Vapor phase epitaxy method

Abstract

A vapor phase epitaxy method of growing a III-V layer with a doping that changes from a first conductivity type to a second conductivity type on a surface of a substrate or a preceding layer in a reaction chamber from the vapor phase from an epitaxial gas flow comprising a carrier gas, at least one first precursor for an element from main group III, and at least one second precursor for an element from main group V, wherein when a first growth height is reached, a first initial doping level of the first conductivity type is set by means of a ratio of a first mass flow of the first precursor to a second mass flow of the second precursor in the epitaxial gas flow, the first initial doping level is then reduced to a second initial doping level of the first or low second conductivity type.

Claims

1. A vapor phase epitaxy method comprising: growing a III-V layer with a doping that changes from a first conductivity type to a second conductivity type in a reaction chamber from the vapor phase from an epitaxial gas flow comprising a carrier gas, at least one first precursor for an element from main group III, and at least one second precursor for an element from main group V, wherein the first conductivity type is p and the second conductivity type is n; during said growing the III-V layer, setting, when a first growth height is reached, a first initial doping level of the first conductivity type via a ratio of a first mass flow of the first precursor to a second mass flow of the second precursor in the epitaxial gas flow and with or without the addition of a further precursor for a dopant of the first conductivity type to the epitaxial gas flow; after said growth height is reached, reducing the first initial doping level to a second initial doping level of the first conductivity type or set to a second initial doping level of the second conductivity type of at most 1.Math.10.sup.15 cm.sup.3 by adding a third mass flow of a third precursor for a dopant of the second conductivity type to the epitaxial gas flow and/or by changing the ratio of the first mass flow to the second mass flow; and after said setting the second initial doping level of the first conductivity type or the second initial doping level of the second conductivity type, increasing, stepwise or continuously, the mass flow of the third precursor and/or by changing, stepwise or continuously, the ratio between the first mass flow and the second mass flow, a doping of the III-V layer over a junction region layer with a growth height of at least 10 m is changed stepwise or continuously until a target doping level of the second conductivity type is reached.

2. The vapor phase epitaxy method according to claim 1, wherein the first initial doping level of the first conductivity type is at most 5.Math.10.sup.16 cm.sup.3.

3. The vapor phase epitaxy method according to claim 1, wherein the second initial doping level of the first conductivity type is at most 5.Math.10.sup.16 cm.sup.3.

4. The vapor phase epitaxy method according to claim 1, wherein the target doping level of the second conductivity type is at most 1.Math.10.sup.16 cm.sup.3.

5. The vapor phase epitaxy method according to claim 1, wherein a growth height of the junction region layer is at least 30 m.

6. The vapor phase epitaxy method according to claim 1, wherein the doping over the junction region layer is changed in steps of at most 1.Math.10.sup.13 cm.sup.3 over 5 m.

7. The vapor phase epitaxy method according to claim 1, wherein the doping over the junction region layer is changed in at least four steps.

8. The vapor phase epitaxy method according to claim 1, wherein the element of main group III is gallium and the element of main group V is arsenic.

9. The vapor phase epitaxy method according to claim 1, wherein the third precursor is monosilane.

10. The vapor phase epitaxy method according to claim 1, wherein, after the target doping level of the second conductivity type has been reached over a growth height, a second target n-doping level is set by abruptly changing the third mass flow and/or by abruptly changing the ratio of the first mass flow to the second mass flow, wherein the second target n-doping level is greater than the doping level of the second conductivity type.

11. The vapor phase epitaxy method according to claim 1, wherein the first initial doping level of the first conductivity type is at most 1.Math.10.sup.16 cm.sup.3.

12. The vapor phase epitaxy method according to claim 1, wherein the second initial doping level of the first conductivity type is at most 1.Math.10.sup.15 cm.sup.3.

13. The vapor phase epitaxy method according to claim 1, wherein the second initial doping level of the first conductivity type is at most 5.Math.10.sup.4 cm.sup.3.

14. The vapor phase epitaxy method according to claim 1, wherein the second initial doping level of the first conductivity type is at most 1.Math.10.sup.14 cm.sup.3.

15. The vapor phase epitaxy method according to claim 1, wherein the target doping level of the second conductivity type is at most 5.Math.10.sup.14 cm.sup.3.

16. The vapor phase epitaxy method according to claim 1, wherein the target doping level of the second conductivity type is at most 1.Math.10.sup.14 cm.sup.3.

17. The vapor phase epitaxy method according to claim 1, wherein a growth height of the junction region is at least 60 m.

18. A vapor phase epitaxy method, comprising: growing a III-V layer with a doping that changes from a first conductivity type to a second conductivity type in a reaction chamber from the vapor phase from an epitaxial gas flow comprising a carrier gas, at least one first precursor for an element from main group III, and at least one second precursor for an element from main group V, wherein the first conductivity type is p and the second conductivity type is n; then setting, when a first growth height is reached, a first initial doping level of the first conductivity type via a ratio of a first mass flow of the first precursor to a second mass flow of the second precursor in the epitaxial gas flow and with or without the addition of a further precursor for a dopant of the first conductivity type to the epitaxial gas flow; then reducing the first initial doping level to a second initial doping level of the first conductivity type or set to a second initial doping level of the second conductivity type of at most 1.Math.10.sup.15 cm.sup.3 by adding a third mass flow of a third precursor for a dopant of the second conductivity type to the epitaxial gas flow and/or by changing the ratio of the first mass flow to the second mass flow; then increasing, stepwise or continuously, the mass flow of the third precursor and/or by changing, stepwise or continuously, the ratio between the first mass flow and the second mass flow, a doping of the III-V layer over a junction region layer with a growth height of at least 10 m is changed stepwise or continuously until a target doping level of the second conductivity type is reached.

