Silicon diaphragm piezoresistive pressure sensor and fabrication method of the same

A process or method for fabricating a pressure sensor comprising:

• forming a buried layer in a substrate with a cavity material that can be later altered and, removed without affecting surrounding structure said substrate having a planar surface extending over said buried layer;
• overlaying said buried layer with a diaphragm;
• forming a plurality of connections comprising cavity material from the substrate surface through said diaphragm to said buried layer;
• removing the cavity material from both the buried layer and connections without damaging or altering the surrounding structure to simultaneously form a cavity under the diaphragm and trenches connecting the cavity to the substrate surface;
• creating an air tight seal around the cavity by filling the trenches with a sealing material;
• and
• placing on an outside surface of the diaphragm and the substrate, means to detect changes of pressure between the sealed cavity and the outside surface.

A process or method for fabricating a pressure sensor comprising:

• using as a base a semiconductor substrate;
• forming a low resistance layer on one side of the semiconductor substrate, under a predetermined diaphragm region;
• forming a diaphragm in the predetermined diaphragm region;
• forming one or more trenches located at an edge of the predetermined diaphragm region through the diaphragm to the low resistance layer under the diaphragm;
• filling the trenches with a low resistance material;
• converting the low resistance material in the trenches and the low resistance layer under the diaphragm to porous silicon by anodization;
• removing the porous silicon by etching, to produce a chamber under the diaphragm;
• filling the trenches with a sealing material to form a pressure reference chamber;
• and
• forming means on an exposed surface of the substrate and diaphragm to detect changes in pressure with the pressure reference chamber.

A process or method for fabricating a pressure sensor comprising:

• using a semiconductor substrate as a base;
• forming a chamber on the top of the semiconductor substrate;
• filling the chamber with a layer of low resistance material;
• forming a diaphragm over the layer of low resistance material;
• forming at an edge of the diaphragm one or more trenches which extend from the surface of the substrate and diaphragm down to the layer of low resistance material under the diaphragm;
• filling the trenches with low resistance material;
• anodizing the low resistance material in the layer under the diaphragm and in the trenches to produce porous silicon;
• removing the porous silicon beneath the diaphragm and in the trenches;
• filling the trenches with a sealing material to form a sealed buried reference chamber;
• and
• forming means on an exterior surface of the substrate and the diaphragm to detect changes in pressure between the buried reference chamber and the exterior surface.

A process or method for fabricating a pressure sensor comprising:

• using a semiconductor substrate as a base;
• defining a nitrogen ion implantation region on the top of the semiconductor substrate;
• implanting nitrogen ions to a specific depth in the nitrogen implantation region to form a diaphragm;
• defining a proton implantation region on the top of the semiconductor substrate which encompasses the diaphragm as well as one or more trench regions adjacent to the diaphragm;
• implanting protons in the proton implantation region to a predetermined depth in the semiconductor substrate, the proton implantation region extending below the diaphragm as well as into the adjacent trench regions;
• annealing the semiconductor substrate to form a low resistance material in the proton implantation region beneath the diaphragm and in the trench regions;
• anodizing the low resistance material to produce porous silicon;
• removing the porous silicon to form a chamber beneath the diaphragm and one or more trenches in the trench regions connected to said chamber;
• filling the trenches to seal the chamber beneath the diaphragm and form a sealed reference chamber;
• and
• forming means on the exterior of the diaphragm and substrate to detect changes in pressure between the chamber and the exterior surface.

A process or method for fabricating a pressure sensor comprising:

