Chemical Planarization Tools

Abstract

Examples related to planarizing a substrate without the use of abrasives are disclosed. One example provides a method for chemically planarizing a substrate, the method including: introducing an abrasive-free planarizing solution onto a porous pad; contacting the substrate with the porous pad while moving the porous pad and the substrate relative to each other so that higher portions of the substrate contact the porous pad and lower portions of the substrate do not contact the porous pad; and removing material from the higher portions of the substrate through contact with the porous pad to reduce the height of the higher portions of the substrate relative to the lower portions of the substrate.

Description

[Background technology]

[0001] Chemical-mechanical planarization (CMP) is commonly used in integrated circuit manufacturing processes to remove material and smooth surfaces, such as semiconductor substrates, through a combination of chemical action and mechanical force. A typical CMP process uses a chemical slurry, which is abrasive and corrosive to the material being removed, in combination with a polishing pad. The substrate and polishing pad are pressed together and rotated relative to one another on non-concentric axes. The combined force and slurry remove topologically high areas of the substrate relative to topologically low areas, thereby smoothing the surface. Summary of the Invention

[0002] This Summary is provided to introduce in a simplified form some of the concepts discussed below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Moreover, the claimed subject matter is not limited to implementations that solve any or all of the disadvantages noted in any part of this disclosure.

[0003] Embodiments related to planarizing a substrate without the use of abrasives are disclosed. In one embodiment, a method for chemically planarizing a substrate is provided, the method including: introducing an abrasive-free planarizing solution onto a porous pad; contacting the substrate with the porous pad while moving the porous pad and the substrate relative to each other so that higher portions of the substrate contact the porous pad and lower portions of the substrate do not contact the porous pad; and removing material from the higher portions of the substrate through contact with the porous pad to reduce the height of the higher portions of the substrate relative to the lower portions of the substrate.

[0004] In another embodiment, a porous pad for chemical planarization of a substrate is provided, including a first polymer layer and a second polymer layer, the first polymer layer configured to contact the substrate during planarization, the first polymer layer having a first, larger average pore size and a first, smaller thickness, and a second polymer layer disposed on an opposite side of the first polymer layer from the substrate contacting side, the second polymer layer having a second, smaller average pore size and a second, larger thickness. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a block diagram of an example chemical planarization system. [Figure 2] FIG. 2 shows a schematic diagram of an example of a porous pad for chemical planarization, showing the contact between the topological high points of the substrate and the upper layer of the pad. [Figure 3] FIG. 3 is a schematic diagram illustrating an example of a rotating platform for applying a chemical planarizing solution to a substrate. [Figure 4] FIG. 4 is a schematic diagram illustrating an example of a hollow fiber membrane platform for delivering chemical planarization solutions to a substrate. [Figure 5] FIG. 5 is a flow diagram showing an example of a method for performing chemical planarization. DETAILED DESCRIPTION OF THE INVENTION

[0006] Current CMP techniques are widely used in device manufacturing, but they also suffer from various drawbacks. For example, current CMP processes have a relatively high level of contamination compared to other manufacturing processes, due in part to the polishing slurries and pads that mechanically remove material during conditioning and planarization. Defects caused by CMP can be a significant source of yield loss for fabs. Defects and scratches during CMP are often caused by mechanical aspects of the process, such as the abrasives in the slurry, the pressure of the pad against the substrate, pad conditioning, and the tribological aspects of the process. Furthermore, the abrasives in the slurry can scratch the device layers, creating pits and leaving residue that can lead to defects. Furthermore, pad residue is generated during polishing and pad conditioning. This pad residue can generate particles and agglomerates that contaminate the processed substrate, and the force with which the pad is pressed against the wafer can cause pad deformation. This can result in shear stresses at the interface due to intimate contact with the substrate and relative motion between the substrate and pad. Furthermore, CMP processes are not always predictable and can be dominated by a trial-and-error approach rather than an analytical one. Furthermore, handling, delivering, and stabilizing slurries can pose challenges to fabrication facilities due to solids, increasing the cost of maintaining the facility. Consequently, traditional CMP processes can require redundant depositions and over-polishing, resulting in wasted resources, increased costs, and reduced productivity.

