US20020004317A1 - Ceria based slurry for chemical-mechanical polishing - Google Patents
Ceria based slurry for chemical-mechanical polishing Download PDFInfo
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- US20020004317A1 US20020004317A1 US09/151,370 US15137098A US2002004317A1 US 20020004317 A1 US20020004317 A1 US 20020004317A1 US 15137098 A US15137098 A US 15137098A US 2002004317 A1 US2002004317 A1 US 2002004317A1
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- ceria
- slurry
- polishing
- particles
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- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 title claims abstract description 59
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 title claims abstract description 59
- 239000002002 slurry Substances 0.000 title claims abstract description 56
- 238000005498 polishing Methods 0.000 title claims abstract description 54
- 239000002245 particle Substances 0.000 claims abstract description 42
- 239000000126 substance Substances 0.000 claims abstract description 10
- 238000000034 method Methods 0.000 claims description 26
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 23
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 12
- 229920000620 organic polymer Polymers 0.000 claims description 11
- 239000000377 silicon dioxide Substances 0.000 claims description 11
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Chemical compound [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 claims description 10
- 229910052710 silicon Inorganic materials 0.000 claims description 7
- 239000010703 silicon Substances 0.000 claims description 7
- 239000008367 deionised water Substances 0.000 claims description 6
- 229910052684 Cerium Inorganic materials 0.000 claims description 5
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 claims description 5
- 235000015497 potassium bicarbonate Nutrition 0.000 claims description 5
- 239000011736 potassium bicarbonate Substances 0.000 claims description 5
- 229910000028 potassium bicarbonate Inorganic materials 0.000 claims description 5
- 229910000027 potassium carbonate Inorganic materials 0.000 claims description 5
- 235000011181 potassium carbonates Nutrition 0.000 claims description 5
- TYJJADVDDVDEDZ-UHFFFAOYSA-M potassium hydrogencarbonate Chemical compound [K+].OC([O-])=O TYJJADVDDVDEDZ-UHFFFAOYSA-M 0.000 claims description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 5
- 239000011268 mixed slurry Substances 0.000 claims description 3
- 239000006174 pH buffer Substances 0.000 claims description 3
- 229920000052 poly(p-xylylene) Polymers 0.000 claims description 3
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 claims description 2
- 239000005977 Ethylene Substances 0.000 claims description 2
- 230000005484 gravity Effects 0.000 claims description 2
- 229910021641 deionized water Inorganic materials 0.000 claims 1
- 229920002313 fluoropolymer Polymers 0.000 claims 1
- 235000011118 potassium hydroxide Nutrition 0.000 claims 1
- 239000000463 material Substances 0.000 abstract description 13
- 229920006254 polymer film Polymers 0.000 abstract description 9
- 229920000642 polymer Polymers 0.000 abstract description 8
- 230000002902 bimodal effect Effects 0.000 abstract description 3
- 235000012431 wafers Nutrition 0.000 description 19
- 239000010409 thin film Substances 0.000 description 13
- 239000010408 film Substances 0.000 description 9
- 239000010410 layer Substances 0.000 description 8
- 239000004020 conductor Substances 0.000 description 7
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 6
- 230000008901 benefit Effects 0.000 description 6
- 239000000758 substrate Substances 0.000 description 5
- 239000003989 dielectric material Substances 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 238000004377 microelectronic Methods 0.000 description 4
- 238000006748 scratching Methods 0.000 description 4
- 230000002393 scratching effect Effects 0.000 description 4
- 239000003082 abrasive agent Substances 0.000 description 3
- 239000012212 insulator Substances 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 235000012239 silicon dioxide Nutrition 0.000 description 3
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 229910052731 fluorine Inorganic materials 0.000 description 2
- 239000011737 fluorine Substances 0.000 description 2
- 238000009472 formulation Methods 0.000 description 2
- 239000011810 insulating material Substances 0.000 description 2
- 239000011229 interlayer Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000007517 polishing process Methods 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 229910001218 Gallium arsenide Inorganic materials 0.000 description 1
- 208000029523 Interstitial Lung disease Diseases 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- QLOAVXSYZAJECW-UHFFFAOYSA-N methane;molecular fluorine Chemical compound C.FF QLOAVXSYZAJECW-UHFFFAOYSA-N 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 239000011368 organic material Substances 0.000 description 1
