CA1134055A - Semiconductor device - Google Patents

Semiconductor device

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Publication number
CA1134055A
CA1134055A CA332,190A CA332190A CA1134055A CA 1134055 A CA1134055 A CA 1134055A CA 332190 A CA332190 A CA 332190A CA 1134055 A CA1134055 A CA 1134055A
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Prior art keywords
region
junction
semiconductor device
zone
source
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CA332,190A
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French (fr)
Inventor
Johannes A. Appels
Marnix G. Collet
Paul A. H. Hart
Johannes F.C.M. Verhoeven
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Koninklijke Philips NV
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Individual
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  • Microelectronics & Electronic Packaging (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Physics & Mathematics (AREA)
  • Ceramic Engineering (AREA)
  • Computer Hardware Design (AREA)
  • Insulated Gate Type Field-Effect Transistor (AREA)
  • Junction Field-Effect Transistors (AREA)
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  • Electrodes Of Semiconductors (AREA)
  • Thin Film Transistor (AREA)

Abstract

28-2-1979 l PHN 9188 ABSTRACT.
"Semiconductor device".

A semiconductor device having a field effect transistor of the lateral or vertical type with an island-shaped region which comprises a contact region and is bounded at the bottom by a first p-n junction having a comparatively high breakdown voltage and laterally by a second p-n junction having a comparatively low breakdown voltage. The doping and thickness of the island-shaped region are so small that the region situated between the second p-n junction and the contact region is fully depleted before breakdown at the second p-n junction occurs.

Description

~ ~L 3 LJ~

10.5.79 1 . PHN 9188 "Semiconduc-tor device"

The invention rel.ates to a semiconductor clevice with a semiconductor body hav:ing a substantlally flat sur:~ace comprîsing at least one ~ield e:~fect transi.s~
tor having a sou:rce electrode and a drain ele~tr'ode, a channel region between said source and drain electrodes and a gate elec-trode adjacent the charmel region to in:~luen-ce, by means o~ a gate voltage applied to -the gate e].ec-trode, a depletion zone :ror con-troll:i.ng a :~low of charge carriers between the source and drain' electrodes, the field ef`fect transistor comprising a layer-shaped first regi.on o~ a first conductivity type which, with an unde-r~
lying second region of the second conductivi.ty type~ forms a first p-n junction extending substant.ially parallel to the surface whereby, at least in the operating condition an island-shaped portlon of -the first region is bounded laterally at least partly, by a second ~-n junction with associated depletion zone wh:ich is formed between the fi.rst region and a third regio~ o.~ the second conductivity type which adjoins -the f.i.rst region, said second ~n junction having a ].ower ~reakdown ~oltage than the first ~-n junction, at least the gate elect:rode adjoining the is.land shapcd region portion~ a voltage i:tl t,lle :revers~ directlon being applied be-twee:ll the second reglon and a contact region o:~ the f`i.eld ef:fect transistor belongi.ng to -the
2 PHN. 9188.

source-, drain- and gate electrodes and forming a non-rectifying contact with the island-shaped region portion.
A semiconductor device of the kind descrihed is known, for example, from United States Patent Specification 3,586,931 - R. J. Nienhuis - issued June 22, 1971.
Influencing a depletion zone for controlling the flow of charge carriers is to be understood to mean in this Application either the narrowing or widening, by means of variation of the thickness of a depletion zone, of a current channel bounded by said depletion zone, or the variation, by means of variation of the potential distri-bution in a depletion zone, of a flow of charge carriers moving through said depletion zone.
The said field effect transistor may have various structures in accordance with the form of the source, drain and gate electrode. For example, these electrodes may have the form of metal layers which form on the semiconductor surface ohmic source and drain con~
tacts, and one or more rectifying gate electrodes with Schottky contacts. Alternatively, the source, drain and gate electrodes may be formed by metal layers adjoining semiconductor electrode zones which form, with the adjoin-ing part of the semiconductor body, ~-_ junctions (in the case of gate electrodes) or non-rectifying junctions (for the source and drain electrodes). Furthermore, the gate electrodes may have the form of a conductive layer which is separatecl from the semiconductor surface by an insula-ting layer and with which the said depletion zone is formed in the channel region as, for example, in a so-called "deep depletion" field effect transistor. Conse-quently, when in this Application there is referred to source, drain and gate electrodes, this includes the elec-trode zones and insulating layers, respectively, possibly associated with said electrodes.
In the known field effect transistors of the kind described, in general no high voltages can be applied across the first and second p-_ junctions. This is due inter alia to the fact that, long before the breakdown 11.~ 3405S

~o 5.79 3 PlIN 91~8 voltage o~ the first ~-n junctiorl to be expected theore-tically on the bas:is of the dopi.ng pro-~ile is reached, breakdown occurs already at the second p-n junctlon as a result of the unfavourable fleld distrl'butlon prevailing t'here. Said breakdown usually occurs at or in the immedia-te proximity o:E' the surface. The said ~avourable field distri-bution may be caused by a high doping concentration of the third region and/or by a high doping gradi.ent near the second ~-n junction, but also, fo:r instance~ by a local l h:igh curvature of th.e second ~-n junction.
In order to increase the admissible voltage, the doping concentration of the first region may be rcduced and also, in order to make space for th.e deple-tion zone thereby further extending in the first region, the thickness thereof may be increased. ~Iowever, since -the cha~mel conductivity is proport:io:nal to the thic'k.ness, but the pinch-of~ vol-tage is proportional -to the square o:E`
the thickncss of the channel region, said measure will have for its result that, with the length and width of the chal~lel remaining the same and ~ith the pi.nch-off voltage remaining the same, the channel conductivj.ty is reduced.
In fact, :E`or the pinch-off voltage V it is ~ound that V _ a q and for -the channel conducti~ity it is found p 2~ Wq uNa that G = ~ , where a is the thickness of -the channel L
region pinched-off by the ga-te el.ectrod.e, N is the doping concentration of the channel region, W is -the width and L is the length of the channel reg:ion, /u is -the mobility of the charge carrlers, ~ is the electron charge and ~ is the dielectric constant of the semiconductor material. When N is reduced to a value N = ~ 1), then it is found (for the pinch-off voltage Vp remaining~-the same) -that:
af = ~ 2~a'~/~

and 1~q uNa G~ G.