[0007] Thus, disclosed herein are examples of chemical planarization that avoid the contaminating and defect-prone mechanical processes used in conventional CMP methods. Briefly, the disclosed embodiments use an abrasive-free planarization solution instead of an abrasive slurry and selectively remove material from topologically high versus low portions of the substrate at a higher rate by controlling the contact of the planarization solution with the substrate surface. "Abrasive-free" refers to a planarization solution that does not contain mechanically abrasive solid components for substrate removal. As described in more detail below, in some embodiments, the abrasive-free planarization chemistry resides within the porous pad, rather than on the pad between the pad and the substrate. In this way, contact between the porous pad and the topologically high features of the substrate can be controlled, while contact between the porous pad and the low features of the substrate can be controlled. The planarization chemistry acts on the portions of the substrate that are in contact with the porous pad, thereby selectively removing material from those portions of the substrate. In this way, it is possible to achieve a smoother substrate surface topology without the use of abrasives and with relatively light pressure on the substrate. This avoids scratches and other damage to the device layers, thereby avoiding the generation of defects and improving yield compared to conventional CMP processes.

[0008] FIG. 1 shows a schematic diagram of an example chemical planarization system 100 according to the present disclosure. The system 100 includes a platen 102 supporting a porous pad 104. The system 100 further includes a substrate holder 106 configured to hold a substrate 108 against the surface of the porous pad 104 and a planarization solution introduction system 110 for introducing a planarization solution 112 onto the porous pad 104. The system 100 may further include a pad cleaning system 114 configured to clean possible contaminants from the porous pad 104, such as compound materials removed from the surface of the substrate 108. The pad cleaning system 114 may also be used to clean the pad between uses of different planarization solutions, as described below. Other components that may be incorporated into the system 100 include, but are not limited to, a used solution recovery system, a material recirculation system (e.g., for recirculating the planarization solution in a closed-loop process), and a chemical stripping system.

[0009] In a conventional CMP process, a substrate holder presses a substrate against a polishing pad supported on a platen, and the pad and substrate rotate non-concentrically relative to one another. In such conventional processes, a relatively high rotational speed, e.g., 40-100 rpm, is used. Furthermore, the substrate is pressed against the pad with a relatively high pressure, such as 1-4 pounds per square inch. In contrast, the embodiments disclosed herein may use lower pressures, such as, but not limited to, 0.25-0.75 pounds per square inch. Using lower pressures avoids distortion of the pad shape and reduces shear stress compared to conventional CMP processes. Similarly, the embodiments disclosed herein may use lower rotational speeds than conventional CMP processes because rotational motion is not used for polishing. Instead, the rotation of the platen 102 serves to distribute the planarizing fluid throughout the porous pad 104. Any suitable rotational speed may be used. Examples include, but are not limited to, speeds in the range of 0-60 rpm, preferably 5-30 rpm.

[0010] The planarizing solution may include chemical components for the purpose of hydrolyzing the substrate (e.g., by oxidation and dissolution). The planarizing solution may be configured to remove any suitable material. As one example, polysilicon may be removed via a planarizing solution consisting of poly(diallyldimethylammonium chloride) (PDADMAC) in deionized water. In some such examples, the PDADMAC solution may be mixed with oxalic acid and / or hydrogen peroxide and may further include an appropriate acid or alkaline agent (e.g., nitric acid or potassium hydroxide) for pH adjustment. Other reagents may also be used for polysilicon planarization, including, but not limited to, poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine), poly(allylamine), and poly(ethyleneimine) (PEI). As another example, copper or cobalt may be removed using a planarizing solution consisting of hydrogen peroxide and guanidine carbonate, again with a pH adjuster to achieve the desired solution pH. As another example, ammonium persulfate may be used for cobalt removal, along with a pH adjuster to achieve the desired solution pH. Examples of other suitable hydrolyzing agents include, but are not limited to, nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, and the like.

