Geri Dön

Silisyumun yönlü aşındırılması ve mikroalgılayıcılar

Anisotropic etching of silicon and microsensors

  1. Tez No: 14425
  2. Yazar: F.ALİ ALDEMİR
  3. Danışmanlar: PROF.DR. DURAN LEBLEBİCİ
  4. Tez Türü: Yüksek Lisans
  5. Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1991
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 104

Özet

SİLİSYUM' UN YÖNLÜ ASI NDI RI LMASI VE Ml KROALGI LAYI CI LAR ÖZET Son yıllarda hızla gelişen mikroelektronik tekno lojisi ile birlikte elektroniğin, diğer bilim dalları i- le etkileşimi de artmış ve ortaya yeni teknolojik Ürün ler çıkmaya başlamıştır. Mikromekanik düzenler de bun lardan biridir. Mekanik elemanların çok küçük geometri lerde, yarıiletken malzemeler kullanarak üretilmesi ge leceğin dünyasında yeni teknolojik ufuklar açacaktır. Henüz uygulama alanı oldukça sınırlı olan mikromekanik düzenler, gelecekte özellikle uzay araştırmaları ve ro boti k alanında geniş uygulama alanları bulacaktır. Bu tezin amacı; Günümüzde yaygın olarak kullanı lan bazı mikromekanik düzenleri tanıttıktan sonra, mik romekanik yapıların Üretiminde kullanılan tekniklerden elektrokimyasal yönlu aşındırma mekanizmasını incelemek tir. Bu inceleme yapılırken konuya kimyasal bir yakla şım yerine elektronik mühendisliği açısından yaklaşılmış ve elektrod-çozelti ikilisi arasında meydana gelen elek trokimyasal olaylar enerji bantları teorisi ile açıklan maya çalışılmıştır. Tezin konuya giriş niteliği taşıyan ilk bölümün den sonra ikinci bolümde, mikromekanik ve elektroniğin birlikte kullanıldığı basınç algılayıcı ve dönüştürücü düzenler ele alınarak incelenmiştir. Bölüm sonunda, ya pılar arasında bir de karşılaştırma verilmiştir. Üçüncü bolümde, mikromekanik yapıların Üretilmesinde Silisyum' un yonlu aşındın İması tanıtılmaya çalışılmış ve konunun daha iyi kavranması açısından kimyasal olaylar da verilmiştir. Dorduncü bolümde, yarıiletken elektrokimyası, elektronik açıdan ele alınmış, bir kimyasal çözeltiye daldırılan ya rıiletken elektrod ile çözelti arasında meydana gelen yük alış-verişi açıklanmıştır. Beşinci bölü m, elektriksel ku- tuplama sonucu yarıiletken ile çözelti arasındaki yük a- lış-verişinde meydana gelen değişmeler ve bunun aşındırma ya etkileri üzerinedir. Kutuplama şartlarının değiştiril mesinin aşındırmaya etkisi ve sonuç olarak akım-gerilim karakteristiklerinin değişmesi bu bolümde anlatılmıştır. Altıncı bolümde, önceki bölümlerde anlatılan olayların pratikte labaratuvar şartlarında gerçeklenebilmesi için yapılan çalışmalar anlatılmıştır. Sonuç bolümü, tezin ge nel değerlendirilmesi niteliğini taşır.

Özet (Çeviri)

