DEPOSIT

In this step a material layer is deposited onto an existing structure. The amount of material deposited is equal to the value specified by the THICKNESS key. The deposition can be an overall deposition or a selective one restricted to the rectangular window specified by the START and END keywords. Selective deposition can also be specified by naming the material onto which the layer will be deposited with the HETERO key. The layer can be doped with the specified ELEMENT either uniformly by specifying the CONCENTRATION, or with a exponentially (or linearly) varying profile by also specifying SURFACE (and LINEAR).

• MATERIAL=(s)
• THICKNESS=(r)
• [XDEL=(s)]
• [START=(r[,r])]
• [END=(r[,r])]
• [HETERO=(s)]
• [ELEMENT=(s)]
• [CONCENTRATION=(r)]
• [SURFACE=(s)]
• [LINEAR=(i)]
• [TYPE=(s)]
• [MASK=(s)]
• [XMOLE=(s)]
• [YMOLE=(s)]
• [ZIPPER=(l)]

The following list itemizes the valid keywords, their units, and their meaning.

MATERIAL: [string]

material to be deposited. Possible materials are found in the database in library/physics. Commonly used materials are "nitride", "oxide", "poly", "resist", and "shipley". Note that "resist" is opaque to all implants, whereas ion implant penetration through "shipley" photoresist is a function of ion species, ion energy and Shipley material thickness.

THICKNESS: [real or real array (microns)]

thickness of the layer to be deposited. Several thickness values can be specified in real array format (e.g., ``0.0,0.1'') in order to have greater control over the vertical grid spacing. In this sense, the THICKNESS keyword plays a similar role as the XLOC keyword for the GRID command (see the section on the GRID command for more detailed information).

XDEL: [real or real array (microns)]

grid spacing in the layer to be deposited. It is possible to specify the thickness and the spacing as arrays; the thickness should start at zero and increase to the total thickness while the spacing should have the same number of values and indicate the spacing at each thickness value. A spacing of zero indicates a ``don't care'' condition. This XDEL plays a similar role as the XDEL of the GRID command, but with an important difference in convention. For the GRID command, the first XDEL grid spacing value refers to the top of the initial structure; however, for the DEPOSIT command, the first XDEL refers to the bottom of the deposited layer.

If XDEL is not specified, the deposited layer will have a spacing given by the database parameter library/physics/M/default.tdel, where M is the material deposited. If that parameter does not exist, the layer will have one grid spacing. For insulators, it does not exist; for semiconductors, the parameter is currently 0.02 microns.

START: [real or real array (microns)]

coordinates of one corner of the rectangular window in which to deposit. If only one coordinate is given, a stripe parallel to the z-axis will be deposited. If START is not set, the beginning of the simulation domained is assumed.

END: [real or real array (microns)]

coordinates of the opposite corner of the rectangular window in which to deposit. If only one coordinate is given, a stripe parallel to the z-axis will be deposited. If END is not set, the end of the simulation domained is assumed.

HETERO: [string]

name of the material to selectively deposit on.

ELEMENT: [string]

impurity element in the layer. If ELEMENT is not set, the layer is assumed to be intrinsic. CONCENTRATION must also be set if ELEMENT is specified.

CONCENTRATION: [real ( )]

concentration of ELEMENT in the layer. ELEMENT must also be specified. If SURFACE is specified, CONCENTRATION refers to the concentration in the bulk.

SURFACE: [real ( )]

a nonuniform doping profile, this is the concentration at the surface of the layer. ELEMENT and CONCENTRATION (referring to the concentration at the bulk side) must also be specified. The profile will vary exponentially between SURFACE and CONCENTRATION unless LINEAR is set.

LINEAR: [logical]

set to 1, the doping profile will vary linearly between SURFACE and CONCENTRATION. If set to 0 or not set, the doping profile will vary exponentially. ELEMENT, CONCENTRATION and SURFACE must also be specified.

MASK: [string]

parameter is a file in which to find mask data. The deposit will occur only inside the rectangles described in the mask datafile, unless the INVERT parameter is specified. At present the maskfile format is one line per rectangle, each line formatted as (y-start) (y-end) (z-start) (z-end) box

TYPE: [string]

model to be used for deposition. Currently there are two models: default and smooth. The default model deposits exactly THICK microns of material above each point on the exposed surface. The smooth model uses an isotropic deposition model to calculate the thickness above each point. In the case of a planar surface, the two models give the same result. When there are steps on the surface, the smooth model causes thicker oxide to be deposit in the shadows of the steps. This provides a simple way to define sidewall spacers.

ZIPPER [logical]

depositing materials which are laterally adjacent, the last of the deposit commands must contain this zipper option. The zipper algorithm searches for nodes in adjacent materials which have the same location, and adds this information to the geometry description. Note that the deposition of two laterally adjacent materials must be done with identical vertical grid spacing. (See poly spacer example below.)

XMOLE [real]

``xmole'' (stochiometry) for deposited layer. Value must be between 0.0 and 1.0.

YMOLE [real]

``ymole'' (stochiometry) for deposited layer. Value must be between 0.0 and 1.0.

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Examples:

Blanket deposition
deposit material=nitride thick=0.05 xdel=0.005

Local deposition in 2D
deposit material=poly start=0 end=1.0 thick=0.5 xdel=0.05

Local deposition in 3D
deposit material=poly start=0,0 end=1.0,0.5 thick=0,0.5 xdel=0.01,0.1
+ elem=arsenic concen=1e16

Poly gate with oxide spacer:

# Gate Oxide:
deposit mat=oxide thick=0.002 xdel=0.002
# Poly Gate:
deposit mat=poly  start=-0.03 end=0.03  thick=0.0,0.1 xdel=0.002,0.05
# Left Oxide Spacer:
deposit mat=oxide start=-0.05 end=-0.03 thick=0.0,0.1 xdel=0.002,0.05
# Right Oxide Spacer:
deposit mat=oxide start=0.03  end=0.05  thick=0.0,0.1 xdel=0.002,0.05 zipper

Less Used DEPOSIT Keywords

NO-EPI-COMPLAINT [logical]

off warning message that suitable deposition surface could not be found.

CMODEL

- should be removed.