[0011] In some examples, the planarizing solution may include additional components. For example, the planarizing solution may include a complexing / chelating agent to transport materials removed from the substrate after hydrolysis. Examples of suitable chelating agents include, but are not limited to, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DPTA), nitrilotriacetic acid (NTA), iminodisuccinic acid (IDS), ethylenediamine-N,N'-disuccinic acid (EDDS), sulfosalicylic acid, naphthol (PAN), cyclodextrin, dithizone, organophosphate esters, polyethylene glycol, amines, and thioxine. Furthermore, in some examples, the planarizing solution may include a passivator and / or a corrosion inhibitor. Examples include, but are not limited to, benztriazole (BTA), tolyltriazole (TTA), thiols (e.g., PTAT (5-(phenyl)-4H-1,2-4-triazole-3-thiol)), thiodiazoles, carboxylic acids, benzoic acid, and ammonium benzoate. Other examples of materials that may be included in the planarization solution include, but are not limited to, surfactants, surface modifiers other than passivators and / or corrosion inhibitors, catalysts, heat-activated chemicals, light-activated chemicals, species tracers, additives, and stabilizers.

[0012] In some instances, as described in further detail below, the hydrolysis agent and complexing agent can be bound to a functionalized polymer of the porous pad. In such instances, the planarization solution dispensed onto the porous pad includes deionized water, and chemical planarization is performed by the functionalized polymer. In such instances, the planarization solution may include additional components other than deionized water, as described above.

[0013] FIG. 2 is a schematic diagram illustrating an example of a porous pad 200 suitable for use as the porous pad 104. The porous pad 200 includes a first layer 202 and a second layer 204. Such a two-layer structure can be used to implement a two-part material removal or separation process, where the first step involves hydrolysis (and possibly dissolution) of the species to be removed and the second step involves chemical complexation of the species. The first layer 202 may be relatively thin compared to the second layer and may be configured for hydrolysis of the material to be removed in the planarization process (e.g., oxidation of metal species in some instances). As such, the first layer 202 may include relatively large pores, may be hydrophilic, or may be surface-modified to functionalize the polymer surface, thereby enabling the polymer of the first layer 202 to participate in the hydrolysis reaction. In some instances, the first layer may have a thickness ranging from 0.1 microns to 5 microns. In some instances, the first layer 202 and / or the second layer 204 may include surface irregularities such as defects, cavities, microcracks, edges, or other surface features. Furthermore, in some examples, the first layer may have an average pore size ranging from 10 nm to 1000 nm, preferably from 30 nm to 200 nm. The first and second layers may be made of any suitable material. In some examples, the first layer 202 and / or the second layer 204 may be composed of one or more of polyurethane, polycarbonate, polyacrylate, polysulfone, polyester, polyacrylonitrile, polyethersulfone, polyarylsulfone, polyacrylonitrile, polyamide, polyimide, polyether, polyetherketone, alkyl terephthalate, aryl terephthalate, and polyvinylidene fluoride. Furthermore, the first and / or second layer may have a hardness of 60 to 90 Shore A or a hardness of 30 to 60 Shore D. While porous pads can be used as polishing pads, in other examples, the polishing pad may be composed of a non-porous microtextured pad.

[0014] Additionally, the porous polymer of the first and / or second layers may be designed to be stiff enough to handle the wafer load and hold down force / applied pressure, and to have viscoelastic properties and physical attributes as determined by standard DMA, DSC, and TGA methods, such as a storage modulus of 15 MPa to 1200 MPa, preferably 400 to 800 MPa, a loss modulus of 100 to 600 MPa, preferably 150 to 500 MPa, a loss tangent (loss ÷ storage) of 0.2 to 0.9, preferably 0.4 to 0.8, a compressibility of less than 20%, and a surface tension of less than 40 mN / m.

[0015] The second layer 204 may be relatively thicker than the first layer and may have relatively smaller pores than the first layer. In some examples, the second layer may be configured to retain materials removed by the first layer. For example, the second layer may include a chemically modified surface with a metal-complexing agent adsorbed or bonded to the second layer within the pores to retain metal ions removed from the substrate. In some examples, the second layer may have a thickness of several microns to 3 mm, and more particularly, a thickness of 40 microns to 2 mm. Furthermore, in some examples, the second layer may have an average pore size ranging from 5 nm to 500 nm. The first and second layers may be bonded together in any suitable manner, such as via an adhesive. In some examples, the porous pad 200 may be glued or otherwise bonded to an additional sublayer, such as a woven matrix or a flexible polymer sheet (e.g., a subpad of the type currently used in conventional CMP polishing pads). In some examples, the two layers are integrated to form an apparent composite porous pad. In such examples, the top and bottom layers may have different properties, resulting in an asymmetric porous medium. Such asymmetric porous media may in some instances exhibit a gradual and systematic transition in pore properties at the interface between the two layers, or may exhibit an abrupt transition.

