- Email: [email protected]
19th International symposium on GaAs and related compounds, Karuizawa, Japan, Sept. 28 – Oct. 2, 1992
Microelectronics Journal, 24 (1993) 4
19th Internati l Symposium on GaAs and Related Compounds,
Karuizawa, Japan, Sept. 28- Oct. 2, 1992. Gunther Weimann, Walter Schottky Institute, Germany.
The 19th International Symposium on GaAs and Related Compounds was held in Japan, again in the pleasant highland resort of Karuizawa. The conference was well attended, participation being strongly dominated byJapan, possibly due to the worldwide lack of travelfunds, but also due to the Japanese dominance in thefield of lII-Vs. 259 attendees of a total of 329 camefrom Japan, 28from the USA and 30 from Europe. 95 oral and 54 poster contribtions were selected by the program committee from approximately 200 submissions. Seven invited talks and 20 late news papers completed the program. Two very different aspects of the III-V business were evident in Karuizawa during the four rainy days, filled with w e l l - a t t e n d e d sessions and long discussions. It was generally accepted that costs and reliability are essential factors if GaAs is to find a reasonable share of the device and IC market. The unbroken belief in the future of GaAs, on the other hand, could be taken from numerous contributions about novel technologies and III-V structures.
308
The symposium thus covered the full scope of the field from the growth of 6-in diameter GaAs ingots to quantum effect devices with technologies in the atomic scale. 100
I
I I I I II!l!
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0.11 0.1
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l
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I illl.I
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= il::i
; ,
100 Power dissipation (HW/bit)
~_K~
[
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Figure 1. The address access time versus power dissipation of the HEMT static RAMs compared with CMOS, BiCMOS, and GaAs MESFET static RAMs.
0026-2692/93/$5.00 © 1993, Elsevier Science Publishers Ltd.
Microelectronics Journal, VoL 24, No. 4
given. The well organized and rewarding conference was held in two parallel sessions, with the main topics being: • crystal growth: bulk, epitaxial layers and doping • process technologies devices including optical devices and novel devices based on quantum confinement effects.
Crystal Growth
Figure 2. Shows a microphotograph of the H E M T 64-kbit static RAM.
The plenary introduction of M. Fujuta from Fujitsu Ltd. described the present and predicted GaAs IC business realistically with today's market of US$187 million expected to rise to US$ 550 million in 1997 worldwide. The good part of the message of Dr. Fukuta was the introduction o f Fujitsu's new supercomputer VPP 500, operating with 200 parallel GaAs RISC processors and a maximum capability of 355 GFLOPS. The cost and reliability issue, however, led to the use of the conventional workhorse of GaAs ICs, ion implanted MESFETs with gate lengths of 0.8 ~tm (Vitesse process technology). The next generation will still see the MESFET with Lg = 0.5 Bm in use, HEMTs will find their application in GaAs LSI circuits when gate lengths are reduced below a quarter micron. The recently founded plant of Fujitsu Quantum Device Ltd. near Mt. Fuji, concentrating the III-V activities of the company, • with a 3000 m 2 super cleanroom, shows that there Is hope for the future of GaAs and other III-Vs. In the following a personal, and necessarily incomplete review of the GaAs Symposium will be
Considerable progress has been made in the growth of bulk GaAs, with a marked trend to increase wafer size to 4 and 6-in diameter. The progress was made essentially in Japan where there are several competent competitors. Mitsubishi Materials Co. described the arsenic pressure controlled Czochralski growth of 4-in wafers. The melt is formed by in-situ synthesis, thermal gradients are kept low by using an inner hot wall in the crystal puller, th~s giving low dislocation densities below 15 000 cm A similar process is used at Sumitomo Electric Industries giving 6-in diameter GaAs ingots witt; etch2Pit density (EPD) between 10 000 and 20 000 cm , as the residual strain is lower than in 4-in
Figure 3. H E M T bus driver logic LSI.
