Temprature compensated chemical mechanical polishing apparatus and method

Abstract

A chemical mechanical polishing (CMP) system (22) having a radiant heating apparatus (30) for direct radiant heating of the polishing surface (26) of the polishing pad (16). Radiant energy (28) is impinged onto a selected area of the polishing surface to provide temperature compensation of the material removal rate across the surface (24) of the wafer (14). The radiant energy may be in the form of infrared radiation, a laser beam or microwave energy. The power level, angle of impingement, duration of exposure and footprint of the radiant energy may be controlled to achieve a desired temperature gradient on the polishing surface. The temperature of the polishing surface may further be regulated by impinging a temperature conditioning gas (32) onto the polishing surface.

Description

FIELD OF THE INVENTION

[0001] This invention relates generally to the field of semiconductor device fabrication, and more particularly, to the field of chemical mechanical polishing of semiconductor wafers.

BACKGROUND OF THE INVENTION

[0002] The fabrication of microelectronics devices involves the deposition and removal of multiple layers of material on a semiconductor substrate to form active semiconductor devices and circuits. Such devices utilize multiple layers of metal and dielectric materials that can selectively connect or isolate device elements within a layer and between layers. Integrated circuits using up to six levels of interconnects have been reported and even more complex circuits are expected in the future. Device geometries have gone from 0.50 micron to 0.12 micron and will soon be 0.08 micron. Multi-levels of metallization are required in such devices. With these reductions in device geometry, each inter-metal level must be planarized before forming a subsequent level. The generally accepted process for creating sufficiently planar surfaces is chemical mechanical polishing (CMP). CMP may be used to remove high topographic variations and to remove defects, scratches or embedded particles from the surface of a semiconductor wafer.

[0003] The CMP process generally involves rubbing a surface of a semiconductor wafer against a polishing pad under controlled pressure, temperature and rotational speed in the presence of a chemical slurry. An abrasive material is introduced between the wafer and the polishing pad, either as particles affixed to the polishing pad itself or in fluid suspension in the chemical slurry. The chemical and abrasive combination functions to to remove a portion of the surface of the wafer in a polishing action. The slurry movement assures temperature control and facilitates the movement of the polishing debris away from the wafer.

[0004] As may be seen in FIG. 1, a chemical mechanical polishing system 10 may include a carrier 12 for holding and moving a semiconductor wafer 14 against a polishing pad 16 supported on a rotatable platen 18. Slurry 20 is used to provide the desired chemical interaction and abrasion when the wafer 14 is pressed and rotated against the polishing pad 16. The rate of material removal from the wafer 14 will depend upon many variables, including the amount of force F exerted between the wafer 14 and the polishing pad 16, the speeds of rotation R.sub.1 of the carrier and R.sub.2 of the platen, the transverse location of the carrier 12 relative to the axis of rotation of the platen 18, the chemical composition of the slurry 20, the temperature, and the composition and history of use of the polishing pad 16. Numerous configurations of CMP machines are known and are available in the industry. One manufacturer of such CMP machines is Applied Materials, Inc. of Santa Clara, Calif. (www.appliedmaterials.com) One manufacturer of polishing pads is Rodel, Inc. of Phoenix, Ariz. (www.rodel.com)

[0005] A known difficulty with CMP operations is that the rate of material removal may be uneven across the surface of the wafer 14. U.S. Pat. No. 5,873,769 issued to Chiou, et al., describes a method and apparatus for achieving a uniform removal rate across the surface of a wafer. Chiou describes dividing both the platen and the carrier into concentric circular segments, and controlling the temperature of the various segments to adjust the rate of removal of material across the surface of the wafer. Chiou describes the use of multiple electric heating elements for controlling the temperature of the respective multiple circular segments. Alternatively, Chiou describes the use of multiple tubes in the platen and carrier for delivering fluid that is heated or cooled to a desired temperature. Such a system requires a large amount of energy to heat the platen and the carrier. Furthermore, because of the thermal inertia of these structures, the system of Chiou may not respond as quickly as desired to a required change in temperature. The segmented and heated platen and carrier are more expensive to manufacture and maintain than non-segmented, non-heated components. Finally, the definition of the number and location of the segments is fixed and can not be changed without a corresponding equipment redesign.

