Flanged optical endpoint detection windows and CMP polishing pads containing them

Abstract

The present invention provides a chemical mechanical (CMP) polishing pad with a top surface, one or more apertures adapted to receive an endpoint detection window, an underside having a recessed portion and having one or more flanged endpoint detection windows (windows), each window having a flange adapted to fit snugly into the recessed portion of the underside of the polishing layer, the flange having a thickness slightly less than the depth of the recessed portion of the polishing layer (to allow for adhesive), having a detection area that fits snugly into an aperture in the polishing layer so that its top surface that lies substantially flush with the top surface of the polishing layer.

Claims

1. A chemical mechanical (CMP) polishing pad for polishing a substrate chosen from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate comprising (i) a CMP polishing layer or top layer of a polymer material having in the CMP polishing layer on the top layer (a) a top surface having in it a series of grooves, having for each of one or more endpoint detection windows an aperture A extending all the way through the polishing layer having a center point when viewed looking in a direction normal down on the top of the polishing layer when in use and an exclusion zone free of grooves adjacent the aperature A, the exclusion zone having a lateral dimension, and (b) a substantially flat underside that contains for each of the one or more endpoint detection windows a recessed portion having a constant depth that extends laterally coterminous with the lateral dimension of each exclusion zone; (ii) a sub pad or sub layer of a polymeric material, having a substantially flat top surface, having a flat underside surface and having for each of one or more endpoint detection windows an aperture extending all the way through the sub pad and having a center point aligned to match the center point of each aperture A in the polishing layer; and (iii) one or more endpoint detection windows each window having a flange adapted to fit snugly into the recessed portion of the underside of the polishing layer, having a thickness equal to or, to accommodate an adhesive layer, slightly less than the depth of the recessed portion of the (i) polishing layer, having a detection area that fits snugly into an aperture in the (i) polishing layer so that its top surface that lies substantially flush with the top surface of the (i) polishing layer.

2. The chemical mechanical (CMP) polishing pad as claimed in claim 1, wherein the polymer material of the CMP polishing layer is a polyurethane foam layer.

3. The chemical mechanical (CMP) polishing pad as claimed in claim 1, wherein the (ii) a sub pad or sub layer of a polymeric material is a polyurethane foam material.

4. The chemical mechanical (CMP) polishing pad as claimed in claim 1, wherein the (iii) one or more endpoint detection windows is a transparent polymer window.

5. The chemical mechanical (CMP) polishing pad as claimed in claim 1, wherein each of the (iii) one or more endpoint detection windows is adhered to each of the (i) polishing layer and the (ii) sub pad via ultrasonic welding or with an adhesive chosen from pressure sensitive adhesives, hot melt adhesives, contact adhesives and combinations thereof.

6. The chemical mechanical (CMP) polishing pad as claimed in claim 4, wherein each of the (iii) one or more endpoint detection windows is adhered to the (i) polishing layer with a pressure sensitive adhesive and is adhered to the (ii) sub pad with a pressure sensitive adhesive or a hot melt adhesive.

7. The chemical mechanical (CMP) polishing pad as claimed in claim 1, wherein the one or more endpoint detection windows wherein the CMP polishing pad contains no gap or open space of greater than 150 m in any dimension within the lateral area bound by the flange of each of the one or more (iii) endpoint detection windows and between the underside of the sub pad and the top surface of the polishing layer.

8. The chemical mechanical (CMP) polishing pad as claimed in claim 1, comprising from one to three (iii) endpoint detection windows.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a top view of a CMP polishing pad with a flanged endpoint detection window.

(2) FIG. 2 is a three quarter view of a cutaway of a CMP polishing pad revealing a flanged endpoint detection window and a subpad.

(3) FIG. 3A is a side view of a cutaway portion of a polishing layer not containing an endpoint detection window.

(4) FIG. 3B is a side cutaway view of a flanged endpoint detection window with an adhesive for attachment to a polishing layer.

(5) FIG. 3C is a side view of a cutaway portion of a sub pad attached to a platen for polishing.

DETAILED DESCRIPTION

(6) Unless otherwise indicated, conditions of temperature and pressure are ambient temperature and standard pressure. All ranges recited are inclusive and combinable.

(7) Unless otherwise indicated, any term containing parentheses refers, alternatively, to the whole term as if no parentheses were present and the term without them, and combinations of each alternative. Thus, the term (poly)isocyanate refers to isocyanate, polyisocyanate, or mixtures thereof.

