SE501079C2

SE501079C2 - Method for etching silicon areas on insulating substrates

Info

Publication number: SE501079C2
Application number: SE9301246A
Authority: SE
Inventors: Goeran Alestig; Kjell Bohlin; Nils Oegren
Original assignee: Asea Brown Boveri
Priority date: 1993-04-16
Filing date: 1993-04-16
Publication date: 1994-11-07
Also published as: SE9301246L; WO1994024695A1; SE9301246D0

Abstract

A method of manufacturing integrated circuits on a wafer, which at least comprises an insulating substrate (10) coated with a silicon film (11). Silicon regions (11b) are etched out on the silicon film applied to the insulating substrate by a process whereby the surface on the silicon film is oxidized such that a thin layer of silicon oxide (12) is formed, a thin layer of silicon nitride (13) is deposited on the oxide layer, a photoresist is applied (14) and patterned with photolithographic methods to define protected resist regions, whereupon the nitride is etched away from unprotected regions with an etching medium which interrupts the etching when the underlying oxide layer is reached whereas the silicon nitride remains on those regions which are covered by photoresist, the photoresist is removed before the wafer is subjected to an oxidation in which unprotected regions of the silicon film are oxidized wheras regions (11a) coated with silicon nitride are not oxidized, and the oxide and the nitride are finally removed with an etching medium which does not attack silicon.

Description

20 25 30 35 501 079 2 En process för att vid tillverkning av integrerade kretsar definiera de kiselomraden där de aktiva komponenterna ska bildas kallas LOCOS, LOCal Oxidation of Silicon. LOCOS- metoden används huvudsakligen för homogena kiselskivor utan isolerande substrat men kan även användas för kiselfilmer palagda pa isolerande substrat. I LOCOS-metoden deponeras ett kiselnitridskikt pa kislet. Med fotolitografiska metoder palägges därefter en fotoresist pa de omraden där aktiva komponenter skall bildas. Nitriden etsas bort fran de omraden där den ej skyddas av fotoresist varefter fotoresis- ten avlägsnas. Därefter oxideras de omraden vilka ej är skyddade med kiselnitrid. Denna oxid gros med hjälp av syrgas eller vattenanga vid hög temperatur. Slutligen etsas kvarvarande kiselnitridfilm bort med en lämplig syra, sasom fosforsyra, som ej angriper oxiden. De aktiva komponenterna tillverkas sedan i de omraden vilka ej täcks av oxid, medan oxiden ger isolering mellan komponenterna. 20 25 30 35 501 079 2 A process for defining the silicon areas where the active components are to be formed in the manufacture of integrated circuits is called LOCOS, LOCal Oxidation of Silicon. The LOCOS method is mainly used for homogeneous silicon wafers without insulating substrates but can also be used for silicon films deposited on insulating substrates. In the LOCOS method, a silicon nitride layer is deposited on the silicon. Using photolithographic methods, a photoresist is then applied to the areas where active components are to be formed. The nitride is etched away from the areas where it is not protected by photoresist, after which the photoresist is removed. The areas which are not protected by silicon nitride are then oxidized. This oxide is grown with the help of oxygen or water vapor at high temperature. Finally, the remaining silicon nitride film is etched away with a suitable acid, such as phosphoric acid, which does not attack the oxide. The active components are then manufactured in the areas not covered by oxide, while the oxide provides insulation between the components.

När LOCOS-metoden används för kisel pa isolerande substrat kommer kanterna pa kiselomradena att täckas av den isole- rande oxiden. Man kan da ej odla den tunna styroxid som används för aktiva komponenter, t.ex. transistorer,pa kant- ytorna. Därigenom kommer ocksa den elektrod, styret, som kontrollerar strömmen genom transistorn att befinna sig längre ifran kanten. Kontrollen över strömmar i kanten blir da sämre. Detta ger upphov till läckströmmar i komponenten, speciellt om den utsätts för joniserande stralning. Talighet mot joniserande stralning är viktig för manga komponenter vilka tillverkas i kisel pa isolerande substrat eftersom dessa komponenter ofta är avsedda att användas i sadan miljö.When the LOCOS method is used for silicon on insulating substrates, the edges of the silicon regions will be covered by the insulating oxide. The thin gate oxide used for active components, e.g. transistors, cannot be grown on the edge surfaces. This also means that the electrode, the gate, that controls the current through the transistor will be further from the edge. The control over currents at the edge will then be worse. This gives rise to leakage currents in the component, especially if it is exposed to ionizing radiation. Resistance to ionizing radiation is important for many components that are manufactured in silicon on insulating substrates because these components are often intended to be used in such an environment.

