8.25 Sspd_chapter 6_part 7_introduction to athena 6_process simulator  (Page 7/7)

Two important points have now been established:

1. For sound device physics reasons, most RTA processes consist of high temperature, short duration anneals.

2. Damage-enhanced diffusion will only occur for a few seconds at typical RTA temperatures.

For accurate simulation of RTA, the second point is most important and often wrongly neglected. Suppose an RTA consists of a 10 second ramp up to 1000°C, followed by a 20 second anneal and a 10 second cool down. From the second point, it is apparent that most of the Total Dopant Diffusion would have taken place during the Ramp Up Phase of the RTA.

Therefore, always model the temperature ramp up accurately when simulating an RTA process. In most cases, the ramp down can be neglected, since all the diffusion has already taken place at the beginning when the silicon was still damaged.

7.7.9: Simulating Oxidation

It has already been stated that the pull down menu for simulating oxidations is the same as that for simulating inert diffusions described in the “Simulating Diffusion” Section on page 2-37. See this section for advice on selecting the appropriate pull down menu from DECKBUILD.

The default method for oxidation is Compress. In SSUPREM4 examples there are a number of examples which illustrate the use of different models for different processes and structures.

In our previous example described in the “Simulating Diffusion” Section on page 2-37, if the next temperature step is going to be at a constant temperature of 1000°C in dry O2 with 3% of HCL in the ambient, select the Dry O2 box and set HCL% equal to 3 in the Ambient section of the Diffuse menu. The following input file fragment will appear:

# GATE OXIDE

DIFFUSE TIME=60 TEMP=1000 DRYO2 PRESS=1.00 HCL.PC=3

If the ambient is a mixture consisting of more than one oxidant, the total oxidation rate will depend on the combined effect of all species in the ambient. To specify the contents of the ambient mixture, select the Gas Flow button in the Ambient section and an additional ATHENA Gas Flow Properties Menu (Figure 7-38) will appear.

Figure 7.38. ATHENA Gas Flow Properties

If the Gas Flow components are selected, as shown in Figure 7.38, the following statement will be generated:

# GATE OXIDE

DIFFUSE TIME=60 TEMP=1000 F.H2O=5.3 F.HCL=0.06 F.O2=8.0 \ PRESS=1.00

One or several impurities can be present in the ambient. To set ambient in the Impurity Concentration section of the ATHENA Diffuse Menu (See Figure 7-37), check the corresponding checkboxes, and set the values using sliders and the Exp menus.

For example, by selecting the appropriate boxes and values, the following DIFFUSE statement will be inserted into the input file:

# FIELD OXIDE

DIFFUSE TIME=100 TEMP=850 T.FINAL=1060 WETO2 PRESS=1.00 \ HCL.PC=0 C.ARSENIC=9.0E19 C.PHOSPHOR=4.0E20

Several other parameters not included on the menu are available in the DIFFUSE statement (Chapter 6: “Statements”, Section 6.15:“DIFFUSE”). The DUMP, DUMP.PREFIX, and NO.DIFF parameters can be useful. DUMP and DUMP.PREFIX can be used to make a movie using TONYPLOT. The NO.DIFF parameter specifies that impurity redistribution will be neglected. This provides a good approximation for low temperature processes, such as silicidation.

Several other model specification statements are important for diffusion processes. These are as follows:

• IMPURITY, INTERSTITIAL, and other impurity and point defect statements, which specify model parameters (e.g., diffusivity or segregation) of these species.

• The OXIDE statement, which specifies parameters for different oxidation models.

• The MATERIAL statement, which specifies some basic parameters for all materials.

• The SILICIDE statement, which specifies silicidation coefficients.

Table 7.7 shows the basic diffusion and oxidation models.

Table 7.7. Basic Diffusion and Oxidation Models.

For a detailed description of all diffusion and oxidation models, see Chapter 3: “SSUPREM4 Models”, Sections 3.1: “Diffusion Models” and 3.3: “Oxidation Models”.