ETCH
Etch a layer.
SYNOPSIS
- etch
- [ silicon | oxide | oxynitr | nitride | poly | photores | alumin | gaas ]
[ left | right | start | continue | done | dry | all ]
[ x = n ] [ y = n ] [ thick = n ]
[ p1.x = n ] [ p1.y = n ] [ p2.x = n ] [ p2.y=n ]
[ file = string ]
DESCRIPTION
This statement provides an etching capability. Material is etched from the structure, and the underlying regions are marked as the "exposed" surface. The etch shape can be described in several different ways. The user must specify the final shape of the region to be etched, there is no capability at present to simulate the etch region shape.
- silicon, oxide, oxynitr, nitride, poly, photores, alumin, gaas
- The material to be etched. If a material is specified, only that material is etched even if other materials lie within the etch region. If no material is specified, all materials in the etch region are removed.
- left, right
- These provide the user with a quick means of doing trapezoidal shaped etches. The etch region is to the left / right of the line specified by the coordinates given in p1.x, p1.y and p2.x, p2.y.
- start, continue, done
- This allows the user to specify an arbitrarily complex region to be etched. Several lines can be combined to specify the several points that make up the region. See the examples.
- dry
- This parameter indicates that the etch shape should be a replica of the current surface, but straight down "thickness" microns.
- all
- All of the specified material is removed.
- x, y
- These parameters allow the user to specify point in the start / continue / done mode of etch region specification.
- p1.x, p1.y, p2.x, p2.y
- These parameters allow the specification of a line for left / right etching.
- thick
- This parameter allows specification of a thickness in microns for the dry etch type.
- file
- This string parameter specifies the name of a file that contains a string that contains the coordinates associated with the etched surface. This file could be generated using a topography simulator such as SAMPLE.
EXAMPLES
- etch nitride left p1.x = 0.5 p1.y=0.0 p2.x=0.5 p2.y=-1.0
- This command etches all the nitride left of a vertical line at 0.5.
- etch oxide start x=0.0 y=0.0
etch continue x=1.0 y=0.0
etch continue x=1.0 y=1.0
etch done x=0.0 y=1.0
- This etches the oxide in the square defined at (0,0), (1,0), (1,1), and (1,0).
- etch dry thick=0.1
- This etch will find the exposed surface, lower it straight down 0.1 mm and this line will be the new surface.
BUGS
Uses no physical model.
This code is sensitive to grid placement. It often helps to prepare the substrate by having a vertical grid line at the foot of the etched part of a deposited layer. Otherwise a fascinating ripped nylon mesh is generated. Contrary to what some commercial vendors maintain, the mesh produced is the best possible one to solve PDE's given the constraints. However, It is usually better to place a line at the etch locations.
The code currently does distinguish between surface and subsurface materials. "Etch silicon left p1.x=0.2" will etch the silicon to the left of 0.2 microns, including the substrate. Use the start / cont / done sequence to work around this.