1. A method comprising:
irradiating a bottom surface of a substrate of a semiconductor wafer with a laser beam,
wherein the substrate is constructed of a wide band gap material comprising silicon carbide,
wherein the bottom surface of the substrate is exposed,
wherein the semiconductor wafer comprises the substrate and at least one layer configured on a top surface of the substrate, and
wherein the laser beam is of sufficient energy to alter a band gap of the wide band gap material to generate a graphitic layer area on the bottom surface of the substrate; and
depositing a metal layer on the bottom surface of the substrate to form an ohmic contact at the graphitic layer area.
2. The method of claim 1, further comprising, before irradiating the bottom surface of the substrate, grinding the bottom surface of the substrate to thin the substrate.
3. The method of claim 1, wherein the substrate material is 4H-silicon carbide.
4. The method of claim 1, wherein irradiating the bottom surface of the substrate comprises:
before irradiating the bottom surface of the substrate, depositing an optically thin metal film on the bottom surface of the substrate; and
irradiating the bottom surface of the substrate with the laser beam.
5. The method of claim 4, wherein the optically thin metal film is deposited to a thickness less than a penetration depth of the laser beam in the optically thin metal film.
6. The method of claim 4, wherein the optically thin metal film is one of an aluminum metal film, a titanium metal film, a nickel metal film, a tantalum metal film, a tungsten metal film, or a palladium metal film.
7. The method of claim 4, wherein the thickness of the optically thin metal film is less than 100 nm.
8. The method of claim 4, further comprising, after irradiating the bottom surface of the substrate and before depositing a metal layer on the bottom surface of the substrate, removing remaining optically thin metal film from the bottom surface of the substrate.
9. The method of claim 1, wherein the laser beam has a wavelength of 315 nm to 400 nm.
10. The method of claim 1, wherein the laser beam has a photon energy below the band gap of the wide band gap material.
11. The method of claim 1, further comprising:
before irradiating the bottom surface of the substrate with the laser beam, grinding the bottom surface of the substrate to thin the substrate; and
after grinding the bottom surface of the substrate and before irradiating the bottom surface of the substrate with the laser beam, ion-implanting the bottom surface of the substrate with dopant atoms.
12. The method of claim 11, wherein the laser beam comprises a wavelength, a pulse duration, and a fluence sufficient to melt the wide band gap material and cause simultaneous activation of the dopant atoms.
13. The method of claim 1, wherein, before irradiating the bottom surface of the substrate with the laser beam, irradiating the bottom surface of the substrate with a second laser beam of insufficient energy to alter the band gap of the wide band gap material, wherein the second laser beam is of sufficient energy to repair crystal damage of the wide band gap material.
14. The method of claim 13, further comprising:
after irradiating the bottom surface of the substrate with the laser beam of sufficient energy to alter the band gap of the wide band gap material to generate the graphitic layer area on the bottom surface of the substrate, depositing an optically thin metal film on the bottom surface of the substrate; and
irradiating the bottom surface of the substrate with a third laser beam of sufficient energy to alter the band gap of the wide band gap material to generate the graphitic layer area on the bottom surface of the substrate.
15. The method of claim 14, wherein the laser beam of sufficient energy to alter the band gap of the wide band gap material has an incident fluence range of 1 Jcm2 to 5 Jcm2, and wherein the third laser beam of sufficient energy to alter the band gap of the wide band gap material has an incident fluence range of 5 Jcm2 to 10 Jcm2.
16. The method of claim 13, further comprising:
after irradiating the bottom surface of the substrate with the second laser beam of insufficient energy to alter the band gap of the wide band gap material, depositing an optically thin metal film on the bottom surface of the substrate; and
irradiating the bottom surface of the substrate with the laser beam of sufficient energy to alter the band gap of the wide band gap material to generate the graphitic layer area on the bottom surface of the substrate.
17. The method of claim 1, wherein irradiating the bottom surface of the substrate comprises irradiating the bottom surface of the substrate with the laser beam using a plurality of laser pulses.
18. The method of claim 17, wherein each of the plurality of laser pulses has a temporal pulse width from 50 ns to 200 ns.
