Method for dissolving a silicon dioxide layer

Abstract

This disclosure relates to a method for dissolving a silicon dioxide layer in a structure, including, from the back surface thereof to the front surface thereof, a supporting substrate, the silicon dioxide layer and a semiconductor layer, the dissolution method being implemented in a furnace in which structures are supported on a support, the dissolution method resulting in the diffusion of oxygen atoms included in the silicon dioxide layer through the semiconductor layer and generating volatile products, and the furnace including traps suitable for reacting with the volatile products, so as to reduce the concentration gradient of the volatile products parallel to the front surface of at least one structure.

Claims

1. A method for dissolving a silicon dioxide layer in a semiconductor-on-insulator type structure, the method comprising: providing semiconductor-on-insulator type structures on a support in a furnace, each of the semiconductor-on-insulator type structures comprising a rear face and a front face and including a supporting substrate, a silicon dioxide layer over the supporting substrate, and a semiconductor layer on a side of the silicon dioxide layer opposite the supporting substrate, the support configured for holding the semiconductor-on-insulator type structures with a predetermined distance between the semiconductor-on-insulator type structures, the front face of one of the semiconductor-on-insulator type structures opposite the rear face of another of the semiconductor-on-insulator type structures adjacent to the front face of the one of the semiconductor-on-insulator type structures; providing a non-oxidizing atmosphere within the furnace by providing an inert or reducing gas flow entering the furnace through a gas inlet; heating the semiconductor-on-insulator type structures within the furnace and causing diffusion of oxygen atoms included in the silicon dioxide layers through the semiconductor layers and resulting in generation of oxygen-based volatile products within the furnace; and reacting oxygen included in the inert or reducing gas flow with traps located within the furnace between the gas inlet and a gas outlet of the furnace so as to reduce a concentration of oxygen in the inert or reducing gas flow within the furnace.

2. The method of claim 1, wherein reacting oxygen in the inert or reducing gas flow with traps located within the furnace comprises reacting the oxygen with the traps disposed close to an inert or reducing gas inlet of the furnace.

3. The method of claim 1, wherein reacting oxygen in the inert or reducing gas flow with traps located within the furnace comprises reacting the oxygen with the traps disposed upstream of the inert or reducing gas flow with respect to the semiconductor-on-insulator type structures.

4. The method of claim 1, wherein reacting oxygen in the inert or reducing gas flow with traps located within the furnace comprises reacting the oxygen with trap substrates disposed on the support in place of certain semiconductor-on-insulator structures.

5. The method of claim 1, wherein reacting oxygen in the inert or reducing gas flow with traps located within the furnace comprises reacting the oxygen with traps comprising silicon substrates.

6. The method of claim 1, wherein providing a non-oxidizing atmosphere within the furnace by providing an inert or reducing gas flow comprises providing the inert or reducing gas comprising an oxygen content of less than 10 ppm.

7. The method of claim 1, wherein providing a non-oxidizing atmosphere within the furnace comprises providing at least one of argon and dihydrogen within the furnace.

8. The method of claim 1, wherein heating the semiconductor-on-insulator type structures within the furnace comprises maintaining a temperature of the furnace at a temperature between 900 C. and 1300 C.

9. The method of claim 1, wherein the front faces of the semiconductor-on-insulator type structures comprise a free face of the semiconductor layer.

10. The method of claim 1, wherein reacting oxygen in the inert or reducing gas flow with traps comprises reacting the oxygen with traps comprising titanium, tungsten, aluminium nitride, alumina, or combinations thereof.

11. The method of claim 1, wherein reacting oxygen in the inert or reducing gas flow with traps comprises reacting the oxygen with traps comprising silicon dioxide.

12. A method for dissolving a silicon dioxide layer in a semiconductor-on-insulator type structure, the method comprising: providing semiconductor-on-insulator type structures on a support in a furnace, each of the semiconductor-on-insulator type structures comprising a rear face and a front face and including a supporting substrate, a silicon dioxide layer over the supporting substrate, and a semiconductor layer on a side of the silicon dioxide layer opposite the supporting substrate, the front face of one of the semiconductor-on-insulator type structures opposite the rear face of another of the semiconductor-on-insulator type structures adjacent to the front face of the one of the semiconductor-on-insulator type structures; flowing a non-oxidizing atmosphere within the furnace; heating the semiconductor-on-insulator type structures and causing diffusion of oxygen atoms included in the silicon dioxide layers through the semiconductor layers and resulting in generation of oxygen-based volatile products within the furnace; and reacting oxygen of the oxygen-based volatile products in the non-oxidizing atmosphere with traps within the furnace between a gas inlet and a gas outlet of the furnace so as to reduce a concentration of the oxygen-based volatile products within the furnace.

13. The method of claim 12, wherein flowing a non-oxidizing atmosphere within the furnace comprises flowing an inert or reducing gas comprising an oxygen content of less than 10 ppm within the furnace.

