EP2151299B1

EP2151299B1 - Chemical mechanical polishing pad

Info

Publication number: EP2151299B1
Application number: EP09154680.4A
Authority: EP
Inventors: Mary Jo Kulp; T. Todd Crkvenac
Original assignee: Rohm and Haas Electronic Materials CMP Holdings Inc; Rohm and Haas Electronic Materials LLC
Current assignee: Rohm and Haas Electronic Materials CMP Holdings Inc; Rohm and Haas Electronic Materials LLC
Priority date: 2008-08-05
Filing date: 2009-03-09
Publication date: 2014-06-11
Anticipated expiration: 2029-03-09
Also published as: TWI482789B; TW201006854A; US20100035529A1; EP2151299A3; JP2010041056A; KR20100017064A; CN101642897B; EP2151299A2; CN101642897A

Description

BACKGROUND

This specification relates to polishing pads useful for polishing or planarizing semiconductor substrates. The production of semiconductors typically involves several chemical mechanical polishing (CMP) processes. In each CMP process, a polishing pad in combination with a polishing solution, such as an abrasive-containing polishing slurry or an abrasive-free reactive liquid, removes excess material in a manner that planarizes or maintains flatness for receipt of a subsequent layer. The stacking of these layers combines in a manner that forms an integrated circuit. The fabrication of these semiconductor devices continues to become more complex due to requirements for devices with higher operating speeds, lower leakage currents and reduced power consumption. In terms of device architecture, this translates to finer feature geometries and increased numbers of metallization levels. These increasingly stringent device design requirements are driving the adoption of smaller and smaller line spacing with a corresponding increase in pattern density. The devices' smaller scale and increased complexity have led to greater demands on CMP consumables, such as polishing pads and polishing solutions. In addition, as integrated circuits' feature sizes decrease, CMP-induced defectivity, such as, scratching becomes a greater issue. Furthermore, integrated circuits' decreasing film thickness requires improvements in defectivity while simultaneously providing acceptable topography to a wafer substrate; these topography requirements demand increasingly stringent planarity, line dishing and small feature array erosion polishing specifications.
Historically, cast polyurethane polishing pads have provided the mechanical integrity and chemical resistance for most polishing operations used to fabricate integrated circuits. For example, polyurethane polishing pads have sufficient tensile strength and elongation for resisting tearing; abrasion resistance for avoiding wear problems during polishing; and stability for resisting attack by strong acidic and strong caustic polishing solutions. Unfortunately, the hard cast polyurethane polishing pads that tend to improve planarization, also tend to increase defects.
M. J. Kulp, in US Pat. No. 7,169,030 , discloses a family of polyurethane polishing pads having high tensile modulus. The disclosed polishing pads comprise a polymeric matrix and hollow polymeric particles within the polymeric matrix, wherein the polymeric matrix is a polyurethane reaction product of an amine-based curative agent and an isocyanate-terminated polytetrmethylene ether glycol. These polishing pads provide excellent planarization and defectivity for several combinations of polishing pads and polishing slurries. For example, these polishing pads can provide excellent polishing performance for ceria-containing polishing slurries, for polishing silicon oxide/silicon nitride applications, such as direct shallow trench isolation (STI) polishing applications. For purposes of this specification, silicon oxide refers to silicon oxide, silicon oxide compounds and doped silicon oxide formulations useful for forming dielectrics in semiconductor devices; and silicon nitride refers to silicon nitrides, silicon nitride compounds and doped silicon nitride formulations useful for semiconductor applications. Unfortunately, these pads do not have universal applicability for improving polishing performance with all polishing slurries for the multiple substrate layers contained in today's and future semiconductor wafers. Furthermore, as the cost of semiconductor devices decreases, there remains a need for further and further increases in polishing performance.
Increasing a polishing pad's removal rate can increase throughput to decrease a semiconductor fabrication plant's equipment footprint and expenditure. Because of this demand for increasing performance, there remains a desire for a polishing pad to remove substrate layers with increased performance. For example, oxide dielectric removal rates are important for removing dielectrics during inter-layer dielectric ("ILD") or inter-metallic dielectric ("IMD") polishing. Specific types of dielectric oxides in use include the following: BPSG, TEOS formed from the decomposition of tetraethyloxysilicates, HDP ("high-density plasma") and SACVD ("sub-atmospheric chemical vapor deposition"). There is an ongoing need for polishing pads that have increased removal rate in combination with acceptable defectivity performance and wafer uniformity. In particular, there is a desire for polishing pads suitable for ILD polishing with an accelerated oxide removal rate in combination with acceptable planarization and defectivity polishing performance.