[0016] The porous polymer of the first and / or second layers may be fabricated by any suitable method. In some instances, phase inversion or phase separation of the polymer can be used. In other instances, vapor-induced phase separation (air casting) can be used. Yet another example is liquid-induced phase separation (immersion casting), where the polymer is dissolved in a solvent at room temperature and immersed in a liquid non-solvent to induce phase separation. This allows for a variety of morphologies, including asymmetric membranes. Methods for forming asymmetric structures (e.g., multilayer porous matrices) include manipulating the phase separation conditions during single-layer casting, casting a small-pore membrane on a large-pore substrate, simultaneously casting multiple layers with different pore sizes, stacking layers with different pore sizes, and utilizing temperature-induced phase separation (TIPS or melt casting), where a polymer is heated above its melting point to dissolve in a porogen and then cooled to induce phase separation. In some instances, asymmetry using fillers can be introduced by size differences due to processing methods. For example, size differences can be induced by thermal, gravitational, or fluid dynamics during polymer processing. In yet another example, the pores may be symmetrical, having the same pore structure throughout the polymer layer of the porous pad.

[0017] In other examples, both hydrolysis and complexation may be provided by different functionalized species in first layer 202 and / or second layer 204. Additionally, in some examples, a single layer porous pad may be used that is configured so that hydrolysis and complexation occur in the same layer.

[0018] Also depicted in Figure 2 is contact between substrate 206 and porous pad 200. Substrate 206, in some examples, may represent substrate 108 from Figure 1. As shown in Figure 2, contact between substrate 206 and porous pad 200 is limited to the topologically high regions of substrate 206, such that porous pad 200 does not contact the topologically low regions of the substrate. The relatively low pressure of substrate 206 against porous pad 200, combined with the hydrolysis chemicals being located within porous pad 200 rather than in the space between the pad and substrate, helps achieve a higher rate of material removal from the topologically high regions of substrate 206 compared to, or to the exclusion of, the topologically low regions, as the topologically high regions are in contact with the hydrolysis environment within the porous pad.

[0019] First layer 202 and second layer 204 may each have any suitable configuration, including, in various examples, laminar, hollow tubular or fibrous, spirally wound, or sheet-like configurations.

[0020] The chemical planarization techniques disclosed in the examples herein offer various advantages over conventional chemical mechanical planarization. For example, selective material removal from topologically elevated regions on a substrate can be achieved with less pressure and motion between the substrate and pad and without the use of abrasive materials in the slurry. This reduces or eliminates randomness introduced by the mechanical aspects of conventional CMP (e.g., pad-to-substrate friction and relative rotations per minute), making the process more predictable and amenable to modeling through a clear understanding of chemical kinetics and diffusion. Furthermore, the use of pad conditioners can be avoided. All of these factors may help avoid defects caused by mechanical processes in conventional CMP processes and therefore may help improve yield compared to conventional CMP processes. The disclosed examples are chemically customizable for specific applications and can be extended to advanced materials and device designs in the future.

[0021] Additionally, the embodiments described herein can be implemented as a drop-in solution in conventional CMP equipment, for example, by using the disclosed abrasive-free planarization solutions in combination with lower pressures on the pad and lower rotation speeds. Other possible modifications to conventional CMP equipment as part of a drop-in solution include replacing the conventional CMP pad with the disclosed porous pad and replacing the pad conditioner with deionized water or other suitable cleaning fluids. These modifications can be beneficial in that they eliminate problematic processes or materials and reduce costs compared to using conventional CMP equipment.

[0022] Returning to FIG. 1 , system 100 is illustrated as including a rotary tool, with the illustrated platen and / or substrate holder configured to rotate to impart rotational motion of the substrate relative to the pad. In such an example, planarizing solution may be dispensed at a central location on the porous pad. This is shown schematically in FIG. 3 , which shows planarizing solution (represented by arrow 302) dispensed at a central portion of porous pad 304. The substrate location is indicated at 306. The centrally located planarizing solution may flow outward through the porous pad, thereby distributing throughout the volume of the porous pad. Such flow is facilitated by rotating the platen to which the porous pad is attached. As noted above, because rotational motion is not used to abrade material from the substrate in the examples herein, the rotation speed may be lower than the speed at which the platen rotates in a conventional CMP process.

