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High-Temperature Recessed Channel SiC CMOS Inverters and Ring Oscillators
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.ORCID iD: 0000-0002-1016-6085
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.ORCID iD: 0000-0001-6459-749X
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.ORCID iD: 0000-0001-8108-2631
2019 (English)In: IEEE Electron Device Letters, ISSN 0741-3106, E-ISSN 1558-0563, Vol. 40, no 5, p. 670-673Article in journal (Refereed) Published
Abstract [en]

Digital electronics in SiC find use in high-temperature applications. The objective of this study was to fabricate SiC CMOS without using ion implantation. In this letter, we present a recessed channel CMOS process. Selective doping is achieved by etching epitaxial layers into mesas. A deposited SiO2-film, post-annealed at lowtemperature and re-oxidized in pyrogenic steam, is used as the gate oxide to produce a conformal gate oxide over the non-planar topography. PMOS, NMOS, inverters, and ring oscillators are characterized at 200 °C. The PMOS requires reduced threshold voltage in order to enable long term reliability. This result demonstrates that it is possible to fabricate SiC CMOS without ion implantation and by low-temperature processing.

Place, publisher, year, edition, pages
2019. Vol. 40, no 5, p. 670-673
Keywords [en]
Inverter, recessed channel, ring oscillator (RO), silicon carbide (4H-SiC), static CMOS
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-250275DOI: 10.1109/LED.2019.2903184Scopus ID: 2-s2.0-85064992240OAI: oai:DiVA.org:kth-250275DiVA, id: diva2:1307544
Funder
Knut and Alice Wallenberg Foundation, Working on VenusSwedish Foundation for Strategic Research , CMP Lab
Note

QC 20190428

Available from: 2019-04-27 Created: 2019-04-27 Last updated: 2019-05-16Bibliographically approved
In thesis
1. SiC CMOS and memory devices for high-temperature integrated circuits
Open this publication in new window or tab >>SiC CMOS and memory devices for high-temperature integrated circuits
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

High-temperature electronics find use in extreme environments, like data logging in downhole drilling for geothermal energy production, inside of high-temperature turbines, industrial gas sensors and space electronics. The simplest systems use a sensor and a transmitter, but more advance electronic systems would additionally require a microcontroller with memory. Silicon carbide (4H-SiC) integrated circuits target high-temperature electronics, although the current integration level is low due to immature process technology and non-volatile memory has not been demonstrated. SiC CMOS would allow highly dense integrated circuits for microcontrollers and random access memory (RAM). Ferroelectric capacitors could serve as high-temperature non-volatile memory devices.

In this work, significant efforts have been taken to develop a SiC CMOS process and ferroelectric capacitors. SiC CMOS is challenging and mostly unexplored technology. A recessed channel transistor design was investigated. Several key challenges in the SiC CMOS process was identified, leading to a polyoxide-based field oxide, a deposited gate-dielectric process, reproducible Ni-Al semi-salicide contacts to p-type SiC, and a high-temperature CMP enabled two-level TiW-based metallisation. Self-aligned cobalt silicide contacts were investigated, and was found to produce low-resistance ohmic contactsto n-type SiC. Inverters and ring oscillators that operate at 200 °C were achieved in this recessed channel SiC CMOS process. It was found that steam-treating the gate oxide interface produced both NMOS and PMOS transistors that could be used for circuits. However, the reliability suffered due to poor PMOS performance. Wafer-level statistical measurements of interface trap density was performed on NMOS transistors treated by steam, dry oxygen and nitrided by nitrous oxide. A deposition and etch process for ferroelectric capacitors, using vanadium-doped bismuth titanate as ferroelectric material, was developed. High-temperature operation was demonstrated, and several scalability challenges for the etched process was identified.

The implication of this thesis is that while operational recessed channel SiC CMOS was demonstrated at high temperature, more promising technologies like ion implanted bulk transistors should be investigated instead, due to the numerous difficulties in optimising both NMOS and PMOS with this recessed channel design. The presented recessed channel process technology can be used to fabricate short channel length NMOS-logic. Ferroelectric capacitors is a good candidate for high-temperature non-volatile memory applications, although more work is needed in the CMOS integration.

