{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/108610"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/108610","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Nucleation inhibition and enhancement in chemical vapor deposition","abstract":"Area selective deposition (ASD) is becoming increasingly attractive as a bottom-up approach to nanomanufacturing. Most ASD processes developed so far concern selective deposition of metal on metal (i.e., not on non-metallic surfaces) or oxide on oxide (i.e., not on metallic surfaces), but nanomanufacturing also demands other film-substrate combinations such as deposition of metal on one oxide vs. another oxide or a metal surface. In this dissertation, I report one example of ASD that affords these new capabilities: chemical vapor deposition (CVD) of cobalt from Co2(CO)8 is fast on some oxides (Al2O3) but slow on others (SiO2). We also show that the addition of ammonia as an inhibitor improves the selectivity between oxides: a coflow of ammonia strongly inhibits nucleation on SiO2 (an acidic oxide) but has negligible effect on the nucleation and growth on Al2O3 (a basic oxide). We also show that the cobalt deposition process can, in some cases, be tuned to enable nucleation of Co on metal but not on oxide, or Co on oxide but not on metal. If, however, film growth is required on a relatively unreactive surface (e.g., one otherwise used for nongrowth), then the nucleation step will be kinetically difficult: a relatively small areal density of islands will form over an extended period of time. As a consequence, islands of different sizes populate the surface, and full coalescence (coverage of the substrate) occurs only when a relatively large thickness has been deposited, and the morphology is rough due to the distribution of island heights. To enhance film smoothness on unreactive substrates, I demonstrate that the sequential use of (i) a self-limiting substrate pretreatment by tetrakis-(dimethylamino)¬metal (TDMA-M) molecules (M = V, Hf, or Ti), followed by (ii) growth inhibition using a co-flow of ammonia during film growth of cobalt. The film grown by the combination of steps has a much smaller roughness than either step alone. I also investigate the nucleation of HfB2 from Hf(BH4)4 on Al2O3 vs. on SiO2 substrates. In both cases nucleation begins rapidly. However, on Al2O3 a high density of nuclei forms, and these nuclei rapidly coalesce into a smooth continuous film; by contrast, on SiO2 the island density remains smaller and coalescence occurs at larger film thickness. The method of pretreatment from self-limiting adsorption of tetrakis¬(dimethylamino)¬hafnium can increase nuclei density, and thus, speed up nucleation and reduce film roughness. Chemical design of a CVD precursor can be used to afford rapid nucleation but slow film growth, thus, smooth ultra-thin films. In a collaborative effort with S. Liu in the group of G. S. Girolami, I demonstrate the CVD of smooth platinum films using the newly-synthesized Pt[CH2CMe2CH2CH=CH2]2 precursor. This molecule has a rapid nucleation, which is the consequence of the availability of low barrier C-H activation pathways, and slow growth rate due to the formation of carbon-containing species that passivate the Pt surface. I used reflection IR absorption in real time to analyze the steady-state population of adsorbates during CVD. This information is needed to fully understand the surface kinetics that govern conformal and superconformal growth, as well as nucleation inhibition and enhancement. We show that use of a metal substrate used at high angle of incidence provides enough signal enhancement in p-polarization to observe sub-monolayer coverages. The intrinsic cancellation of the absorption signal in s-polarization means that the unwanted absorption due to gas phase molecules in the beam path, and molecules adsorbed on the IR chamber windows, can be cancelled out by subtraction of the p- and s- signals. In the last section, I demonstrate a superconformal process for cobalt deposition by adding a consumable inhibitor. The films are, however, contaminated by incorporation of the inhibitor molecules. Therefore, I propose an innovative approach that can potentially achieve superconformal growth of contamination-free films. This method requires two precursors that deposit the same film, but with quite different rates of adsorption and reaction.","abstract_html":"Area selective deposition (ASD) is becoming increasingly attractive as a bottom-up approach to nanomanufacturing. Most ASD processes developed so far concern selective deposition of metal on metal (i.e., not on non-metallic surfaces) or oxide on oxide (i.e., not on metallic surfaces), but nanomanufacturing also demands other film-substrate combinations such as deposition of metal on one oxide vs. another oxide or a metal surface. In this dissertation, I report one example of ASD that affords these new capabilities: chemical vapor deposition (CVD) of cobalt from Co2(CO)8 is fast on some oxides (Al2O3) but slow on others (SiO2). We also show that the addition of ammonia as an inhibitor improves the selectivity between oxides: a coflow of ammonia strongly inhibits nucleation on SiO2 (an acidic oxide) but has negligible effect on the nucleation and growth on Al2O3 (a basic oxide). We also show that the cobalt deposition process can, in some cases, be tuned to enable nucleation of Co on metal but not on oxide, or Co on oxide but not on metal. If, however, film growth is required on a relatively unreactive surface (e.g., one otherwise used for nongrowth), then the nucleation step will be kinetically difficult: a relatively small areal density of islands will form over an extended period of time. As a consequence, islands of different sizes populate the surface, and full coalescence (coverage of the substrate) occurs only when a relatively large thickness has been deposited, and the morphology is rough due to the distribution of island heights. To enhance film smoothness on unreactive substrates, I demonstrate that the sequential use of (i) a self-limiting substrate pretreatment by tetrakis-(dimethylamino)¬metal (TDMA-M) molecules (M = V, Hf, or Ti), followed by (ii) growth inhibition using a co-flow of ammonia during film growth of cobalt. The film grown by the combination of steps has a much smaller roughness than either step alone. I also investigate the nucleation of HfB2 from Hf(BH4)4 on Al2O3 vs. on SiO2 substrates. In both cases nucleation begins rapidly. However, on Al2O3 a high density of nuclei forms, and these nuclei rapidly coalesce into a smooth continuous film; by contrast, on SiO2 the island density remains smaller and coalescence occurs at larger film thickness. The method of pretreatment from self-limiting adsorption of tetrakis¬(dimethylamino)¬hafnium can increase nuclei density, and thus, speed up nucleation and reduce film roughness. Chemical design of a CVD precursor can be used to afford rapid nucleation but slow film growth, thus, smooth ultra-thin films. In a collaborative effort with S. Liu in the group of G. S. Girolami, I demonstrate the CVD of smooth platinum films using the newly-synthesized Pt[CH2CMe2CH2CH=CH2]2 precursor. This molecule has a rapid nucleation, which is the consequence of the availability of low barrier C-H activation pathways, and slow growth rate due to the formation of carbon-containing species that passivate the Pt surface. I used reflection IR absorption in real time to analyze the steady-state population of adsorbates during CVD. This information is needed to fully understand the surface kinetics that govern conformal and superconformal growth, as well as nucleation inhibition and enhancement. We show that use of a metal substrate used at high angle of incidence provides enough signal enhancement in p-polarization to observe sub-monolayer coverages. The intrinsic cancellation of the absorption signal in s-polarization means that the unwanted absorption due to gas phase molecules in the beam path, and molecules adsorbed on the IR chamber windows, can be cancelled out by subtraction of the p- and s- signals. In the last section, I demonstrate a superconformal process for cobalt deposition by adding a consumable inhibitor. The films are, however, contaminated by incorporation of the inhibitor molecules. Therefore, I propose an innovative approach that can potentially achieve superconformal growth of contamination-free films. This method requires two precursors that deposit the same film, but with quite different rates of adsorption and reaction.","abstract_has_math":false,"creators":["Zhang, Zhejun"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Materials Science & Engr","degree_department":null,"school":null,"contributors":["Abelson, John R","Girolami, Gregory S","Cao, Qing","Krogstad, Jessica A"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2020,"date_issued":"2020-10-07T22:44:36Z","date_published":"2020-10-07T22:44:36Z","updated_at":"2026-07-22T22:24:48Z","subjects":["CVD","Thin film","Surface"],"languages":["en"],"rights":["Copyright 2020 Zhejun Zhang"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/108610","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Abelson, John R","Girolami, Gregory S","Cao, Qing","Krogstad, Jessica A"]},{"key":"dc:creator","label":"Author","values":["Zhang, Zhejun"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2020-10-07T22:44:36Z","2022-10-07T22:44:53Z","2020-07-16","2020-08"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Materials Science & Engr"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["CVD","Thin film","Surface"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2020 Zhejun Zhang"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/108610"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Area selective deposition (ASD) is becoming increasingly attractive as a bottom-up approach to nanomanufacturing. Most