-~L~3~
. .
10.5.79 4 P~ 9188 Generally, h'owever, such a reduction o~ -t'he channel conductivity is very de-tri.mental ~or the goocl operation of the field effect transistor.
~ ne of the objects of the ln-vention is to provide a semiconduc-tor device with a flat surface compris-ing a field effect transistor of a new structure, which device may be used at very rmuch higher voltages than kno~n field ef~ect transistors of the kind described, without reducing the channel conductivi-ty.
The inverltion is based _nter alia on the re-cognition of the fact that, in contrast wi-th what could be expec-ted, this can be achieved by no-t increasing the thickness of the first region bu-t by decreasing it.
Therefore, according to the invention, a semiconductor device of the kind described is characterized iIl that the doping concentration N in atoms per cm3 ancl the thlckness d in Clll of the island-shaped region portion satis~y the condition 2.6.10 ~ E ~ . ~ Nd ~ 5.1.105 ~ E
wherein ~ is the relati~e die.Lect:ri.c ConSta:llt and E the critical field strength in Volt/cm at which avalanche multiplication occurs in the semiconductor material of the ~irst region, L is the d;.stance in cm from the said con-tact region up to the second ~-n junc-tion, and VB is -the unidimensionally computed value o~ the breal~down ~oltage o~ the first ~-n junction in Volts.
If the said concli-tion is ful~illed, the product of the doping concentration and -the -thickness o~
the first region is such that on applying said reverse voltage the depletion zone, at leas-t between said contact region and the second ~-n junction, extends ~rom the ~irst p-n junction -throughout the thicliness of the island-shaped region portion at a voltage whicll is lower than the break-down voltage of the second P-n junction.
Tlle sai.d contact- region may be an elec-trode or an electrode zcne which is connected directly to the ~3~ 5 .. . .. . . . . .. . .. . .. .. . . ....
10.5.79 5 PHN 9-188 source of the sa:icl reverse voltage but may alternatively -be, for example1 a semiconductor zone which itsel~ is not provided rith a connection cond-uc-tor but is brought at the dcsired potential in a differen-t manner, for examplc, via an acljoining semiconductor æone.
Since the island-shaped region portion of the first conductivi-ty type between the said contact region and the second ~-n junction is already fully depleted at a voltage which is lower than the breakdown voltage of the 1b second ~n junction, the field strength at the surface is reduced to such an extent that the breakdown voltage is no longer determined substantially entirely by said second ~-n junction bu-t to a conslderable extent by -the first ~-n junction extending parallel to the surface.
In this manner a very high breakdown voltage can be obtained between -the first and the second region which in certain circumstances can approach the high brea~
down voltage to be expected theoreticall~r on the basis of the dopings of the first and second regions.
The condit:ion according -to the invention prevents also that upon increasing the voltage between -the first and the second reg:ion too h:igh a f`ield strength occurs prematurely at tlle surface between the contact region and the second ~-n junction as a result of the penetrat:ion of the depletion ~one from the second ~-n junction up to said con-tact region. ~n optimum field distri-bution is obtained by the fact -that with the N.d product according to the invention the maxima in the ~ield strength which occur at the second ~-n junction and at the edge o~ the said con-tact region are also approximately of the same value.
l~len the conditions are moreover chosen to be so that N.d is substantially equal to 3Ø105~ E and L ~
1 L~,10 5 VB, it is ensured that -the maxlmum ~ield strength at the first p-n junction will always be larger than in tlZe above-menlioned m~xima occurring at the surface so that the breal~-down always occu-rs at the first ~-n Junction and not at the 28-2-1~79 -6- PI-IN 9188 surface.
In order to be able to store the rnajor part of the charge in the depletion region :in the second reg:ion, thus reclucing the minimum thic~ness of the ~irst rcgi.on~ it is often prefe1-Ied that tile seco:nd region at least adjacent the first reg;on has a lower doping concentra-tion than the firs-t region r Although in many cases the depletion zone of the . .first ~-n junction may e~tend 1~ithou-t harrn throughout the thickness of the second region,in other cases it is pre-ferably ensured -that the second region has such a thickness that at the breakdown voltage of the first p-n junction the depletion ~one extends in the second region over a distance sma.ller t:han the thickness of said region. In that case it is ensured t:llat the b:reakdo1~n voltage calmot be adversely influenced by the th:Lckness of -the second reglon..
~ lthough the semiconductor structure described may also be ~ormed dif`ferently, a constr1lction is.preferred, _ ter~ ~ia for technological reasons, in l~hich the first region is formed by an epita~ial :la~e:r of the ~irst conduc-tivity type provided on the second regionO The third regio:n adjoini.ng the first region need not e~tend throughout the thickness of the first regionD I-t is s~lfficient -that7 at least in the operating condition, the associated depletion zone e~tends over the ~hole thickness of the first regi.on and, over at least a part o~ its circumference, bounds an island-shaped portion thereof. Preferably, however, the island-shaped portion o~ the .first region. is bounded la-terally entirely by -the second ~-n junction, although other struc-tures 1~ill sometimes be preferred in which -t~le said portion o:~ the .first region is bounded laterally, for e~ample, partly by the second p-n junction and for -the remaining part in a different manner~ ~or .example by a recessed insula-ting material or by a groove f:illed, for e~ample~ ~ith passi~ati:ng glass.
~ le inve:l-Ltion is of pa:r-ti.cular i.mportance .in lateral fi.eld e~fect transi.stors in ~hich the current be---t~een 1;he sou:rce electrode alld the dr~in elec-trode flo~s 9~

2~ 2-l979 . -7- P1-IN 9188 substantially parallel to the surface. Therefore, a pre-~erred embod:imellt i.s chara.cterized in -tha-t the source and drain electrodes on either sicle oP the gate electrocle con-stitute non-roct:i.Pying contacts wi.th t:he Pirst region, -the said contact region being thc drain electrode oP the transistor. In this case the gate elec-trode :is usually connected to the second regiol~ which then serves as seconcl gate electrode, although this is not necessary.
In certain cases an embocliment will be prePe:rred in which the drai.n electrode is surrounded substant:ia~3r en-tirely by -the gate electrode and this lat-ter substa:ntial-ly entirely by the source electrode, A particular prePerred embodimen-t is characterized in -that a semiconductor layer o~ the second conductivi-ty type is present 0:l1 the P.irst region, that -the source and drain elec-trodes comprise electrode zones oP the Pirst conductivit5r~type and the gate electrode comprises an electrode zone o:f -the second conductivity typs~ and that al:l. the said electrode zones extend -throug11ol1t the thickness oP the said sem:i.conductor layer down to t;he Pirst regi.on. This la-tter pre~erred embocliment enables the ju~taposed arrangement in the same semi.conductor plato o~ compleme11-tary juncti.on P:i.elcl-eP:rect transistors~ that is n-channel a:nd p-chan:nel ~i.eld e~ect transistors, as will be described hereinaPter.
Besides in lateral junction ~ield e:CPect t:ransis--tors the in~rention nlay also be used advan-tageousl~r il'L
junction ~ield e:~Pect -transistors o:~ -the so-called vertical type. In connection herewitl1 a prePerred embodiment is characterized in that the Pield ePfec-t transistor is oP the ver-tical type, that the drai:n elec-trode ~o:rms a non-recti.-fying contact wi-th -the second region9 tha-t the source elec1rode constitutes a recti~ying contact wit~. the Pirst region9 and that the gate electrode compr:ises an electrode 20ne o~ the Pirst conducti.vity type w11ich surrounds at least one part o~ the .~:irst region associated wi-th the channel region and :t`orms the said con-tact regio:n.
1`he i~lvel1tio-[1 will now be described in greater detail with :re~erence to a lew embodiments and the drawing, - - .. .. . . .. ... . . . .. . . . .. . . .... . .. .. .... . . .. . .. . . .. . . ... . .

