#
Measuring Metal-Semiconductor Junction Contact Resistance

Using the Transmission Line Method (TLM)

#
Measuring Metal-Silicon Contact Resistance

Using the Transmission Line Method (TLM)

Expand All
Compress All
## First: Prepare the Junction

#### The first step in measuring the contact resistance of a metal-semiconductor junction is to deposit the metal on the semiconductor and

- pattern it so that you have lots of identical pads spaced varying distances apart.

#### This is an example of the metal pattern. Ideally, the pattern includes many rows of various pad sizes.

#### All the pads in any one row must be the same size, and the distances between pads must vary.

- After the metal is patterned, anneal according to your specific recipe.

## Second: Take measurements

#### The measurements required are simple IV curves. This is most easily done at a probe station,

- and using a parameter analyzer like our HP4145.

- Apply a voltage between several pairs of adjacent pads in a row, and measure the current flow. From this, calculate the
- resistance between those two pads (R=
^{V}/_{I}).

## Third: Calculate the Contact Resistance

#### As illustrated in the picture above, we can think of the total resistance between any two pads as the

- series combination of 3 resistors: metal to semiconductor, through the semiconductor, and back into metal.

- Since ohmic contacts are the same for both polarities, what we have is 2R
_{pad} + R_{semi}.

- In the limit where the distance between the pads approaches 0, R
_{semi} goes to 0 and what is left is 2R_{pad}

- Now that you have R
_{pad}, multiply that value by the area of the metal pads (in cm^{2}).

- That's all! You now know the contact resistance of your metal-semiconductor junction.

## So why is contact resistance so important?

#### 10^{-5}ohm-cm^{2} sounds pretty small to me...

- Consider that in the modern 90nm processes, the vias that contact the silicon have a contact area of about
- (.1um)
^{2}, or 10^{-8}cm^{2}. If your contact resistance is 10^{-5}ohm-cm^{2},
- that amounts to 1 kohm resistor just to get into the silicon. (plus another to get out!)

- A good contact resistance is on the order of 10
^{-7}ohm-cm^{2}.