CA2548083A1 - Process and apparatus to continuously form a uniform sheet for use as a semiconductor polishing pad - Google Patents

Abstract

A process and apparatus are disclosed for the continuous manufacture of a polyurethane sheet to be used as polishing pad for chemical-mechanical polishing. The process uses urethane pre-polymers and fillers/additives fed from a tank (10) which is mixed with a curing agent stored in a nitrogen blanked tank (20) inside a dynamic mixer (30). The reacting composition (32) is fed to a feed end of a double steel belt press (40) which is heated and compressed therein. A continuous sheet exits that the belt press (40) and is cut to length by a roller blade cutter (62). Cut sheets (32B) are then stacked (70) and post cured in an oven (80).

Description

PROCESS AND APPARATUS TO CONTINUOUSLY FORM
A UNIFORM SHEET FOR USE
AS A SEMICONDUCTOR POLISHING PAD
Cross Reference to Related Applications The present application claims the benefit of the filing date of U.S.
Provisional Application Ser. No. 60/527,507, filed December 5, 2003, the teachings of which are incorporated herein by reference.
l0 Field of the Invention The present invention relates to the field of making polishing pads used in polishing and planarization, and especially in chemical-mechanical planarization (CMP) of electronic devices such as integrated circuits, semiconductors, hard disks, magnetic recording heads and silicon wafers, etc., and more specifically to a continuous process for producing a highly is efficient polishing pad of uniform thickness.
Bacl~round of the Invention For many years, precision optics, quartz crystals, ceramics, metallographic alloys, silicon wafers, hard disks and integrated circuits, etc. have been polished by 2o chemical-mechanical means. More recently, this technique has been applied as a means of planarizing intermetal dielectric layers of silicon dioxide and for removing portions of conductive layers within integrated circuit devices as they are fabricated on various substrates.
For example, a conformal layer of silicon dioxide may cover a metal interconnect such that the upper surface of the layer is characterized by a series of non-planar steps corresponding in 25 height and width to the underlying metal interconnects. The non-planar topography of the upper surface is then flattened or planarized by means of chemical mechanical planarization (CMP) enabling subsequent layers of dielectric and interconnecting wires to be added.
The rapid advances in semiconductor technology has seen the advent of very large scale integration (VLSI) and ultra large scale integration (ULSI) circuits resulting in the packing of 3o very many more devices in smaller areas in a semiconductor substrate. The greater device densities combined with multiple layers of interconnect circuitry require greater degrees of topographic planarity to maintain the depth of focus of the photo-lithographic processes in the manufacture of advance integrated circuits. Moreover, copper, because of its low resistance, is increasingly being used as interconnects. Conventionally, etching techniques are used to 35 planarize conductive (metals) and insulator surfaces. However, certain metals, desirable for their conductive properties when used as interconnects (e.g. Au, Ag, and Cu) are not readily amenable to etching due to the rapid build up of complex xxide by-products, therefore chemical-mechanical polishing (CMP) is employed to remove these by-products from the polished surface.
s Typically, the various metal interconnects are formed through lithographic or damascene processes. For example, in a lithographic process, a first blanket metal layer is deposited on a first insulating layer, following which electrical lines are formed by subtractive etching through a first mask. A second layer is placed over the first metalized layer, and holes are patterned into the second insulating layer using a second mask. Metal columns or plugs are 1o formed by filling the holes with metal. A second blanket metal layer is formed over the second insulating layer, the plugs electrically connecting the first and second metal layers. The second metal layer is masked and etched to form a second set of electrical lines.
This process is repeated as required to generate the desired device. The damascene technique is described in Untied Stated Patent No. 4,789,648, to Chow, et al.
15 Presently, VLSI uses aluminum for the wiring and tungsten for the plugs because of their susceptibility to etching. However, the resistively of copper is superior to either aluminum or tungsten, making its use desirable, however copper does not have desirable properties with respect to etching.
Variations in the height of the upper surface of the intermetal dielectric layer have 2o several undesirable characteristics. The depth of focus of subsequent photolithographic processing steps may be degraded by non-planar dielectric surfaces. Loss of the depth of focus lowers the resolution at which lines may be printed. Moreover, where the step height is large, the coverage of a second layer over the dielectric layer may be incomplete, leading to open circuits.
2s In view of these problems, methods have been evolved to planarize the upper surface of the metal and dielectric layers. One such technique is chemical-mechanical planarization or polishing (CMP) using an abrasive polishing agent worked by a rotating pad. A
chemical-mechanical polishing method is described in United States Patent No.
4,944,836, to Beyer, et al. Conventional polishing pads are made of a relatively soft and flexible material, 3o such as non-woven fibers interconnected together by a relatively small amount of polyurethane adhesive binder, or may comprise laminated layers with variations of physical properties throughout the thickness of the pad. Multilayer pads generally have a flexible top polishing layer backed by a layer of stiffer material.
Polishing pads may also be made of a uniform material such as a polyurethane