~iL3~055 2~-2-1979 -8- PIIN 9188 in which Figure .1 shows diagramn1at:i.cally a known semi-conductor device partly as a cro~3s-sectional view and partLy as a perspective viewS
Figure 2 shows diagram1nati.call.y a semicond.uctor device accordlng to the invent:ion partly as a cross-~
sec-tlonal view and part:Ly as a perspective v:iew, Figure 3 shows another embodi.ment of the semi-conductor device according to the inven-tion, 1D Figures l~ and 5 show further embodiments of the semico:nductor device according to the inventionS
Figure 6 shows a semiconductor device with a vertical field e:~fect transistor according to the inven-tion, ~igure 7 shows a deep depletion field e~fec-t transistor according to the invent.i.on, Fi~ures 8A to E show the :~.iel.d d:istribution ~or various di.me3lsions and dopi:ngs and, ~igure 9 shows *or a pre:E'erred. embodiment the rela-tionship between the doping and d-i.mensions of the ~irst region.
The Figures are dia.g~rarni11at:i.c and, :~o-r. cla:rity, not draw:~l to scale. Corresponding parts are gene:rally refelred to 'be t'he same re~erence numerals~ Semiconductor region5 o.~ the same conductivity type are as a rule shaded i.n the same direction.
In al:l. the embod.iments, silicon has been chosen as a semiconductor material. However, the i.nvention is not restricted thereto but ma.y be applied while using any other semiconductor material 5 for example germaniurn ox a so-called III-~ compound, for example GaAs.
Figure 1 shows a l~nown semiconductor device par-tly as a cross-sectiona.l. view and par-tly as a pers-pecti.ve view. '~he device comprisos a ~emicond1lctor body with a field effect transistor comprisi.ng a source elect:rode and drai.n elec-trode with associated elec-trQde ~ones 1~ and 1~i, an intermediately loca-ted chanr1el regi.on 'I and a ga-te elec-t:rode ~ith associated electrode ~.one 13 il3405~

28-2--19'79 -~- PHN 9'l88 adjoining the channel reglon 1. Said gate electrode serves to i.nf.Luence a depletion ~on.e by means of a gate voltage applied -to the gate electrode for controll.i1lg a flow of charge carliers, iIl this e~amp:Le an electron flo~, between the source electrode 12 and the drai.n electrode 4. :In this e~arnple the source electrode, the drain electrode and the gate elec-trode all consist of a semi.concl-uc-tor zone and a metal layer which i5 pro~ided -thcreon and which makes an ohmic contact with the associated elect:rode zone and which lD is not show.n in the ~`igure ~or reasons of claril,y. The channel regiorl 1 in this e~ample is n-conduc-t:ive, t:he electrode zones 12 and 4 are n-conductive with a higher doping than the region 1~ and -the gate electrode zone 13 is ~-conduc-tive and forms a rectifying ~-n junction 7 with the channel region 1.
.As appears :~:rom Flgure 1, the field ef:~ect tra.nsis tor compr:ises a l.ayer-shaped fi:rst region 1 o:~ a ~irs-t condu~,tivity type~ in this case t:he n-coIlductivit~ type.
This :~i:rst regio.n 1 whic.1l in the presen-t case also is the channel region adjoining the gate electrode const:itu.~es, with an underlying p-type conduct:i.ve second regi.on 2 7 a first ~)-n junct.i.on 5 e~t,ending substalltially parallel to the surface 8. An island--shaped po.rtion O:r the region 1 is bounded latera].ly be a ~3econd ~-n junction 6 wi.th associat-ed cleplet:ion zo-lle. Said second ~-n junct:ion 6 is formed between the first region 1 and a ~-type con.duct:i.ve 1;hir~ :
region 3 which e~tends between the second region 2 and the surface 8 and which has a ~.higher dopillg concen.tration than the second region 2. The p-n junctioll 6 thus has a lower breakdown voltage than th.e firs-t ~-n JUnCti.OIl ~, ~: The ga-te el(3ctr~?de adjo:ins the isl.and-shaped port:i.on of the region 1.
As sho~l in Figure 1~ tlle gate electrode is connected to the su'bst:rate ~in th:is case the second region 2), al-thol3gh this is not necessaryO Upon app].y:ing a vol.t-age VD betweell the connection te:rm.i.nals S and. D of -the source and drai:n.electrodes~ e.lectroIls flo~ through the region 1 from 1,he z,one 12 to the zone 4. B~- applyingr a , . ~ . . ~ , ,,, j .. , .. , . ... .. , .. ... , .......... ,,.. ,.. .. .. .... .~.. ..... ,.. ., -, . - .

s~

28-2~197~ -10~ P}IN 9188 voltage in the reverse dl:rec-ti.on between the gate electrode zone }3 and the r~g;.on 'I and betwecn the second region 2 and the region 1, dep:l.et:ion zones are ~ormed the boun-- daries (9, 10, 14) o:f` w}llcll are show:n i.n broken llnes in Figure 1~ These deple-ti.on zones are shown wi-thout any shading In the abo~e-de s crlb ed known devl c e the doping concentratloll and the dlmenslons are such that at the breakdown voltage of' the E~-n junction 6 the regi.on 1 near 1~ -the draln el.ect:rode 4 ls no t dep:l.e ted. The voltage ln the reverse di.rection across the ~-n junc tlons 6 and 7 whi.ch is hlghest near the drain electrode 4 gives rise to a f'ield st:rength distribu tion a t uhi ch the maximulrl value of' the field streng-th occurs near the place where the E~-n 15 juncti.ons 6 and 7 intersect the sur:E`ace ~ and i.t ls near said surface that breakdc,wn ultim;Ltely occurs at a ~rol tage which is considerably lo~er than the 'breal;do~rn oltage of` the ~E.-n junction 5 wi thln the bu Ll~ o:f the sem:Lconductor bod)r.
Figure 2 shows a senliconcluctor cle~rice accordi.-ng to the invent:i.on. This de~r:ice equals to a conslderab:le e:xtent the Icnow.rl de~ice sho~ n I;`igure 'I ~ccording to the invention, however~ in the devlce sllown in Fi~ure 2 the doping concentration and the thic~;:ness of` the ~i.rst 25 re~ion 1 are so sma:l.l that upon applylng a vol tage in the re~rerse direction be-tween the second region 2 and a con-~
tact region belonging to the source, draill and gate electl~-des (in this example the drain elec-t:rode l~) and f`ortning a non-:rectifyi.ng contac-t Wit1l -the island~shaped regi.o:n 30 the deple ti o:n zone, at least be tween -the drain electrode 4 and t.he second ~-n jw~c tion 6, ex tends ~rom the f`irs1;
~-n juncti.on 5 throughout -the thickness of' the island-shaped region 1 at a voltage ~`lh:iCtl iS l ower than the brea~down ~ol tage of the second e-n junction 6. ~igure 2 35 shows -the cond:i tion 11l whi.clt the regioIl 1 be tween the z;ones 7 and 4 ls f~llly dep:l.eted u~ to -I:.he p ~ ju~lccLiorl 60 T'lle ~oltage acros s the ~-ll junct:i.oMs 5, 6 and 7 ls no~./
taken up ontirel.y 'by the coheren-t clepletion zone exte:[lding ... . .