- 230000003071 parasitic effect Effects 0.000 description 1
- 230000002572 peristaltic effect Effects 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000007639 printing Methods 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 229910052594 sapphire Inorganic materials 0.000 description 1
- 239000010980 sapphire Substances 0.000 description 1
- 239000007779 soft material Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000012876 topography Methods 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K3/00—Materials not provided for elsewhere
- C09K3/14—Anti-slip materials; Abrasives
- C09K3/1454—Abrasive powders, suspensions and pastes for polishing
- C09K3/1463—Aqueous liquid suspensions
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09G—POLISHING COMPOSITIONS; SKI WAXES
- C09G1/00—Polishing compositions
- C09G1/02—Polishing compositions containing abrasives or grinding agents
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
- H01L21/3105—After-treatment
- H01L21/31058—After-treatment of organic layers
Definitions
- the present invention relates to the field of planarization, and more specifically, to ceria based abrasives for chemical-mechanical polishing (CMP).
- CMP chemical-mechanical polishing
- patterned conductive material on one interconnect level is electrically insulated from patterned conductive material on another interconnect level by films of material such as silicon dioxide. Connections between the conductive material at the various interconnect levels are made by forming openings in the insulating layers and providing an electrically conductive structure such that the patterned conductive material from different interconnect levels are brought into electrical contact with each other. These electrically conductive structures are often referred to as contacts or vias.
- a consequence of having multiple layers of patterned conductive material separated by an insulating layer is the formation of undesired capacitors.
- the parasitic capacitance between patterned conductive material, or more simply, interconnects, separated by insulating material on microelectronic devices contributes to effects such as RC delay, power dissipation, and capacitively coupled signals, also known as cross-talk.
- One way to reduce the unwanted capacitance between the interconnects is to use an insulating material with a lower dielectric constant.
- polymers have been introduced for use in integrated circuit manufacturing as dielectrics having a lower dielectric constant than conventionally used oxides of silicon.
- Nonplanar surfaces when present in integrated circuits having complex, high density multilevel interconnections, may cause the optical resolution of photolithographic processing steps to be poor, which could inhibit the printing of high density lines.
- Another problem that may be caused by nonplanar surface topography relates to step coverage of metal layers. If steps are too high or uneven, open circuits could be created. It is thus important, when making such complex integrated circuits, to planarize the surface of many of the layers that make up the device.
- a ceria based slurry is used in a chemical mechanical polishing operation at low polish pressure, and a predetermined pH range, to achieve high polish rates and good uniformity when planarizing films formed from low dielectric constant materials, such as polymers.
- the distribution of ceria particle sizes in a slurry is bimodal, that is, controlled such that there are two distinct particle size ranges.
- a ceria based polishing slurry containing a bimodal distribution of ceria particle sizes is used in a CMP polisher apparatus with a polishing pressure of approximately 3 psi and a pH of approximately 10.6 to planarize fluorinated organic polymers.
- FIG. 1 is a cross-sectional view of a CMP apparatus using a convex solid to bend a wafer, and a conventional retaining ring.
- FIG. 2 is a top view of a polishing pad covered platen, retaining ring, and slurry delivery arm, indicating the slurry delivery point to the polishing pad.
- FIG. 3 is a flowchart showing the operations in a process of making a slurry in accordance with the present invention.
- FIG. 4 is a flowchart showing the operations in a process of polishing a thin film in accordance with the present invention.
- Substrate refers to the physical object that is to be planarized by means of the CMP process.
- a substrate may also be referred to as a wafer.
- Wafers may be made of semiconducting, non-semiconducting, or combinations of semiconducting and non-semiconducting materials.
- Silicon wafers may have thin films of various materials formed upon them. These thin films may be planarized with CMP processing.
