Patent Application
20080182413
1. Field of the Invention
Embodiments of the invention generally relate to planarization of semiconductor devices and to methods and compositions for material removal using polishing techniques.
2. Description of the Related Art
Reliably producing sub-half micron and smaller features is one of the key technologies for the next generation of very large-scale integration (VLSI) and ultra large-scale integration (ULSI) of semiconductor devices. However, the shrinking dimensions of interconnects in VLSI and ULSI technology has placed additional demands on the processing capabilities. The multilevel interconnects that lie at the heart of this technology require precise processing of high aspect ratio features, such as vias, contacts, lines, and other interconnects. Reliable formation of these interconnects is important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates and die.
Multilevel interconnects are formed by the sequential deposition and removal of materials from the substrate surface to form features therein. As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar across its surface and require planarization prior to further processing. Planarizing a surface, or “polishing” a surface, is a process where material is removed from the surface of the substrate to form a generally even, planar surface. Planarization is useful in removing excess deposited material and in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials to provide an even surface for subsequent processing.
Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize substrates. In conventional CMP techniques, a substrate carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing media in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate urging the substrate against the polishing media. The substrate and polishing media are moved in a relative motion to one another.
A polishing composition is provided to the polishing media to effect chemical activity in removing material from the substrate surface. The polishing composition may contain abrasive material to enhance the mechanical activity between the substrate and polishing media. Thus, the CMP apparatus effects polishing or rubbing movement between the surface of the substrate and the polishing media while dispersing a polishing composition to effect both chemical activity and mechanical activity. The chemical and mechanical activity removes excess deposited materials as well as planarizing a substrate surface.
Chemical mechanical polishing may be used in the fabrication of shallow trench isolation (STI) structures. STI structures may be used to separate transistors and components of a transistor, such as source/drain junctions or channel stops, on a substrate surface during fabrication. STI structures can be formed by depositing a series of dielectric materials and polishing the substrate surface to remove excess or undesired dielectric materials. An example of a STI structure includes depositing a silicon nitride layer on an oxide layer formed on a silicon substrate surface, patterning and etching the substrate surface to form a feature definition, depositing a silicon oxide fill of the feature definitions, and polishing the substrate surface to remove excess silicon oxide to form a feature. The silicon nitride layer may perform as a barrier layer, a hard mask during etching of the features in the substrate and/or as a polishing stop during subsequent polishing processes. Such STI fabrication processes require polishing the silicon oxide layer to the silicon nitride layer with a minimal amount of silicon nitride removed during the polishing process in order to prevent damaging of the underlying materials, such as oxide and silicon.
The STI substrate is typically polished using conventional, abrasive-free, polishing media and an abrasive containing polishing slurry. However, polishing STI substrates with conventional polishing articles and abrasive containing polishing slurries has been observed to result in overpolishing of the substrate surface and forming recesses in the STI features and other topographical defects such as microscratches on the substrate surface. This phenomenon of overpolishing and forming recesses in the STI features is referred to as dishing. Dishing is highly undesirable because dishing of substrate features may detrimentally affect device fabrication by causing failure of isolation of transistors and transistor components from one another resulting in short-circuits. Additionally, overpolishing of the substrate may also result in nitride loss and exposing the underlying silicon substrate to damage from polishing or chemical activity, which detrimentally affects device quality and performance.
STI polishing with fixed-abrasive polishing articles have shown reduced dishing and improved polishing uniformity compared with conventional slurry polishing processes. A fixed-abrasive polishing article generally contains fixed-abrasive particles held in a containment media, or binder, which provides mechanical activity to the substrate surface, along with a plurality of geometric abrasive composite elements adhered to the containment media. However, conventional fixed-abrasive polishing processes have an inherently low removal rate of oxide material thereby increasing polishing times and reducing substrate throughput. Increased processing time may also occur in conventional deposition processes that use excess material deposition on the substrate surface, referred to as overfill, to ensure fill of features formed in the substrate surface.
