FKA196 Fundamentals of Micro- and Nanotechnology Exam 2023/2024 PDF

Examination in FKA196-2023/2024: Fundamentals of micro- and nanotechnology, 7.5p Responsible teachers: August Yurgens, tel. +46 709 29 69 56 Department of Microtechnology and Nanoscience (MC2)...

Examination in FKA196-2023/2024: Fundamentals of micro- and nanotechnology, 7.5p Responsible teachers: August Yurgens, tel. +46 709 29 69 56 Department of Microtechnology and Nanoscience (MC2) (Dated: 23 Oct, 2023; 08.30 − 12.30) ˆ Answer Quiz questions, by marking cells in the answering table that correspond to the alternatives included in the questions. Please fill the table tidily, it will be scanned and read automatically. In particular, make sure not to cross cell borders with your markings. Some good- and bad examples can be found in Fig. 1. In case of errors, please fill in anew another sheet. Only one answering sheet should be returned to avoid confusion. FIG. 1. Examples of acceptable (left) and unacceptable (right) markings in the answering sheet. ˆ Please note: a) There can be several correct answers to the questions. It can happen that all choices are correct or false. You will still earn some fractional points even if you failed to correctly mark all correct answers. b) The questions have different weights indicated by numbers from 1 to 9 proceeded by ♡, e.g. ♡5. ˆ In total, 70 credit points for the exam quiz; 10 points for presenting a literature project/poster, 5 points for lab sessions, and maximum 15 points for home assignment. Grading is the following: ⩾ 40 points- passed (G); ⩾ 60 points- well passed (VG); ⩾ 80 points- excellent (MVG) ˆ Allowed materials: Physics and Mathematics Handbook, Standard Math Tables, or similar, a simple calculator, and a dictionary. One side of an A4 paper with handwritten notes. ♦ Electronic devices which can store large amounts of information or connect to the internet (electronic organizers, smart phones, etc.) are NOT allowed.  2 Intentionally empty  3 1. Take h, k, and l to be the Miller indices, in this of total sites that will be unoccupied at room tem- order. What is correct? (♡1) perature (22 C). (♡2) (a) 3.3e-5; (b) 1.2e-12; (c) 1.1e-15; (d) *** 4.8e-14; (a) *** (h, k, l) is the corresponding crystallo- (e) 3.2e-21; graphic plane; (b) *** [h, k, l] is the normal to the crystallo- 5. Which solid-state bonds are not directional? (♡1) graphic plane; (a) All. (b) *** Metallic. (c) Covalent. (d) *** (c) (h, k, l) is the normal to the corresponding Ionic. (e) *** Van der Waals. crystallographic plane; 6. Which of the following is/are correct for pumps? (d) [h, k, l] is the corresponding crystallographic (♡1) plane; (a) *** Roots Pump: requires forepumping and (e) [l, k, h] is the normal to the corresponding susceptible to overheating. crystallographic plane; (b) *** Diffusion Pump: forepumping is required. (c) Cryo-Pump: gas particles are ionized by high voltage. (d) *** Turbo-molecular Pump: 20-30 thousand revolutions per min. (e) *** Sputter Ion Pump: no oil contamination. (f) Diffusion Pump: no oil contamination. FIG. 2. To question 2 2. Calculate angle between the two planes shown in Fig. 2 (cos(α) = √ 2h1 h22 +k21√ k2 +l1 l2 2 2 2 ) (♡4) h1 +k1 +l1 h2 +k2 +l2 (a) ≈ 16 ; (b) ≈ 28 ; (c) ≈ 32◦ ; (d) *** ≈ 56◦. ◦ ◦ 3. Why does immersion photolithography give higher resolution? (♡2) (a) Because the incident light has shorter wave- length. (b) Because of no dust particles in the liquid. (c) Because of smaller mechanical vibrations due to high viscosity of the liquid. (d) *** Because of a larger numerical aperture that can be used without decrease of the depth of focus. (e) Because of stronger lenses with large refractive FIG. 3. To question 7. index. 4. The most elementary of crystal-lattice defects are 7. Apart from its toxicity, can mercury be used in- vacancies. Assuming the activation energy for cre- stead of oil (or organic fluid, see the table) in a ation of a vacancy of 0.78 eV, estimate the fraction diffusion pump (see Fig. 3)? (♡5)  4 (a) Yes, the pumping speed will be much higher (b) No. Photoresists must be dissolved in acetone, while minimum pressure - much lower when cleaning up the surface. replacing oil by mercury. (c) No. Even if a photoresist cannot be dissolved (b) No, one cannot reach high enough vapor pres- in acetone, it must be removed by e.g. oxygen sure by heating mercury to create jet streams plasma. that would capture gas molecules. 12. Room-temperature high-vacuum pumping speed (c) *** Yes, but the minimum pressure will not depends on (♡2) be any lower. (d) No, mercury boiling temperature is too high (a) chamber volume for any practical diffusion pump. (b) *** pipe line diameter 8. What is(are) distinct use(s) of e-beam lithography? (c) *** gas impingement rate (♡1) (d) critical-point pressure of the gas (a) *** Direct exposure of resist for device fabri- 13. What is typical degree of gas ionization in the glow cation. discharge used in thin-film processing? (♡1) (b) Thin-film morphology modification. (a) 1; (b) 0.1-0.01; (c) *** 1e-4; (d) 1e-6; (e) 1e-8 (c) Device trimming by high-density electron − 1e-9; beam bombardment 14. Consider a reversible reaction used in CVD of Si: (d) *** Mask fabrication for subsequent optical SiH4(g) ↔ Si(s) + 2H2(g) , where ”g” and ”s” mean lithography. gas and solid, respectively. Which direction the re- 9. Are there any general advantages of the e-beam action will shift to upon increasing pressure? (♡1) metal evaporation compared to evaporation from (a) To the right. (b) *** To the left. (c) Will not a resistive boat by Joule heating? (♡1) shift. (a) The methods are completely equivalent (b) *** In the e-beam deposition melted metal is not in contact with holder material thereby avoiding contamination. (c) *** Melted metal can alloy the boat material rendering it brittle and difficult to re-use; this does not happen in the e-beam evaporation (d) The e-beam evaporation is much more energy- efficient for small quantities of evaporated ma- terial. 