- Other substrate materials such as GaAs, silicon-on-sapphire, or silicon on insulator (SOI) may be planarized with CMP processing.
- SOI silicon on insulator
- contact and via both refer to structures for electrical connection of conductors from different interconnect levels. These terms are sometimes used in the art to describe both an opening in an insulator in which the structure will be completed, and the completed structure itself. For purposes of this disclosure contact and via refer to the completed structure.
- low dielectric constant material refers to materials having a lower dielectric constant than oxides of silicon.
- vertical as used herein, means substantially orthogonal to the surface of a substrate.
- RPM also rpm refers to revolutions per minute.
- Ceria is an oxide of the rare earth element Cerium (Ce) and is often referred to by the chemical formula CeO 2 .
- CeO 2 CeO 2
- Ceria has been used for glass polishing applications such as lens and mirror manufacturing in the past.
- Ceria is typically mined, and is commercially available as a powder wherein the particles have rough edges.
- Polishing with relatively large, rough-edged ceria particles provides a fast polish, that is, a high polishing rate, but results in scratches on the surface being polished.
- polishing with relatively small ceria particles reduces the scratching problem but also reduces the polish rate to such an extent that polishing with these small particles is impractical.
- the polishing process is observed to “shut down”, that is, to stop polishing.
- organic polymer dielectrics are subjected to chemical mechanical polishing operations using a slurry that contains a predetermined ratio of ceria particle sizes.
- Polymer films such as those used to form low dielectric constant insulating layers in ICs, are much softer than the oxides of silicon that have been commonly used to form inter-layer dielectrics.
- these polymer films are polished in a chemical mechanical polishing operation, with conventional abrasives such as silica and alumina, significant scratching of the polymer film occurs as a result of the softness of the film. Additionally, these organic polymer films tend to be somewhat resistant to chemical attack from water based slurry chemistries.
- a slurry in accordance with the present invention is based on ceria rather than the conventional abrasives such as silica or alumina.
- a ceria based slurry according to the present invention enables high polish rates and substantially reduces scratching of polymer films.
- a slurry, in accordance with the present invention, for chemical mechanical polishing of thin films, such as polymer dielectric layers on microelectronic devices includes ceria particles of at least two size ranges, silica particles, water, and a compound for determining the pH of the slurry.
- An example of a slurry in accordance with the present invention includes 1 part of a pre-mixed slurry, (CABOT EP7391-100 (2 wt. % silica, 6.5 wt % small particle ceria, potassium hydroxide and de-ionized water)), 7 parts de-ionized water, 2 grams/liter large particle ceria, 4 grams/liter potassium carbonate, and 1 gram/liter potassium bicarbonate.
- large particle ceria can be added in amounts as low as 0.75 grams/liter.
- the potassium carbonate and potassium bicarbonate act as pH buffers.
- This exemplary slurry has a pH of approximately 10.6 and a specific gravity of approximately 1.015. Those skilled in the art will recognize that the slurry may be buffered to other values of pH.
- Small particle ceria refers to crushed ceria that is filtered to a size of approximately 0.43 microns, such that approximately 99% of the particles are of this size.
- Large particle ceria refers to crushed ceria that is filtered to a size of approximately 2.8 microns, such that approximately 99% of the particles are of this size.
- the large ceria particles are typically added to the small particle slurry and mixed with a motor driven stirrer. By combining the materials described above, a slurry is obtained having a predetermined ratio between large and small ceria particles.
- FIGS. 1 - 3 An embodiment of the method of polishing a thin film on a wafer containing microelectronic devices, in accordance with the present invention is described in conjunction with FIGS. 1 - 3 .
- a wafer 102 is placed face down on a rotating table 104 covered with a polishing pad 106 , which has been coated with a slurry 108 .
- a carrier 100 which may be made of a thick nonflexible metal plate 114 that is attached to a rotatable shaft 105 , is used to apply a downward force against the backside of wafer 102 .
