Pub Date : 1984-04-03DOI: 10.1109/IRPS.1984.362039
Tom P. L. Li, E. Zigler, D. E. Hillyer
The choice of a die bonding material and processes for a microelectronic application, especially of accommodating the large size (up to 400 mils) and high density (up to 200 I/O connections) of VLSI chips, presents a matrix of considerations. They are the material properties, bonding surface characteristics, packaging compatibility and assembly procedures, etc. Above all, the die bond has to meet stringent reliability requirements. Die bonding failures have been reported numerously in the past. Only the failure modes and specu-lated failure mechanisms were documented. The present study uses the Perkin Elmer Auger/ESCA system to study the surface elements and their chemical states on the bonding surface; uses the Cambridge SEM/EDX system to study the failure modes and the cross-sectional profile; and uses the Dupont thermal analysi-s system to determine the physical and/or chemi-cal reactions of the die attach materials. It is the intention to provide a better understanding of the die bonding materials and material/ process related failures, and to help eliminate the problems of hot spots and thermal stressing of the interface caused by void formation.
{"title":"AES/ESCA/SEM/EDX Studies of Die Bond Materials and Interfaces","authors":"Tom P. L. Li, E. Zigler, D. E. Hillyer","doi":"10.1109/IRPS.1984.362039","DOIUrl":"https://doi.org/10.1109/IRPS.1984.362039","url":null,"abstract":"The choice of a die bonding material and processes for a microelectronic application, especially of accommodating the large size (up to 400 mils) and high density (up to 200 I/O connections) of VLSI chips, presents a matrix of considerations. They are the material properties, bonding surface characteristics, packaging compatibility and assembly procedures, etc. Above all, the die bond has to meet stringent reliability requirements. Die bonding failures have been reported numerously in the past. Only the failure modes and specu-lated failure mechanisms were documented. The present study uses the Perkin Elmer Auger/ESCA system to study the surface elements and their chemical states on the bonding surface; uses the Cambridge SEM/EDX system to study the failure modes and the cross-sectional profile; and uses the Dupont thermal analysi-s system to determine the physical and/or chemi-cal reactions of the die attach materials. It is the intention to provide a better understanding of the die bonding materials and material/ process related failures, and to help eliminate the problems of hot spots and thermal stressing of the interface caused by void formation.","PeriodicalId":326004,"journal":{"name":"22nd International Reliability Physics Symposium","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1984-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129430889","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1984-04-03DOI: 10.1109/IRPS.1984.362031
Steven B. Herschbein, Paul A. Zulpa, J. Curry
A higher than average failure rate-was recorded during high-temperature life testing of a vendor 16K SRAM. Failure analysis of the fallout determined the predominant failure mode to be open metal bit-lines at a topography step in the array. A unique method of unlayering-was used which left all metal-line constituents intact. Rather than finding physical voids in the lines, silicon nodules were found. The formation and possible subsequent growth of nodules is related to wafer-process parameters and life stress, eventually leading to an electromigration-type failure. Special test sites were used to substantiate failure modes and mechanisms found on functional product.
{"title":"Effect of Silicon Inclusions on the Reliability of Sputtered Aluminum-Silicon Metallization","authors":"Steven B. Herschbein, Paul A. Zulpa, J. Curry","doi":"10.1109/IRPS.1984.362031","DOIUrl":"https://doi.org/10.1109/IRPS.1984.362031","url":null,"abstract":"A higher than average failure rate-was recorded during high-temperature life testing of a vendor 16K SRAM. Failure analysis of the fallout determined the predominant failure mode to be open metal bit-lines at a topography step in the array. A unique method of unlayering-was used which left all metal-line constituents intact. Rather than finding physical voids in the lines, silicon nodules were found. The formation and possible subsequent growth of nodules is related to wafer-process parameters and life stress, eventually leading to an electromigration-type failure. Special test sites were used to substantiate failure modes and mechanisms found on functional product.","PeriodicalId":326004,"journal":{"name":"22nd International Reliability Physics Symposium","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1984-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133995352","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1984-04-03DOI: 10.1109/IRPS.1984.362035
D. Baglee
The electrical characteristics and the long term reliability of 100Å silicon dioxide films is examined in detail. In this paper the initial "as grown" properties are presented and the effects of subsequent process steps are discussed. The long term reliability of 100Å oxide having undergone a full double level polysilicon process is examined. An activation energy of 0.3eV was found and electric field acceleration was determined to be 100/MV/cm.