ASD processes developed so far concern selective deposition of metal on metal (i.e., not on non-metallic surfaces) or oxide on oxide (i.e., not on metallic surfaces), but nanomanufacturing also demands other film-substrate combinations such as deposition of metal on one oxide vs. another oxide or a metal surface. In this dissertation, I report one example of ASD that affords these new capabilities: chemical vapor deposition (CVD) of cobalt from Co2(CO)8 is fast on some oxides (Al2O3) but slow on others (SiO2). We also show that the addition of ammonia as an inhibitor improves the selectivity between oxides: a coflow of ammonia strongly inhibits nucleation on SiO2 (an acidic oxide) but has negligible effect on the nucleation and growth on Al2O3 (a basic oxide). We also show that the cobalt deposition process can, in some cases, be tuned to enable nucleation of Co on metal but not on oxide, or Co on oxide but not on metal. If, however, film growth is required on a relatively unreactive surface (e.g., one otherwise used for nongrowth), then the nucleation step will be kinetically difficult: a relatively small areal density of islands will form over an extended period of time. As a consequence, islands of different sizes populate the surface, and full coalescence (coverage of the substrate) occurs only when a relatively large thickness has been deposited, and the morphology is rough due to the distribution of island heights. To enhance film smoothness on unreactive substrates, I demonstrate that the sequential use of (i) a self-limiting substrate pretreatment by tetrakis-(dimethylamino)¬metal (TDMA-M) molecules (M = V, Hf, or Ti), followed by (ii) growth inhibition using a co-flow of ammonia during film growth of cobalt. The film grown by the combination of steps has a much smaller roughness than either step alone. I also investigate the nucleation of HfB2 from Hf(BH4)4 on Al2O3 vs. on SiO2 substrates. In both cases nucleation begins rapidly. However, on Al2O3 a high density of nuclei forms, and these nuclei rapidly coalesce into a smooth continuous film; by contrast, on SiO2 the island density remains smaller and coalescence occurs at larger film thickness. The method of pretreatment from self-limiting adsorption of tetrakis¬(dimethylamino)¬hafnium can increase nuclei density, and thus, speed up nucleation and reduce film roughness. Chemical design of a CVD precursor can be used to afford rapid nucleation but slow film growth, thus, smooth ultra-thin films. In a collaborative effort with S. Liu in the group of G. S. Girolami, I demonstrate the CVD of smooth platinum films using the newly-synthesized Pt[CH2CMe2CH2CH=CH2]2 precursor. This molecule has a rapid nucleation, which is the consequence of the availability of low barrier C-H activation pathways, and slow growth rate due to the formation of carbon-containing species that passivate the Pt surface. I used reflection IR absorption in real time to analyze the steady-state population of adsorbates during CVD. This information is needed to fully understand the surface kinetics that govern conformal and superconformal growth, as well as nucleation inhibition and enhancement. We show that use of a metal substrate used at high angle of incidence provides enough signal enhancement in p-polarization to observe sub-monolayer coverages. The intrinsic cancellation of the absorption signal in s-polarization means that the unwanted absorption due to gas phase molecules in the beam path, and molecules adsorbed on the IR chamber windows, can be cancelled out by subtraction of the p- and s- signals. In the last section, I demonstrate a superconformal process for cobalt deposition by adding a consumable inhibitor. The films are, however, contaminated by incorporation of the inhibitor molecules. Therefore, I propose an innovative approach that can potentially achieve superconformal growth of contamination-free films. This method requires two precursors that deposit the same film, but with quite different rates of adsorption and reaction.","Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2022-08-01","The student, Zhejun Zhang, accepted the attached license on 2020-07-14 at 17:39.","The student, Zhejun Zhang, submitted this Dissertation for approval on 2020-07-14 at 17:56.","This Dissertation was approved for publication on 2020-07-16 at 15:40.","DSpace SAF Submission Ingestion Package generated from Vireo submission #15616 on 2020-10-02 at 15:33:18","Made available in DSpace on 2020-10-07T22:44:36Z (GMT). No. of bitstreams: 2 ZHANG-DISSERTATION-2020.pdf: 4863160 bytes, checksum: f2f81dfde6838922c732ce0fccf92745 (MD5) LICENSE.txt: 4209 bytes, checksum: 3b8095eeaed2236c7b87c1e758ea767f (MD5) Previous issue date: 2020-07-16","Embargo set by: Seth Robbins for item 116237 Lift date: 2022-10-07T22:44:53Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","U of I Only"]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Nucleation inhibition and