- a retaining ring 117 may be used to center wafer 102 onto carrier 100 and to prevent wafer 102 from slipping laterally. Typically, the surface of wafer 102 extends outwardly beyond the polishing side surface of retaining ring 117 .
- a resilient carrier pad 112 positioned between metal plate 114 and wafer 102 is typically used to press against the backside of wafer 102 .
- plate 114 will be manufactured with a slight convex curvature so as to bend the central portion of a wafer outward.
- a desired amount of material may be removed from the upper surface of a thin film such that the surface of wafer 102 is planarized.
- FIG. 2 provides a top view of a conventional CMP system, showing polishing pad 202 , retaining ring 204 , and slurry delivery arm 206 .
- the ceria based slurry of the present invention is typically delivered to the polishing pad through the use of peristaltic pumps.
- polishing typically takes place in a range of temperatures from about 10° C. to about 25° C.
- further chilling the pad, slurry, or wafer may improve polymer polishing results.
- hard materials polish more easily than soft materials.
- Polymers tend to be softer than other materials that are routinely planarized by chemical mechanical polishing. Since polymers tend to harden with decreasing temperatures, chilling the polymer film on the wafer will tend to provide a harder surface for polishing.
- the ceria based slurry in accordance with the present invention is suitable for polishing any low dielectric constant thin film, including but not limited to fluorine doped oxides of silicon, amorphous fluorinated carbon, parylenes, and PAE (para arol ethylene).
- Organic polymers used for low dielectric constant insulators in microelectronic devices can be doped with fluorine to further reduce their dielectric constant, and these can also be polished with the ceria based slurry of the present invention.
- FIG. 3 shows a flow diagram of a process 400 embodying the present invention.
- a slurry containing two distinct size ranges of ceria is prepared by mixing together large size and small size ceria particles.
- An exemplary formulation of a slurry in accordance with the present invention is described above in the preceding section.
- the slurry is then delivered to the polishing pad as shown at block 404 .
- a film is polished as a wafer coated with the thin film is brought into contact with a rotating polishing pad onto which the slurry containing large and small ceria particles has been delivered.
- FIG. 4 shows a flow diagram of an alternative process 500 embodying the present invention.
- a ceria containing slurry is prepared.
- the ceria containing slurry is delivered to, and dispensed onto, a polishing pad.
- an organic polymer film is polished as a wafer coated with the thin organic polymer film is brought into contact with a rotating polishing pad onto which the slurry containing ceria has been delivered.
- Typical polishing conditions are down force of approximately 3 psi, 180 rpm effective rotational speed, temperature between approximately 10° C. and 25° C.
- Polishing pads such as the Politex Supreme, and Suba-4, made by Rodel, Inc. of Newark, Del., can be used with the ceria based slurry to polish organic films. Removal rates of greater 2250 angstroms/minute have been obtained when polishing organic material such as parylene.
- Embodiments of the present invention provide ceria based slurries for chemical mechanical polishing of thin films, at low pressure and high polish rates.
- These thin films are typically comprised of materials that are softer than silicon dioxide films.
- organic polymer thin films are softer than silicon dioxide thin films.
- An advantage of some embodiments of the present invention is that the polish time can be reduced thus reducing manufacturing cost.
- a further advantage of some embodiments of the present invention is that dishing is reduced when polishing polymer films.
- a still further advantage of some embodiments of the present invention is that scratching of polymer films during polishing is reduced.
Abstract
A ceria based abrasive is used in a chemical mechanical polishing operation at low polish pressure, and a predetermined pH range, to achieve high polish rates and good uniformity when planarizing layers formed from low dielectric constant materials, including but not limited to polymers. The distribution of ceria particle sizes in an exemplary slurry is bimodal and controlled.
In a particular embodiment a polishing abrasive containing a controlled distribution of ceria particle sizes is used in a CMP polisher apparatus with a polishing pressure of approximately 3 psi and a pH of approximately 10.6 to planarize polymer films.
Description
- 1. Field of the Invention
- The present invention relates to the field of planarization, and more specifically, to ceria based abrasives for chemical-mechanical polishing (CMP).
