National Semiconductor Corporation

National Semiconductor Corportaion

Abul Ehsanul Kabir

Rashid Bashir

Francois Hebert

Process for the formation of epitaxial layers with controlled n-type dopant concentration depth profiles for use in NPN bipolar transistors. The process includes first providing a semiconductor substrate (e.g. a &lsqb;100&rsqb;-oriented silicon wafer substrate) with an n-type collector precursor region formed on its surface, followed by forming an n-type (e.g. phosphorous or arsenic) in-situ doped epitaxial layer of a thickness t on the n-type collector precursor region. Next, an undoped epitaxial layer of a thickness t is formed on the n-type in-situ doped epitaxial layer. A p-type (e.g. boron) in-situ doped epitaxial base layer is subsequently formed on the undoped epitaxial layer. The process can also include the sequential formation of an undoped Si Ge epitaxial layer and a p-type in-situ doped Si Ge epitaxial layer between the undoped epitaxial layer and the p-type in-situ doped epitaxial base layer. Accumulation of the n-type dopant concentration in p-type epitaxial layers (such as the p-type in-situ doped epitaxial base layer or the p-type in-situ doped Si Ge epitaxial layer) that are formed subsequent to a non-p-type epitaxial layer (such as the undoped epitaxial layer or undoped Si Ge epitaxial layer, respectively) is controlled by manipulating the thickness ratio of t to t , while keeping the thickness of N-layer fixed at t (i.e. t &plus;t ).

Method for controlling an N-type dopant concentration depth profile in bipolar transistor epitaxial layers

A method of making a pressure sensor or acoustic transducer having high sensitivity and reduced size. A thin sensing diaphragm is produced by growing a single crystal, highly doped silicon layer on a substrate using a chemical vapor deposition process. The diaphragm is incorporated into a pressure sensor or acoustic transducer which detects pressure variations by a change in the capacitance of a capacitor which includes the diaphragm as a movable member. The thin diaphragm produces a highly sensitive device which can be fabricated in a smaller size than sensors or transducers having thicker diaphragms.

High sensitivity micro-machined pressure sensors and acoustic transducers

Method of making high sensitivity micro-machined pressure sensors and

A process for anisotropically etching a tungsten silicide or tungsten polycide structure. If the silicide/polycide film has an overlying oxide layer, the insulating layer is removed by a gas mixture composed of CHF.sub.3 and C.sub.2 F.sub.6. The WSi.sub.x silicide layer is then etched in a reactive ion etch using a gas mixture formed from Cl.sub.2 and C.sub.2 F.sub.6, with sufficient O.sub.2 added to control polymer formation and prevent undercutting of the silicide. The polysilicon layer is then etched using a gas mixture formed from Cl.sub.2 and C.sub.2 F.sub.6. The result is a highly anisotropic etch process which preserves the critical dimension of the etched structures. The etch parameters may be varied to produce a tapered sidewall profile for use in the formation of butted contacts without the need for a contact mask.

Tungsten silicide/ tungsten polycide anisotropic dry etch process

A method of making a surface micro-machined accelerometer using a silicon-on-insulator (SOI) wafer structure. Both the acceleration (or deceleration) sensor and associated signal conditioning circuitry are monolithically fabricated on the same substrate. The top silicon layer of the SOI wafer is used as the sensing member, corresponding to the movable, common electrode of a differential capacitor pair. The components of the signal conditioning circuitry are fabricated in the SOI layer using standard SOI processing techniques. Because the top silicon layer is single crystal silicon, it does not suffer from the stress related warping common with polysilicon members. In addition, because the method described is compatible with bipolar, BiCMOS, or CMOS process flows, it may be used to fabricate faster and lower noise level signal conditioning circuitry than can be obtained using current techniques for making monolithic accelerometers.

Growing community of inventors

Sunnyvale, CA, United States of America

Abul Ehsanul Kabir