SILICON CARBIDE (SIC) WAFER POLISHING WITH SLURRY FORMULATION AND PROCESS

Abstract

A method for polishing a silicon carbide surface. The silicon carbide surface is polished with a particulate abrasive while exposed to a composition of water, an oxidizing agent and an electrophile.

Claims

1. A composition of matter comprising: (1) water, (2) a metal ion electrophile with a ligand, the metal ion electrophile present in a concentration between 0.005 wt % and 0.05 wt %, based on a total weight of the composition and the ligand being present in a metal:ligand weight ratio between 1:8 and 1:12, and (3) a particulate abrasive, wherein the composition of matter has a pH of 2-5.

2. The composition as recited in claim 1, wherein the metal ion electrophile is a metal ion selected from the group consisting of Mg.sup.2+, Ca.sup.2+, Sr.sup.2+, Ba.sup.2+, Fe.sup.3+, Ti.sup.4+, V.sup.5+, Mo.sup.6+, Cr.sup.6+ and Mn.sup.7+.

3. The composition as recited in claim 2, wherein the ligand is a monoprotic carboxylic acid.

4. The composition as recited in claim 2, wherein the ligand is a monoprotic carboxylic acid selected from a group consisting of formic acid, acetic acid, glycolic acid, propionic acid, butanoic acid, hexanoic acid, heptanoic acid, octanoic acid, decanoic acid, pyruvic acid and t-cinnamic acid.

5. The composition as recited in claim 2, wherein the ligand is a diprotic carboxylic acid.

6. The composition as recited in claim 2, wherein the ligand is a diprotic carboxylic acid selected from a group consisting of carbonic acid, itaconic acid, malonic acid and tartaric acid.

7. The composition as recited in claim 1, wherein the metal ion electrophile is a metal ion selected from the group consisting of Cu.sup.2+, Co.sup.3+ and Zn.sup.2+.

8. The composition as recited in claim 7, wherein the ligand is an amino acid.

9. The composition as recited in claim 7, wherein the ligand is an amino acid selected from a group consisting of glycine, serine, arginine, cystine and phenylalanine.

10. The composition as recited in claim 7, wherein the ligand is a diprotic carboxylic acid.

11. The composition as recited in claim 1, further comprising an oxidizing agent.

12. The composition as recited in claim 11, wherein the oxidizing agent is hydrogen peroxide.

13. The composition as recited in claim 11, wherein the particulate abrasive is alumina.

14. A composition of matter consisting of: (1) water, (2) a metal ion electrophile with a ligand, the metal ion electrophile present in a concentration between 0.005 wt % and 0.05 wt %, based on a total weight of the composition and the ligand being present in a metal:ligand weight ratio between 1:8 and 1:12, and (3) a particulate abrasive, wherein the composition of matter has a pH of 2-5.

15. The composition as recited in claim 14, wherein the metal ion electrophile is a metal ion selected from the group consisting of Mg.sup.2+, Ca.sup.2+, Sr.sup.2+, Ba.sup.2+, Fe.sup.3+, Ti.sup.4+, V.sup.5+, Mo.sup.6+, Cr.sup.6+ and Mn.sup.7+.

16. The composition as recited in claim 15, wherein the ligand is a diprotic carboxylic acid.

17. The composition as recited in claim 14, wherein the metal ion electrophile is a metal ion selected from the group consisting of Cu.sup.2+, Co.sup.3+ and Zn.sup.2+.

18. The composition as recited in claim 17, wherein the ligand is an amino acid.

19. The composition as recited in claim 14, wherein the metal ion electrophile is Cu.sup.2+ and the ligand is an amino acid.

20. A composition of matter consisting of: (1) water, (2) a metal ion electrophile with a ligand, the metal ion electrophile present in a concentration between 0.005 wt % and 0.05 wt %, based on a total weight of the composition and the ligand being present in a metal:ligand weight ratio between 1:8 and 1:12, and (3) a particulate abrasive, wherein the composition of matter has a pH of 2-5 and (4) an oxidizing agent.

