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Use Of Si-Ge Alloys For Thin Resistors

IP.com Disclosure Number: IPCOM000048781D
Original Publication Date: 1982-Mar-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Campbell, DR: AUTHOR [+2]

Abstract

In lightly doped polysilicon needed for high resistance structures, the resistivity principally arises from majority carrier barriers which occur at the grain boundaries. The resistivity takes the form, p approximately e/E/b//kT/, where E(b) is energy barrier created by band bending at the boundries. The temperature coefficient of resistance, (TCR), thus has a strong (exponential) dependence on E(b), and even a relatively small reduction in E(b) could substantially reduce the TCR. Diminishing the magnitude and consequently the influence of E will result in resistivities which are more controllable; i.e., resistivities will depend more on intentional doping and less on grain size. The quantity E(b) is related to the band gap E(g), such that lowering E(g) will also lower E(b).

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Use Of Si-Ge Alloys For Thin Resistors

In lightly doped polysilicon needed for high resistance structures, the resistivity principally arises from majority carrier barriers which occur at the grain boundaries. The resistivity takes the form, p approximately e/E/b//kT/, where E(b) is energy barrier created by band bending at the boundries. The temperature coefficient of resistance, (TCR), thus has a strong (exponential) dependence on E(b), and even a relatively small reduction in E(b) could substantially reduce the TCR. Diminishing the magnitude and consequently the influence of E will result in resistivities which are more controllable; i.e., resistivities will depend more on intentional doping and less on grain size. The quantity E(b) is related to the band gap E(g), such that lowering E(g) will also lower E(b). It is only necessary and advantageous, to lower E(g) locally at the grain boundary. A mechanism for accomplishing this is grain boundary segregation. That is, annealing a Si-rich alloy of Si and Ge will cause the larger Ge atom to segregate into the boundary region, thus enriching the Ge content there and consequently lower the local value of E (g).

Alloy films of Si and Ge can be prepared by cosputtering or co-evaporation. Doping can be accomplished by conventional methods, such as ion implantation. Normal processing steps for polysilicon should be applicable since the overall Ge content in the film (i.e., in the interior of the grains) can be relativel...