groove portion has a width of less than about 2% (measured along a radial direction of the wafer) to an inner diameter of the retainer ring 28 considering a deterioration of wafer flatness after the final grinding process.
At least one of the substrate layer, the foaming layer, and the pressure sensitive adhesive layer may be formed with a different material.
In addition, at least one of the substrate layer, the foaming layer, and the pressure sensitive adhesive layer may have a different thickness.
At this time, the secondary backing film may be further formed by removing or attaching a first backing film at a portion of the backing film corresponding to the correctable portion of the wafer.
With such a structure, when the grinding head 25 applies a great pressure to the grinding plate 21 as shown in FIG. 2 when grinding, the backing film 24 and the grinding pad 22 may be compressed without deforming the grinding head 25, wafer 23, and the grinding plate 21 because of the relatively great elastic coefficient of the backing film 24.
Since the heterogeneous backing film is compressed on the bottom surface of the wafer 23, the elastic recuperative power is varied, and accordingly different grinding pressures are applied to a front surface of the wafer 23.

TABLE 1

TA	E2mm standard	E3mm standard

condition	GBIR	SBIR	SFQR	GBIR	SBIR	SFQR

Normal TA	FP	0.632	0.363	0.173	0.552	0.295	0.115
	before
	FP	0.567	0.331	0.183	0.489	0.261	0.148
	after
E3mm	FP	0.657	0.379	0.207	0.573	0.305	0.153
processing	before
TA	FP	0.440	0.296	0.159	0.365	0.218	0.124
	after
E5mm	FP	0.591	0.350	0.184	0.510	0.277	0.123
processing	before
TA	FP	0.294	0.181	0.134	0.258	0.154	0.106
	after

Hereinafter, E3 mm and E5 mm respectively mean a width of the edge portion of the backing film, FP means a final grinding, and TA means a test after.
FIG. 7A and FIG. 7B respectively illustrate graphs showing a variance of a thickness along a radial direction of a wafer before and after a convex wafer having a thicker center portion is finally polished according to an exemplary embodiment.
It will be known that when the wafer after the dual-side grinding has a convex shape being thinner at an edge portion thereof and being thicker at a center portion thereof, the flatness of the front surface may be increased because the grinding amount of the center portion of the wafer is increased finely by using a relative hard backing at the center portion thereof.
In addition, FIGS. 8A and 8B respectively shows results of an SBIR of the whole surface of a wafer based on E.E. 3 mm before and after the wafer is finally polished according to an exemplary embodiment of the present invention.
Also, in a local flatness aspect, it may be known that the flatness of the wafer edge portion is maintained to be less than about 0.1.
Such a wafer flatness correcting method may be achieved by changing at least one physical property of the constituent elements of the backing film 32 as shown in FIG. 3A and FIG. 3B and partly changing a thickness of the backing film 42 as shown in FIG. 4.
For example, when a wafer 23 has a concave shape having a thicker edge portion and a thinner center portion after grinding both sides of the wafer 23, the backing film may use a hard backing material at the edge portion thereof, and accordingly it may increase a grinding amount at the edge portion of the wafer, thereby improving flatness of the entire surface of the wafer.
According to an exemplary embodiment, a silicon wafer retaining assembly may correct grinding non-uniformity as well as a thickness deviation of a wafer 23.
The wafer may be largely warped due to a remaining stress after the grinding and a film stress generated because silicon dioxide film is deposited on the back surface of an epi wafer.
In this case, since the grinding is performed while the wafer 23 is factitiously spread by factitious grinding pressure, the grinding may be non-uniform. However, according to an exemplary embodiment the non-uniform grinding may be compensated by configuring a heterogeneous backing film 24.
By forming a diameter or physical properties of a part of the backing film of the wafer retaining assembly, the wafer flatness of the final grinding may be corrected.
While practical exemplary embodiments are disclosed above, it is to be understood that this disclosure is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1-20. (canceled)

21. A wafer retaining assembly comprising: a circular retainer ring having an inner diameter greater than a wafer diameter, the retainer ring also having an outer diameter and a backing film including a pressure sensitive adhesive layer attached at a lower portion of the grinding head, a substrate layer formed on the pressure sensitive adhesive layer, a foaming layer formed on the substrate layer, which may be partly attached or detached, and an alignment mark marked at a center thereof.

22. The wafer retaining assembly of claim 21, wherein the backing film further includes a cutting line for detaching at least one of the substrate layer and the foaming layer along a circumference direction.

23. The wafer retaining assembly of claim 22, wherein the backing film further includes a cutting line for detaching all of the substrate layer and the foaming layer along a circumference direction.

24. The wafer retaining assembly of claim 22, wherein the cutting line is formed at a predetermined interval of at least about 3 mm to about 5 mm from an inner wall of the retainer ring.

25. The wafer retaining assembly of claim 22, wherein the cutting line is formed at an external periphery corresponding to about 40% of a radius of the backing film.

26. The wafer retaining assembly of claim 21, wherein the backing film includes a groove portion along a circumference direction at a predetermined distance from the center thereof.

27. The wafer retaining assembly of claim 21, wherein the groove portion has a width of from about 3 to about 5 mm from the inner wall of the retainer ring.

28. The wafer retaining assembly of claim 27, wherein the groove portion has a width of less than about 2% to an inner diameter of the retainer ring.

29. The wafer retaining assembly of claim 21, wherein at least one of the substrate layer, the foaming layer, and the pressure sensitive adhesive layer is formed with a different material than the other of the substrate layer, the foaming layer, and the pressure sensitive adhesive layer.

30. The wafer retaining assembly of claim 21, wherein at least one of the substrate layer, the foaming layer, and the pressure sensitive adhesive layer has a different thickness than the other of the substrate layer, the foaming layer, and the pressure sensitive adhesive layer.