2

3 PCT/US2004/039322 composition which is typically formed by placing reactive precursors in a closed mold and allowing the precursors to react and cure to form the pad material.
Subsequently, the pad material may be die-cut to size and shape and the top surface conditioned to form the polishing pad. Alternatively, the reactive precursors may be placed in a cylindrical container to form a s log or loaf from which slices may be cut that may be subsequently used as a polishing pad. The formed polishing pads may also be further modified by annealing, pressing, embossing, casting, sintering or photolithographic processes.
The aforementioned processes are typically batch processes where one pad or sheet of material is produced in step function followed by another pad. This method usually results in t0 pad to pad or sheet to sheet variability of both physico-chemical and/or morphological properties and dimensions. Variability in these properties and/or dimensions of the polishing pads leads to non-uniformity and defects in polishing, and CMP of electronic devices in particular.
Some processes for producing polishing pads have been disclosed in the art.
United is States Patent Nos. 6,126,532; 6,117,000 and 6,062,968, all assigned to Cabot Corporation, disclose pad manufacture using a belt line sintering method. The patents define the thermoplastic sintering method as one "that applies minimal or no pressure beyond atmospheric pressure to achieve the desired pore size, porosity and density and thickness of the substrate". Reference is made therein to United States Patent No. 3,835,212, assigned to 2o Congoleum Industries, Inc. which discloses the use of an endless belt, preheating of the belt, depositing thermoplastic chips, compacting the chips on the belt and heating the chips with a heater above the belt as well as a heater positioned below the belt. This is followed by compressing the chips through a nip roller to form a sheet, heating the sheet, passing it through a calendar, and then "burnishing" the sheet via a nip roller and applying a fluid cooling spray 25 and stripping.
United States Patent Application 09/995,025, filed November 27, 2001, is entitled "Polishing Pad Comprising Particles With A Solid Core And Polymeric Shell" and relates to a pad which is described as having a solid core encapsulated by a polymeric shell wherein the two materials are different. The solid core is said to be an abrasive material. The 3o application refers to a closed-mold sintering technique as well as sintering via a continuous process.
United States Patent No. 6,428,586, assigned to Rodel, is entitled "Method of Manufacturing A Polymer Or Polymer Composite Polishing Pad". It is directed at the manufacture of a polishing pad for polishing semiconductor substrates, and relies upon "transporting a continuous material forming a transported backing layer to successive manufacturing stations...supplying a fluid phase polymer composition onto the transported backing layer...shaping the polymer...and curing in a curing oven".
United States Application No. 09/766,155, also assigned to Rodel, is entitled "Printing Of Polishing Pad". The application states that "a pad manufacturing process is needed that forms a pad having a uniform surface, and in particular, a continuous process is needed that forms a sheet having a uniform surface". The application goes to offer a solution to this challenge and emphasizes the use of "flexible base sheet" that is continuously printed upon by passing between a cylinder (containing a pattern for printing on the pad) and a roller.
to Each of these references disclose a rather complicated process lacking the control of critical process parameters to ensure optimal uniformity of product. What is therefore needed is a process for providing polishing pads which may be used for chemical-mechanical polishing which are manufactured on a continuous basis which through process control provides a pad having a uniform surface, uniform thickness and highly efficient polishing is characteristics.
Summary of the Invention The present invention relates to a continuous process for making polishing pads, which are particularly useful for chemical-mechanical planarization (CMP). The process of this 20 invention comprises a two step approach which utilizes a series of networked process control and feedback loops to ensure uniformity in sheet surface and thickness resulting in efficient, continuous production of a highly uniform polishing pad in both properties and dimensions.
In a first step, one or more high viscosity liquid precursor polymers are mixed with one or more fillers under vacuum and controlled temperature, to yield a liquid mixture having a 25 controlled viscosity and consistency. The liquid polymers contain functional groups which are chemically active. Such chemically active polymers (aka precursors) encompass the realm of monomers, oligomers, pre-polymers and high molecular weight polymers of organic and inorganic origin. In addition, various modifiers such as thickening or thinning agents, colorants, UV and heat stabilizers, surface tension modifiers (surfactants) etc. may be added 3o into the mix. In a second step, a hardening or curing agent is dispersed uniformity into the polymer mix to chemically react with the liquid polymers. The amount of the hardening or curing agent is precisely controlled at a specified ratio to the polymer mix to achieve the desired product properties. In addition, the temperature and viscosity of the reactant mixture as well as the ambient pressure and atmosphere are precisely controlled to a pre-determined

