Wet Etching of Silicon Germanium Nanowires

Abstract

The aim of this project is to understand the wet etching mechanism of SiGe at the nanoscale. We will use the etching of SiGe nanowires as a case study and we will optimize the etchant solution in order to achieve high selectivity over Si, preserve the shape of SiGe nanowire (isotropic etching) and control their diameter below the threshold of ten nanometers.

Popular Abstract

Transistors are the devices used to control the flow of current across electronic devices. Transistors’ working principle is analogous to how a valve controls the flow of water: applying voltage to a transistor enables to regulate the flow of current. When the voltage is turned off, the transistor prevents the current from flowing and subsequently the device stops working. This is rather similar to valve opening/closing and consequentially increasing/decreasing the water flow.

But why are transistors so important? Transistors are the building blocks of logic devices used for computation and information storage, such as our computers and phones. More transistors mean faster processing power which improves your device’s performance and working speed. So, if you want a faster computer with greater computing power, more transistors are needed. Nowadays, the technology of transistors has gone a long way. 20 years ago the transistors were about 250 nanometers. The smallest transistors available today are only about 10 nanometers and any electronic device that you used today has several billion transistors. And to fit more transistors on the same chip, smaller transistors are needed.

The next question you might be asking is what is the problem with making the transistors smaller? “Look at the data! In the past 20 years we have reduced the transistor size 25 times! Just continue with what we have been doing”. Yes, but if only things were so simple.

The problem that we have to face is the current shortage between the transistors elements which will turn a transistor into a “never-closing valve with water always flowing”. The shortened transistors will always allow the flow of current, causing huge power losses. The transistors smaller than 7 nanometers will experience that problem, so producing transistors smaller than 7 nanometers will just create an energy loss problem instead of solving a space problem. To conclude, we have reached a physical barrier that doesn’t allow us to reduce the size of transistors using the traditional approach. Therefore, a new solution has been proposed.

Similar to how humans build skyscrapers when there is little space on the ground left, transistors which were previously build next to each other are now going to be built on top of each other. The new transistors are called vertical transistors. Even though the transistors reach their size limitation, we will be able to fit a lot more of them on a chip. Now, instead of having planar transistors or “single-storey transistor houses”, we will have vertical transistors or “transistor skyscrapers” all over the chip. Of course, a skyscraper is just an analogy. In reality, the vertical transistors have a cylindrical shape. Scientists call these cylinders nanowires, as their diameter is only a few nanometers.

In order to fit as many nanowires as possible, we need to reduce their size after they have been manufactured. The material used for the nanowires is silicon germanium and the process of reducing the nanowire size is called etching which is what the thesis focused on. Our research group carried out experiments in order to understand the mechanism of silicon germanium etching. We have proposed a model which describes the etching regimes and under what conditions they occur. Furthermore, we described when SiGe nanowires are etched isotropically so the shape of the nanowire is preserved. We have also studied the selectivity of the used etchant solutions over silicon which is the measure of how well the etchant solution etches SiGe and leaves Si untouched.

• author: Liubchenko, Grigory
• supervisor: Ivan Maximov
• organization: Solid State Physics; Department of Physics
• course: FYSB06 20171
• year: 2017
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• keywords: Wet Etching, Nanowires
• language: English
• id: 8920492
• date added to LUP: 2017-07-01 10:36:24
• date last changed: 2017-07-01 10:36:24