21. The composition as recited in claim 20, wherein the oxidizing agent is hydrogen peroxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] So that the manner in which the features of the invention can be understood, a detailed description of the invention may be had by reference to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only certain embodiments of this invention and are therefore not to be considered limiting of its scope, for the scope of the invention encompasses other equally effective embodiments. The drawings are not necessarily to scale, emphasis generally being placed upon illustrating the features of certain embodiments of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views. Thus, for further understanding of the invention, reference can be made to the following detailed description, read in connection with the drawings in which:

[0010] FIG. 1 is an illustration of activation of a silicon carbide surface using the disclosed method;

[0011] FIG. 2 depicts examples of non-metal electrophiles for use with the disclosed method;

[0012] FIG. 3 depicts examples of various ligands for use with metal ion electrophiles;

[0013] FIG. 4 is a graph depicting the material removal rate (MRR) of two non-metal electrophiles used with the disclosed method. Conventional ferro KMnO.sub.4 MRR is shown in gray;

[0014] FIG. 5 is a graph depicting the material removal rate (MRR) of copper metal electrophiles used with four different ligands. Conventional ferro KMnO.sub.4 MRR is shown in gray; and

[0015] FIG. 6 is a graph depicting the material removal rate (MRR) of vanadium metal electrophiles used with two different ligands. Conventional ferro KMnO.sub.4 MRR is shown in gray.

DETAILED DESCRIPTION OF THE INVENTION

[0016] This disclosure provides slurry formulations for silicon carbide polishing with tunable performance upon the addition of certain additives that enhance removal rates under a less aggressive physicochemical environment. More specifically this disclosure provides formulations, as well as systems, that enhance the development of silicon carbide polishing processes and chemical-mechanical polishing (CMP) processes, including planarization, in particular.

[0017] Generally, the formulation comprises (1) water (2) a water-soluble electrophile (E.sup.+) such as a metal ion chelated with a ligand via an Organometallic Complex Ligand Exchange (OMC-LE) or a non-metallic electrophile (3) an oxidizing agent (Ox) and (4) a particulate abrasive. The particulate abrasive, such as alumina is used at a pH above the isoelectric point (e.g. >2, such as a pH 4-5 or a pH of 8-9) while a mechanical polishing force is applied (e.g. between 3 psi and 7 psi (0.21 bar to 0.48 bar) applied by a rotating pad or brush). The abrasive is generally present in a concentration of about 2% to about 5% (wt/wt) and is water-insoluble. In one embodiment, the abrasive is alumina nanoparticles with an average diameter of less than 100 nm. In one embodiment, the formulation consists of the water-soluble electrophile, the oxidizing agent and water. In another embodiment, the abrasives are nanoparticles of silica, zirconia, titania, diamond or a metal oxide. The polishing method is generally performed at room temperature (e.g. between 20 C. and 25 C.).

[0018] Without wishing to be bound by any particular theory, FIG. 1 depicts one possible mechanism to aid in understanding the disclosed method. Panel A of FIG. 1, shows an oxide surface of a silicon carbide substrate complexing with an water-soluble electrophile (E.sup.+). The surface hydroxyl groups are deprotonated and highly anionic (i.e., they serve as a nucleophile) within a complexation layer between the additive-surface interface resulting in the weaking of the SiC bonds. Panel B shows the activated surface being oxidizing by an oxidizing agent (Ox). In panel C, an abrasive (e.g. alumina) liberates the topmost silicon layer to produce the polished surface shown in panel D.

[0019] Examples of suitable oxidizing agents include hydrogen peroxide (H.sub.2O.sub.2), permanganate (e.g. KMnO.sub.4 (KPS)) and persulfates such as ammonium persulfate (APS, (NH.sub.4).sub.2S.sub.2O.sub.8). Without wishing to be bound to any particular theory, these oxidizing agents are believed to generate hydroxyl radicals in situ. The oxidizing agent is generally present in a concentration between 1% and 10% by weight. In one embodiment, the oxidizing agent is present in a concentration between 1% and 5% by weight. In yet another embodiment, the oxidizing agent is present in a concentration between 2% and 4% by weight.

[0020] Referring to FIG. 2, in one embodiment, the water-soluble electrophile is a non-metallic electrophile such as an aldehyde, an acyl halide (or carboxylic acid therefrom) or a boron-based compound. Examples of boron-based compounds include boronic acids such as ethylboronic acid, cyclopentylboronic acid, isopropylboronic acid, cyclohexylboronic acid, cyclopentylboronic acid, p-tolylboronic acid, phenylboronic acid, borax, or boric acid. Other suitable boron-based compounds include boroglycine or borates such as trimethyl borate or triethylborate. Due to the electron deficient nature of these supramolecular molecules, an enhanced nucleophilic attack from the silicon carbide substrate can occur.

[0021] In the case of OMC-LE, the M.sup.+ center of the organometallic complex acts as the electrophile which undergoes the nucleophilic attack from the silicon carbide substrate. Furthermore, the organometallic complex facilitates the in situ formation of hydroxyl radicals from the oxidizing agent.

