DE2061061C - Electrochemically controlled shaping of silicon semiconductor bodies - Google Patents

Description

The invention relates to a method for the selective etching of a core of a silicon semiconductor body, in which the semiconductor body and a counter electrode are immersed in an etching medium, whereupon a voltage between the semiconductor

body and the counter electrode is applied.

U.S. Patent 2,847,287 is a Vei drive to the selective etching of p-conductive zones of a silicon body, the other areas of others Has line types specified. With this

drive, however, only a relatively low etching speed can be achieved, and the process is limited to the etching of p-conductive layers from a L'atergrjr: d of the n-conductive type.

U.S. Patent 3,418,226 is one method for selective electrolytic etching of degenerate p-Leltung type material from a described less doped material with p-conduction in the same semiconductor body. This procedure however, it is limited to the selective etching of degenerate p-conductor material in gallium arsenide and is therefore of limited use in other countries Interest.

A more recent one, on the Dutch patent application Dutch patent based on 6,703,013 discloses an electrochemical process for the production of thin silicon layers, which for the production of ultra-thin (I μπι) silicon layernn can be used as they are in high-performance and high-frequency components with high packing density, as well as air-insulated or dielectric-insulated silicon semiconductor integrated circuits Find use. This known method is, however, aimed at removing unwanted silicon very low resistivity limited by η-conductive areas of relatively high resistance In contrast, in the majority of the integrated silicon circuit components used today the opposite is desired, namely the high resistivity portions of to remove a relatively low resistivity epitaxial layer. In particular is it is desirable to have a substrate of relatively high specificity

Resistance from an overlying ,,, cpitactic to a potassium hydroxide, is submerged. When

see or from a found layer relatively _low , _{h on the} silicon body em positive potential

ngcn specific resistance is bent without back-skid, which is relative to a platinum counter-

guna of the line type to remove. so that the cue electrode is about 0.5 V larger. then will

rubbing splint only mm, sometimes to the parasitic 3 all sections of the Sili / u.ms. the at least about

Resistance of m or positive on these layers is -0.5 V, essentially passivated. The

components provided. bcucuL that these sections of the positive potential

> .. s of the German interpretation I 0IH SS _{4 is} , _C s _lia Is of about 0.5 V at least ten times slower

also mentioned, in the case of a semiconductor body in which (typically 200 to 10000 times slower) is etched

a. · cit.r.ne p-type layer at least on one of the sections, which a voltage

Sea-bordering an n-conductingc zone, have less than 0 5 Y on this side. This is why

to expose oliM-mmen by creating the flowing zone the »Pas'sivierunespotentia!« of the Siliziuni-KaÜL-m-

is eccolytically etched off, starting at about 0.5 V during the etching hydroxide-platinum system.

vo ^ .snges at the η-conductive zone a higher In a group of embodiments of the

^P T \ η ^an P- ^{| cit} ^ ^{n (J} - "layer aulrecht- 15 invention, the semiconductor body has a pn-over-

Erii uen ^w · · ™ o _{ang au} f ^ about _we i _c | _{lcn c} j _n voltage drop occurs-

v. also is obtained in U.S. Patent 2,656,406, so that some areas of the semiconductor

ei! -, .experienced in the different material distances on one above the passivation potential

, v .; ms semiconductor zones of the one or the one to send positive potential are, while the

he -connected lines, ^ ,, ^ H.ilHeiierbau- so semiconductor zones on the other side of the pn-over-

e ^! ..nt described in which his' i.uielemeni in gangs is at a potential below the passive

The electrolyte is immersed in the electrolyte and exposed to zones of the four potential. With this potential

1 line type one i. with respect to the. The dis- tribution will be applied to a voltage below the

I. jX) voltage is applied to this passivation potential! Laying semiconductor zones

/.·■■. π to obtain a preferred material section. 25 etched until enough material has been removed and the

I- . Semiconductor bodies can thus be produced. Transition is exposed. As soon as the transition is clear,

have a step at the pn junction. "The semiconductor is passivated with respect to the solution

It is now the task of the lind us, ,, η, and the etching process ceases. that is, the etching

I; · : <\ to selectively etch off a zone a speed is increased by a factor in a

S .; :; to be indicated in the semiconductor body, which decreases in the substantial 30 order of magnitude from 200 to 10,000.