Abstract [sv]

Högtemperaturelektronik används i extrema miljöer, såsom borrhålsloggning för geotermisk energiutvinning, inuti högtemperaturturbiner, industrigassensorer och rymdelektronik. De enklaste systemen använder sig av en sensor och en radio, men mer komplicerade system använder sig dessutom av en mikrokontroller med minne. Integrerade kretsar i kiselkarbidsteknik (4H-SiC) är lämpade för högtemperaturelektronik, men den nuvarande integrationsnivån är låg p.g.a. den nuvarande omogna processtekniken. Icke-flyktiga minnen för högtemperaturtillämpningar har inte demonstrerats. CMOS-elektronik i kiselkarbidsteknik (SiC CMOS) skulle möjliggöra mikrokontroller och direktminne (eng. random access memory, RAM) tack vare den höga integrationstätheten. Ferroelektriska kondensatorer kan fungera som icke-flyktiga minneskomponenter för högtemperaturtillämpningar.

Denna avhandling presenterar ett omfattande utvecklingsarbete av SiC CMOS och ferroelektriska kondensatorer. SiC CMOS är en utmanande och till stor del outforskad teknologi. En recessad kanal transistordesign undersöktes. Några nyckelutmaningar identifierades för SiC CMOS processen. Dessa utmaningarresulterade i en polyoxidbaserad fältoxid, en deponerad grinddielektrikumprocess, reproducerbara Ni-Al halv-självlinjerade kontakter till p-typ kiselkarbid, och en högtemperatur CMP-möjliggjord tvånivås titanvolframbaserad metallisering. En självlinjerad koboltsilicid-kontaktprocess undersöktes, och det visade sig att den gav lågresistiva ohmska kontakter till n-typ kiselkarbid. Inverterare och ringoscillatorer som fungerar vid 200 °C kunde demonstreras med denna recessad kanal transistordesign. Ångbehandlad grindoxidgränssnitt ger fungerande NMOS- och PMOS-transistorer som kunde användas för CMOS kretsar. Dock så led pålitligheten hos CMOS kretsarna p.g.a. PMOS transistorernas låga prestanda. Statistisk mätning av gränssnittsfälltäthet på skivnivå genomfördes för NMOS transistorer som hade blivit behandlade med ånga, torr syrgas och nitriderade via lustgas. En deponering- och etsprocess för tillverkning av ferroelektriska kondensatorer, där det ferroelektriska materialet var vanadiumdopat vismuttitanat, togs fram. Högtemperaturfunktionalitet påvisades, och flera nedskalningsutmaningar hos den etsade processen identifierades.

Trots att den recessade kanal SiC CMOS processen var bra nog för att demonstrera högtemperaturkretsar, så visar resultatet av denna avhandling att det kan finnas bättre alternativ till denna process. Inneboende processutmaningari transistordesignen i sig gör det svårt att optimera NMOS och PMOS transistorer som är bra nog för CMOS. Jonimplanterade bulktransistorer är mer lovande. Den utvecklade processen kan användas för att tillverka NMOS-logik med kortkanalstransistorer. Ferroelektriska kondensatorer är en lämplig kandidat som icke-flyktigt minne för högtemperaturtillämpningar, men mer arbete krävs för CMOS-integration.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. 241
Series
TRITA-EECS-AVL ; 2019:42
Keywords
bismuth titanate (Bi4Ti3O12), CMOS, ferroelectric capacitor, field oxide, inverter, metallisation, metal oxide semiconductor field effect transistor (MOSFET), ohmic contacts, ring oscillator, semiconductor processing, silicon carbide (4H-SiC), CMOS, ferroelektrisk kondensator, fältoxid, halvledartillverkning, inverterare, kiselkarbid (4H-SiC), metallisering, MOSFET, ohmska kontakter, ringoscillator, vismuttitanat (Bi4Ti3O12)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Information and Communication Technology
Identifiers
urn:nbn:se:kth:diva-250276 (URN)978-91-7873-180-0 (ISBN)
Public defence
2019-05-24, Sal B, Kistagången 16, Kista, 10:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation, Working on VenusSwedish Foundation for Strategic Research , CMP Lab
Note

QC 20190428

Available from: 2019-04-29 Created: 2019-04-28 Last updated: 2019-04-29Bibliographically approved

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