[0022] Examples of suitable metal ions include group II metals such as Mg.sup.2+, Ca.sup.2+, Sr.sup.2+, Ba.sup.2+ and divalent transition metals such as Cu.sup.2+, Zn.sup.2+. Further examples of suitable metal ions include Fe.sup.3+, Co.sup.3+, Ti.sup.4+, V.sup.4+, V.sup.5+, Cr.sup.6+, Mo.sup.6+ and Mn.sup.7+. Generally, the metal is water-soluble or is rendered water-soluble by complexation with the ligand or with a micelle. The metal is generally present in a concentration between 0.005% and 0.05% by weight. In another embodiment, the metal is present in a concentration between 0.005 and 0.015% by weight.

[0023] Referring to FIG. 3, examples of suitable ligands include amino acids (e.g. glycine, serine, arginine, cystine, phenylalanine, etc.), monoprotic carboxylic acids (e.g. formic acid, acetic acid, glycolic acid, propionic acid, butanoic acid, hexanoic acid, heptanoic acid, octanoic acid, decanoic acid, pyruvic acid, t-cinnamic acid, etc.) diprotic carboxylic acids (e.g. carbonic acid, itaconic acid, malonic acid, tartaric acid, etc.), carbamates (e.g. tert-butyl N-(benzyloxy) carbamate), hydroxamic acids and hydroxamic esters (e.g. suberohydroxamic acid, salicylhydroxamic acid, ethyl acetohydroxamate), hydroxyurca and aliphatic amides (e.g. butyramide). Generally, the ligand is water-soluble. The ligand is present in a weight ratio of from about 1:5 to about 1:20 (metal:ligand). In another embodiment, the ligand is present in a weight ratio from about 1:8 to about 1:12 (metal:ligand). In yet another embodiment, the ligand is present in a weight ratio of 1:10 (metal:ligand).

[0024] The disclosed compositions are competitive with conventional ferro KMnO.sub.4 polishing techniques and, in some cases, have a superior material removal rate (MRR). FIGS. 4-6 depict typical MMR for conventional KMnO.sub.4 shown in gray.

[0025] FIG. 4 depicts a control (see Example 1), a boric acid example (see Example 11) and a borax example (see Example 12). Both the Cu-boric acid and Cu-borax examples outperformed conventional KMnO.sub.4 MRR (shown in gray) under identical conditions.

[0026] FIG. 5 depicts a control (see Example 1), and three copper-ligand examples including a glycine ligand (Example 2), a serine ligand (example 3), a cystine example (Example 5) and a salicylhydroxamic acid example (example 6). The Cu-serine outperforms conventional KMnO.sub.4 MRR (shown in gray) under identical conditions. The Cu-glycine, Cu-cystine and Cu-salicylhydroxamic acid is competitive with conventional KMnO.sub.4 techniques but avoids the drawbacks associated with these conventional reagents.

[0027] FIG. 6 depicts a control (see Example 1) and two vanadium-ligand examples including a serine ligand (Example 7) and a tartaric acid ligand (Example 8). The V-serine example is competitive with conventional ferro KMnO.sub.4 techniques but avoids the drawbacks associated with these conventional reagents. The V-tartaric acid example outperforms conventional KMnO.sub.4 MRR (shown in gray) under identical conditions with nearly double the material removal rate (MRR).

DETAILED EXAMPLES

[0028] All polishing trials were run on an Allied METPREP polisher, using a 100 mm diameter and a 350 mm thick 4HSiC N-type wafer that was repeatedly re-polished. A Dupont SUBA 800-II-12 X-Y grooved pad on a 200-mm rotating platen was used. The 3M (PB33A-1) bristle brush conditioning disc was used in an in-situ conditioning mode for the duration of the polish and for 1 minute during an ex-situ disc conditioning after the polish. The Si face of the wafer was polished for 10 minutes using a slurry that consisted of -Al.sub.2O.sub.3 nanoparticles (NPs), water, hydrogen peroxide, and the respective additives (organometallic complexes or electrophilic additives) as described in each example. The process pressure ranged between 3 and 7 PSI. The relative sliding velocity ranged between 0.25 to 1.05 m/s. Slurry flow rate was kept constant at 25 cc per minute. Examples are summarized in Table 1.

