Patent Application
20180169827
The present invention relates to methods for producing porous polyurethane (PU) chemical mechanical planarization (CMP) polishing pads comprising endpoint detection windows that do not leak, and which do not bulge or buckle in use.
Chemical mechanical planarization (CMP) polishing pads have contained one or more windows so that users can detect the status of a polishing operation from beginning to end. CMP polishing pads having an integral window, defined as a window incorporated or bonded into a polishing pad prior to the shaping of the pad or its surface, can be formed by known methods. In a molding and skiving process, the methods comprise embedding a piece of window stock into molded polyurethane cakes so that when individual CMP polishing pads are skived or cut from the cake after curing, the window is cut along with the pad. During the curing process, the block of window material will bond with the pad material to keep it in place. In such a process, the window is the exact thickness of the pad and a groove exclusion area must be incorporated into the grooving step to prevent marring the surface of the window. Thus, the pad is lathed or ground to include grooves with the one or more windows present. This requires a labor intensive method in which the window is protected. However, the mechanical force and heat generated by skiving invariably causes damage to the window surface and leads to window shrinkage and/or buckling (where a deformity is concave) or excessive bulging (where a deformity is convex). The force generating by lathing or grinding can also damage the windows and cause buckling. Another known method of making windows for CMP polishing pads is a plug in place (PIP) method wherein, after a CMP polishing pad has been made and grooved, an area is cut out of the CMP polishing pad to seat a window piece that has already been cut to a specified thickness and outer dimension. The adhesion of the window to the CMP polishing pad relies on a pressure sensitive adhesive (PSA), such as a synthetic rubber, acrylic hot melt, polyvinylacetate or cyanoacrylate plastisol to hold the window in place. This method can lead to CMP slurry leakage through the windows when the CMP polishing pads are in use.
U.S. Pat. No. 8,609,001 B2, to Pai et al, discloses methods for making CMP polishing pads having a detection window, the methods comprising forming a polishing layer with a detection window space without cutting the pad. The polishing layer is formed in the presence of a separable dummy detection window or mold protrusion section in an enclosed mold. After molding the polishing layer, removing the dummy detection window or mold protrusion section yields a polishing layer with a detection window space; a window precursor is filled into the detection window space and is cured. Separate curing of the window precursor is needed after removal of the dummy window or protrusion section. The process in Pai et al. suffers from the disadvantages of injection molding, which leads to uniformity problems within single moldings and difficulties in demolding; further, only a narrow range materials can be injection molded as they must be able to flow throughout the mold before curing and then cure well enough in the mold to allow for demolding.
The present inventors have sought to solve the problem of providing application or spray methods for making chemical mechanical polishing pads that have improved uniformity.
1. In accordance with the present invention, methods of making chemical mechanical planarization (CMP) polishing pads or layers comprise providing an open mold having a surface with a female topography that generates a flat or shaped CMP polishing layer surface and having held in place thereon one or more window pieces, mixing a liquid isocyanate component with a liquid polyol component to form a reaction mixture, preferably, a solvent free and substantially water free reaction mixture, spraying the reaction mixture onto the open mold while the one or more window pieces is held in place, with each window piece at a predefined location, followed by: curing the reaction mixture to form a gel polishing layer from the reaction mixture, demolding, and curing the gel polishing layer to form a polyurethane reaction product as a CMP polishing layer.
2. In accordance with the methods of the present invention as in item 1, above, wherein the one or more window pieces is masked or blocked on the back side away from the open mold surface, thereby preventing buildup of the reaction mixture on the masked or blocked side of the window pieces and eliminating the need for back side facing to expose the surface of the one or more window pieces.
3. In accordance with the methods of the present invention as in any one of items 1 or 2, above, wherein the reaction mixture has a gel time at 80° C. of from 2 to 600 seconds, or, preferably, from 5 to 300 seconds or, preferably, from 5 to 120 seconds.
4. In accordance with the methods of the present invention as in any one of items 1, 2, or 3, above, wherein the curing comprises initially curing to form the gel polishing layer at from ambient temperature to 130° C. for a period of from 30 seconds to 30 minutes, or, preferably, from 30 seconds to 5 minutes, demolding the gel polishing layer from the open mold, and then finally curing at a temperature from 60 to 130° C. for a period of 1 minutes to 16 hours, or preferably from 5 min to 15 minutes, to form a porous polyurethane reaction product as a CMP polishing layer having one or more endpoint detection windows and having a density ranging from 0.5 gm/cc to 1 gm/cc or, preferably, from 0.75 gm/cc to 0.95 gm/cc.
5. In accordance with the methods of the present invention as in any one of items 1, 2, 3, or 4, above, wherein the one or more window pieces comprises a polyurethane chosen from one formed from the reaction of a polyol with an aromatic, aliphatic or cycloaliphatic diisocyanate or polyisocyanate, or one formed from a isocyanate terminated urethane prepolymer or one formed from a two-component reaction mixture of an isocyanate component and a polyol component.
