DE10006108A1 - Process for the epitaxial growth of single crystalline aluminum nitride layers on silicon substrates comprises preparing substrate to form terrace layer, vaporizing an aluminum layer - Google Patents

Abstract

Process for the epitaxial growth of single crystalline aluminum nitride layers on silicon substrates having a surface comprises using a Si off-axis substrate (1) whose surface norm (2) is tilted by an angle alpha opposite the direction to the flat diagonal (or additional equivalent directions); preparing the Si (001) off-axis substrate surface at a temperature of more than 1100 deg C so that a terrace structure (4) with an atomic double layer (3) is produced; vaporizing a one to two monolayer thick aluminum layer on the silicon surface before growing the aluminum nitride layer; introducing nitrogen; and increasing the substrate temperature during the epitaxial growth. Preferred Features: The tilting angle alpha is 2-8 deg . The aluminum nitride layer is grown using plasma-supported molecular beam epitaxy.

Description

The invention relates to a method for the epitaxy of single-crystalline aluminum nitride Layers on silicon substrates with a (001) surface.

Single-crystalline aluminum nitride (AlN) layers on Si (001) substrates can Basis for the manufacture of semiconductor components for high performance and high frequency electronics, for optoelectronic applications such as Light emitters and light receivers in the short-wave spectral range and for Form acoustic surface wave filters. It is known that single-crystalline AlN Layers of high crystal perfection and smooth surface for the subsequent one Epitaxy of electronic and optoelectronic semiconductor components on the Based on gallium nitride (GaN) are very suitable. Thin layers of AlN are therefore generally used as a buffer layer for the epitaxy of GaN Semiconductor components used.

A major problem of semiconductor devices based on group III Nitrides consists in the fact that so far no sufficiently large ones have been made from this material Crystals for the production of substrates can be grown. Therefore must AlN is also deposited on other substrate materials. To mainly sapphire and silicon carbide (US 5670798) are used. This However, substrate materials are expensive and are not as large in diameter such as Si. Si single crystal substrates, on the other hand, are very inexpensive and are currently available with diameters up to. 30 cm to Manufacture of semiconductor devices used. It is also very beneficial Growing AlN on Si substrates because of the possibility of integration of components from group III nitrides with conventional Si electronics is opened.

In the previously known attempts to use Si substrates for epitaxial deposition of AlN, however, the following problem has arisen:  

Successful growth of single-crystalline AlN layers was only possible on Si Substrates with a (111) surface can be achieved (DE 198 27 198), but not on the substrates usually used by the semiconductor industry with a (001) surface. This is a deficiency in that, on the one hand, large-area Si (111) - Substrates are not readily available and on the other hand one Integration of electronic or optoelectronic components based on III nitrides with standard Si-CMOS circuits is hardly possible. That is exactly but very important for the practical use of III-nitride components. At the Growth of AlN on Si (001) is due to the lattice misfit and the different crystallographic structure of the unit cell of cubic Si and Wurzitic AlN in the nucleation of the AlN domains different Orientation and, as a result, a columnar layer structure that allows use of these layers for electronic or optoelectronic components in the way stands.

There is an essential one regardless of the orientation of the Si substrate Problem in that the lattice constant of AlN does not match that of Si agrees, which makes successful heteroepitaxy very difficult. To this It has been proposed to solve the problem (EP 0352471, DE 197 25 900, EP 0352472, US 4925810, US 5959308, DE 187 15 572), with pre-structured substrates for Epitaxy of III-V semiconductor layers to work on Si substrates. Independently of the extent to which such a method is successful for the epitaxy of AlN can be used on Si (001) substrates, has the use of pre-structured Substrate surfaces have the disadvantage that only a part of the total Substrate surface for the components from the applied III-V layers can be used. For heteroepitaxy of GaAs on Si (100) substrates was proposed (US 4872046, EP 0232082), the substrate surface in the Tilt <001 <direction. However, this procedure can be used for heteroepitaxy of AlN on Si (001) cannot be applied because AlN is in contrast to GaAs does not grow as a cubic layer.

The heteroepitaxy of GaN on Si has also been proposed before  Applying the GaN layer first a GaAs layer as a buffer layer to apply the Si substrate (EP 0884767). For the heteroepitaxy of. AlN on Si However, this method is not suitable because the thermal stability of the GaAs Layer for the epitaxy of AlN is not sufficient.

The object to be achieved by the present invention is there in a method for the epitaxy of single-crystalline, domain-free AlN layers Specify Si (001) substrates.

