VAPOR PHASE EPITAXY METHOD

Abstract

A vapor phase epitaxy method of growing a III-V layer with a doping profile that changes from n-doping to p-doping on a surface of a substrate or a preceding layer in a reaction chamber from the vapor phase of an epitaxial gas flow, comprising at least one carrier gas, a first precursor for a first element from main group III and at least one second precursor for a first element from main group V, and fed into the reaction chamber, wherein, when a first growth level is reached, an initial n-doping level is set by means of a ratio, leading to a p-doping, 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 the addition of a third mass flow of a third precursor for an n-type dopant to the epitaxial gas flow, subsequently.

Claims

1. A vapor phase epitaxy method comprising: growing a III-V layer with a doping profile that changes from n-doping to p-doping 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 a first element from main group V; setting, when a first growth height is reached, an initial n-doping level in the epitaxial gas flow via a ratio, leading to a p-doping, of a first mass flow of the first precursor to a second mass flow of the second precursor and with the addition of a third mass flow of a third precursor for an n-type dopant to the epitaxial gas flow; changing the third mass flow and/or the ratio between the first and second mass flow stepwise or continuously over a junction region layer with a growth height of at least 10 μm until a target p-doping level is reached.

2. The vapor phase epitaxy method according to claim 1, wherein the initial n-doping level is at most 1.Math.10.sup.16 cm.sup.−3 or at most 1.Math.10.sup.15 cm.sup.−3 or at most 5.Math.10.sup.14 cm.sup.−3.

3. The vapor phase epitaxy method according to claim 1, wherein the target p-doping level is at most 5.Math.10.sup.15 cm.sup.−3 or at most 1.Math.10.sup.15 cm.sup.−3.

4. The vapor phase epitaxy method according to claim 1, wherein, after the target p-doping level has been reached, growth is continued further over a growth height of at least 10 μm with the settings for the target p-doping level.

5. The vapor phase epitaxy method according to claim 1, wherein after the target p-doping level has been reached, a second target p-doping level is set by changing the third mass flow and/or by changing the ratio between the first and second mass flow, wherein the second target p-doping level is greater than the target p-doping level.

6. The vapor phase epitaxy method according to claim 1, wherein the growth height of the junction region layer is at least 30 μm or at least 60 μm.

7. 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 μm.

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

9. The vapor phase epitaxy method according to claim 1, wherein, after the initial n-doping level has been reached and before the junction region layer has grown, the initial n-doping level is abruptly reduced to a second initial n-doping level or set abruptly to an initial p-doping level of at most 1.Math.10.sup.15 cm.sup.−3 or at most 5.Math.10.sup.14 cm.sup.−3 by reducing the third mass flow in the epitaxial gas flow.

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

11. 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.

12. The vapor phase epitaxy method according to claim 1, wherein, after the target doping level has been reached over a growth height, a second target p-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, and wherein the second target p-doping level is greater than the target n-doping level.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] 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:

[0050] FIG. 1 shows a cross section of substrates arranged in a reaction chamber;

[0051] 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;

[0052] 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;

[0053] 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;

[0054] FIG. 5 shows the profile of the mass flow of the third precursor versus the growth height; and

[0055] FIG. 6 shows a dopant concentration profile over a grown III-V layer according to a third embodiment of the vapor phase epitaxy method according to the invention.

DETAILED DESCRIPTION

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 shown 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.

[0060] 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, in that the doping changes undesirably between p and n.

[0061] One advantage of this embodiment is that the vapor phase epitaxy method can be carried out preferably using a low flow of the second precursor for group V. If arsine or TGMa is used in particular for the second precursor, the production costs can be significantly reduced by means of a low flow of the second precursor and the environmental friendliness of the production process can be greatly increased.

[0062] A first embodiment of the vapor phase epitaxy method of the invention is illustrated in the diagram in FIG. 3 using a profile of the doping D from n through zero to p versus growth height x.

[0063] First or at a first growth height x.sub.1, an initial p-doping level D.sub.A1 is set by means of the ratio, leading to a p-doping, 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 (left part of the profile in FIG. 2), and with the addition of a third mass flow of a third precursor for an n-type dopant, e.g., silane, to the epitaxial gas flow F.

[0064] The third mass flow of the third precursor is then continuously reduced during the growth of a junction region layer ÜB until a target p-doping level D.sub.Z is reached at the layer thickness x.sub.2. It is understood that the junction region layer ÜB extends from the level x.sub.1 to the level x.sub.2.

[0065] The epitaxial gas flow 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.

[0066] Alternatively and shown by dashed lines in FIG. 3, the third mass flow is abruptly reduced starting from the initial n-doping level D.sub.A1 to an initial p-doping level D.sub.A2* of at most 1.Math.10.sup.15 cm.sup.−3 or at most 5.Math.10.sup.14 cm.sup.−3, before the doping is changed in the form a ramp up to the target p-doping level D.sub.Z.

[0067] After the target p-doping level D.sub.Z is reached, the doping is again increased abruptly to a second target p-doping level D.sub.Z2 by changing the third mass flow M.sub.Dot and/or the ratio between the first and second mass flow and then a layer with constant p-doping is grown without further changes to the epitaxial gas flow.

[0068] 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.

[0069] Starting from the initial n-doping level D.sub.A1, the doping is abruptly reduced to a second initial n-doping level D.sub.A2 by reducing the third mass flow in the epitaxial gas flow F before the doping over the junction region layer ÜB is changed continuously or stepwise until the target p-doping level D.sub.Z is reached.

[0070] In the diagram in FIG. 5, a further embodiment of the vapor phase epitaxy method of the invention is illustrated on the basis of a profile of the third mass flow M.sub.Dot of the third precursor for the n-type dopant.

[0071] Starting from an initial mass flow level M.sub.A1 to achieve the initial n-doping level D.sub.A1, the third mass flow M.sub.Dot is abruptly reduced, so that a second initial mass flow level M.sub.A2 and thereby also an abruptly reduced doping are set.

[0072] Then the third mass flow M.sub.Dot is continuously reduced to zero, as a result of which the ramp-shaped change in the doping up to the target p-doping level D.sub.Z results.

[0073] In the diagram of FIG. 6, 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 diagrams in FIGS. 3 and 4 will be explained below.

[0074] The change in the doping from the initial n-doping level D.sub.A1 to the target p-doping level D.sub.Z takes place in multiple steps, so that a step-shaped profile of the doping over the junction region layer ÜB is established.

[0075] 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.