US20070167110A1 - Multi-zone carrier head for chemical mechanical polishing and cmp method thereof - Google Patents

Abstract

A multi-zone carrier head includes a housing; a retaining ring secured to a lower edge of the housing; a backing plate having a plurality of non-concentric pressure zones defined by a plurality of isolated apertures on the backing plate; wherein the backing plate has a wafer side and a non-wafer side, the wafer side facing a backside of a wafer during a CMP operation; and a plurality of pneumatic bladder for independently controlling pressure exerted in the respective non-concentric pressure zones on the backside of the wafer during the CMP operation.

Description

BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates generally to chemical mechanical polishing of substrates and, more particularly, to a multi-zone carrier head for chemical mechanical polishing.
• 2. Description of the Prior Art
• In the process of fabricating integrated circuits, it is essential to form multi-level material layers and structures on a wafer. However, the prior formations often leave the top surface topography of an in-process wafer highly irregular. Such irregularities cause problems when forming the next layer over a previously formed integrated circuit structure. For example, when printing a photolithographic pattern having small geometries over previously formed layers, a very shallow depth of focus is required. Therefore, there is a need to periodically planarize the wafer surface.
• One technique for planarizing the surface of a wafer is chemical mechanical polishing (CMP). In CMP processing, a wafer is placed face down on a rotating platen. The wafer, held in place by a carrier or polishing head, independently rotates about its own axis on the platen. Typically, the head is a floating polishing head with a flexible membrane. On the surface of the platen is a polishing pad over which there is dispensed a layer of polishing slurry. The slurry chemistry is essential to proper polishing. Typically, it consists of a colloidal solution of silica particles in a carrier solution.
• Conventional CMP suffers from some problems that need to be accounted for during the process integration. When polishing a wafer that has step features, only the top of the features touch the polishing pad, concentrating the pressure on these contact points. This increases the polishing rate above that of a blanket wafer. In addition, it causes non-uniformity in the removal rate across patterns of different densities due to variations in the pressure distribution across the pattern. This pattern density effect on removal rate can cause problems if there are both dense pattern and very sparse pattern on the wafer surface.
SUMMARY OF THE INVENTION
• In one aspect, the invention is directed to a multi-zone carrier head for chemical mechanical polishing (CMP). The multi-zone carrier head includes a housing; a retaining ring secured to a lower edge of the housing; a backing plate having a plurality of non-concentric pressure zones defined by a plurality of isolated apertures on the backing plate; wherein the backing plate has a wafer side and a non-wafer side, the wafer side facing a backside of a wafer during a CMP operation; and a plurality of pneumatic bladder for independently controlling pressure exerted in the respective non-concentric pressure zones on the backside of the wafer during the CMP operation.
• In another aspect, the invention is directed to a method for polishing a substrate or wafer. The method includes the following steps:
• (a) mounting a substrate into a carrier head, the carrier head comprising a pneumatic means controlled by a control unit for independently controlling pressure exerted in respective non-concentric pressure zones on backside of the substrate;
• (b) rotating the carrier head and a polishing pad on which the substrate is resting;
• (c) providing a down force on the substrate; and
• (d) polishing a material layer of the substrate away.
• These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• The accompany drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:
• FIG. 1 is a diagram showing a table based CMP tool;
• FIG. 2 is a schematic, cross-sectional diagram illustrating the structure of a carrier head in accordance with one preferred embodiment of this invention;
• FIG. 3 illustrates a plane view of the backing plate according to one preferred embodiment;
• FIG. 4 illustrates a plane view of the backing plate according to another preferred embodiment; and
• FIG. 5 is a schematic, cross-sectional diagram illustrating the structure of a carrier head in accordance with another preferred embodiment of this invention.
DETAILED DESCRIPTION
• FIG. 1 is a diagram showing a table basedCMP tool50. The table basedCMP tool50 includes acarrier head52, which holds awafer54, and is attached to a translation arm. In addition, the table basedCMP tool50 includes apolishing pad56 that is disposed above a polishing table58, which is often referred to as a polishing platen.
• In operation, thecarrier head52 applies downward force to thewafer54, which contacts thepolishing pad56. Reactive force is provided by the polishing table58, which resists the downward force applied by thecarrier head52. Apolishing pad56 is used in conjunction with slurry to polish thewafer54. Typically, thepolishing pad56 comprises foamed polyurethane or a sheet of polyurethane having a grooved surface. Thepolishing pad56 is wetted with polishing slurry having both an abrasive and other polishing chemicals. In addition, the polishing table58 is rotated about itscentral axis60, and thecarrier head52 is rotated about itscentral axis62.
