Competitive Semiconductor Manufacturing (CSM) Program Excel Spreadsheet

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Competitive Semiconductor Manufacturing (CSM) Program Excel Spreadsheet

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This Excel workbook provides spreadsheet models for calculating revenues and costs of wafer fabrication. The intent is to provide the engineering analyst with the means to evaluate the economic impacts of changes to process and equipment, changes in the timing of when process or equipment are installed and qualified, changes in the time to ramp up die yield, and changes in manufacturing cycle time. Cash flows for both expenditures and revenues from fabrication are computed.

At present, the models assume the fabrication line operates a single process technology consisting of up to 300 major process steps utilizing up to 50 major types of process equipment. The user may compute costs and revenues for one of two basic cases: (1) wafer start volumes are pre-specified over time, or (2) equipment counts are pre-specified over time. In case (1), higher equipment efficiencies or reduced process times result in reduced investment in equipment and facilities to accommodate the pre-specified wafer starts. Higher yields in this case result in reduced investment costs as well as higher revenues for the given wafer start volumes. In case (2), higher equipment efficiencies or reduced process times result in higher wafer throughput for the given equipment set and hence both higher revenues and lower costs per wafer. Higher yields in this case result in higher die throughput for the given equipment set and both higher revienues and lower costs per wafer.

The calculation of fab expenses uses an enhanced version of SEMATECH's Cost-Resource Model (CRM). This model accounts for expenses of fab construction and operation. In order to compute wafer and die costs, all wafers and die produced over the life of the technology are burdened equally with capital expenses. Important differences compared to CRM include (1) staffing costs are computed for varying levels of fab automation, and (2) equipment performance is defined by the user in terms of theoretical throughput rates and capability for equipment efficiency (CEE), rather than average throughput rates and equipment availability as is traditionally done using CRM.

The calculation of fab revenues accounts for a user-specified decline of die prices over time. Delays for fab construction, process development and qualification, equipment installation and qualification, yield ramp, and manufacturing cycle time depress revenues obtained from the process technology over its life. Our Delay Cost Model expresses a die cost equivalent to the foregone revenues resulting from delays for process development and qualification, equipment installation and qualification, factory construction, time to ramp die yield, and manufacturing cycle time.

These models are explained in detail for the static wafer-starts case in the Competitive Semiconductor
Manufacturing (CSM) Program Report "Understanding Fab Economics", CSM-47, authored by Robert C.
Leachman, John Plummer and Nancy Sato-Misawa.

The important mathematical formulas also are displayed below.

This workbook is organized into seven spreadsheets to facilitate data input and visualization of results:

1. The "Introduction" spreadsheet briefly explains these cost models, summarizes the required input data and provides the formulae used in the calculations.

2. The "Input Data" spreadsheet includes shaded cells where the user defines the parameters in the cost models that can be modified to simulate different situations. These input parameters include unit costs of equipment, masks, staff and space; space consumption by equipment and staff; equipment efficiencies and lifetimes; wafer start rates or tool counts; yields and yield ramp times; process lifetime; factory life; time until process qualification; total cycle time; initial revenue per die (at start of process development), and rate of revenue decline.

The user must define additional more detailed input parameters for the Expense Model in the "Process Data" spreadsheet (discussed below).

3. The "Process Data" spreadsheet contains the detailed process data. Input parameters for each step of the process, including machine type, mask type (if any), theoretical wafer throughput for the step, direct and indirect material costs for the step, and actual step cycle times (or step batch size and handling time). These factors should be input in the appropriate shaded cell . The only allowable machine types and mask types are those appearing in the tables of machine types and mask types appearing on the "Input Data" spreadsheet. SEMATECH nomenclature for tool types and mask types is used. At present it is not possible to include more than 300 process steps or more than 50 tool types in the spreadsheet. It is possible to rename the tool types from the names given in the sample data. Renaming of a tool type is allowed in the "Tool Set" table (any name change in this list will be automatically updated in the "Expense Cost Calculation" and "Number of tools" spreadsheets). After modifying tool type names or other input data, be sure to press "control-n" to make the changes take effect.

4. The "Expense Cost Calculation" spreadsheet contains the model that calculates the fab expense per wafer. This spreadsheet uses the data in the "Input Data" spreadsheet and process data in the '"Process" spreadsheet. After modifying data in this spreadhseet, press "control-u" to update calculations of required numbers of tools. Cells shaded in 'blue' provide partial cost totals.

5. The "Total Cost" spreadsheet summarizes the results of cost and revenue calculations. First it presents a table of cost components (fab expenses) for four possible levels of automation and for two calculation assumptions (fractional and integer numbers of tools). Below this table is shown the number of die produced over the life of the factory (TD). This is used to calculate the Expense Cost per die and the Delay Cost per die which are shown next. Finally, the Total Cost per die (the sum of these two costs) is shown.

6. The "Number of Tools" spreadsheet presents a table of the calculated number of tools per type, for the two cases (fractional numbers of process tools and integer numbers of tools). It also shows the CEE and OEE factors.

7. The "Personnel Requirements" spreadsheet presents the caculated numbers of each personnel type, for each of the four alternative automation levels. One table corresponds to the case in which fractional tools are assumed and the other case corresponds to the assumption of integer tools.

8. The "Phased Capacity" spreadsheet presents the results for each of the capacity phases. The expense related cost table shows the expense in each phase. The revenue related cost table calculates the fab's real die output and revenue over product life. And the tool requirement table shows the number of tools and OEE in each phase.

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