NUCLEATION LAYER DEPOSITION METHOD

Abstract

A nucleation layer comprised of group III and V elements is directly deposited onto the surface of a substrate made of a group IV element. Together with a first gaseous starting material containing a group III element, a second gaseous starting material containing a group V element is introduced at a process temperature of greater than 500° C. into a process chamber containing the substrate. It is essential that at least at the start of the deposition process of the nucleation layer, a third gaseous starting material containing a group IV element is fed into the process chamber, together with the first and second gaseous starting material. The third gaseous starting material develops an n-doping effect in the deposited III-V crystal, which causes a decrease in damping at a dopant concentration of less than 1×10.sup.18 cm.sup.−3.

Claims

1. A method for depositing a nucleation layer (3) comprised of group III and V elements directly onto a surface (2) of a substrate (1) made of a group IV element, the method comprising: introducing a first gaseous starting material containing a group III element together with a second gaseous starting material containing a group V element into a process chamber (8) containing the substrate (1) at a process temperature greater than 500° C.; at least at a start of the deposition of the nucleation layer (3), feeding a third gaseous starting material containing a group IV element into the process chamber (8) together with the first and second gaseous starting materials; and depositing a buffer layer (4) on the nucleation layer (3) and depositing an active layer (6) on the buffer layer (4) in such manner that a two-dimensional electron gas develops on a boundary surface (5) between the active layer (6) and the buffer layer (4), wherein a partial pressure and/or mass flow of the third gaseous starting material in the process chamber (8) is chosen so as to result in a dopant concentration between 1×10.sup.17 and 1×10.sup.18 cm.sup.−3, and a decrease in high-frequency damping.

2. The method of claim 1, wherein the process temperature is in a range between 800° C. and 1,200° C.

3. A method for depositing a nucleation layer (3) comprised of group III and V elements directly onto a surface (2) of a substrate (1) made of a group IV element, the method comprising: introducing a first gaseous starting material containing a group III element together with a second gaseous starting material containing a group V element into a process chamber (8) containing the substrate (1) at a process temperature greater than 500° C.; and at least at a start of the deposition of the nucleation layer (3), a third gaseous starting material containing a group IV element is fed into the process chamber (8) together with the first and second gaseous starting materials, wherein a partial pressure and/or mass flow of the third gaseous starting material in the process chamber (8) is chosen so as to result in a dopant concentration of not more than 1×10.sup.18 cm.sup.−3, and wherein the nucleation layer (3) is deposited under total pressures between 30 and 300 mbar.

4. The method of claim 1, wherein a molar ratio of the second gaseous starting material to the first gaseous starting material is in a range between 10 and 5,000.

5. The method of claim 1, wherein the feeding of the third gaseous starting material causes an n-dopant concentration of the nucleation layer (3) to be in a range from 1×10.sup.17 to 1×10.sup.18 cm.sup.−3.

6. The method of claim 1, wherein the substrate (1) is made of silicon or germanium, and/or the third gaseous starting material is Si.sub.nH.sub.2n°2, Ge.sub.nH.sub.2n+2, or another gaseous starting material that contains silicon or germanium.

7. The method of claim 1, wherein the group III element is Al and/or the first gaseous starting material is TMAl.

8. The method of claim 1, wherein the group V element is nitrogen, and/or the second gaseous starting material is NH.sub.3.

9. The method of claim 3, further comprising depositing a buffer layer (4) on the nucleation layer (3), and depositing an active layer (6) on the buffer layer (4), in such manner that a two-dimensional electron gas develops on a boundary surface (5) between the active layer (6) and the buffer layer (4).

10. A layer sequence produced by the method of claim 1, wherein the nucleation layer (3) is doped with the group IV element at least in a region of the nucleation layer (3) directly adjacent to the surface (2) of the substrate (1).

11. The layer sequence of claim 10, wherein the buffer layer (4) is disposed over the nucleation layer (3), the active layer (6) is disposed over the buffer layer (4), and the two-dimensional electron gas is located at the boundary surface (5) between the buffer layer (4) and the active layer (6).

12. (canceled)

13. The method of claim 2, wherein a molar ratio of the second gaseous starting material to the first gaseous starting material is in a range between 10 and 5,000.

14. The method of claim 3, wherein the substrate (1) is made of silicon or germanium, and/or the third gaseous starting material is Si.sub.nH.sub.2n+2, Ge.sub.nH.sub.2n+2, or another gaseous starting material that contains silicon or germanium.

