METHOD OF FABRICATING SEMICONDUCTOR-BASED POROUS STRUCTURE
First Claim
1. A fabrication method of making coherent pores in a semiconductor substrate, the fabrication method, comprising:
- heavily doping a back surface of a semiconductor substrate via dopant diffusion;
passivating a front surface of the semiconductor substrate with silicon nitride via low pressure chemical vapor deposition (LPCVD);
forming a photoresist pattern on the front surface of the semiconductor substrate through a photolithography process;
wherein the photoresist pattern determines the regions of the semiconductor substrate where pores are to be formed;
selectively etching the silicon nitride via reactive ion etching (RIE) to remove silicon nitride from regions of the semiconductor where pores are to be formed;
depositing a metallic layer on the back surface of the semiconductor substrate and removing the metallic layer from regions of the semiconductor where pores are to be formed via liftoff photolithography;
anisotropically etching the regions of the semiconductor substrate where pores are to be formed from the front surface with an aqueous solution;
applying a bias between the semiconductor substrate and an electrolyte in which the semiconductor substrate is immersed;
illuminating the back surface of the semiconductor substrate; and
providing energy to dislodge hydrogen bubbles from the pores formed during etching of the semiconductor substrate by the electrolyte
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Abstract
The present invention is a MEMS-based two-phase LHP (loop heat pipe) and CPL (capillary pumped loop) using semiconductor grade silicon and microlithographic/anisotrophic etching techniques to achieve a planar configuration. The principal working material is silicon (and compatible borosilicate glass where necessary), particularly compatible with the cooling needs for electronic and computer chips and package cooling. The microloop heat pipes (μLHP™) utilize cutting edge microfabrication techniques. The device has no pump or moving parts, and is capable of moving heat at high power densities, using revolutionary coherent porous silicon (CPS) wicks. The CPS wicks minimize packaging thermal mismatch stress and improves strength-to-weight ratio. Also burst-through pressures can be controlled as the diameter of the coherent pores can be controlled on a sub-micron scale. The two phase planar operation provides extremely low specific thermal resistance (20-60w/cm2). The operation is dependent upon a unique micropatterened CPS wick which contains up to millions per square centimeter of stacked uniform micro-through-capillaries in semiconductor-grade silicon, which serve as the capillary “engine,” as opposed to the stochastic distribution of pores in the typical heat pipe wick. As with all heat pipes, cooling occurs by virtue of the extraction of heat by the latent heat of phase change of the operating fluid into vapor.
In the cooling of a laptop computer processor the device could be attached to the processor during laptop assembly. Consistent with efforts to miniaturize electronics components, the current invention can be directly integrated with a unpackaged chip. For applications requiring larger cooling surface areas, the planar evaporators can be spread out in a matrix and integrally connected through properly sized manifold systems.
87 Citations
25 Claims
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1. A fabrication method of making coherent pores in a semiconductor substrate, the fabrication method, comprising:
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heavily doping a back surface of a semiconductor substrate via dopant diffusion; passivating a front surface of the semiconductor substrate with silicon nitride via low pressure chemical vapor deposition (LPCVD); forming a photoresist pattern on the front surface of the semiconductor substrate through a photolithography process;
wherein the photoresist pattern determines the regions of the semiconductor substrate where pores are to be formed;selectively etching the silicon nitride via reactive ion etching (RIE) to remove silicon nitride from regions of the semiconductor where pores are to be formed; depositing a metallic layer on the back surface of the semiconductor substrate and removing the metallic layer from regions of the semiconductor where pores are to be formed via liftoff photolithography; anisotropically etching the regions of the semiconductor substrate where pores are to be formed from the front surface with an aqueous solution; applying a bias between the semiconductor substrate and an electrolyte in which the semiconductor substrate is immersed; illuminating the back surface of the semiconductor substrate; and providing energy to dislodge hydrogen bubbles from the pores formed during etching of the semiconductor substrate by the electrolyte - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of etching a semiconductor substrate to form pores, the etching method, comprising:
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applying a voltage potential between the semiconductor substrate and an electrolyte;
wherein the semiconductor substrate is immersed in the electrolyte;illuminating a back surface of the semiconductor substrate to create electron-hole pairs in the semiconductor substrate; and providing energy to dislodge hydrogen bubbles from the pores formed during etching of the semiconductor substrate by the electrolyte. - View Dependent Claims (14, 15, 16, 17, 18)
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19. A method of fabricating a microfluidics assembly, the fabrication method, comprising:
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cleaning a surface of a substrate having an orifice where a connection to a metallic channel is to be made; evaporating a first metallic seed layer on the surface; evaporating a second metallic layer on the first metallic seed layer; substantially aligning the metallic channel to the orifice of the substrate; and applying heat and solder material to a junction of the metallic channel and the orifice of the substrate and securing the interconnect. - View Dependent Claims (20, 21, 22, 23)
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24. A method of fabricating a microfluidics assembly, the fabrication method, comprising:
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cleaning a surface of a substrate having an orifice where a connection to a glass channel is to be made; coating an external surface of the glass channel with a first conductive seed layer; coating the first conductive seed layer with a second metallic layer; evaporating a first conductive seed layer on the surface of the substrate; evaporating a second conductive layer on the first conductive seed layer; substantially aligning the channel to the orifice of the substrate; and applying heat to a junction of the glass channel to the orifice of the substrate and securing the interconnect. - View Dependent Claims (25)
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Specification