Μι- ί regardless of the type of line or of the In another group of execution

G ₁ - ■ is the resistivity. In particular, examples of the invention is used within a half

see dn self-ending procedure for selective conductor body e ^; ne potential distribution generated by

Λ: / s predetermined sections of a semiconductor electrode and potentials in a suitable manner

k · rs can be created in such a way that the depth of the 35 are ordered, and in the resistance and

^Λ ; ng relatively independent of the immersion! of the field effect method can be used. Once this

Kr> crs in the corrosive medium. Potential distribution, regardless of what

According to the invention, this object is achieved in that the configuration is the semiconductor

gc '-.- t that the etchant selected from solutions is etched on all the areas exposed to the etching solution

vvi.i. the silicon on failure, one between the 40, and which are at a potential below the

Si! -ium semiconductor body and the solution applied passivation potential are located.

th voltage chemically etch, and that in the silicon- The invention is described in the following

Semiconductor body such a potential distribution exercise of several exemplary embodiments in

1 "-ijgt and maintained that the etching binding is explained in more detail with the drawing, namely

ü ■>. Parts related to the counter electrode an under- 45 shows

potential lying half of the passivation potential FIG. I a schematic view of an arrangement

have while the non-etch parts rely on to carry out the selective removal of

a positive potential, which is related to p-conducting semiconductor material from n-conducting

on the counter electrode at least equal to the Passi semiconductor material according to the invention,

potential is. 50 Fig. 2 is a schematic view of an arrangement

It is therefore essential to the invention that the calf to carry out the selective removal of

conductor body is etched in a solution, which is an η-conductive semiconductor material of p-Ieitcndem

chemical etchant for silicon independent of semiconductor material according to the invention,

whose line type is. This means that the etching Fig. 3 and 4 partial cross-section through half-liter

solution is such that it silicon noticeably 55 platelets, which in a suitable manner according to the invention

etched, if a voltage is not relatively etched on this,

is applied to a counter electrode, the larger Fig. 5 one for the selective etching of a slot

than a predetermined passivation potential. of a predetermined depth into a semiconductor surface

More precisely, the selective removal of the prepared zone of a semiconductor wafer and semiconductor material ^{takes place according to the} invention in a 6o Fig. 6, a partial cross-section through a semiconductor solution, which etches the silicon semiconductor wafer in one of many possible types in the absence of an applied voltage , whose application of a potential to a zone of the half-etching attack is significantly reduced, conductor body for controlling the inventive cn when a positive voltage is shown relative to a counter-etching process.

electrode is applied. ^{For example, a concentration of less than about 10 20} foreign atoms is shown schematically in FIGS. I and 2, regardless of the type of conduction, of the apparatus for carrying out the invention ³ contains, is etched relatively quickly if it is made of a resistant to the etchant used.

good material. F. a counter electrode 13 is and will be known to those skilled in the art

at least partially immersed in the etchant 12, and therefore not described below,

suitable devices 14 for connecting the The illustration according to FIG. 2 essentially corresponds to

(Lie electrode to an external circuit for the borrowed from Fig. I with the exception that the

A control potential (+ V) is applied to semiconductor bodies 18 made of silicon, an n-conductive type

see. The counter electrode consists of an advantageous zone which is to be removed, and a

Way of a material that does not dissolve p-conductive cndc zone (denoted by N or P), which

and the electrolyte is disadvantageously contaminated after the end of the atomization process. the

cleans. / .. H. made of platinum. Gold or the same n-conductive zone is obtained by connecting the p-conductive

Material of which the body to be etched is made. io removed the layer 19 to a voltage (+ V) that As shown in FIG. I shows, a half-litcnder must be high enough to cover the entire p-litcndc Body IS a p-active zone and layer to be etched at a potential above the passive

an n-conducting zone (the zones are to be held with P or N voltage potentials.

on which after the end of the etching there can be a variety of modifications and

Operation should remain behind. The semiconductor IC is the _IS-described improvements in the preceding

advantageously be taken at a distance from the Gcgcnelek procedure to the procedure for

trodc immersed in the electrolyte. Facilities practically usable for the special application

16 for connecting a zone of the semiconductor 15 to make. For example, the semiconductor body

to the circuit for generating the control potential on pre-metallized conductive or dielectric

tials (+ V) are also provided. From Fig. 1 _ao carrier layers with a wax or a resin

it can be seen that the positive potential is merely wasted, so that only the surface to be etched

on the n-copper zone of the semiconductor are exposed, and the surfaces that are not to be etched

scn is. and that the p-icing zone is additionally protected against the etching agent by the surface,

n-conductive zone through a pn-junction 17, whereby the handling of the semiconductor body; and

is separating. as the generation of tax potentials are facilitated

It can be seen that the devices 16 are in front

are partly arranged so that the entire length of the silicon semiconductor body _{to be etched has to be etched}