~'~3~1~S~ ' -- --2 8 - 2 ~ ) 7 ~ . PI:fN 9 1 8 8 from -the clra:in zone Ll up to the bouJldary 9, I!.s a resul t o:E` th:is t;lle f:i.eld strength at the surface is reduced con-s:iderabl~. The b:rea.~;:down voltage is conseq~le:ntly de-termined - -to at leas-t a considerable extellt by the properties of the 5 ~-n junc-tl.on 5 ex-tcnd:i..ng wi thin -the bulk of the semi-conduc-to.r body. 'rhis brea:lcdol,Jn vol tage ]nay be very h:i gh and ma-y closely approach the 'oreal{down vol tage to be 'èXpècted theoretica].ly on the basis o:f the doping .o:E the regions I and 2, lûIn order -to achi.eve the desc:rlbed result endeavoured b~ the invention the :E ollowing dopings and dimensions are used in -the device shown in Figure 2 which has a semiconductor bocly of` silicon:
Zones 4 and 12: thickness 1 /um 15 Region 1: n-type , doping concent:ration 1. 5 .1 0 5 atoms/crn3 7 thickness 5 /um ~egion 2~ type5 doping concentratiotl 1.7. lO ~ atoms/cm3, thicklless 250 /uln Zone 1 3:
p-type9 thickness 2;5 /um dista:noe L from -the dra:in elec-trode 4 up to the ;?-n ;jUlLC tion 6: 50/um.
In this case the urLidirnellsional:Ly computed break-down voltage VB o:f the first ;e-n junc-ti.on ~as 1270 Volts~
2 5 The actual breakdown ~roltage proved to be 700 Vol-ts O At the given thickness~-3s a~ld doping concentrat:i.on.s the -depletion zone in the region 2 ex-tends over a thickness hich is srnalle:r than t:he thickness of` the regioll 2, ~Thile it i s also avoi ded that the deple-tion zone of -the p,-n 30 junc t:ion 6 :reaches the zone l~ at a volt,age value which is smaller than -the breal~:do~n v-olti3ge of the ~-n Junc tion 6 ta]~en i.n itsel:l` (in the absence o:~ p~n junctio:rl 5).
Usil~g the said values :~or N:,- d9 L and. VB~ in -this exalnp:Le for silicoll ( ~ = 1 1, 7; E ~ 2.5.105 Vol-t/cm) the con~
35 di~tion.
\ /V
2.6,102 L E V ~-L~ ~N. d .~5. 1 0 105 ~ E
i s sa ti sfi ed .
3~

28-2~ 3 -12- PIIN 91g~

~ the .semi.conducto:r dev:Lce shown i.n Figure 2.
the f`irst regi.on 1 is formf.~d by an epi-taxial layer prov.ided on the second reglon 2 In this example the :is~.and-s:h~.Lped portion o:f the first region is latera:Lly en-tirely boundecl by the second p-n junction 6. Altllough other configurations are possible, as wi:l..l. be seen later on, this tech:nologically i.s the simplest confi.gllration. The is:land--shaped regioIi portion may, :~or example,be bounded over a part o~ its circunl~erence in a di~,~erent mallner~ ~or example by a sun-ken ox.ide pattern of by a groove ~illed wi.th, :~or example,passi.vati.ng glass.
In the devices sho~rrn in Figu:res 1 a:nd Z -the gate electrode forms a recti~ying contact and the source and.
drain elect:rodes ~orm nol1-reet:ifyillg contaets w:L-th the region 1 by Ineans o~ the doped surf`ace zones 12, 4 and l3~
I-Iowever, the presence of said surface zones is no-t strict-ly necessary. Illstead o~ the semiconductor ~ones 12 and 11 ol~ni.c metal-to--semiconductor contacts rnay be provided a:nd instead o~ the ~one 13 a recti:~yl.ng me-tal-to-semicondu~tor eontact (Schottky contact) may be prov:ided Otl .the regi.on.
1. Instead o~ a gate elee~rode ~i-th reetifyillg jullction9 a eondu.ct:ive layer separa-ted ~rom the semiconductor sur:~ace 8 by an insulating layer may also be used with which a depletion ~one is formed in the epitaxial la~er 1, ~or e~ample, as is -the case in a deep depletion 1ransi.stor.
Figure 3 shows how -the i.n-vention may be used to pro~ide in the same monolithic integrated circuit juxta-posed p~ehannel and n-channel junction field e:~fect transis~
tors (J~`~T)-~ ~-channel field ef~ect translstor 1~hich in pri.nc.iple is equal to -the f`ield e~fect tra:nsistor described with re~erenee to Figwre 2 but in which the conc1.uctivity types o:~` all eorresponding semiconductor ~ones are opposite -to -those oI` Fi.gwre 2 is provided a-t I. Furthern1ore~ the "second. region " 2 o:t sa:Ld transis-tor is :~ormed by all n-type epitaxial ].ayer whic1l is provicled on a ~-lype sub~
strate 3llo ~ higb.ly doped n-type buried layer 36 is situat-ed b.et~een -the epitc~xia.:L l.aye.r 2 aIld -the substrate 3~ so ~ ~, .. .... ... ... . . . .... . ... .

