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Design >> Analog Design >> What is off-axis drain-source implantation?
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Message started by ywguo on Mar 20^th, 2007, 7:53pm

Title: What is off-axis drain-source implantation?
Post by ywguo on Mar 20^th, 2007, 7:53pm

Hi, Guys,

I am studying Yasuyuki Nakamura's "A 10-b 70-MS/s CMOS D/A Converter" in JSSC, April, 1991. It claims that A differential linearity error caused by an off-axis drain-source implantation is reduced by the layout technique of current sources. Any explanation of the off-axis drain-source implantation is welcome.

Thanks
Yawei

Title: Re: What is off-axis drain-source implantation?
Post by Croaker on Mar 21^st, 2007, 7:06am

I think it means the implanting of the S/D is happening at an angle.

Title: Re: What is off-axis drain-source implantation?
Post by ywguo on Mar 21^st, 2007, 6:33pm

Thanks. Does it mean the implantation is not orthogonal to the wafer?

One more question, is that technique applied in DSM CMOS technology like 0.18um and nano technology like 90nm and 65nm?

Thanks
Yawei

Title: Re: What is off-axis drain-source implantation?
Post by sheldon on Mar 21^st, 2007, 6:47pm

Yawei,

First, implantation is used to precisely control the doping of Silicon.
The knobs for controlling implanation are dose, concentration, and the
energy, depth. The challenge is that Silicon is a crystal and the implanted
dopant tends to find the lattice and travel much father than intended. The
dopant stops when it "hits" something. To prevent this phenomena, process
engineers use several approaches, including off-axis implantation. By
implanting "across" the lattice, the likelyhood of hitting the lattice increases
and the depth of the implant can be more precisely controlled. To be honest,
I have never heard of anybody actually intentionally implanting on-axis. BTW,
other mtehods include scattering oxide and amorphization. Scattering oxides
are usually thin oxide layers that tend to randomly scatter the dopant.
Amorphization, sorry the spelling may be incorrect, is done by hurling
something big and neutral, usually Aragon, at the Silicon prior to the
implant. The Aragon, turns the Silicon matrix into amorphous mush so
Silicon scatters the dopant.

Best Regards,

Sheldon

Title: Re: What is off-axis drain-source implantation?
Post by ywguo on Mar 21^st, 2007, 6:59pm

Hi, Sheldon,

So clear. Thanks.