Silicon carbide (SiC) power electronics development problems

I. Introduction

The past two decades the semiconductor material silicon carbide is valued people in the beginning , because it has many advantages. Early

In Shangshi remember the 1950s, Huang Kun , Xie Xide coauthored "Semiconductor Physics " book has been described semiconductor silicon carbide. The first to enter fabricating a semiconductor device material is germanium, then silicon and III and V semiconductor materials boarded the stage of history. Until now the field of power electronics , such as thyristors and IGBT high voltage, high current devices are still using silicon single crystal materials. Since SiC devices breakthrough design theory , expectations for higher performance power semiconductor devices are increasingly urgent.

In 2002, there was a prophecy researcher with the text :

Currently , the company has to sell in Germany Infineon SiC Schottky barrier diode in the market. The world have developed many large semiconductor companies to reduce channel resistance of SiC devices and reduce the overall device power consumption technology. 2006 is expected to be sold after these advanced devices on the market .

Currently , low-power silicon carbide devices have from the laboratory into practical production stage devices. Currently the price is also high silicon carbide wafer , its flaws are many. Through continuous research and development, projected to the year 2010 , the SiC device will dominate the power device market .

Is not the case . The following table is the world leader in silicon carbide device level parameters:




It seems to let people disappointed !

Second, how people evaluate silicon carbide ?

Almost all who can read this article describes the silicon carbide :

The energy band gap of silicon carbide is 2.8 times the silicon ( wide band gap ) , to 3.09 eV. Its insulation breakdown field strength of 5.3 times the silicon up 3.2MV/cm. Whose thermal conductivity is 3.3 times the silicon is 49w/cm.k. Made of silicon carbide Schottky diodes and MOS field-effect transistors, the same voltage as compared with a silicon device, the drift region of the thin thickness of the resistance an order of magnitude . The impurity concentration of the order of two silicon . Thus, the impedance per unit area of silicon carbide devices are only one of 100 silicon devices . It 's almost equal to the whole drift of resistance resistance of the device . SiC devices thus very low heat . This helps to reduce conduction and switching losses , higher operating frequency than silicon devices generally more than 10 times . In addition, there are inherent silicon carbide semiconductor strong resistance to radiation .

In recent years, the production of silicon carbide using IGBT ( insulated gate bipolar transistors ) and other power devices, such processes have minority carrier injection may be used to reduce the on-state resistance is generally one tenth of the silicon devices . SiC device itself plus a small amount of heat , and thus the thermal conductivity of SiC devices Excellent. Also, SiC power devices can work at a high temperature of 400 ℃ . Its small size of the device can be used to control large currents. Voltage is much higher .

Third, the current development situation of how SiC devices ?

1 , the technical parameters : for example, a Schottky diode voltage increased from 250 volts to 1000 volts , the chip area is small , but the current of only a few dozen security . Operating temperature up to 180 ℃, 600 ℃ from the presentation can be reached very far . Drop even more unsatisfactory, there is no difference with the silicon material , to achieve high forward voltage drop of 2V.

2 , the market price : about 5-6 times the silicon material.

Fourth, where silicon carbide (SiC) power electronics development problems in ?

Comprehensive various reports , the problem is not the principle of chip design, especially the chip design is not difficult to solve . Difficulty in achieving chip structure production process.

For example:

A silicon carbide wafer defect density of microtubules . Microtubules are visible to the naked eye is a macroscopic defects in SiC crystal growth technology before to be able to completely eliminate micro- tube defects , high- power electronic devices with silicon carbide would be difficult to manufacture . Despite the high density of microtubules wafer has reached the level of no more than 15cm-2 's . But the device manufacturing requirements than 100mm diameter silicon carbide crystals, microtubule density is less than 0.5cm-2.

2, low epitaxial process efficiency. Gas SiC homoepitaxial generally carried out at temperatures above 1500 ℃ . Because of the problem of sublimation , the temperature is not too high , generally can not exceed 1800 ℃, and thus a lower growth rate . Low temperature liquid phase epitaxy , the higher rate , but low yield.

3, the doping process have special requirements . Diffusion method as miserable heteroaryl , much higher than the diffusion temperature of silicon carbide , then the SiO2 layer has been masked with a masking effect lost , and silicon carbide itself is not stable at such high temperatures , it is not appropriate dopant diffusion method using , but rather use the ion implantation doping . If the p -type impurity ion implantation using aluminum . Due to aluminum atomic ratio greater carbon atoms , into lattice damage and without impurities in the active state are more serious , often at a relatively high substrate temperature , and annealing at higher temperatures. This brought the decomposition of the silicon carbide wafer , a silicon atom sublimation problems. At present , p -type ion implantation problems still more, the annealing temperature selected from the range of impurities to the process parameters to be optimized further .

4 , making ohmic contact . The ohmic contact electrode lead is a very important process of the device . Manufacture of metal electrodes on silicon carbide wafer , the contact resistance is lower than required 10 - 5Ωcm2, Ni and Al electrode material can be achieved, but at above 100 ℃ poor thermal stability. Using Al / Ni / W / Au thermal stability of the composite electrode can be increased to 600 ℃, 100h, but the ratio of the contact resistance of up to 10 - 3Ωcm2. So to form a good ohmic contact with the silicon carbide is more difficult .

5, the supporting material temperature . SiC chip can operate at temperatures 600 ℃, but not necessarily its supporting material on this high-temperature capability . For example , the electrode material , the solder , the housing , the insulating material and so increase the operating temperature limit .

More than just a few examples , not all. There are many technological problems have not the ideal solution , as the interface state silicon carbide semiconductor surface trenching process , terminal passivation process , the gate oxide layer on the long-term stability of SiC MOSFET devices , the industry still not reached the same conclusion , greatly hinder the rapid development of SiC power devices .

V. Conclusions

Learn all kinds of technology development experience , everything has its own law of development. For example thyristor Shangshi remember the fifties appeared in China for electrical control, subject to all walks of life are welcome , but not easy. First SCR heat , due to the design principles have not completely clear , frequent product failure , the emergence of social fear " terrible silicon " is . Through the efforts , determined to overcome the problem, ushered in the popularity of the use of thyristor . Therefore , the development of SiC power devices is also impossible leap.