(8) All ranges are inclusive and combinable. For example, the term a range of 50 to 3000 cPs, or 100 or more cPs would include each of 50 to 100 cPs, 50 to 3000 cPs and 100 to 3000 cPs.

(9) As used herein, the term ASTM refers to publications of ASTM International, West Conshohocken, Pa.

(10) As used herein, the term polyisocyanate means any isocyanate group containing molecule having three or more isocyanate groups, including blocked isocyanate groups.

(11) As used herein, the term polyurethanes refers to polymerization products from difunctional or polyfunctional isocyanates, e.g. polyetherureas, polyisocyanurates, polyurethanes, polyureas, polyurethaneureas, copolymers thereof and mixtures thereof.

(12) As used herein, the term reaction mixture includes any non-reactive additives, such as microelements and any additives to lower wet hardness (Shore D or Shore A according to ASTM D2240-15 (2015)) of a polyurethane reaction product in the polishing pad.

(13) As used herein, the term semiconductor wafer is intended to encompass a semiconductor substrate, such as an unpatterned semiconductor or one having a pattern, a semiconductor device, various packages for various levels of interconnection, including a single-chip wafer or a multiple-chip wafer, a substrate for a light emitting diode (LED), or other assemblies requiring solder connections.

(14) As used herein, the term semiconductor substrate is defined to mean any construction comprising semiconductive material. A semiconductor substrate includes semiconductor devices and any substrate having one or more semiconductor layers or structures which include active or operable portions of semiconductor devices.

(15) As used herein, the term semiconductor device refers to a semiconductor substrate upon which at least one microelectronic device has been or is being fabricated.

(16) As used herein, the terms Shore D hardness, Shore 0 hardness and Shore A hardness are the hardness values of a given material as measured after a given time period according to ASTM D2240-15 (2015), Standard Test Method for Rubber PropertyDurometer Hardness. Hardness was measured on a Rex Hybrid hardness tester (Rex Gauge Company, Inc., Buffalo Grove, Ill.), equipped, respectively, with a sharp (Shore D), spherical (Shore 0), or flat (Shore A) probe. Four samples were stacked and shuffled for each hardness measurement; and each specimen tested was conditioned by placing it in 50 percent relative humidity for five days at 23 C. before testing and using methodology outlined in ASTM D2240-15 (2015) to improve the repeatability of the hardness tests.

(17) As used herein, the term SG or specific gravity refers to the weight/volume ratio of a rectangular cut out of a polishing pad or layer in accordance with the present invention. Density is equivalent in value to SG.

(18) As used herein, the term substantially flush means within 150 m or, preferably, within 50 m of a given surface but not above that given surface.

(19) As used herein, the term substantially flat means that a given surface is within 150 m or, preferably, within 50 m of being perfectly two dimensional or a perfect plane segment.

(20) In accordance with the present invention, CMP polishing pads comprise one or more flanged endpoint detection windows that adhere well to the pad material. A flanged endpoint detection window allows greater landing area for adhesion, both to the top pad or polishing layer and to the subpad. The one or more flanged endpoint detection windows to sit between the top and sub pads, allowing the window to have substantially similar compressibility to the overall CMP polishing pad for minimizing process impact. The diameter of the flange is selected to be within the exclusion area of the CMP polishing pad, thereby limiting any irregularity in how the CMP polishing pad responds to endpoint detection to a small area of the pad that hydroplanes below the substrate surface. Accordingly, the flange diameter and groove pattern are coordinated to minimize process impact.

(21) The top pad or (i) polishing layer includes a recess or recessed portion for the flange of the (iii) endpoint detection window so that the detection portion of the endpoint detection window lies flush with the top of the (ii) subpad.

(22) In accordance with the CMP polishing pads of the present invention, both sides of the flange of the endpoint detection window are adhered to the pad assembly, one side to the sub pad and the other side to the top pad or polishing layer.

(23) In accordance with the present invention, the endpoint detection window may, preferably, include a recess for platen instrumentation, such as an eddy current sensor.

(24) The present invention further provides a method of making a CMP polishing pad according to the present invention, comprising: providing a CMP polishing layer having a polishing surface as well as grooves and one or more apertures; separately, forming an endpoint detection window from a moldable polymer or reaction mixture; interfacing the endpoint detection window with the polishing layer to provide a chemical mechanical polishing pad; wherein the endpoint detection window is a window shaped to fit snugly within the dimensions of the aperture and the recessed portion of the polishing layer, allowing for any adhesive layer.