4 specification. Typically, a high vacuum no less than 28 in. of water may be applied during the entire mixing process, and nitrogen gas may be used to 'blanket' the mix if it has to be stored for an extended period of time.
The reactive mix may then be dispensed into a preset gap space formed between a vertically stacked pair of endless steel belts with heaters on the back of one or both belts, accompanied by feedback control of such parameters as conveyor speed, belt pressure, temperature and belt gap to form a uniform sheet. Subsequently, the sheet may be cut to length, post cured in an oven and die cut to form the polishing pads of the present invention.
It is therefore an object of the present invention to provide a continuous process to comprising a series of in-line automatic and/or manual networked process controls and testing and inspection metrology equipment, in order to form uniform polishing pads particularly for Chemical-Mechanical Planarization.
It is a further object of the present invention to provide an apparatus for use in a continuous process comprising a series of networked process controls to form a uniform polishing pad, particularly for chemical-mechanical planarization.
It is still a further object of the present invention to provide polishing pads with a high degree of uniformity within each pad and from pad to pad, particularly for chemical-mechanical planarization, which are produced by a continuous process comprising a series of process controls to ensure product uniformity.
2o It is still a further object of the present invention to provide an automated two-step process for providing polishing pads of high uniformity.
It is also an object ofthe present invention to produce a polishing pad where all raw and in-process materials are maintained in a well controlled enclosed environment to avoid the inadvertent contamination by foreign substances which may be detrimental to the final polishing application.
Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein it is shown and described preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modification in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.

