The present invention relates to a process of obtaining a hybrid substrate, that is to say one consisting of several layers, comprising at least one layer of a nitrided material of III/N type.
Such a substrate is intended to be used in applications in the field of electronics, optics, photovoltaics or optoelectronics.
Nitrided materials of III/N type are materials in which nitrogen is combined with an element from column III of the Periodic Table, especially gallium nitride (GaN) and various nitrides or nitrided alloys based on indium (In), boron (B) and aluminum (Al).
These are promising materials for applications in high-power high-frequency electronic devices or for those subjected to high temperatures, such as a light-emitting diode (LED) emitting in the visible or the ultraviolet, or a blue/violet laser diode.
For information, it will be recalled below that the crystal structure of GaN has hexagonal symmetry, this being shown schematically in the appended FIG. 1.
It may be seen in this figure that gallium nitride has a hexagonal crystal structure defined by a crystal unit cell which is a prism, the base of which has edges of the same length a (3.1896 Å or 0.31896 nm) and oriented at 120° to each other. The height of the prism is denoted by c (5.1855 Å or 0.51855 nm). In hexagonal crystals, it is common practice to use a notation based on 4 indices (h, k, i, l) associated with the vectors a1, a2, a3 and c for naming the crystallographic planes.
The most common gallium nitride (GaN) substrates have the crystallographic c-axis normal to their surface. Their growth is said to be along the c-axis or their growth plane is the c-plane. These substrates are called “standard GaN” substrates in the rest of the description and are termed polar.
Substrates made of standard GaN have the drawback of having undesirable spontaneous and piezoelectric polarization effects, as explained in the article “Structural and morphological characteristics of planar (11 20) a-plane gallium nitride grown by hydride vapor phase expitaxy” Applied Physics Letters, Volume 83, Number 8, 25 Aug. 2003, pp 1554-1556 by B. A. Haskell et al.
They are therefore not always perfectly suitable for the production of electronic components for the aforementioned technological applications.
In addition, there is no industrial process for easily transferring a layer of III/N-type nitrided material onto a substrate.
The article “Transfer of two-inch GaN film by the Smart-Cut™ technology” Electronics Letters 26 May 2005, Vol. 41, No. 11 by A. Tauzin et al. describes the possibility of transferring a standard GaN film onto a support substrate by the Smart-Cut™ technology. This article studied the conditions for blistering in a GaN material. Blistering occurs only when the GaN is implanted with doses of hydrogen of at least 2×1017 H+/cm2.
The articles “Formation of nanovoids in high-dose hydrogen implanted GaN”, from Applied Physics Letters 89,031912 (2006) by I. Radu et al., “Investigation of hydrogen implantation induced blistering in GaN”, Phys Stat. Sol. (c) 3, No. 6, 1754-1757, (2006) by R. Singh et al. and “Blistering of H-implanted GaN” Journal of Applied Physics, Volume 91, Number 6, 15 Mar. 2002, pp 3928-3930 by S. O. Kucheyev et al. also mention the appearance of blister-defects following the annealing of standard GaN implanted with hydrogen at doses equal to or greater than 2.6×1017 H+/cm2.
The article “Infrared and transmission electron microscopy studies of ion-implanted H in GaN”, Journal of Applied Physics, Volume 85, Number 5, 1 Mar. 1999, pp 2568-2573 by C. H. Seager et al. also shows the appearance of pyramidal cavities in standard GaN implanted with H+ ions with doses between 2×1016 H+/cm2 and 1×1017 H+/cm2 followed by a thermal budget of one hour at around 890° C.
All the values mentioned show that the implantation doses for fracturing the GaN are at least five times higher than those needed to fracture silicon, and are therefore more difficult to apply in an industrial process. This is because, depending on the implantation current density used, the application of doses as high as these requires an implantation operation that may last up to several tens of hours.
Finally, the article “Interaction between dislocations and He-implantation-induced voids in GaN epitaxial layers”, Applied Physics Letters 86, 211911 (2005) by D. Alquier et al. describes results of experiments in which He+ helium ions are implanted into standard GaN.
It is mentioned in this article that an implantation of He+ ions in GaN, with doses above 1×1016 He+/cm2 followed by a heat treatment at around 1000-1100° C. for 2 minutes leads to the formation of cavities, some of which are of cylindrical shape and others of pyramidal shape.
However, this document in no way describes the implementation of an industrial layer transfer process.
One of the objects of the present invention is to provide a process for transferring a layer of a nitrided material of hexagonal crystal structure and of the III/N type, especially gallium nitride (GaN), which is easily industrialized, that is to say which uses implantation doses lower than those described in the literature, for example in the article “Transfer of two-inch GaN film by the Smart-Cut™ technology”, Electronics Letters 26 May 2005 Vol. 41 No. 11 by A. Tauzin et al. in which the doses described range from 2×1017 H+/cm2 to 5×1017 H+/cm2.
Another object of the invention is to provide a layer of a nitrided material of hexagonal crystal structure, of III/N type and of good crystal quality, including after it has undergone ion implantation and layer transfer steps.