[0006] In a further embodiment, Chiou describes the use of a polishing pad with multiple concentric grooves and the supply of polishing slurry to the various grooves at various different temperatures to effect the desired temperature compensation. This embodiment suffers from many of the same limitations as the segmented carrier/platen embodiment. A special pad design is required, and the definition of the number and location of the grooves can not be easily changed. The abrasive slurry supply system is necessarily more complicated and expensive to manufacture, to operate and maintain than would be the traditional single supply system. The transient response time of this embodiment is also limited by whatever system is used to heat the slurry and by the transit time of the slurry from the point of heating to the polishing pad grooves. Furthermore, this design would be of no use in a system that does not utilize a slurry for abrasion or material removal. Accordingly, an improved apparatus and method is needed for controlling the material removal rate across the surface of a wafer during a chemical mechanical polishing operation.

SUMMARY OF THE INVENTION

[0007] A device for polishing a wafer is described herein as including: a polishing pad having a polishing surface; a wafer carrier adapted to urge a surface of a wafer against the polishing surface; and a radiant heating apparatus impinging radiant energy onto the polishing surface remote from the surface of the wafer. The radiant heating apparatus may be a source of infrared radiation, a laser, or a source of microwave energy. The radiant heating apparatus may be disposed in a predetermined position with respect to the polishing surface to establish a predetermined radiant energy footprint on the polishing surface.

[0008] In a further embodiment, a device for polishing a wafer is described as including: a polishing pad having a polishing surface; a wafer carrier adapted to urge a surface of a wafer against the polishing surface; and a means for applying heat energy directly to the polishing surface remote from the surface of the wafer.

[0009] Further, a device for polishing a wafer is described as including: a polishing pad having a polishing surface; a wafer carrier adapted to urge a surface of a wafer against the polishing surface; and a flow of a temperature conditioning gas directed onto the polishing surface. The flow of temperature conditioning gas may be provided at a temperature greater than or less than a temperature of the polishing surface. The device may further include a radiant heating apparatus impinging radiant energy onto the polishing surface remote from the surface of the wafer.

[0010] A method of polishing a wafer is described herein as including: providing a polishing pad having a polishing surface; urging a wafer surface against the polishing surface while providing relative motion there between; and impinging the polishing surface with radiant energy at a location remote from the wafer surface to regulate a polishing surface temperature. The intensity of the radiant energy may be varied during the step of impinging. The radiant energy may be applied prior to and/or during the step of urging. The radiant energy may be infrared radiation, laser energy, and/or microwave energy. A predetermined radiant energy footprint may be projected onto the polishing surface to effect a desired temperature gradient.

[0011] An alternate method of polishing a wafer is described as including the steps of: providing a polishing pad having a polishing surface; urging a wafer surface against the polishing surface while providing relative motion there between; and impinging the polishing surface with at least one of radiant energy and a temperature conditioning gas remote from the wafer surface to regulate a polishing surface temperature.

BRIEF DESCRIPTION OF THE INVENTION

[0012] The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings. Like numerals are used to designate similar components in multiple figures.

[0013] FIG. 1 is a schematic illustration of a prior art chemical mechanical polishing system.

[0014] FIG. 2 is a schematic illustration of a chemical mechanical polishing system including a radiant heating apparatus impinging radiant energy onto the polishing surface of the polishing pad and a conditioned gas supply impinging a conditioned gas upon the polishing surface.

DETAILED DESCRIPTION OF THE INVENTION

[0015] FIG. 2 is a schematic illustration of a chemical mechanical polishing apparatus 22 providing localized temperature compensation for controlling the material removal rate across the surface of a wafer being polished. The polishing apparatus 22 contains many components that are similar to those of the prior art apparatus 10 illustrated in FIG. 1. A polishing pad 16 is disposed over a rotatable platen 18. A wafer 14 having a surface to be polished 24 is urged against a polishing surface 26 of the polishing pad 16 by a rotatable carrier 12. Chemical slurry 20 containing abrasive particles is delivered to the polishing surface 26 to provide the desired polishing action. The term polishing surface as used herein includes not only a top-most layer of the polishing pad 16 but also any portion of the slurry 20 entrained thereon.