STATEMENT OF INVENTION

The present invention is as set out in the accompanying claims.
The invention provides a polishing pad suitable for polishing patterned semiconductor substrates containing at least one of copper, dielectric, barrier and tungsten, the polishing pad comprising a polymeric matrix and hollow polymeric particles within the polymeric matrix, the polymeric matrix being a polyurethane reaction product of a curative agent and an isocyanate-terminated polytetramethylene ether glycol at an NH₂ to NCO stoichiometric ratio of 80 to 97 percent, the isocyanate-terminated polytetramethylene ether glycol having an unreacted NCO range of 8.75 to 9.05 weight percent, the curative agent containing curative amines that cure the isocyanate-terminated polytetramethylene ether glycol to form the polymeric matrix; and the hollow polymeric particles having an average diameter of 2 to 50 µm and a wt%_b and density_b of constituents forming the polishing pad as follows: $\frac{wt %_{a} * {density}_{b}}{{density}_{a}} = wt %_{b}$

where density_a equals an average density of 60 g/l,
where density_b is an average density of 5 g/l to 500g/l,
where wt%_a is 3.25 to 4.25 wt%,
the polishing pad having a porosity of 30 to 60 percent by volume and a closed cell structure within the polymeric matrix forming a continuous network surrounding the closed cell structure.

Another embodiment of the invention provides a polishing pad suitable for polishing patterned semiconductor substrates containing at least one of copper, dielectric, barrier and tungsten, the polishing pad comprising a polymeric matrix and hollow polymeric particles within the polymeric matrix, the polymeric matrix being a polyurethane reaction product of a curative agent and an isocyanate-terminated polytetramethylene ether glycol at an NH₂ to NCO stoichiometric ratio of 80 to 90 percent, the isocyanate-terminated polytetramethylene ether glycol having an unreacted NCO range of 8.75 to 9.05 weight percent, the curative agent containing curative amines that cure the isocyanate-terminated polytetramethylene ether glycol to form the polymeric matrix; and the hollow polymeric particles having an average diameter of 2 to 50 µm and a wt%_b and density_b of constituents forming the polishing pad as follows: $\frac{wt %_{a} * {density}_{b}}{{density}_{a}} = wt %_{b}$

where density_a equals an average density of 60 g/l,
where density_b is an average density of 10 g/l to 300g/l,
where wt%_a is 3.25 to 3.6 wt%,
the polishing pad having a porosity of 35 to 55 percent by volume and a closed cell structure within the polymeric matrix forming a continuous network surrounding the closed cell structure.

DESCRIPTION OF THE DRAWING

Figure 1 is a 250X magnification post-polishing scanning electron photomicrograph of the polishing surface of a pad of the invention.
Figure 2 is a 500X magnification post-polishing scanning electron photomicrograph of the polishing surface of a pad of the invention.
Figure 3 is a 500X EDS image of the polishing pad of Figures 1 and 2, in the same region as Figure 2,illustrating a high concentration of silicon after polishing with a silica-containing polishing slurry.

