5.2.3 Simulation Results

 

The presented BiCMOS process is performed with VISTA's Simulation Flow Controller (SFC) [Pic93]. A tabularized process flow including all process parameters is given in Table 5.2-2. Each step of the flow represents a process simulation tool which reads the last result from the previous one and performs the simulation according to the specifications. After the tool has finished, the actual wafer state is evaluated. This includes merging of the geometry and the doping information.

The following simulation tools are available within the SFC:

SKETCH:

Simulation module for resist spin-on, exposure, and stripping.

PROMIS:

Process simulation modules for several steps:

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ETCH: Etching tool for isotropic, anisotropic and plasma etching [Str95].

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DEPO: Deposition tool for isotropic, anisotropic and hemispherical deposition of material layers. Additionally, EPI-layer deposition and in-situ doping techniques are performed.

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ANALYTIC IMPLANT: Ion implantation module based on analytic distribution function.

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MONTE CARLO IMPLANT: Ion implantation module based on Monte Carlo technique. Available for amorphous as well as crystalline targets.

PROMIS-NT:

Simulation module for diffusion processes.

SAMPLE:

Etching and deposition module incorporated by a wrapper approach [Old80].

TSUPREM-4:

Process simulator for diffusion, oxidation, implantation [Tec94].

# Simulator SFC operation Specification & Parameters

1 SKETCH create-subdomain

2 SKETCH spin-on

3 SKETCH spin-on

4 SKETCH mask pattern buried layers: exposed, mask: 7.0, 13.5; 14.5, 22.0;

5 PROMIS etch open nitride

6 SKETCH strip-material mask

7 PROMIS analytic-implant

8 TSUPREM-4 oxidation

9 SKETCH strip-material strip mask: resist

10 PROMIS analytic-implant

11 SKETCH strip-material strip oxide: SiO2

12 PROMIS iso-depo

13 PROMIS iso-depo

14 PROMIS iso-depo

15 SKETCH mask pattern N-well: exposed, mask: 7.0, 13.5; 14.5, 22.0;

16 PROMIS etch open nitride

17 SKETCH strip-material mask

18 PROMIS analytic-implant

19 TSUPREM-4 oxidation

20 SKETCH strip-material strip resist

21 PROMIS analytic-implant

22 PROMIS-NT diffusion

23 PROMIS iso-etch planarize

24 SKETCH spin-on

25 SKETCH spin-on

# Simulator SFC operation Specification & Parameters

26 SKETCH spin-on

27 SKETCH mask pattern field oxide: exposed, mask: 0.0 ,0.5; 6.5, 7.5; 13.5, 14.5; 19.5, 20.2; 21.8, 22.0;

28 PROMIS etch open nitride

29 SKETCH strip-material mask

30 PROMIS plasma-etch open channel stop

31 PROMIS analytic-implant

32 TSUPREM-4 oxidation

33 SKETCH strip-material strip nitride

34 SKETCH mask pattern subcollector: exposed, mask: 20.5,21.5;

35 PROMIS analytic-implant

36 SKETCH strip-material strip resist

37 SKETCH mask pattern base: exposed, mask: 14.8,19.2

38 PROMIS analytic-implant

39 PROMIS iso-depo

40 SKETCH strip-material strip resist

41 PROMIS iso-etch pregate oxide

42 PROMIS iso-depo

43 SKETCH mask pattern open emitter: mask: 17.6,18.4;

44 PROMIS plasma-etch open emitter

45 SKETCH strip-material strip resist

46 PROMIS iso-depo

47 PROMIS analytic-implant

48 SKETCH mask pattern emitter/gate: mask: 0.0, 3.1; 3.9, 10.1; 10.9, 17.1; 18.9, 22.0;

49 PROMIS etch form gates and emitter

50 SKETCH mask pattern S/D + deep collector: mask: 0.0,5.5; 7.5, 8.5;20.5,21.5;

 