Layer or of the transition <7 a suitable chipboard _a uf a main zone or substrate (either epitaxially

Form voltage barrier so that the n-lcitende zone table-formed, cindiffundicrtc, or in both ways

can be kept at a voltage, the higher ₃₀ manufactured) applied semiconductor layers. In

than the passivation potential. during the one iypnenen fail the substrate was on a con-

The p-conductive zone has a potential which, based on the concentration, is less than 10 * atoms per cm ¹

doped on the counter electrode 13 lower than the Passi. The thickness of the semiconductor layer was between

vicrungspotential is. 1 to I5 | im. This thickness of the half-liter layer is

However, the etchant is obviously not critical from a group of chemical 35. To facilitate- Etchants selected which were only those zones of handling in the electrolyte Noticeably etch the silicon semiconductor body, using a silicon semiconductor body

drew a potential below the counter electrode - resin or wax on a ceramic disk

have half of a passivation potential. attached, and were then plugged into the electrolyte

Bcim the progress of the etching process makes itself 40 immersed, the z. B. from 1- to 7-normal potassium

This consisted of a visually observable development of hydroxide. A platinum counterpart was

of hydrogen gas on the etched semiconductor crober-trodc, although any other material is used in

areas noticeable. Conversely, it shows that the same way can be used, beforehand

Atzmittet not noticeably attacked surfaces that it does not use the electrolyte

no observable hydrogen evolution. As soon as «5 is substantially contaminated. The temperature of the elec-

the p-lcitcndc material is completely eroded, so trolyten was generally down to about 70 to

that the area around the metallurgical transition 17 100 ^C C held in order to achieve an optimal etching effect

around exposed to the caustic, tubes all achieve that. Although the etching effect was similar to that of the on

The semiconductor surface exposed to the etching medium changes the applied bias voltage, becomes p-conductivec « Potential which is greater than the passive potential of silicon, which is based on a concentration of approx

tial is: and the etching process is essentially doped 10 »atoms per cm *, in an on elw«

ends. The etching process is terminated by means of 5 normal potassium hydride kept at 95 ° C

a sudden and clearly noticeable cessation solution is etched away by about 2 to 4 pm per minute

the development of hydrogen. As soon as the pn junction is reached, au occurs

no hydrogen. As more is developed, the exposed surfaces are immediately an oxide

At least in the order of magnitude and layer. The etching rate of this oxide lies

typically by a factor of 200 to 10,000 200 times lower than the etching speed

reduced compared to the etching effect during the p-type material,

the time in which hydrogen gas is evolved. The examples described above sim

To monitor the hydrogen gas development 60 in connection with the use of voi

cip hydrogen gas detector can be explained in the caustic or potassium hydroxide as caustic, but can

can be arranged in the vicinity, and the other metal hydroxides of the element can also be used

use electrical and mechanical equipment with that of group I A of the periodic table

Hydrogen gas detector coupled 'so that the. This group excludes the hydroxides de Semiconductors automatically out of the etchant - sodium, rubidium, cesium and de

taken when the evolution of water- lithium a. Ammonium hydroxide and alkylammc

fuel gas has stopped. The actual design irium hydroxide, e.g. B. Telramethylammoniumh]

Such an automatic device lies in the specialist hydroxide uad Tclraäthylammonnimhydroxid, can

ehenf-ills can be used. Satisfactory Er-Sn Nc is also obtained when aqueous mixtures of TnS hydrofluoric acid and nitric acid are used as the caustic.

4 are partial cross-sections of

äää; is etched, but is not yet high enough to generate a sufficiently high bias voltage in the pn junction two, six of the layer 32 and the n-type junction M so that the Subst.at 31 is passivated before it is completely removed is.

a layer 23 from n-TJj · geb.We ^l ' ^st _ ⁰ ^ ₆ J ₈ ΑχμΪα ^ of silicon is ä for example layer 23 is a slide2> from "JJ ^ JgJ g ™? _that ^ etching effect in parallel to (100) shown, which is so selected, ^ ^M «'^ Sf'g crystallographic plane running planes er the solution used w' ^ tejit in honor of the m« g P ^ _{etching effect in} planes parallel etching process an additional Schute: to Meiert «crystallographic plane is. To be more precise, the p-conductive layer21 advantageously has anen to the Uli; ^ ™ "^^. _{D (m) level M} relatively high specific ^ deri ^ to ^" Srig that the person working in the area

of

äsKSS

zw, see the layers 211 and I " _{available in} that a sufficiently high current to the semiconductor

body causes ^te ^ ^r *

has been constantly removed, is gj

The etching process is either different

or the layer 23 (N) or an electrical connection on both nuts ^ ff ^ S? Zf d, .- sc electrical connection on e ^'11 P ⁰ * ¹ " _{di