DETAILED DESCRIPTION

The invention provides a polishing pad suitable for planarizing at least one of semiconductor, optical and magnetic substrates, the polishing pad comprising a polymeric matrix. The polishing pads are particularly suitable for polishing and planarizing ILD dielectric materials as in inter-layer dielectric (ILD) applications, but could also be used for polishing metals such as copper or tungsten. The pad provides increased removal rate over current pads-especially in the first 30 seconds of polishing. The accelerated response of the pad during the early part of polishing makes possible increased wafer throughput by shortening needed polishing time to remove a specified amount of material from a wafer surface.
The removal rate for ILD polishing with fumed silica at 30 seconds can be greater than 3750 Å/minute. Furthermore, the invention may provide at least a 10% higher removal rate than the removal rate at 30 seconds given by IC1010™ polyurethane polishing pads in the same polishing test. (IC1010 is a trademark of Rohm and Haas Company or its affiliates.) Advantageously, the removal rate for the polishing pads of the invention at thirty seconds for polishing TEOS sheet wafers with a silica-containing abrasive is equal to or greater than the removal rate for IC1000 polishing pads for polishing TEOS sheet wafers with a silica-containing abrasive at both thirty and sixty seconds. IC 1000™ may increase TEOS removal rate with polishing time because it comprises aliphatic isocyanate that tends to impart thermoplastic character to parts made from the ingredients. (IC 1000 is a trademark of Rohm and Haas Company or its affiliates.) The thermoplastic character of IC1000 polishing pads appears to facilitate an increase in contact between the polishing pad and the wafer along with an increase in removal rate until some maximum in removal rate occurs. Increasing pad to wafer contact area to ever higher levels appears to decrease removal rate as the localized asperity to wafer contact pressure decreases. Similarly, formulations not comprising aliphatic isocyanate will have more thermoplastic character as the degree of cross-linking or molecular weight decreases; and they may show more of an increase in removal rate with a wafer's polishing time. The pad of the invention, however, has sufficient levels of porosity to maximize pad to wafer contact very early in the polishing process; and the relatively high level of cross-linking appears to provide the pad sufficient localized stiffness to facilitate the polishing process.
Although removal rate can increase with abrasive content, an improvement over IC1010 polishing pad's removal rate independent of abrasive level represents an important advance in polishing performance. For example, this facilitates increasing removal rate with low defectivity and may decrease slurry costs. In addition to removal rate, wafer-scale nonuniformity also represents an important polishing performance consideration. Typically, because polished wafer uniformity is important for getting the maximum number of well-polished dies, the wafer-scale nonuniformity should be less than 6%.
For purposes of this specification, "polyurethanes" are products derived from difunctional or polyfunctional isocyanates, e.g. polyetherureas, polyisocyanurates, polyurethanes, polyureas, polyurethaneureas, copolymers thereof and mixtures thereof. Cast polyurethane polishing pads are suitable for planarizing semiconductor, optical and magnetic substrates. The pads' particular polishing properties arise in part from a prepolymer reaction product of a prepolymer polyol and a polyfunctional isocyanate. The prepolymer product is cured with a curative agent selected from the group comprising curative polyamines, curative polyols, curative alcohol amines and mixtures thereof to form a polishing pad. It has been discovered that controlling the ratio of the curative agent to the unreacted NCO in the prepolymer reaction product can improve porous pads' defectivity performance during polishing.
The urethane production involves the preparation of an isocyanate-terminated urethane prepolymer from a polyfunctional aromatic isocyanate and a prepolymer polyol. The prepolymer polyol is polytetramethylene ether glycol [PTMEG]. Example polyfunctional aromatic isocyanates include 2,4-toluene diisocyanate, 2,6- toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, naphthalene-1,5-diisocyanate, tolidine diisocyanate, para-phenylene diisocyanate, xylylene diisocyanate and mixtures thereof. The polyfunctional aromatic isocyanate contains less than 20 weight percent aliphatic isocyanates, such as 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate and cyclohexanediisocyanate. Preferably, the polyfunctional aromatic isocyanate contains less than 15 weight percent aliphatic isocyanates and more preferably, less than 12 weight percent aliphatic isocyanate.
Typically, the prepolymer reaction product is reacted or cured with a curative amine such as a polyamine or polyamine-containing mixture. For example, it is possible to mix the polyamine with an alcohol amine or a monoamine. For purposes of this specification, polyamines include diamines and other multifunctional amines. Example curative polyamines include aromatic diamines or polyamines, such as, 4,4'-methylene-bis-o-chloroaniline [MBCA], 4,4'-methylene-bis-(3-chloro-2,6-diethylaniline) [MCDEA]; 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; 4,4'-methylene-bis-aniline; diethyltoluenediamine; 5-tert-butyl-2,4- and 3-tert-butyl-2,6- toluenediamine; 5-tert-amyl-2,4- and 3-tert-amyl-2,6-toluenediamine and chlorotoluenediamine. A MBCA addition represents the preferred curative amine. Optionally, it is possible to manufacture urethane polymers for polishing pads with a single mixing step that avoids the use of prepolymers.
The components of the polymer used to make the polishing pad are preferably chosen so that the resulting pad morphology is stable and easily reproducible. For example, when mixing 4,4'-methylene-bis-o-chloroaniline [MBCA] with diisocyanate to form polyurethane polymers, it is often advantageous to control levels of monoamine, diamine and triamine. Controlling the proportion of mono-, di- and triamines contributes to maintaining the chemical ratio and resulting polymer molecular weight within a consistent range. In addition, it is often important to control additives such as anti-oxidizing agents, and impurities such as water for consistent manufacturing. For example, because water reacts with isocyanate to form gaseous carbon dioxide, controlling the water concentration can affect the concentration of carbon dioxide bubbles that form pores in the polymeric matrix. Isocyanate reaction with adventitious water also reduces the available isocyanate for reacting with chain extender, so changes the stoichiometry along with level of crosslinking (if there is an excess of isocyanate groups) and resulting polymer molecular weight.
The polyurethane polymeric material is preferably formed from a prepolymer reaction product of toluene diisocyanate with polytetramethylene ether glycol and an aromatic diamine. Most preferably the aromatic diamine is 4,4'-methylene-bis-o-chloroaniline or 4,4'-methylene-bis-(3-chloro-2,6-diethylaniline). Preferably the range of unreacted prepolymer %NCO is 8.75-9.05. A particular example of a suitable prepolymer within this unreacted NCO range is Adiprene® prepolymer LF750D manufactured by Chemtura. In addition, LF750D represents a low-free isocyanate prepolymer that has less than 0.1 weight percent each of free 2,4 and 2,6 TDI monomers and has a more consistent prepolymer molecular weight distribution than conventional prepolymers. This "low-free" prepolymer with improved prepolymer molecular weight consistency and low free isocyanate monomer facilitates a more regular polymer structure, and contributes to improved polishing pad consistency. In addition to controlling weight percent unreacted NCO, the curative and prepolymer reaction product typically has an OH or NH₂ to unreacted NCO stoichiometric ratio of 80 to 97 percent, preferably 80 to 90 percent; and most preferably, it has an OH or NH₂ to unreacted NCO stoichiometric ratio of 83 to 87 percent. It is possible to achieve this stoichiometry either directly, by providing the stoichiometric levels of the raw materials, or indirectly by reacting some of the NCO with water, either purposely or by exposure to adventitious moisture.
