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, then the first initial doping level is 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 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 the first conductivity type is p and the second conductivity type is n; 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 increasing, stepwise or continuously, a mass flow of a third precursor for a dopant of the second conductivity type, a doping of the III-V layer over a junction region layer with a growth height of at least 10 μm 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 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 1.Math.10.sup.14 cm.sup.−3.

3. 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.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 growth height of the junction region is at least 30 μm or at least 60 μm.

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

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

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

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

9. 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.

10. The vapor phase epitaxy method according to claim 1, wherein said setting the first initial doping level of the first conductivity type via the ratio of the first mass flow of the first precursor to the second mass flow of the second precursor in the epitaxial gas flow is conducted with the addition of a further precursor for a dopant of the first conductivity type to the epitaxial gas flow.

11. 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 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 the first conductivity type is p and the second conductivity type is n; 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 with the addition of a further precursor for a dopant of the first conductivity type to the epitaxial gas flow; and increasing, stepwise or continuously, a mass flow of a third precursor for a dopant of the second conductivity type and by stepwise or continuously changing 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 μm is changed stepwise or continuously 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 the profile of the mass flow of the third precursor versus the growth height.

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 at least starting at a first growth height x1, 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 wafer or a substrate result in different dopings and that such fluctuations have a particularly strong effect, especially at low dopings.

(12) 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.

(13) A first 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.

(14) First or at a first growth height x.sub.1, a first initial doping level D.sub.A1 of the first conductivity type LT1 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.

(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 Ü, until a target p-doping level D.sub.Z is reached at a second growth height x.sub.2. 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.

(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. Alternatively (not shown), the doping is increased again abruptly to a second target doping level following the ramp.

(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.Z takes place in several steps, so that a step-shaped course of the doping over the junction region layer Ü is established.

(19) The diagram in FIG. 5 shows a further embodiment of the vapor phase epitaxy method of the invention on the basis of a profile of the mass flow M.sub.W of the further precursor for a p-type dopant and the mass flow M.sub.Dot of the third precursor for the n-type dopant.

(20) Based on an initial mass flow level M.sub.wa, to achieve the initial p-doping level D.sub.A1, the mass flow M.sub.w of the further precursor for a p-type dopant is reduced stepwise at the layer thickness x.sub.1 from the growth of the junction region layer Ü until at the layer thickness x.sub.2 the mass flow is reduced to zero or close to zero. This allows the doping profile corresponding to FIG. 4 to be generated.

(21) Alternatively, the mass flow M.sub.W of the further precursor for a p-type dopant is reduced continuously at the layer thickness x.sub.1 starting from the growth of the junction region layer Ü until at the layer thickness x.sub.2 the mass flow is reduced to zero or close to zero. This allows the ramp-shaped doping profiles corresponding to FIG. 3 to be generated.

(22) It is understood that the doping profile can also be adjusted continuously, i.e., not in the form of a ramp, by changing the mass flow of the further precursor accordingly.

(23) In a different approach, proceeding from an initial mass flow level M.sub.dotN at zero or close to zero, in order to achieve the initial p-doping level D.sub.A1, the mass flow M.sub.dot of the third precursor for an n-type dopant is increased stepwise at the layer thickness x.sub.1 starting from the growth of the junction region layer Ü until at the layer thickness x.sub.2 the mass flow reaches the target level M.sub.dotZ. This allows the doping profile corresponding to FIG. 4 to be generated.

(24) Alternatively, the mass flow M.sub.dot of the third precursor for an n-type dopant is increased continuously at the layer thickness x.sub.1 starting from the growth of the junction region layer Ü until at the layer thickness x.sub.2 the mass flow reaches the target level M.sub.dotZ. This allows the ramp-shaped doping profiles corresponding to FIG. 3 to be generated.

(25) It is understood that the doping profile can also be adjusted continuously, i.e., not in the form of a ramp, by changing the mass flow of the third precursor accordingly.

(26) It is understood that both the mass flow of the further precursor and the mass flow of the third precursor can be changed at the same time.

(27) 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.