[0016] The temperature of at least a portion of the polishing surface 26 may be increased by the direct impingement of radiant energy 28 onto the polishing surface 26. The term direct (or directly) as used herein refers to the application of heat energy to the top polishing surface 26 without applying the heat energy through the thickness of the polishing pad 16, as is done in the prior art systems. The polishing surface 26 may be heated in an area remote from the area of contact with the wafer surface 24. By controlling the area exposed to the radiant energy 28, one may induce a change in the temperature profile of the polishing surface 26 across the wafer surface 24 as the heated portion of the polishing surface 26 is rotated to be in contact with the wafer 14. A change in the temperature of the polishing pad material will alter the hardness of the pad material, thereby changing the visco-elastic characteristics and wafer material removal rate of the pad in that localized area. Every visco-elastic material has a stress-strain characteristic that is dependent upon the temperature of the material. The stress-strain characteristic defines the rate of deformation (deformation per unit time) upon the relaxation of the applied stress resulting from the down force during the polishing operation. The temperature of the pad material directly impacts this relaxation. Pad deformation is, in turn, related to the amount of reaction force that is exerted onto the abrasive material in the slurry and upon the raised areas of the surface being polished. The reaction force determines the mechanical component of the CMP process, thereby impacting the material removal rate. Thus, the application of radiant energy 28 to the polishing surface 26 provides a mechanism for temperature compensation of the wafer material removal rate. For most pad/slurry applications, an increase in the temperature is expected to increase the material removal rate during a CMP operation. However, one skilled in the art will appreciate that the response of the material removal rate to a change in temperature must be evaluated for each particular pad/slurry application.

[0017] The radiant energy 28 is provided by a radiant heating apparatus 30. The radiant heating apparatus 30 is located proximate the polishing pad opposed the platen 18, thereby avoiding the need for conductive heating of the polishing surface 26. By applying the energy 28 directly onto the polishing surface 26, it is possible to affect the material removal rate without heating of the entire platen 18 and without heating the entire thickness of the polishing pad 16 to the desired temperature. Accordingly, a relatively low amount of energy 28 is needed to achieve a desired temperature rise. It may be desired to achieve a temperature rise of up to 90.degree. C. or preferably in the range of 20-60.degree. C. above the ambient temperature.

[0018] The proximity of the radiant heating apparatus 30 to the polishing surface 26 may vary depending upon the particular design of the CMP apparatus 22. Furthermore, the proximity of the radiant heating apparatus 30 may vary depending upon the type and power level of radiant energy 28 utilized. The radiant heating apparatus 30 is located at any distance from the polishing surface 26 appropriate for exposing the surface to a desired energy flux. In one embodiment, the means for providing the radiant heating may be a source of infrared radiation, such as a heat lamp located directly above the polishing surface 26. In a further embodiment, a laser may be used to provide the radiant energy 28, with the delivery of the laser energy being through a conventional mirror system or through an optical fiber. Due to the congruence of a laser beam, it may be possible to locate the source of the laser energy at a greater distance away from the polishing pad 16 than would be possible with an infrared radiation source. Alternatively, a microwave radiation source may be used at any desired frequency or combination of frequencies. One or more such sources of radiant energy may be used singly or in combination.

[0019] The radiant heating apparatus 30 may be placed in a predetermined position with respect to the polishing surface 26 in order to impinge energy onto a predetermined energy footprint on the polishing surface 26. A change in energy intensity across the footprint may be achieved by locating the radiant heating apparatus 30 at an appropriate angle with respect to a plane of the polishing surface 26. Such an energy gradient will generate a corresponding change in the temperature rise generated in the polishing surface 26 across the footprint. Furthermore, a lens or other beam-spreading device may be used to accomplish a desired energy gradient across the footprint. In one embodiment, only an edge portion of the polishing surface 26 is heated. In other embodiments, various other portions of the polishing surface 26 may be heated. More than one portion of the polishing surface 26 may be heated to the same or differing temperatures.

[0020] The operation of chemical mechanical polishing apparatus 22 provides a high degree of flexibility for temperature compensation of the CMP process. In one embodiment, radiant heating apparatus 30 may be operated for a predetermined period of time at a predetermined power level as the platen 18 is rotated prior to the wafer 14 being brought into contact with the polishing pad 16. This would allow a selected area of the polishing surface 26 exposed to the energy footprint to be brought to a desired temperature prior to initiating the polishing action. The flux of energy 28 may then be terminated and the radiant heating apparatus 30 moved away from the platen 18 in order to protect it from possible exposure to splashing of the slurry 20. Alternatively, the radiant energy 28 may be initiated concurrently with the polishing activity, and/or the energy 28 may continue to impinge upon the polishing surface 26 during the polishing process.

[0021] It is also possible to change the power level of the radiant heating apparatus 30 at various times before and throughout the polishing process. For example, a first power level may be used to pre-heat the polishing surface 26 prior to the initiation of the flow of slurry 20, then a second power level may be used to maintain a desired temperature after the slurry 20 begins to flow. Changes in temperature may be quickly achieved due to the low thermal inertia of the polishing surface 26, since there is no need to change the temperature of the platen 18 or the entire thickness of the polishing pad 16.