If the polishing pad is a polyurethane material, then the finished polishing pad preferably has a density of 0.4 to 0.8 g/cm³. Most preferably, the finished polyurethane polishing pads have a density of 0.5 to 0.75 g/cm³. A hollow polymeric particle loading density (before casting) of 3.25 to 4.25 weight percent and preferably 3.25 to 3.6 weight percent of the nominal 20 µm pores or hollow polymeric particles based on the total pad formulation can produce the desired density with excellent polishing results. In particular, the hollow polymeric particles provide a random pore distribution throughout the polymer matrix. In particular, the polishing pad has a closed cell structure with the polymeric matrix forming a continuous network surrounding the closed cell structure. Despite this high porosity, the polishing pad typically has a Shore D hardness of 44 to 54. For purposes of the specification, the Shore D test includes conditioning pad samples by placing them in 50 percent relative humidity for five days at 25 °C before testing and using methodology outlined in ASTM D2240 to improve the repeatability of the hardness tests.
The hollow polymeric particles have a weight average diameter of 2 to 50 µm. For purposes of the specification, weight average diameter represents the diameter of the hollow polymeric particle before casting; and the particles may have a spherical or non-spherical shape. Most preferably, the hollow polymeric particles have a spherical shape. Preferably, the hollow polymeric particles have a weight average diameter of 2 to 40 µm. Most preferably, the hollow polymeric particles have a weight average diameter of 10 to 30 µm; these hollow polymeric particles typically have an average density of 60 grams per liter. For purposes of this specification, average density of the hollow polymeric particles represents the close-packed-non-crushed density of the hollow particles within a one liter volume. Hollow particles with an average diameter of 35 to 50 µm typically have lower density averaging 42 grams per liter because there are fewer pores and less wall material. Hollow particles of different sizes and types can be added at equivalent pore volumes by taking the mass of the hollow polymeric particles of one size and dividing by their density to determine the volume of pores. This volume can then be multiplied by the density of the other pore to determine the mass of the hollow polymeric particles of that size and type to give equivalent pore volume For example, a formulation with 3 wt% of 20 µm hollow polymeric particles with a density of 60 grams per liter would be equivalent to 2.1 wt% of 42 µm hollow polymeric particles with a density of 40 grams per liter as shown by the equation that follows. $\frac{wt %_{a} * {density}_{b}}{{density}_{a}} = wt %_{b}$
In forming polishing pads of the invention, density_a equals an average density of 60 g/l, density_b is an average density of 5 g/l to 500g/l and wt%_a is 3.25 to 4.25 wt%. Preferably, density_b is an average density of 10 g/l to 150g/l and wt%_a is 3.25 to 3.6 wt%.
The nominal range of expanded hollow-polymeric particles' weight average diameters is 15 to 90 µm. Furthermore, a combination of high porosity with small pore size can have particular benefits in reducing defectivity. If the porosity level becomes too high, however, the polishing pad loses mechanical integrity and strength. For example, adding hollow polymeric particles of 2 to 50 µm weight average diameter constituting 30 to 60 volume percent of the polishing layer facilitates a reduction in defectivity. Furthermore, maintaining porosity between 35 and 55 volume percent or specifically, 35 and 50 volume percent can facilitate increased removal rates. For purposes of this specification, volume percent porosity represents the volume percent of pores determined as follows: 1) subtracting the measured density of the formulation from the nominal density of the polymer without porosity to determine the mass of polymer "missing" from the a cm³ of formulation; then 2) dividing the mass of "missing" polymer by the nominal density of the polymer without porosity to determine the volume of polymer missing from a cm³ of formulation and multiplying by 100 to convert it to a porosity volume percentage. Alternatively, the volume percent of pores in a formulation or volume percent porosity can be determined as follows: 1) subtracting the mass of hollow polymeric particles in 100 g formulation from 100 g to determine the mass of polymer matrix in 100 g of formulation; 2) dividing the mass of polymer matrix by the nominal density of the polymer to determine the volume of polymer in 100 g of formulation; 3) dividing the mass of hollow polymeric particles in 100 g of formulation by the nominal hollow polymeric particle density to determine the volume of hollow polymeric particles in 100 g of formulation; 4) adding the volume of polymer in 100 g of formulation to the volume of hollow particles or pores in 100 g of formulation, to determine the volume of 100 g of formulation; then 5) dividing the volume of hollow particles or pores in 100 g of formulation by the total volume of 100 g of formulation and multiplying by 100 to give the volume percent of pores or porosity in the formulation. The two methods will produce similar values for volume percent porosity or pores, although the second method will show lower values of volume percent pores or porosity than the first method where parameters during processing, such as the reaction exotherm, can cause hollow polymeric particles or microspheres to expand beyond their nominal "expanded volume." Because a decrease in pore size tends to increase polishing rate for a specific pore or porosity level, it is important to control the exotherm during casting to prevent further expansion of the pre-expanded hollow polymeric particles or microspheres. For example, casting into a room temperature mold, limiting cake height, reducing prepolymer temperature, reducing curative amine temperature, reducing the NCO and limiting the free TDI monomer all contribute to reducing the exotherm produced by the reacting isocyanate.
As with most conventional porous polishing pads, polishing pad conditioning, such as diamond disk conditioning, serves to increase removal rate and improve wafer-scale nonuniformity. Although conditioning can function in a periodic manner, such as for 30 seconds after each wafer or in a continuous manner, continuous conditioning provides the advantage of establishing steady-state polishing conditions for improved control of removal rate. The conditioning typically increases the polishing pad removal rate and prevents the decay in removal rate typically associated with the wear of a polishing pad's surface. In particular, the abrasive conditioning forms a roughened surface that can trap fumed silica particles during polishing. Figures 1 to 3 illustrate that silica particles can accumulate in the roughened surface adjacent the polishing pad's pores. This accumulation of silica particles into the polishing pad appears to increase the polishing pad's efficiency by contributing to a high removal rate. In addition to conditioning, grooves and perforations can provide further benefit to the distribution of slurry, polishing uniformity, debris removal and substrate removal rate.

