Method of laser separation of the epitaxial film or the epitaxial film layer from the growth substrate of the epitaxial semiconductor structure (variations)
The present invention proposes variations of the laser separation method allowing separating homoepitaxial films from the substrates made from the same crystalline material as the epitaxial film. This new method of laser separation is based on using the selective doping of the substrate and epitaxial film with fine donor and acceptor impurities. In selective doping, concentration of free carries in the epitaxial film and substrate may essentially differ and this can lead to strong difference between the light absorption factors in the infrared region near the residual beams region where free carriers and phonon-plasmon interaction of the optical phonons with free carriers make an essential contribution to infrared absorption of the optical phonons. With the appropriate selection of the doping levels and frequency of infrared laser radiation, it is possible to achieve that laser radiation is absorbed in general in the region of strong doping near the interface substrate-homoepitaxial film. When scanning the interface substrate-homoepitaxial film with the focused laser beam of sufficient power, thermal decomposition of the semiconductor crystal takes place with subsequent separation of the homoepitaxial film. The advantage of the proposed variations of the method for laser separation of epitaxial films in comparison with the known ones is in that it allows the separation of homoepitaxial films from the substrates, i.e., homoepitaxial films having the same width of the forbidden gap as the initial semiconductor substrate has. The proposed variations of the method can be used for separation of the epitaxial films.
1. A method of laser separation of an epitaxial film or of an epitaxial film layer from a growth substrate of an epitaxial semiconductor structure, the method comprising:
using selective doping of some regions of the epitaxial semiconductor structure with fine donor or acceptor impurities when growing the epitaxial film or the epitaxial film layer, so that a resulting concentration of fine donor or acceptor impurities in selectively doped regions essentially exceeds a background concentration in undoped regions;
gluing the epitaxial semiconductor structure onto a temporary substrate;
directing a focused laser beam of a laser to the epitaxial semiconductor structure glued onto the temporary substrate so as to place a beam focus of the focused laser beam in the selectively doped regions of the epitaxial semiconductor structure in which absorption of laser radiation takes place;
moving the focused laser beam so as to scan the selectively doped regions of the epitaxial semiconductor structure with the beam focus with partial thermal decomposition of the selectively doped regions and weakening of their mechanical strength; and
separating the epitaxial film or the epitaxial film layer from the growth substrate or from the growth substrate with a part of the epitaxial film by applying mechanical or thermomechanical stress.
2. The method according to claim 1 , wherein the epitaxial film or the epitaxial film layer is grown by a homoepitaxy method.
3. The method according to claim 1 , wherein a selectively doped region is a substrate or a surface layer of the substrate.
4. The method according to claim 1 , wherein a selectively doped region is the epitaxial film or a lower layer of the epitaxial film.
5. The method according to claim 1 , wherein a material of the epitaxial semiconductor structure is a semiconductor from an element of fourth group of the periodic system.
6. The method according to claim 1 , wherein a material of the epitaxial semiconductor structure is a semiconductor compound from elements of fourth group of the periodic system.
7. The method according to claim 1 , wherein a material of the epitaxial semiconductor structure is a semiconductor compound from elements of third and fifth groups of the periodic system.
8. The method according to claim 1 , wherein a material of the epitaxial semiconductor structure is a semiconductor compound from elements of second and sixth group of the periodic system.
9. The method according to claim 1 , wherein for separating the epitaxial film or the epitaxial film layer from the growth substrate, the method comprises using the laser with a wave length which is within following wave length ranges: for silicon, germanium and gallium arsenide semiconductors within a wave length range of 6 μm≤λ≤48 μm; for gallium nitride within a wave length range of 4 μm≤λ≤32 μm; for silicon carbide within a wave length range of 3 μm≤λ≤24 μm; for alumina nitride within a wave length range of 2.5 μm≤λ≤20 μm; and for diamond within a wave length range of 2 μm≤λ≤16 μm.
10. The method according to claim 1 , wherein the laser is an infrared gas pulse pumped CO 2 or CO laser.