14. The method of claim 12, wherein reacting oxygen in the non-oxidizing atmosphere with traps within the furnace comprises reacting the oxygen with traps on the rear faces of the semiconductor-on-insulator type structures.

15. The method of claim 12, wherein reacting oxygen in the non-oxidizing atmosphere with traps within the furnace comprises reacting the oxygen with traps on the support.

16. The method of claim 15, wherein reacting the oxygen with traps on the support comprises reacting the oxygen with a coating on the support.

17. The method of claim 12, wherein reacting oxygen in the non-oxidizing atmosphere with traps within the furnace comprises reacting the oxygen with trapping layers of trap substrates on the support, each trap substrate comprising a front face opposite the rear face of the semiconductor-on-insulator type structures.

18. The method of claim 12, wherein reacting oxygen in the non-oxidizing atmosphere with traps within the furnace comprises reacting the oxygen with traps comprising a thickness of greater than 100 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages will emerge from the following description of embodiments of a dissolution method according to this disclosure, given by way of non-limitative examples with reference to the accompanying drawings, in which:

(2) FIGS. 1A and 1B are schematic representations of a structure treated by a method for dissolution of a structure of the semiconductor-on-insulator type according to the techniques known from the prior art;

(3) FIG. 2 is a schematic representation of a furnace intended for executing a heat treatment for dissolution of a silicon dioxide layer according to the techniques known from the prior art;

(4) FIGS. 3A and 3B are schematic representations of a structure treated according to the disclosure;

(5) FIG. 4 is a schematic representation of a furnace intended for executing a heat treatment for dissolution of a silicon dioxide layer according to the disclosure;

(6) FIG. 5 is a schematic representation of a structure treated according to one embodiment of the disclosure; and

(7) FIG. 6 is a schematic representation of a trap and substrate according to the disclosure.

DETAILED DESCRIPTION

(8) For the various embodiments and for reasons of simplification of the description, the same references will be used for identical elements or ones fulfilling the same function.

(9) The dissolution method illustrated in FIGS. 3A and 3B is a method for dissolving a silicon dioxide layer 90 in a structure 50 of the semiconductor-on-insulator type.

(10) The structure 50 of the semiconductor-on-insulator type comprises, from its rear face 60 to its front face 70, a supporting substrate 80, the silicon dioxide layer 90 and a semiconductor layer 100.

(11) The dissolution method is implemented in a furnace 11, illustrated in FIG. 4, in which a plurality of structures 50 is held on a support 40, the structures 50 being parallel to one another. The front face 70 of a structure 50 is opposite the rear face 60 of the structure 50 adjacent to the front face 70. The support 40 is suitable for holding the structures 50 with a predetermined distance between each structure 50. The predetermined distance between each structure 50 may be less than 15 nm, preferably less than 10 nm. The atmosphere of the furnace 11 is a non-oxidizing atmosphere.

(12) The dissolution method causes the diffusion of oxygen atoms included in the silicon dioxide layer 90 through the semiconductor layer 100. Volatile products resulting from the reaction of the oxygen atoms with the semiconductor layer 100 are generated. The volatile products comprise semiconductor monoxide (ScO).

(13) Traps 110 (see FIG. 5), suitable for reacting with the volatile products, are disposed in the furnace 11 so as to reduce the concentration gradient of the volatile products parallel to the front face 70 of at least one structure 50. The oxygen content of the non-oxidizing atmosphere is preferably less than 10 ppm (parts per million). The non-oxidizing atmosphere of the furnace 11 is provided by an inert or reducing gas flow. The inert or reducing gas flow can enter the furnace 11 through an inlet 20, and emerges therefrom through an outlet 30.

(14) The atmosphere of the furnace 11 may comprise at least one species chosen from one of the following species: argon and dihydrogen.

(15) During the dissolution process, the temperature of the furnace 11 can be maintained at a temperature between 900 C. and 1300 C., for example 1150 C.

(16) The conditions of implementation of this dissolution method, in particular, its duration, can be adapted in order to partially dissolve the silicon dioxide layer 90.

(17) The supporting substrate 80 may comprise at least one of the following materials: silicon, germanium, alumina, and quartz.

(18) The semiconductor layer 100 may comprise at least one of the following materials: silicon, germanium, and silicon germanium alloy.

(19) According to a particularly advantageous embodiment, and as illustrated in FIG. 5, the traps 110 are disposed on the rear face 60 of the structures 50. Advantageously, a coating comprising the traps 110 may be formed on the rear face 60 of the structures 50. Thus, the traps 110 are as close as possible to the front face 70 of each structure 50. Such proximity of the traps 110 and the front face 70 of the structures 50 affords better efficacy of the trapping of the volatile products. Moreover, the front face 70 of each structure 50 is exposed uniformly to the layer comprising the traps 110. The concentration of the volatile products on the front face 70 of each structure 50 is, thus, more uniform and, therefore, the parallel gradient is reduced. Furthermore, the arrangement of the traps 110 in the immediate vicinity of the front face 70 of each structure 50 limits the quantity of volatile products entrained by the gas flow. Consequently, the variations in concentration of volatile products in the furnace 11 are reduced. Thus, the variabilities in dissolution from one structure 50 to another are reduced. Consequently, the silicon dioxide layer 90 is dissolved substantially in the same proportions from one structure 50 to another.