[0023] In other examples, any mechanism other than a rotary mechanism may be used to distribute the planarizing solution. Figure 4 shows a schematic of one example of a hollow fiber membrane mechanism 400 in which planarizing solution 402 flows through hollow fibers 404. A substrate is shown schematically at 406. It will be appreciated that many different configurations and designs are possible for the various platform styles (rotary, linear or belt, vertical, roller, hollow fiber). Additionally, in some examples, chemical materials can be regenerated and reused for cost-effective and environmental reasons.

[0024] As some examples, when metal or alloy layers are being processed, the platen with the attached porous pad can be configured as the anode and the conductive substrate as the cathode. Chemicals between and in contact with high-topography regions act as electrolytes, and electrolytic forces are used to promote selective removal, thereby promoting planarization. In this manner, electrochemically assisted selective removal for planarization can be achieved.

[0025] In various examples, a planarization solution may be applied onto the porous pad at the point of use (POU) before and / or during the substrate planarization process. In some examples, chemistry can be changed during the planarization process by modifying recipe steps. Different chemistries can also be added or changed in situ to ensure proper separation (e.g., dissimilar materials on device layers) and for process control purposes. Furthermore, in some examples, switching from one chemistry to another can be done in situ during substrate planarization (e.g., using a cleaning system between chemistries) or can be specific to different planarization / polishing chambers of a tool (e.g., a multi-plate tool). Furthermore, if a functionalized polymer is used on the porous pad, the functionalization can be regenerated in situ (e.g., through a planarization solution dispensing mechanism) by adding new functional groups, for example, to bond to the polymer material of the pad. In some examples, regeneration is possible by dispensing a stripper solution. Suitable stripping solutions may include applying an acidic solution (e.g., HCl, H2SO4, HNO3) to the pad surface to strip the polished species (e.g., metal species) and leave functional groups on the pad.

[0026] As mentioned above, in some examples, the surface of a polymeric material may be functionalized to impart hydrolytic, complexation, and / or other functionality to the polymer. Functionalizable polymeric materials may include pores, irregularities, and bulk polymers. In such examples, chemicals used to remove and complex the material from the substrate are immobilized on the polymer surface and within the pores rather than released into solution. As an example, a polyvinylidene fluoride (PVDF) porous layer or other suitable porous layer may be functionalized with a chelating agent, such as poly(acrylic acid), to complex metal ions after removal from the substrate. The PVDF porous layer may be used as either the first or second layer in the example of Figure 2. The polymer molecules may be ubiquitous from the surface to the depth of the layer, transporting metal ions from the substrate surface after hydrolysis and helping to prevent surface contamination and resulting defects. In one example, metal ions are complexed by functional groups in the first layer of the porous pad and chelated by functional groups in the second layer. However, the complexation and chelation functionality may be imparted by functional groups in either layer. As another example, a porous PVDF polymer layer can be functionalized with hyperbranched polyethylene by first hydroxylating the PVDF surface, then adding excess adipoyl chloride, and then reacting with the hyperbranched polyethylene. In yet another example, the surface can be functionalized with a hydrolyzable substance, such as polydiallyldimethylammonium chloride, to hydrolyze the substrate during planarization. In other examples, any other suitable functionalization can be performed to impart any desired chemical functionality to the porous pad. Other examples of functional groups include, but are not limited to, COOH, -NH, -SOH, -COOCHCHOH, -N(CH), -POH, -N(CHCHOH), and -CONHR.

[0027] Any suitable method can be used to functionalize the polymer of the porous pad. In some instances, the polymer may be functionalized by coating, in which case the functional groups are not crosslinked to the polymer substrate but are instead adsorbed. In some instances, the functional groups are electrostatically bound. In some instances, the functional groups are physically bound. In other instances, the functional groups may be crosslinked. For example, a crosslinked copolymer can be deposited onto the porous polymer matrix of the porous pad. As yet another example, the functional groups may be chemically bound to the polymer by a covalent bond.

