High removal rate chemical mechanical polishing pads and methods of making

Abstract

A chemical mechanical polishing pad for polishing a semiconductor substrate is provided containing a polishing layer that comprises a polyurethane reaction product of a reaction mixture comprising (i) one or more diisocyanate, polyisocyanate or polyisocyanate prepolymer, (ii) from 40 to 85 wt. % based on the total weight of (i) and (ii) of one or more blocked diisocyanate, polyisocyanate or polyisocyanate prepolymer which contains a blocking agent and has a deblocking temperature of from 80 to 160 C., and (iii) one or more aromatic diamine curative. The reaction mixture has a gel time at 80 C. and a pressure of 101 kPa of from 2 to 15 minutes; the polyurethane reaction product has a residual blocking agent content of 2 wt. % or less; and the polishing layer exhibits a density of from 0.6 to 1.2 g/cm.sup.3.

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 a polishing layer adapted for polishing the substrate which is a polyurethane reaction product of a reaction mixture consisting essentially of (i) polytetramethylene ether glycol polyisocyanate prepolymer, wherein the prepolymer has an unreacted 8 to 10 wt. % NCO content, in the amount of from 15 to 60 wt. % polyisocyanate prepolymer, based on the total weight of all diisocyanates, polyisocyanates and polyisocyanate prepolymers in the reaction mixture, (ii) blocked polyisocyanate prepolymer that contains 3,5-dimethylpyrazole blocking agent and has a deblocking temperature of from 80 to 160 C. in the amount of from 40 to 85 wt. % based on the total weight of all diisocyanates, polyisocyanates and polyisocyanate prepolymers in the reaction mixture, and (iii) 4,4-methylenebis(3-chloro-2,6-diethylaniline) curative, wherein the reaction mixture has a gel time at 80 C. and a pressure of 101 kPa of from 2 to 15 minutes, further wherein, the polyurethane reaction product has a residual blocking agent content of 2 wt. % or less and, still further wherein, the polishing layer exhibits a density of from 0.6 to 1.2 g/cm.sup.3 and wherein the polishing layer includes polymeric microspheres and the polymeric microspheres comprise shell walls of either polyacrylonitrile or polyacrylonitrile copolymer.

2. The CMP polishing pad as claimed in claim 1, wherein the polishing pad has a free isocyanate content of 0.1 wt. %, or less, based on the total weight of the polyurethane reaction product.

3. The CMP polishing pad as claimed in claim 1, wherein the stoichiometric ratio of the sum of the amine (NH.sub.2) groups and the hydroxyl (OH) groups) in the (iii) amine curative plus any free hydroxyl groups in the reaction mixture to the unreacted and blocked isocyanate groups in reaction mixture is from 0.80:1 to 1.20:1.

Description

COMPARATIVE EXAMPLE 1

(1) 98.8 g of blocked prepolymer 1 (5.88 wt. % blocked NCO content) preheated to 70 C. was mixed with 22 g of MCDEA (0.95 equiv. NH.sub.2 groups per total equiv. NCO groups in the reaction mixture) preheated to 100 C. in a high speed mixer, DAC 600.1 FVZ, (FlackTek speed mixer, FlackTek Inc., Landrum, S.C.) at 2300 rpm for 30 s. The material was then cast in an open circular (10.16 cm diameter) mold and cured at 120 C. for 17 h. The resulting 0.36 cm thick plaque did not show any warping or cracks. Tensile data was collected according to ASTM D-1708-13 (2013) this material showed an ultimate elongation of 446% and a tensile strength of 18.8 MPa.

EXAMPLE 1

(2) 31 g of blocked prepolymer 1 (5.95 wt. % blocked NCO content) preheated to 80 C. was mixed with 7 g of MCDEA (0.95 equiv NH.sub.2 groups per total equiv. of NCO groups in the reaction mixture) preheated to 100 C. in a high speed mixer, DAC 600.1 FVZ, FlackTek speed mixer (FlackTek Inc.) at 2300 rpm for 60 s. The material was then cast in a square (10.16 cm10.16 cm) open mold and cured at 120 C. for 22 h. The resulting (0.15 cm) thick plaque showed a few cracks. Tensile data was collected according to ASTM D-1708, this material showed an ultimate elongation of 474% and a tensile strength of 48 MPa

(3) Example 1 demonstrates that curing a material for a longer period above the deblocking temperature of the blocking agent leads to improved properties, including a boost in tensile strength. This is because the blocking agent is released from the matrix and does not plasticize the resulting product.

