4.3.1 Implementation Details

The latest version of the etching tool uses a hybrid approach [77] to simulate the etching process. The discretization of the simulation domain is restricted to a thin layer around the attacked surface. The surface is discretized in two levels of (recursive) cell resolution, where a cell can either contain the material information or a regular grid of sub cells with a smaller resolution. Additionally to the cell information the topology of the simulation domain as it is stored in the WAFER-STATE-SERVER is used.

Upon start of the simulation the data are transferred from the persistent Wafer description into memory using the I/O layer of the WAFER-STATE-SERVER. Since the etching tool performs a lot point location operations the finite oct-tree data structures (as opposed to jump-and-walk, c. f. Section 3.4.3) are used to hold the data. Once the data are available in the WAFER-STATE-SERVER data structures the cellular discretization process takes place in the following manner.

1. The surface to attack is extracted from the WAFER-STATE-SERVER.

2. Around each point of the extracted surface a refined cell is created. The material type of a cell is thereby determined via the point location operation of the WAFER-STATE-SERVER.

3. The so-called structuring elements are determined depending on the material type. Structuring elements are used to model different etching rates (for different materials) [78].

Fig. 4.14 illustrates the discretization process.

Figure 4.14: Illustration of cellular discretization process. The cells at the attacked surface (refined cells) contain sub cells of smaller size. The other cells directly contain the material information determined via the WAFER-STATE-SERVER.

Once the discretization is finished the topography simulation is initiated. Thereby, the structural elements are applied to the simulation domain. Cells that are covered by the smallest possible rectangular prism that surrounds a structural element are defined. Defining means that the cell is allocated and assigned the material determined via the WAFER-STATE-SERVER. The actual cellular simulation algorithm is quite similar to traditional algorithms with the following exceptions.

• Memory allocation for cells is deferred until a cell is actually attacked.

• Cells that are close to the attacked surface are refined.

• As the etch front moves, refined cells move away from the front. If all refined cells of their corresponding unrefined counterpart contain only one material type they are converted back to the unrefined cell and the memory associated with the refined cells is freed.

Subsections

• 4.3.1.1 Post Processing

2003-03-27