Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means
Reexamination Certificate
2000-04-28
2001-07-24
Smith, Matthew (Department: 2825)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With microwave gas energizing means
C451S056000, C451S059000, C451S060000, C451S303000, C451S307000, C451S091000, C438S692000
Reexamination Certificate
active
06264789
ABSTRACT:
This invention relates to a system, including a method and an apparatus, for dispensing polishing liquid during chemical mechanical polishing (CMP) of a semiconductor wafer, e.g., of silicon, and more particularly, to such a system for feeding a polishing liquid to the wafer surface periphery in the vicinity of a polishing surface during relative periodic movement between such surfaces, especially while also adjusting the temperature of the polishing liquid in the vicinity of the wafer.
As used herein, “semiconductor wafer” means any microelectronic device, substrate, chip or the like, e.g., of silicon, used to provide an integrated circuit or other related circuitry structure subject to chemical mechanical polishing procedures such as for achieving planarization over an entire surface of the wafer.
BACKGROUND OF THE INVENTION
In fabricating microelectronic semiconductor devices and the like on a wafer substrate or chip, e.g., of silicon, to form an integrated circuit (IC), etc., various metal layers and insulation layers are deposited in selective sequence. To maximize integration of device components in the available substrate area to fit more components in the same area, increased IC miniaturization is utilized. Reduced pitch dimensions are needed for denser packing of components per present day very large scale integration (VLSI), e.g., at sub-micron (below 1 micron, i.e., 1,000 nanometer or 10,000 angstrom) dimensions.
One type of wet chemical process used in the IC fabrication of a semiconductor wafer concerns the chemical mechanical polishing (CMP) of a surface of the wafer against a polishing pad during relative periodic movement therebetween, such as with a caustic slurry containing finely divided abrasive particles, e.g., colloidal silica in an aqueous potassium hydroxide (KOH) solution, as the polishing liquid. This removes, i.e., by chemical etching and mechanical abrasion, a thin layer of material, e.g., of 1 micron or less thickness, so as to planarize a top surface of the wafer. Close control of the slurry flow rate, temperature and pH are necessary to attain in a reproducible manner a uniform removal rate per the CMP operation.
The conventional CMP process involves introducing the slurry from a stationary overlying tube dropwise onto a polishing pad of a rotating table (platen) which rotates about a stationary platen axis and against which the wafer, which is carried by a retaining ring, makes frictional contact while the wafer and ring rotate and oscillate relative to the platen. The wafer is positioned in a medial aperture of the ring such that the ring also makes frictional contact with the polishing pad. As the position of the wafer relative to the platen varies during wafer rotation and oscillation, the slurry dispensing tube is always spaced a minimum clearance distance from the wafer.
Consequently, different portions of the wafer necessarily encounter dispensed slurry droplets having different thermal histories. This depends on the continuously varying distance between the relative position of rotation and oscillation of the wafer, and in particular of its leading and trailing edges during oscillation, and the position of the centrifugally outwardly travelling slurry droplets dispensed onto the rotating platen from the stationary tube. As a result, the operating temperature at the local polishing site of the wafer is non-uniform, leading to non-uniformity of the CMP operation.
Also, some of the slurry on the polishing pad is pushed off the platen by the retaining ring which surrounds the wafer, inasmuch as the ring is also in frictional contact with the pad and in some cases is pressed under positive mechanical pressure thereagainst. This loss of slurry constitutes wastage which increases operating costs. By its inherent wafer-captively surrounding arrangement, the retaining ring also impedes flow of slurry to the central area of the wafer surface being polished. This causes poor center-to-edge uniformity, further detracting from the uniformity of the CMP operation.
Where the process requires heating of the slurry, such as in the case of polysilicon CMP, then a separate heating module, which occupies expensive floor space (module footprint), must be provided to supply heated slurry to the tube for dispensing.
The above prior art drawbacks cause adverse variation in the local removal rate of wafer material from different parts of the wafer due to variation in the amount and temperature of the slurry coming into contact with the wafer surface being polished. This diminishes the degree of within-wafer uniformity. Also, slurry wastage increases its consumption rate and cost.
It is desirable to have a system, including a method and an apparatus, permitting CMP operations to be performed on a semiconductor wafer under reproducible uniform conditions of polishing liquid temperature, polishing liquid dispensing flow rate, and supplying of polishing liquid locally to all portions of the wafer regardless of its relative position of movement with respect to the platen polishing pad, and optionally also under reproducible uniform conditions of selective temperature adjustment of the polishing liquid in the vicinity of the wafer.
SUMMARY OF THE INVENTION
The foregoing drawbacks are obviated in accordance with the present invention by providing a system, including a method and an apparatus, which permits chemical mechanical polishing (CMP) operations to be performed on a semiconductor wafer, e.g., of silicon, under reproducible uniform conditions of polishing liquid temperature, polishing liquid dispensing flow rate, and supplying of polishing liquid locally to all portions of the wafer regardless of its relative position of movement with respect to the platen polishing pad, and optionally also under reproducible uniform conditions of selective temperature adjustment of the polishing liquid in the vicinity of the wafer.
The system of the invention minimizes variation in the local removal rate of material from different parts of the wafer being polished since the CMP operation is carried out so as to limit variation in the amount and temperature of the polishing liquid coming into contact with the wafer surface being polished. This improves, i.e., increases, the degree of within-wafer uniformity attainable. Polishing liquid wastage is avoided, so that its consumption rate and cost are reduced to a minimum.
Furthermore, the need for a stand-alone polishing liquid heating module is eliminated, thereby conserving floor space.
According to a first aspect of the invention, a method is provided for CMP of a surface of a semiconductor wafer having a surface periphery. The method comprises periodically relatively moving a substantially flat polishing surface and the wafer with respect to each other while maintaining the wafer surface in frictional contact with the polishing surface, and dispensing a chemical mechanical polishing liquid to the wafer surface periphery in the vicinity of the polishing surface. The dispensing is effected at a plurality of perimetrically spaced apart points maintained in fixed relation to the wafer surface periphery during the relative periodic movement.
The polishing liquid may be, e.g., a caustic aqueous slurry containing finely divided abrasive particles, such as an aqueous potassium hydroxide (KOH) slurry containing colloidal silica.
Typically, the polishing liquid is dispensed at a temperature of about 15-50° C. and the wafer surface is maintained in frictional contact with the polishing surface under a mechanical pressure of about 2-8 pounds per square inch (psi) periodic movement. More specifically, the adjusting comprises heating the polishing liquid to a selective elevated temperature, such as about 25-50° C., in the vicinity of the wafer surface and in fixed relation thereto during the relative periodic movement, especially while maintaining the wafer surface in frictional contact with the polishing surface under a mechanical pressure of about 2-8 psi.
In particular, the polishing surface is in the form of a rotating platen which is rota
Jamin Fen Fen
Pandey Sumit
Braden Stanton C.
Infineon Technologies Corp.
Smith Matthew
Yevsikov V.
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