19. The method of claim 1, wherein the substrate material is 6H-silicon carbide.
20. The method of claim 1, wherein the substrate material is 3C-silicon carbide.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A process for preparing an ester of a hydroxyl-bearing polymers, containing repeat structural units of the formulae (I) and (II) in alternating or random sequence
in which
D is a direct bond between polymer backbone and hydroxyl group, a C1- to C6-alkylene group, a C5- to C12-arylene group, an oxyalkylene group of the formula \u2014O\u2014R2\u2014, an ester group of the formula \u2014C(O)\u2014O\u2014R2\u2014 or an amide group of the formula \u2014C(O)\u2014N(R3)R2\u2014,
E is a hydrocarbyl radical having 1 to 10 carbon atoms,
R1 is hydrogen, a hydrocarbyl radical having 1 to 50 carbon atoms or an acyl radical of the formula \u2014C(O)\u2014R4,
R2 is a C2- to C10-alkylene radical,
R3 is hydrogen or a C1- to C10-alkyl radical which may bear substituents,
R4 is a hydrocarbyl radical having 1 to 50 carbon atoms,
A is a C2- to C10-alkylene radical,
k is a number between 1 and 100,
n is a number from 0 to 4999,
m is a number from 1 to 5000,
n+m is a number from 10 to 5000, with the proviso that
a) the molar proportion of the structural units (I) in the polymer is between 0 and 99.9 mol %, and
b) the molar proportion of the structural units (II) in the polymer is between 0.1 and 100 mol % of the repeat units,
by irradiating hydroxyl-bearing polymers A) containing the repeat structural unit of the formula (I) together with an ether carboxylic acid B1) of the formula (III) or ether carboxylic ester B2) of the formula (IV)
R1\u2014O-A-Ok-E-COOH\u2003\u2003(III)
R1\u2014O-A-Ok-E-COOR5\u2003\u2003(IV)
in which R1, A, E and k are as defined above and R5 is a C1-C4-alkyl radical
with microwaves in the presence of water, wherein the reaction mixture is heated by the microwave irradiation to temperatures above 100\xb0 C.
2. The process as claimed in claim 1, in which the hydroxyl-bearing polymer further comprises, as well as the structural units of the formula (I), structural units derived from further ethylenically unsaturated monomers.
3. The process as claimed in claim 1, in which the structural units of the formula (I) derive from vinyl alcohol.
4. The process as claimed in claim 2, in which the hydroxyl-bearing polymer further comprises, as well as the structural units of the formula (I), structural units derived from vinyl acetate.
5. The process as claimed in claim 1, in which R1 is a hydrocarbyl radical having 2 to 20 carbon atoms.
6. The process as claimed in claim 1, in which the ether carboxylic acid B1) or the ether carboxylic ester B2) is a mixture of at least one ether carboxylic acid and at least one ether dicarboxylic acid or a mixture of at least one ether carboxylic ester and at least one ether dicarboxylic ester.
7. The process as claimed in claim 1, in which the reaction mixture used for conversion contains 5 to 98% by weight of water.
8. The process as claimed in claim 1, in which the reaction mixture used for conversion contains 5 to 98% by weight of a mixture of water and one or more water-miscible organic solvents.
9. The process as claimed in claim 8, in which the proportion of the water-miscible organic solvent in the solvent mixture is between 1 and 75% by weight.
10. The process as claimed in claim 1, in which the reaction mixture is heated by means of microwave radiation to temperatures above 110\xb0 C.
11. The process as claimed in claim 1, in which ester-bearing comonomer units of hydroxyl-bearing polymer A) are transesterified with ether carboxylic acids B1) or ether carboxylic esters B2).
12. The process as claimed in claim 1, in which the microwave irradiation is effected in a flow tube made from microwave-transparent, high-melting material.
13. The process as claimed in claim 12, in which the longitudinal axis of the reaction tube in the direction of propagation of the microwaves is within a monomode microwave applicator.