- 2. Background
- Advances in semiconductor manufacturing technology have led to the development of integrated circuits having multiple levels of interconnect. In such an integrated circuit, patterned conductive material on one interconnect level is electrically insulated from patterned conductive material on another interconnect level by films of material such as silicon dioxide. Connections between the conductive material at the various interconnect levels are made by forming openings in the insulating layers and providing an electrically conductive structure such that the patterned conductive material from different interconnect levels are brought into electrical contact with each other. These electrically conductive structures are often referred to as contacts or vias.
- A consequence of having multiple layers of patterned conductive material separated by an insulating layer is the formation of undesired capacitors. The parasitic capacitance between patterned conductive material, or more simply, interconnects, separated by insulating material on microelectronic devices contributes to effects such as RC delay, power dissipation, and capacitively coupled signals, also known as cross-talk.
- One way to reduce the unwanted capacitance between the interconnects is to use an insulating material with a lower dielectric constant. Recently, polymers have been introduced for use in integrated circuit manufacturing as dielectrics having a lower dielectric constant than conventionally used oxides of silicon.
- Nonplanar surfaces, when present in integrated circuits having complex, high density multilevel interconnections, may cause the optical resolution of photolithographic processing steps to be poor, which could inhibit the printing of high density lines. Another problem that may be caused by nonplanar surface topography relates to step coverage of metal layers. If steps are too high or uneven, open circuits could be created. It is thus important, when making such complex integrated circuits, to planarize the surface of many of the layers that make up the device.
- Various techniques have been developed to planarize certain layers formed during the process of making integrated circuits. In one approach, known as chemical-mechanical polishing, protruding steps, such as those that may be formed along the upper surface of interlayer dielectrics (“ILDs”), are removed by polishing. Chemical-mechanical polishing may also be used to planarize conformally deposited metal layers to form planar plugs or vias.
- Accordingly, there is a need for CMP methods and apparatus to polish low dielectric constant materials such as polymers.
- Briefly, a ceria based slurry is used in a chemical mechanical polishing operation at low polish pressure, and a predetermined pH range, to achieve high polish rates and good uniformity when planarizing films formed from low dielectric constant materials, such as polymers.
- In a further aspect of the present invention, the distribution of ceria particle sizes in a slurry is bimodal, that is, controlled such that there are two distinct particle size ranges.
- In a particular, exemplary embodiment of the present invention, a ceria based polishing slurry containing a bimodal distribution of ceria particle sizes is used in a CMP polisher apparatus with a polishing pressure of approximately 3 psi and a pH of approximately 10.6 to planarize fluorinated organic polymers.
- FIG. 1 is a cross-sectional view of a CMP apparatus using a convex solid to bend a wafer, and a conventional retaining ring.
- FIG. 2 is a top view of a polishing pad covered platen, retaining ring, and slurry delivery arm, indicating the slurry delivery point to the polishing pad.
- FIG. 3 is a flowchart showing the operations in a process of making a slurry in accordance with the present invention.
- FIG. 4 is a flowchart showing the operations in a process of polishing a thin film in accordance with the present invention.
- An improved method and apparatus for the chemical-mechanical polishing of thin films formed on a substrate is described. In the following description numerous specific details are set forth to provide an understanding of the present invention. It will be apparent, however, to those skilled in the art and having the benefit of this disclosure, that the present invention may be practiced with apparatus and processes that vary from those specified here.
- Terminology
- Substrate, as used herein, refers to the physical object that is to be planarized by means of the CMP process. A substrate may also be referred to as a wafer. Wafers, may be made of semiconducting, non-semiconducting, or combinations of semiconducting and non-semiconducting materials. Silicon wafers may have thin films of various materials formed upon them. These thin films may be planarized with CMP processing. Other substrate materials such as GaAs, silicon-on-sapphire, or silicon on insulator (SOI) may be planarized with CMP processing.