{"title":"Characteristics & Reliability of 100Å Oxides","authors":"D. Baglee","doi":"10.1109/IRPS.1984.362035","DOIUrl":"https://doi.org/10.1109/IRPS.1984.362035","url":null,"abstract":"The electrical characteristics and the long term reliability of 100Å silicon dioxide films is examined in detail. In this paper the initial \"as grown\" properties are presented and the effects of subsequent process steps are discussed. The long term reliability of 100Å oxide having undergone a full double level polysilicon process is examined. An activation energy of 0.3eV was found and electric field acceleration was determined to be 100/MV/cm.","PeriodicalId":326004,"journal":{"name":"22nd International Reliability Physics Symposium","volume":"65 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1984-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114645441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1984-04-03DOI: 10.1109/IRPS.1984.362045
L. Manchanda
This paper reports on a comparative study on the properties of small channel TaSi2/n+ poly gate MOSFETs. Measurements of threshold voltage as a function of effective channel length show that these TaSi2 gate transistors have less short-channel effects for channel lengths ¿1.5 ¿m. In order to determine the threshold stability under voltage stress, poly gate and TaSi2/poly gate MOSFETs were subjected to various drain and gate voltage stresses for a long duration. It is observed that, after the stress, poly gate transistors with channel lengths ¿1.5 ¿m show significant change in the threshold voltage and ß of MOSFETs. This instability seems to be due to hot-electron trapping in the oxide. but under the same stress conditions, these TaSi2/poly gate transistors do not show significant instability. SEM studies show that the poly layer of the TaSi2/poly gate was undercut near the drain-gate and source-gate overlap regions. This undercutting apparently helps in making lightly doped n-junctions near the drain-gate and source-gate overlap region. We postulate that the presence of this lightly doped junction near the drain-gate overlap region moves the high-electric field near the drain junction and reduces the hot-electron instability in the small channel-length TaSi2/poly gate MOSFETs.
{"title":"The Effect of TaSi2/n+ Poly Gate on Hot-Electron Instability of Small Channel MOSFETs","authors":"L. Manchanda","doi":"10.1109/IRPS.1984.362045","DOIUrl":"https://doi.org/10.1109/IRPS.1984.362045","url":null,"abstract":"This paper reports on a comparative study on the properties of small channel TaSi2/n+ poly gate MOSFETs. Measurements of threshold voltage as a function of effective channel length show that these TaSi2 gate transistors have less short-channel effects for channel lengths ¿1.5 ¿m. In order to determine the threshold stability under voltage stress, poly gate and TaSi2/poly gate MOSFETs were subjected to various drain and gate voltage stresses for a long duration. It is observed that, after the stress, poly gate transistors with channel lengths ¿1.5 ¿m show significant change in the threshold voltage and ß of MOSFETs. This instability seems to be due to hot-electron trapping in the oxide. but under the same stress conditions, these TaSi2/poly gate transistors do not show significant instability. SEM studies show that the poly layer of the TaSi2/poly gate was undercut near the drain-gate and source-gate overlap regions. This undercutting apparently helps in making lightly doped n-junctions near the drain-gate and source-gate overlap region. We postulate that the presence of this lightly doped junction near the drain-gate overlap region moves the high-electric field near the drain junction and reduces the hot-electron instability in the small channel-length TaSi2/poly gate MOSFETs.","PeriodicalId":326004,"journal":{"name":"22nd International Reliability Physics Symposium","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1984-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130244875","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1984-04-03DOI: 10.1109/IRPS.1984.362020
K. Katsukawa, Y. Kose, M. Kanamori, S. Sando
Failure modes have been studied on 0.5 ¿m gate power GaAs MESFETs with Al, Ti/Al and Ti/Al/Ti gate metallization, respectively. It has been found that the dominant failure modes are gate metal disconnection for Al gate, catastrophic burn out for the Ti/Al gate and gate breakdown voltage degradation for the Ti/Al/Ti gate under D.C. operational life tests. The degradation mechanisms have been clarified using SEM, microprobe-AES and SIMS. It is shown that Ti/Al, gate is the most reliable among these three kinds of FETS.