[0028] FIG. 5 is a flow diagram illustrating an example method for performing a chemical planarization process. Method 500 includes, at 502, introducing an abrasive-free planarization solution onto a porous pad. In some examples, the planarization solution includes a chemical species that hydrolyzes chemical species on the substrate. Thus, in various embodiments, the planarization solution may include hydrogen peroxide 504, poly(diallyldimethylammonium chloride) 506, and / or any other suitable hydrolyzing compounds, such as various acids (nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, etc.). Additionally, in some embodiments, the planarization solution includes a complexing agent 507 and any other suitable components (stabilizers, passivators / preservatives, etc.). Examples of complexing agents may include copper complexing agents, cobalt complexing agents, tantalum complexing agents, titanium complexing agents, ruthenium complexing agents, and molybdenum complexing agents. In other examples, the hydrolysis agent and complexing agent are functionally bound to the polymeric material of the porous pad. In such an example, the planarizing solution may include deionized water 508, or other suitable solvent.

[0029] The method 500 further includes contacting the substrate with the porous pad at 510, which may occur while the porous pad and the substrate are moving relative to one another such that topologically high portions of the substrate contact the porous pad and topologically low portions of the substrate do not contact the porous pad. In some examples, the pad may be a functionalized polymer pad, as shown at 512. The functionalized polymer pad may include bound or adsorbed functional molecules / groups for hydrolysis, complexation, and / or any other additional chemical processes.

[0030] The method 500 further includes, at 514, removing material from topologically high portions of the substrate faster than material from topologically low portions of the substrate through contact with the porous pad, thereby planarizing the substrate. In some examples, the removed material includes copper 516 or copper-containing species, cobalt 518 or cobalt-containing species, or polysilicon 520. In other examples, any other suitable material may be removed in the planarization process. Other examples include one or more of tantalum, tantalum nitride, titanium, titanium nitride, and / or other similar refractory materials. Further examples include one or more of ruthenium and molybdenum. As described above, hydrolysis and complexing chemicals are present in the pad, so that material may be selectively removed from the substrate in areas contacting the pad, thereby planarizing the substrate.

[0031] Experimental results Experiments were conducted to measure the material removal rates (RR) of polysilicon (poly-Si), copper (Cu), and cobalt (Co) films as proof-of-concept for functionalized pads using abrasive-free chemistries and to determine the conditions for simulating polishing with chemically modified pads.

[0032] Introduction Abrasive-free slurries of polydiallyldimethylammonium chloride (PDADMAC) were used to study removal rates for polysilicon polishing. A 250 ppm PDADMAC solution at pH 10 on a commercial IC1000 pad was used as a benchmark for comparison. A mixture of oxalic acid and H2O2 was used to polish Cu without silica abrasives. A solution of 0.065 M oxalic acid and 1 wt% H2O2 was used with a low Cu dissolution rate (DR).

[0033] Here, an abrasive-free slurry was used. The experiment was designed to pre-soak the pad with the chemicals before wafer polishing and then stop the chemical supply during polishing. This mimics the situation where the polishing pad is functionalized with the chemicals. Polishing of polysilicon, Cu, and Co films was performed without the continuous supply of the abrasive-free slurry. [Example]

[0034] material These experiments used polysilicon films (~1000 nm), Cu films (~1500 nm), and Co films (~300 nm) deposited on 200 mm Si wafers. Abrasive-free slurries were prepared using ACS reagent-grade PDADMAC (MW 200,000–350,000), oxalic acid, and ammonium persulfate. The pH of the slurries was adjusted as needed using HNO or KOH.

[0035] Polishing experiment The pads were first wetted with deionized water for 10 minutes and then conditioned. Prior to polishing, the pads were immersed in each abrasive-free slurry for 5 minutes at a flow rate of 120 mL / min while the platen was rotating. The platen rotation was then stopped, and the pads were allowed to soak for an additional 2 minutes. The pads were then polished without the abrasive-free slurry dispensed onto the pad while the platen and carrier were rotating. For comparison, three types of films were polished while the abrasive-free slurry was dispensed at a flow rate of 60 mL / min or 120 mL / min. Two different polishers were used to polish the polysilicon film and two types of metal films (Cu and Co). The polishing conditions are listed in Table 1.

[0036] [Table 1]

[0037] The soaked pad case represents a direct observation of a chemically modified pad and may approximate the behavior of functionalized pads. Because these are commercially available pads and not customized with any functionalization, the results are expected to serve as proof of concept only. The removal rates achieved in this situation are evidence that a removal mechanism that does not require the application of abrasives or chemical reagents to the top surface of the pad is feasible.