Counterelectrode in the ^. ^^ Sdnung with the v, potential is. "^" »", ^^ general

^F 'g3g «« 8t ^e " ^Αϋ ^ ^ϋ * ⁶ χ Z manufacture

";. _stop !

«^ 3335 338

? both

as a beneficial exit of air-insulated. mono gen viewed as i

are described. Semiconductor-

Fig. 4 shows the section 30 <a π

plate, which ^ J ^ SZSSS ^ the one in F i g. 3 shown p

that is, the section 30 has a strat 31 over which a: layer 32j ρ ^ J and a less heavily doped ^ "^ _ςηβη _ p-type is formed before

solution offers ^ / ^ «S ^^ T? i

Layer 33 (P) or Layers, as in before

one in relation to *%

Potential connected It is

that for the size of the positive

for this procedure ^^^

There is a limit because em posiu too coarse

at the pn junction between the wrou _dadmch

Layer 32 biases _h

a sufficiently large S ^^ uB Suchennosi ^

that lier n-luminous section Ji ener κ, _lead .

is etched. If the section Ju ^ae *

a silicon substrate

has layers and if the

applied electrolyte about 7-nonna ¹ ^^ _ρ

is and if the counter electrode α _{ht 32 aani} _

then has a suitable, an öer? " _{hr o 65 v}

legendei, Potenüal an ore from _B -

This potential is sufficient around d * P ^ ⁰ T = J, passivate as soon as the n-conductive substrate 31 is gone

establish £ _7h

_w . However, the etching effect points to another advantageous one

Embodiment of the invention out. In Fig. 5 is

«SrSenaSchnitt shown to be selective

Etching of a surface slot after the following

_d described embodiment of the

proper procedure is prepared. The ^ a ^ gem _ _{Ha! B! Ei! Srzone}

4 Tlübstrat adjoins a semiconductor layer 42 of the retarded conductivity type and forms with its pn junction, over the surface of the layer 42 is a mask 44 provided with an opening and made of a mask against the etching solution used

resistant material formed As shown in Figures 3 and 4, the _FiÄ not to atzende Oblrriche. that is, the surface of zone 41, ^ ^^ ^ _{n the etchant} , resistant

Material 45 coated to provide additional protection _laundri during the etching process to create.

In this exemplary embodiment, the surface of _{the half-} layer 42 is placed essentially parallel to the (S ₀ ) plane of the semiconductor substrate. The arrival ^ ^ ^ ^ _Kaüumhydrox i _d iösung placed, _{and the} substrate 41 is under these conditions exposed portion of layer 42 as long as 2 * £ until you pS-transition to a posiüveSpannungsangeschlossen equal to or greater than the Passivierungsspannung is between the Layers \ _% ^ ₄ , _exposed ^ _woratl f the etching process _stops . _The etching is due to that described in the above preferred Atzwirkung relative to _the crystallographic planes only laterally to the gSricheiSn side lines 46 A and 46 B on.

. The in connection with Figure 5 method explained ^ _n, of course, the formation of voids "je, - columns of any shape and in particular for the _Bi | _dui , _g of slots are used as rie often ^ ^ ^, ^^^ ^^^ integrated circuit-

S _{0 genes} . The depth of the gap is of course _{determined by the} metallurgical control of the first pn transition below the surface

In FIG. 6, a portion "of a cross section _{By J} h a semiconductor die is shown at which a potential _of ^« ^ types of applying a _Potent i _a i _s to a portion of a semiconductor body for controlled selective etching according to the invention are explained in soil.

9 10

The plate is prefabricated with the aim of creating a stand for the respective semi- air-insulated or dielectric-insulated conductor zones underneath. To create over the passivating integrated semiconductor circuit. As from dielectric layer 56 and over the in the front drawing F i g. 6, above a standing electrode mentioned is a p-conductive substrate 51 having a relatively high specific 5 and relatively uniform conductor layer 62 resistance, a semiconductor layer 52 of the n + -type made of an inert metal such as e.g. B. Platinum or Child and a less heavily doped n-layer 53 is formed. educated.