Example

The polymeric pad materials were prepared by mixing various amounts of isocyanates as urethane prepolymers with 4,4'-methylene-bis-o-chloroaniline [MBCA] at 49 °C for the prepolymer and 115 °C for MBCA for examples of the invention (Comparative Examples included 43 to 63 °C for the prepolymer). In particular, a certain toluene diiosocyanate [TDI] with polytetramethylene ether glycol [PTMEG] prepolymer provided polishing pads with different properties. The urethane/polyfunctional amine mixture was mixed with the hollow polymeric microspheres (EXPANCEL^® 551DE20d60 or 551DE40d42 manufactured by AkzoNobel) either before or after mixing the prepolymer with the chain extender. The hollow polymeric microspheres were either mixed with the prepolymer at 60 rpm before adding the polyfunctional amine, then mixing the mixture at 4500 rpm or were added to the urethane/polyfunctional amine mixture in a mixhead at 3600 rpm. The microspheres had a weight average diameter of 15 to 50 µm, with a range of 5 to 200 µm The final mixture was transferred to a mold and permitted to gel for about 15 minutes.

The mold was then placed in a curing oven and cured with a cycle as follows: thirty minutes ramped from ambient temperature to a set point of 104°C, fifteen and one half hours at 104°C and two hours with a set point reduced to 21°C. Comparative Examples F to K used a shorter cure cycle of 100°C for about eight hours. The molded article was then "skived" into thin sheets and macro-channels or grooves were machined into the surface at room temperature-skiving at higher temperatures may improve surface roughness and sheet thickness uniformity. As shown in the Tables, samples 1 to 2 represent polishing pads of the invention and samples A to Z represent comparative examples.

