EP1349704B1

EP1349704B1 - Polishing platen with pressurized membrane

Info

Publication number: EP1349704B1
Application number: EP01992420A
Authority: EP
Inventors: Rod Kistler; John Boyd; Alek Owczarz
Original assignee: Lam Research Corp
Current assignee: Lam Research Corp
Priority date: 2000-12-21
Filing date: 2001-12-21
Publication date: 2004-08-11
Anticipated expiration: 2021-12-21
Also published as: CN1481295A; AU2002232889A1; CN1209228C; EP1349704A1; US20020081945A1

Description

1. Field of the Invention

This invention relates to a system as per the preamble of claim 1. An example of such a system is disclosed by EP 920 956 A

2. Description of the Related Art

In the fabrication of semiconductor devices, there is a need to perform Chemical Mechanical Polishing (CMP) operations, including polishing, buffing and wafer cleaning. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. Patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material increases. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to the higher variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then metal CMP operations are performed to remove excess metallization.

In the prior art, CMP systems typically implement belt, orbital, or brush stations in which belts, pads, or brushes are used to scrub, buff, and polish one or both sides of a wafer. Slurry is used to facilitate and enhance the CMP operation. Slurry is most usually introduced onto a moving preparation surface, e.g., belt, pad, brush, and the like, and distributed over the preparation surface as well as the surface of the semiconductor wafer being buffed, polished, or otherwise prepared by the CMP process. The distribution is generally accomplished by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the friction created between the semiconductor wafer and the preparation surface.

Figure 1 illustrates an exemplary prior art CMP system 10. The CMP system 10 in Figure 1 is a belt-type system, so designated because the preparation surface is an endless belt 18 mounted on two drums 24 which drive the belt 18 in a rotational motion as indicated by belt rotation directional arrows 26. A wafer 12 is mounted on a wafer head 14, which is rotated in direction 16. The rotating wafer 12 is then applied against the rotating belt 18 with a force F to accomplish a CMP process. Some CMP processes require significant force F to be applied. A platen 22 is provided to stabilize the belt 18 and to provide a solid surface onto which to apply the wafer 12. Slurry 28 composing of an aqueous solution such as NH₄OH or DI containing dispersed abrasive particles is introduced upstream of the wafer 12. The process of scrubbing, buffing and polishing of the surface of the wafer is achieved by using an endless polishing pad glued to belt 18. Typically, the polishing pad is composed of porous or fibrous materials and lacks fix abrasives.

Figure 2 is a detailed view of a conventional wafer head and platen configuration 30. The wafer head and platen configuration 30 includes the wafer head 14 and the platen 22 positioned below the wafer head 14. The wafer head 14 includes a fixed retaining ring 32 that holds the wafer 12 in position below the wafer head 14. Between the wafer head 14 and the platen 22 is the polishing pad and belt 18. The polishing platen 22 is closely spaced from a polishing pad or belt 18 with a very thin air space, referred to as an "air bearing", being defined between the platen 22 and the polishing pad 18. The air bearing between the platen 22 and the pad 18 has been conventionally used in an attempt to create a uniform polishing of the surface.

To maintain the air bearing, air source holes generally are formed in the platen 22 and are arranged in concentric ring patterns from the center of the platen 22 to the outer edge of the platen 22. Each ring establishes an air delivery zone where air from an air source is directed through the holes during polishing, thus establishing the air bearing. Air is exhausted past the platen edge.

With multiple air delivery zones, the air distribution profile of the air bearing can be varied radially as necessary to achieve optimal polishing by vary the polishing rate in each zone. Unfortunately, the distribution profiles of the zones are not completely independent of each other. This complicates establishing different distribution profiles for different zones.

Moreover, the air bearing is very sensitive to conditions. For example, the pressure of the air bearing varies with the gap between the pad 18 and the platen 22. Thus, if the pad 18 is pushed toward the platen 22 in one area, the pressure of all areas of the air bearing are affected, thus adding unwanted complexity to the CMP process.

In view of the foregoing, there is a need for a method that establishes greater independence of the air distribution profiles, zone to zone, thereby facilitating establishing a polishing rate in each zone independently of the other zones and, hence, improving manufacturing flexibility and functionality.

SUMMARY OF THE INVENTION

Broadly speaking, the present invention fills these needs by providing improved performance in a CMP process using a system having the features of claim 1.

Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

Figure 1 illustrates an exemplary prior art CMP system;

Figure 2 is a detailed view of a conventional wafer head and platen configuration;

Figure 3 is a diagram showing a platen configuration, in accordance with an embodiment of the present invention;

Figure 4 is a detailed diagram showing a platen configuration, in accordance with an embodiment of the present invention;

Figure 5 is a diagram showing a platen configuration having varied annular bladders, in accordance with an embodiment of the present invention;

Figure 6A is a top view of an annular bladder configuration, in accordance with an embodiment of the present invention;

Figure 6B is a top view showing an annular bladder configuration, in accordance with an embodiment of the present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An invention is disclosed for improved performance in a CMP process using pressurized membranes and piezoelectric elements as replacements for a platen air bearing. In one embodiment, a pressurized membrane is provided, which provides zonal control during the CMP process via concentric bladders. In a further embodiment, piezoelectric elements are provided atop a platen, which provide zonal control during the CMP process. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order not to unnecessarily obscure the present invention.