enhancement in chemical vapor deposition"]}]}],"canonical_facts":{"dc:contributor":["Abelson, John R","Girolami, Gregory S","Cao, Qing","Krogstad, Jessica A"],"dc:creator":["Zhang, Zhejun"],"dc:date":["2020-10-07T22:44:36Z","2022-10-07T22:44:53Z","2020-07-16","2020-08"],"dc:description":["Area selective deposition (ASD) is becoming increasingly attractive as a bottom-up approach to nanomanufacturing. Most ASD processes developed so far concern selective deposition of metal on metal (i.e., not on non-metallic surfaces) or oxide on oxide (i.e., not on metallic surfaces), but nanomanufacturing also demands other film-substrate combinations such as deposition of metal on one oxide vs. another oxide or a metal surface. In this dissertation, I report one example of ASD that affords these new capabilities: chemical vapor deposition (CVD) of cobalt from Co2(CO)8 is fast on some oxides (Al2O3) but slow on others (SiO2). We also show that the addition of ammonia as an inhibitor improves the selectivity between oxides: a coflow of ammonia strongly inhibits nucleation on SiO2 (an acidic oxide) but has negligible effect on the nucleation and growth on Al2O3 (a basic oxide). We also show that the cobalt deposition process can, in some cases, be tuned to enable nucleation of Co on metal but not on oxide, or Co on oxide but not on metal. If, however, film growth is required on a relatively unreactive surface (e.g., one otherwise used for nongrowth), then the nucleation step will be kinetically difficult: a relatively small areal density of islands will form over an extended period of time. As a consequence, islands of different sizes populate the surface, and full coalescence (coverage of the substrate) occurs only when a relatively large thickness has been deposited, and the morphology is rough due to the distribution of island heights. To enhance film smoothness on unreactive substrates, I demonstrate that the sequential use of (i) a self-limiting substrate pretreatment by tetrakis-(dimethylamino)¬metal (TDMA-M) molecules (M = V, Hf, or Ti), followed by (ii) growth inhibition using a co-flow of ammonia during film growth of cobalt. The film grown by the combination of steps has a much smaller roughness than either step alone. I also investigate the nucleation of HfB2 from Hf(BH4)4 on Al2O3 vs. on SiO2 substrates. In both cases nucleation begins rapidly. However, on Al2O3 a high density of nuclei forms, and these nuclei rapidly coalesce into a smooth continuous film; by contrast, on SiO2 the island density remains smaller and coalescence occurs at larger film thickness. The method of pretreatment from self-limiting adsorption of tetrakis¬(dimethylamino)¬hafnium can increase nuclei density, and thus, speed up nucleation and reduce film roughness. Chemical design of a CVD precursor can be used to afford rapid nucleation but slow film growth, thus, smooth ultra-thin films. In a collaborative effort with S. Liu in the group of G. S. Girolami, I demonstrate the CVD of smooth platinum films using the newly-synthesized Pt[CH2CMe2CH2CH=CH2]2 precursor. This molecule has a rapid nucleation, which is the consequence of the availability of low barrier C-H activation pathways, and slow growth rate due to the formation of carbon-containing species that passivate the Pt surface. I used reflection IR absorption in real time to analyze the steady-state population of adsorbates during CVD. This information is needed to fully understand the surface kinetics that govern conformal and superconformal growth, as well as nucleation inhibition and enhancement. We show that use of a metal substrate used at high angle of incidence provides enough signal enhancement in p-polarization to observe sub-monolayer coverages. The intrinsic cancellation of the absorption signal in s-polarization means that the unwanted absorption due to gas phase molecules in the beam path, and molecules adsorbed on the IR chamber windows, can be cancelled out by subtraction of the p- and s- signals. In the last section, I demonstrate a superconformal process for cobalt deposition by adding a consumable inhibitor. The films are, however, contaminated by incorporation of the inhibitor molecules. Therefore, I propose an innovative approach that can potentially achieve superconformal growth of contamination-free films. This method requires two precursors that deposit the same film, but with quite different rates of adsorption and reaction.","Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2022-08-01","The student, Zhejun Zhang, accepted the attached license on 2020-07-14 at 17:39.","The student, Zhejun Zhang, submitted this Dissertation for approval on 2020-07-14 at 17:56.","This Dissertation was approved for publication on 2020-07-16 at 15:40.","DSpace SAF Submission Ingestion Package generated from Vireo submission #15616 on 2020-10-02 at 15:33:18","Made available in DSpace on 2020-10-07T22:44:36Z (GMT). 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