[0022] The location of the impingement of energy 28 may be changed as a CMP process progresses, or it may be changed in response to a changed polishing requirement. The operation of the radiant heating apparatus 30 may be controlled manually or by an automatic control system responsive to a measurement of the temperature of the polishing surface 26 and/or to any other appropriate control parameter. Such control parameters may be determined by developing correlations between measurable parameters such as removal rate, removal uniformity or slurry composition, and they may be used as a tool for generating an appropriate control response. For example, removal rates may be measured for sequential polishing experiments. The effect of temperature can be correlated to the amount of material removed and the removal rate during such sequential polishing operations. A feedback loop incorporating such correlations may be used as a calibration tool for temperature control.

[0023] The polishing surface temperature may also be regulated by impingement of a temperature conditioning gas 32 onto polishing surface 26. The gas 32 may be air or other gas compatible with the polishing operation, and it may be supplied from a gas conditioning apparatus 34 such as a heater, air conditioner, or combined heating-ventilating-air conditioning (HVAC) system. The gas 32 may be supplied from conditioning apparatus 34 at a temperature greater than or less than the temperature of the polishing surface 26. Accordingly, temperature conditioning gas 32 serves to add or to remove heat energy directly to/from the surface 26 of pad 16 in order to raise or lower the temperature of at least a portion of the polishing surface 26 to a predetermined temperature. Temperature conditioning gas 32 may be used together with or separately from radiant energy 28 to effect a desired temperature control scheme.

[0024] While the preferred embodiments of the present invention have been shown and describe herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.

Claims

I claim as my invention:

1. A device for polishing a wafer, the device comprising: a polishing pad having a polishing surface; a wafer carrier adapted to urge a surface of a wafer against the polishing surface; and a radiant heating apparatus positionable to provide radiant energy onto the polishing surface remote from the surface of the wafer.

2. The device of claim 1, wherein the radiant heating apparatus comprises a source of infrared radiation.

3. The device of claim 1, wherein the radiant heating apparatus comprises a laser.

4. The device of claim 1, wherein the radiant heating apparatus comprises a source of microwave energy.

5. The device of claim 1, wherein the radiant heating apparatus is disposed in a predetermined position with respect to the polishing surface to establish a predetermined radiant energy footprint on the polishing surface.

6. A device for polishing a wafer, the device comprising: a polishing pad having a polishing surface; a wafer carrier adapted to urge a surface of a wafer against the polishing surface; and a means for applying heat energy directly to the polishing surface from a source remote from the surface of the wafer.

7. The device of claim 6, wherein the means for applying heat energy further comprises a flow of a temperature conditioning gas directed onto the polishing surface.

8. The device of claim 7, wherein the flow of temperature conditioning gas is provided at a temperature greater than a temperature of the polishing surface.

9. The device of claim 7, wherein the flow of temperature conditioning gas is provided at a temperature less than a temperature of the polishing surface.

10. The device of claim 7, further comprising a radiant heating apparatus impinging radiant energy onto the polishing surface remote from the surface of the wafer.

11. A method of polishing a wafer, the method comprising: providing a polishing pad having a polishing surface; urging a wafer surface against the polishing surface while providing relative motion there between; and impinging the polishing surface with radiant energy at a location remote from the wafer surface to regulate a polishing surface temperature.

12. The method of claim 11, further comprising varying an intensity of the radiant energy during the step of impinging.

13. The method of claim 11, further comprising impinging the at least a portion of the polishing surface with radiant energy prior to the step of urging.

14. The method of claim 11, further comprising impinging the at least a portion of the polishing surface with radiant energy during the step of urging.

15. The method of claim 11, wherein the step of impinging further comprises exposing the at least a portion of the polishing surface to infrared radiation.

16. The method of claim 11, wherein the step of impinging further comprises exposing the at least a portion of the polishing surface to laser energy.

17. The method of claim 11, wherein the step of impinging further comprises exposing the at least a portion of the polishing surface to microwave energy.

18. The method of claim 11, further comprising disposing a source of radiant energy at a predetermined position in relation to the polishing surface in order to establish a predetermined radiant energy footprint on the polishing surface.

19. A method of polishing a wafer, the method comprising: providing a polishing pad having a polishing surface; urging a wafer surface against the polishing surface while providing relative motion there between; and impinging the polishing surface with at least one of radiant energy and a temperature conditioning gas remote from the wafer surface to regulate a polishing surface temperature.

20. The method of claim 19, further comprising impinging only an edge portion of the polishing surface with the at least one of radiant energy and a temperature conditioning gas.