~3~

10.5.79 13 , Pl-IN 918~

as to prevent penetration o~ the depletion zone associated ' with the p-n junction 5 clown to the substrate 34 .
A second j-unction ~ield e:~ect -transistor II
is provided besicLe the :ri.eld e:~ec-t transistor I. This, too, is a ~ield e~ect transistor according to -the invention.
This second transistor I:[ also comprises an island~shaped region portion 32 which is .~ormed by a portion o-~ the same epitaxial layer ~rom whicll the region 2 of transis-tor I is :~orn~ed. ~`he n-type source zone 22, the n-type clrain zone 2L~ and the ~-typè gate electrode zone 23 extend throughout the thickness o~ the ~-type semiconduc-tor layer 21 present on -the island 32 and ~rom which the region 1 o~ transistor I has also been formed down to the n-type region 32. The source and drain zones 22 and 24 ~orm the p-n junctions 26 and 26A ~ith -the region 21, alld the regions 21 and 32 ~orm the ~-n junction 39. I.n thi.s second :~ield e~ect transi.stor the channel :region i5 formed b~ the region 32.
For the mutual insulation o:~ -the transist.ors I and II the highly doped ~-type zone 33 i.s provided which surrounds both the region 2 and the region 32 entirely and ~orms with the region 32 the ~-n junctio:n 38.
Upon applying a sui-table yol-tage between the source zone 22 and the drain zone 24, electrons Ir!ove ~rom the source' zone to the drain zone through the region 32.
'l'his ~low of electrons c.an be in~luencecl by applyillg a gate voltage in the reverse direction between the zone 23 and the regions 32 (and possibly also by the reverse voltage between the regions 32 and 34). As in the exa~nple o~ Figure 2, the doping concentration and the thickness o~
the layer (2, 32) have been chosen acco:rding -to the inven-tion, so that long be~ore the occu:rrence o:~ breakc10wn the region 1 is ~ully cLepl.eted at least between the drain zone L~ and the ~n juncl,ion 6 and the region 32 is :~ully 3 depleted at least between -the drain zone 24 and -the ~-n junction 27. As a result o~ this -tha :field strength at tl~e surface 8, anc'L i.n transis-tor II that at the sur.~ace 3,~
be-tween the regions 21 and 32, is strongly reducecl and the 10.5 7'~ 14 PHN 9188 breakdown voltage conside~ably increased.
In Figure 3, as in I?igure 2, the insulating (o~ide) layers and contact la~ers present at the su:r~ace are not shown. The source, drai.n a:nd gate elec-trod.e connec~
tions are denoted diagrammatlcaLly by S, D and G.
Figure 4 shows a fur-the* modi.:~ied embodiment of the semiconductor device according to the invention. As in the second field ef`.~ect transistor II of Fi.gure 3, the n-type draln zone Li4 is sur:rounded by the p-type gate l~ electrode ~one 43 and this in -turn by'the n-type source zone 42. All electrode zones a-re'provided t~rithi.n a first region 1 which constitu-tes, with an underlying second, ~--type region 2, a ~irst p-n junction 5 and, with a highly doped ~-type reg:ion 47, a ~-n junction 48 terminating at the surface 8. The source, drain and ga-te electrode zones 42, 41l. and 43 ext,end only over El part o~ the -thickness o~`
the ~irst region 1. T.he field effec-t transistor can be ope:rated in the same manner as I,he preceding transisto:rs;
the bo~mdaries (49 and 40) o~ the depletion zone which are shown in -the Figure have been drawn ~or a reverse voltage be-tween the regions 'I arld 2 which is lower than the breakdown voltage. The region 1 is fulLy depletecl ; between the gate electrode zone 43 and the drain zone 44.
As in the fi'eld effect transistor II of Fi.gure 3, the island-shaped portion o~ the first :region is surrounded by the gate electrode trhich in th:is case fulfils -the ~unction o~ "t'hird region"; the ~-~n junc-tion 46 bet~treen the gate elec-trode zone and the region 1 ~orms th.e "second"
~-n junc-tion. Since the doping and the thickness o:~ -the ~i.rst region 1 have been chosen according -to the inventi.on, so that the said region is ~ully depleted with irnc:reaciing gate--l:rai.n vol-tage be~ore breakdown o~ the ~-n junc-tion 6 occurs, the ~iel.d e~ect tran.sistor can be used at very high voltage between contro:L electrode and drain electrode.
Moreover ? the device S'lOW~l in l?igure 4 is very interest:i.ng because, with a small varia-tio}l, it mcly 'be use~
as a switclling dlode for high voltages. Such a switchi.ng .

135~
.
10.5.79 15 PHN 9188 diode is shown in Figuro 5. The semico:nductor structure of this device may equal -that oP l~igure Ll w:ith the only dif:Cerence -that in this case the zone 42 need not be con-tacted, hence may be covered everywhe~re by an lnsulating layer L~1, and -that it is ensured that the breakdo~ vol-t,age between the regions 47 and 42 is low. In order -to achieve this, the regi.on 42 is providecl at a smalL clistance from the region 47, possibly even against the region 47, or penetrating into the region L~7.
A voltage V.l in the reverse direc-tion is applied across the ~-n junction 5 via ohmic contacts on the zones 44 and 2. An impedance, in this example a resistor R, is comlec-ted in series with the voltage source V1. A variable voltage V2 in the reverse direction is applied across the ~-n junc-tion 46.
Figure ~ shows the cond.ition i.n which the voltage V.l is sti:ll smal:L and in which such a high voltag~e V2 is appli.ed to the ~ate elect:rode that the associ,a-tcd depletion zone (boundary 45) ha~ rcached -the deplet:ion zone boundary 1l0 of the ~-n junc-tion 5. In -these circums-tances an island-shaped port.ion 1A is surrounded by the depletion 7,0lles and cut~oPP electrical:Ly Prom the :remaining parl, o~
the Pirs-t region 1.
The voltage V1 may now be increased to very hi~h values since the isl.and-shapecl r~gion por-tlon 1A is fully depleted Prom the ~-n junction 5 up -to the surPac,e already at a comparatively low voltage V1 and, when the voltage V1 is further increased~ the breakdow~ voltage i.s no longer determined by the comparatively low breakdown voltage of the p-n junction 46 but by -that oP the Plat ~-n junction 5 not eme:rging at the surPace, Hence in -thi.s case also , the gate electrode zone 43, and not the region ~T7S :~ulPils the fullction O:r the above-mentionecl "third region".

The high vo:Ltage V,l now is substant:i.ally enti:rely across the deple-tio1l zone between -the sur.~ace 8 and the bounda:r5~ 43, ancl -the depleti.on zone extends appro-~:~L3~L055i .. . ..
10.5.79 1~ P~IN ~188 xima-tely as is shown in Figure 4. There is substan-tially no voltage drop across the in1peclance R since only small lea1cage current flo~s throug11 it a1ld said impedance R is chosen to be muc1l smaller than that of the blocked semicon-ductor device connected i.n series therewith~
When the control voltage V2 is reduced to suchan extent that -the dep:letion zone no longer cuts o~ the region 1 between the ga-te electrode zone 43 and the ~-n junction 5, then a d:ri:~t :~ield is formed as a result c~f 1a which the source zone 42 tends -to reach -the potenti.al o~
the drain zone 44. Long be~ore this can happeng however, breakdown occurs between the regions 47 and 42 so -that the voltage across the seniconductor device disappears subs-tan-tially entirely and -the voltage V1 comes sub-stant:Lally ent:irely across the impedance Ro In this manncr, the voltage across the in1pe-dance R can be sw:itched between a low and a high value by n~eans of 1;he cont;:rol vo:Ltage V2.
Figure 6 is a cliagrammatic cross-sectional ~ view of a ve:rtlcal field e:r:~ect transistor according to the invention. It consists o~ an isl.ancl-shapecd region 1 which in this eYample i.s ~-conduc-tive. In this case the region 1 is a part o~ a ~-type epitaxial layer having a thickness of 4 /um and a doping concentra-tioll of 1.3.10 5 atoms/cm3 2 which is g.rown on an n-type substrate 2 having a thickness of 250 /um and a dopi.ng concentration of 3.2.10 atoms/cm3.
The island-shaped region 1 is bouncled laterally by an n-type diffused zone 30 Wi-thin the island 1 a pattern o~
silicon oxide 50 counter-sunk partly in the semicond~lctor 30 material- is p:rovided by selec-tive thermal oxidation in the ~ornn oI` an oxide layer in which apertures a:re present surrounded entirely by the oxicle. Withir1 the semiconduc-tor ma-terial the oxicle 50 is bounded by a thin, highl-y doped p~type zo.ne 54 which is cGntact- outside the insulating pattern 50 and ~orms the ga-l;e electrode zo:ne. The shortest dista:nce be-tween the zone 54 and -c1le ~-n ~unct:ion 5 is 2~5 /um.

.. . . . .