{"title":"Reliability of Gate Metallization in Power GaAs MESFETs","authors":"K. Katsukawa, Y. Kose, M. Kanamori, S. Sando","doi":"10.1109/IRPS.1984.362020","DOIUrl":"https://doi.org/10.1109/IRPS.1984.362020","url":null,"abstract":"Failure modes have been studied on 0.5 ¿m gate power GaAs MESFETs with Al, Ti/Al and Ti/Al/Ti gate metallization, respectively. It has been found that the dominant failure modes are gate metal disconnection for Al gate, catastrophic burn out for the Ti/Al gate and gate breakdown voltage degradation for the Ti/Al/Ti gate under D.C. operational life tests. The degradation mechanisms have been clarified using SEM, microprobe-AES and SIMS. It is shown that Ti/Al, gate is the most reliable among these three kinds of FETS.","PeriodicalId":326004,"journal":{"name":"22nd International Reliability Physics Symposium","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1984-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131663147","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1984-04-03DOI: 10.1109/IRPS.1984.362030
H. Hieber, K. Pape
Gold beams and wires are microwelded to a stable gold/platinum/titanium thin-film sandwich on silicon wafers. The contacts are subjected to simultaneous thermal and mechanical loads. The measured times-to-fracture are analyzed by mechanisms of creep-crack propagation. A creep rupture equation contains the stress exponent and the thermal activation energy of plastic f low as the material-specific parameters. The time-to-fracture is strongly affected by the texture of the beams and wires and by the geometry of the welded contact. The equation can be used for extrapolation in a temperature interval between 300 and 650K.
{"title":"Lifetime of Bonded Contacts on Thin Film Metallizations","authors":"H. Hieber, K. Pape","doi":"10.1109/IRPS.1984.362030","DOIUrl":"https://doi.org/10.1109/IRPS.1984.362030","url":null,"abstract":"Gold beams and wires are microwelded to a stable gold/platinum/titanium thin-film sandwich on silicon wafers. The contacts are subjected to simultaneous thermal and mechanical loads. The measured times-to-fracture are analyzed by mechanisms of creep-crack propagation. A creep rupture equation contains the stress exponent and the thermal activation energy of plastic f low as the material-specific parameters. The time-to-fracture is strongly affected by the texture of the beams and wires and by the geometry of the welded contact. The equation can be used for extrapolation in a temperature interval between 300 and 650K.","PeriodicalId":326004,"journal":{"name":"22nd International Reliability Physics Symposium","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1984-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114407481","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1984-04-03DOI: 10.1109/IRPS.1984.362058
S. Iyer, C. Ting
We have investigated unpassivated Al-Cu(4.5%)/Ti/Al-Cu laminated structures for their electromigration behavior for linewidths between 5 ¿ and 1.5 ¿ We find that although line opens are not the dominant failure mode, significant mass accumulation occurs all along the line leading to the real possibility of extrusion induced shorts. In our experiments laminated structures had lifetimes in excess of conventional Al-Cu lines by at least a factor of 10. Cu migration takes place in the early part of the stripe life. Al migration occurs preferentially from the top layer. Furthermore, a decrease of the line resistance, unlike in conventional structures, is observed during current stress. The Ti intermetallic layer does not show any motion.