Several approaches have been examined for limiting the extent of oxide overfill in forming STI features for improved processing throughput. One approach includes using multiple deposition steps, for example high density plasma chemical vapor deposition (HDP CVD) and etching steps to deposit, etch back, and re-fill substrate features. Another approach uses a sputter or etching process to thin the overfill deposited on the substrate surface. Other approaches include using a post deposition wet etch process to etch the oxide film so that there is still topography remaining for use with fixed-abrasive polishing articles. However, these processes have been observed to increase integration complexity and also have increased processing times and reduced substrate throughput.
Therefore, there exists a need for a method and related polishing apparatus, which facilitates the removal of dielectric materials with minimal or reduced dishing and minimal or reduced loss of underlying materials.
Embodiments of the present invention generally provide methods and compositions for planarizing a substrate surface with selective removal rates and low dishing.
One embodiment provides a method for selectively removing a dielectric disposed on a substrate having a first dielectric material and a second dielectric material disposed thereon. The method generally includes positioning the substrate in proximity with a fixed abrasive polishing pad, dispensing an abrasive free polishing composition having at least one organic compound and at least one polishing enhancement compound therein between the substrate and the polishing pad, and selectively polishing the second dielectric material relative to the first dielectric material. In one embodiment, the second dielectric material is removed at a higher removal rate than the first dielectric material.
Another embodiment provides a method for processing a substrate to selectively remove an oxide material disposed on a nitride material. The method generally includes positioning the substrate in proximity with a fixed abrasive polishing pad, dispensing an abrasive free polishing composition having at least one organic compound, at least one surfactant, at least one pH adjusting agent, and deionized water, between the substrate and the polishing pad, and removing the oxide material and nitride material at a removal rate ratio of the oxide material to the nitride material between about 10:1 or greater.
Another embodiment provides an abrasive free composition for removing dielectric materials using a fixed abrasive polishing pad. In one embodiment, the composition initially consists of at least one organic compound, at least one polishing enhancement compound, at least one pH adjusting agent, and deionized water. In one embodiment, the at least one polishing enhancement compound comprises a surfactant.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures. It is contemplated that elements and/or process steps of one embodiment may be beneficially incorporated in other embodiments without additional recitation.
Embodiments of the invention will be described below in reference to a planarizing process and composition that can be carried out using chemical mechanical polishing process equipment, such as the Applied Reflexion® LK CMP System, the Applied Reflexion® LK Tungsten CMP System, the Applied Reflexion® LK ECMP System, the Applied Reflexion® LK Copper CMP System, and the Applied Reflexion® LK STI CMP, all of which are available from Applied Materials, Inc., of Santa Clara, Calif. In addition, any system enabling chemical mechanical polishing using the methods or compositions described herein can be used to advantage. Examples of other suitable polishing apparatuses include the Applied Mirra Mesa® CMP System also available from Applied Materials, Inc. of Santa Clara, Calif. The following apparatus description is illustrative and should not be construed or interpreted as limiting the scope of the invention.
The CMP apparatus 100 effects a polishing or rubbing movement between the surface of the substrate 112 and the polishing pad 106 by applying an external force 116 between them either linearly or in rotationally while dispensing a polishing composition 118 or slurry with or without abrasive particles in order to effect both chemical and mechanical activities.
Embodiments of the invention include CMP processes and compositions comprised of organic compounds, for example, amino acids, and polishing enhancement compounds, for example, surfactants. In one embodiment, a method of processing a substrate having an oxide material disposed on a nitride material is provided. The method includes positioning the substrate in proximity with a fixed abrasive polishing pad, dispensing a polishing composition between the substrate and the polishing pad, and removing the oxide material at a higher removal rate than the nitride material. Polishing compositions containing organic compounds in combination with a polishing enhancement compound and fixed abrasive polishing pads enable modification of the removal rates for polishing different dielectric materials and reduce dishing and loss of adjacent layers.
In another embodiment, the invention provides a chemical mechanical polishing composition for removing dielectric materials, including at least one organic compound, at least one polishing enhancement compound, at least one pH adjusting agent, and deionized water. The combination of organic compounds with the polishing enhancement compound improved polishing selectivity with fixed abrasive pads.
