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The Process flow for fabrication the resister IC

Step I: The Beginning-Choosing a substrate

Before actual wafer fabrication, we must choose the starting wafers. The major choices are the type (N or P), resistivity, and orientation.

In most IC circuits, the substrate has a resistivity in the range of 25-50cm, which corresponds to a doping level on the order of 1015cm-3.

The other major parameter we need to specify in the starting substrate is

the crystal orientation. Virtually all modern silicon integrated circuits are manufactured today from wafer with a (100) surface orientation. The principal reason for this is that the properties of Si/Sio2 interface are significantly better when a (100) crystal is used.

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Lecture # 2

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CMOS Process Flow

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Cross section of the final CMOS integrated circuit.

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3SiH4+4NH3Si3N4+12H2

Silicon nitride form a barrier against the impurities moving toward the Si surface.

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Photolithography

• In order to transfer resister information from the design to the wafer, a process known as photolithography is used.

• For this process a material known as photoresist is first spread on the wafer. It is usually baked at about 100oC in order to drive off

• solvants from the layer (photolithographic process will be covered in chapter 5 through.

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Lecture # 2

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Open windows for thick oxidation

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Bird’s beak

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P Well Formation

1016 -1017 cm-3

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N Well Formation

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High temperature Drive-In

2-3 micron

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NMOS gate formation and adjusting VTH

The single most important parameter in the both NMOS and PMOS devices is the threshold voltage

To adjust VTH , two terms that are important are the doping concentration and the oxide capacitance.

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PMOS Gate Formation

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Why oxide layer is stripped and then regrown?

Regrown of gate oxide

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SiH4 Si+2H2

Low ploy sheet resistivity and low gate resistance is required.

Deposition of polysilicon layer

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Selective Etching: to locate MOS gates

Selectivity and anisotropy are big deal hare

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Tip or extension (LDD) formation

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Tip or extension (LDD) formation

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Sidewall Spacer fabrication

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Aniostropic Etching

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Formation of NMOS source and Drain region

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Formation of PMOS source and Drain region

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High temperature Drive-In

TED is a big issue hare!

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Contact and local Interconnect formation

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TiSi2

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Multilevel metal formation

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Basic NMOS process flowchart.8

Lecture # 2

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Basic bipolar process flowchart.9

Lecture # 2