{"title":"Electromigration Study of the Al-Cu/Ti/Al-Cu System","authors":"S. Iyer, C. Ting","doi":"10.1109/IRPS.1984.362058","DOIUrl":"https://doi.org/10.1109/IRPS.1984.362058","url":null,"abstract":"We have investigated unpassivated Al-Cu(4.5%)/Ti/Al-Cu laminated structures for their electromigration behavior for linewidths between 5 ¿ and 1.5 ¿ We find that although line opens are not the dominant failure mode, significant mass accumulation occurs all along the line leading to the real possibility of extrusion induced shorts. In our experiments laminated structures had lifetimes in excess of conventional Al-Cu lines by at least a factor of 10. Cu migration takes place in the early part of the stripe life. Al migration occurs preferentially from the top layer. Furthermore, a decrease of the line resistance, unlike in conventional structures, is observed during current stress. The Ti intermetallic layer does not show any motion.","PeriodicalId":326004,"journal":{"name":"22nd International Reliability Physics Symposium","volume":"10 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1984-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113964119","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1984-04-03DOI: 10.1109/IRPS.1984.362040
R. Pyle, H. Stevens
Failure to attach an IC die to its side-braze or leadless chip carrier (LCC) package can represent a serious problem in integrated circuit assembly. Consequently, the need to understand the mechanisms involved in furnace eutectic die attach failure is very critical. The purpose of this experimental investigation was to characterize the various die attach failure modes occurring in the furnace eutectic die attach process of LCC packages utilizing Pb/In/Ag preform material. Results from analytical investigations utilizing surface analysis techniques on a large number of sample die attach failures in LCC's are presented. An explanation of the causes and mechanisms involved in furnace die attach failure are proposed from both the experimental analytical results obtained and from theoretical investigations.
在集成电路组装中，未能将IC芯片连接到其侧钎焊或无引线芯片载体(LCC)封装可能是一个严重的问题。因此，需要了解机制所涉及的炉共晶模具连接失败是非常关键的。本实验研究的目的是表征利用Pb/ in /Ag预制体材料的LCC封装的炉共晶贴模过程中出现的各种贴模失效模式。本文介绍了利用表面分析技术对LCC中大量模具连接失效样品进行分析研究的结果。从实验分析结果和理论研究两方面阐述了炉模接头失效的原因和机理。
{"title":"Characterization of Die Attach Failure Modes in Leadless Chip Carrier (LCC) Packages by Auger Electron Spectroscopy","authors":"R. Pyle, H. Stevens","doi":"10.1109/IRPS.1984.362040","DOIUrl":"https://doi.org/10.1109/IRPS.1984.362040","url":null,"abstract":"Failure to attach an IC die to its side-braze or leadless chip carrier (LCC) package can represent a serious problem in integrated circuit assembly. Consequently, the need to understand the mechanisms involved in furnace eutectic die attach failure is very critical. The purpose of this experimental investigation was to characterize the various die attach failure modes occurring in the furnace eutectic die attach process of LCC packages utilizing Pb/In/Ag preform material. Results from analytical investigations utilizing surface analysis techniques on a large number of sample die attach failures in LCC's are presented. An explanation of the causes and mechanisms involved in furnace die attach failure are proposed from both the experimental analytical results obtained and from theoretical investigations.","PeriodicalId":326004,"journal":{"name":"22nd International Reliability Physics Symposium","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1984-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123999415","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1984-04-03DOI: 10.1109/IRPS.1984.362017
R. J. Gale
Previous high temperature aging studies have shown that the presence of epoxy in integrated circuit packages degrades the strength and contact resistance of Au-Al bonds [1-3]. Cl impurities in the resin or Br from the flame retardant or both are associated with this phenomenon. High temperature aging experiments were performed with Au wire bonded, Al metallized 4K NMOS Static RAMs and epoxy molding compounds in two types of DIPs. The initial study focussed on the effect of the flame retardant by using the epoxy with and without flame retardant in the cavities of epoxy sealed ceramic DIPs. The apparent activation energy for the degradation was determined by aging devices molded in DIPs using the standard flame-retardant formulation at three temperatures. The Cl and Br content of the epoxies was measured by neutron activation analysis and water extraction. Electron and ion microprobe analysis showed that Cl and Br are present in the bond zone with the Au-Al intermetallics. The median life at 180°C was only a factor of three higher without the flame retardant, even though the Br content was 600 times lower, suggesting that the Cl plays a major role. The apparent activation energy for the bond degradation in the flame-retardant molding compound is ~0.8 eV, within experimental error of that for pure Au-Al intermetallic formation [4] and that for the breakdown of the brominated flame retardant determined by water extraction. The water extraction results also indicate that the chlorinated impurities are less thermally stable than the brominated flame retardant.