As used herein “substrate” refers to the object being polished and may include, for example, a silicon based material having materials disposed thereon. The substrates that may be polished by step 210 include shallow trench isolation structures formed in a series of dielectric layers, such as silicon oxide and silicon nitride. The invention contemplates chemical mechanical polishing of dielectric materials conventionally employed in the manufacture of semiconductor devices, for example, silicon dioxide, silicon nitride, silicon oxynitride, phosphorus-doped silicon glass (PSG), boron-doped silicon glass (BSG), boron-phosphorus-doped silicon glass (BPSG), silicon dioxide derived from tetraethyl orthosilicate (TEOS), and silane, which are deposited by various chemical vapor deposition (CVD) techniques, and combinations thereof.
The polishing composition delivered to the fixed abrasive polishing pad at step 220 may include at least one organic compound present in an amount between about 0.5 weight percentage (wt. %) and about 10 wt. % of the polishing composition. A concentration of organic compounds between about 2.5 wt. % and about 4 wt. % is preferably used in the polishing composition. Most preferably, the at least one organic compound may comprise about 2.5 wt. % of the composition. The polishing composition may be delivered or supplied to the fixed abrasive polishing pad at a flow rate of, for example, between about 5 ml/min and about 500 ml/min from a storage medium disposed in or near the CMP system.
Organic compounds useful in the composition include those which may selectively modify the removal rate of one or more dielectric materials in relation to other dielectric materials. In one embodiment, the organic compounds are selected to result in a higher removal rate for silicon oxide material than that for silicon nitride material. Examples of organic compounds include amino acids having amino (NH2) and carboxyl (—COOH) terminal ends, and derivatives thereof, such as, for example, glycine, proline, arginine, histidine, lysine, and combinations thereof. Examples of other organic compounds include picolinic acid, amphoteric compounds containing amine and carboxylic acid functional groups, such as Amphoteric 400 available from Tomah Products, Inc. of Milton, Wis., hydroxyl acids, for example, gluconic and lactic acid, polyanionic polymers, for example, polyacrylic acid and polyvinylsulfonate.
Polishing enhancement compounds useful in the composition generally include surfactants which may selectively modify the removal rate of one or more dielectric materials in relation to other dielectric materials. Surfactants may be used to increase the dissolution or solubility of materials, such as metals and metal ions or by-products produced during processing, reduce any potential agglomeration of abrasive particles in the polishing composition, and improve chemical stability and reduce decomposition of components of the polishing composition. The one or more surfactants can comprise a concentration between about 0.001 wt. % and about 1 wt. % of the polishing composition. A concentration between about 0.05 wt. % and about 0.1 wt. % may be used in one embodiment of the polishing composition.
The one or more surfactants may include non-ionic surfactants as well as ionic surfactants including anionic surfactants, cationic surfactants, amphoteric surfactants, and ionic surfactants having more than one ionic functional group, such as Zwitter-ionic surfactants. Dispersers or dispersing agents are considered to be surfactants as surfactants are used herein. Compositions containing the polymeric abrasives are stable over a broad pH range and are not prone to aggregating to each other, which allow the abrasives to be used with reduced or no surfactant or no dispersing agent in the composition.
Examples of polishing enhancement compounds generally include anionic surfactants, such as DuPont™ Zonyl® FS-610, non-ionic surfactants, such as DuPont™ Zonyl® FSN, cationic surfactants, such as cetyl pyridinium bromide hydrate, and amphoteric surfactants, such as Amphoteric 400. Additional non-ionic fluorosurfactants include: 3M™ Novec™ FC-4430 and PolyFox™ PF-151N and PF-154N available from Omnova Solutions, Inc of Fairlawn, Ohio.