19. A vapor phase epitaxy method comprising: growing a III-V layer with a doping that changes from a first conductivity type to a second conductivity type in a reaction chamber from the vapor phase from an epitaxial gas flow comprising a carrier gas, a first precursor for an element from main group III, and a second precursor for an element from main group V, wherein the first conductivity type is p and the second conductivity type is n; during said growing the III-V layer, setting, when a first growth height is reached, a first initial doping level of the first conductivity type via a ratio of a first mass flow of the first precursor to a second mass flow of the second precursor in the epitaxial gas flow; after said growth height is reached, reducing the first initial doping level to a second initial doping level of the first conductivity type by changing the ratio of the first mass flow to the second mass flow; and increasing a mass flow of a third precursor to a level at which the doping level changes.

20. The method according to claim 19, wherein the first initial doping level is reduced to the second initial doping level of the first conductivity type by changing the ratio of the first mass flow to the second mass flow and by adding the third mass flow of the third precursor for a dopant of the second conductivity type to the epitaxial gas flow.

21. The method according to claim 19, further comprising, by changing the ratio between the first mass flow and the second mass flow, changing a doping of the III-V layer over a junction region layer with a growth height of at least 10 m until a target doping level of the second conductivity type is reached.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 shows a cross section of substrates arranged in a reaction chamber;

(3) FIG. 2 shows a relationship between a doping and a ratio of elements of main group V to elements of main group III during epitaxial growth;

(4) FIG. 3 shows a dopant concentration profile over a grown III-V layer according to a first embodiment of the vapor phase epitaxy method according to the invention;

(5) FIG. 4 shows a dopant concentration profile over a grown III-V layer according to a second embodiment of the vapor phase epitaxy method according to the invention; and

(6) FIG. 5 shows a profile of the mass flow of the third precursor over a grown III-V layer of the vapor phase epitaxy method.

DETAILED DESCRIPTION

(7) The illustration of FIG. 1 schematically shows a cross section of a reactor chamber K of a vapor phase epitaxy system. Substrates S are arranged on a bottom of reactor chamber K. In addition, reactor chamber K has a gas inlet member O through which epitaxial gas flow F is introduced into reactor chamber K.

(8) The epitaxial gas flow F has a carrier gas, at least one first organometallic precursor for an element of main group III, e.g., TMGa, a second precursor for an element of main group V, e.g., arsine, and a third precursor for an n-type dopant, e.g., silane.

(9) The gas inlet member O has a plurality of lines ending in reactor chamber K, through which one component or multiple components of epitaxial gas flow F are fed into reactor chamber K.

(10) In the illustration of FIG. 2, the dependence of the doping on a quantity ratio of the elements of main groups V and III is plotted in a diagram. It becomes clear in particular that not only the level of doping but also the type of doping, therefore, n or p, can be set by the V/III ratio, therefore, the quantity ratio in the gas flow.

(11) On the other hand, it becomes clear that fluctuations in the V/III ratio across a semiconductor wafer or a substrate result in different dopings and that such fluctuations have a particularly strong effect, especially at low dopings.

(12) An exemplary embodiment of the vapor phase epitaxy method of the invention is illustrated in the diagram in FIG. 3 using a profile of doping D versus growth height x.

(13) First or at a first growth height x.sub.1, a first initial doping level D.sub.A1 of the first conductivity type is set by means of the ratio of a first mass flow of the first precursor, e.g., TMGa, to a second mass flow of the second precursor, e.g., arsine, in the epitaxial gas flow F, and with or without the addition of a further mass flow of a further precursor for a dopant of the first conductivity type, e.g., carbon tetrabromide or dimethyl zinc, to the epitaxial gas flow F.

(14) A third mass flow of a third precursor for a dopant of the second conductivity type, e.g., silane, is then added and/or the ratio between the first and second mass flow is changed abruptly in order to set a second initial doping level D.sub.A2 of the first conductivity type or (shown by dashed lines) a second initial doping level D.sub.A1 of the second conductivity type.

(15) The third mass flow of the third precursor and/or the ratio between the first and second mass flow are then continuously changed over a junction region layer , until a target p-doping level D.sub.2 is reached at a second growth height x.sub.2. It is understood that the junction region layer extends from the first growth height x.sub.1 to the second growth height x.sub.2.

(16) The epitaxial gas flow F is then not changed further over a further region of the growth height x, so that the doping of the subsequent III-V layer remains constant.

(17) In the diagram of FIG. 4, a further embodiment of the vapor phase epitaxy method of the invention is illustrated on the basis of the doping profile D, wherein only the differences from the diagram in FIG. 3 will be explained below.

(18) The change in the doping from the initial n-doping level D.sub.A1 to the target p-doping level D.sub.2 takes place in multiple steps, so that a step-shaped profile of the doping over the junction region layer is established.

(19) A further embodiment of the vapor phase epitaxy method of the invention based on the course of the mass flow MD over the thickness of the junction region layer from the first growth height x.sub.1 to the second growth height x.sub.2 is illustrated in the diagram in FIG. 5, wherein only the differences from the diagram in FIG. 4 will be explained below.

(20) The change in the mass flow MD occurs from an initial level MA which is at zero or close to zero to a target level MZ of the mass flow MZ of the third precursor. The increase in the mass flow can be carried out continuously or at least steadily; i.e., there is a straight or at least steady increase in the doping over the thickness of the junction region layer . Only a linear increase in the mass flow is shown in the present case.

(21) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.