309
crystals. Hitachi Cable Ltd. grows large GaAs ingots by the LEC method with diameters of 3, 4 and 6-in with length of 500, 320 and 170 mm, respectively. 4-in diameter wafers are already commercially available, 6-in wafers are under test. From the same company there was a report on carbon doped LEC crystals with carbon levels between 6x1014 and 2.5x1016cm -3, y i e l d i n g highly resistive semi-insulating (SI) substrates. Alternative substrates, e.g. for optoelectronic devices, can be obtained from ternary ingots of In0.05Ga0.95As (crystal length 4.5 cm, Fujitsu Labs Ltd.). Epitaxial g r o w t h techniques are focused on metallorganic vapour phase epitaxy (MOVPE) and molecular beam epitaxy (MBE). T h e results presented at the conference showed that MOVPE is being favoured for the growth on large wafers, with
the claim of being closer to production and less costly. Low pressure MOVPE reactors of different designs are used, e.g. a barrel-type multiwafer reactor for the growth of H E M T structures on 4-in wafers (12 wafer per run, variations in thickness and carrier density are below +1% with defect densities of 6.5 cm-2).A horizontal reactor with substrate rotation gives comparable results on 6-in wafers, doping levels are constant within _-1:3%. Low pressure MOVPE is also used for the quaternary material system of AlGaInP and strained GalnAs superlattices. Novel materials included p-type cubic GaN (by MOVPE), InSb on glass substrates with intermediate GaSe buffer layers by plasma assisted deposition, and GaAsN alloys (MOVPE with plasma cracked NH3 as a nitrogen source).
Figure 4. Fujitsu's $200 m "Quantum" fabrication plant at Yamanashi, J ~ a n , is the world's first to mass-produce ASICs on 4" GaAs wafers. It is currently fabricating wafers with 3,000 - 30,000 gates, and with gate delays as low as 80ps.
310
Microelectronics Journal, VoL 24, No. 4
A considerable n u m b e r o f talks reported the investigation of the initial stages of epitaxial growth by in-situ characterization, such as ~t-RHEED, .photoluminescence, low energy ion scattering or reflectance difference. The ultimate goal is the epitaxial growth or selective area growth with control in atomic dimensions, a prerequisite for the direct growth of low dimensional structures for quantum effect devices. This field is dominated by MBE and related growth techniques, such as chemical beam epitaxy (CBE) or atomic layer epitaxy (ALE). Different approaches were reported for selective area growth or the direct growth of quantum wires or dots. The formation of GaN masks in the U H V by catalytic cracking of ammonia, mask opening by focused argon ions and subsequent M O V P E regrowth is one example for such an aI1-UHV process (OTL, Tsukuba). Two topics related to the d o p i n g o f III-V semiconductors found attention, namely pulse doping with silicon, essentially to obtain high carrier densities in modulation doped structures and the use of carbon as an acceptor. The incorporation of carbon in GaAs g r o w n by C B E or M O M B E (metallorganic-MBE) with tri-methyl gallium (TMG) as the Ga source yields extremely high carbon concentrations. InGaAs, on the other hand, • 19 -3 can be doped to concentrations of 1.2x 10 cm with CC14 as the dopant source in MOVPE. The properties of carbon as acceptor were discussed in an invited talk by Cammy Abernathy (AT&T Bell Labs.) and in a lively rump session. There as general agreement that carbon is an excellent acceptor with high doping levels above 1019 cm -3, low diffusion and high thermal stability, although there remain open questions concerning crystal quality and diffusion mechanisms. The results on carbon doping by solid source sublimation in MBE were controversial.