COMPARATIVE EXAMPLE 2

(4) 50 g of blocked prepolymer 2 preheated to 80 C. was mixed with 15.8 g of MCDEA (0.95 equiv NH.sub.2 groups per total equiv. of NCO groups in the reaction mixture) (melted at 110 C. then cooled to 80-90 C.) in a high speed mixer, DAC 600.1 FVZ, FlackTek speed mixer (FlackTek Inc.) at 2300 rpm for 60 s. The material was then cast in a square (10.12 cm10.12 cm) open mold and cured at 120 C. for 22 h. The resulting 0.15 cm thick plaque showed a few cracks.

(5) Comparative Example 2 shows that warping/cracking occurs when the reaction mixture comprises more than the inventive proportion of one or more blocked diisocyanate, polyisocyanate or polyisocyanate prepolymer.

COMPARATIVE EXAMPLE 3

(6) 50 g of blocked prepolymer 2 heated to 80 C. was mixed with 7.5 g of Ethacure-100 (0.95 equiv NH.sub.2 groups per total equiv. NCO groups in the reaction mixture) diamine curative heated at 80 C. in a high speed mixer, DAC 600.1 FVZ, FlackTek speed mixer (FlackTek Inc.) at 2300 rpm for 60 s. The material was then cast in a square (10.12 cm10.12 cm) open mold and cured at 120 C. for 20 h. The resulting 0.15 cm. thick plaque was warped but did not show cracks.

(7) As shown in Comparative Example 3, above, a warping and/or cracking phenomenon occurs when too much of a blocked diisocyanate, polyisocyanate or to polyisocyanate prepolymer is used to make a casting.

EXAMPLE 2

(8) 5 g of Adiprene LF 750 D (8.75 wt. % NCO) polyisocyanate prepolymer was mixed with 18.8 g of blocked prepolymer 2 to furnish an 80 wt. % blocked prepolymer. This material was heated to 50 C. and then mixed with 8.5 g of MCDEA (melted at 110 C. then cooled to 90-100 C.) (1.05 equiv NH.sub.2 groups per total equiv. of NCO groups in the reaction mixture) in a high speed mixer, DAC 600.1 FVZ, FlackTek speed mixer (FlackTek Inc.) at 2300 rpm for 60 s. The material was then cast in a square (10.12 cm10.12 cm) open mold and cured at 120 C. for 23 h. The resulting molding was a flat square plaque without defects. Accordingly, the present invention allows for the synthesis of defect free elastomers from the reaction mixtures of the present invention including amines that would be too reactive without the incorporation of blocking agent. For example, warping and cracks can be avoided with use of a mixture of a limited amount of polyisocyanate prepolymer with a blocked polyisocyanate prepolymer and MCDEA as a diamine curative in accordance with the present invention.

COMPARATIVE EXAMPLE 4

(9) 25 g of Adiprene LF 750 D (8.85 wt. % NCO) polyisocyanate prepolymer heated to 60 C. was mixed with 9.7 g of MCDEA heated at 100 C. (0.95 equiv NH.sub.2 per blocked NCO) in a high speed mixer, DAC 600.1 FVZ, FlackTek speed mixer (FlackTek Inc.) at 2300 rpm for 60 s. The material in the cup gelled less than 90 s after mixing was completed. The gel time is too rapid for the synthesis of CMP pads which typically require at least 2 min of open time for casting.

EXAMPLE 3

(10) 4 g of Adiprene LF 750 D (8.75 wt. % NCO) polyisocyanate prepolymer was mixed with 16.1 g of blocked prepolymer 2 to furnish a mixture containing 80 wt. % of blocked prepolymer. This material was heated to 50 C. and then mixed with 6.6 g of MCDEA (melted at 110 C. then cooled to 80-90 C.) in a high speed mixer, DAC 600.1 FVZ, FlackTek speed mixer (FlackTek Inc.) at 2300 rpm for 60 s. This material was then loaded onto an AR2000 rheometer (TA Instruments, New Castle Del.) and the viscosity was recorded under isothermal conditions at 85 C. under constant shear of 10/s for 6 min. The initial viscosity of the mixture was 2131 mPa.Math.s. After 5.5 min the viscosity was 9008 mPa.Math.s

(11) As Comparative Example 4 and Example 3 demonstrate, mixtures of blocked and unblocked prepolymers have an increased open time or gel time relative to completely unblocked systems that allows them to be used in the synthesis of CMP pads; whereas use of just a polyisocyanate prepolymer results in a composition that gels too rapidly for use in making polishing pads.