TABLE-US-00001 TABLE 1 Exam- H.sub.2O.sub.2 Al.sub.2O.sub.3 E.sup.+ Ligand ple (wt %) (wt %) (wt %) E.sup.+ (wt %) Ligand 1 3 3 0 0 2 3 3 0.01 Cu.sup.2+ 0.1 glycine 3 3 5 0.01 Cu.sup.2+ 0.1 serine 4 3 3 0.01 Cu.sup.2+ 0.1 serine 5 3 3 0.01 Cu.sup.2+ 0.1 cystine 6 3 3 0.01 Cu.sup.2+ 0.1 salicylhydro- xamic acid 7 3 3 0.01 V.sup.4+ 0.1 serine 8 3 3 0.01 V.sup.4+ 0.1 tartaric acid 9 3 3 0.02 V.sup.4+ 0.1 tartaric acid 10 3 3 0.005 V.sup.4+ 0.1 tartaric acid 11 3 3 1.0 boric acid 12 3 3 1.0 borax 13 5% 3 0.01 Cu.sup.2+ 0.1 Serine ammonium persulfate

Example 1Control (Electrophile-Free)

[0029] A silicon carbide (SiC) slurry comprised of 3% -Al.sub.2O.sub.3 nanoparticles (NPs), water, and 3% hydrogen peroxide was used for the experiment. A Dupont SUBA 800-II-12 X-Y grooved pad on a 200-mm rotating platen was used. The 3M (PB33A-1) bristle brush conditioning disc was used in an in-situ conditioning mode for the duration of the polish and for 1 minute during ex-situ conditioning after the polish. The silicon face of 4HSiC N-Type wafers having a 100 mm diameter and a thickness of 350 m were polished. Process pressure ranged between 3 and 7 PSI. Sliding velocity was kept constant at 1.05 m/s. Slurry flow rate was kept constant at 25 cc per minute.

[0030] The observed SiC removal rates ranged from 348 to 532 nanometers per hour. At 3 PSI, SiC removal rates averaged at 348 nanometers per hour. A comparison at 7 PSI gave an average removal rate of 532 nanometers per hour, corresponding to an increase of 35% from the lower downforce.

Example 2Cu.SUP.2+.-Glycine

[0031] Example 2 was substantially identical to Example 1 except in that the silicon carbide (SiC) slurry was comprised of 3% -Al.sub.2O.sub.3 nanoparticles (NPs), water, 3% hydrogen peroxide, and Cu.sup.2+-glycine (0.01% metal, 0.1% ligand).

[0032] After polishing, and depending on the process conditions, the observed SiC removal rates ranged from ranged from 936 to 1,198 nanometers per hour. At 3 PSI, SiC removal rates averaged at 936 nanometers per hour. A comparison at 7 PSI gave an average removal rate of 1,198 nanometers per hour, corresponding to an increase of 22% from the lower downforce. See FIG. 5.

Example 3Cu.SUP.2+.-Serine with 5% Alumina

[0033] Example 3 was substantially identical to Example 1 except in that the silicon carbide (SiC) slurry was comprised of 5% -Al.sub.2O.sub.3 nanoparticles (NPs), water, 3% hydrogen peroxide, and Cu.sup.2+-serine (0.01% metal, 0.1% ligand).

[0034] After polishing and depending on the process conditions, the observed SiC removal rate of 1563 nanometers per hour at 7 PSI.

Example 4Cu.SUP.2+.-Serine with 3% Alumina

[0035] Example 4 was substantially identical to Example 1 except in that the silicon carbide (SiC) slurry was comprised of 3% -Al.sub.2O.sub.3 nanoparticles (NPs), water, 3% hydrogen peroxide, and Cu.sup.2+-serine (0.01% metal 0.1% ligand).

[0036] After polishing and depending on the process conditions, the observed SiC removal rates ranged from 1,371 to 1,709 nanometers per hour. At 3 PSI, SiC removal rates averaged at 1,371 nanometers per hour. A comparison at 7 PSI gave an average removal rate of 1,709 nanometers per hour, corresponding to an increase of 20% from the lower downforce. See FIG. 5.

Example 5Cu.SUP.2+.-Cystine

[0037] Example 5 was substantially identical to Example 1 except in that the silicon carbide (SiC) slurry was comprised of 3% -Al.sub.2O.sub.3 nanoparticles (NPs), water, 3% hydrogen peroxide, and Cu.sup.2+-cystine (0.01% metal, 0.1% ligand).

[0038] After polishing and depending on the process conditions, the observed SiC removal rates at 7 PSI, 1.05 sliding velocity and 25 cc/min flow rate was 883 nm/hr. See FIG. 5.

Example 6Cu.SUP.2+.-Salicylhydroxamic Acid

[0039] Example 6 was substantially identical to Example 1 except in that the silicon carbide (SiC) slurry was comprised of 3% -Al.sub.2O.sub.3 nanoparticles (NPs), water, 3% hydrogen peroxide, and Cu.sup.2+-salicylhydroxamic acid (0.01% metal, 0.1% ligand).

