Patent Grant
11541506
The present disclosure relates to a reliable Chemical Mechanical Polishing (CMP) head used in polishing a wafer. In particular, the present disclosure relates to a CMP head with improved vacuum sealing.
As critical dimension CD continues to shrink, planarity of a wafer surface becomes more and more important. CMP is employed to provide a planar surface on a wafer during semiconductor processing. A CMP system includes a CMP head which holds a wafer which is to be polished by a polishing pad disposed on a rotatable platen. Vacuum pressure is employed to pick up the wafer and hold it in position on a carrier head for polishing.
We have observed that existing CMP polishing heads may exhibit leakage in the vacuum pressure with use. Since the pressure holding the wafer in place is quite low, it is difficult to identify when vacuum leakage occurs. For example, with high pressure, the sound of vacuum leakage can be heard. However, at low pressure, vacuum or pressure leakage is virtually silent and undetectable. Further, the leakage usually occurs and remains within the CMP polishing head. Such leakages are often undetected by the electronic pressure transducers which can only monitor leakages that escape out of the polishing head. Pressure leakage can lead to non-uniformity in the polishing process, negatively affecting the planarity of the wafer surface. In addition, leakage in vacuum or pressure can cause wafer slippage from the CMP head during processing or shifting of the wafer position during loading or unloading, which can damage the wafer.
Accordingly, there is a need to provide a CMP head with improved sealing, which reduces vacuum pressure leakage.
Embodiments of the present disclosure generally relate to CMP polishing head which includes a seal to improve sealing, thereby reducing vacuum pressure leakage. In one embodiment, a method of processing a wafer on which a plurality of devices is formed includes loading the wafer onto a polishing head assembly of a CMP tool for polishing the wafer. The polishing head assembly includes a wafer carrier unit on which the wafer is loaded, and the wafer carrier unit includes a support plate having a first and second major support plate surfaces and a side surface. The second major support plate surface serves as a surface which supports the wafer while the side surface includes a seal region surrounding the support plate. The wafer carrier unit further includes a seal disposed on the seal region, a flexible support membrane which encases the support plate and covers the second major support plate surface while extending below the support plate. The seal is configured to improve sealing of the wafer carrier unit to reduce vacuum pressure leakage. The method continues with polishing the wafer by the CMP tool and unloading the wafer from the CMP tool. The seal which is disposed on the seal region of the support plate improves vacuum pressure sealing of the wafer carrier unit to reduce damaging the wafer during loading, polishing, and unloading.
In another embodiment, a device includes a polishing head assembly of a CMP tool which includes a wafer carrier unit on which a wafer is loaded for polishing and unloaded after polishing. The wafer carrier unit includes a support plate having a first and second major support plate surfaces and a side surface. The second major support plate surface serves as a surface which supports the wafer while the side surface includes a seal region surrounding the support plate. The wafer carrier further includes a seal disposed on the seal region and a flexible support membrane encasing the support plate. The flexible support membrane covers the second major support plate surface and extends below the support plate. The seal is configured to improve sealing of the wafer carrier unit to reduce vacuum pressure leakage.
In other embodiment, a device includes a wafer carrier unit of a CMP tool which includes a support plate having a first and second major support plate surfaces and a side surface. The second major support plate surface serves as a surface which supports the wafer while the side surface includes a seal region surrounding the support plate and a clamp region disposed below the seal region distal from the second major support plate surface. The wafer carrier unit further includes a seal disposed on the seal region, a flexible support membrane encasing the support plate to cover the second major support plate surface and extend below the support plate and a membrane clamp which clamps the flexible support membrane to the clamp region of the support plate. The seal is configured to improve sealing of the wafer carrier unit to reduce vacuum pressure leakage.
These and other advantages and features of the embodiments herein disclosed, will become apparent through reference to the following description and the accompanying drawings. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations.
In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily drawn to scale, emphasis is instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:
In operation, the polishing head assembly picks up a wafer for polishing. For example, an inactive surface of the wafer is mounted onto the polishing head assembly by, for example, vacuum pressure. The platen and head assembly are rotating, for example, in a clockwise direction and the slurry dispenser dispenses slurry onto the pad. The head assembly presses the active surface of the wafer onto the polishing pad with the slurry to polish the active surface of the wafer. The head assembly includes pressure controls for controlling the downward pressure of the wafer against the pad. The pressure can be controlled locally to ensure planarity of the polishing process.
The CMP polishing head module includes a housing 205. The housing is generally circular in shape and may include a cavity. For example, the housing may include housing sidewall and housing bottom which define the housing cavity. The housing includes various inlets for pneumatically controlling the polishing head module. The housing can be coupled to a drive shaft to rotate the polishing head module during polishing.
A rolling diaphragm 234 is attached to the housing. The rolling diaphragm is a ring-shaped diaphragm and is formed of a flexible sealing material, such as silicone. Other types of flexible sealing materials may be used. In one embodiment, an inner edge of the rolling diaphragm is attached to the housing sidewall by, for example, an inner ring clamp 235.
The module includes a base 230. The base is a ring-shaped base and is formed of a rigid material. For example, the base may be formed of aluminum, steel or other rigid materials. An outer edge of the rolling diaphragm is attached to the base. For example, the outer edge of the rolling diaphragm is attached to a circumference of a first major surface of the base by an outer clamp ring 210. The rolling diaphragm serves to seal the space between the housing and the base, defining a loading chamber 250. A loading chamber control inlet 212 provides fluid communication to the loading chamber by an external load chamber control pump, which controls the pressure in the loading chamber and thereby controls the load applied to the base.