6. In accordance with the methods of the present invention as in any one of items 1, 2, 3, 4 or 5, above, wherein the one or more window pieces comprises a polyurethane chosen from (i) the product of a polyol component and an isocyanate component containing 2 wt. % of less of aromatic isocyanate groups, based on the total weight of the polyol in the polyol component and the isocyanate in the isocyanate component, and (ii) a polyurethane of a polyol component and an isocyanate terminated urethane prepolymer having from 5.5 to 9.5 wt % unreacted NCO group sand which is a reaction product of (a) an aromatic polyfunctional isocyanate, (b) a prepolymer polyol and, (c) a curative comprising: 0 to 90 wt % of a difunctional curative; and, 10 to 100 wt % of an amine initiated polyol curative having at least one nitrogen atom per molecule and an average of at least three hydroxyl groups per molecule; and, wherein the window piece exhibits a density of >1 g/cm3; a porosity of less than 0.1 vol %; a Shore D hardness of 35 to 65; and an elongation to break of <300%.
7. In accordance with the methods of the present invention as in item 6, above, wherein the liquid isocyanate component used to form the one or more window pieces comprises aliphatic diisocyanates, such as ethylene diisocyanate, 2,2,4-trimethyl hexamethylene diisocyanate and 1,6-hexamethylene diisocyanate; alicyclic diisocyanates, such as 1,4-cyclohexane diisocyanate, 4,4′-dicyclohexyl methane diisocyanate, isophorone diisocyanate, norbornane diisocyanate; and mixtures thereof.
8. In accordance with the methods of the present invention as in any one of items 1, 2, 3, 4, 5, 6, or 7, above, wherein the one or more window pieces has a hardness ranging from a Shore D hardness using Rex Type D gauge which features a Sharp Cone Point 35° indentor of from 15 to 90.
9. In accordance with the methods of the present invention as in any one of items 1, 2, 3, 4, 5, 6, 7, or 8, above, wherein the CMP polishing layer has a Shore D hardness using a Rex Type D gauge which features a Sharp Cone Point 35° indentor ranging from 15 to 90 or, preferably, from 20 to 70.
11. In accordance with the methods of the present invention as in any one of items 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, above, wherein each of the one or more window pieces is round, square or rectangular, or polygonal, and the open mold has a flat area or recess adapted to accommodate and having the same shape and outer dimension as each of the one or more window pieces, for example, the same diameter as a round window piece or the same length and width as a square or rectangular window piece.
12. In accordance with the methods of the present invention as in any one of items 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, above, wherein the one or more window pieces is held in place on the surface of the open mold by any of: applying vacuum to the underside of the one or more window pieces during spraying and curing to form a gel polishing layer, applying adhesive or double sided tape to the open mold where the one or more window pieces is placed on the open mold, and providing the open mold with a flat area or pocket that is slightly recessed from the surrounding surface of the open mold and sized to allow the one or more window pieces to fit tightly into place in the open mold.
13. In accordance with the methods of the present invention as in any one of items 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, above, wherein the open mold has a female topography that generates grooves in the resulting gel polishing layer and which topography does not generate any exclusion area around one or more window pieces.
14. In accordance with the methods of the present invention as in any one of items 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13, above, wherein one or more of the window pieces is placed on a window spacer having the same outer dimensions as the window piece and lying flush to the underside of the window piece during molding and curing, preferably, a releasable window spacer, such as one made of polytetrafluoroethylene.
15. In accordance with the methods of the present invention as in any one of items 1 to 14, above, the methods further comprising facing or lathing the CMP polishing layer on the back side of the window to expose the surface of the one or more window pieces.
16. In another aspect of the present invention, a method of using the CMP polishing layers made by the methods of any one of items 8 to 15, above, comprises providing a chemical mechanical polishing apparatus having a platen, a light source and a photosensor; providing at least one substrate; providing the chemical mechanical (CMP) polishing layer; installing the CMP polishing layer onto the platen with the CMP polishing layer surface exposed to the substrate; optionally, providing a polishing medium, such as an aqueous metal or semimetal oxide slurry, at an interface between the CMP polishing layer surface and the substrate; creating dynamic contact between the CMP polishing layer 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.
For purposes of this specification, the formulations are expressed in wt. %, unless specifically noted otherwise.
Unless otherwise indicated, conditions of temperature and pressure are ambient temperature and standard pressure. All ranges recited are inclusive and combinable.
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.
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.
Unless otherwise indicated, as used herein, the term “average molecular weight” of a polymer refers to the result determined by gel permeation chromatography against the indicated or, if not indicated, known appropriate standards, such as poly(ethylene glycol)s for polyols.
As used herein, the term “exclusion area” in the top or polishing side of a CMP polishing layer refers to a flat area surrounding an endpoint detection window.
