Sheet Resistance in metal layer

For metal lines in the metal layers, why is Rs ( the sheet resistance, Ohms/square)
lower when the spacing between metal lines are larger?


For example, width = 0.2 um space = 2 um Rs=0.137 ohms/square
width = 0.2 um space = 0.2um Rs = 0.037 ohms/square


Thanks.

Sheet Resistance depends on the metal ...
I think there is no relation between metal spacing...
where did u get this information.
can u send it to me...

If u get the answer mail to me
shankar.mit@gmail.com

Thanks


Regards
Shankar

Hi,

When metal are closly spaced, the metals are under-etch, and thus Rs is lower. When the metal are spacing far apart, the metal are over-etch, and thus there are "less metal" per unit volume, and thus Rs is higher.

For example, in the "wee" effect, the metal is not rectangular, but has a slope on the side wall. I think 0.13um and below Rs have model this effect.

Regards,
Eng Han
www.eda-utilities.com

I think to overcome IR drop issues .

I agree with Shankar, there is no dependence on sheet resistance with metal spacing, normaly. You have to more specify your geometry. Your materials (substrate, metal) could play role in your experiments probabely.

BR
Dalicko

for 90nm or below, the sheet resistance will be different if the metal spacing and width are different, it's because of process variation like leeenghan pointed out, but for 0.13 and above, there are same.

i dont find any relationship between sheet resistance and metal spacing. sheet resistance is a property of that particular metal. it is fixed by foundry people. where as metal spacing is fixed by a physical design team of an ASIC

I think the reason is that the draw width not always the silicon width. When you tapeout your design, foundry will generate the lithography mask based on your layout firstly. But normmaly mask is different from your layout especially when OPC techonlogy is used to achieve better yield in 013u or below. Wire width adjustment is one of the result. Normmaly in litho process,50% pattern density will get best print result. So when width/space is 0.2u/2u in layout, the sizes on mask may be 0.3u/1.8u(depended on foundry). Then you see different Rs.

Added after 12 minutes:

leeenghan said:

Hi,

When metal are closly spaced, the metals are under-etch, and thus Rs is lower. When the metal are spacing far apart, the metal are over-etch, and thus there are "less metal" per unit volume, and thus Rs is higher.

For example, in the "wee" effect, the metal is not rectangular, but has a slope on the side wall. I think 0.13um and below Rs have model this effect.

Regards,
Eng Han
www.eda-utilities.com

Click to expand...

Hi Leeenghan:
WEE stands for Wire Edge Enlargement. Any effect (from manufacturing behaviors) that causes the real dimension not equal to the drawing is known as WEE. Bias, Dishing, Erosion, trapezoid shape are included.