Lucent Technologies Inc.

Agere Systems Guardian Corp.

Alcatel-lucent USA Inc.

Thi-Hong-Ha Vuong

Hans-Joachim Ludwig Gossmann

John M Khoury

Ya-Hong Xie

Maurice J Tarsia

Michel Ranjit Frei

Venugopal Gopinathan

Ali Eshraghi

John Michael Khoury

A method of fabricating an IC comprises the steps of: (a) forming trench isolation regions in a surface of a semiconductor body; and (b) forming a tub-tie region between at least one pair of the trench isolation regions (when viewed in cross-section) by a process that includes the following steps: (b1) forming a first photolithographic mask that covers and is in registration with the tub-tie region; (b2) implanting ions of a first conductivity-type to form a tub region adjacent the tub-tie region; (b3) removing the first mask; (b4) forming a second photolithographic mask that has an opening that exposes most of the underlying tub-tie region but overlaps a first peripheral section on one side of the tub-tie region; (b5) implanting ions to form a pedestal portion of a second conductivity-type within the tub-tie region; and (b6) implanting ions of the first conductivity-type at an acute (preferably non-zero) angle &minus;&oplus; with respect to the normal to the surface to the body so as to form a conductivity-type localized first zone that extends into the first peripheral section. In a preferred embodiment, the first conductivity-type tub of step (b2) and the second conductivity-type pedestal of step (b5) are formed by implanting ions at an acute (non-zero) angle &plus;&bgr; to the normal to the surface of the body. In another embodiment, between steps (b1) and (b3), the cap portion is angle-implanted to form a highly doped peripheral localized second zone of the second conductivity type located adjacent a different portion of one of said isolating regions. The second zone prevents any significant amount of charge build-up from taking place in the pedestal portion.

Integrated circuits with tub-ties and shallow trench isolation

The specification describes MOS transistors for analog functions which have increased output impedance. The increased output impedance is the result of reduced drain depletion width. This is accomplished without adverse effects on other device parameters. The MOS transistor structures have an implant added to the lightly doped drain (LDD) with a conductivity type opposite to that of the LDD and a doping level higher than the channel doping. The added implant confines the spread of the depletion layer and reduces its width. A relatively small confinement results in a significant increase in output impedance of the device, and a corresponding increase in transistor gain.

Analog MOSFET devices

A process for device fabrication in which transient enhanced diffusion (TED) is used to obtain a desired distribution of dopants in a crystalline substrate is disclosed. In the process, at least two dopants and a non-dopant are introduced into the same region of a substrate. The diffusion of the dopants in the substrate during a subsequent thermal anneal is affected by the non-dopant. The amount of non-dopant introduced into the substrate is selected to obtain, in conjunction with the subsequent thermal anneal, the desired distribution of dopants in the substrate. The concentration of the non-dopant is in the range of about 6.times.10.sup.16 atoms/cm.sup.3 to about 3.times.10.sup.21 atoms/cm.sup.3. The substrate is then annealed at a temperature in the range of about 700.degree. C. to about 950.degree. C. to obtain the desired dopant profile.

Process utilizing selective TED effect when forming devices with shallow

An IC comprises a tub of a first conductivity type, at least one transistor embedded in the tub, and a first pair of isolating regions defining therebetween a tub-tie region coupled to the tub. The tub-tie region comprises a cap portion of the first conductivity type and an underlying buried pedestal portion of a second conductivity type. At least a top section of the pedestal portion is surrounded by the cap portion so that a conducting path is formed between the cap portion and the tub. In a CMOS IC tub-ties of this design are provided for both NMOS and PMOS transistors. In a preferred embodiment, the cap portion of each tub-tie comprises a relatively heavily doped central section and more lightly doped peripheral sections, both of the same conductivity type. In accordance with another aspect of our invention, a reduced-mask-count CMOS IC process includes forming the isolating regions so that each has a protrusion which extends over the surface regions where the peripheral sections of the cap portion are to be formed. Then, a combination of ion implantation energies and concentrations, as well as suitable PR masking, in conjunction with the shape of the isolating regions, enables selective doping of the pedestal portion.

Method of making integrated circuits with tub-ties

Integrated circuits with tub-ties

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Thi-Hong-Ha Vuong