As used herein, unless otherwise indicated, the term “gel time” means, for gel times of longer than 30 seconds, the result obtained by mixing a given reaction mixture at 80° C. in an VM-2500 vortex lab mixer (StateMix Ltd., Winnipeg, Canada) set at 1000 rpm for 30 s, while, at the same time setting a timer to zero and switching the timer on so that it starts at the end of mixing, immediately pouring the reaction mixture into an aluminum cup and placing the cup into a hot pot of a gel timer (Gardco Hot Pot™ gel timer, Paul N. Gardner Company, Inc., Pompano Beach, Fla.) set at 65° C., stirring the reaction mixture with a wire stirrer at 20 RPM and recording the gel time when the wire stirrer stops moving in the sample. For gel times shorter than 30 seconds, the vortex lab mixer is set at 80° C. and 1000 rpm and the reaction mixture is mixed for 2 seconds; the timer is set to start at the end of 2 seconds mixing, followed by pouring the reaction mixture into an aluminum cup, placing the cup into a hot pot of the gel timer set as above and recording the gel time. If a given reaction mixture cannot be poured after 2 seconds of mixing, it is assigned a gel time of 2 seconds.
As used herein, the term “ASTM” refers to publications of ASTM International, West Conshohocken, Pa.
As used herein, the term “polygonal” refers to a two dimensional boundary or shape having three (e.g. triangle) or more sides, preferably, from 3 to 12 sides.
As used herein, the term “polyisocyanate” means any isocyanate group containing molecule containing two or more isocyanate groups, and includes diisocyanates.
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.
As used herein, the term “reaction mixture” includes any non-reactive additives, such as surfactants and additives to lower the hardness of a polyurethane reaction product in the CMP polishing pad as measured according to ASTM D2240-15 (2015).
As used herein, the term “Shore D hardness” refer to the resistance to permanent indentation as defined by ASTM D2240 (2015). Data reported for the endpoint detection windows was determined according to ASTM D2240 (2015). The Rex Type D gauge uses a sharp cone point 35° indentor (Rex Gauge Company, Buffalo Grove, Ill.).
As used herein, the term “stoichiometry” of a reaction mixture refers to the ratio of molar equivalents of (free OH+free NH2 groups) to free NCO groups in the reaction mixture.
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.
As used herein, the term “solids” refers to any materials that remain in the polyurethane reaction product of the present invention; thus, solids include reactive and non-volatile additives that do not volatilize upon cure. Solids exclude water and volatile solvents.
As used herein, unless otherwise indicated, the term “substantially water free” means that a given composition has no added water and that the materials going into the composition have no added water. A reaction mixture that is “substantially water free” can comprise water that is present in the raw materials, in the range of from 50 to 2000 ppm or, preferably, from 50 to 1000 ppm, or can comprise reaction water formed in a condensation reaction or vapor from ambient moisture where the reaction mixture is in use.
As used herein, unless otherwise indicated, the term “viscosity” refers to the viscosity of a given material in neat form (100%) at a given temperature as measured using a rheometer, set at an oscillatory shear rate sweep from 0.1-100 rad/sec in a 50 mm parallel plate geometry with a 100 μm gap.
As used herein, unless otherwise indicated, the term “wt. % NCO” refers to the amount of unreacted or free isocyanate groups a given isocyanate or isocyanate-terminated urethane prepolymer composition.
As used herein, the term “wt. %” stands for weight percent.
The present invention enables a simple spray application method for making endpoint detection window containing porous polyurethane CMP polishing layers or pads from a two component reaction mixture. The spray application methods of making CMP polishing layers on open molds opens a wide formulation window of polyurethane forming compositions, such as those having a short gel time. Short gel times mean less cure and less chance for the cure to do damage to the window or the pad. And the methods enable the endpoint detection windows to become embedded into the pad as it is being cast, forming a strong bond with the polishing layer material. In addition, curing the polishing layer material and not the window pieces last permits better bonding as the material being cured surrounds the window pieces. Overall, the methods of the present invention allow for the making of leak free endpoint detection windows and prevents windows from buckling, bulging or popping out of the surface of the CMP polishing pads.
The methods of the present invention enable the formation of CMP polishing layers or pads having endpoint detection windows in any configuration. The present invention provides, for example, simple methods for making CMP polishing layers having grooves in the polishing surface of the extending right up to the window edge, i.e. with no window exclusion area. Further, the methods of the present invention enable CMP polishing layers to have many windows of customized and variable configurations in any pad, including different shapes, sizes, thicknesses, window materials, and the presence or lack of exclusion areas.
Enabling integral window formation in the methods of the present invention for making CMP polishing pads allows for the polishing pads to be compatible with more CMP polishing systems that have endpoint detection. The methods of the present invention can be adjusted to change the relation of the window surface with the CMP pad polishing surface. In addition, the exclusion area around the window can be changed by changing the mold used to create the window. A mask or block can be used on the back side of the window when creating the polishing pad. This prevents deposition of the pad material on the back side of the window for either the top pad or the sub pad, eliminating the need for back side facing to expose the window.
The methods of the present invention enable the provision of CMP polishing layers having one or more endpoint detection windows containing an eddy current sensor, such as a Real Time Profile Control™ sensor (Applied Materials, Santa Clara, Calif.).
Preferably, one or more endpoint detection window pieces are arranged on a flat or recessed portion of an open mold which is slightly recessed from the surrounding mold surface so that the resulting endpoint detection window protrudes slightly from the CMP polishing layer or pad. Such a slight bulge is desirable so the endpoint detection window will be planarized in use and no pocket of slurry will forms over the window in use.
