HW_2-2007Solutions - EECS 414 Introduction to MEMS Reading Assignments Homework#2 Total 165 Points Fall 2007 Class Handouts and Notes Introduction

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1 EECS 414 Introduction to MEMS Fall 2007 Reading Assignments Class Handouts and Notes, “Introduction to Microfabrication Technologies” Homework #2 Total: 165 Points Handed Out: Thursday Sept. 13, 2007 Due: Friday Sept. 21, 2007 1. Thermal and e-beam evaporation techniques have been used to deposit thin films of different materials. However, nowadays, e-beam is almost exclusively used. Why? 5 points E-beam evaporation is very versatile and can be used to deposit a variety of materials. In addition, it is a much cleaner process than thermal evaporation 2. Provide two different approaches, and list the major process steps for each, to create a 100 µ m by 100 µ m square of Si0 2 film on a silicon wafer. 10 points A: Deposit silicon nitride, lay down and pattern photoresist to have a 100 μ m x 100 μ m square opening, oxidize with wet or dry oxidization, remove silicone nitride through selective wet etch. B. Alternatively, deposit thin film of silicon dioxide with LPCVD/CVD, lay down and pattern photoresist to only cover a 100 μ m x100 μ m square, etch thin film with selective wet etch. 3. Dry plasma etching often does not provide as good a selectivity as standard wet etching techniques. However, we often use dry etching in many applications. Name at least three reasons why? 5 points 1. Plasma etching is compatible with using photoresist as a mask for most materials 2. Plasma etching can be used to etch more variety of films than wet etching. For example silicon nitride is etched easily in plasma but not easily in wet etchants. 3. When used like an RIE, Plasma etching can provide anisotropic etching. 4. Can a single-crystal silicon layer be grown/deposited on top of a silicon oxide layer? Explain why or why not? 5 points No, because silicon oxide is amorphous and whatever material we deposit/grow on top of this film will be either amorphous or polycrystalline. To get a single-crystal; silicon we either have to bond and etch back like we do for SOI wafers, or somehow crystallize the deposited amorphous/polycrystalline film into a crystalline film. 5. It has been said that silicon dioxide cannot be grown to a thickness much larger than about 1- 2 µ m. Briefly explain why? 5 points
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2 To grow an oxide layer thicker than about 2 µ m or so, we require a very long oxidation time, even in a wet ambient. The long time for creating thick oxide layers is not practical, although it is possible theoretically. 6. Name two advantages of sputtering over e-beam evaporation? 5 points Wider range of materials can be deposited Sputtering has a better step coverage 7. Explain the solid-solubility limit of impurities in silicon and what it represents. Find the solid solubility limit of boron in silicon at 1000, 1050, 1100, and 1200°C?
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This note was uploaded on 09/23/2008 for the course EECS 414 taught by Professor Maharbiz during the Fall '06 term at University of Michigan.

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HW_2-2007Solutions - EECS 414 Introduction to MEMS Reading Assignments Homework#2 Total 165 Points Fall 2007 Class Handouts and Notes Introduction

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