Table 1

Formulation	Formulation	NCO (wt%)	Prepolymer	Stoichiometry (%)	Hollow Polymeric Spheres (wt%)	Nominal Sphere Diameter (um)
1	MJK1859C	8.75-9.05	LF750D	85	3.36	20
2	MJK1859C	8.75-9.05	LF750D	85	3.36	20
A	S58	8.75-9.05	LF750D	85	2.25	40
B	T58	8.75-9.05	LF750D	85	3.21	20
C	S52	8.75-9.05	LF750D	105	0.75	40
D	S53	8.75-9.05	LF750D	85	0.75	40
E	T53	8.75-9.05	LF750D	85	1.07	20
F	MJK3101A	11.4-11.8	Royalcast 2505	85	3.01	20
G	MJK3101C	11.4-11.8	Royalcast 2505	85	3.01	20
H	MJK3101B	11.4-11.8	Royalcast 2505	95	2.93	20
I	MJK3101D	11.4-11.8	Royalcast 2505	95	2.93	20
J	MJK1864A	11.4-11.8	Royalcast 2505	105	2.86	20
K	MJK1864J	11.4-11.8	Royalcast 2505	105	2.86	20
L	MJK3122B	8.75-9.05	LF750D	85.00	3.87	20
M	MJK3122F	8.75-9.05	LF750D	90.00	3.83	20
N	MJK3122E	8.75-9.05	LF750D	95.00	3.79	20
O	MJK3122D	8.75-9.05	LF750D	100.00	3.74	20
P	MJK3122A	8.45-8.75	LF750D	105.00	3.70	20
Q	MJK3122C	8.45-8.75	LF750D	110.00	3.66	20
R	VP3000	7.1-7.4	LF600D	85	1.8	40
S	MJK1803C	8.75-9.05	LF750D	90.00	2.94	20
T	MJK1803E	8.75-9.05	LF750D	90.00	2.94	20
U	MJK1803A	8.75-9.05	LF750D	115.00	2.94	20
V	MJK1803F	8.75-9.05	LF750D	115.00	2.94	20
W	MJK1803D	8.75-9.05	LF750D	90.00	2.20	20
X	MJK1803H	8.75-9.05	LF750D	90.00	2.20	20
Y	MJK1803B	8.75-9.05	LF750D	115.00	2.20	20
Z	MJK1803G	8.75-9.05		115.00	2.20	20

Adiprene LF600D, LF750D and Royalcast 2505 correspond to blends of toluene diiosocyanate and PTMEG products manufactured by Chemtura. LF600D and LF750D are low-free isocyanate prepolymers while Royalcast 2505 has high levels of free isocyanate monomer.

Example polishing pads were tested on a Mirra® polisher from Applied Materials, Inc. using a platen rotation rate of 93 rpm, a wafer carrier head rotation rate of 87 rpm and a downforce of 5 psi to polish TEOS sheet wafers. The polishing slurry was ILD3225 used as a 1:1 mixture with DI water and supplied at the polishing pad surface a rate of 150 ml/min. A Diagrid® AD3BG150855 conditioning disk was used to diamond-condition the polishing pad using an in situ conditioning process. TEOS sheet wafers were polished for 30 seconds or for 60 seconds and each test with example pads also included wafers polished with the IC1010 pad as a baseline. The greatest importance was placed on the 30 second polish rates relative to IC1010 because they would have the greatest effect on reducing polishing times over the standard polishing pad. The polishing results are below in Table 2.

Table 2

Formulation	Formulation	Hollow Polymeric Spheres (wt%)	Nominal Sphere Diameter (um)	RR at 30 sec (Å/min)	RR, 30 sec norm	RR at 60 sec (Å/min)	RR, 60 sec norm	NU, %
Target				>3750	≥1.10	≥4100	≥1.08	< 6.0
1	MJK1859C	3.36	20	3778	1.18	4183	1.15	2.5
2	MJK1859C	3.36	20	3949	1.10	4235	1.08	5.7
A	S58	2.25	40	3802	1.08	4263	1.10	3.0
B	T58	3.21	20	4043	1.15	4414	1.17	2.8
C	S52	0.75	40	3786	1.07	4070	1.04	5.5
D	S53	0.75	40	3582	1.02	4043	1.01	3.4
E	T53	1.07	20	3736	1.06	4175	1.05	3.1
F	MJK3101A	3.01	20	3303	0.94	3755	0.95	4.2
G	MJK3101C	3.01	20	3123	0.89	3600	0.91	4.6
H	MJK3101B	2.93	20	3162	0.90	3652	0.92	4.6
I	MJK3101D	2.93	20	3087	0.88	3587	0.91	4.5
J	MJK1864A	2.86	20	3180	0.91	3611	0.91	4.3
K	MJK1864J	2.86	20	3114	0.89	3583	0.91	5.4
L	MJK3122B	3.87	20	3886	1.09	4219	1.07	6.0
M	MJK3122F	3.83	20	3788	1.06	4050	1.03	6.0
N	MJK3122E	3.79	20	3747	1.05	4079	1.04	11.4
O	MJK3122D	3.74	20	3715	1.04	4015	1.02	7.8
P	MJK3122A	3.70	20	3683	1.03	3915	1.00	7.1
Q	MJK3122C	3.66	20	3450	0.97	3647	0.93	8.4
R	VP3000	1.8	40			3330	0.80	2.3
S	MJK1803C	2.94	20	3893	1.06	4219	1.03	3.2
T	MJK1803E	2.94	20	4025	1.11	4251	1.05	7.6
U	MJK1803A	2.94	20	3803	1.03	4025	0.98	4.8
V	MJK1803F	2.94	20	3673	1.01	3856	0.95	8.2
W	MJK1803D	2.20	20	3688	1.00	4029	0.98	3.8
X	MJK1803H	2.20	20	3692	1.01	3976	0.98	5.5
Y	MJK1803B	2.20	20	3783	1.03	4053	0.99	4.6
Z	MJK1803G	2.20	20	3654	1.00	3859	0.95	7.6