Preferably, the methods of the present invention comprise providing an open mold with a topography to create one or more endpoint detection windows having a recessed exclusion area, such as a groove around the window to direct slurry flow during polishing, and having the window in a coplanar relationship with the recessed area or the land area of the CMP polishing layer surface.
Preferably, so that an endpoint detection window is left untouched during pad conditioning or until polishing occurs, the methods of the present invention comprise providing an open mold with a topography to create one or more endpoint detection windows having no exclusion area and the window slightly recessed from the land areas of the CMP polishing layer surface.
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The CMP polishing pads of the present invention are formed by spray application methods which enable higher throughput and lower cost. Porosity is introduced into the pad by spraying the reaction mixture.
Mixing to form the reaction mixture of the present invention can be achieved by high pressure impingement mixing inside an internal chamber, or low pressure static mixing inside a static mixer.
In the methods of the present invention, spraying comprises discharging a stream of the reaction mixture from the open end of the internal chamber under pressure, such as an airless spray gun or device equipped with a nozzle of the desired orifice size or a static mixer equipped with a nozzle and an air blast cap or an impingement mixer equipped with inlets for two components and having a downstream nozzle or opening, and through a narrow orifice or nozzle, preferably, a round orifice having diameter of from 0.5 to 2.0 mm. In the airless or airblast spraying, no air or gas and no blowing agents, including chemical or mechanical blowing agents, is added to the reaction mixture.
In airblast spraying, a suitable static mixer includes an air blast cap over a nozzle located at the downstream end of a static mixer. A suitable nozzle is equipped with an atomizing air inlet or air blast cap surrounding the outside of the nozzle, whereby a stream of air flows past the tip of the nozzle and then axially along the discharged stream of the reaction mixture. Atomization is produced by ejecting a reaction mixture, still under high pressure, through a narrow orifice to create pores from the ambient air through which the fluid droplets travel from the spray tip of the device to the substrate
Spraying methods can include spraying gas pressurized reaction mixtures from a mixing chamber, such as an impingement mixer, having a nozzle at its downstream end. The gas pressurized mixtures incorporate air or gas to introduce porosity in the gel polishing layer and resulting CMP polishing layer. In such methods, the gas pressure in the gas pressurized reaction mixtures ranges well above ambient pressure, such as from 7000 to 28,000 kPa.
In air blast cap spraying, the reaction mixture is spray at or slightly above ambient pressure. Accordingly, in such methods, the reaction mixture can further comprise microelements such as hollow polymeric microspheres to introduce porosity into the CMP polishing layer. A suitable spray device is the Nordson Series 160AA disposable static mixer equipped with a Nordson Air Cap™ air blast assembly, Nordson EFD, Providence, R.I.
In the internal chamber of airless spray guns, the pressure at which each component is injected ranges from, for example, 7500 to 18,000 kPa (1100 to 2600 psi) is high enough to insure homogeneous mixing. The upper limit of the pressure is determined by the limits of the equipment; however, it is preferably kept low so that density of the resulting CMP polishing pad stays above the lower acceptable limits. Examples of suitable equipment are a Graco Probler™ P2 two component spray gun (Graco, Minneapolis, Minn.), fed by a high pressure metering pump or other Graco Airless spray guns equipped with a spray head having an orifice of the desired diameter and connected to a pump or metering device that can deliver the two component reaction mixture to the spray gun at the desired pressure for making the CMP polishing pads of the present invention.
The two leads, one for each of the liquid polyol component and the liquid isocyanate component, going into a gas pressurized spray device, an airblast nozzle static mixer device or airless spray gun in accordance with the present invention can comprise meter or delivery systems, such as a pair of pneumatically driven positive displacement piston pumps. An example of this equipment is commercially available as the Posiratio™ Mini PRM meter (Liquid Control Corp, Lake Bluff, Ill.).
In accordance with the methods of the present invention, the spraying of a stream of the reaction mixture onto an open mold can comprise over spraying the mold, followed by initially curing the reaction mixture to form a gel polishing layer and removing the gel polishing layer from the mold, and curing the gel polishing layer to form a CMP polishing layer or pad, and then punching or cutting the perimeter of the to the desired diameter of the CMP polishing pad.
Spraying can be automated via an airless spray gun or other spray device held in place by a mechanical actuator that enables movement in a plane parallel to the surface of the open mold, such as, for example, a programmable electronic actuator having mechanical linkage enabling the programmed movement, preferably, a robot having a four axis arm capable of XY axial movement or a six axis arm capable of XYZ axial movement and rotational movement.
The open mold of the present invention is made of or is lined with a non-stick material or urethane releasing surface, such as polytetrafluoroethylene. Preferably, the mold is machined to form a female topography so that the resulting molded polyurethane reaction product has a desired groove configuration.
In accordance with the methods of the present invention each of the liquid polyol component and the liquid isocyanate component may be separately preheated, respectively, to a temperature T1 and T2, of from 30 to 100° C. before mixing it to form a reaction mixture.
In accordance with the methods of the present invention, upon mixing the liquid polyol component at temperature T1 and the liquid isocyanate component at temperature T2, each has a viscosity of from 1 to 1000 cPs or, preferably, from 100 to 500 cPs.