3L ~3L~1~35~j ;
10.5.~ . 17 PHN 9188 Furthermore, a highly c10ped n-type layer 52 of polycrystalllne silicon is provideci on the surPace and conta.cts, between the counter-sunk oxide par-ts 50, the semicondllctor sur:race at su:rface zones 53 ob-tained by dif-fusion from the layer ~2. A metal layer 51 is provided onthe layer 52, while the region 2 is contacted by means of a highly doped semiconductor contact layer 55 and a metal layer 56. The connections o:~ the source, drain and gate electrodes are denoted diag:rammati.cally by S, D and G.
1U In the operating condi-tion a voltage which is posi.tive with respect to the source electrode S is applied to the drain electrode D. A voltage which is at least so negative ~ith respect to the drain elect:rode that the deple-tion zone extends from the p-n junction 5 between the regions 1 and 2 up to the surface is present at the gate elect;:rode G, so that the reg:ion I is fu:l.ly depletecL.
The ~low o:~ elec-trons ~hich move ~rom the source electrode to the drain electrode is substall-tially not impecled by the depleted region 1. By varying the voltage at the ga-te electrode, the potenti.al distribution within tlle depleted region 1 may be varied and, for example, a poten-tial th.res-hold may be forn1ed so tha-t the :[`:Low of electrons from the source electrode to the drain electrode via -the depl~ted region 1 can be controlled. Since the region 1 i.s fully de-pleted at a voltage lower tllan the breakdown voltage o~ the ~-n junction 6, a vertical field e~:Pec-t -transistor for very high vo3.tage can be obtained since as cL result of the above-: described principle the voltage at which brealcdown occurs between the regions 1 and 2 may be very high.
The semiconductor device shown in Figure 6 maybe manu~actured as follot~rs. Sta:rting material ls an n~type substr~ate 2 having a ~type epitaxial layer with the abovc--mentioned dopings anc1 thicknesses~ The islancl insulation ~one 3 is formed by conventional cliffusion me-thods, for example by phosphor-us diffusiorl. Si.multaneously, the higl1.].y doped n-type contact layer ~ is di.f:Cused on the lower side.

- ~ .. .. .... , . ~.. , . ~ ... ....... ..... ........ ... .. .. .... .. .. .. . . . .

~ll3~ iS

. .
10.5.~9 18 Pl-~ 9188 An anti-ox:idatlon mask, at the same time implantation mask, wllich contains silicon nitrlde and which will hereinafter be referred to as nitride mask is then provided in the ~orm of a quadratic :~rame consistlng of masking strips, 1~ /un1 wide, wl~ic]l are situated at 10 /um distance rrom each otherO Boron is then implanted in a dose o~ 10 5 ions/cm2 with an energy o~ 60 I~eV. The photo-lacquer which is used ~or etcll~ng the ma.sk remains and . also serves as a mask against the implantation. In this manner the ~-type layer 5LI is I`ormed.
The photolacquer is then removed and a~ter annealing at 900C ~or 30 minutes the oxide pa-ttern is provided by thermal oxidation in a thickness Or, ~or example, 1 /um. The technologies to f`orm a counter-sun~
oxide pat-tern by selective oxidation are elaborately described in Philips Resea:rch Reports, Vol. 25, 1970, pp. 118-13Z. ~ter remo-ving the nitride mask a layer 52 of polycrystalline silicon, 0.5 /um thick~ is provided which is doped n-type, ~or example, by phospl~or-us implan-tation. Heating at 1050C for 30 minutes in nitrogen is then carried out, tho channel regions 53 being :~ormed by di~uslon ~:rom the layer 520 The aluminium me-tallization (51, 56, 57) is then provided by vapour deposition and mas~ing (i~ desired af-ter providing an extra ~-type dope for extending layer 5~l within its contact window), and the device may be assembled in an envelope.
The distance L (see Figure 6) in this example is '70 /um. The unidimensionally computed breakdown voltage VB of the P~P ~ structure (5~, 1, 2) is approximately 688 Volts. With (~or silicon) = 11.7 and E = 2.5.105 Volt/cm the condi-tion .~
- 2.6.10 ~ E \ / L ~ N . d ~ 5.1.l05 E, is satis~ied~
~ hen the region 53 is low-doped, cont:rol of -the current between source and drain electrode may also occur in that the ;~ n junction between the regions 51l and .... . . . ..