range of 100 nm. Dry etching techniques, combined with subsequent overgrowth to reduce defects, were described in several papers• E C R plasma etching with low bias voltages is a viable technique, so with a mixture of C12/He for the material system InGaAs/A1GaAs or with a H2 plasma to clean A1GaAs surfaces for regrowth.The efforts are directed towards all-UHV processes, with etching, either offthe epitaxially grown materials or ofin-situ masks (native oxides or nitrides) assisted by focussed electron or ion beams• Since ion beams increase damage, they are usually applied for local implantation. Chlorine assisted MOVPE, for instance, is used for the selective growth o f A1GaAs or GaAs. The background o f the processing technologies presented was generally the development of lateral and vertical structuring in atomic dimensions•
Devices GaAs devices and ICs presented at the conference i n c l u d e d GaAs R I S C m i c r o p r o c e s s o r s and applications in mobile communications. A number of semiconductor companies - - mostly Japanese - developed GaAs IC for TV/DBS systems, TV tuners with ICs having low supply voltages, Ku-band VCO converters, and wideband receiver ICs. Low power ICs and M M I C s at 1.9 G H z for m o b i l e communication were also presented. These circuits
Process Technology The processing technologies covered in the s y m p o s i u m dealt m a i n l y w i t h low damage processing, especially for semiconductor quantum structures, i.e. structures with dimensions in the
Figure 5. FURY VSC30K - 30 000 gate GaAs array. Vitesse Semiconductor Corp.
311
all used MESFETs with gate lengths between 0.5 and 1.0 ]xm. Operational amplifiers based on HBTs are being developed for automobile applications. A contribution from the IAF in Freiburg, Germany demonstrated, on the other hand, that the H E M T is well suited for higher integration levels (20 000 enhancement / depletion (E/D) HEMTs (high electron mobility transistors), with a selective dry etch for the gate recess and 0.15 ~tm long gates. One of the highlights of the conference was an invited talk by R.B. Brown (Univ. Michigan) on "Device R e q u i r e m e n t s for VLSI" w i t h c o m p o u n d semiconductors, which demonstrated that fast device switching times are not sufficient. Necessary requirements include high integration levels, low power dissipation, high interconnect densities, but above all, a good yield. A variety of novel optical devices were presented, including UV/blue LEDs based on GaN, surface emitting laser diodes with grown-in mirrors, multiple quantum well (MQW) electro-absorption modulators integrated with distributed feedback (DFB) lasers and pseudomorphic InGaAs/(A1)GaAs QW-lasers for high bit rates. The highest level of optoelectronic integration was demonstrated in a smart pixel array with less than 100 t'J switching energy. These fast switching times were obtained by putting amplifying doped channel FETs between the receiving M Q W diodes and the output M Q W modulators. This SEED/FET smart pixel array consisted of 400 FETs and 272 M Q W devices. These arrays will find application in future optical free space switching systems. The power requirements, however, are severe, as 1 W CW single lasers are necessary (S.S. Pei, AT&T Bell Labs). Quantum functional devices are a must for modern III-V s e m i c o n d u c t o r c o n f e r e n c e , t h e n this symposium was no exception. Numerous papers addressed the required technologies, such as selective epitaxy or epitaxy on structured substrates, e.g. on ribs, to grow quantum wires and dots. The low dimensional quantization was observed in these oneor zero-dimensional structures, as well as electron
312
waveguiding. Devices based on these effects will hopefully emerge at future symposia. The resonant tunnelling o f electrons has been extensively studied in the past years and Fujitsu is leading in the application. Again, from the laboratories of this company came a static memory cell using two InGaAs/InA1As resonant tunnelling diodes, which works at room temperature. In this last talk of the conference high expectations were raised, the goal being a 1 Gbit SRAM on a chip ofl.4 cm 2. The present difficulties, however, are severe, as peak to valley ratios of the tunnelling current of I 000 are required for reasonable power consumption, with today's value at 16. In summary, it can be said that the 19th GaAs Symposium x~as a good conference. It demonstrated the steady progress going on in material growth and process technology. It was dominated by the Japanese hosts, both in attendance and presentations. The message of the Kuruizawa Symposium to the III-V community was obvious: "the III-V compounds are good for novel physics based on quantum effects, the future is bright if devices and circuits can be sold at a price of one dollar per square millimetre chip area (US$1/mm2)! ''
Acknowledgement I would like to thank Professor Ikoma and his colleagues for the 19th Symposium on GaAs and Related Compounds.
1993 The 20th Symposium on GaAs and Related Compounds will take place in the Novotel, Freiburg in Germany from 27th of August to the 3rd of September.
Forfurther information please contact: Conference Chairman, Prof. Gunther Weimann, Walter Schottky Institute, Technical University Munich, D-8046 Garching, Germany. Tel~fax: [49] 89 320 92 780 / 6620.
