LAM 9400/Processes/POLY ETCH 2

About this Process
Process Details
Equipment	LAM 9400
Technology	RIE
Material	Poly
Mask Materials	PR
Gases Used	HBr, He
Date Created	2008

POLY_ETCH_2 is a recipe designed for etching polysilicon in the LAM 9400. It works well for etching polysilicon and N-type single crystal silicon, where as with P-type wafers it can cause micro-pitting. This recipe first has a more aggressive Cl₂ breakthrough to get through native oxide layers, then the main etch is HBr which produces a very straight sidewall and is useful for stopping on oxide.

Due to the nature of this recipe a significant amount of Si must be exposed during the etch in order for it to run, therefore it is recommended to us a plain Si carrier wafer when etching 100 mm wafers

Parameters

Parameter	Breakthrough	Etch
Pressure	100 mTorr	12 mTorr
TCP Power	300 W	500 W
Bias Power	50 W	30 W
Cl2 Flow	100 sccm	0 sccm
C4F8 Flow	0 sccm	100 sccm
He Flow	0 sccm	100 sccm
HBr	0 sccm	100 sccm

Capabilities

Etch Rate

• Blanket Si Etch: 1350 Å/min
  • Wafers with a small % open area may etch faster

Limitations

The recipe is known to fail if there isn't enough exposed silicon to etch. It is highly recommended to use a plain Si carrier wafer for that reason. Also the recipe has difficulty stabilizing, so very short etches (under 10 seconds) may be unreliable.

P-Type Pitting

When the poly etch is run with a P-Type Si wafer micro-pitting can be seen. The two images below show a P and N type wafer after 5 minutes of etching. A similar affect can be seen when wet etching P-Type wafers with bromine when a voltage is applied to the wafer as per this paper.

• 

  A pure HBr etch can cause micro-pitting on P-Type wafers

• 

  A pure HBr etch doesn't cause micro-pitting on N-Type wafers

Temporary Testing

Increase	Pressure	TCP	Bias	CF4
Oxide Etch Rate
Uniformity
Poly to Oxide Sel.
Poly Etch Rate