The resulting CMP polishing pad has an average pore diameter of from 10 to 80 μm, or, preferably, 10 to 40 μm.
The methods of the present invention enable the manufacturing a CMP polishing pad suitable for planarizing at least one of semiconductor, optical and magnetic substrates.
The methods of the present invention also enable the formation of stacked CMP polishing pads wherein the reaction mixture is discharged onto an already formed base surface of a chemical mechanical polishing layer having one or more window pieces arranged therein, and allowing the reaction mixture to solidify on the base surface of the chemical mechanical polishing layer to form a subpad; wherein the subpad is integral with the chemical mechanical polishing layer and the subpad has a subpad porosity that is different from that of the chemical mechanical polishing layer; and, wherein the chemical mechanical polishing layer has a porosity of 10 vol. % and a polishing surface adapted for polishing a substrate. The window pieces will be thicker than the base surface so as to accommodate the CMP polishing layer on top. The window pieces are held in place in the formation of the base surface in the same manner as they are held in place in the formation of a polishing layer.
In the methods of making a stacked pad in accordance with the present invention, the base surface of the CMP polishing layer can be formed by mixing of the two component liquid polyol component and liquid isocyanate component to form a base layer reaction mixture, followed by discharging that reaction mixture onto the surface of an open mold and curing in the mold to form a base surface or layer, followed by discharging onto the base surface the reaction mixture of the present invention and curing as in items 1 and 4, above. All such discharging in conducted in the same manner as in items 1 to 15, above, with the exception that the reaction mixtures differ and the layers they form are separate.
The reaction mixtures of the present invention comprise no solvent, and no added water except that up to 2000 ppm of water can be added to the liquid polyol component to facilitate pore formation.
The reaction mixture of the present invention can comprise a very rapid curing composition wherein the isocyanate component and the polyol component can gel in a gel time as short as 2 seconds or as long as 600 seconds, or, preferably, from 10 to 300 seconds. The reaction to form a polyurethane has to be slow enough that the reaction mixture can be mixed in a static or impingement mixer after combining the two components. The only limit on gel time is that the reaction mixture must react slowly enough so as not to clog the mix head in which it is mixed, and to adequately fill a mold when applying it to the mold surface.
The liquid isocyanate component of the present invention may comprise any of a diisocyanate, triisocyanate, isocyanurate isocyanate-terminated urethane prepolymer, or mixtures thereof. Preferably, the liquid isocyanate component comprises aromatic polyisocyanates, such as an aromatic diisocyanate chosen from methylene diphenyl diisocyanate (MDI); toluene diisocyanate (TDI); napthalene diisocyanate (NDI); paraphenylene diisocyanate (PPDI); o-toluidine diisocyanate (TODI); a modified diphenylmethane diisocyanate, such as a carbodiimide-modified diphenylmethane diisocyanate, an allophanate-modified diphenylmethane diisocyanate, a biuret-modified diphenylmethane diisocyanate: an aromatic isocyanurate, such as the isocyanurate of MDI; a linear isocyanate-terminated urethane prepolymer, for example, a linear isocyanate-terminated urethane prepolymer of MDI or an MDI dimer with one or more isocyanate extenders.
Suitable aromatic polyisocyanates can be selected from the group consisting of 2,4-toluene diisocyanate; 2,6-toluene diisocyanate; 4,4′-diphenylmethane diisocyanate; naphthalene-1,5-diisocyanate; toluidine diisocyanate; para-phenylene diisocyanate; xylylene diisocyanate; and, mixtures thereof
Suitable isocyanate extenders are ethylene glycol; 1,2-propylene glycol; 1,3-propylene glycol; 1,2-butanediol; 1,3-butanediol; 2-methyl-1,3-propanediol; 1,4-butanediol; neopentyl glycol; 1,5-pentanediol; 3-methyl-1,5-pentanediol; 1,6-hexanediol; diethylene glycol; dipropylene glycol; tripropylene glycol, and mixtures thereof.
The liquid isocyanate component of the present invention can have a very high unreacted isocyanate (NCO) concentration of from 10 to 40 wt. %, or, preferably, from 15 to 35 wt. %, based on the total solids weight of the aromatic isocyanate component.
Suitable isocyanate-terminated urethane prepolymers are low free isocyanate terminated urethane prepolymers having less than 0.1 wt % free toluene diisocyanate (TDI) monomer content.
The liquid polyol component of the present invention can be anyone or more diols or polyether polyols having terminal hydroxyl groups, such as diols, polyols, polyol diols, copolymers thereof and mixtures thereof. Preferably, one or more polyol is chosen from polyether polyols (e.g., poly(oxytetramethylene)glycol, poly(oxypropylene)glycol and mixtures thereof); polycarbonate polyols; polyester polyols; polycaprolactone polyols; mixtures thereof; and, mixtures thereof with one or more low molecular weight polyols selected from the group consisting of ethylene glycol; 1,2-propylene glycol; 1,3-propylene glycol; 1,2-butanediol; 1,3-butanediol; 2-methyl-1,3-propanediol; 1,4-butanediol; neopentyl glycol; 1,5-pentanediol; 3-methyl-1,5-pentanediol; 1,6-hexanediol; diethylene glycol; dipropylene glycol; and, tripropylene glycol.