5 Brief Description of the Drawings The features, operation and advantages of the invention may be better understood from the following detailed description of the preferred embodiments taken in conjunction with the attached drawings, in which FIG. 1 is a block diagram of the general features of the continuous process of the present invention.
FIG. 2 is a simplified schematic view of the apparatus for continuous manufacture of a polishing pad of the present invention.
Description of Preferred Embodiments The present invention is directed at a high volume essentially continuous manufacturing process for forming polishing pads to be used for chemical-mechanical polishing. One key to the process are numerous networked process controls which are used to monitor and feed back information in real time as the product is being produced. This provides Is extremely consistent sheet material in terms of composition, properties, thickness and surface uniformity, resulting in polishing pads which provide a high degree of polishing consistency and efficiency.
As diagrammed in FIG. 1, the manufacturing process of the present invention comprises two basic steps: Step A, the compounding of the preferable high viscosity liquid 2o polymer precursor and Step B, the continuous dispensing and sheet formation of the liquid polymer precursor mixed with a hardening agent. Subsequently, the sheet material may be cut to length, postcured to establish optimal properties and cut to shape to form polishing pads.
In step A (see FIG. 1), the compounding step, a highly viscous mixture of liquid polymer, preferably polyurethane is first equilibrated under vacuum and elevated temperature 25 for several hours. Examples of such sources of polymers are the Adiprene Polyurethane Pre-polymer offered by the Crompton Corporation, and the Airthane Polyurethane Pre-polymer from Air Products, respectively. Any required additives such as antifoaming agent, UV and heat stabilizers, surface tension modifiers, etc. are also blended uniformity into the polymer mix. Any required organic or inorganic filler materials, soluble or insoluble, and 3o in various particulate configurations and sizes are then added preferably under vacuum or a blanket of nitrogen gas and dispersed uniformity within the mix. Again the temperature, viscosity of the entire mixture, the vacuum or ambient nitrogen (in the headspace of the mixing vessel) are kept precisely controlled throughout the mixing, storing and subsequent operations.
Furthermore, the amounts and relative ratios of all components in the entire mixture are