{"title":"Epoxy Degradation Induced Au-Al Intermetallic Void Formation in Plastic Encapsulated MOS Memories","authors":"R. J. Gale","doi":"10.1109/IRPS.1984.362017","DOIUrl":"https://doi.org/10.1109/IRPS.1984.362017","url":null,"abstract":"Previous high temperature aging studies have shown that the presence of epoxy in integrated circuit packages degrades the strength and contact resistance of Au-Al bonds [1-3]. Cl impurities in the resin or Br from the flame retardant or both are associated with this phenomenon. High temperature aging experiments were performed with Au wire bonded, Al metallized 4K NMOS Static RAMs and epoxy molding compounds in two types of DIPs. The initial study focussed on the effect of the flame retardant by using the epoxy with and without flame retardant in the cavities of epoxy sealed ceramic DIPs. The apparent activation energy for the degradation was determined by aging devices molded in DIPs using the standard flame-retardant formulation at three temperatures. The Cl and Br content of the epoxies was measured by neutron activation analysis and water extraction. Electron and ion microprobe analysis showed that Cl and Br are present in the bond zone with the Au-Al intermetallics. The median life at 180°C was only a factor of three higher without the flame retardant, even though the Br content was 600 times lower, suggesting that the Cl plays a major role. The apparent activation energy for the bond degradation in the flame-retardant molding compound is ~0.8 eV, within experimental error of that for pure Au-Al intermetallic formation [4] and that for the breakdown of the brominated flame retardant determined by water extraction. The water extraction results also indicate that the chlorinated impurities are less thermally stable than the brominated flame retardant.","PeriodicalId":326004,"journal":{"name":"22nd International Reliability Physics Symposium","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1984-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115480426","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1984-04-03DOI: 10.1109/IRPS.1984.362043
F. Fischer, F. Neppl
It is shown that an Al-Si-Ti alloy containing 0.1-0.2wt.% Ti used as an IC-interconnect material reaches the electromigration strength of Al-Si-Cu and simultaneously avoids the disadvantages of Al-Si-Cu like enhanced corrosion susceptibility or dry etching problems. The stabilizing effect of Ti is demonstrated by life testing and additonally by monitoring changes of residual resistivity and heat transfer to the substrate during temperature current stress.
{"title":"Sputtered Ti-Doped Al-Si for Enhanced Interconnect Reliability","authors":"F. Fischer, F. Neppl","doi":"10.1109/IRPS.1984.362043","DOIUrl":"https://doi.org/10.1109/IRPS.1984.362043","url":null,"abstract":"It is shown that an Al-Si-Ti alloy containing 0.1-0.2wt.% Ti used as an IC-interconnect material reaches the electromigration strength of Al-Si-Cu and simultaneously avoids the disadvantages of Al-Si-Cu like enhanced corrosion susceptibility or dry etching problems. The stabilizing effect of Ti is demonstrated by life testing and additonally by monitoring changes of residual resistivity and heat transfer to the substrate during temperature current stress.","PeriodicalId":326004,"journal":{"name":"22nd International Reliability Physics Symposium","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1984-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121966991","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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