Process of forming a curved profile on a semiconductor substrate
View Patent ↗A semiconductor substrate shaped to have a curved surface profile by anodization. Prior to being anodized, the substrate is finished with an anode pattern on its bottom surface so as to be consolidated into a unitary structure in which the anode pattern is precisely reproduced on the substrate. The anodization utilizes an electrolytic solution which etches out an oxidized portion as soon as it is formed as a result of the anodization, to thereby develop a porous layer in a pattern in match with the anode pattern. The anode pattern brings about an in-plane distribution of varying electric field intensity by which the porous layer develops into a shape complementary to a desired surface profile. Upon completion of the anodization, the curves surface is revealed on the surface of the substrate by etching out the porous layer and the anode pattern from the substrate.
1. A process of forming a curved profile on a semiconductor substrate, said process comprising the steps of:
preparing said semiconductor substrate having a top surface and a bottom surface opposed to each other;
forming an anode on said bottom surface,
placing said semiconductor substrate in an electrolyte solution;
flowing a current between said anode and a cathode within said solution to convert the top surface of said substrate to a varying depth from portions to portions, leaving a porous layer in said top surface; and
removing said porous layer from said substrate to leave a curved surface on said top surface,
wherein
said anode is deposited on said bottom surface to provide a consolidated structure and is configured to provide a predetermined distribution of an electric field intensity which varies from portion to portions of said substrate across said to and bottom surfaces of said substrate, thereby providing said porous layer having the varying depth in order to match the distribution of said electric field intensity,
wherein
said anode is formed partially on said bottom surface of the semiconductor substrate to provide a predetermined anode pattern which defines said predetermined distribution of said electric field intensity, and
wherein
said anode pattern is formed by the steps of:
depositing an electrically conductive layer on the bottom surface of said substrate;
removing a portion of said conductive layer to form a corresponding opening in said conductive layer.
2. A process of forming a curved profile on a semiconductor substrate, said process comprising the steps of:
preparing said semiconductor substrate having a top surface and a bottom surface opposed to each other;
forming an anode on said bottom surface;
placing said semiconductor substrate in an electrolyte solution having a cathode;
flowing a current between said anode and said cathode to convert the top surface of said substrate to a varying depth from portions to portions, leaving a porous layer in said top surface; and
removing said porous layer from said substrate to leave a curved surface on said top surface,
wherein said anode is deposited on said bottom surface to provide a consolidated structure and is configured to provide a predetermined distribution of an electric field intensity which varies from portion to portions of said substrate across said top and bottom surfaces of said substrate, thereby providing said porous layer having the varying depth to match the distribution of said electric field intensity, and
wherein said anode is formed on the bottom surface of said semiconductor substrate over a dielectric mask which is formed partially on said bottom surface to realize said predetermined distribution of said electric field intensity.
3. The process as set forth in claim 2 , wherein
said mask is formed by the steps of:
providing a dielectric layer on the entire bottom surface of said semiconductor substrate;
removing a portion of said dielectric layer to leave said mask on the bottom surface of said semiconductor substrate.
4. The process as set forth in claim 2 , wherein
said semiconductor substrate is made of silicon, and said dielectric layer is made of silicon oxide or silicon nitride.
5. A process of forming a curved profile on a semiconductor substrate, said process comprising the steps of:
preparing said semiconductor substrate having a top surface and a bottom surface opposed to each other;
forming an anode on said bottom surface;
placing said semiconductor substrate in an electrolyte solution having a cathode;
flowing a current between said anode and said cathode to convert the top surface of said substrate to a varying depth from portions to portions, leaving a porous layer in said top surface; and
removing said porous layer from said substrate to leave a curved surface on said top surface,
wherein said anode is deposited on said bottom surface to provide a consolidated structure and is configured to provide a predetermined distribution of an electric field intensity which varies from portion to portions of said substrate across said top and bottom surfaces of said substrate, thereby providing said porous layer having the varying depth to match the distribution of said electric field intensity,
said process further includes the steps of:
forming an additional anode partially on said top surface of said semiconductor substrate finished with said curved surface;
placing said semiconductor substrate in said electrolyte solution;
flowing a current between said additional anode and said cathode within said solution to convert the bottom surface of said substrate to a varying depth from portions to portions, leaving an additional porous layer in said bottom surface; and
removing said additional porous layer and said additional anode from said substrate to leave another curved surface on said bottom surface.
6. A process of forming a curved profile on a semiconductor substrate, said process comprising the steps of:
preparing said semiconductor substrate having a top surface and a bottom surface opposed to each other;
forming an anode on said bottom surface;
placing said semiconductor substrate in an electrolyte solution having a cathode;
flowing a current between said anode and said cathode to convert the top surface of said substrate to a varying depth from portions to portions, leaving a porous layer in said top surface; and
removing said porous layer from said substrate to leave a curved surface on said top surface,
wherein said anode is deposited on said bottom surface to provide a consolidated structure and is configured to provide a predetermined distribution of an electric field intensity which varies from portion to portions of said substrate across said top and bottom surfaces of said substrate, thereby providing said porous layer having the varying depth to match the distribution of said electric field intensity, and
wherein said current is regulated to decrease in a final stage of developing the porous layer.
7. The process as set forth in any one of claims 1 , 2 , 5 and 6 , wherein
said semiconductor substrate is made of silicon, and said electrolyte solution includes an aqueous solution of hydrogen fluoride.
8. The process as set forth in any one of claims 1 , 2 , 5 and 6 , wherein
said semiconductor substrate is made of a p-type semiconductor.
9. The process as set forth in any one of claims 1 , 2 , 5 and 6 , wherein
said substrate is selected to have a resistance of several ohm centimeters (Ω·cm) to several hundreds ohm centimeters (Ω·cm).