(20) Alternatively, or in a complementary manner, and as illustrated in FIG. 6, the traps 110 may be included in trapping layers on the front face 70 of the substrates referred to as trap substrates 120. The trap substrates 120 are disposed on the support 40 in place of certain structures 50. Consequently, the variations in concentration of volatile products in the furnace 11 are reduced. Thus, the variabilities of dissolution from one structure 50 to another are reduced.

(21) Particularly advantageously, the traps 110 disposed on the rear face 60 of the structures 50 or on the front face 70 of the trapping layers of the trap substrates 120 may comprise silicon dioxide. On the other hand, the native oxide naturally present on the rear face of a structure of the silicon-on-insulator, through its small thickness and its chemical composition, evaporates during such treatment and cannot fulfill the role of a trap.

(22) The traps 110 comprising silicon dioxide are advantageously formed by thin film deposition techniques. Among film deposition techniques, low-pressure vapor deposition and plasma-activated vapor deposition techniques known to persons skilled in the art will be cited.

(23) Alternatively, the formation of a silicon dioxide film on the rear face 60 of a supporting substrate 80 made from silicon or on the front face of a trap substrate 120 can be advantageously executed by thermal oxidation.

(24) The film formed on the rear face 60 of a structure 50 or on the front face of a trap substrate 120 may have a thickness greater than 30 nm, preferentially greater than 50 nm.

(25) Alternatively, the traps 110 may comprise at least one of the following materials: titanium, tungsten, aluminium nitride, and alumina.

(26) These materials can absorb the semiconductor monoxide formed during the process of dissolution of the silicon dioxide layer 90.

(27) These materials may be formed in the form of films by film deposition techniques known to persons skilled in the art. For example, evaporation techniques are particularly well suited to the formation of films of titanium and tungsten. Aluminium nitride and alumina are advantageously formed by chemical vapor deposition or atomic layer deposition techniques.

(28) Alternatively, or in a complementary fashion, traps 110 may be included in a coating covering all or part of the support 40. Thus, the traps 110 are close to the front face 70 of the structures 50. Consequently, the volatile products are effectively trapped. Particularly advantageously, the traps 110 comprise silicon dioxide. The traps 110 comprising silicon dioxide are advantageously formed by vapor deposition techniques or by thermal oxidation. The coating formed on the support 40 may have a thickness greater than 50 nm, or even greater than 500 nm.

(29) Alternatively, the traps 110 may comprise at least one of the following materials: titanium, tungsten, aluminium nitride, and alumina.

(30) These materials may be formed in the form of a film by film deposition techniques known to persons skilled in the art, for example, chemical vapor deposition or atomic layer deposition techniques.

(31) In a complementary fashion, the traps 110 are included in a coating wholly or partly covering the internal wall of the furnace 11. Particularly advantageously, the traps 110 comprise silicon dioxide.

(32) Alternatively, the traps 110 may comprise at least one of the following materials: titanium, tungsten, aluminium nitride, and alumina.

(33) Particularly advantageously, the semiconductor layer 100 has a thickness greater than 100 nm, preferentially greater than 200 nm, even more preferentially greater than 300 nm. For such thicknesses of semiconductor layer 100, the dissolution speed is less than 0.5 /minute.

(34) Thus, the volatile products formed during the dissolution process have the time to diffuse toward the traps 110. Consequently, the variations in concentration of volatile products are reduced. Advantageously, the layer of silicon dioxide 90 has a thickness of less than 50 nm, preferentially less than 25 nm, even more preferentially less than 15 nm.

(35) Advantageously, trap substrates 120 suitable for reacting with the dioxygen included in the atmosphere of the furnace 11 may also be disposed in the furnace 11. The trap substrates 120 intended to react with dioxygen may be silicon substrates disposed on the support 40 in place of certain structures 50. Preferably, the silicon substrates intended to react with the dioxygen included in the atmosphere of the furnace are disposed close to the inert or reducing gas inlet.

(36) Even more preferentially, the silicon substrates are disposed upstream of the inert or reducing gas flow with respect to the structures 50. Thus, the oxygen included in the inert or reducing gas flow reacts with the traps 120 before reaching a structure 50.

(37) The method for dissolving a layer of silicon dioxide 90 according to the disclosure makes it possible to make the composition of the atmosphere of the furnace 11 homogeneous. The accumulation of volatile products is reduced.

(38) Consequently, it is possible to limit the degradation in the uniformity and thickness of the silicon dioxide layer 9 and of the semiconductor layer 10 found in the prior art. Moreover, the method according to the disclosure allows a more uniform dissolution from one structure 50 to another, compared with the method of the prior art.