15. The method of claim 3, wherein the group III element is Al and/or the first gaseous starting material is TMAl.

16. The method of claim 3, wherein the group V element is nitrogen, and/or the second gaseous starting material is NH.sub.3.

17. The method of claim 3, wherein the partial pressure and/or the mass flow of the third gaseous starting material in the process chamber (8) is chosen so as to result in a decrease in high-frequency damping.

18. A layer sequence produced by the method of claim 3, wherein the nucleation layer (3) is doped with the group IV element at least in a region of the nucleation layer (3) directly adjacent to the surface (2) of the substrate (1).

19. The layer sequence of claim 18, wherein a buffer layer (4) is disposed over the nucleation layer (3), an active layer (6) is disposed over the buffer layer (4), and a two-dimensional electron gas is located at a boundary surface (5) between the buffer layer (4) and the active layer (6).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In the following text, an exemplary embodiment of the invention will be explained with reference to accompanying drawings. In the drawings:

[0018] FIG. 1 is a schematic representation of the layer structure of a high electron mobility transistor,

[0019] FIG. 2 is a schematic representation of a CVD reactor for depositing the layer sequence represented in FIG. 1, and

[0020] FIG. 3 shows the S.sub.21 damping parameter of a coplanar line on an AlN/Si structure with various dopants in the AlN layer.

DETAILED DESCRIPTION

[0021] FIG. 1 is a schematic representation of the structure of a HEMT on which a nucleation layer 3 has been deposited on the surface 2 of a silicon substrate 1. The surface 2 of the silicon substrate 1 is prepared appropriately before the nucleation layer 3 is deposited. For this purpose, the silicon substrate 1 is introduced into a process chamber 8 of a CVD reactor 7. It is heated to a temperature of 900 to 1,200° C. under a typical total pressure between 50 and 800 mbar in a hydrogen atmosphere. During this preparatory step, the natural SiO.sub.2 layer of the substrate is thermally removed. This is followed by an optional further pretreatment of the substrate at lower or higher temperature and adjusted pressure with for example TMAl or NH.sub.3 or other gaseous starting materials.

[0022] The actual epitactic application of the AlN nucleation layer 3 is performed by simultaneously introducing TMAl and NH.sub.3. The nucleation layer 3 may be deposited in a multistage process, wherein the temperature, pressure and gas flows may be altered. The temperature range for the deposition of the nucleation layer 3 is typically in the region between 800 and 1,200° C., while the total pressure inside the process chamber 8 is in the range between 30 and 300 mbar.

[0023] The gaseous starting materials are fed into the process chamber 8 together with a carrier gas, hydrogen for example, through a gas inlet member 11. One or more substrates 1 are present in the process chamber 8 on a susceptor 9 which is heated by a heating device 10 and are coated with the nucleation layer 3. The gaseous precursors, in particular TMAl and NH.sub.3, are fed into the process chamber 8 through the gas inlet member 11 in a molar ratio for V starting material to III starting material in the range of 10 to 5,000. The flow rates of the gaseous starting materials are adjusted such that the growth rage of the AlN nucleation layer 3 is in the range between 0.01 and 2 μm/h.

[0024] However, it is essential to the invention that during the deposition of the nucleation layer 3, but at least at the start of the deposition of the nucleation layer 3, a further gaseous starting material is fed into the process chamber 8, resulting in a weak n-conductivity. This third gaseous starting material is preferably silane or germanium with the structural formula Si.sub.nH.sub.2n+2 or Ge.sub.nH.sub.2n+2.

[0025] The additional n-doping of the III-V nucleation layer results in a substantial reduction in the dispersion effects described in the introduction and a decrease of the damping, as is shown in FIG. 3 by the examples [0026] a) undoped AlN, [0027] b) 1×10.sup.18 cm.sup.−3 doped AlN or [0028] c) 2×10.sup.17 cm.sup.−3 doped AlN [0029] d) 5×10.sup.17 cm.sup.−3 doped AlN.

[0030] FIG. 3 shows a significant decrease in damping at dopant concentrations of 2×10.sup.17 cm.sup.−3 and 5×10.sup.17 cm.sup.−3, whereas with more doping of 1×10.sup.18 cm.sup.−3 the damping increases again and reaches roughly the same value as the undoped AlN.