[0038] Results and Discussion Polysilicon film removal rate Table 2 shows the RR of polysilicon films on Suba400 polishing pads immersed in an abrasive-free slurry of 250 ppm PDADMAC solution at pH 10, as well as the RR on Suba400 (available from Eminess Technologies, Inc., Scottsdale, Arizona), IC1000 (also available from Eminess Technologies), and Fujibo-Polypas (available from Fujibo Holdings) polishing pads continuously supplied with the abrasive-free slurry. The RR of polysilicon on the immersed Suba400 is ~639 nm / min, only 5–7% lower than the RR of polysilicon films polished with a continuous flow of PDADMAC abrasive-free slurry. The RR on the IC-1000 is nearly identical to that of Suba-400, while the RR on the soft Fujibo pad is <1 nm / min. Penta et al. reported RR of <200 nm / min for polysilicon films polished with pH 10 deionized water (without PDADMAC), which is significantly lower than the RR on a Suba-400 pad immersed in a PDADMAC abrasive-free slurry. This suggests that immersing a Suba-400 pad can maintain sufficient levels of PDADMAC during polishing, even without a continuous supply of abrasive-free slurry.

[0039] However, the Fujibo-Polypas results indicate that a chemical reformulation (or pH regime) is required to produce the expected removal rate, which is not true when the pads are soaked or dispensed, as the chemicals appear to be ineffective under the conditions selected for the Fujibo-Polypas pads.

[0040] [Table 2]

[0041] Removal rate of Cu and Co films The effect of abrasive-free slurry flow and pad type on the removal rates of Cu and Co was investigated, and the obtained removal rates are shown in Table 3. Cu removal rates of ~60 nm / min and ~74 nm / min were obtained using Fujibo-Polypas pads soaked with abrasive-free slurries of 1 wt% H2O2 + 50 mM guanidine carbonate at pH 9 and 1 wt% H2O2 + 65 mM oxalic acid at pH 6, respectively. The choice of chemistry was based on previous studies. The use of soaked Fujibo-Polypas and Politex pads demonstrated good removal rates, demonstrating the feasibility of this concept. This is a promising result when compared to commercially available pads, especially since we did not custom-design materials to optimize the functionalized pads.

[0042] For Co polishing, using a 1 wt% ammonium persulfate (APS) abrasive-free slurry at pH 9 did not result in a noteworthy RR when comparing the two polishing methods. However, lowering the pH to 8 significantly improved the RR. This is another evidence of the importance of the chemistry and customization required for functionalized pads that can completely remove abrasives.

[0043] [Table 3]

[0044] Summary of experimental results Abrasive-free chemistries were compared against various commercially available pad materials for all three major semiconductor polishing processes: polysilicon, copper, and cobalt. The immersion pad condition represented a situation in which the pad contained chemical reagents and no slurry was applied during polishing. The "immersion" pad condition demonstrated feasibility of removal rates, sometimes comparable to those achieved with conventional polishing. This result is promising because the pad materials were not chemically functionalized to the desired extent in this proof-of-concept study. Customization of functionality will be achieved in subsequent prototyping and product development phases. These results are crucial for forming the basis for developing innovative pads that require neither abrasives nor complex chemistries by formulating polymeric materials and functionalizing the matrix.

[0045] It will be understood that the configurations and / or approaches described herein are exemplary in nature and that numerous variations are possible, and therefore, these specific embodiments or examples should not be taken in a limiting sense. The particular routines or methods described herein may represent one or more of any number of strategies. As such, the various acts shown and / or described may be performed in the order shown and / or described, in other orders, in parallel, or omitted. Similarly, the order of the steps described above may be changed.

[0046] The subject matter of the present disclosure includes novel and non-obvious combinations and sub-combinations of the various processes, systems, structures, and other features, functions, acts, and / or properties disclosed herein, and all equivalents thereof.