• FIG. 2 is a schematic, cross-sectional diagram illustrating the structure of a carrier head in accordance with one preferred embodiment of this invention. As shown inFIG. 2, thecarrier head52 generally includes ahousing150, aretaining ring152, a disk-shaped backing plate154 and abacking film156.
• Thehousing150 can be connected to a drive shaft (not shown) to rotate therewith during polishing about an axis ofrotation62, which is substantially perpendicular to the surface of apolishing pad56. Thehousing150 may be generally circular in shape to correspond to the circular configuration of the wafer to be polished. Passages (not shown) may extend through thehousing150 for pneumatic control of thecarrier head52. O-ring may be used to form airtight seals between the passages through thehousing150 and passages through the drive shaft.
• Thewafer54 is held in place on thecarrier head52 by theretaining ring152. Theretaining ring152 may be a generally annular ring secured along a lower, outer edge of thehousing150. The retaining ring110 defines a pocket area for accommodating thewafer54. An inner surface of theretaining ring152 engages thewafer54 to prevent it from escaping from beneath thecarrier head52.
• Thebacking film156 is attached to thebacking plate154 between thebacking plate154 and thewafer54. Thebacking film156 cushions thewafer54 during the polishing and compensates for slight flatness variations in thewafer54 orbacking plate154. Thebacking film156 may be made of polymer materials and attached to thebacking plate154 with a pressure sensitive adhesive, but not limited thereto.
• In addition, thecarrier head52 may includes adiaphragm seal158 that is generally an annular ring of a flexible material. An outer edge of thediaphragm seal158 is clamped between thehousing150 and the retainingring152, and the inner edge of thediaphragm seal158 is secured to thebacking plate154 by, for example, a clamp ring (not shown). Thediaphragm seal158 may be formed of rubber, such as neoprene, an elastomeric-coated fabric, such as NYLON™ or NOMEX™, plastic, or a composite material, such as fiberglass.
• Thebacking plate154 may be a flat stainless steel disk slightly larger than thewafer54. Thebacking plate154 presses against the backside of thewafer54 and transfers the polishing force to the wafer during a CMP operation.
• Thebacking plate154 has a plurality of non-concentric pressure zones defined by an isolatedcentral aperture162 that is formed in a central location of thebacking plate154 and a plurality of isolatedperipheral apertures164 surrounding thecentral aperture162.
• Thebacking plate154 has a wafer side and a non-wafer side, the wafer side facing a backside of thewafer54 during a CMP operation. Preferably, the number of the non-concentric pressure zones is equal to or larger than five.
• FIG. 3 illustrates a plane view of thebacking plate154 according to one preferred embodiment.FIG. 4 illustrates a plane view of thebacking plate154 according to another preferred embodiment. InFIG. 3, there are six non-concentric pressure zones distributed on thebacking plate154, wherein thecentral aperture162 is surrounded by theperipheral apertures164. Thecentral aperture162 is circular, while theperipheral apertures164 are sector shaped.
• InFIG. 4, there are nine non-concentric pressure zones distributed on thebacking plate154, wherein thecentral aperture162 is square or rectangular. However, it is understood that the number of the non-concentric pressure zones provided by the backing plate may exceed nine and the arrangement and distribution of the non-concentric pressure zones depicted inFIGS. 3 and 4 are exemplary.
• Referring back toFIG. 2, thecarrier head52 further comprises a plurality ofpneumatic bladders182 and184 that are provided within correspondingcentral aperture162 andperipheral apertures164 for independently controlling the down force within each of the non-concentric pressure zones on the back side of thewafer54. The inflation or deflation is accomplished by using the respective passages that connects with air supply or pumps.
• According to another preferred embodiment of this invention, referring toFIG. 5, thecarrier head52 further comprises pressure-sensingelements192 and194 provided in respective non-concentric pressure zones. The pressure-sensing element192 is installed in thecentral aperture162, while the pressure-sensingelements194 are installed in respectiveperipheral apertures164.
• The pressure-sensingelements192 and194 may be piezo-materials, piezo-crystals, piezo sensors or piezoelectric ceramic sensors. For example, the pressure-sensingelements192 and194 may comprise BaTiO₃, AIN, ZnO, lead zirconium titanate (PbZrTi) or PZT ceramic, tantalum oxide (Ta₂O₅), barium strontium tantanite (BST) or the like.
• It is one salient feature of the present invention that the pressure-sensingelements192 and194 can detect the topography of the wafer surface during a CMP operation and transmit feedback signals to a control unit of the CMP tool. According to the feedback signals, the control unit, for example, a computer, which is capable of controlling the air supply or pumps, can alter, in real time, the pressure exerted in each non-concentric pressure zones by means of thepneumatic bladders182 and184, thereby improving uniformity and better planarization.
• Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