ANISOTROPIC ETCHING OF SILICON AND MICROSENSORS SUMMARY Nowadays, fast changing and developing that are seen in microelectronics, open new fields to semicon ductor materials particularly Silicon. One of these applications is 'Semiconductor Micromeehanical Struc tures'. They are micron-sized machines and experts say that micromeehanical chips will be commercial in five years. These micro-machines are made of Silicon using manufacturing techniques employed in Silicon chip production and may eventually be made with processor control units in a single-step process. Most of the world giants in semiconductor manufacturing and univer sities are working on to develope better micro-structu re. First Silicon micromeehanical structures were made in late I960' s and they were used in biomedical applications. In Sensors & Actuator Center of Univer sity of California-Berkeley, the first working micro- turbine, a 60-1S0 micron 2-D unit, was made in June 1988 as a research project. Using micromachining of Silicon some kind of sensors and actuators can be made such as ; Temperature sensors Hal 1 -effect sensor s Pressure sensors Acceleration sensors Thermal conductivity sensors Specific gas detectors Electric field sensors Microvalves Their applications are in; - Bi omedi cal appl i cati ons - Space applications - Automotive industry - Robotics viIn this work, some of Silicon mi cr ©mechanical structures are explained and one of the common way to produce micromechanical devices that is electrochemical etching of semiconductor particularly Silicon, is exa mined. Popular semiconductor material in world of mic romechanical devices and also in this work is Silicon. Thi s is due ; 1- to excellent mechanical properties of single crystal Silicon 2- to high volume and low-cost manufacturing fa cilities afforded by the integrated circuit CI CD fabrication technologies Single crystal Silicon can be obtained with a high degree of purity and perfection. It has the elas tic modules of stainless steel while having the specific density of Aluminium. Thus providing light and stiff structures with fast response times and high over stress capabilities. Silicon microelectronics technology al lows batch-production of the sensors, which, in turn, dramatically reduces the cost of the sensors. Second chapter is an introduction to common used micromechanical devices which are pressure sensors in industry. This chapter is describes type of pressure sensors as capacitive and resistive, respectively. Capacitive pressure sensors based on Silicon technology are relatively new devices, which are known to offer improved pressure sensitivity when compared with resistive types. Their principal advantage is lower temperature sensitivity. A typical capacitive pressure sensor is shown in Figure 1. A Silicon thin diaphragm formed by selective Silicon etching is bended to a thicker glass substrate having a temperature coef ficient which closely matches that of the Si. This bond is usually made electrostatically to glass. The Si di aphragm typically forms one plate of the capacitor and since the diaphragm is normally the Si substrate, this plate is grounded. The other plate is formed by metal lization on the glass. The plates are separated by a reference cavity having a depth of a few micrometers. The basic principles of capacitive pressure sensor is to sens and transduce small changing of capacitance of capacitor which is made between Si diaphragm and glass with applied pressure. The capacitance variations with applied pressure is a function of the diaphragm deflection. Differantial capacitance can be expressed by; AC= C- C C1D o viiBONDING FADS METAL. FILM ELECTRONIC CIRCUIT SENSOR CAPACITANCE! CLASS ELECTROSTATIC LEAD REFERANCE CAVITY Fig.l Typical capacitive pressure sensor where C is the capacitance at a dif ferantial applied pressure, Co is the zero-pressure capacitance. The dynamic range of AC is limited by the distance between two capacitor plates. Typical zero-pressure capacitan ce of the sensor is about 11,65 pF. Also a parasitic capacitance which is due to misalignment tolerance of capacitor plates is about 3,5 pF. The electronic cir cuit sens the variations of capatitance then convert them appropriate signals such as voltage or current. On the other hand, resistive pressure sensors transform an applied pressure in to an electronics signal based on the pi ezor esi stance effect. It typi cally consist of a thin Si diaphragm and pi ezor esi stive gauge resistors made by diffusing impurities into the diaphragm. The structure of a resistive sensor is shown in Figure 2. It consists of a thin square Si diaphragm, selectively e-tched and piezoresistors diffused into the diaphragm. As the diaphragm is quite thin, it is easily deflected by pressure applied to its top or bottom. Re sistors are connected as a Wheatstone bridge circuit. When a pressure is applied to the top of the diaphragm. viiiELECTRONIC CIRCUIT RESISTORS I ^/ rrr**'' Atımı fâTlıj ı 1 1 ı f71[ ıı 1 1 1 pjz I III 1 1 I I I II I: I DIAPHRAGM \ Si02 n - epi p-Si GLASS SUBS. PACKING PRESSURE INLET-HOLE Fig. 2 Typical pi ezor esi stive pressure sensor resistance values for two resistors of four increase, where others decrease as shown in Figure 2. Bridge outputs are sensed by an electronic circuit and conver ted appropriate values such as voltage or current. In chapter 3, the principals of chemical and elec trochemical etching of Si are described. Anisotropic etchants have been found much more useful for Si micro- machinirig because; - They are orientation dependent, resulting in 30-400 times lower etch rates of planes - They show high sel ectivi ties and can be masked by a variety of materials such as SiOz, SiaN4 - They are all dopant concentration-dependent and show nearly zero etch rates at high Boron con- centrati ons. - Etching can be electrochemically stopped by an external y applied bias potential. However, the orgins of the high etch rate of over planes are not yet fully understood but it is believed that the slow etch rate of planes is due to the facts Cor the combination facts!) that, 1- These planes are the closest packed low index pi anes and, 2- They have the minimum number of dangling bonds. IXIn this thesis, KOH is used as a et chant for mic- romachining Si. Out of KOH most of alkaline solutions, organic basic solutions like EDP-W and Hydrazine can be used. Althouh the nature of chemical anisotropic etch ing is not adequatily explained, it is supposed by se veral authors that in KOH etching proceeds first by in jection of holes from a localized anodic site into the surface to raise Si to a higher oxidation state. The etching reaction then transfers an electron from OH in to surface bond of Si and finally to the etch products in the form of dissolved Si. There are not very well evidenced clear explanations about the nature of the mechanism underlying etch-stop effect, but it is sug gested that owing to an excessive hole concentration, which can be created that by an externally applied po tential to Si, an anodic oxide layer can be grown on the surface, and etching completely stopped. Chapter 4 is an introduction to electrochemistry of semiconductors. The subject of electrochemistry