- The terms contact and via, both refer to structures for electrical connection of conductors from different interconnect levels. These terms are sometimes used in the art to describe both an opening in an insulator in which the structure will be completed, and the completed structure itself. For purposes of this disclosure contact and via refer to the completed structure.
- The expression, low dielectric constant material, refers to materials having a lower dielectric constant than oxides of silicon.
- The term vertical, as used herein, means substantially orthogonal to the surface of a substrate.
- RPM (also rpm) refers to revolutions per minute.
- Overview
- Ceria is an oxide of the rare earth element Cerium (Ce) and is often referred to by the chemical formula CeO2. Ceria has been used for glass polishing applications such as lens and mirror manufacturing in the past. Ceria is typically mined, and is commercially available as a powder wherein the particles have rough edges.
- Polishing with relatively large, rough-edged ceria particles provides a fast polish, that is, a high polishing rate, but results in scratches on the surface being polished. On the other hand, polishing with relatively small ceria particles reduces the scratching problem but also reduces the polish rate to such an extent that polishing with these small particles is impractical. In some cases of polishing with small ceria particles the polishing process is observed to “shut down”, that is, to stop polishing.
- In accordance with the present invention, organic polymer dielectrics are subjected to chemical mechanical polishing operations using a slurry that contains a predetermined ratio of ceria particle sizes.
- Polymer films, such as those used to form low dielectric constant insulating layers in ICs, are much softer than the oxides of silicon that have been commonly used to form inter-layer dielectrics. When these polymer films are polished in a chemical mechanical polishing operation, with conventional abrasives such as silica and alumina, significant scratching of the polymer film occurs as a result of the softness of the film. Additionally, these organic polymer films tend to be somewhat resistant to chemical attack from water based slurry chemistries.
- A slurry in accordance with the present invention is based on ceria rather than the conventional abrasives such as silica or alumina. A ceria based slurry according to the present invention enables high polish rates and substantially reduces scratching of polymer films.
- The Slurry
- A slurry, in accordance with the present invention, for chemical mechanical polishing of thin films, such as polymer dielectric layers on microelectronic devices, includes ceria particles of at least two size ranges, silica particles, water, and a compound for determining the pH of the slurry.
- An example of a slurry in accordance with the present invention includes 1 part of a pre-mixed slurry, (CABOT EP7391-100 (2 wt. % silica, 6.5 wt % small particle ceria, potassium hydroxide and de-ionized water)), 7 parts de-ionized water, 2 grams/liter large particle ceria, 4 grams/liter potassium carbonate, and 1 gram/liter potassium bicarbonate. Alternatively, large particle ceria can be added in amounts as low as 0.75 grams/liter.
- The potassium carbonate and potassium bicarbonate act as pH buffers. This exemplary slurry has a pH of approximately 10.6 and a specific gravity of approximately 1.015. Those skilled in the art will recognize that the slurry may be buffered to other values of pH.
- Those skilled in the art and having the benefit of this disclosure will further recognize that it is not necessary to use pre-mixed slurry formulations as part of the present invention. Rather, this example is provided to illustrate the present invention.
- Small particle ceria refers to crushed ceria that is filtered to a size of approximately 0.43 microns, such that approximately 99% of the particles are of this size. Large particle ceria refers to crushed ceria that is filtered to a size of approximately 2.8 microns, such that approximately 99% of the particles are of this size. The large ceria particles are typically added to the small particle slurry and mixed with a motor driven stirrer. By combining the materials described above, a slurry is obtained having a predetermined ratio between large and small ceria particles.
- Method
- An embodiment of the method of polishing a thin film on a wafer containing microelectronic devices, in accordance with the present invention is described in conjunction with FIGS.1-3.
