Subsections

• 5.2.1 Semiconductor Process Flows in Development
• 5.2.2 Semiconductor Process Flows in Production
• 5.2.3 Diffusion Recipes
• 5.2.4 Other Recipes
• 5.2.5 Conclusions

5.2 Process Flow Interface

There are levels of integration differentiated by the status of the semiconductor process flow.

5.2.1 Semiconductor Process Flows in Development

Typically these flows are subject to frequent changes during development. Therefore the detailed flow descriptions are not implemented in the MES system until the process flow is frozen. Normally the flow description is tabulated in a simple file format (like MS EXCEL or ASCII-table) for reference during the process development phase. This system supports also the fast setup of short process sequences by simply typing the relevant process steps into an EXCEL-sheet. An example screen-shot of this format is given in Figure 5.1.

Figure 5.1: Screen-shot of EXCEL-Sheet description for research&development short-loops or semiconductor processes in development

By standardizing the flow description information for this stage, it is possible to define an automated converter which transfers the information identified in Section 4.2.2 into the abstracted semiconductor process simulator input language called SPR (Simple Process Representation) which is the input language for the commercial tool LIGAMENT. This tool generates the final process simulator input command files. This task is implemented via PERL-converter scripts. By using the SPR language it is possible to use various different process simulators even from different vendors like DIOS or SUPREM4.

5.2.2 Semiconductor Process Flows in Production

Once the semiconductor process flow is frozen and released, the MES system provides any input on the process flow which is necessary for process simulation. However this information must be reduced to the subset relevant for process simulation. This task is again performed with PERL-converter scripts and results in the table shown in Figure 5.1.

The overall scheme of conversion is outlined in Figure 5.2.

Figure 5.2: Conversion scheme for semiconductor process flow information

Two different data sources have been established for process flow conversion. First the MES database and second a simple ASCII table representation. Both sources are converted into a common reduced process flow information subset suitable to get a good, compact overview of the relevant process flow information. A second converter script is transferring this information into the simple process representation syntax as input to the TCAD framework tool LIGAMENT. This tool is able to generate different types of process simulator (e.g. DIOS or TSUPREM4) command files. After a full process flow simulation was performed the resulting structural and doping information can be used to generate a HTML documentation of every simulated process step.

5.2.3 Diffusion Recipes

One of the most important information to be provided to the process simulator in detail are the diffusion and oxidation recipes. These recipes are normally not stored in the MES but in a local diffusion furnace database. An example for such a system is the Supervisor Station from ASM. These systems have an internal format representation which has to be converted into a meta-syntax including the relevant information for the process simulator. An example of the original format of such a diffusion recipe is given in Listing 5.1. The listing shows the typical level of detail of a diffusion program. The program includes the analog output level and the alarm limits of the gas flow controllers, alarm patterns of the digital input channels and temperature and time settings of the diffusion program.

The compressed representation of the program shown in Listing 5.1 is obtained by the diffusion recipe converter as given in Listing 5.2 in the meta-syntax format. The first column gives the step number, the second the position of the quartz boat with the wafers. The third column shows the boat speed indicating how fast the boat is moved into and out of the quartz tube in the furnace. The next column shows the duration of the step. The following two columns give the target temperature and if the temperature has to be ramped with a certain ramp rate over the duration of the step. Finally the remaining rows give the targets for the gas flows set during the diffusion step.

The final simulator diffusion program is obtained by the meta-syntax to SPR converter as shown in Listing 5.3. This syntax is already very close to the process simulator syntax. However it does not include special model commands, specific to the process simulator. The syntax is targeted to give the generic inputs similar to every process simulator. Specific process simulator commands have to be defined with include statements.

The final simulator syntax is then generated by the TCAD environment.

5.2.4 Other Recipes

The conversion of the other recipes (implantation, etching and deposition) is quite straightforward. For implantation the database contains exactly the same information as needed by the process simulator. For isotropic etching and deposition only the etch rates and time are needed to simulate the change of geometry. The only not well developed interface is the anisotropic etch interface because of the unavailability of reliable and fast process simulators for this step. The equipment simulators needed for simulation of the effects of changes in the dry etch recipes on the overall etch profiles are still not available for routinely simulation tasks.

5.2.5 Conclusions

Because of the established system the turnaround time for setting up a process simulation flow has been reduced from days to hours. The probability of faults in the first setup of the process flow has been dramatically reduced. Especially the diffusion recipe conversion is inevitable to guarantee that a possible mismatch between simulation and measurements is not due to a wrong entered simulation recipe but because of poor calibration or new effects not covered by simulation.