6 precisely measured and controlled.
As noted, a filler component may also optionally be included, preferably the hollow Expancel~ microspheres from Expancel, Inc. having diameters from 20 to 90 microns, at a level of about 1-5 wt. percent, and preferably at 3 wt. percent of the formulation. The dry filler component preferably has a specific weight of from about 0.03 to about 0.12 grams per cubic centimeter. One purpose of the dry filler component is to provide a porous surface on the polishing pad after it is conditioned for use. The conditioning of the surface of the pad by abrading its top surface removes a thin layer of reacted polymer and breaks the microspheres at the surface providing a controlled level of porosity. Alternatively, other materials may be used to as the filler component to provide specific abrasive or porous properties of the polishing pad, and include, but are not limited to, water soluble fibers and soluble products such as salts that may be washed out after surface buffing to create a porous surface, particulate or powder polymers, etc.
The homogenous liquid precursor compounded in Step A, preferably has a specific weight from about 0.50 to about 1.2 grams per cubic centimeter and is stored for use in the continuous process phase (Step B) at 25 - 40 degrees C. under vacuum or nitrogen and constant but gentle blending action.
Turning now to the step of dispensing and the sheet forming continuous process, Step B
is shown in simplified schematic representation in FIG. 2. The liquid polymer precursor comprising, preferably, a blend of polyurethane pre-polymers with an additives) and filler components dispersed therein, can be pumped or gravity fed to a continuously replenished feed tank 10 which is preferably maintained under vacuum conditions or inert gas (e.g. nitrogen) and preferably at about 20 - 40 degrees C. A hardening or curing agent, for example (MOCA
or Ethacure), can be stored in an ambient or nitrogen blanketed tank 20. For reacting, the curing agent and the liquid polymer precursor are precisely metered by Coriolis mass flow regulations 12, 22 and pumped into, preferably, a continuous static or a dynamic mixer 30. The stoichiometric ratio of the curing agent to the polyurethane precursor is preferably between 0.85 to 1.05. This ratio and set of processing conditions preferably provides a viscosity of the mixture in the range of 20,000 - 400,000 Pascal seconds.
3o Dynamic or mechanical mixers may be used providing that minimal air is introduced.
Upon exiting the mixer, the reacting composition 32 is uniformly fed into the feed end 42 of a double steel belt press 40. The feed end of the double belt press as well as the double belt press itself is preferably kept under an atmospherically controlled chamber 60 at uniform temperature and pressure prior to the compressed heated zones and to ensure a more efficient polymerization during heating.
The double belt press 40 will generally comprise two endless steel belts driven over rollers revolving in opposing directions, with mutually facing outer sides thereof. pressed against material passed there between. Heating can be accomplished by means of one or more temperature controlled press plates, pressure chambers or IR heaters at the back sides of the compressed areas. The steel belts which form the top and bottom surface of the continuously molded urethane sheet can be heated and maintained preferably at 80-110 degrees C to provide polymerization of the urethane into a solid compound under isobaric conditions. The pressing zone 44 is formed between mutually opposing outer sides of the pressing belts.
1o The endless belts are preferably of stainless steel and can be maintained at a precisely controlled pressure level preferably about 4 MPa (S50 - 600 psi) although in the broad context of the present invention, the pressure may range from 1-10 MPa (145 psi - 1450 psi). The pressure may be generated by the weight of the upper unit plates of the endless belt and/or by mechanical or hydraulic means. As the molded sheet moves between the opposing steel belts, the sheet is compressed, over a distance of preferably about 4.5 meters at 44, to its final thickness and solidified by the heat provided from the heated belts. In the preferred embodiment of the present invention, the curing process can be initiated by the exothermic heat of reaction of the urethane and amine components and by the heat from the endless belts.
The process to form a continuous uniform sheet may be fully PLC controlled with 2o interactive information exchange between mechanical components, each having built-in tools for process control, data trending and process enhancements. All liquid as well as solid raw material components are monitored as to precise temperature and viscosity, and dosed for compounding and mixing. The system preferably uses a fast communication protocol -PROFIBUS- to monitor and control all system components. The system is set up for easy operator control and interface, via touch screens, to monitor and adjust process parameters. An in-line, real-time testing and inspection metrology equipment for monitoring material properties such as thickness, density, hardness, compressibility and surface roughness, as well as inspection with an imaging system for contaminants, can be fully integrated. The system also incorporates online continuous data storage, statistical analysis, trending and CRT display 3o as well as operator alert on process excursions.
The belt press 40 can produce a continuous urethane sheet 32A having a uniform density of preferably less than 1.0 g/cc due to the process controls in use.
Density variation measured on a square yard is less than 2.0 percent. Thickness of the sheet is controlled by micrometer adjustment at 50 to +/- O.OSmm. The nominal thickness of the sheet 32A formed as described above, may preferably be between lmm to 3mm or higher.
The resulting urethane sheet 32A is discharged from the belt press 40 at the takeoff end and is cut to length using preferably a roller blade cutter at 62. Other types of cutters may also be used. The cut to length sheets 32B are next stacked at 70 and transferred to an oven 80 for post curing for preferably 16-24 hours at a temperature specified for a given type of urethane and curing agent, said temperature typically varies from 150 to 450 degree F.
The cured urethane sheets can be subsequently cooled to ambient temperature under controlled cooling rates, tested and inspected again, and buffed or napped to remove any surface polymeric 'skin' to expose the bulk structure of the sheet. The buffing or napping is 1o also designed and controlled to impart a pre-determined micro texture to the urethane sheet surface which reduces the 'break-in' time in end-use polishing applications.
While the preferred material composition to continuously produce polishing pads of the present invention is a blend of liquids with filler(s), other material precursor compositions may also be processed through the apparatus of the present invention, including, but not limited to, dry polymers, powders and other solid compounds and fillers, both soluble and insoluble. The incorporation of these materials may require corresponding change in processing temperature and other parameter.
Table I lists some properties of the polishing pads contemplated and targeted for manufacture by the continuous process of the present invention.
TABLE I
Thickness: 10 - 130 mils; preferably 50 - 100 mils Density: 0.3 - 1.2 g/cc; preferably 0.5 - 0.9 g/cc Pore Size distribution: 20 - 100 micrometers; preferably 20 - 60 micrometers Pore or Void Volume: 15 - 60 % of total volume; preferably 20 - 40 % of total volume Hardness: 30 - 80 Durometer Shore D; preferably 45 - 75 Durometer Shore D
Compressibility: 0 - 10 %; preferably 0 - 4 Glass Transition (Softening) Temperature (Tg): 50 - 200 degree C
3o Surface Roughness, Ra: 0 - 10 micrometers Abrasion Resistance: Ranking > 2 (for Tabor Abrasion Tester) Compression Modulus: 1 - 8 MPa; preferably 3 - 5 MPa Deflection from lay flat: edge and bulk waviness < 0.5"; preferably < 0.1 "*

