8.21 Sspd_chapter 6_part 7_introduction to athena 2_process simulator

SSPD_Chapter 6_Part 7_Introduction to ATHENA2

SECTION 7.7 Background of ATHENAcontinued.

7.7.2. Creating Device Structure using ATHENA

7.7.2.5. Simple Geometrical Etches

The next step in this tutorial process simulation is to define the polysilicon gate definition. (Implant and thermal steps will be discussed in later Section :“Choosing Models In SSUPREM4”). To set a geometrical etch step, select Process→Etch→Etch... from the Command menu of DECKBUILD. The ATHENA Etch Menu (Figure 7.24) will appear.

The Geometrical etch is the default method. Other methods will be discussed in later Section called “Deposition and Wet/Dry Etching using the Physical Models in ATHENA/ELITE”. Select Polysilicon from the Material menu. This example will use a polysilicon gate edge at x=0.3 and set the center of the gate at x=0.0 for the initial grid. Therefore, polysilicon should be etched to the right from x=0.3. To do so, select Right from the Geometrical type , and set the Etch location to 0.3. This will give the following statement: # POLY DEFINITION

ETCH POLY RIGHT P1.X=0.3

The structure created by this ETCH statement is shown in the left hand plot of Figure 7.25.

You can obtain an arbitrary shape of geometrical etching by using the Any Shape button. For example, to make a tilted etch, specify X and Y locations of four Arbitrary points as shown in Figure 7.26 .

The following four etch lines will be inserted into the input file:

# POLY DEFINITION

ETCH POLY START X=0.2 Y= -1

ETCH CONT X=0.4 Y= 1

ETCH CONT X=1 Y= 1

ETCH DONE X=1 Y= -1

If this input file fragment is run instead of the previous one (using the INIT statement from the History capability), the structure after this etch sequence will appear as displayed in the right hand plot in Figure 7.25. ATHENA etches all polysilicon material within the specified polygon [ polygon is defined by the points P1(x= 0.2,y= -1),P2(0.4,+1),P3(1,1)&P4(1,-1)]. The polygon etch can consist of any number of points. If you use the Insert button, an additional point will appear after the currently selected point.

Figur7.25: Structure Created by Etch Statement (a)Right etch (b) Any Shape.

Figure 7.26. ATHENA Etch Menu for arbitrary etch.

An additional option for geometrical etching is a dry etch with a specified thickness. This can be used for spacer formation as follows: deposit an oxide of a specified thickness (e.g., 0.5µm) right to poly-Si and then etch the same thickness again beyond x = 0.6µm.

# CLEAN GATE OXIDE

ETCH OXIDE DRY THICK=0.02

# SPACER DEPOSITION

DEPOSIT OXIDE THICK=0.5 DIVISIONS=8

# SPACER ETCHING

ETCH OXIDE DRY THICK=0.53

The dry etching step etches the specified material in the region between the top (exposed) boundary of the structure and a line obtained by translating the boundary line down in the Y direction. The etch distance is specified by the THICK parameter. Figure 7-27 shows the resulting spacer.Figure 7.27 is given in the next module.