(25) Generally, in casting to form the endpoint detection windows of the present invention, a vacuum is applied to the reaction mixture before the molding step to remove or prevent the formation of pores or bubbles.

(26) Preferably, the endpoint detection windows of the present invention can be formed from reaction mixtures containing as one component (A) a cycloaliphatic di- or poly-isocyanate and, as the other component a polyol mixture of (i) a polymeric diol and (ii) a triol in a weight ratio of from 1.6:1 to 5.2:1 and a catalyst chosen from a tin containing catalyst in the amount of from 0.00001 to 0.1 wt. % or an amine catalyst in the amount of from 0.01 to 1 wt. %, all weight percents based on the total solids weight of the reaction mixture. The polymeric diol may be a polycarbonate diol having a molecular weight of from 500 to 1,000, or preferably, from 500 to 800. The mole ratio of isocyanate groups in (A) the cycloaliphatic diisocyanate or polyisocyanate to the number of moles of hydroxyl groups in the (B) polyol mixture ranges from 0.9:1 to 1.10:1. Such reaction mixtures insure the hardness of endpoint detection windows, thereby enabling the provision of hard CMP polishing pads with endpoint detection windows that do not bulge or buckle from the surface thereof during or after processing.

(27) The chemical mechanical polishing pads of the present invention further comprise at least one additional layer interfaced with the polishing layer, such as a sub pad. The additional layer can have a slightly smaller opening or aperture than the polishing layer of the CMP polishing pad which is concentric with or having the same center point as the hole, aperture or opening in the polishing layer so as to enable optical detection while providing a shelf that the endpoint detection window can rest upon and interface with. Preferably, the polishing layer is interfaced with the at least one additional layer using an adhesive. The adhesive can be selected from pressure sensitive adhesives, hot melt adhesives, contact adhesives and combinations thereof. Preferably, the adhesive is a hot melt adhesive or a pressure sensitive adhesive. More preferably, the adhesive is a hot melt adhesive.

(28) The present invention is illustrated by reference to the figures.

(29) As shown in FIG. 1, a top view of a CMP polishing pad with grooves (11), reveals the top surface of a polishing layer (10), a detection area of a flanged endpoint detection window (14) and an exclusion zone (12) in the polishing layer where there are no grooves (11). The exclusion zone (12) corresponds in lateral dimension to the each of the recessed portion (not shown) in the underside of the polishing layer (10) and the flange (not shown) of the endpoint detection window (14).

(30) As shown in FIG. 2, a three quarter view of a cutaway of a CMP polishing pad reveals a polishing layer (10), a flanged endpoint detection window (14), and a sub pad (22). There are no grooves (11) in the area immediately above the window flange (18), the area designated as the exclusion zone (12).

(31) As shown in FIG. 3A, a side view of a cutaway portion of a polishing layer (10) not containing an endpoint detection window, wherein the polishing layer contains a top polishing grooved area (16), an aperture (15) for the detection area of an endpoint detection window (not shown) and an exclusion zone (12) where there are no grooves (11).

(32) As shown in FIG. 3B, a side cutaway view of a flanged endpoint detection window (14) in accordance with the present invention, has a detection area (18) and an adhesive (20) applied to the flange (19) whereby the endpoint detection window can be attached to a polishing layer.

(33) As shown in FIG. 3C, a side view of a cutaway portion of a sub pad (22), reveals an aperture (23) and an adhesive layer (not labelled) on each of the flat top surface of the sub pad (22) and its underside (24), whereby the sub pad (22) is attached to a platen (not shown) for polishing.

(34) In accordance with the present invention, methods of polishing a substrate, comprise: Providing a substrate selected from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate; providing a chemical mechanical (CMP) polishing pad having an endpoint detection window as in any one of items 1 to 3, above; creating dynamic contact between a polishing surface of the polishing layer of the CMP polishing pad and the substrate to polish a surface of the substrate; and, conditioning of the polishing surface of the polishing pad with an abrasive conditioner.

(35) The present invention also provides a method of polishing a substrate, comprising: providing a chemical mechanical polishing apparatus having a platen, a light source and a photosensor; providing at least one substrate; providing a chemical mechanical polishing pad as in any one of items 1 to 3, above; installing onto the platen the chemical mechanical polishing pad; optionally, providing a polishing medium at an interface between the polishing surface and the substrate; creating dynamic contact between the polishing surface and the substrate, wherein at least some material is removed from the substrate; and, determining a polishing endpoint by transmitting light from the light source through the endpoint detection window and analyzing the light reflected off the surface of the substrate back through the endpoint detection window incident upon the photosensor.