19th Internati l Symposium on GaAs and Related Compounds,
Karuizawa, Japan, Sept. 28- Oct. 2, 1992. Gunther Weimann, Walter Schottky Institute, Germany.
The 19th International Symposium on GaAs and Related Compounds was held in Japan, again in the pleasant highland resort of Karuizawa. The conference was well attended, participation being strongly dominated byJapan, possibly due to the worldwide lack of travelfunds, but also due to the Japanese dominance in thefield of lII-Vs. 259 attendees of a total of 329 camefrom Japan, 28from the USA and 30 from Europe. 95 oral and 54 poster contribtions were selected by the program committee from approximately 200 submissions. Seven invited talks and 20 late news papers completed the program. Two very different aspects of the III-V business were evident in Karuizawa during the four rainy days, filled with w e l l - a t t e n d e d sessions and long discussions. It was generally accepted that costs and reliability are essential factors if GaAs is to find a reasonable share of the device and IC market. The unbroken belief in the future of GaAs, on the other hand, could be taken from numerous contributions about novel technologies and III-V structures.
308
The symposium thus covered the full scope of the field from the growth of 6-in diameter GaAs ingots to quantum effect devices with technologies in the atomic scale. 100
I
I I I I II!l!
t
i [1111
I I [: r!i!i
I '
i :~i
~o "-
0.11 0.1
H e MTt~64 K -.~
l
lilt[
1
I illl.I
I
10
= il::i
; ,
100 Power dissipation (HW/bit)
~_K~
[
1000
Figure 1. The address access time versus power dissipation of the HEMT static RAMs compared with CMOS, BiCMOS, and GaAs MESFET static RAMs.
0026-2692/93/$5.00 © 1993, Elsevier Science Publishers Ltd.
Microelectronics Journal, VoL 24, No. 4
given. The well organized and rewarding conference was held in two parallel sessions, with the main topics being: • crystal growth: bulk, epitaxial layers and doping • process technologies devices including optical devices and novel devices based on quantum confinement effects.
Crystal Growth
Figure 2. Shows a microphotograph of the H E M T 64-kbit static RAM.
The plenary introduction of M. Fujuta from Fujitsu Ltd. described the present and predicted GaAs IC business realistically with today's market of US$187 million expected to rise to US$ 550 million in 1997 worldwide. The good part of the message of Dr. Fukuta was the introduction o f Fujitsu's new supercomputer VPP 500, operating with 200 parallel GaAs RISC processors and a maximum capability of 355 GFLOPS. The cost and reliability issue, however, led to the use of the conventional workhorse of GaAs ICs, ion implanted MESFETs with gate lengths of 0.8 ~tm (Vitesse process technology). The next generation will still see the MESFET with Lg = 0.5 Bm in use, HEMTs will find their application in GaAs LSI circuits when gate lengths are reduced below a quarter micron. The recently founded plant of Fujitsu Quantum Device Ltd. near Mt. Fuji, concentrating the III-V activities of the company, • with a 3000 m 2 super cleanroom, shows that there Is hope for the future of GaAs and other III-Vs. In the following a personal, and necessarily incomplete review of the GaAs Symposium will be
Considerable progress has been made in the growth of bulk GaAs, with a marked trend to increase wafer size to 4 and 6-in diameter. The progress was made essentially in Japan where there are several competent competitors. Mitsubishi Materials Co. described the arsenic pressure controlled Czochralski growth of 4-in wafers. The melt is formed by in-situ synthesis, thermal gradients are kept low by using an inner hot wall in the crystal puller, th~s giving low dislocation densities below 15 000 cm A similar process is used at Sumitomo Electric Industries giving 6-in diameter GaAs ingots witt; etch2Pit density (EPD) between 10 000 and 20 000 cm , as the residual strain is lower than in 4-in
Figure 3. H E M T bus driver logic LSI.