• using an N-type silicon semiconductor substrate as a base;
• forming a silicon dioxide layer on one surface of the N-type silicon substrate;
• photoetching a pattern on to the silicon dioxide layer to define an ion implantation region;
• removing the silicon dioxide in the defined ion implantation region;
• implanting arsenic ions using the pattern of silicon dioxide layer as a mask;
• thermally annealing the implanted region to form a low resistance layer;
• removing the remainder of the silicon dioxide from the surface of the substrate;
• forming a lightly doped N-type silicon epitaxial layer to serve as a diaphragm on the surface of the substrate above the low resistance layer, the epitaxial layer being formed by vapor phase epitaxy;
• forming a second layer of silicon dioxide on top of the surface of the substrate and the epitaxial layer;
• defining a first ion implantation region on the second silicon dioxide layer, said defined first implantation region being at the edge of the diaphragm;
• removing the silicon dioxide in the first defined ion implantation region;
• implanting phosphorous ions in the first ion implantation region using the second silicon dioxide layer as a mask;
• annealing of the phosphorous ion implantation region to form low resistance material filled trenches which run from the surface of the substrate at the edge of the diaphragm to the low resistance layer beneath the diaphragm;
• reforming the silicon dioxide layer over the first ion implantation region;
• defining one or more second ion implantation regions on the diaphragm;
• implanting boron ions in the second implantation regions to form strain gages;
• forming a silicon nitrate layer over the entire surface;
• forming a high resistance layer of polysilicon over the layer of silicon nitrate;
• photoetching a pattern aligned with the first ion implantation region to expose the top of the trenches filled with the low resistance material;
• converting the low resistance material in the trenches and the low resistance layer under the diaphragm to porous silicon by anodization;
• removing the porous silicon in the trenches and beneath the diaphragm by etching, to form a chamber beneath the diaphragm;
• filling the trenches with silicon to form a sealed chamber beneath the diaphragm;
• insulating the top of the substrate and diaphragm;
• and
• forming means to make contact between the strain gauges and other circuit elements on the diaphragm and substrate to form contacts off the diaphragm and substrate.

A process or method for fabricating a pressure sensor comprising:

• using an N-type silicon substrate as a base;
• forming a first silicon dioxide layer on a top surface of the N-type silicon substrate;
• photoetching a pattern on the first silicon dioxide layer to define a boron ion implantation region;
• removing the silicon dioxide in the defined boron ion implantation region;
• implanting boron ions in the defined boron ion implantation region using the patterned silicon dioxide layer as a mask;
• annealing the silicon substrate to form piezoresistive elements in the boron ion implantation region;
• forming a thick photoresist layer on the top of the surface of the N-type silicon substrate;
• forming a pattern on top of the thick photoresist layer for a nitrogen implantation region by photography;
• using the patterned photoresist layer as a mask for implantation of nitrogen ions, implanting nitrogen ions in the defined nitrogen ion implantation region, said nitrogen ion implantation region serving as a diaphragm;
• defining a proton implantation region on top of the N-type silicon substrate by enlarging the size of the nitrogen ion implantation region to include trench regions adjacent to the edge of the nitrogen implantation region, said step being done by enlarging the photoresist mask;
• implanting protons in the proton implantation region, said proton implantation region extending below the diaphragm;
• annealing the proton implantation region at a temperature of 400.degree.-500.degree. C. in dry nitrogen to form a low resistance layer beneath the diaphragm and one or more low resistance material filled trenches adjacent to the diaphragm in the trench regions;
• removing the remainder of the first silicon dioxide layer;
• forming on top of the substrate a second silicon dioxide layer;
• forming over the second silicon dioxide layer a layer of silicon nitride;
• forming over the layer of silicon nitride a layer of polysilicon;
• forming a pattern on top of the polysilicon layer which is aligned with the trenches adjacent to the diaphragm, and removing in the pattern region successive layers of polysilicon, silicon nitride and silicon dioxide to expose the tops of the trenches;
• converting the low resistance material in the trenches and the low resistance material beneath the diaphragm into porous silicon by anodization;
• removing the porous silicon by etching to form a chamber beneath the diaphragm;
• filling the trenches with silicon to seal the chamber beneath the diaphragm and form a buried reference chamber;
• removing unnecessary parts of the polysilicon layer;
• removing the remainder of the portions of the silicon nitride and silicon dioxide layers from the top of the substrate;
• forming an insulating layer over the top of the substrate surface;
• forming contact holes by photoetching to provide contact to the strain gauges formed on the surface of the diaphragm;
• forming a passivation layer over the top of the silicon substrate and diaphragm;
• and
• forming bonding pads to the contact holes.