These data indicate that a loading of 3.36 weight percent hollow polymeric microspheres provided an unexpected increase in removal rate. In particular, Samples 1 and 2 had excellent removal rate at thirty seconds and sixty seconds. The Sample 1 and 2 removal rates at thirty seconds indicate that the polishing pad has high removal rate during an earlier part of a shortened polishing process that supports higher throughput polishing. The comparative examples with 3.01(2.94 for same prepolymer) or of 3.66 weight percent and above resulted in a lower removal rate at thirty seconds and a lower overall removal rate. In addition, Figures 1 to 3 illustrate that the polishing pad's surface appears to trap fumed-silica in an advantageous location for polishing. This affinity to fumed silica appears to contribute to the increased polishing performance.

Table 3

Formulation	Formulation	Hollow Polymeric Spheres (wt%)	Nominal Sphere Diameter (µm)	Calculated # spheres in cm³ formulation based on formulation	Calculated # spheres in cm³ formulation based on pad density	Difference in Calculated # of Spheres
Preferred		>3.1	20	>9.25E+07
1	MJK1859C	3.36	20	9.79E+07	9.50E+07	2.89E+06
2	MJK1859C	3.36	20	9.79E+07	9.34E+07	4.42E+06
A	S58	2.25	40	1.18E+07	1.27E+07	-8.73E+05
B	T58	3.21	20	9.52E+07	1.05E+08	-9.55E+06
C	S52	0.75	40	5.30E+06	5.95E+06	-6.53E+05
D	S53	0.75	40	5.30E+06	5.80E+06	-4.99E+05
E	T53	1.07	20	4.25E+07	4.33E+07	-8.60E+05
F	MJK3101A	3.01	20	9.21E+07	1.10E+08	-1.80E+07
G	MJK3101C	3.01	20	9.21 E+07	9.56E+07	-3.46E+06
H	MJK3101B	2.93	20	9.04E+07	1.10E+08	-2.00E+07
I	MJK3101D	2.93	20	9.04E+07	9.55E+07	-5.01E+06
J	MJK1864A	2.86	20	8.90E+07	9.56E+07	-6.53E+06
K	MJK1864J	2.86	20	8.90E+07	9.98E+07	-1.07E+07
L	MJK3122B	3.87	20	1.07E+08	1.14E+08	-7.20E+06
M	MJK3122F	3.83	20	1.06E+08	1.30E+08	-2.40E+07
N	MJK3122E	3.79	20	1.05E+08	1.18E+08	-1.32E+07
O	MJK3122D	3.74	20	1.04E+08	1.17E+08	-1.26E+07
P	MJK3122A	3.70	20	1.04E+08	1.20E+08	-1.63E+07
Q	MJK3122C	3.66	20	1.03E+08	1.22E+08	-1.92E+07
R	VP3000	1.8	40	1.00E+07	2.98E+07	-1.98E+07
S	MJK1803C	2.94	20	9.01 E+07	9.21 E+07	-2.02E+06
T	MJK1803E	2.94	20	9.01 E+07	1.06E+08	-1.60E+07
U	MJK1803A	2.94	20	9.01 E+07	1.07E+08	-1.68E+07
V	MJK1803F	2.94	20	9.01 E+07	1.17E+08	-2.70E+07
W	MJK1803D	2.20	20	7.41 E+07	6.82E+07	5.91 E+06
X	MJK1803H	2.20	20	7.41 E+07	9.73E+07	-2.32E+07
Y	MJK1803B	2.20	20	7.41 E+07	8.71 E+07	-1.31E+07
Z	MJK1803G	2.20	20	7.41 E+07	9.45E+07	-2.04E+07

Table 3 illustrates that the hollow polymeric microspheres achieve a loading level in excess of one million microspheres per cubic centimeter of pad formulation.