Figures 1-2 have been described in terms of the prior art. Figure 3 is a diagram showing a platen configuration 300, in accordance with an embodiment of the present invention. The platen configuration 300 includes a wafer head 302 having a retaining ring 304 and a wafer 306 positioned below the wafer head 302. The platen configuration 300 also includes a platen 308 disposed below a polishing belt 310. The platen 308 includes a pressurized membrane 312 pressurized via annular bladders 314.

During operation the platen 308 is placed against the polishing pad or belt 310 that polishes the surface of the wafer 306. To promote polishing uniformity, each bladder 314 may be individually pressurized via an air source. Advantageously, the annular bladders 314 improve performance in the CMP process by providing increased zonal control to the pressurized membrane 312. Unlike a conventional air bearing, the pressurized membrane 312 of the embodiments of the present invention greatly reduces the amount of air needed during the CMP process.

Moreover, a CMP process using the pressurized membrane 312 of the present invention is not as sensitive to conditions as conventional CMP processes utilizing air bearings. Unlike air bearings, the pressure of the pressurized membrane 312 of the present invention does not experience as great a variance as experienced by air bearings when the gap between the polishing pad 310 and the platen 308 varies. Thus, if the polishing pad 310 is pushed toward the platen 308 in one area, the pressure in other areas of the pressurized membrane 312 are not as affected as other areas would be when utilizing an air bearing because the bladders are decoupled from each other.

Figure 4 is a detailed diagram showing a platen configuration 400, in accordance with an embodiment of the present invention. The platen configuration 400 shows a polishing belt 310 positioned above a platen 308 having a pressurized membrane 312 pressurized by annular bladders 314. As shown in Figure 4, each annular bladder 314 comprises a thin tubular material 402. In one embodiment, the tubular material 402 of each annular bladder 314 is pressurized via air. However, it should be noted that the tubular material 402 can be pressurized utilizing any other means capable of pressurizing an annular bladder 314, such as a fluid, as will be apparent to those skilled in the art.

The pressurized membrane 312 preferably comprises a smooth, flexible material. Suitable materials include; polyurethane, silicon, thin metals (e.g., stainless steel), poly ether ether ketone (PEEK), and Teflon. As previously mentioned, the annular bladders 314 provide increased zonal control during a CMP process. To further increase zonal control, the size of the annular bladders 314 within the pressurized membrane 312 can be varied, as described in greater detail subsequently.

Figure 5 is a diagram showing a platen configuration 500 having varied annular bladders, in accordance with an embodiment of the present invention. The platen configuration 500 includes a platen 308 having a pressurized membrane 312 pressurized via annular bladders 314. As shown in Figure 5, the platen configuration 500 includes annular bladders 314 having varying sizes.

More specifically, the annular bladders 314 decrease in size as the annular bladders 314 approach the edge of the platen 308. Generally, during a CMP process, more difficulty occurs within about 10-15 mm of the wafer edge. For this reason, one embodiment of the present invention increases resolution near the wafer edge by decreasing the size of the annular bladders 314 near the edge of the platen 308. Similarly, since the center of the wafer typically requires less resolution, the central annular bladders 314 often are larger than those at the edge of the platen 308.

Figure 6A is a top view of an annular bladder configuration 600a in accordance with an embodiment of the present invention. The annular bladder configuration 600a includes the annular bladder configuration 600a forms a complete circle about the center of the platen. In this manner each annular bladder 314a can be individually pressurized to provide zonal control during the CMP process. To further increase zonal control during the CMP process, the length of each annular bladder can be reduced, as discussed next with reference to Figure 6B.

Figure 6B is a top view showing an annular bladder configuration 600b in accordance with an embodiment of the present invention. The annular bladder configuration 600b includes concentric annular bladders 314b. Unlike the embodiment of Figure 6A, each concentric annular bladder 314b of the annular bladder configuration 600b does not form a complete circle about the center of the platen. Each concentric annular bladder 314b of the annular bladder configuration 600b varies in size depending on a particular annular bladder's 314 proximity to the edge of the platen.

As mentioned above, during a CMP process, more difficulty generally occurs within about 10-15 mm of the wafer edge. For this reason, one embodiment of the present invention increases resolution near the wafer edge by decreasing the size of the annular bladders 314b near the edge of the platen. Similarly, since the center of the wafer typically requires less resolution, the central annular bladders 314b often are larger than those at the edge of the platen.

Advantageously, embodiments of the present invention improve performance in CMP applications by providing increased zonal control via a membrane pressurized using internal annular bladders.

Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.

Claims

A system for improving performance in chemical mechanical polishing (CMP) applications, comprising:

a wafer head (302) capable of carrying a wafer (306),

a polishing belt (310) disposed below the wafer head;

characterized by

a platen having a membrane (312) positioned below the polishing belt (310), the platen further including annular bladders (314) disposed below the membrane (312), wherein the annular bladders are capable of exerting force on the membrane (312).
A system as claimed in claim 1, wherein the membrane (312) of the platen comprises as soft and flexible material.
A system as claimed in claim 1 or 2, wherein the annular bladders (314) are of varying dimensions.
A system as claimed in claim 3, wherein annular bladders (314) near an edge of the platen are smaller than annular bladders near the centre of the platen.
A system as claimed in any preceding claim, wherein each annular bladde (314) can be individually pressurized to exert force against the membrane (312).
A system as claimed in claim 5, wherein the force exerted against the membrane is transferred to the polishing belt (310) to provide zonal control during a CMP process.
A system as claimed in claim 5 or 6, wherein each annular bladder (314) is pressurized utilizing a gas.
A system as claimed in claim 5 or 6, wherein each annular bladder (314) is pressurized utilizing a liquid.