309
crystals. Hitachi Cable Ltd. grows large GaAs ingots by the LEC method with diameters of 3, 4 and 6-in with length of 500, 320 and 170 mm, respectively. 4-in diameter wafers are already commercially available, 6-in wafers are under test. From the same company there was a report on carbon doped LEC crystals with carbon levels between 6x1014 and 2.5x1016cm -3, y i e l d i n g highly resistive semi-insulating (SI) substrates. Alternative substrates, e.g. for optoelectronic devices, can be obtained from ternary ingots of In0.05Ga0.95As (crystal length 4.5 cm, Fujitsu Labs Ltd.). Epitaxial g r o w t h techniques are focused on metallorganic vapour phase epitaxy (MOVPE) and molecular beam epitaxy (MBE). T h e results presented at the conference showed that MOVPE is being favoured for the growth on large wafers, with
the claim of being closer to production and less costly. Low pressure MOVPE reactors of different designs are used, e.g. a barrel-type multiwafer reactor for the growth of H E M T structures on 4-in wafers (12 wafer per run, variations in thickness and carrier density are below +1% with defect densities of 6.5 cm-2).A horizontal reactor with substrate rotation gives comparable results on 6-in wafers, doping levels are constant within _-1:3%. Low pressure MOVPE is also used for the quaternary material system of AlGaInP and strained GalnAs superlattices. Novel materials included p-type cubic GaN (by MOVPE), InSb on glass substrates with intermediate GaSe buffer layers by plasma assisted deposition, and GaAsN alloys (MOVPE with plasma cracked NH3 as a nitrogen source).
Figure 4. Fujitsu's $200 m "Quantum" fabrication plant at Yamanashi, J ~ a n , is the world's first to mass-produce ASICs on 4" GaAs wafers. It is currently fabricating wafers with 3,000 - 30,000 gates, and with gate delays as low as 80ps.
310
Microelectronics Journal, VoL 24, No. 4
A considerable n u m b e r o f talks reported the investigation of the initial stages of epitaxial growth by in-situ characterization, such as ~t-RHEED, .photoluminescence, low energy ion scattering or reflectance difference. The ultimate goal is the epitaxial growth or selective area growth with control in atomic dimensions, a prerequisite for the direct growth of low dimensional structures for quantum effect devices. This field is dominated by MBE and related growth techniques, such as chemical beam epitaxy (CBE) or atomic layer epitaxy (ALE). Different approaches were reported for selective area growth or the direct growth of quantum wires or dots. The formation of GaN masks in the U H V by catalytic cracking of ammonia, mask opening by focused argon ions and subsequent M O V P E regrowth is one example for such an aI1-UHV process (OTL, Tsukuba). Two topics related to the d o p i n g o f III-V semiconductors found attention, namely pulse doping with silicon, essentially to obtain high carrier densities in modulation doped structures and the use of carbon as an acceptor. The incorporation of carbon in GaAs g r o w n by C B E or M O M B E (metallorganic-MBE) with tri-methyl gallium (TMG) as the Ga source yields extremely high carbon concentrations. InGaAs, on the other hand, • 19 -3 can be doped to concentrations of 1.2x 10 cm with CC14 as the dopant source in MOVPE. The properties of carbon as acceptor were discussed in an invited talk by Cammy Abernathy (AT&T Bell Labs.) and in a lively rump session. There as general agreement that carbon is an excellent acceptor with high doping levels above 1019 cm -3, low diffusion and high thermal stability, although there remain open questions concerning crystal quality and diffusion mechanisms. The results on carbon doping by solid source sublimation in MBE were controversial.
range of 100 nm. Dry etching techniques, combined with subsequent overgrowth to reduce defects, were described in several papers• E C R plasma etching with low bias voltages is a viable technique, so with a mixture of C12/He for the material system InGaAs/A1GaAs or with a H2 plasma to clean A1GaAs surfaces for regrowth.The efforts are directed towards all-UHV processes, with etching, either offthe epitaxially grown materials or ofin-situ masks (native oxides or nitrides) assisted by focussed electron or ion beams• Since ion beams increase damage, they are usually applied for local implantation. Chlorine assisted MOVPE, for instance, is used for the selective growth o f A1GaAs or GaAs. The background o f the processing technologies presented was generally the development of lateral and vertical structuring in atomic dimensions•
Devices GaAs devices and ICs presented at the conference i n c l u d e d GaAs R I S C m i c r o p r o c e s s o r s and applications in mobile communications. A number of semiconductor companies - - mostly Japanese - developed GaAs IC for TV/DBS systems, TV tuners with ICs having low supply voltages, Ku-band VCO converters, and wideband receiver ICs. Low power ICs and M M I C s at 1.9 G H z for m o b i l e communication were also presented. These circuits
Process Technology The processing technologies covered in the s y m p o s i u m dealt m a i n l y w i t h low damage processing, especially for semiconductor quantum structures, i.e. structures with dimensions in the
Figure 5. FURY VSC30K - 30 000 gate GaAs array. Vitesse Semiconductor Corp.