~y~

10.5-7(~ 19 PMN 9188 53 f`orms a clepletion zone in the region 52 which, by variatioll :in l;he gate -voltage, varies the cross-section O:r tlle curren-t path t]lrough t~]e region 53. In ce:rtain ci.r~
cumstances both this and the above-mentioned mecl~anism may plaST a part.
The invention is not res-tr:ic-ted to field effect transistors having a ~-n junct:ion or a Schottky -junction. ~or example, the gate elect:rode may be separated from the semiconductor surface by an insulating layer.
Figure 7 shows as an example a diagrammatic cross-sectional view of a deep depletion transistor which is en-ti.rely equal in s-truc-ture and operation -to the transistor shown in Figure 2 wi-th the only clifference that the depletion zone of the gate electrode (boundary 1l~) is no-t fo:rmed by a ~-n junction but by a gate elect:rocle consisting of an elec-trode layer 60 whi.ch is sep-~rated from the semiconductor surface by an insulating layer (for example an oxide layer) 61. ~urthermore, in the device sholrn in Figure 7 the same dopi.ng concen-trations and dimensiolls and the same manner o:~ switching may be uscd as in ~igure 2.
Wi.-th reference to ~igures ~ to E and 9 the above~mentioned preferred cloping concentra-tions and dimen-sions will be f'urt.her exp:Lained.
Figur~ 8~ to E are diagrammatic cross~-sectional views of five differen-t possibi.lities for the field distri--bution in a diode which corresponds -to the island-shaped portion of the first region in the preceding examp:Les. ~or clarity, only hal-P of the diode ls shown; the diode is assumed to be rotationally symme-trical about the a~is denoted by E . 'l~le region 1 corresponds to the island-shaped "I`irst region portion" in each of the preceding examples, the ~-n junc-tion 5 co:rresponds to the "fi-rst p~n junction" an~ the ~-n junction ~) corresponds to -the "second ~-n jwnct:ion"~ In the fi.gures t]~e region 'I is assumed to be n-condllcti~Te and -the region 2 :i.s assumed to be ~~con-duc-tivey howeve-r, the collducti.vity types may also be reversed. The dopi.ng conceIltratiorl of the region 2 is the 113~Ci 55 ~ ~
10.5.79 - 20 PHN 9188 same in all the Figures ~A to E. - -~ hen between the N regioll l (via -the N~
contact region l~) and the P regi.on 2 a voll;age is applied in the reverse direction across the ~-n junctions 5 and 6, a variation o:~ -the fielcl strength distribution Es occurs along the surface accord:ing to the line S, while in the ver-tical direction the field strength Eb varies according to the line B.
Figure c~A shows the ease in which full l~ depletion of the layer 1 does not yet occur at the break-down voltage. A high maximum value of the field s-trength E
occur.s a-t the surface at the p-n junction 6 which, due to the high doping of the P region 3, is higher than the maximum value of the fielcl strength Eb which, viewed in a vertical direction, occurs a-t the ~-n junct-ion 5. 1~hen the critical field s-trength E is ~xceeded (for sil:lcon approximately ~.5.105 ~rolts/cm ancl s:Lightly clependent on the doping), breakdown occurs at; the surface near the junction 6 before the depletion ~.one (shown in brokeII lines in Eigure 8A and referellce 9 and lO) extends in -the vert:ical directi.on :Ero~l the ;junc-tion 5 up to the surface.
. Figures 8B to 8E show cases in which the doping concentration N and th.e thicl~ness d of the layer 1 are such that prior to the occurrence of sur:~ace breakdown at the junction 6 the layer 1 is fully depleted from the junctioll 5 up to the surface. O~rer a par-t of the track bet~reen the regions 3 and ll the field streng-th E along -the surface is constant Irhile both at -the area of the ~-n ju.rLction 6 and of -the N N junction at the edge of -the 3 region ~ (as a result of the edge curvature of the N+N
junction) peaks are formed in the field strength distri-bution.
In the case sho~rn in Figu:re 8B the peak value is highest at the ju:nc-tion 6 and higher than the maximum value o~ Eb at the junction 5 so t.hat breakdown will occur at that area at the surface but at comparatively higher values -than in the cases of F~gure 8~ slnce the field ~IL3~
.
10.5.~ 21 PMN 9188 streng-t]l clistribution at the sur:race is more homogeneous alld the lllaXil]la will thllS decrease. The case Or I?igure 8B
may be obtained ~rom -t]-lat oI` Figure 8~ o:r example, by reducing the -thickness d of the ]ayer 1, with tl~e doping remalning the same.
Figure 8C shows the reverse case o~ Figure 8B.
In this case the :~ield strength peak a-t the edge o~ region l~ i.s much hi.gher than at the ~-n junction 6. This case may oecur, ~or example, when the layer 1 has a very high resis-tivity and the region 1 is clepleted be~ore the breakdownvoltage oecurs. :Cn that case, breakdown may occur, at the edge of region 4 when the maximum field s-treng-th at said edge is higher than that at -the ~n junction 5.
More favourable is the case sho~l i.n Figure l 8D. In this case i-t is ensu:recl that the cl.oping eoneentra-tion and the thiekness o~ the region 1 are such that -the -two ~ield strengt~L pealcs at the sur~`aee a:re substantially equal.. Although breakdown at the surfaee will sti:Ll oecur wh.en7 as shown in Figu:re 8D, the maximum fielcl strength Eb at the p-n junction 5 is sma:l:ler than the maxinla at the sur:~ace, the maximum :fie1d strength at the sur:~ace becomes lower in this case, by making the field strengtlh distribution S at ~the sur~ace to be symmetrical, than in an .asymmetrical ~ield streng-th distribu-tion, so -that the breakdown occurs at a higher voltage.
Figure 8E finally shows a case in which th.e maximum field streng-th at the sur:~ace at an arbitrary reverse voltage is lower than the ~laci.mum :~ield s-treng-th a-t the ~-n junction 5 by an e~icacious choice of doping and thiclcness of the layer 1 ancl by increasing the distance L with a given doping concentra-tion of the region 2. As a resul-t of thisg the breakdown in this case will always occur within the semiconductor body at the ~-n junction 5 and not at the surface.
It is :~u:rt:hermore -to be noted that at too small a value o~ said cListance :L -the I`ield strength at the surface will increase (as a ma-tter o:~ :~ac-t the overall ~3~

10.5-79 22 PIIN 9188 voltage between the regions 3 and 1~ determines -the area between the CUrVQ S and the line Es = )~ so that breakdown at the surraee'occurs at lower vol-tage.
Calcu:Lations have proved that the most favou~
ra'ble values for the breakdown voltage are obtained with the area enclosed in Figure 9 by -the lines A and B. In ~gure 9 the produc-t of the doping eoncentra-tion N in atorns per em3 and the thicl~ness d in cm of' the region 1 is plotted ' OIl the hori~o~tal axis for silicon as a semiconductor and the value of 10 VB wi-th L in cm and VB in Volts is plotted~
on the vertical axis. VB is the unidimensionally computed value of the hreakdown voltage of -the ~-n junction 5, that is to say in Figures 8A to E -the breakdown voltage of the'N~N P structure wllen it is assumed that the doping concentrations of the regions 1 and 2 are homogeneous, so the ~-n junction 5 is abrupt, tha-t the N region l~ has a subs-tantially negligi.ble series resis-tance, ancl that the N~N P structure extends in~init;ely fa:r in all direetions perpendieular to -the axis Es. This f,ietitious breakdown voltage VB ean very s:imply be eomputed with -the said assu3nptions. ~'or that purpose see, ~or example, S.M. Sze~, Physies o~ Semieonduetor Deviees~ l~iley & Sons, New York 1969, ehapter 5.
For the ease in whieh silicon is chosen as a, semieonductor material it appears -tha-t ~or values of N x d which ~ie between the lines A ancl B, that is to say for 7.6.10 ~ ~ ~ N.d ~ 1.5.1012 the eondi-tion of Figure 8D (symme-trical ~ield dis-t:ribu-tion at the surfaee) is satisfiecl.
If the eonditlon of Figure ~E is also to be ' satisfied (symmetrieal field dis-tribution at the surfaee, with breakdown at the p-n julietion 5~ values fc,r 1" N' and 35 cl shoulcl be chosen which lie c~n or nea:r the line C of ~igure 9- For V~ ~ 1.4.10 5 it; holcls suhstantially that N.d-= 9 10 11 em~2 3~

.. ., , ~ . . ..
10.5.79 23 PIIN 9188 As already said, -the values of Figure 9 apply 1;o silicon which has a crit:ical field strength ~ of appro~
ximately 2.5.105 Volts per Clll and a dielectric constant ~
Or approximately 11.7. In general, for serniconcluctor mate-rials having a relative dielec-tric constant and a critical field strength L it holds that between -the lines A
r~jr--`
and B 2.6.10 E ~ L ~ N.cl ~ 5.1.105 E and for the line C: N.d substantially equal to 3.'lO5 ~ and, in this case, also V ~ 1.4.10 5.
' The values and E can 'be found from the available literature by those skilled in the art. For the critical field strength E reference may be made, f`or example, to S.M. Sze, Physics of Semiconduc-tor Devices, Wiley & Sons, New York 19~9, p. 117, Figure 25.
By means of what has been described above wi-th reference to Figures 8A to L and 9, those sl~illed Ln the art ean select the~ dopings and d-lmensions ~hich are most favourable in given circumC;tances for all the semi-conductor st:ructures clescribed in the preceding examples.
~t will not al~ays be necessary Ol-` desirable tha-t in all circumstances (~'igu~e 9, curve C) surf`ace 'breakdown i5 avoided, as long as one stays ~rithin or on the lines A
and B of Figure 9.
The invention is not restricted -to the embodl-ments described. For example, semiconductor materials other than silicon, insulating layers ot'her than silicon oxide, for example silicon nitride, aluminium oxifle, and metal layers other than alurninium rnay be used. In each 3~
embodiment the conductivity -types may also be replaced by their opposite types. It should be stressed that ? although in the given e~amples the th;rd region 3 ic~ always higher doped than the second region 2, said third region may also have the same doping concen-tration as the second region~
this f`ormillg an extension O:r the seconcl region. In such cases the lower breakclown voltage of`-the second p-n junction 6 is caused by the strong curvature in the tran~
S:i'tiOll reg:ion bet~re~n the firs-t andsec~lcl E~n jLmctions-~ and 6.