*It should be noted that the values reported for such deflection from lay flat are measured over a 1 meter by 1 meter area of the pad. Accordingly, when the edge and bulk waviness are < 0.5"
it corresponds to a 1 meter by 1 meter area of the pad that does not indicate, when laying flat, an upward deflection or wave in the pad that exceeds 0.5", and is preferably <
0.1 ".
Due to the scale and nature of this continuous process, variations in the composition and properties of the finished product will be minimized. The raw materials can be blended in large quantities to provide a recirculating feed system that continuously supplies the mixer.
These materials can therefore be blended under precise process control of temperature, vacuum, ratio and viscosity. The continuous nature of the sheet forming process enables precise control to for producing a uniform sheet as process controls monitor and feed back data regarding feed temperature, belt temperature, pressure, feed rate, conveyor speed, sheet thickness and density.
From the sheets, large quantities of polishing pads having little variability can be cut.
The foregoing embodiments have been described merely as examples of the invention and are not intended to limit its scope. Since modification of the described embodiments may is occur to persons skilled in the art, the scope of the invention is intended to cover all such modifications which come within the true spirit and full scope of the invention.

Claims (22)

What is claimed is:

1. A method of continuously forming a polymer sheet for use as a polishing pad, comprising the steps of:
(a) providing a pair of endless pressing belts stacked one above the other in a controlled atmosphere, said stacked belts having a common feed end and a common takeoff end;
(b) supplying a reactive blend comprising a precursor and curing agent to said belts;
(c) heating said pair of stacked endless pressing belts to the curing temperature of the precursor and curing agent;
(d) revolving said stacked endless pressing belts at a selected speed and in converging direction from said feed end to said takeoff end to compress and supply pressure to said reactant blend in between said belts to form a polymer sheet with a selected thickness, (e) passing said polymer sheet through said takeoff end of said opposed endless belts.

2. The method of claim 1 wherein said controlled atmosphere comprises an inert gas.

3. The method of claim 1 wherein said reactive blend comprising a precursor and curing agent is a liquid at room temperature with a viscosity within the range of about 20,000 - 400,000 Pascal seconds.

4. The method of claim 1, wherein step (d) further includes the continuous monitoring of one or more of the thickness of the polymer sheet, the temperature of the belts, the pressure on the sheet between the belts, the speed of the belts, via a closed loop process control system, wherein said closed loop process control compares the values of thickness, temperature, pressure and/or speed to selected target values ranges, and maintains said thickness, temperature, pressure and/or speed to fall within said target value ranges.

5. The method of claim 1, which further includes the steps of one or more of the following:
(i) cutting said polymer sheet to desired length, and (ii) post-curing said polymer sheet to establish the final properties of said sheet.

6. The method of claim 1, wherein said opposed endless pressing belts comprise a double steel belt press.

7. The method of claim 1, wherein said polymer sheet comprises a polyurethane.

8. The method of claim 1, wherein step (c) comprises the providing of a molten precursor.

9. The method of claim 7, wherein said polyurethane comprises a toluene diisocyanate prepolymer blended with an isopherone diisocyanate prepolymer.

10. The method of claim 1, wherein the step of supplying said reactive blend comprising a precursor and curing agent to said belts includes the step of mixing said precursor and curing agent in a mixer prior to supplying said reactive blend to said belts.

