SiC Epi Wafer for MOS Capacitor

SiC Epi Wafer for MOS Capacitor

Due to its excellent electrical, thermal, and radiation resistance, silicon carbide has become a potential material for applications in high-frequency, high-power, and strong radiation environments. MOS capacitors are an important means of studying semiconductor surfaces and interfaces, as well as the basic structure of MOSFETs. Therefore, systematic research on SiC MOS capacitors is of great significance for improving the radiation resistance of SiC based electronic devices and the service life of devices. As one of leading epitaxial wafer manufacturers, PAM-XIAMEN can provide SiC epi wafer manufacturing process for MOS capacitors. See the following table for specific parameters:

SiC Epi Wafer Manufacturing Process

1. Specification of 4HN SiC Epitaxial Wafer

PAM210218 – MOSC

SL No. Specification
1 Wafer Material 4H-Silicon Carbide
2 Wafer Configuration N+ with epi
3 Number of Epi-Layers 2 layers
Layer 1: buffer layer
Layer 2: top layer
4 Layer 2 Thickness 5/8/10 um±10%
5 Layer 2 Dopant Nitrogen
6 Thickness Uniformity <=5%
7 Surface Defect Density <1/cm2
8 Layer 2 Doping Concentration 1.0×1016cm-3+/-20%
9 Concentration Uniformity <=10%
10 Layer 1 Thickness 0.5 um±10%
11 Layer 1 Dopant Nitrogen
12 Layer 1 Doping Concentration 1.0×1018 cm-3+/-50%
13 Front Surface Si-face
14 Substrate Conductivity Type Heavily doped n-type
15 Dopant Nitrogen
16 Crystal Orientation (0001)±0.25°
17 Off-Orientation 4° towards <11-20>
18 Micropipe Density ≤1 cm-2
19 Electrical Resistivity 0.015~0.028 ohm-cm
20 Diameter 100±0.4 mm
21 Thickness 350±25 um
22 TTV ≤10 um
23 LTV ≤4 um
24 Warp ≤35 um
25 Primary Flat Orientation <11-20>
26 Secondary Flat Orientation <1-100>
27 Si-face Surface Finish CMP polished
28 C-face Surface Finish Optically polished

 

2. How to Control the Epilayer Doping Concentrationin SiC Epi Wafer Manufacturing Process ?

Controlling the doping type and concentration of epitaxial layers is crucial to the performance of SiC power devices, which directly determines important electrical parameters such as specific on-resistance and blocking voltage of subsequent devices. The competitive epitaxy method discovered by researchers can effectively change the doping concentration of N-type and P-type in a large range, and is widely used in practical production. Here, we briefly explain the principle of nitrogen (N) and aluminum (Al) as N-type and P-type doping elements, respectively.

During epitaxy wafer manufacturing, nitrogen (N) atoms compete with carbon (C) atoms for lattice positions. To reduce the doping concentration of nitrogen (N) atoms, the concentration of carbon (C) atoms in the epitaxial gas source should be increased; in contrast, to reduce the concentration of carbon (C) atoms in the epitaxial gas source, the doping concentration of nitrogen (N) atoms should be increased. While aluminum (Al) atoms compete with silicon (Si) atoms for lattice positions, you can increase the concentration of silicon (Si) atoms in the epitaxial gas source to reduce the doping concentration of aluminum (Al) atoms; In contrast, you can reduce the concentration of silicon (Si) atoms in the epitaxial gas source to increase the doping concentration of aluminum (Al) atoms.

In the SiC epitaxy processing, the commonly used gas source for Si sources is SiCl4 or SiH4; The commonly used gas source for C source is CCl4 or C3H8. We can control the flow ratio of the two to control the C/Si component ratio, thereby effectively controlling the doping concentration of different elements.

Besides, the doping concentration of the SiC epitaxial layer is related to the gas source flow rate, gas pressure and growth temperature in the CVD process. Take the nitrogen (N) doping as an example for further explanation. Nitrogen (N) doping can be quickly achieved by introducing nitrogen (N2) into the CVD epitaxial growth. From Fig.1, we can know that the doping concentration on both the Si and C surfaces is positively proportional to the N2 flow rate within four orders of magnitude at a fixed C/Si component ratio. The doping concentration of SiC epi wafer manufacturing process covers the doping range of E14-E18, which is most commonly used in devices.

Fig.1 Relationship between nitrogen (N) doping concentration and nitrogen (N2) flow rate in 4H-SiC epitaxy at 1550 ℃

Fig.1 Relationship between nitrogen (N) doping concentration and nitrogen (N2) flow rate in 4H-SiC epitaxy at 1550 ℃

The relationship between gas pressure and doping concentration of SiC epi wafer manufacturing process in a CVD cavity were studied. As shown in Fig. 2, the relationship between N element concentration and pressure is investigated under the conditions of epitaxial temperature of 1600 ℃, C/Si ratio of 3.5, and nitrogen flow rate of 12 ml/min. Whatever on the C-plane or Si plane epitaxy of 4H-SiC, the doping concentration of epi semiconductor wafer manufacturing increases with increasing pressure.

Fig. 2 Relationship between N element concentration and pressure of SiC Epitaxial Wafer Manufacturing Process

Fig. 2 Relationship between N element concentration and pressure of SiC Epi Wafer Manufacturing Process

3. FAQ about SiC Epitaxy for MOS Device

Q: Based on the spec given by you, the structure of the 4H-SiC wafer is as below:

2nd layer 4H-SiC epilayer (Doping concentration = 1 x 10^16 cm-3)/ 1st layer 4H-SiC epilayer (Doping concentration = 1 x 10^18 cm-3)/ 4H-SiC wafer (resistivity = 0.015-0.028 ohm cm-3)

We are planning to use this wafer to fabrication into MOS capacitor and perform capacitance-voltage measurement.

Usually for Silicon wafer (resistivity= 1-10 ohm), we will deposit a layer of metal oxide on top of the silicon wafer. After that, we will deposit top metal contact and bottom metal contact to obtain Al/Metal Oxide/Silicon/Metal structure (MOS capacitor) and perform capacitance-voltage measurements.

Based on our previous understanding using silicon wafer, we will not be able to obtain capacitance-voltage curve if the resistivity of silicon wafer is 0.005 ohm (which is known as highly doped n-type Silicon wafer).

We would like to ask for your opinion whether the proposed 4H-SiC wafer is suitable for our research work as the resistivity of 4H-SiC wafer is considered as highly doped (0.015-0.028 ohmcm-3) and the 1st layer of 4H-SiC epilayer is having a high doping concentration of 10^18 cm-3.

Actually, the thickness of 4H-SiC epilayer is not very crucial for our research work but we need to have the doping concentration in the range of 5 x 10^15 to 5 x 10^16 cm-3. Do you have any standard product produced by your company that will be cheaper when compared with customized wafer?

A: 1) The doping concentration of SiC epitaxial layer is between 5×10 ^ 15 and 5×10 ^ 16 cm-3, which can be achieved in epitaxial technology.

2) For the resistivity between 0.8 and 0.1 ohmcm-3, if the capacitance voltage curve can not be obtained due to the low resistivity, it is suggested that the epitaxial concentration should consider the lower doping concentration (higher resistivity).

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For more information, please contact us email at victorchan@powerwaywafer.com and powerwaymaterial@gmail.com.

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