₂SO₄, HNO₃) on the pad surface to strip polished species (e.g., metal species) leaving behind the functional groups on the pad.

As described above, in some examples, a surface of a polymer material may be functionalized to provide hydrolytic, complexing, and/or other functionalities to the polymer. Polymer material that may be functionalized includes pores, asperities, and the bulk polymer. In such examples, the chemistries used for removing materials from a substrate and complexing the materials are fixed to the polymer surface and within the pores, rather than being loose in solution. As one 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 either for a first layer or second layer in the example of FIG. 2. The polymer molecules may extend from a surface of the layer into a depth of the layer, and thus may transport metal ions away from a substrate surface after hydrolysis, thereby helping to prevent contamination of the surface and resulting defects. In some examples, metal ions are complexed by functional groups in the first layer of the porous pad, and chelated by functional groups in the second layer of the porous pad. However, complexing and chelating functionalities may be provided by functional groups in either layer. As another example, a porous PVDF polymer layer may be functionalized with a hyperbranched polyethylene by first hydroxylating the PVDF surface, then adding excess adipoyl chloride, and then reacting with the hyperbranched polyethylene. In yet other examples, the surface may be functionalized with a hydrolytic material, such as polydiallyldimethylammonium chloride, to hydrolyze substrate material during planarization. In other examples, any other suitable functionalization may be performed to impart any desired chemical functionality to the porous pad. Other examples of functional groups include, but are not limited to, COOH, —NH2, —SO3H, —COOCH2CH2OH, —N(CH3)2, —PO3H2, —N(CH2CH2OH)2, and —CONHR.

Any suitable method may be used to functionalize the polymers of the porous pad. In some examples, the polymer may be functionalized by coating, in which the functional groups are not cross-linked to the polymer substrate, but instead adsorbed. In some examples, the functional groups are electrostatically attached. In some examples, the functional groups are physically bonded. In another example, the functional group may be cross-linked. For example, a crosslinked co-polymer can be precipitated onto the porous polymer matrix of the porous pad. As yet another example, the functional group could be chemically bonded by covalent bonding to the polymer.

FIG. 5 shows a flow diagram depicting an example method 500 for performing a chemical planarization process. Method 500 comprises, at 502, introducing an abrasive-free planarization solution onto a porous pad. In some examples, the planarization solution comprises chemical species to hydrolyze species on a substrate. As such, in various examples, the planarization solution may comprise hydrogen peroxide 504, poly(diallyldimethylammonium chloride) 506, and/or any other suitable hydrolyzing compound, such as various acids (nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, etc.). Further, in some examples, the planarization solution comprises a complexing agent 507, and other any other suitable components (stabilizers, passivators/anticorrosives, etc.). Examples of complexing agents can include 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. In other examples, hydrolyzing and complexing agents are functionally bonded to a polymer material of the porous pad. In such examples, the planarization solution may comprise deionized water 508, or another suitable solvent.

Method 500 further comprises, at 510, contacting a substrate with the porous pad, which may occur while moving the porous pad and substrate relative to one another, such that topologically higher portions of the substrate contact the porous pad while topologically lower portions of the substrate do not contact the porous pad. In some examples, the pad may be a functionalized polymer pad, as indicated at 512. The functionalized polymer pad may include bonded or adsorbed functional molecules/groups to perform hydrolysis, complexing, and/or any other additional chemical processes.

Method 500 further comprises, at 514, removing material from topologically higher portions of the substrate at a higher rate than materials from topologically lower portions of the substrate via contact with the porous pad to thereby planarize the substrate. In some examples, the material removed may comprise copper 516 or a copper-containing species, cobalt 518 or a cobalt-containing species, or polysilicon 520. In other examples, any other suitable materials may be removed in a 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, as the hydrolyzation and complexing chemistry resides in the pad, material may be selectively removed from the substrate in areas that contact the pad, thereby planarizing the substrate.

EXPERIMENTAL RESULTS

Experiments were performed to determine the material removal rate (RR) of polysilicon (poly-Si), copper (Cu) and cobalt (Co) films using abrasive-free chemistries and simulating conditions for polishing with a pad embodying the chemical reagent as a proof of concept of a functionalized pad.

Introduction

Abrasive-free slurry of poly(diallyldimethylammonium chloride), or PDADMAC was used for poly-Si polishing removal rate studies. 250 ppm PDADMAC solution at pH 10 on a commercial IC1000 pad was used as a benchmark to compare with. Mixtures of oxalic acid and H₂O₂were used to polish Cu without silica abrasives. Solution of 0.065 M oxalic acid and 1 wt % of H₂O₂along with low Cu dissolution rate (DR).

In this work, abrasive-free slurries were used. Experiments were designed to pre-soak the pads with the chemistry before wafer polish, but terminate the chemical delivery during polish. Doing so, the polishing pad resembled the situation of embodying the chemistry in functionalized form. Polishing of poly-Si, Cu and Co films were conducted in the absences of a continuous supply of abrasive-free slurry.

Experimental
Materials

Poly-Si (˜1000 nm), Cu (˜1500 nm), and Co (˜300 nm) films deposited on 200 mm Si wafers were used in these experiments. ACS reagent grade, PDADMAC (MW 200,000-350,000), oxalic acid and ammonium persulfate were used to prepare the abrasive-free slurries. The pH of the slurries was adjusted using HNO₃or KOH as necessary.

Polishing Experiments

Initially, pads were wet with DI water for 10 min, followed by conditioning. Before the polishing, pads were soaked with the respective abrasive-free slurry for 5 min at a flow rate of 120 mL/min while rotating the platen. Then the rotation of the platen was stopped, and the soaking continued for 2 more min. Subsequently, wafers were polished by rotating the platen and carrier but without delivering the abrasive-free slurry on the pads. For comparison, the three types of films were polished while supplying the abrasive-free slurries at a flow rate of 60 or 120 mL/min. Two different polishers were employed to polish the poly-Si and two metal films (Cu and Co). The polishing conditions are given in the Table 1.