EXAMPLE 4: Pad According to the Present Invention

(12) 700 g of blocked prepolymer 2, DMP blocked Adiprene LF750D polyisocyanate prepolymer heated to 80 C., was mixed to 500 g of Adiprene LF750D polyisocyanate prepolymer heated to 60 C. and 10.5 g of Expancel 920DE40d30 fluid filled microspheres in a Vortex mixer, (VM-2500 StateMix Ltd, Winnipeg, Canada) at 1000 rpm for 30 s, forming a preblend containing about 58 wt. % of blocked prepolymer 2 and having a stoichiometry of total NH.sub.2 groups to total NCO groups of 1.05:1. The preblend was then mixed with 491 g of MCDEA heated to 110 C. in the Vortex mixer for another 30 s at 1000 rpm. The final mixture was drawn down on a 914 by 914 mm Teflon polymer (DuPont, Wilmington, Del.) coated plate with a gap of 2 mm formed by a Teflon polymer coated bar. The drawn-down pad was cured in an oven at 104 C. for 16 h, and later post-cured for an additional 24 h at 120 C. to remove residual blocking agent.

(13) The post cured pad was conditioned at 23 C. and 50% relative humidity for 5 days before testing for mechanical properties. Tensile properties were obtained at 500 mm/min cross-head speed using an Alliance RT/5 materials testing system (MTS Systems Corp., Berlin, N.J.). Dynamic properties were tested in rectangular shear torsion mode (ASTM 5279-13, 2013) at 10 rad/s frequency and 3 C./min temperature ramp using a RDA 3 instrument from Rheometrics (now TA Instruments, New Castle, Del.). Table 1, below shows the properties of the resulting pad.

(14) TABLE-US-00001 TABLE 1 Pad Properties Hardness Hardness Density, (Shore D (Shore D G 30 C., G 40 C., G 40 C., G 30 C./ G 90 C., Example g/cm.sup.3 2 Sec) 15 Sec) MPa MPa MPa G90 MPa 4 0.86 61 59 195 174 12.9 1.7 111 Tensile 25% 50% Density, Strength, Elongation Modulus, Modulus Modulus Toughness Example g/cm.sup.3 MPa % MPa MPa MPa MPa 4 0.86 21.8 71 227 19.5 22.2 14.3

EXAMPLE 4A

(15) The Example 4 pad was machined on both sides to reduce the thickness down to 1.27 mm (50 mils) and perforated with 1.7 mm diameter through holes spaced 5.4 mm in machine direction and 9.8 mm in cross direction. The perforated Example 4 pad was stacked to a Suba 400 non-woven polyurethane impregnated polyester felt sub-pad (Nitta Haas, Osaka, Japan) using a double sided pressure sensitive adhesive (PSA).

COMPARATIVE EXAMPLE 5

(16) As a control, an IC1000 pad (The Dow Chemical Co., Midland, Mich.) of the same 1.27 mm (50-mil) thick was finished with the same configuration and stacked with the same Suba 400 sub-pad and the same pressure sensitive adhesive. The polishing comparison used the following method.

(17) Polishing Evaluation:

(18) Polishing was carried on a 300 mm CMP polisher (model FREX 300 by EBARA Corporation, Tokyo, Japan). The polishing medium (e.g., slurry) used in the polishing experiments was a cerium oxide containing slurry (average abrasive size 236 nm, abrasive loading of 5 wt %, and pH of 8.4) diluted with deionized water (DIW) at 1 to 9 slurry to DIW ratio. The polishing conditions used in all of the polishing experiments included a platen speed of 80 rpm, a carrier speed of 83 rpm, with a polishing slurry flow rate of 200 ml/min and a polishing down force of 50 kPa. An EP1AG-150730-NC diamond conditioning disk (Kinik Company, Taipei City, Taiwan) was used to condition the chemical mechanical polishing pads. The chemical mechanical polishing pads were each broken in with the conditioner ex situ using a down force of 100 N for 20 minutes, with pad table rotating at 20 rpm, and dresser at 16 rpm. The polishing pads were further conditioned ex situ prior to polishing each wafer substrate using a down force of 100 N for 30 seconds, at 20 rpm table speed and 16 rpm dresser speed. The removal rates (RR) of silicon oxide film from tetraethoxy silicate (TEOS) were determined by measuring the film thickness before and after polishing.

(19) The substrates polished were a tetraethoxy silicate (TEOS) blanket wafer, a blanket oxide wafer with minimal topography, followed by an oxide pattern wafer. The oxide pattern wafer has a typical step height of 5500 of various pattern densities, i.e., varying line/space width and pitch. The film stack for the oxide pattern wafer is about 10,000 of TEOS and 1500 of silicon nitride deposited on a patterned silicon substrate.