The polishing composition may also include at least one pH adjusting agent to adjust the pH of the polishing composition to improve polishing performance, such as by allowing a positive or negative charge to be developed on the one or more materials disposed on a substrate surface and attract the appropriately charged organic amino acid compounds. The at least one pH adjusting agent in the composition may be added to adjust the pH level of the composition to between about 4 and about 12. For example, a pH-adjusting agent may be added to the composition in an amount sufficient to produce a pH between about 7 and about 11, for example, a pH of about 10.5. The at least one pH adjusting agent may comprise bases such as potassium hydroxide (KOH) and ammonium hydroxide or acids such as nitric acid or sulfuric acid.
The at least one pH adjusting agent may serve as a pad lubricant or a coolant and may increase or decrease the hydration of the silicon-based dielectric materials resulting in the formation of silanol (Si—OH) groups, which enhance removal of materials from the substrate surface. The at least one pH adjusting agent also affects selective formation of certain complexes between the polishing composition and one or more surface dielectric materials and thus affects removal rates of different surface dielectric materials. For example, an acidic pH increases the formation of silanol on silicon oxide and increases the ability of the polishing composition to complex with the silicon oxide material but not the silicon nitride material.
One possible mechanism for the polishing composition to work with fixed abrasive CMP is that the at least one organic compound may complex with silanol (Si—OH) surface groups of the silicon nitride film and suppress removal of the silicon nitride film. Another possible mechanism is that the at least one organic compound in the polishing composition modifies the removal rates of the dielectric materials by forming a removal resistant or passivation layer on at least one material on the substrate surface and this modification of removal rates is favored by, in this case, an increasing pH.
An example of a polishing composition includes between about 0.5 wt. % and about 10 wt. % of proline, for example, about 2.5 wt. % proline, between about 0.0001 to about 1 wt. % of a surfactant, for example, about 0.05 wt. % of a fluorosurfactant, and potassium hydroxide as a pH adjusting agent in a sufficient amount to produce a pH level of about 10.5. A fixed abrasive polishing pad containing ceria-based abrasives in an equivalent concentration between about 1 wt. % and about 50 wt. % of the polishing pad may be used with the polishing composition to remove material from the substrate surface.
At step 230, the substrate and the fixed abrasive polishing pad are contacted and one dielectric material is removed at a higher removal rate than the other dielectric material from the substrate surface. The material may be removed at a rate between about 50 Å/min and about 5000 Å/min. In one embodiment, a removal rate ratio, or selectivity, of the first material, such as silicon oxide, to the second material, such as silicon nitride, of about 10:1 or greater may be achieved through the use of the organic compounds in a composition described herein. In another embodiment, a removal rate of first material to second material from about 100:1 or greater to about 1200:1 or greater may be achieved from the processes described herein. However, the removal rates and removal rate ratios can vary with the processing parameters and polishing composition used.
An example of a polishing process at step 230 includes moving the polishing pad relative to the substrate at a rate between about 10 rpm and about 200 rpm for a polishing pad disposed on a polishing system. The polishing media is moved relative to the substrate at a rate between about 10 rpm and about 100 rpm for a polishing pad disposed on a round or rotatable platen polishing system. A pressure between about 0.5 psi and about 6.0 psi between the substrate and the polishing pad can be used to provide mechanical activity to the polishing process. Alternatively, the invention contemplates polishing the substrate on a variety of polishing platens, such as rotatable platens, rotatable linear platens, and orbital polishing platens.
Addition of at least one organic compound, for example, an amino acid, and a polishing enhancement compound, for example a surfactant, at the proper concentration and pH vastly enhances the performance and flexibility of fixed abrasive CMP. The silicon oxide removal rate is greatly increased while the silicon nitride removal rate is retarded. This enhancement enables shorter polishing times, increased throughput, polishing of thicker overburden substrates, polishing of substrates with a range of feature sizes and densities (e.g., logic applications), improved within-wafer and within-die uniformities, minimized dishing and silicon nitride loss, improved wafer-to-wafer polishing stability, decreased performance degradation due to overpolish, and improved pad wetting.
