VAPOR PHASE EPITAXY METHOD

Abstract

A vapor phase epitaxy method of growing a III-V layer with a doping profile that changes from a p-doping to an n-doping on a surface of a substrate or a preceding layer from the vapor phase from an epitaxial gas flow, at least one first precursor for an element of main group III, and at least one second precursor for an element of main group V. When a first growth height is reached, a first initial doping level 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, and subsequently, by stepwise or continuously changing the ratio of the first mass flow to the second mass flow and by stepwise or continuously increasing a mass flow of a third precursor for an n-type dopant in the epitaxial gas flow.

Claims

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

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

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

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

6. The vapor phase epitaxy method according to claim 1, wherein the doping over the junction region layer is changed over every 5 μm of growth height by at most 1.Math.10.sup.13 cm.sup.−3.

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 the first initial doping level is set starting from a second initial p-doping level by an abrupt change in the ratio of the first mass flow to the second mass flow.

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

12. The vapor phase epitaxy method according to claim 1, wherein the doping of III-V layer in a layer region, preceding the first growth height is reduced by continuously and/or stepwise changing the ratio of the first mass flow to the second mass flow from a starting p-doping level of at least 5.Math.10.sup.16 cm.sup.−3 or at least 1.Math.10.sup.17 cm.sup.−3 to the first initial doping level or to a second initial doping level.

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

14. The vapor phase epitaxy method according to claim 1, wherein after the target n-doping level 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 target n-doping level.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] 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:

[0054] FIG. 1 shows a cross section of substrates arranged in a reaction chamber;

[0055] 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;

[0056] 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; and

[0057] 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.

DETAILED DESCRIPTION

[0058] 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.

[0059] 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 at least starting at a first growth height x1, a third precursor for an n-type dopant, e.g., silane.

[0060] The gas inlet member O has a plurality of lines ending in reactor chamber K, through which one or more components of epitaxial gas flow F are fed into reactor chamber K.

[0061] In the illustration of FIG. 2, the dependence of the doping on a quantity ratio of the elements of main group 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, therefore, the quantity ratio in the gas flow.

[0062] 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 such fluctuations have a particularly strong effect, especially at low dopings.

[0063] One advantage of this embodiment is that the vapor phase epitaxy method can be carried out 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.

[0064] 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.

[0065] First or at a first growth height x1, a first p-doped initial doping level DA1 is set solely 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, i.e., in particular without the addition of a further mass flow of a further precursor for a p-type dopant, e.g., carbon tetrabromide, to the epitaxial gas flow F. A third mass flow of the third precursor for the n-type dopant is also zero.

[0066] Subsequently, the third mass flow of the third precursor, e.g., silane, is added or continuously turned up slowly and continuously over a junction region layer and at the same time the ratio of the first mass flow to the second mass flow is changed until at a layer thickness of x.sub.2 a target n-doping level DZ is reached and a ramp-like doping profile has formed between the first initial doping level and the target n-doping level.

[0067] It is understood that the junction region layer Ü extends from the first growth height x.sub.1 to the second growth height x.sub.2.

[0068] 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 is constant.

[0069] Alternatively, a low n-doped level is set as the first initial doping level DA1′. The corresponding doping profile is shown as a dash-dotted line.

[0070] According to an refinement, the first initial doping level DA1 is set by an abrupt change in the ratio of the first mass flow to the second mass flow, so that the doping of the III-V layer at or before the first growth height x.sub.1 is reduced abruptly from a second initial p-doping level DA2 to the first initial doping level DA1 (shown as a dotted line).

[0071] Alternatively, the doping of the III-V layer is reduced from a starting doping level DS to the first growth height continuously to the first initial doping level DA1 (shown as a dashed line).

[0072] 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.

[0073] The change in the doping from the initial n-doping level DA1 to the target p-doping level DZ takes place in multiple steps, so that a step-like profile of the doping over the junction region layer Ü is established.

[0074] 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.