More preferably, the one or more polyol of the liquid polyol component of the present invention is chosen from polytetramethylene ether glycol (PTMEG); ester containing polyols (such as ethylene adipates, butylene adipates); polypropylene ether glycols (PPG); polycaprolactone polyols; copolymers thereof; and, mixtures thereof.
Suitable polyols can include a high molecular weight polyol having a number average molecular weight, MN, of 2,500 to 100,000. Preferably, the high molecular weight polyol used has a number average molecular weight, MN, of 5,000 to 50,000, or, more preferably 7,500 to 25,000; most preferably 10,000 to 12,000). Such a high molecular weight polyol preferably has an average of three to ten hydroxyl groups per molecule.
The curative of the present invention is a polyamine, or, preferably, an aromatic polyamine, such as aromatic diamines and aromatic polyamines. The curatives must be slow enough to allow the mixing of two component reaction mixture. The curatives must, when combined with the aromatic isocyanate component and the polyol component, cause gelling (so the reactive mixture combination no longer flows) of at least 2 seconds, or, preferably, at least 3-5 seconds. Accordingly, the curatives of the present invention do not comprise more than 10 wt. %, as solids, of N,N-primary alkylaryl diamines, but may comprise N,N-secondary or tertiary alkyl diamines.
More preferably, the curative of the present invention comprises one or more aromatic polyamines selected from the group consisting of dimethylthiotoluenediamine; trimethyleneglycol di-p-aminobenzoate; polytetramethyleneoxide di-p-aminobenzoate; polytetramethyleneoxide mono-p-aminobenzoate; polypropyleneoxide di-p-aminobenzoate; polypropyleneoxide mono-p-aminobenzoate; 1,2-bis(2-aminophenylthio)ethane, toluenediamines, such as diethyltoluenediamine, 5-tert-butyl-2,4-toluenediamine, 3-tert-butyl-2,6-toluenediamine, 5-tert-amyl-2,4-toluenediamine, 3-tert-amyl-2,6-toluenediamine, 5-tert-amyl-2,4-chlorotoluenediamine, and 3-tert-amyl-2,6-chlorotoluenediamine; methylene dianilines, such as 4,4′-methylene-bis-aniline; isophorone diamine; 1,2-diaminocyclohexane, bis(4-aminocyclohexyl)methane, 4,4′-diaminodiphenyl sulfone; m-phenylenediamine; xylene diamines; 1,3-bis(aminomethyl cyclohexane); and mixtures thereof, preferably, dimethylthiotoluenediamine (DMTDA).
The curative of the present invention may comprise from 5 to 20 wt. %, or, preferably, from 10 to 20 wt. %, or more preferably 13-17 wt. %, based on the total solids weight of the reaction mixture.
To increase the reactivity of the polyol component with the diisocyanate or polyisocyanate, a catalyst may be used. However, reaction mixtures in accordance with the present invention may not comprise any added catalyst. Suitable catalysts include any known catalysts to those skilled in the art, for example, oleic acid, azelaic acid, dibutyltindilaurate, tin octoate, bismuth octoate, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), tertiary amine catalysts, such as Dabco™ TMR catalyst, triethylenediamine, such as DABCO™ 33 LV, and mixtures of the above.
Generally, the stoichiometric ratio of the sum of the total moles of amine (NH2) groups and the total moles of hydroxyl (OH) groups in the reaction mixture to the total moles of unreacted isocyanate (NCO) groups in the reaction mixture ranges from 0.8:1.0 to 1.1:1.0, or, preferably, from 0.90:1 to 1.05:1.0.
Preferably, the liquid polyol component contains a sufficient amount of from 0.1 to 1.0 wt. % or, preferably, from 0.2 to 0.8 wt. %, based on the total solids weight of the reaction mixture, of a nonionic surfactant, preferably, an organopolysiloxane-co-polyether surfactant to facilitate growth of pores within the reaction mixture.
The specific gravity of the resulting CMP polishing pad ranges from 1.17 down to 0.5, preferably, from 0.7 to 1.0. As porosity increases, the bulk properties of the CMP polishing pad diminish, removal rate (RR) goes up, but planarization efficiency (PE) goes down.
The chemical mechanical polishing pads made by the methods of the present invention can comprise just a polishing layer of the polyurethane reaction product or the polishing layer stacked on a subpad or sub layer. The polishing pad or, in the case of stacked pads, the polishing layer of the polishing pad of the present invention is useful in both porous and non-porous or unfilled configurations.
Preferably, the polishing layer used in the chemical mechanical polishing pad of the present invention has an average thickness of from 500 to 3750 microns (20 to 150 mils), or, more preferably, from 750 to 3150 microns (30 to 125 mils), or, still more preferably, from 1000 to 3000 microns (40 to 120 mils), or, most preferably, from 1250 to 2500 microns (50 to 100 mils).