According to the invention, this object is achieved with the features of claim 1. Further configurations result from the dependent claims 2 and 3. The following aspects are of particular importance:

The Si (001) substrate is not a substrate with an exact orientation of the Surface normal in the <001 <direction, probe a substrate, whose (001) surface is tilted a few degrees in the <110 <direction. It was found experimentally that the epitaxy of AlN on Si (001) - Surfaces whose surface normal is parallel to the <001 <direction or is tilted in a different direction by a small angle of less than 0.5 °, which does not match the <110 <direction, to form by 30 ° moves AlN domains twisted azimuthally against each other. The reason for this is that these two domains are crystallographically equal and therefore the same occur frequently. The domain boundaries form an interruption of the Translation symmetry of the AlN crystal lattice and therefore have a negative effect the electrical and optical properties of the components made on the AlN layer can be grown. It has been found experimentally that this Domain formation of the AlN layer by tilting the above-mentioned Surface normal in the <110 <direction can be avoided. The cause for this is that by tilting the surface normal to the corresponding Surface preparation creates a terrace structure on the Si (001) surface, which prefers the growth of only one domain, so that the AlN layer grows mono-crystalline in the strict sense.

Before the actual epitaxy of the AlN layer, the substrate must be well off  Surface impurities cleaned and an atomic terrace structure with Double steps are prepared, the step edges parallel to <-110 < Direction. Subsequently, 1 to 2 monolayers of aluminum evaporated onto the substrate before the AlN layer is then grown.

If the epitaxy process is prepared and carried out as described, this results a one-domain, single-crystalline, Würzitic AlN layer on the <110 < Direction of tilted Si (001) surface. The crystallographic c-axis of this AlN (0001) layer is not parallel to the <001 <direction of the Si substrate, but directed towards the surface normal of the Si substrate.

The method according to the invention enables heteroepitaxy to be single-crystalline AlN layers with very good crystalline quality on Si (001) surfaces. This AlN layers on Si (001) wafers can be used for acoustic Surface wave devices and as buffer layers for the epitaxy of GaN Semiconductor components are used.

The method according to the invention is described below using a Embodiment will be explained in more detail. In the accompanying drawings demonstrate

Fig. 1 is a cross sectional view of a Si (001) off-axis substrate after the surface preparation

Fig. 2 is a perspective plan view of a Si (001) off-axis substrate after the surface preparation

Fig. 3 shows the cross-section of an epitaxially grown AlN layer on the off-axis Si (001) substrate.

An off-axis Si (001) substrate 1 , the surface normal 2 of which is tilted by an angle α = 5 ° with respect to the <001 <direction to the surface diagonal <110 <(or equivalent directions), is subjected to chemical cleaning under ultra-high vacuum conditions at a temperature of 1120 ° C with Si until an ordered 2 × 1 superstructure is visible in the electron diffraction pattern. As a result of the specified tilt angle α, an atomic terrace structure (see FIG. 1) forms on the substrate surface as a result of the Si homoepitaxy, the terrace edges of which form atomic double steps which run parallel to the <-110 <direction (see FIG. 2). Subsequently, two monolayers of aluminum are evaporated at a substrate temperature of 650 ° C., as a result of which a 6 × 4 superstructure is formed on the terraces 4 . A stream of activated nitrogen vapor is then directed onto the substrate from a high-frequency plasma source, so that AlN nuclei form on the Si surface. Then, together with the vapor stream of the activated nitrogen, an aluminum vapor stream is directed onto the substrate surface and the substrate temperature is slowly increased to the epitaxial temperature of 900 ° C. A single-crystalline, single-domain, Würzitic AlN (0001) layer 5 with a sixfold symmetry grows, whose <0001 <direction is parallel to the surface normal 2 of the off-axis Si (001) substrate 1 and therefore by the angle α = 5 ° deviates from the <0001 <direction of the Si substrate 1 .

List of the reference symbols used

1

off-axis Si (001) substrate

2

Surface normal of the Si (001) substrate

3

double stage

4

Terrace

5

monocrystalline, wurtzitic AlN layer
α Angle between the surface normal and the <001 <direction of the Si substrate

Claims (3)

1. A method for the epitaxy of single-crystalline aluminum nitride layers on silicon substrates with a (001) surface, characterized in that

• that an Si (001) off-axis substrate ( 1 ) is used, the surface normal ( 2 ) of which is tilted by an angle α relative to the <001 <direction to the surface diagonal <110 <(or directions equivalent to it),
• - that the Si (001) off-axis substrate surface is prepared at a temperature greater than 1100 ° C. so that a terrace structure ( 4 ) with atomic double steps ( 3 ) is formed,
• that before the actual aluminum nitride (AlN) epitaxy at a temperature lower than the usual growth temperature of the AlN, a one to two monolayer thick aluminum layer is first evaporated onto the Si surface,
• - that the epitaxy of AlN is then initiated by adding nitrogen and
• - That the substrate temperature during the epitaxy of the AlN layer ( 5 ), the temperature is gradually increased to the usual epitaxial temperature of the AlN.

2. The method according to claim 1, characterized, that the tilt angle α is in the range from 2 ° to 8 °. 3. The method according to claim 1, characterized, that the AlN layer by means of plasma-assisted molecular beam epitaxy is grown.