Table 4 below shows prepolymer %NCO and compares mechanical strength properties of MBCA-cured elastomers, without filler or porosity, made from the prepolymers used in the example formulations as tested using methodology in ASTM D412. The tensile properties shown are defined in ASTM D1566-08A. In addition, Table 4 shows the nominal density of the prepolymer cured with MBCA as reported by the prepolymer manufacturer.

Table 4

Prepolymer	Prepolymer NCO (wt%)	Tensile strength unfilled cured with MBCA, psi (MPa)	Tensile Stress at 100% Elongation, psi (MPa)	Tensile Stress at 200% Elongation, psi (MPa)	Nominal Polymer Density (g/cm³)
Adiprene
LF600D	7.1-7.4	6700 (46.2)	3600 (24.8)	4800(33.1)	1.16
Adiprene
LF750D	8.75-9.05	7100 (48.9)	5300 (36.5)	5900 (40.7)	1.20
Royalcast 2505	11.4-11.8	9200 (63)	-	-	1.21

Table 4 illustrates that in addition to filler concentration, the polishing pad's mechanical properties also appear to impact polishing performance. Specifically, the polymer of Comparative Example R with LF600D appears to have inadequate stiffness, as best indicated by its 100% modulus, for high removal rates for fumed silica polishing; and Comparative Examples F to K made with Royalcast® 2505 quasi-prepolymer, which appears to be excessively stiff for high removal rates in fumed silica polishing. Polyurethane materials cast from Royalcast 2505 were so brittle that they broke prior to elongation at 100%.
In summary, the polishing pad is effective for polishing copper, dielectric, barrier and tungsten wafers. In particular, the polishing pad is useful for ILD polishing and in particular, ILD polishing applications with fumed silica. The polishing pad has a rapid ramp to efficient polishing that provides a high removal rate at thirty seconds. The removal rate of polishing pads of the invention at both thirty and sixty seconds can exceed the removal rate of IC1000 polishing pads at thirty seconds and at sixty seconds. This rapid polishing response of the pads of the invention facilitates high wafer throughput in comparison to conventional porous polishing pads.

Claims

A polishing pad suitable for polishing patterned semiconductor substrates containing at least one of copper, dielectric, barrier and tungsten, the polishing pad comprising a polymeric matrix and hollow polymeric particles within the polymeric matrix, characterized in that the polymeric matrix is a polyurethane reaction product of a curative agent and an isocyanate-terminated polytetramethylene ether glycol at an NH₂ to NCO stoichiometric ratio of 80 to 97 percent, the isocyanate-terminated polytetramethylene ether glycol having an unreacted NCO range of 8.75 to 9.05 weight percent, the curative agent containing curative amines that cure the isocyanate-terminated polytetramethylene ether glycol to form the polymeric matrix; and the hollow polymeric particles having an average diameter of 2 to 50 µm and a wt%_b and density_b of constituents added on an equivalent pore volume basis to wt%_a and density_a by forming the polishing pad as follows: $\frac{wt %_{a} * {density}_{b}}{{density}_{a}} = wt %_{b}$

where density_a equals an average density of 60 g/l,
where density_b is an average density of 5 g/l to 500g/l,
where wt%_a is 3.25 to 4.25 wt%,
the polishing pad having a porosity of 30 to 60 percent by volume and a closed cell structure within the polymeric matrix forming a continuous network surrounding the closed cell structure.
The polishing pad of claim 1 wherein the continuous network forms a roughened surface upon conditioning with an abrasive; and the roughened surface is capable of trapping fumed silica particles during polishing.
The polishing pad of claim 1 wherein the polishing pad has a Shore D hardness of 44 to 54.
The polishing pad of claim 1 wherein the polishing pad has a porosity of 35 to 55 vo lume percent.
The polishing pad of claim 1 wherein the hollow polymeric particles have an average diameter of 10 to 30 µm.
The polishing pad of claim 1, wherein said polymeric matrix is a polyurethane reaction product of a curative agent and an isocyanate-terminated polytetramethylene ether glycol at an NH₂ to NCO stoichiometric ratio of 80 to 90 percent; density_b is an average density of 10 g/l to 300g/l;
wt%_a is 3.25 to 3.6 wt%; and
the polishing pad has a porosity of 35 to 55 percent by volume.
The polishing pad of claim 6 wherein the continuous network forms a roughened surface upon conditioning with an abrasive; and the roughened surface is capable of trapping fumed silica particles during polishing.
The polishing pad of claim 6 wherein the polishing pad has a Shore D hardness of 44 to 54.
The polishing pad of claim 6 wherein the polishing pad has a porosity of 35 to 50 volume percent.
The polishing pad of claim 6 wherein the hollow polymeric particles have an average diameter of 10 to 30 µm.