UPPFINNINGEN Framställning av integrerade kretsar pa en skiva innefat- tande ett elektriskt isolerande substrat belagd med en kiselfilm ur vilken kiselomraden frametsas enligt uppfinningen genom att 10 15 20 25 30 35 501 079 - ytan pà kiselfilmen oxideías sä att ett tunt skikt kiseloxid bildas, - ett tunt skikt av kiselnitrid deponeras pà oxidskiktet, - en fotoresist pälägges med fotolitografiska metoder för att definiera skyddade resistomräden, - varefter nitriden etsas bort fràn de oskyddade omräden med ett etsmedel som avbryter etsningen dä det underliggande oxidskiktet näs medan kiselnitriden blir kvar pà de områden som täcks av fotoresist. - fotoresisten avlägsnas innan skivan utsattes för en oxida- tion där oskyddade omräden av kiselfilmen oxideras medan omräden belagda med kiselnitrid ej oxideras och ' - slutligen frilägges det underliggande isolerande substra- tet i de oxiderade områdena och pá detta substrat utetsade kiselomräden genom att oxid och nitrid samt eventuell i de oskyddade omrádena kvarlämnad kisel bortetsas.THE INVENTION Production of integrated circuits on a wafer comprising an electrically insulating substrate coated with a silicon film from which the silicon regions are etched according to the invention by 10 15 20 25 30 35 501 079 - the surface of the silicon film is oxidized so that a thin layer of silicon oxide is formed, - a thin layer of silicon nitride is deposited on the oxide layer, - a photoresist is applied using photolithographic methods to define protected resist regions, - after which the nitride is etched away from the unprotected regions with an etchant which interrupts the etching when the underlying oxide layer is removed while the silicon nitride remains on the regions covered by photoresist. - the photoresist is removed before the wafer is subjected to oxidation where unprotected areas of the silicon film are oxidized while areas coated with silicon nitride are not oxidized and - finally the underlying insulating substrate is exposed in the oxidized areas and the silicon areas etched on this substrate by etching away the oxide and nitride as well as any silicon left in the unprotected areas.

När oskyddade omräden av kiselfilmen oxideras kan oxidatio- nen tillätas fortgä till dess att kiselfilmen har oxiderats ända ned till det underliggande substratet.When unprotected areas of the silicon film are oxidized, the oxidation can be allowed to continue until the silicon film has been oxidized all the way down to the underlying substrate.

I en föredragen utföringsform av uppfinningen avbrytes dock oxidationen innan det isolerande substratet natts varefter den reserande kiseloxidfilmen avlägsnas frän dessa omräden medelst etsning, företrädesvis plasma-etsning, vilket ökar möjligheterna att kontrollera kiselkanternas avrundning.In a preferred embodiment of the invention, however, the oxidation is interrupted before the insulating substrate is etched, after which the remaining silicon oxide film is removed from these areas by etching, preferably plasma etching, which increases the possibilities of controlling the rounding of the silicon edges.

Med den uppfunna metoden erhälles de önskade kiselomrädena pä det isolerande substratet utan mellanliggande kiseloxid omräden och med mer avrundade kanter än om man direktetsar med plasmaetsning eller vätetsning.With the invented method, the desired silicon areas are obtained on the insulating substrate without intermediate silicon oxide areas and with more rounded edges than if direct etching is carried out with plasma etching or hydrogen etching.

FIGURER Uppfinningen beskives i det följande mer ingäende med hänvisning till bifogade figurer.FIGURES The invention is described in more detail below with reference to the accompanying figures.

Claims

DESCRIPTION OF THE DRAWINGS The invented process for producing integrated circuits starting from a disk which consists of an electrically insulating substrate 10 coated with a thin silicon film is shown in Figures 1a, 1b and 1c. in the invented process, the surface of a silicon film 11 which lies on an insulating substrate 10 as shown in Fig. 1a is oxidized to form a thin layer of silicon oxide 12, after which a layer 13 of silicon nitride is applied to the oxide layer. Finally, a photoresist 14 with photolithographic methods is applied to define the resist areas. Thereafter, the nitride 13 is etched away from the areas not covered by photoresist 14. This etching is interrupted when the underlying oxide layer 12. The photoresist 14 is removed and the wafer is introduced into an oxidizing environment, preferably it is introduced into an oxidation furnace where the silicon film 11 is oxidized. The areas of the silicon film 11a covered by silicon nitride 13 will not be oxidized as shown in Figure 1b while the rest of the silicon film is oxidized. Oxidation can continue down to the underlying substrate 10 but also according to a preferred embodiment of the invented method is interrupted before the oxidation reaches the underlying insulating substrate 10. Thereafter both the remaining nitride 13 and the oxide 12 formed in the various oxidation steps are removed with an etchant which is not attacker silicon. In oxidation according to the preferred embodiment of the invention, the remaining residues of silicon film are then removed from the unprotected areas by etching, preferably plasma etching. The end result is silicon areas 11b with the desired rounded edges of the insulated substrate. PATENT REQUIREMENTS

1. Way to produce integrated circuits on a disk. which at least comprises an insulating substrate (10) coated with a silicon film (11), silicon areas (11b) being etched from a silicon film deposited on the insulating substrate on the insulating substrate by a process, characterized in that - the surface of the silicon film is oxidized so that a thin layer of silicon oxide (12) is formed. a thin layer of silicon nitride, - a photoresist is applied (14) and patterned by photolithography (13) deposited on oxide layered methods to define protected resist areas, - after which the nitride is etched away from unprotected areas with an etchant which interrupts the etching. the underlying oxide layer is retained while the silicon nitride remains in the areas covered by photoresist, - the photoresist is removed before the disk is subjected to an oxidation in which unprotected areas of the silicon film are oxidized while ( oxidized and the tet in the oxidized areas and on this substrate silicon areas were etched out by etching away oxide and nitride and any silicon left in the unprotected areas.

2. A method according to claim 1, characterized in that the unprotected areas of the silicon film are oxidized down to the underlying insulating substrate (10) after which oxide and nitride are etched away, with a non-attacking silicon etchant, to expose the underlying insulating substrate and thereon substrate uncut silicon areas.

3. A method according to claim 1, characterized in that the oxidation of the unprotected areas of the silicon film is interrupted (10), leaving a remaining silicon film on it (10). at a later stage, before the underlying insulating substrate is left out, preferably by plasma etching to expose the underlying insulating substrate, the remaining silicon film is etched, the underlying insulating substrate.