The chemical mechanical polishing pad of the present invention optionally further comprises at least one additional layer interfaced with the polishing layer. Preferably, the chemical mechanical polishing pad optionally further comprises a compressible sub pad or base layer adhered to the polishing layer. The compressible base layer preferably improves conformance of the polishing layer to the surface of the substrate being polished.
The polishing layer of the chemical mechanical polishing pad of the present invention has a polishing surface adapted for polishing the substrate. 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 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 and chosen from curved grooves, linear grooves, perforations and combinations thereof. Preferably, the groove pattern comprises a plurality of grooves. More preferably, the groove pattern is selected from a groove design, such as one 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.
In accordance with the methods of making polishing pads in accordance with the present invention, chemical mechanical polishing pads can be molded with a macrotexture or groove pattern in their polishing surface to promote slurry flow and to remove polishing debris from the pad-wafer interface. Such grooves may be formed in the polishing surface of the polishing pad from the shape of the mold surface, i.e. where the open mold has a female topographic version of the macrotexture.
The chemical mechanical polishing pad of the present invention can be used for polishing a substrate selected from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate. For example, the CMP polishing pads of the present invention are efficacious for interlayer dielectric (ILD) and inorganic oxide polishing. For purposes of the specification, the removal rate refers to the removal rate as expressed in A/min.
Preferably, the method of polishing a substrate of the present invention, comprises: providing a substrate selected from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate (preferably a semiconductor substrate, such as a semiconductor wafer); providing a chemical mechanical polishing pad according to the present invention; creating dynamic contact between a polishing surface of the polishing layer and the substrate to polish a surface of the substrate; and, conditioning of the polishing surface with an abrasive conditioner.
Conditioning the polishing pad comprises bringing a conditioning disk into contact with the polishing surface either during intermittent breaks in the CMP process when polishing is paused (“ex situ”), or while the CMP process is underway (“in situ”). The conditioning disk has a rough conditioning surface typically comprised of imbedded diamond points that cut microscopic furrows into the pad surface, both abrading and plowing the pad material and renewing the polishing texture. Typically the conditioning disk is rotated in a position that is fixed with respect to the axis of rotation of the polishing pad, and sweeps out an annular conditioning region as the polishing pad is rotated.
The present invention will now be described in detail in the following, non-limiting Examples:
In the following examples, unless otherwise stated, all units of pressure are standard pressure (˜101 kPa) and all units of temperature are room temperature (21-23° C.).
Notwithstanding other raw materials disclosed below, the following raw materials were used in the Examples:
Ethacure™ 300 curative: Dimethylthiotoluenediamine (DMTDA), an aromatic diamine (Albemarle, Charlotte, N.C.).
Voranol™ V5055HH polyol: Multifunctional polyether polyol (OH Eq. wt 2000), high molecular weight ethylene oxide capped propylene oxide polyol with functionality=6 having a number average molecular weight, MN, of 12,000 (The Dow Chemical Company, Midland, Mich. (Dow)).
MDI prepolymer: A linear isocyanate-terminated urethane prepolymer from MDI and the small molecules dipropylene glycol (DPG) and tripropylene glycol (TPG), with ˜23 wt. % NCO content and equivalent weight of 182. 100 wt. % of this MDI prepolymer is treated as hard segment.
Niax™ L5345 surfactant: A non-ionic organosilicon surfactant (Momentive, Columbus, Ohio).
DABCO 33 LV amine catalyst (Air Products, Allentown, Pa.) made from diazobicyclononane (triethylene diamine), DABCO 33 LV is a blend of 33 wt. % triethylene diamine and 67 wt. % dipropylene glycol.
Unilink™ 4200 curative: N,N′-dialkylamino-diphenylmethane (Dorf Ketal, Stafford, Tex.) PTMEG####: poly(THF) or polytetramethylene glycol, made via the ring-open polymerization of tetrahydrofuran (THF), and sold as PolyTHF™ polyol (BASF, Leverkusen, DE). The number (####) following PTMEG is the average molecular weight as reported by the manufacturer.
The following abbreviations appear in the Examples:
PO: propylene oxide/glycol; EO: ethylene oxide/glycol; MDI: methylene diphenyl diisocyanate TDI: toluene diisocyanate (˜80% 2,4 isomer, ˜20% 2,6 isomer); DEG: diethylene glycol; DPG: dipropylene glycol; pbw: parts by weight.
2-Component Air Spray System:
An axial mixing device (a MicroLine 45 CSM, Hennecke GmbH, Sankt Augustin, DE) having a (P) side liquid feed port, an (I) side liquid feed port and four tangential pressurized gas feed ports. The poly side (P) liquid component and the iso side (I) liquid component were fed to the axial mixing device through their respective feed ports with a (P) side charge pressure of 16,500-18,500 kPa, an (I) side charge pressure of 15,500-17,500 kPa. The flow ratio of (I)/(P) is defined in each example. The pressurized gas was fed through the tangential pressurized gas feed ports with a supply pressure of 830 kPa to give a combined liquid component to gas mass flow rate ratio through the axial mixing device of 3.7:1 to form a combination. The combination was discharged from the axial mixing device toward a mold to form a cake on the mold base.
