Patent Application
20080090101
Preferred embodiments of the method for coating a substrate according to an aspect of the invention will be described below with reference to the attached FIGURE.
In the FIGURE:
In a first embodiment, two solutions are prepared. A first solution is prepared by mixing 35 g propanol, 20 g polyethylene glycol 600, 45 g acetylacetone and 20 g water. A second solution is prepared by mixing 50 g decanol and 160 g zirconium tetra propoxide (70% in propanol; ZrO2 content 26.47%).
Then, the first solution is added to the second solution and stirring was maintained over 5 minutes. After this intimate mixing of the first and second solutions, 165 g solvent (50%) was removed at a pressure of 150 mbar and a temperature of 80° C. The removal of the solvent takes approximately 30 minutes. The removed solvent was replaced by 165 g pentanol. The viscosity of this solution is 13.5 MPa·s. The solution thus contains 50% by weight pentanol, 15% by weight decanol, 13% by weight ZrO2, 13% by weight acetylacetone and 6% by weight PEG. The remainder of 3% by weight is water and propanol. By reduction of the amount of pentanol added to the solution, the content of ZrO2 in the solution may be increased up to 22% by weight.
The thus prepared coating solution may be coated onto a wafer by spin-coating.
The still liquid layer of the coating on the wafer is dried at 200° C for 10 minutes. To dry the coating, the wafer is placed onto a hot plate at a temperature of 200° C. The thickness of the dry coating is 630 nm. Then, a very quick thermal anneal step (RTP) at 700° C. is applied. The temperature of 700° C. was achieved at a heating rate of 3.375 K/min within 12 seconds from room temperature. The wafer with the coating was maintained at this temperature for 60 seconds. The resulting coating is a crack free coating with a thickness of 257 nm. The refractive index of the annealed coating is 2.
In a second embodiment, 25 g propanol, 15 g polyethylene glycol 400, 40 g acetyl acetone and 25 g water are mixed to form a first solution. A second solution is prepared by mixing 65 g decanol and 200 g zirconium tetrapropoxide.
In an analogous way to the first embodiment, the two solutions are mixed and the solvent is removed from the mixture and replaced by pentanol. The spin-coating, drying and annealing of the layer is performed in the same manner as in the first embodiment.
In a third embodiment, a coating of Al2O3 is achieved. A fist solution is prepared by mixing 10 g isopropoxy ethanol, 12 g polyethylene glycol 600, 5.5 g water at a pH of 4 (adjusted by addition of nitric acid) and 15 g ethyl acetoacetate. The second solution contains 15 g isopropoxyethanol and 25 g aluminium sek-butoxide. After mixing the two solutions, the mixture is heated to 80° C. under reflux of the solvent. Then, the solvent is removed to obtain a solution of a concentration of Al2O3 of 10% by weight. The spin-coating, drying and annealing of the layer is performed in the same manner as in the first embodiment.
Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of this contribution to the art.
The additional use of yttrium propoxide in the preparation of the second solution results in a yttrium stabilised zirconia coating on a wafer. By adjusting the concentration of the solution before coating a substrate, the thickness of the layer can be influenced.