# Simulator SFC operation Specification & Parameters

51 PROMIS analytic-implant

52 SKETCH strip-material strip resist

53 PROMIS iso-depo

54 PROMIS iso-etch

55 SKETCH mask pattern S/D + deep collector: mask: 0.0,5.5; 7.5, 8.5;20.5,21.5;

56 PROMIS analytic-implant

57 SKETCH strip-material strip resist

58 SKETCH mask pattern PMOS S/D + extr. base: mask: 5.5, 7.0; 8.5, 17.0

59 PROMIS analytic-implant

60 SKETCH strip-material strip resist

61 PROMIS-NT diffusion

 

Figure 5.2-14 shows the doping profiles of the N-buried layers after an oxidation process (step 8). The grown oxide is used for the self-aligned implant of the P-buried layer. Figures 5.2-15 depicts the buried layer profiles after step 19, where additional thermal budget due to the N-well oxidation is applied onto the buried layers.

Figure 5.2-16 gives the actual dopant concentrations after the channel-stop implant (step 27) prior to the field oxide isolation, where the n-wells and the p-well doping concentrations are also given.

The final BiCMOS structure is given in Figure 5.2-17. The complexity of the simulated structure can be figured out. For further analyses we give details of all three devices.

The final PMOS device including the N-buried layer doping and the channel stop implant directly under the field oxide is given in Figure 5.2-18. The according simulation grid is shown in Figure 5.2-19 containing 7278 nodes. The n-well contact is realized by the source/drain implantation used for the NMOS device. Details of the active area dopings including the simulation grid are given in Figure 5.2-20 and Figure 5.2-21, respectively.

The NMOS device is given in Figure 5.2-22. The corresponding NMOS device exhibits a shallower buried layer doping due to the higher mobility of boron as compared to the antimony, which is used as N-buried layer dopant. The corresponding simulation grid for the NMOS device uses 7148 nodes to resolve the dopant concentrations (see Fig 5.2-23). For the source/drain fabrication of the NMOS device the well-known LDD technique is applied [Ogu80]. The active area dopings of the PMOS device as well as the corresponding simulation grid are given in Figure 5.2-24 and Figure 5.2-25, respectively.

    
Figure 5.2-14: Simulation results for the N-buried layers of PMOS and NPN device as result of step 8.
Figure 5.2-15: Simulation results for the P-buried layer, the P-punchthrough and the N-buried layers obtained after step 19.

  
Figure 5.2-16: Simulation results for the P-buried layer, the P-punchthrough and the N-buried layers obtained after step 19.

  
Figure 5.2-17: Simulation results for the final BiCMOS device including NMOS, PMOS and NPN dopings.

  
Figure 5.2-18: Simulation results for the final structure of the PMOS device.

  
Figure 5.2-19: The simulation grid used for the results given in 5.2-18. The grid resolves the dopant information by using 7278 grid nodes.

    
Figure 5.2-20: The active area of the PMOS device showing source-drain dopings and N-well.
Figure 5.2-21: Details on the simulation grid of the active area for the PMOS device.

  
Figure 5.2-22: Simulation results for the final structure of the NMOS device.

  
Figure 5.2-23: The simulation grid used for the results given in 5.2-22. The grid resolves the dopant information by using 7148 grid nodes.

    
Figure 5.2-24: The active area of the NMOS device showing LDD source-drain dopings and P-well.
Figure 5.2-25: Details on the simulation grid of the active area for the NMOS device.

Finally, we present the bipolar NPN device structure. A lower collector contact resistance is achieved by a deep-subcollector implant. Additionally, all N-type implants during the fabrication of the active regions are applied to the subcollector. The simulation grid for the whole NPN device is given in Figure 5.2-27, where 7533 grid nodes are used to resolve the solution quantities. Due to the low diffusivity for antimony the N-buried layer changes very steep from the substrate into the epitaxial layer. The active region of the NPN device including extrinsic base, intrinsic base and emitter doping is shown in Figure 5.2-28. Details on the corresponding simulation grid are depicted in Figure 5.2-29.

  
Figure 5.2-26: Simulation results for the final structure of the bipolar NPN device.

  
Figure 5.2-27: The simulation grid used for the results given in 5.2-26. The grid resolves the dopant information by using 7533 grid nodes.

    
Figure 5.2-28: The active area of the NPN device showing intrinsic and extrinsic base, emitter and collector.
Figure 5.2-29: Details on the simulation grid of the active area for the NPN device.