MULTI-ZONE CARRIER HEAD FOR CHEMICAL MECHANICAL POLISHING AND CMP METHOD THEREOF

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 based CMP tool 50. The table based CMP tool 50 includes a carrier head 52, which holds a wafer 54, and is attached to a translation arm. In addition, the table based CMP tool 50 includes a polishing pad 56 that is disposed above a polishing table 58, which is often referred to as a polishing platen.

In operation, the carrier head 52 applies downward force to the wafer 54, which contacts the polishing pad 56. Reactive force is provided by the polishing table 58, which resists the downward force applied by the carrier head 52. A polishing pad 56 is used in conjunction with slurry to polish the wafer 54. Typically, the polishing pad 56 comprises foamed polyurethane or a sheet of polyurethane having a grooved surface. The polishing pad 56 is wetted with polishing slurry having both an abrasive and other polishing chemicals. In addition, the polishing table 58 is rotated about its central axis 60, and the carrier head 52 is rotated about its central axis 62.

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 in FIG. 2, the carrier head 52 generally includes a housing 150, a retaining ring 152, a disk-shaped backing plate 154 and a backing film 156.

The housing 150 can be connected to a drive shaft (not shown) to rotate therewith during polishing about an axis of rotation 62, which is substantially perpendicular to the surface of a polishing pad 56. The housing 150 may be generally circular in shape to correspond to the circular configuration of the wafer to be polished. Passages (not shown) may extend through the housing 150 for pneumatic control of the carrier head 52. O-ring may be used to form airtight seals between the passages through the housing 150 and passages through the drive shaft.

The wafer 54 is held in place on the carrier head 52 by the retaining ring 152. The retaining ring 152 may be a generally annular ring secured along a lower, outer edge of the housing 150. The retaining ring 110 defines a pocket area for accommodating the wafer 54. An inner surface of the retaining ring 152 engages the wafer 54 to prevent it from escaping from beneath the carrier head 52.

The backing film 156 is attached to the backing plate 154 between the backing plate 154 and the wafer 54. The backing film 156 cushions the wafer 54 during the polishing and compensates for slight flatness variations in the wafer 54 or backing plate 154. The backing film 156 may be made of polymer materials and attached to the backing plate 154 with a pressure sensitive adhesive, but not limited thereto.

In addition, the carrier head 52 may includes a diaphragm seal 158 that is generally an annular ring of a flexible material. An outer edge of the diaphragm seal 158 is clamped between the housing 150 and the retaining ring 152, and the inner edge of the diaphragm seal 158 is secured to the backing plate 154 by, for example, a clamp ring (not shown). The diaphragm seal 158 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.

The backing plate 154 may be a flat stainless steel disk slightly larger than the wafer 54. The backing plate 154 presses against the backside of the wafer 54 and transfers the polishing force to the wafer during a CMP operation.

The backing plate 154 has a plurality of non-concentric pressure zones defined by an isolated central aperture 162 that is formed in a central location of the backing plate 154 and a plurality of isolated peripheral apertures 164 surrounding the central aperture 162.

The backing plate 154 has a wafer side and a non-wafer side, the wafer side facing a backside of the wafer 54 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 the backing plate 154 according to one preferred embodiment. FIG. 4 illustrates a plane view of the backing plate 154 according to another preferred embodiment. In FIG. 3, there are six non-concentric pressure zones distributed on the backing plate 154, wherein the central aperture 162 is surrounded by the peripheral apertures 164. The central aperture 162 is circular, while the peripheral apertures 164 are sector shaped.

In FIG. 4, there are nine non-concentric pressure zones distributed on the backing plate 154, wherein the central aperture 162 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 in FIGS. 3 and 4 are exemplary.

Referring back to FIG. 2, the carrier head 52 further comprises a plurality of pneumatic bladders 182 and 184 that are provided within corresponding central aperture 162 and peripheral apertures 164 for independently controlling the down force within each of the non-concentric pressure zones on the back side of the wafer 54. 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 to FIG. 5, the carrier head 52 further comprises pressure-sensing elements 192 and 194 provided in respective non-concentric pressure zones. The pressure-sensing element 192 is installed in the central aperture 162, while the pressure-sensing elements 194 are installed in respective peripheral apertures 164.

The pressure-sensing elements 192 and 194 may be piezo-materials, piezo-crystals, piezo sensors or piezoelectric ceramic sensors. For example, the pressure-sensing elements 192 and 194 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-sensing elements 192 and 194 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 the pneumatic bladders 182 and 184, 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

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 to claim 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 to claim 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 to claim 1, wherein the multi-zone carrier head further comprises a diaphragm seal.

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

6. (canceled)

7. The multi-zone carrier head for CMP according to claim 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 to claim 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 to claim 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 of claim 10, wherein the pressure-sensing element includes piezo-materials, piezo-crystals, piezo sensors or piezoelectric ceramic sensors.

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