Patterned aluminum nitride composite substrate and preparation method thereof

A method for preparing a patterned AlN composite substrate, comprising:

• 1) providing a high temperature-resistant substrate, wherein the high temperature-resistant substrate has a single crystal structure with a band gap not less than 5.4 eV, allows ultraviolet light in a band of 230 nm to 400 nm to penetrate through, and does not undergo surface decomposition in an inert atmosphere at a high temperature;
• 2) conducting low-temperature and low-pressure primary AlN deposition:
• conducting the low-temperature and low-pressure primary AlN deposition on an upper surface of the high temperature-resistant substrate at a deposition temperature of not greater than 700° C. under a deposition pressure of not greater than 1×10−2 Pa to form a bottom AlN;
• wherein the deposition temperature of not greater than 700° C. causes the bottom AlN deposited on the high temperature-resistant substrate to have crystal defects at a high density, such that the bottom AlN has an absorption capability in an ultraviolet band;
• 3) patterning the bottom AlN:
• allowing a laser beam in the ultraviolet band to be incident from a back side on a lower surface of the high temperature-resistant substrate, and penetrate through the high temperature-resistant substrate to the bottom AlN, such that the bottom AlN absorbs the laser beam in the ultraviolet band and then is decomposed into nitrogen and aluminum;
• and
• controlling the laser beam to scan along a straight line with a scanning path comprising multiple scanning straight lines and a spacing between two adjacent parallel scanning straight lines being at least twice a diameter of a laser spot, wherein a zone on the bottom AlN scanned by the laser spot is an irradiated zone, the irradiated zone comprising multiple long strips, and two ends of each of the long strips passing through an edge of the bottom AlN;
• and a zone on the bottom AlN not scanned by the laser spot is a non-irradiated zone, a width of the irradiated zone being not greater than a width of the non-irradiated zone, such that AlN in the irradiated zone is decomposed, and AlN in the non-irradiated zone is retained, and AlN thereby forms a stripe-like or grid-like periodic distribution, forming a patterned bottom AlN;
• 4) obtaining a patterned primary photoresist:
• applying a primary photoresist onto a surface of the patterned bottom AlN by spin coating, wherein the spin coating is continued after the primary photoresist fills the irradiated zone without AlN to cover the non-irradiated zone with AlN, and a surface of the primary photoresist is higher than a surface of the non-irradiated zone with AlN;
• exposing the primary photoresist with a mask to light, wherein a projection of a primary exposure zone falls within a projection of the non-irradiated zone, and a width of the primary exposure zone is less than a width of the non-irradiated zone;
• and
• removing the primary photoresist in the primary exposure zone using a developing solution, meanwhile retaining the primary photoresist in a non-primary exposure zone, thereby forming the patterned primary photoresist on the surface of the patterned bottom AlN, wherein a period of the patterned primary photoresist is consistent with a period of the patterned bottom AlN;
• 5) conducting low-temperature and low-pressure secondary AlN deposition:
• conducting the low-temperature and low-pressure secondary AlN deposition on a surface of the patterned primary photoresist at a deposition temperature of not greater than 700° C. under a deposition pressure of not greater than 1×10−2 Pa to form a top AlN, wherein the top AlN continuously covers the primary exposure zone without the primary photoresist and the non-primary exposure zone with the primary photoresist retained;
• and a surface of the top AlN is higher than a surface of the primary photoresist retained in the non-primary exposure zone during the patterning the primary photoresist;
• 6) removing the patterned primary photoresist:
• removing the patterned primary photoresist in the non-primary exposure zone between the top AlN and the patterned bottom AlN, such that AlN of the top AlN corresponding to the non-primary exposure zone is no longer supported by the primary photoresist and becomes a suspended AlN, and AlN of the top AlN corresponding to the primary exposure zone is supported by AlN retained in the patterned bottom AlN and becomes a non-suspended AlN, thereby forming a semi-suspended AlN structure;
• 7) annealing and then recrystallizing:
• subjecting the semi-suspended AlN structure to high-temperature thermal annealing in an inert atmosphere, and adjusting a temperature and a pressure such that the semi-suspended AlN structure is recrystallized and meanwhile does not decompose, wherein the suspended AlN of the top AlN that corresponds to the irradiated zone is not affected by an interface lattice mismatch and a thermal expansion coefficient mismatch brought by the high temperature-resistant substrate, thus achieving annihilation of a dislocation density and relaxation of a mismatch stress, such that the suspended AlN after the high-temperature thermal annealing has a low dislocation density and a low mismatch stress;
• and
• recrystallizing the patterned bottom AlN and the top AlN after annealing to form a single crystal AlN;
• 8) obtaining a patterned secondary photoresist:
• applying a secondary photoresist onto a surface of the single crystal AlN by spin coating, exposing the secondary photoresist with a mask to light, wherein a secondary exposure zone is directly opposite to the suspended AlN;
• and removing the secondary photoresist in the secondary exposure zone using a developing solution, namely removing the secondary photoresist on the suspended AlN, thereby forming the patterned secondary photoresist on the surface of the single crystal AlN;
• 9) conducting deposition of an optical medium material:
• depositing the optical medium material on a surface of the patterned secondary photoresist to inhibit nucleation growth of a nitride semiconductor;
• and
• 10) removing the patterned secondary photoresist:
• removing the patterned secondary photoresist on the surface of the single crystal AlN, such that a surface of the suspended AlN does not have the optical medium material while a surface of the non-suspended AlN has the optical medium material, thereby obtaining the patterned AlN composite substrate comprising the high temperature-resistant substrate, the single crystal AlN, and the optical medium material.