[0040] After polishing and depending on the process conditions, the observed SiC removal rates at 7 PSI, 1.05 sliding velocity and 25 cc/min flow rate was 753 nm/hr. See FIG. 5.

Example 7V.SUP.4+.-Serine

[0041] Example 7 was substantially identical to Example 1 except in that the silicon carbide (SiC) slurry was comprised of 3% -Al.sub.2O.sub.3 nanoparticles (NPs), water, 3% hydrogen peroxide, and V.sup.4+-serine (0.01% metal, 0.1% ligand).

[0042] After polishing and depending on the process conditions, the observed SiC removal rates ranged from 926 to 1,132 nanometers per hour. At 3 PSI, SiC removal rates averaged at 926 nanometers per hour. A comparison at 7 PSI gave an average removal rate of 1,132 nanometers per hour, corresponding to an increase of 18% from the lower downforce. See FIG. 6.

Example 8V.SUP.4+.-Tartaric Acid

[0043] Example 8 was substantially identical to Example 1 except in that the silicon carbide (SiC) slurry was comprised of 3% -Al.sub.2O.sub.3 nanoparticles (NPs), water, 3% hydrogen peroxide, and V.sup.4+-tartaric acid (0.01% metal, 0.1% ligand).

[0044] After polishing and depending on the process conditions, the observed SiC removal rates ranged from 1,837 to 2,152 nanometers per hour. At 3 PSI, SiC removal rates averaged at 1,837 nanometers per hour. A comparison at 7 PSI gave an average removal rate of 2,152 nanometers per hour, corresponding to an increase of 15% from the lower downforce. See FIG. 6.

Example 9V.SUP.4+.-Tartaric Acid

[0045] Example 9 was substantially identical to Example 1 except in that the silicon carbide (SiC) slurry was comprised of 3% -Al.sub.2O.sub.3 nanoparticles (NPs), water, 3% hydrogen peroxide, and V.sup.4+-tartaric acid (0.02% metal, 0.1% ligand).

[0046] After polishing and depending on the process conditions, the observed SiC removal rates at 7 PSI, 1.05 sliding velocity and 25 cc/min flow rate was 999 nm/hr.

Example 10V.SUP.4+.-Tartaric Acid

[0047] Example 10 was substantially identical to Example 1 except in that the silicon carbide (SiC) slurry was comprised of 3% -Al.sub.2O.sub.3 nanoparticles (NPs), water, 3% hydrogen peroxide, and V.sup.4+-tartaric acid (0.05% metal, 0.1% ligand).

[0048] After polishing and depending on the process conditions, the observed SiC removal rates at 7 PSI, 1.05 sliding velocity and 25 cc/min flow rate was 1442 nm/hr.

Example 11Boric Acid

[0049] Example 11 was substantially identical to Example 1 except in that the silicon carbide (SiC) slurry was comprised of 3.0% -Al.sub.2O.sub.3 nanoparticles (NPs), water, 3.0% hydrogen peroxide, and 1.0% boric acid. See FIG. 4.

[0050] After polishing and depending on the process conditions, the observed SiC removal rates ranged from 1,427 to 1,904 nanometers per hour. At 3 PSI, SiC removal rates averaged at 1,427 nanometers per hour. A comparison at 7 PSI gave an average removal rate of 1,904 nanometers per hour, corresponding to an increase of 25% from the lower downforce.

Example 12Borax

[0051] Example 12 was substantially identical to Example 1 except in that the silicon carbide (SiC) slurry was comprised of 3.0% -Al.sub.2O.sub.3 nanoparticles (NPs), water, 3.0% hydrogen peroxide, and 1.0% borax.

[0052] After polishing and depending on the process conditions, the observed SiC removal rates at 7 PSI, 1.05 sliding velocity and 25 cc/min flow rate was 2446 nm/hr. See FIG. 4.

Example 13Ammonium Persulfate

[0053] Example 13 was substantially identical to Example 1 except in that 5% ammonium persulfate was used instead of H.sub.2O.sub.2 and the pH was 4.0. The slurry comprised 3.0% -Al.sub.2O.sub.3 nanoparticles (NPs), water, the aforementioned 5% (m/m) ammonium persulfate and Cu.sup.2+-serine (0.01% metal 0.1% ligand).

[0054] After polishing and depending on the process conditions, the observed SiC removal rates ranged from 1,162 to 1,408 nanometers per hour. At 3 PSI, SiC removal rates averaged at 1,162 nanometers per hour. A comparison at 7 PSI gave an average removal rate of 1,408 nanometers per hour.

[0055] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.