- In a typical CMP system, as shown in FIG. 1, a
wafer 102 is placed face down on a rotating table 104 covered with apolishing pad 106, which has been coated with aslurry 108. Acarrier 100, which may be made of a thicknonflexible metal plate 114 that is attached to arotatable shaft 105, is used to apply a downward force against the backside ofwafer 102. A retainingring 117 may be used tocenter wafer 102 ontocarrier 100 and to preventwafer 102 from slipping laterally. Typically, the surface ofwafer 102 extends outwardly beyond the polishing side surface of retainingring 117. Aresilient carrier pad 112 positioned betweenmetal plate 114 andwafer 102, is typically used to press against the backside ofwafer 102. Often,plate 114 will be manufactured with a slight convex curvature so as to bend the central portion of a wafer outward. By applying the downward force, androtating wafer 102, while simultaneously rotating slurry coveredpad 106 for a selected amount of time, a desired amount of material may be removed from the upper surface of a thin film such that the surface ofwafer 102 is planarized. - FIG. 2 provides a top view of a conventional CMP system, showing
polishing pad 202, retainingring 204, andslurry delivery arm 206. The ceria based slurry of the present invention is typically delivered to the polishing pad through the use of peristaltic pumps. - Although polishing typically takes place in a range of temperatures from about 10° C. to about 25° C., further chilling the pad, slurry, or wafer may improve polymer polishing results. Generally, hard materials polish more easily than soft materials. Polymers tend to be softer than other materials that are routinely planarized by chemical mechanical polishing. Since polymers tend to harden with decreasing temperatures, chilling the polymer film on the wafer will tend to provide a harder surface for polishing.
- Although polymer films are described in the illustrative embodiment herein, the ceria based slurry in accordance with the present invention is suitable for polishing any low dielectric constant thin film, including but not limited to fluorine doped oxides of silicon, amorphous fluorinated carbon, parylenes, and PAE (para arol ethylene). Organic polymers used for low dielectric constant insulators in microelectronic devices can be doped with fluorine to further reduce their dielectric constant, and these can also be polished with the ceria based slurry of the present invention.
- FIG. 3 shows a flow diagram of a
process 400 embodying the present invention. Atblock 402, a slurry containing two distinct size ranges of ceria is prepared by mixing together large size and small size ceria particles. An exemplary formulation of a slurry in accordance with the present invention is described above in the preceding section. The slurry is then delivered to the polishing pad as shown atblock 404. Then, as shown atblock 406, a film is polished as a wafer coated with the thin film is brought into contact with a rotating polishing pad onto which the slurry containing large and small ceria particles has been delivered. - FIG. 4 shows a flow diagram of an
alternative process 500 embodying the present invention. Atblock 502, a ceria containing slurry is prepared. As shown atblock 504, the ceria containing slurry is delivered to, and dispensed onto, a polishing pad. Then, as shown atblock 506, an organic polymer film is polished as a wafer coated with the thin organic polymer film is brought into contact with a rotating polishing pad onto which the slurry containing ceria has been delivered. Typical polishing conditions are down force of approximately 3 psi, 180 rpm effective rotational speed, temperature between approximately 10° C. and 25° C. Polishing pads such as the Politex Supreme, and Suba-4, made by Rodel, Inc. of Newark, Del., can be used with the ceria based slurry to polish organic films. Removal rates of greater 2250 angstroms/minute have been obtained when polishing organic material such as parylene. - Conclusion
- Embodiments of the present invention provide ceria based slurries for chemical mechanical polishing of thin films, at low pressure and high polish rates. These thin films are typically comprised of materials that are softer than silicon dioxide films. For example, organic polymer thin films are softer than silicon dioxide thin films.
- An advantage of some embodiments of the present invention is that the polish time can be reduced thus reducing manufacturing cost.
- A further advantage of some embodiments of the present invention is that dishing is reduced when polishing polymer films.
- A still further advantage of some embodiments of the present invention is that scratching of polymer films during polishing is reduced.
- It will be apparent to those skilled in the art a number of variations or modifications may be made to the illustrative embodiments described above. For example, various combinations of particle sizes, slurry pH, slurry delivery rate, pad rotation speed, pad temperature, and so on, may be used within the scope of the present invention.
- Other modifications from the specifically described apparatus, slurry, and process will be apparent to those skilled in the art and having the benefit of this disclosure. Accordingly, it is intended that all such modifications and alterations be considered as within the spirit and scope of the invention as defined by the subjoined claims.