(36) In accordance with the present invention, methods of using the endpoint detection windows is specifically a method of detecting the end-point of polishing by irradiating a substrate via a CMP polishing pad through the endpoint detection window, with a light beam, and monitoring an interference signal generated by reflection of the light beam. As the light beam, for example, a white LED or white light using a halogen or deuterium lamp having a light of wavelengths ranging from 200 to 1100 nm is generally used. In such methods, the end-point is determined by knowing an approximate depth of surface unevenness through monitoring of a change in the thickness of a surface layer of a wafer. When such change in thickness becomes equal to the thickness of the unevenness, the CMP process is finished. Accordingly, one determines a CMP polishing endpoint by transmitting light from the light source through the endpoint detection window and analyzing the light reflected off the surface of the substrate back through the endpoint detection window incident upon the photosensor. As a method of detecting the end-point of polishing by such optical means and a polishing pad used in the method, various methods and polishing pads have been proposed.

(37) As used in the methods and otherwise herein, an endpoint detection window provides detection during polishing of one, more than one or all layers of a given substrate, including the end of polishing of a single material, layer or feature of a substrate, such as any one or more of a dielectric, a mask, a filler, a conductive layer and/or a semiconducting material, gate forming structure, relational structure, trench forming structure, or via forming structure.

(38) During polishing, a light beam is directed through the window to the wafer surface, where it reflects and passes back through the window to a detector (e.g., a spectrophotometer). Based on the return signal, properties of the substrate surface (e.g., the thickness of films thereon) can be determined for endpoint detection.

(39) The polishing layer of the chemical mechanical polishing pad of the present invention has a polishing surface adapted for polishing a substrate. Preferably, the polishing surface is adapted for polishing a substrate selected from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate. More preferably, the polishing surface is adapted for polishing a semiconductor substrate.

(40) The polishing layer of the chemical mechanical polishing pad of the present invention is preferably made of a polymeric material comprising a polymer selected from polycarbonates, polysulfones, nylons, polyethers, polyesters, polystyrenes, acrylic polymers, polymethyl methacrylates, polyvinylchlorides, polyvinylfluorides, polyethylenes, polypropylenes, polybutadienes, polyethylene imines, polyurethanes, polyether sulfones, polyamides, polyether imides, polyketones, epoxies, silicones, EPDM, and combinations thereof. Preferably, the polishing layer comprises a polyurethane. One of ordinary skill in the art will understand to select a polishing layer having a thickness suitable for use in a chemical mechanical polishing pad for a given polishing operation. Preferably, the polishing layer exhibits an average thickness of 20 to 150 mils (more preferably 30 to 125 mils; most preferably 40 to 120 mils).

(41) Preferably, the polishing surface has macrotexture selected from at least one of perforations and grooves. Perforations can extend from the polishing surface part way or all the way through the thickness of the polishing layer. Preferably, grooves are arranged on the polishing surface such that upon rotation of the chemical mechanical polishing pad during polishing, at least one groove sweeps over the surface of the substrate being polished. Preferably, the polishing surface has macrotexture including at least one groove selected from the group consisting of curved grooves, linear grooves and combinations thereof.

(42) Preferably, polishing layer of the chemical mechanical polishing pad of the present invention has a polishing surface adapted for polishing the substrate, wherein the polishing surface has a macrotexture comprising a groove pattern formed therein. Preferably, the groove pattern comprises a plurality of grooves. More preferably, the groove pattern is selected from a groove design. Preferably, the groove design is selected from the group consisting of concentric grooves (which may be circular or spiral), curved grooves, cross hatch grooves (e.g., arranged as an X-Y grid across the pad surface), other regular designs (e.g., hexagons, triangles), tire tread type patterns, irregular designs (e.g., fractal patterns), and combinations thereof. More preferably, the groove design is selected from the group consisting of random grooves, concentric grooves, spiral grooves, cross-hatched grooves, X-Y grid grooves, hexagonal grooves, triangular grooves, fractal grooves and combinations thereof. Most preferably, the polishing surface has a spiral groove pattern formed therein. The groove profile is preferably selected from rectangular with straight side walls or the groove cross section may be V shaped, U shaped, saw tooth, and combinations thereof.