311
all used MESFETs with gate lengths between 0.5 and 1.0 ]xm. Operational amplifiers based on HBTs are being developed for automobile applications. A contribution from the IAF in Freiburg, Germany demonstrated, on the other hand, that the H E M T is well suited for higher integration levels (20 000 enhancement / depletion (E/D) HEMTs (high electron mobility transistors), with a selective dry etch for the gate recess and 0.15 ~tm long gates. One of the highlights of the conference was an invited talk by R.B. Brown (Univ. Michigan) on "Device R e q u i r e m e n t s for VLSI" w i t h c o m p o u n d semiconductors, which demonstrated that fast device switching times are not sufficient. Necessary requirements include high integration levels, low power dissipation, high interconnect densities, but above all, a good yield. A variety of novel optical devices were presented, including UV/blue LEDs based on GaN, surface emitting laser diodes with grown-in mirrors, multiple quantum well (MQW) electro-absorption modulators integrated with distributed feedback (DFB) lasers and pseudomorphic InGaAs/(A1)GaAs QW-lasers for high bit rates. The highest level of optoelectronic integration was demonstrated in a smart pixel array with less than 100 t'J switching energy. These fast switching times were obtained by putting amplifying doped channel FETs between the receiving M Q W diodes and the output M Q W modulators. This SEED/FET smart pixel array consisted of 400 FETs and 272 M Q W devices. These arrays will find application in future optical free space switching systems. The power requirements, however, are severe, as 1 W CW single lasers are necessary (S.S. Pei, AT&T Bell Labs). Quantum functional devices are a must for modern III-V s e m i c o n d u c t o r c o n f e r e n c e , t h e n this symposium was no exception. Numerous papers addressed the required technologies, such as selective epitaxy or epitaxy on structured substrates, e.g. on ribs, to grow quantum wires and dots. The low dimensional quantization was observed in these oneor zero-dimensional structures, as well as electron
312
waveguiding. Devices based on these effects will hopefully emerge at future symposia. The resonant tunnelling o f electrons has been extensively studied in the past years and Fujitsu is leading in the application. Again, from the laboratories of this company came a static memory cell using two InGaAs/InA1As resonant tunnelling diodes, which works at room temperature. In this last talk of the conference high expectations were raised, the goal being a 1 Gbit SRAM on a chip ofl.4 cm 2. The present difficulties, however, are severe, as peak to valley ratios of the tunnelling current of I 000 are required for reasonable power consumption, with today's value at 16. In summary, it can be said that the 19th GaAs Symposium x~as a good conference. It demonstrated the steady progress going on in material growth and process technology. It was dominated by the Japanese hosts, both in attendance and presentations. The message of the Kuruizawa Symposium to the III-V community was obvious: "the III-V compounds are good for novel physics based on quantum effects, the future is bright if devices and circuits can be sold at a price of one dollar per square millimetre chip area (US$1/mm2)! ''
Acknowledgement I would like to thank Professor Ikoma and his colleagues for the 19th Symposium on GaAs and Related Compounds.
1993 The 20th Symposium on GaAs and Related Compounds will take place in the Novotel, Freiburg in Germany from 27th of August to the 3rd of September.
Forfurther information please contact: Conference Chairman, Prof. Gunther Weimann, Walter Schottky Institute, Technical University Munich, D-8046 Garching, Germany. Tel~fax: [49] 89 320 92 780 / 6620.