In the working example below, integral window CMP polishing pads were created using an air assisted spray device equipped with an impingement mixer to receive, separately, the two components of a polyurethane forming reaction mixture with each component from a tank equipped with a line and a pump leading to the impingement mixer. The spray set up is detailed in the following paragraph. The reaction mixture was sprayed in an X-Y Pattern with an 80 mm wide spray fan. Total spray time to spray a polishing pad was 135 seconds.
The impingement mixer used to form the reaction mixture was mixed from 2 tanks. The first tank (tank 1) contained a liquid polyol component pumped at a flow rate of 15.14 Us (4 g/s) at 48.9° C. (120° F.). Tank 1 contained: Ethacure™ 300 curative (18.816 pbw); PTMEG 650 (49.434 pbw) Niax™ L5345 (1.295 pbw) surfactant; and DABCO 33 LV (0.455 pbw) catalyst. Tank 2 contained liquid MDI prepolymer component pumped at a flow rate of 13.25 L/s (3.5 g/s) at 48.9° C. (120° F.).
The mold surface was a polytetrafluorethylene (PTFE) sheet 6.35 mm (0.25″) thick; the open mold had a female surface adapted to yield a polishing pad with a K7+R32 groove pattern of 0.51 mm wide×0.76 mm deep×1.78 mm pitch annular concentric grooves and 32 0.76 mm wide×0.76 mm deep grooved radii the molds having a 19.1 mm×57.2 mm×4.6 mm (0.75″×2.25″×0.18″) polytetrafluorethylene window spacer. Unless otherwise indicated, the resulting window had the same thickness as the polishing pad.
The window materials used were as indicated below in Table A-1. In the Examples below, the window pieces were formulated from the indicated Formulation in Table A-1, below, and then cast into the given shape and size by degassing the formulation under a vacuum of 1016 millibar for 5 minutes and cured at 50° C. for 5 hours, and then 110° C. for 19 hours, followed by cutting them to the desired thickness. The window pieces were located at 190.5 mm (7.5″ from center of the mold) and were present in a window pocket. When the polyurethane forming two-component material was sprayed, the window bonded to the pad matrix and was held in place during curing. Afterwards, the pad was faced on a lathe using circular lathe cutting tool to expose the back surface of the window.
100%
100%
100%
CMP polishing pads were made with 2 round window materials, as indicated in Table A-1, above, one hard formulation and one soft formulation, with each window having a 6 mm (0.24″) radius and a thickness of 2 mm (0.08″). Each of the hard and soft windows was adhered to a polytetrafluoroethylene coated base mold and a porous polyurethane with a Shore D hardness of 39 and specific gravity of 0.67 was cast from a two-component reaction mixture to a height equal to the window thickness.
In Example 1-1, the CMP polishing pad comprised a hard window insert of Formulation 3 and a porous polyurethane pad cast with a spraying process to a 2 mm (0.08″) thickness. In Example 1-2, the CMP polishing pad comprised the same polyurethane formulation and thickness of Example 1-1 but with a soft window insert of Formulation 1.
The comparative in Example 1-B used a commercially available K2010H™ pad made from a porous polyurethane formulation with a Shore D hardness of 15 and specific gravity of 0.8 and windows of Formulation 1; however, the polyurethane was poured into a 914.4 mm (36″) mold to a height of approximately 101.6 mm (4″), which was then cured at 180° C. for a period of 960 minutes and skived to approximately 2 mm (0.08″ thick pads). The resulting pads were not grooved.
Window Curvature:
Was determined using a 3 point measurement system utilizing a Mitutoyo™ 542-222 linear thickness gauge (Rex Gauge, Buffalo Grove, Ill.) digital thickness gauge and Mitutoyo™ 542-075A digital display (Rex Gauge). Polishing pad samples with integral windows were placed on a flat table surface. Each window was measured on the top, polishing surface at 3 locations: the center point of the window and the intersections of the edge of the window and the diameter. Curvature was calculated by averaging the outer edge points and subtracting it from the center point to determine the general curvature of the window. Positive values indicate a bulge or convex window shape while negative values indicate a recess or concave shape. Results are shown in Table 1, below.
Trials were conducted in the same manner as Example 1 above, except that the porous polyurethane pad material was changed to a harder pad formulation with a Shore D hardness of 57 and specific gravity of 0.8. Window curvature measurements can be found in Table 2, below.
The comparative in Example 2-A used the commercially available IK4250H™ porous polyurethane formulation with a Shore D hardness of 60 and specific gravity of 0.8 and windows of Formulation 3 but the polyurethane was poured into a 914.4 mm (36″) mold to a height of approximately 101.6 mm (4″), which was then cured at 180° C. for a period of 960 minutes and skived to approximately 2 mm (0.08″ thick pads). The resulting pads were not grooved.
As shown in Tables 1 and 2 above, the methods of the present invention enable one to make CMP polishing pads with dramatically flatter or more level window pieces regardless of the hardness of the pad matrix material. Further, in the methods of the present invention both hard and soft pad materials can accommodate hard and soft windows without buckling or bulging.