14. The process as claimed in claim 1, in which the microwave applicator takes the form of a cavity resonator.
15. An ester of a hydroxyl-bearing polymer containing repeat structural units of the formulae (I) and (II) in alternating or random sequence
in which
D is a direct bond between polymer backbone and hydroxyl group, a C1- to C6-alkylene group, a C5- to C12-arylene group, an oxyalkylene group of the formula \u2014O\u2014R2\u2014, an ester group of the formula \u2014C(O)\u2014O\u2014R2\u2014 or an amide group of the formula \u2014C(O)\u2014N(R3)R2\u2014,
E is a hydrocarbyl radical having 1 to 10 carbon atoms,
R1 is hydrogen, a hydrocarbyl radical having 1 to 50 carbon atoms or an acyl radical of the formula \u2014C(O)\u2014R4,
R2 is a C2- to C10-alkylene radical,
R3 is hydrogen or a C1- to C10-alkyl radical which may bear substituents,
R4 is a hydrocarbyl radical having 1 to 50 carbon atoms,
A is a C2- to C10-alkylene radical,
k is a number between 2 and 100,
n is a number from 0 to 4999,
m is a number from 1 to 5000,
n+m is a number from 10 to 5000, with the proviso that
a) the molar proportion of the structural units (I) in the polymer is between 0 and 99.9 mol %, and
b) the molar proportion of the structural units (II) in the polymer is between 0.1 and 100 mol % of the repeat units.
16. The ester of a hydroxyl-bearing polymer as claimed in claim 15, in which the polymer further comprises, as well as the structural units of the formulae (I) and (II), structural units derived from further ethylenically unsaturated monomers.
17. The ester of a hydroxyl-bearing polymer as claimed in claim 15, in which the structural units of the formula (I) derive from vinyl alcohol.
18. The ester of a hydroxyl-bearing polymer as claimed in claim 16, in which the polymer further comprises, as well as the structural units of the formulae (I) and (II), structural units derived from vinyl acetate.
19. The ester of a hydroxyl-bearing polymer as claimed in claim 15, in which R1 is a hydrocarbyl radical having 2 to 20 carbon atoms.
20. The ester of a hydroxyl-bearing polymer as claimed in claim 15, in which R1 is an acyl radical of the formula \u2014C(O)\u2014R4 having 2 to 20 carbon atoms.
21. The ester of a hydroxyl-bearing polymer as claimed in claim 15, in which E is a methylene group.
22. The ester of a hydroxyl-bearing polymer as claimed in claim 15, in which A is an alkylene radical having two or three carbon atoms.
23. An ester of a hydroxyl-bearing polymer containing repeat structural units of the formulae (I) and (II) in alternating or random sequence
in which
D is a direct bond between polymer backbone and hydroxyl group, a C1- to C6-alkylene group, a C5- to C12-arylene group, an oxyalkylene group of the formula \u2014O\u2014R2\u2014, an ester group of the formula \u2014C(O)\u2014O\u2014R2\u2014 or an amide group of the formula \u2014C(O)\u2014N(R3)R2\u2014,
E is an alkylene group having 1 to 4 carbon atoms,
R1 is hydrogen, a hydrocarbyl radical having 1 to 50 carbon atoms or an acyl radical of the formula \u2014C(O)\u2014R4,
R2 is a C2- to C10-alkylene radical,
R3 is hydrogen or a C1- to C10-alkyl radical which may bear substituents,
R4 is a hydrocarbyl radical having 1 to 50 carbon atoms,
A is a C2- to C10-alkylene radical,
k is a number between 1 and 100,
n is a number from 0 to 4999,
m is a number from 1 to 5000,
n+m is a number from 10 to 5000, with the proviso that
a) the molar proportion of the structural units (I) in the polymer is between 0 and 99.9 mol %, and
b) the molar proportion of the structural units (II) in the polymer is between 0.1 and 100 mol % of the repeat units.
24. The ester of a hydroxyl-bearing polymer as claimed in claim 23, in which the polymer further comprises, as well as the structural units of the formulae (I) and (II), structural units derived from further ethylenically unsaturated monomers.
25. The ester of a hydroxyl-bearing polymer as claimed in claim 23, in which the structural units of the formula (I) derive from vinyl alcohol.
26. The ester of a hydroxyl-bearing polymer as claimed in claim 24, in which the polymer further comprises, as well as the structural units of the formulae (I) and (II), structural units derived from vinyl acetate.
27. The ester of a hydroxyl-bearing polymer as claimed in claim 23, in which R1 is a hydrocarbyl radical having 2 to 20 carbon atoms.
28. The ester of a hydroxyl-bearing polymer as claimed in claim 23, in which R1 is an acyl radical of the formula \u2014C(O)\u2014R4 having 2 to 20 carbon atoms.
29. The ester of a hydroxyl-bearing polymer as claimed in claim 23, in which E is a methylene group.
30. The ester of a hydroxyl-bearing polymer as claimed in claim 23, in which A is an alkylene radical having two or three carbon atoms.