(20) Each polishing pad was monitored at 10, 30, 60, and 90 seconds to determine removal of the substrate and removal rate (RR) was measured by optical interference using a RE-3200 Ellipsometric Film Thickness Measurement System (Screen Holdings Co., Ltd. Kyoto, Japan) and recorded. Removal rate is the amount of substrate material removed per minute; average RR is the average of removal rates for 3 substrate trials. NU % refers to non-uniformity as a percentage of RR variation within each wafer excluding 3 mm at the wafer edge. For each substrate tested, five dummy wafers were polished in between each wafer for which RR and NU % were recorded; a total of three wafers of each kind of substrate were tested and observed for the RR and NU % tests. The non-uniformity (NU) of the substrate was measured after polishing. Results are given in Table 2, below.

(21) TABLE-US-00002 TABLE 2 Polishing Results Wafer Run No. Average RR Normalized RR Example 3 9 15 /min % Comparative 5257 5425 5487 5390 100 5 (RR) 4A (RR) 10603 10139 10263 10335 192 Comparative 17.4 17.1 13.9 n/a n/a 5 (NU %) 4A (NU %) 13.8 12.8 13.2 n/a n/a

(22) As shown in Table 2, above, the Example 4A pad of the present invention, exhibited about 90% higher TEOS removal rate than the Comparative Example 5, an IC1000 pad (The Dow Chemical Co., Midland, Mich.) of the same configuration. The Example 4A pad also gave comparable within wafer non-uniformity (NU) compared with the Comparative Example 5 pad.

(23) Planarization Efficiency:

(24) To assess the ability of a pad to remove material in the step height reduction from a non-level and non-uniform substrate, a substrate pattern wafer with a step height of 5000 (CMP Characterization Mask Set, MIT-STI-764 pattern) was formed by chemical vapor deposition of 7000 TEOS in a lined pattern that includes rectangular sections of varying pitches (from 1 to 1000 m at 50% pattern density) and pattern densities (from 0% to 100% at a 100 m line pitch). The pattern wafer having a target step height of 5000 is made by sequential deposition of a 7000 TEOS oxide film on top of a 1500 silicon nitride film on top of a silicon substrate etched 3500 deep with the various pattern densities. Planarization efficiency was evaluated by optical interference using a RE-3200 Ellipsometric Film Thickness Measurement System (Screen Holdings Co) at pattern line/space (L/S) intervals of 4000/4000 m, 500/500 m, 250/250 m, and 25/25 m. Results are shown in Table 3, below. In Table 3, below an Event refers to an observed point in time in the polishing of a single substrate wafer.

(25) TABLE-US-00003 TABLE 3 Planarization Efficiency and Polishing Results Step Height () at given feature sizes Event Polishing 4000/4000 500/500 250/250 100/100 25/25 No. time m m m m m Comparative Example 5 1 0 5404 5393 5428 5463 5476 2 45 5200 2997 2882 2867 2761 3 60 5085 1852 1588 1381 1057 Example 4A 1 0 5412 5393 5428 5462 5475 2 45 5078 2315 2178 2102 1779 3 60 4569 585 385 237 74

(26) As shown in Table 3, above, the pad of Example 4A delivered much faster step height reduction than the control IC1000 pad of Comparative Example 5, due to its much higher RR.

(27) A polishing evaluation, as described above, was repeated except at 41.3 kPa polishing down force, and the results are presented in Table 4, below.

(28) Defectivity:

(29) The creation of defects during polishing was measured using a Hitachi High-Tech LS6600 metrology tool (Hitachi High Technologies Corporation, Tokyo, Japan) wherein the substrate was cleaned with HF (2 wt. % in water) to an etching amount of 400 TEOS. Target remaining TEOS thickness was 6000 . Defect count was determined in a wafer substrate which is not a pattern wafer by an LS6600 wafer surface inspection system with 0.2 m resolution. Results are shown in Table 4, below.

(30) TABLE-US-00004 TABLE 4 Polishing Efficiency and Defects Example 4A Comparative 5 Blanket TEOS RR, /min 8055 4678 Defect count, scratches 17 59 Defect count, particles 16 31

(31) As shown in Table 4, above, the Example 4A pad gave a 72% higher removal rate and better defect performance than the pad of Comparative Example 4. The pad of Example 4A also achieved faster step height reduction, thus better planarization capability.