[0031] The results show that the desired effect is evidently not detectable at higher dopant concentrations.

[0032] After this, first a GaN buffer layer 4 and then an active AlGaN layer 6 are deposited in known manner on the nucleation layer 3, with the result that a two-dimensional electron gas forms on the boundary surface 5 between buffer layer 4 and active layer 6. Gate contacts, source contacts and drain contacts are also produced in known manner.

[0033] The preceding notes are intended to provide an explanation of the inventions collected altogether in the application, which advance the prior art at least by the following combinations of features, as well as independently in each case, wherein two, more, or all of said feature combinations may themselves be combined, namely:

[0034] A method which is characterized in that at least at the start of the deposition of the nucleation layer 3, a third gaseous starting material containing an element of main group IV is fed into the process chamber 8 together with the first and second gaseous starting materials.

[0035] A method which is characterized in that the partial pressure of the third gaseous starting material is lower than the partial pressures of the first and second gaseous starting materials in the process chamber 8 by a factor of at least 10, and/or that the partial pressure or the mass flow of the third gaseous starting material in the process chamber 8 is selected such that it results in a doping not exceeding 1×10.sup.18 cm.sup.−3.

[0036] A method which is characterized in that the process temperature is in a range between 800° C. and 1,200° C., preferably between 950° C. and 1,050° C.

[0037] A method which is characterized in that the nucleation layer 3 is deposited under total pressures between 30 and 300 mbar.

[0038] A method which is characterized in that the molar ratio of the second gaseous starting material to the first gaseous starting material is in the range between 10 and 5,000.

[0039] A method which is characterized in that the addition of the third gaseous starting material causes an n-doping of the nucleation layer in the range from 1×10.sup.17 to 1×10.sup.18 cm.sup.−3.

[0040] A method which is characterized in that the substrate (1) consists of silicon or germanium, and/or that the third gaseous starting material is Si.sub.nH.sub.2n+2 or Ge.sub.nH.sub.2n+2 or another gaseous starting material that contains silicon or germanium.

[0041] A method which is characterized in that the element of the main group III is Al and/or the first gaseous starting material is TMAl.

[0042] A method which is characterized in that the element of the main group V is nitrogen and/or the second gaseous starting material is NH.sub.3.

[0043] A method which is characterized in that a buffer layer 4, particularly of AlN, is deposited on the nucleation layer 3, and an active layer 6 is deposited on the buffer layer 4 in such manner that a two-dimensional electron gas develops on the boundary surface 5 between active layer 6 and buffer layer 4, and/or that the introduction of the third gaseous starting material decreases the damping value of a high-frequency damping.

[0044] A layer sequence which is characterized in that a nucleation layer 3 comprised of elements of the main groups III and V is deposited on a surface 2 of a substrate 1 comprised of an element of the main group IV, which is doped with an element of the main group IV at least in the region thereof directly adjacent to the surface 2.

[0045] A layer sequence which is characterized in that at least one buffer layer 4 is deposited on the nucleation layer 3, on which buffer layer in turn an active layer 6 is deposited, with the result that a two-dimensional electron gas develops on the boundary layer 5 between buffer layer 4 and active layer 6.

[0046] All of the disclosed features are (in and of themselves, but also in combination with each other) essential for the purposes of the invention. The content for disclosure of the associated/accompanying priority documents (copy and previous application) is herewith also incorporated in its entirety in the disclosure of the present application, also for the purpose of including features of said documents in claims of the present application. By their features, the subordinate claims characterize standalone inventive advances of the prior art, even without the features of a referenced claim, in particular with a view to filing divisional applications on the basis of these claims. The invention disclosed in each claim may also include one or more of the features described in the preceding description, in particular such features as are identified with reference numbers and/or in the list of reference numbers. The invention further relates to design forms in which individual features of those identified in the preceding description are not realized, in particular to the extent that they are evidently not essential for the respective intended purpose or can be replaced by other means having technically equivalent effect.

LIST OF REFERENCE NUMBERS

[0047] 1 Substrate [0048] 2 Surface [0049] 3 Nucleation layer [0050] 4 Buffer layer [0051] 5 Boundary surface [0052] 6 Active layer [0053] 7 Reactor [0054] 8 Process chamber [0055] 9 Susceptor [0056] 10 Heating device [0057] 11 Gas inlet member