Claims (14)

1. A multi-zone carrier head for chemical mechanical polishing (CMP), comprising:

a housing;

a retaining ring secured to a lower edge of the housing;

a backing plate having a plurality of non-concentric pressure zones defined by a plurality of isolated apertures on the backing plate; wherein the backing plate has a wafer side and a non-wafer side, the wafer side facing a backside of a wafer during a CMP operation;

a pneumatic means for independently controlling pressure exerted in the respective non-concentric pressure zones on the backside of the wafer during the CMP operation; and

a pressure-sensing element disposed under the pneumatic means in the respective non-concentric pressure zones.

2. The multi-zone carrier head for CMP according toclaim 1, further comprising a backing film attached to the wafer side of the backing plate, wherein the backing film is disposed between the backing plate and the backside of the wafer during the CMP operation.

3. The multi-zone carrier head for CMP according toclaim 1, wherein plurality of isolated apertures on the backing plate include a central aperture and peripheral apertures surrounding the central aperture.

4. The multi-zone carrier head for CMP according toclaim 1, wherein the multi-zone carrier head further comprises a diaphragm seal.

5. The multi-zone carrier head for CMP according toclaim 4, wherein the diaphragm seal is an annular ring of a flexible material.

6. (canceled)

7. The multi-zone carrier head for CMP according toclaim 1, wherein the pressure-sensing element includes piezo-materials, piezo-crystals, piezo sensors or piezoelectric ceramic sensors.

8. The multi-zone carrier head for CMP according toclaim 1, wherein the pressure-sensing element is selected from the group consisting of BaTiO3, AIN, ZnO, lead zirconium titanate, PZT ceramic (PbZrTi), tantalum oxide (Ta205), and barium strontium tantanite (BST).

9. The multi-zone carrier head for CMP according toclaim 1, wherein the pressure-sensing element detects topography of the wafer during the CMP operation and transmits feedback signals to a control unit.

10. A method for polishing a substrate, comprising:

mounting a substrate into a carrier head, the carrier head comprising a pneumatic means controlled by a control unit for independently controlling pressure exerted in respective non-concentric pressure zones on backside of the substrate and a pressure-sensing element under the pneumatic means in the respective non-concentric pressure zones;

respectively rotating the carrier head and a polishing pad on which the substrate is resting;

providing a down force on the substrate; and

polishing a material layer of the substrate away.

11. (canceled)

12. The method ofclaim 10, wherein the pressure-sensing element includes piezo-materials, piezo-crystals, piezo sensors or piezoelectric ceramic sensors.

13. The method ofclaim 10, wherein the pressure-sensing element is selected from the group consisting of BaTiO3, AIN, ZnO, lead zirconium titanate, PZT ceramic (PbZrTi), tantalum oxide (Ta205), and barium strontium tantanite (BST).

14. The method ofclaim 10, wherein the pressure-sensing element detects topography of the substrate during a CMP operation and transmits feedback signals to a control unit.

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