Claims (23)
1. A method of planarizing a film, comprising:
polishing the film with a ceria based slurry;
wherein the film comprises an organic polymer.
2. The method of claim 1 , wherein the organic polymer comprises a fluorinated polymer.
3. The method of claim 1 , wherein the organic polymer is selected from the group consisting of parylene, and para arol ethylene.
4. The method of claim 1 , wherein the ceria based slurry comprises ceria particles having a first size, ceria particles having a second size, and wherein there is a predetermined ratio of the ceria having the first size particles to the ceria having the second size particles.
5. The method of claim 4 , wherein the first size is approximately 0.43 microns and the second size is approximately 2.8 microns.
6. The method of claim 1 , wherein the slurry contains approximately 1% to 3% by weight of ceria.
7. The method of claim 1 , wherein the slurry contains approximately 1.5% by weight of ceria.
8. The method of claim 1 , wherein polishing comprises chemical mechanical polishing with a down force of less than approximately 4 psi.
9. The method of claim 1 , wherein polishing comprises:
engaging the film with a polishing pad with a down force of approximately 3 psi; and
providing an effective rotational speed of approximately 180 rpm.
10. The method of claim 1 , further comprising controlling the temperature of the film such that polishing occurs in the range of approximately 10° C. to 25° C.
11. A method of planarizing a film, comprising:
polishing the film with a ceria based slurry;
wherein the ceria based slurry comprises a first amount of ceria particles having a first size range, and a second amount of ceria particles having a second size range, wherein there is a predetermined ratio of the first amount to the second amount.
12. The method of claim 11 , wherein polishing comprises bringing the film into contact with a rotating polishing pad.
13. The method of claim 11 , wherein the first size range requires approximately 99% of the particles to be filtered to 0.43 microns and the second size range requires approximately 99% of the particles to be filtered to approximately 2.8 microns.
14. The method of claim 11 , wherein the predetermined ratio of ceria particles sizes is selected to prevent shut down.
15. A slurry, comprising:
a first oxide of cerium having a particle size range wherein approximately 99% are approximately 0.43 microns; and
a second oxide of cerium having a particle size range wherein approximately 99% are approximately 2.8 microns.
16. The slurry of claim 15 , further comprising an oxide of silicon.
17. The slurry of claim 15 , further comprising water.
18. The slurry of claim 17 , wherein the water is deionized.
19. The slurry of claim 15 , further comprising:
silica; potassium hydroxide, potassium carbonate, potassium bicarbonate, and deionized water;
wherein the concentration of the first oxide of cerium together with the second oxide of cerium is in the range of approximately 1.0% to 3.0% by weight;
wherein the concentration of the silica is approximately 0.5% by weight; and
wherein the slurry has a pH of approximately 10.6.
20. A slurry comprising:
ceria having a first range of particle sizes; ceria having a second range of particle sizes; silica; potassium hydroxide; and de-ionized water;
wherein the concentration of the ceria having the first range of particle sizes, together with the ceria having the second range of particle sizes is approximately 1.5% by weight; and the concentration of silica is approximately 0.5% by weight.
21. The slurry of claim 19 further comprising a pH buffer.
22. The slurry of claim 21 , wherein the pH buffer comprises potassium carbonate and potassium bicarbonate.
23. A slurry for polishing an organic polymer films on a wafer, comprising:
1 part of a pre-mixed slurry, comprising 2 wt. % silica, 1.5 wt % small particle ceria, potassium hydroxide and de-ionized water; and 7 parts de-ionized water, 2 grams/liter large particle ceria, 4 grams/liter potassium carbonate, and 1 gram/liter potassium bicarbonate;
wherein the slurry has a pH of approximately 10.6 and a specific gravity of approximately 1.015.
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WO2006076857A1 (en) * | 2005-01-19 | 2006-07-27 | Anji Microelectronics (Shanghai) Co., Ltd | Cmp polishing system and abrasive solution |
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