is a combined field of both solid-state physics and elec trochemistry. The basic concept of both discipline are defined in this chapter. Since the reactions at the semi conductor /electrolyte are thought and analyzed in terms of energy levels, most of the terminology and con vention is directly obtained from solid-state physics. They are largely based on the energy-band diagrams. E- nergy level representation of the solid/solution inter face only gives a qualitative description of the charge movement and transfer between energy levels and from so lid to solution or vice versa. It does not provide a full, quantitative and analytical understanding of mec hanisms involved in the electrode reactions. First, the energy-band concept of semiconductors is described and the mean of Fermi level is given. Then the solution and their energy-band concept are explained. Because of chemical interactions of ions in solution with the solvent and with each other, and how the charges of the ionic charges on the ion cause a change in chemical structure surrounding the ions are important in semicon ductor chemistry in two ways, i- The description of the ions in terms of their electronic energy levels become complicated by these chemical transformations, ii- Chemical changes during and/or after the reac tion complicate the description of electron transfer process between the ions in the solu tion and the electrode.Electronicenergy levels on the ions Cor molocu- lesD reflect the tendency of that species to give up or to accept an electron when it approaches the electrode. It classical metal electrochemistry, the tendency to give up an electron or to accept an electron from a me tal is measured as the potential of the electrode and is called the standart electrode potential. The point is, if the reducing agent gives up electrons to the metal electrode, the electrode will become negatively charged and will have negative redox potential. If the couple is an oxidizing agent, it will extract electrons from the metal electrode and the electrode will become posi tively charged and have a positive redox potential. Therefore, a correlation between the measured potential of the metal electrode and the energy level of the redox couple in the solution can be assumed. The only good way to conveniently cnnect the pro perties of semiconductor electrodes with the properties of the solution is to use an energy level description rather than a chemical potential description. The model of energy levels in solution is shown in Figure 3. The ordinate is energy and potential with the references as indicated, and the probabilistic density of energy levels WCED is the abscissa. (a) redox Ec (c) Fig 3 Energy levels in a metal, a solution and a semiconductor from left to right Another important point for solid in a chemical solution is solid-liquid interface. Double layers which form at any interface are important to control the che mical and electrical properties of the surface. They XIaffect both the electrical properties and the kinetics of the chemical reactions involving charge exchange. Three distinct layers of charged regions at the semi conductor-solution interface. They are Gouy-Chapman region, Helmholtz region and space-charge region of the semiconductor. Detailed information about interface region is given in chapter 4. Another important pro perty of electrochemistry is the behaviour of the semi conductor electrode in solutions. The band model for semiconductors differs from the metal band model, partly due to the presence of the band gap, but mainly because of the smaller amounts of available free carriers, which in turn, results in a formation of a spage-charge layer within semiconductor to preserve charge balance. Anot her distinguishing feature of semiconductor electrodes is the Helmholtz potential is not changed with externaly applied voltage. In this chapter a well -described analy sis about semiconductor electrode in solution is given and also behaviour of the semiconductor electrode under externally applied potentials. Last one which is given in chapter 4 is measure ment techniques that is used to gather information about the semiconductor, the solution and reactions occuring upon electron transfer or adsorbtion/desorption process at the surface. Most commonly used measurements tech niques in semiconductor electrochemistry is voltammetry measurements. A basic electrochemical cell for voltam metry measurement is shown in Figure 4. There are three electrodes in solution; Working electrode CSemiconduc- tor electrode!), counter elcirode CMetal electrode} and refer ance electrode to measure voltage in solution. The feedback electronic circuits which are called pot en - tiöstats, are used to adjust the current so that the desired electrode potential V appears between the work ing electrode and the refer ance electrode. A computer controlled potentiostat will be discussed in detail in chapter 6. RE WE CE v/i I MEASUREMENT & CONTROL I unit ; SOLUTION Fig. 4 Basic electrochemical cell xiiIn chapter 5, electrochemical etching of Si and controlling of the etching is discussed. First, the changing of Si electrode under biasing is described. The current through the solution is plotted while the electrode voltage is linearly increased with time. Two important potentials are marked on the abscissa of Fi gure 5. One is the open-circuit potential COCPD. OCP is the electrode potential of an electrolyte-electrode interface for zero electrode current, after equilibrium is reached and the Helmholtz potential is established. Fig. S Important potentials on V/I characteristic The passivation potential PP is to Si with a passivating anodic oxide 1 case of Si, once the PP is reached, cur denly due to the insulating oxide layer positive voltages increase the current sibly because the relatively poor quali layer can be easily tunneled by current roxyl groups, which in turn, give rise thicker oxide layer. char acter i sti c ayer. I n the rent drops sud- Additional slightly, pos- ty anodic oxide carrying hyd- to growth of a The last subject of this chapter, the basic prin ciples of etch-stop using a pn-j unction are given. The advantages of etch-stop using pn-j unction can be listed as fol 1 ows ; - It is possible to implement devices and circu its on the structure after etching because of adequate doping levels. - Using etch-stop technique with pn-j unction, geo metrical structures which are more complex and smooth can be made easily. - This technique can be used with conventional IC processing techniques. xiiiExperimental works are discussed in chapter 6. In this chapter, processing of semiconductor wafers, measurements & control system based on a personal corn- computer PC and set-up of electrochemical cell are described. All Si wafer processing were made in mic roelectronics lab. of ÎTU. The masks are also made in ÎTÜ. There are two essential masks which are used during processing. They are etching window mask and contact mask. The basic processing steps are thick oxide growth for surface masking and anisotropic etch ing window opening. The results of experimental works are given in this chapter with cur ren t -vol t age char ecter i sties of Si XIV