The module also includes a flexure plate 242. The flexure plate secures the base to the housing. As shown, the plate of the flexure plate is securely mounted on a second surface of the base while a rod portion is fixed to the housing. Rotating the housing causes the plate base to rotate as well. The base together with the outer clamp ring and the flexure plate form the lower assembly of the CMP polishing head module.
A wafer carrier unit 255 is attached to the second major base surface. The wafer carrier unit includes a support plate 260. The support plate, in one embodiment, is a perforated plate which includes openings extending through first and second major support plate surfaces. A flexible membrane 270 encases the support plate. The flexible membrane, for example, may be a silicone membrane. Other types of flexible membranes may also be useful. As shown, the flexible membrane covers the second support plate surface and extends below the support plate. The portion below the support plate extends outwardly from the support plate, forming a membrane extended portion. In one embodiment, the flexible membrane is fixed to the support plate by a membrane clamp ring 272. The membrane extended portion is mounted to the circumference of the second major base surface by a retainer ring 220. The wafer carrier unit, which includes the support plate, the flexible membrane and the retainer ring, forms the upper assembly of the CMP polishing head module. The space between the second major base surface and the first major support plate surface defines a pressurizable chamber 240. As for the space between the second major support plate surface and the inner surface of the flexible membrane, it defines a wafer pressure chamber 246. The wafer pressure chamber and the pressurizable chamber are coupled via the openings in the support plate.
A pressurization chamber control inlet 216 is in fluid communication with an external pump, such as a pressurization chamber control pump. The pressurization chamber control pump controls the pressure in the pressurizable and wafer pressure chambers. For example, the pump controls the pressure to either cause the flexible membrane to press the wafer against the pad during polishing or act as a vacuum to pick up wafer for transfer.
The loading chamber includes a bladder membrane 237 attached to the second major base surface to form a bladder 236. The bladder membrane, for example, may be an elastic and flexible membrane. Attaching the bladder membrane to the base may be achieved using a clamp or clamp ring. The bladder is in fluid communication with a bladder control inlet 214, which is coupled to an external bladder control pump. The control pump includes air pressure regulator and valves which control the bladder to provide refined control of the pressure onto the support structure.
The loading chamber includes a wafer sensor 252. The wafer sensor includes a plunger which is in contact with an inner tube configured to facilitate fluid communication between the bladder and the bladder control inlet. The plunger extends from the loading chamber to the wafer pressure chamber and serves to detect the presence of a wafer on the wafer carrier unit. For example, when a wafer is transferred to the carrier unit, pressure exerted on the wafer pressure chamber presses on the plunger which in turn exerts on the inner tube and changes the pressure of the bladder chamber. The wafer sensor detects the presence of a wafer on the wafer carrier unit during the process of loading or before and after the process of polishing.
In one embodiment, the side of the support plate includes a seal 262 to improve sealing of the wafer pressure chamber. The seal, in one embodiment, is a liner film which is disposed on the side of the support plate. In one embodiment, the liner film is disposed on the side of the support plate above where the clamp ring attaches the membrane to the support plate. The liner film, for example, conforms to the profile of the support plate. For example, the liner film may have discontinuities, such as in slots for aligning or accommodating the flexible membrane.
In one embodiment, the liner film, for example, is an adhesive tape with sealing features. For example, the liner film is formed of PU material. The liner film can be configured to be disposed on the side of the support plate by an adhesive backing. The adhesive backing is disposed on one side of the liner film. In one embodiment, the glue tape can be used as the adhesive backing. The liner film has a thickness which is sufficient to improve sealing of the wafer pressure chamber. For example, the thickness of the liner film may be about 0.55 mm to 0.65 mm. The glue tape may have a thickness of about 0.231 mm to 0.239 mm.
It is understood that the thickness should be sufficient to improve sealing of the wafer pressure chamber without negatively affecting the fitting of the flexible membrane over the support plate. As for the width, it should have been configured to accommodate the side of the support plate without hindering the attachment of the flexible membrane to the support plate. For example, the width of the liner film may be about 5 mm to 7 mm. The length of the liner film may be about 622 mm to 628 mm.
The seal improves sealing of the wafer pressure chamber, reducing vacuum leakage. Leakage of pressure from the wafer pressure chamber can cause reliability issues, such as wafer slippage during dechucking stage as well as wafer loading issues due to membrane being out of position.
As shown, the support plate includes a seal 262 which is disposed on the sidewall thereof. In one embodiment the seal is disposed between a second major support surface and a clamp portion 366 of the support plate. The portion in which the seal is disposed may be referred to as the seal portion of the support plate. The seal conforms to the profile or contour of the seal portion of the support plate. For example, the seal may include discontinuities, such as flexible membrane slots to which the membrane is aligned.
The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments, therefore, are to be considered in all respects illustrative rather than limiting the invention described herein. Scope of the invention is thus indicated by the appended claims, rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.
| Number | Name | Date | Kind |
|---|---|---|---|
| 6132298 | Zuniga | Oct 2000 | A |
| 6422927 | Zuniga | Jul 2002 | B1 |
| 6602114 | Wang | Aug 2003 | B1 |
| 6755726 | Chen | Jun 2004 | B2 |
| 7029383 | Lee | Apr 2006 | B2 |
| 10672631 | Mao | Jun 2020 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| 20210094146 A1 | Apr 2021 | US |