(43) The present invention will now be illustrated in detail in the following non-limiting Examples:

(44) In the following Examples, unless otherwise stated, all pressures are standard pressure (101 kPa) and all temperatures are ambient or room temperature (22-23 C.). The following raw materials were used in the Examples:

(45) Polishing layer A was an IKONIC 4000 Series polyurethane polishing layer with a density of 0.75 g/cc and a hardness of 57 shore D (The Dow Chemical Co., Midland, Mich.);

(46) Sub pad A was a polyurethane foam with density of 0.637 g/cc and hardness of 65 shore O (ASTM D2240-15 (2015), pressure sensitive adhesive was an acrylic resin containing adhesive, and the reactive hot melt comprised an aliphatic polyester polyol.

(47) Window materials included: H12MDI: methylene bis (4-cyclohexylisocyanate), a.k.a. dicylohexylmethane-4,4-diisocyanate;

(48) Diol 1: a linear, hydroxyl-terminated, aliphatic polycarbonate diol with an average molecular weight of approx. 650 g/mol;

(49) Polycarbonate triol 1: Trimethylol propane or TMP, MW (molecular weight): 134.17 g/mol;

(50) Catalyst: dibutyltin dilaurate catalyst, MW (molecular weight): 631.56;

(51) Polyisocyanate prepolymer 1: polyether-containing polyisocyanate polymer, was prepared with an aliphatic diisocyanate with available isocyanate content (% NCO) of 7.35-7.65 wt. %;

(52) Curative: 3,5-diethyltoluene-diamine; and

(53) Light stabilizer: cyanoacrylic acid ethylhexyl ester.

Example 1: Hard Flanged Window Containing Pad

(54) A flanged material was vacuum cast using 51 wt. % H12MDI, 37 wt. % diol 1, 12 wt. % polycarbonate triol, all weights based on total weights of polyol and isocyanate materials, and catalyst, to form a solid disk without bubbles. The disk was then milled into the flanged window shape. Nominal flange thickness was 50 m; detection area thickness was 2 mm; detection area was circular and 18 mm in diameter, and the flange was circular and 30 mm in diameter. One 50 m deep; 30 mm recessed area was milled in the underside of the polishing layer A concentric with an 18 mm wide aperture through the polishing layer. Pressure sensitive adhesive was applied to the recessed area and the flanged window was inserted into the recessed area in the polishing layer, such that the detection area surface was flush with the top surface of the polishing layer A. Reactive hot melt adhesive was applied to the top surface of sub pad A and used to permanently adhere the polishing layer A (containing the flanged window) to the sub pad.

Example 2: A CMP Polishing Pad with Prepolymer Flanged Windows

(55) A flanged window material was cast into a cylinder having the diameter desired of the exclusion area from a mixture of 88 wt. % polyisocyanate prepolymer 1, 11 wt. % curative, and light stabilizer. The casting was skived into sheets of 2 mm thick, then sheets then milled into a flanged window shape. Nominal flange thickness was 50 m; detection area thickness was 2 mm; detection area was circular and 18 mm in diameter; and the flange was circular and 30 mm in diameter, which was the size of the exclusion area. One 50 m deep, 30 mm recessed area was milled in the underside of polishing layer A concentric with an 18 mm wide aperture through the polishing layer. Reactive hot melt was applied to the recessed area; and the flanged window was inserted into polishing layer A such that the detection area surface was flush with the top surface of the polishing layer. Reactive hot melt adhesive was also applied to the top surface of sub pad A and used to permanently adhere polishing layer A (containing the flanged window) to sub pad A.

Example 3: Leakage Testing

(56) The CMP polishing pads of Examples 1 and 2 were tested for effectiveness against leakage using two methods. In the first method, a vacuum was applied to the underside of the CMP polishing pad using a porous plate. A liquid dye was placed on the polishing surface, the exclusion zone, and the window detection area and allowed to flow into the pad material. After 10 hours, the CMP polishing pad was removed and the porous plate was inspected for dye discoloration. No discoloration was found, indicating that the flanged window had not leaked.

(57) The second experiment comprised placing each CMP polishing pad on a CMP platen within a functioning CMP machine. The polishing layer top surface, exclusion zone, and window detection area were then subjected to a rotating surface conditioning disk at 2.3 kg downforce for 60 minutes while rinsing with deionized water. The CMP polishing pad was then removed from the platen and inspected for evidence of leakage. None was found.