Claims

1. 1. A method for chemically planarizing a substrate, comprising: applying an abrasive-free planarizing solution to a pad, wherein the abrasive-free planarizing solution comprises a functional compound including one or more of a complexing agent and a hydrolyzing agent, and the pad is surface-functionalized with functional groups configured to complex metal species; contacting the pad with the substrate while moving the pad and substrate relative to one another such that higher portions of the substrate contact the pad and lower portions of the substrate do not contact the pad; removing material from the elevated portions of the substrate through contact with the pads, reducing the height of the elevated portions of the substrate relative to the elevated portions of the substrate, such that species removed from the substrate bond to the functional groups; and applying a stripper solution comprising an acid to the pad to remove the species from the pad and leave the functional groups on the pad; A method comprising:

2. The method of claim 1 , wherein the materials removed include one or more of cobalt, copper, tantalum, titanium, ruthenium, and molybdenum.

3. 3. The method of claim 2, wherein the material to be removed includes copper and the abrasive-free planarizing solution includes one or more of hydrogen peroxide and oxalic acid.

4. 10. The method of claim 1, wherein the material to be removed comprises polysilicon and the abrasive-free planarizing solution comprises poly(diallyldimethylammonium chloride).

6. The method of claim 2 , wherein the abrasive-free planarizing solution includes oxalic acid.

7. 10. The method of claim 1, wherein the abrasive-free planarizing solution includes one or more of a copper complexing agent, a cobalt complexing agent, a tantalum complexing agent, a titanium complexing agent, a ruthenium complexing agent, and a molybdenum complexing agent.

8. The method of claim 1 , wherein the acid in the stripper solution includes one or more of nitric acid, sulfuric acid, and hydrochloric acid.

9. The method of claim 1 , wherein the pad is porous and the complexing agent is disposed within the pores of the pad.

10. The method of claim 1 , wherein the pad is further functionalized with a hydrolysis agent.

11. The method of claim 1 , further comprising pressing the substrate and the pad together with a pressure of no more than 4 pounds per square inch.

12. 10. The method of claim 1, wherein the functional compound of the abrasive-free planarizing solution includes a hydrolyzing agent comprising one or more of poly(diallyldimethylammonium chloride), poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine), poly(allylamine), and poly(ethyleneimine).

13. 1. A method for chemically planarizing a substrate, comprising: introducing an abrasive-free planarizing solution comprising a hydrolyzing agent and a complexing agent onto the pad functionalized with the bonded complexing agent; contacting the metal layer of the substrate with the pad while moving the pad so that a higher portion of the metal layer contacts the pad and a lower portion of the metal layer does not contact the porous pad; removing material from the elevated portions of the substrate via a hydrolysis agent to reduce the height of the elevated portions of the substrate relative to the lower portions of the substrate; and complexing the removed material via the bound complexing agent of the pad and the complexing agent of the planarizing solution; A method comprising:

14. The pad is a first polymer layer configured to contact the substrate during abrasive-free chemical planarization; and a second polymer layer disposed opposite the substrate-contacting side of the first polymer layer; 14. The method of claim 13, comprising:

15. 14. The method of claim 13, wherein the first polymer layer has a first larger average pore size and the second polymer layer has a second smaller average pore size.

16. The method of claim 13 , wherein the pad has a non-porous, textured substrate-contacting surface.

17. The method of claim 13 , wherein the planarizing solution includes one or more of hydrogen peroxide and oxalic acid.

18. 1. A chemical planarization system comprising: a polymer pad having functional groups attached to the polymer of the pad, the functional groups configured to complex with species removed from the substrate by planarization; a planarizing solution delivery system for delivering an abrasive-free planarizing solution to the pad, the abrasive-free planarizing solution including one or more of a complexing agent and a hydrolyzing agent; A pressure platen that supports the pad, a substrate holder configured to hold a substrate against a first surface of a pad, wherein one or more of the platen and the substrate holder are configured to rotate to impart rotational motion of the substrate relative to the porous pad during abrasive-free chemical planarization; and a stripping station having an acid-containing stripping solution; 1. A chemical planarization system comprising:

19. The polymer pad is a first polymer layer configured to contact a substrate during abrasive-free chemical planarization, wherein the first polymer layer has a first, larger average pore size; and a second polymer layer disposed on an opposite side of the first polymer layer from the substrate-contacting side, wherein the second polymer layer has a second, smaller average pore size; 20. The chemical planarization system of claim 18, comprising:

20. 20. The chemical planarization system of claim 18, wherein the planarizing solution includes one or more of hydrogen peroxide and oxalic acid.

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