The formation of these semiconductor layers takes place during the removal of the p-conductive substrate 51, for example, by epitaxial deposition, diffusion of slots from the underside of the ion, ion implantation or any of the other layers 52 into the semiconductor device, by a known method Method for changing the semiconductor air insulation or a dielectric insulation to property of a semiconductor body. Create in the layer 53, the entire plate 50 is immersed in a front are local zones 54 A and 54 B from the p-line direction, for example according to FIG. 1; and the type formed to create resistors or bases for positive potential is applied to the conductive outer layer of transistors within the integrated circuit to 15 62, which serves to distribute the potential. In the p-conductive zones 54 A and 54 B and the surface of the semiconductor during the is to protect a plurality of zones 55 A and SSB from etching against an etching attack. D; is n + type used, for example, to create emitter zone potential is distributed through the conductive surface layer of the transistors within the integrated circuit and is essentially uniform to create dm cn processing. The n ⁺ zone 55C was created for an area, for example the zone 55 C, on the n + -schidit to facilitate the production of a low-resistance 52. In this way, the p-conductive Ma contact at the collector of the transistor is completely removed over a material of the substrate 51 until Jer electrode 59 is created on the surface. A transition between the p-conductive substrate 51 and the more passive dielectric layer 56 lies in all of the n + -layer 52 is exposed. As soon as the overlying sections above the semiconductor surface, with openings 25, is exposed, a current flows, and on the underside of the layer 52, which is then placed where metallic electrodes 57, 58, are placed, one 59 arises , 60 and 61 through the dielectric layer towards the oxide layer, and the semiconductor body will pass through pa> si to a terminal of low resistance.

1 sheet of drawings

Claims (10)

Patent claims: 1. A method for the selective etching off of a zone of a silicon half-letter body, in which the semiconductor body and a counter electrode are immersed in an etching medium, whereupon a voltage is applied between the semiconductor body and the counter electrode, characterized in that the etchant is selected from solutions which Etch silicon chemically in the absence of a voltage applied between the silicon semiconductor body and the solution, and that such a potential distribution is generated and maintained in the silicon semiconductor body that the parts to be etched have a potential below the passivation potential in relation to the counterelectrode, while the parts do not Parts to be etched are at a positive potential, which is at least equal to the passivation potential in relation to the counter electrode. 2. The method according to claim I, characterized in. that the remaining zones of the silicon semiconductor body; ei it then from the Etching media can be removed when essentially all at one below the passivation potential located zones of the semiconductor body are removed. 3. The method according spoke 1 or 2, characterized in that d.e etching solution from a) Metal hydroxides de-. Group I a of the periodic System of elements, and b) ammonium hydroxide or alkylammorsium hydroxides is selected. 4. The method according to any one of the claims! to 3. characterized in that the semiconductor body is removed from the etching medium after the evolution of hydrogen gas can no longer be detected with the naked eye is. 5. The method according to any one of claims 1 to 4, characterized in that the not Zones of the conductor body to be etched with be coated with a material capable of resisting the etching medium. 6. The method according to any one of claims i to 5, characterized in that the etching solution from those containing potassium, sodium, cesium, lithium and rubidium hydroxide and the Counter electrode is selected from the group containing platinum, gold and silicon, and that one Voltage greater than about 0.5V is applied. 7. The method according to claim 6, characterized in that an applied voltage of about 0.65 V and potassium hydroxide is used as the etching solution. 8. The method according to claim 7, characterized in that the silicon semiconductor body removed from the etchant within an hour after evolution of hydrogen gas can no longer be seen with the naked eye. 9. The method according to any one of claims I to 8, characterized in that in a silicon semiconductor body with a serving as a substrate zone (21 or 31) of the first conductivity type and with an α semiconductor layer adjoining the surface of the substrate (22 or 32) of opposite conductivity types, which together form a pn junction, first the surface of the semiconductor layer (22 or 32) is covered with a material (24 or 34) resistant to the etchant, and that after immersion of the semiconductor body and the counter electrode (13) a voltage is applied in the etching solution between the layer (2?. Or 32) and the counter electrode so that the layer is positive with respect to the counter electrode, the substrate being relatively independent of the duration of immersion of the semiconductor body in the solution is etched away to the pn junction. 10. The method according to claim 9, characterized in that the substrate to be etched from higher specific resistance is selected than the half-conductor layer that is not to be etched off.