Claims (15)

10.5.79 PHN 9188 THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A semiconductor device with a semiconductor body having a substantially flat surface, comprising at least one field effect transistor having a source electrode and a drain electrode, a channel region between said source and drain electrodes, and a gate electrode adjacent the channel region to influence, by means of a gate voltage applied to the gate electrode, a depletion zone for con-trolling a flow of charge carriers between the source and drain electrodes, the field effect transistor comprising a layer-shaped first region of a first conductivity type which, with an underlying second region of the second con-ductivity type, forms a first p-n junction extending sub-stantially parallel to the surface, whereby at least in the operating condition, an island-shaped portion of the first region is bounded laterally at least partly, by a second p-n junction with associated depletion zone which is formed between the first region and a third region of the second conductivity type adjoining the first region, said second p-n junction having a lower breakdown voltage than the first p-n junction, at least the gate electrode adjoining the island-shaped region portion, in which between the second region and a contact region of the field effect transistor belonging to the source, drain and gate electro-des and forming a non-rectifying contact with the island-PHN. 9188.

shaped region portion, a voltage in the reverse direction is applied, characterized in that the doping concentra-tion N in atoms/cm3 and the thickness d in cm of the island-shaped region portion satisfy the condition wherein .SIGMA. is the relative dielectric constant and E the critical field strength in Volt/cm at which avalanche multiplication occurs in the semiconductor material of the first region, L is the distance in cm from the said con-tact region up to the second p-n junction, and VB is the unidimensionally computed value of the breakdown voltage of the first p-n junction in Volts.
2. A semiconductor device as claimed in Claim 1, characterized in that N.d is substantially equal to 3Ø105 .SIGMA. E, and L ? 1.4.10-5.VB.
3. A semiconductor device as claimed in Claim 1 or Claim 2, characterized in that the doping concentration of at least the portion of the second region adjacent the first region is lower than that of the first region.
4. A semiconductor device as claimed in Claim 1, characterized in that the second region has such a thick-ness that at the breakdown voltage of the first p-n junc-tion the depletion zone extends in the second region over a distance smaller than the thickness of said region.
5. A semiconductor device as claimed in Claim 1, characterized in that the first region is formed by an epitaxial layer of the first conductivity type provided on the second region.
6. A semiconductor device as claimed in Claim 1, characterized in that the island-shaped part of the first region is bounded laterally entirely by the second p-n junction.
7. A semiconductor device as claimed in Claim 1, characterized in that the gate electrode comprises a semi-conductor gate electrode zone which forms a p-n junction with the adjoining part of the channel region.
8. A semiconductor device as claimed in Claim 1, characterized in that the gate electrode comprises a metal PHN. 9188.

layer which forms a rectifying metal-to-semiconductor junction (Schottky junction) with the adjoining part of the channel region.
9. A semiconductor device as claimed in Claim 1, characterized in that the gate electrode comprises a con-ductive layer which is separated from the adjoining part of the channel region by an insulating layer.
10. A semiconductor device as claimed in Claim 1, characterized in that the field effect transistor is of the lateral type, the source and drain electrodes on either side of the gate electrode forming non-rectifying contacts with the first region, the said contact region being formed by the drain electrode.
11. A semiconductor device as claimed in Claim 1, characterized in that the gate electrode is connected to the second region.
12. A semiconductor device as claimed in Claim 10, characterized in that the drain electrode is surrounded substantially entirely by the gate electrode and that the gate electrode is surrounded substantially entirely by the source electrode.
13. A semiconductor device as claimed in Claim 12, characterized in that a semiconductor layer of the second conductivity type is present on the first region, that the source and drain electrodes comprise electrode zones of the first conductivity type and the gate electrode com-prises an electrode zone of the second conductivity type, and that all the said electrode zones extend throughout the thickness of the said semiconductor layer down to the first region.
14. A semiconductor device as claimed in Claim 12 characterized in that the source electrode comprises a source zone of the first conductivity type which is not connected to an external voltage, that a highly doped zone of the second conductivity type is present on the side of the source zone remote from the gate electrode and extends from the surface down to the second region and is situated so close to the source zone that the breakdown voltage between these two zones is considerably lower than that of PHN. 9188.

the first p-n junction, that the drain electrode and the second region are connected to a voltage source which is connected in series with a load impedance and provides a reverse voltage across the first p-n junction, and that the gate electrode is connected to a voltage source which provides a variable reverse voltage between the gate elec-trode and the first region so that the island-shaped portion of the first region surrounded by the gate elec-trode and the associated depletion zone can be temporarily cut off electrically from the remaining part of the first region.
15. A semiconductor device as claimed in Claim 1, characterized in that the field effect transistor is of the vertical type, that the drain electrode forms a non-rectifying contact with the second region, that the source electrode forms a rectifying contact with the first region, and that the gate electrode comprises an electrode zone of the first conductivity type which surrounds at least one part of the first region associated with the channel region and forms the said contact region.
CA332,190A 1978-07-24 1979-07-19 Semiconductor device Expired CA1134055A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NLAANVRAGE7807835,A NL184552C (en) 1978-07-24 1978-07-24 SEMICONDUCTOR FOR HIGH VOLTAGES.
NL7807835 1978-07-24

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GB2070858B (en) * 1980-03-03 1985-02-06 Raytheon Co Shallow channel field effect transistor
US4523368A (en) * 1980-03-03 1985-06-18 Raytheon Company Semiconductor devices and manufacturing methods
US4300150A (en) * 1980-06-16 1981-11-10 North American Philips Corporation Lateral double-diffused MOS transistor device
NL187415C (en) * 1980-09-08 1991-09-16 Philips Nv SEMICONDUCTOR DEVICE WITH REDUCED SURFACE FIELD STRENGTH.
US4485392A (en) * 1981-12-28 1984-11-27 North American Philips Corporation Lateral junction field effect transistor device
GB2133621B (en) * 1983-01-11 1987-02-04 Emi Ltd Junction field effect transistor
NL8304256A (en) * 1983-12-09 1985-07-01 Philips Nv SEMICONDUCTOR DEVICE.

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US3814992A (en) * 1972-06-22 1974-06-04 Ibm High performance fet
US4037245A (en) 1975-11-28 1977-07-19 General Electric Company Electric field controlled diode with a current controlling surface grid

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SE437094B (en) 1985-02-04
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BR7904692A (en) 1980-04-15
ATA509379A (en) 1986-05-15
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AU4906179A (en) 1980-01-31
AU521670B2 (en) 1982-04-22

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