An example of a polishing process described herein comprises delivering a polishing composition to a fixed abrasive polishing pad containing ceria abrasive particles at a flow rate between 50 ml/min and about 500 ml/min, the polishing composition including between about 0.5 wt. % and about 10 wt. % of proline, for example, about 2.5 wt. % proline, about 0.0001 to about 1 wt. % of a surfactant, for example about 0.05 wt. % of surfactant, deionized water, and potassium hydroxide as a pH adjusting agent in a sufficient amount to produce a pH level between about 10.0 and 12, for example, a pH of about 10.5. A polishing pressure between about 1 and about 6 psi, and a polishing speed between about 10 rpm and about 100 rpm for a polishing duration between about 30 seconds and about 300 seconds may be used to planarize a substrate.
The above-specified components and processing parameters are illustrative and should not be construed as limiting the invention. It is contemplated that the compounds and concentrations used may be varied to provide desired removal rates of 100 Å/min or higher, desired selectivity to stop-on-planar, desired selectivity to stop-on-nitride, and the nature and amount of the desired materials to be removed from the substrate surface. As an example, steps 210, 220, and 230 in
The invention also contemplates modification of other processes and compositions for shallow trench isolation substrates including the processes and compositions described in U.S. Pat. No. 7,063,597, issued Jun. 20, 2006, entitled POLISHING PROCESSES FOR SHALLOW TRENCH ISOLATION SUBSTRATES and U.S. Patent Application Publication No. 2003/0176151, published Sep. 18, 2003, entitled STI POLISH ENHANCEMENT USING FIXED ABRASIVES WITH AMINO ACID ADDITIVES, which are both herein incorporated by reference to the extent they do not conflict with the current specification. For example, the process including a first step using a slurry on a first platen to remove the bulk of the oxide overburden, a second step involving a fixed abrasive polish on a second platen to complete the planarization process, and a particle rinse step may be modified with the current invention.
The addition of the polishing enhancement composition provides increased flexibility in establishing polish processing parameters. For example, increased oxide removal rates may be achieved without increasing polishing speed and/or downforce conditions.
In another embodiment a concentrated version of the polishing composition is provided. Polishing compositions for fixed abrasive CMP contain mostly water with small amounts of specific chemicals added to enhance polish selectivity and/or to enhance oxide removal performance. For example, one embodiment of a polishing composition contains a selectivity-enhancing additive such as proline in a concentration of between about 2 to 4 wt. %. Surfactants may have a concentration of about 0.1 wt. %. Solution pH is adjusted by addition of less than 1 wt. % of a concentrated base such as KOH. Water is by far the dominant component of the polishing composition (95 to 98% of the total fluid volume). It is more cost effective to ship a concentrated version that can be diluted to the correct strength at the customer's site.
In one embodiment a concentrated polishing composition that is at least 5 times more concentrated than the polishing composition used for polishing wafers with fixed abrasive CMP is provided. In another embodiment, the concentrated polishing composition is at least ten times more concentrated than the polishing composition. In certain embodiments, the L-proline concentration in the polishing composition used for polishing wafers is 2.5 to 4 g per 100 ml water. For the concentrated polishing composition which is five times more concentrated than the polishing composition, the concentration of L-proline would increase, for example, to 12.5 to 20 g per 100 ml. For the concentrated polishing composition which is ten times more concentrated than the polishing composition, the concentration of L-proline would increase to 25 to 40 g per 100 ml, which is well below the literature value of 162 g per 100 ml for water solubility of proline (25° C.). The concentrated polishing composition contains about 1 % flourosurfactant.
KOH is used to adjust fluid pH to within the range of 10 to 11, with 10.5 being most common. Proline acts as a pH buffer in this range, so that substantially more KOH must be added as the target pH increases (10→11) and/or as the proline concentration increases (2.5→4 wt. %). The typical KOH concentration in the polish fluid is about 0.25%, ranging up to about 0.9% in the high pH, high proline concentration case. At 10× concentration these values would be 2.5 to 9%. Thus, all of the polish fluid components are well within the solubility or dispersion limits for a 10× concentrated solution.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
| Number | Date | Country | |
|---|---|---|---|
| 60822625 | Aug 2006 | US |