11. The method of claim 10 wherein said mixer is either a static or dynamic mixer.

12. The method claim 1, wherein the reactant blend is compressed at a pressure between 1 and 10 MPa

13. The method of claim 1, wherein the precursor of step (b) further includes a filler.

14. The method of claim 13, wherein the filler comprises of hollow microspheres.

15. The method of claim 13 wherein said filler includes a water soluble polymer.

16. The method of claim 3 further including one or more of the following steps:

(i) cutting said polymer sheet into a polishing pad having a top surface;
(ii) conditioning said polishing pad by abrading said top surface.

17. A polishing pad for chemical-mechanical polishing according to the method of claim 16.

18. A method of continuously forming a polyurethane sheet for use as a polishing pad, comprising the steps of:
(a) providing a pair of endless pressing belts stacked one above the other in an oven in an inert gas atmosphere, said stacked belts having a common feed end and a common takeoff end;
(b) supplying a liquid reactive blend comprising a polyurethane precursor and curing agent to said belts, wherein said reactive blend has a viscosity within the range of about 20,000 - 400,000 Pascal seconds and said reactive blend has a selected curing temperature;
(c) heating said pair of stacked endless pressing belts to the curing temperature of the polyurethane precursor and curing agent;
(d) revolving said stacked endless pressing belts at a selected speed and in converging direction from said feed end to said takeoff end to compress and supply pressure to said reactant blend in between said belts to form a polyurethane sheet with (i) a thickness within the range of about 10-130 mils; and (ii) a density within the range of about 0.3 - 1.2 g/cc; and (iii) a Shore D hardness within the range of about 30 - 80; and (e) passing said polyurethane sheet through said takeoff end of said opposed endless belts.

19. The method of claim 18 further characterized in that said polyurethane sheet has (iv) a compressibility of up to about 10.0%; and (v) a void volume within the range of about 15-60% of the total volume; and (vi) a deflection from lay flat of <= 0.5".

20. An apparatus for forming a polymer sheet for use as a polishing pad, comprising:
a pair of endless pressing belts disposed one above the other in opposing fashion said opposed belts having a feed end and a common takeoff end, a feed system for providing one or more precursors to said feed end of said opposed endless pressing belts, a controlled atmosphere in which said endless pressing belts rotate in converging fashion from said feed end to said takeoff end, wherein said apparatus continuously monitors one or more of the thickness of the polymer sheet, the temperature of the belts, the pressure on the sheet between the belts, the speed of the belts, via a closed loop process control system, wherein said closed loop process control compares the values of thickness, temperature, pressure and/or speed to selected target values ranges, and maintains said thickness, temperature, pressure and/or speed to fall within said target value ranges.

21. A system for making polishing pads, in particular for chemical-mechanical planarization, comprising;
(a) means for storage and conditioning of raw materials prior to mixing;
(b) means for blending under temperature control and vacuum to provide a precursor comprising said raw materials;
(c) means for recirculating said precursor to replenish said precursor;
(d) a pair of endless pressing belts disposed one above the other in opposing fashion, said belts having a common feed end and a common takeoff end, said belts configured to revolve at a selected speed and in converging direction from said feed end to said takeoff end to compress and supply pressure between said belts;
(e) a mixer for feeding said precursor under controlled condition to said feed end of said pair metal endless pressing belts to form a molded polymer sheet;
(f) an inert atmosphere surrounding said feed end of said pair of opposed metal pressing belts;
(g) a closed loop process control for the continuous monitoring of one or more of the thickness of the polymer sheet, the temperature of the belts, the pressure on the sheet between said belts, the speed of the belts, wherein said closed loop process control compares the values of thickness, temperature, pressure and/or speed to selected target values ranges, and maintains said thickness, temperature, pressure and/or speed to fall within said target value ranges;
(h) a means for cutting said polymer sheet into specific lengths; and (i) a means for controlling the dimensions of said polymer sheet to convert said sheet to a polishing pad.

22. The system of claim 21 wherein said polishing pad has a top surface and further including conditioning means for buffing or napping said top surface to provide a desired surface micro texture.