Benzer Tezler

  1. Tez No

    753835

    Fabrication of junctionless silicon nanowire transistors via mix and match patterning based on field emission scanning probe lithography

    Alan-salımlı tarama probu litografisine dayalı karıştır ve eşleştir modelleme ile bağlantısız silisyum nanotel transistörlerin üretimi

    MERT ÖZDEN

    Yüksek Lisans

    İngilizce

    İngilizce

    2022

    Makine MühendisliğiKoç Üniversitesi

    Makine Mühendisliği Ana Bilim Dalı

    PROF. DR. BURHANETTİN ERDEM ALACA

  2. Tez No

    143251

    Humidity sensors using MEMS and standard CMOS technologies

    MEMS ve standart CMOS teknolojileri ile nem sensörleri

    BURAK OKCAN

    Yüksek Lisans

    İngilizce

    İngilizce

    2003

    Elektrik ve Elektronik MühendisliğiOrta Doğu Teknik Üniversitesi

    Elektrik-Elektronik Mühendisliği Ana Bilim Dalı

    DOÇ. DR. TAYFUN AKIN

  3. Tez No

    119179

    A High fill factor CMOS uncooled infrared microbolometer detector

    Yüksek etkin alanlı CMOS soğutmasız kızılötesi mikrobolometre dedektörü

    MAHMUD YUSUF TANRIKULU

    Yüksek Lisans

    İngilizce

    İngilizce

    2002

    Elektrik ve Elektronik MühendisliğiOrta Doğu Teknik Üniversitesi

    Elektrik ve Elektronik Mühendisliği Ana Bilim Dalı

    DOÇ. DR. TAYFUN AKIN

  4. Tez No

    720168

    Effects of crosslinking and nanosilica on waterborne polyurethane dispersions

    Su bazlı poliüretan dispersiyonlarda çapraz bağlanmanın ve nano silikanın etkileri

    YUNUS ERKAHRAMAN

    Yüksek Lisans

    İngilizce

    İngilizce

    2022

    Polimer Bilim ve Teknolojisiİstanbul Teknik Üniversitesi

    Polimer Bilim ve Teknolojisi Ana Bilim Dalı

    DOÇ. DR. NESRİN KÖKEN

  5. Tez No

    98325

    Kaklık-Denizli çevresindeki travertenlerin jeokimyasal özellikleri

    Başlık çevirisi yok

    ZÜLFÜ DEMİRKIRAN

    Doktora

    İngilizce

    İngilizce

    2000

    Maden Mühendisliği ve MadencilikDokuz Eylül Üniversitesi

    PROF.DR. FARUK ÇALAPKULU

Geri Dön