5.3.1 Process Simulation

Table 5.1 shows the process flow and data for the modified device structure. Deposition and stripping steps were performed by the simulator sketch. The simulator animpl was used for implantation steps. For diffusion simulation TSuprem-4 was taken.

The sequence of simulation steps is not exactly the same as the sequence of process steps in reality in order to reduce demand on computational resources. To keep the simulation domain as small as possible and to reduce the number of grid points for the implantation and diffusion steps the homogeneously doped substrate was added after the last epi-layer has been processed. This was necessary because the version of TSuprem-4 used for simulation of diffusion steps did not allow more than 20000 grid points.

During each deposition of an epi-layer heating of the underneath epi-layers occurs. To account for the effects of this heating an additional diffusion step has been introduced into the simulation flow after the the first epitaxial deposition for each layer except the first.

**Table 5.1:** Process flow for the modified device structure
#	SFC	specification
1	substrate	P, 1.5^.10¹⁵ cm^{- 3}
2	deposition, n-epi standard	P, 4.15^.10¹⁵ cm^{- 3}, thickness 5.2 $\mu$ m
layer 1
3	deposition, n-epi	P, 2.8^.10¹³ cm^{- 3}, thickness 1 $\mu$ m
4	deposition, n-bubble mask
5	implantation, n-bubble	P, 2^.10¹² cm^{- 2}, 120 keV
6	strip, n-bubble mask
7	deposition, p-bubble mask
8	implantation, p-bubble	B, 2^.10¹² cm^{- 2}, 80 keV
9	strip, p-bubble mask
10	diffusion	1150^o C, 1 min
layer 2
11	deposition, n-epi	P, 2.8^.10¹³ cm^{- 3}, thickness 1 $\mu$ m
12	diffusion, deposition heating	1110^o C, 1 min
13	deposition, n-epi	P, 2.8^.10¹³ cm^{- 3}, thickness 1 $\mu$ m
14	deposition, n-bubble mask
15	implantation, n-bubble	P, 2^.10¹² cm^{- 2}, 120 keV
16	strip, n-bubble mask
17	deposition, p-bubble mask
18	implantation, p-bubble	B, 2^.10¹² cm^{- 2}, 80 keV
19	strip, p-bubble mask
20	diffusion	1150^o C, 1 min
layer 3
21	deposition, n-epi	P, 2.8^.10¹³ cm^{- 3}, thickness 1 $\mu$ m
22	diffusion, deposition heating	1110^o C, 1 min
23	deposition, n-epi	P, 2.8^.10¹³ cm^{- 3}, thickness 1 $\mu$ m
24	deposition, n-bubble mask
25	implantation, n-bubble	P, 2^.10¹² cm^{- 2}, 120 keV
26	strip, n-bubble mask
27	deposition, p-bubble mask
28	implantation, p-bubble	B, 2^.10¹² cm^{- 2}, 80 keV
29	strip, p-bubble mask
30	diffusion	1150^o C, 1 min
layer 4
31	deposition, n-epi	P, 2.8^.10¹³ cm^{- 3}, thickness 1 $\mu$ m
32	diffusion, deposition heating	1110^o C, 1 min
33	deposition, n-epi	P, 2.8^.10¹³ cm^{- 3}, thickness 1 $\mu$ m
34	deposition, n-bubble mask
35	implantation, n-bubble	P, 2^.10¹² cm^{- 2}, 120 keV
36	strip, n-bubble mask
37	deposition, p-bubble mask
38	implantation, p-bubble	B, 2^.10¹² cm^{- 2}, 80 keV
39	strip, p-bubble mask
40	diffusion	1150^o C, 1 min
layer 5
41	deposition, n-epi	P, 2.8^.10¹³ cm^{- 3}, thickness 1 $\mu$ m
42	diffusion, deposition heating	1110^o C, 1 min
43	deposition, n-epi	P, 2.8^.10¹³ cm^{- 3}, thickness 1 $\mu$ m
44	deposition, n-bubble mask
45	implantation, n-bubble	P, 8^.10¹¹ cm^{- 2}, 120 keV
46	strip, n-bubble mask
47	deposition, oxide	SiO₂, thickness 0.85 $\mu$ m
48	deposition mask
49	implantation, p^-	B, 1^.10¹³ cm^{- 2}, 80 keV
50	strip mask
51	deposition mask
52	implantation, p⁺	B, 5^.10¹⁴ cm^{- 2}, 45 keV
53	strip mask
54	strip oxide
55	oxidation, gate oxide	thickness 50 nm
56	p-diffusion	1100^o C, 200 min
		1100^o C $\rightarrow$ 800^o C, 150 min
57	deposition, gate poly	SiO₂, P, 1^.10¹⁵ cm^{- 3}, thickness 0.5 $\mu$ m
58	deposition, source doping mask
59	implantation, source doping	As, 5^.10¹⁵ cm^{- 2}, 120 keV
60	deposition	SiO₂, thickness 1 $\mu$ m
61	As diffusion	800^o C $\rightarrow$ 1000^o C, 20 min
		1000^o C $\rightarrow$ 800^o C, 100 min
62	deposition, source contact mask
63	etch, recess
64	deposition, source contact	Al, thickness 2 $\mu$ m

**Figure 5.8:** Concentration of the phosphorus doping of the modified device.
$\resizebox{12cm}{!}{ \includegraphics[width=12cm,angle=90]{eps/dmos-np-100V-phosphorus.col.ps}}$

**Figure 5.9:** Concentration of the boron doping of the modified device.
$\resizebox{12cm}{!}{ \includegraphics[width=12cm,angle=90]{eps/dmos-np-100V-boron.col.ps}}$

Fig. 5.8 and Fig. 5.9 show the geometry of the simulated device and the resulting phosphorus and boron concentrations, respectively, of the modified device. The center of the additional vertical n-doping is located at x = 15 $\mu$ m as can be seen in Fig. 5.8. Because of the phosphorus implantation and diffusion in each epi-layer the doping concentration in the vertical direction in the additional doping is not constant. Small variations of the doping concentration in vertical direction are visible in Fig. 5.8 and the epi-layer structure consisting of 5 layers is clearly discernible.

The boron channel doping extends in lateral direction from the source contact to the additional vertical p-doping at the gate contact edge. The center of the additional vertical p-doping is located at x = 11 $\mu$ m. Again the epi-layer structure is clearly visible from the small doping concentration variations in vertical direction.