10. Equation describing time evolution of the pressure P (t) during pump down in the presence of out- gassing or a leak reads: −V (dP/dt) = Sp P − Q, where V is the chamber volume, Sp is the pumping speed, and Q is the leak throughput (torr*liters/sec). (Problem 10 on p.91 of Ohring’s book) After evacuation of a chamber whose volume FIG. 4. To question 15. is 30 liters to the pressure 1e-7 torr, the pumps are isolated. The pressure rises to 1e-5 torr in 3 min. What is the leakage rate (in torr*liters/sec) ? (♡3) 15. Why is the wafer holder bigger in the lower part of the CVD reactor making the gap between the (a) 3.6e-5; (b) *** 1.7e-6; (c) 1.7e-7; (d) 3.6e-8; holder and walls narrower? (see Fig. 4) (♡2) 11. Can a photoresist be left on a wafer during several (a) To make removal of the ready-processed processing steps or it must be removed after each wafers easier. of the steps? (♡1) (b) *** To compensate for depletion of precursor (a) *** Yes. Some photoresists (e.g. SU8) can gases in the perpendicular to the gas-flow di- make parts of devices. rection.  5 (c) To reduce the back-flow of the precursor gases. (e) Ionization pump. (d) To make the lower-lying wafers be closer to 18. Which of the below statements are true for light the heater thereby increasing their tempera- and electron optics? (♡1) ture and, hence, compensate for the depletion of precursor gases. (a) *** Unlike photons, the energy of electron may change. (b) At high energies, electrons have larger wave- lengths than photons. (c) *** In the electron optics, the refraction index changes continuously. (d) *** Electron lenses are converging. (e) Electrostatic optics has no aberration. (f) *** Magnetic lenses twist the beam. (g) *** The electrons interact with each other. 19. Which statement(s) is(are) true for the raster scan? (♡1) (a) *** The beam scans over the substrate line by line. (b) The beam remains on at all times. FIG. 5. To question 16. (c) The beam is deflected to draw out the features in a selected area of the chip. 16. Moving turbine blades of a turbo-molecular pump (d) The beam is deflected in y-direction only. impart additional velocity to gas molecules towards the pump exhaust. Can this be done somehow else, say, by using many piezoelectric crystal oscil- lators instead of turbines (see Figure 5)? Assume the characteristic velocity of gas molecules v = 0.5 km/s, resonance frequency of oscillations f = 20 MHz, and amplitude of resonant oscillations A = 3 µm (PZT plate of 0.1 mm thickness). (♡5) (a) No, because the velocity change due to bounc- ing from the moving surface of the oscillator is too small compared to v. (b) *** Yes, because the velocity change due to bouncing from the moving surface of the os- cillator is quite comparable with v. (c) No, because there will be equally many molecules that will be slowed down- or accel- erated due to bouncing against moving surface FIG. 6. To question 20. during one period of oscillation. (d) Yes, because the velocity change due to bounc- 20. The graph shows the Maxwell distribution of ing from the moving surface of the oscillator molecular √ speeds for several noble gases f (|v|) = is much larger than v. (4v 2 / π)(M/(2RT ))3/2 exp(−M v 2 /(2RT )) (see Fig. 6). Which curve represents gas with the 17. Which of the vacuum pumps can cause oil contam- heaviest atoms? (♡2) ination? (♡1) (a) *** 1; (b) 2; (c) 3; (d) 4; (a) Cryo pump. 21. Why does vacuum leak-testing use helium? Helium (b) *** Diffusion pump. is:(♡1) (c) Turbo-molecular pump. (a) a noble gas; (b) light; (c) *** scarce in ambient (d) *** Rotary vane pump. air; (d) easy to ionize.  6 22. What is/are true about pumping speed? (♡1) (e) *** Size of the pixel (a) It is more efficient to use a better pump than (f) Density of secondary electrons to increase diameter of pumping tube 27. Four 10-cm-long discharge tubes are filled with air, (b) *** It is the volume of gas passing the plane of H2, Ar, and Ne at 0.01, 0.3, 1, and 30 torr, respec- the inlet port per unit time at a given pressure tively, and connected electrically in parallel. 1 kV at the inlet. is then applied to this system. Which tubes will (c) *** It refers to a given plane, while the con- start glowing (see Fig. 7? (♡3) ductance refers to an element across which a given pressure difference is set. (a) All. (d) *** It depends on a pump but also on a pipe (b) None. line. (c) Air- and Ne- filled only. 23. Why are registration marks important in e-beam (d) Ar-filled only. lithography? (♡1) (e) Ar- and Ne-filled only. (a) *** They improve accuracy of alignment. (f) *** H2- and Ar-filled only. (b) They compensate for wafer-thickness varia- 28. In photolithography, developer dissolves the ex- tions. posed areas of (♡1) (c) They are used for protection of important pat- (a) Negative photoresist tern parts. (b) Hard-baked photoresist 24. Vacuum is important in thin film deposition be- (c) *** Positive photoresist cause (♡1) 29. Pre-baking in oven is slower than pre-baking on on (a) It makes films thinner. hot plate because (♡1) (b) *** It makes thin films cleaner. (a) solvent is absorbed in photoresist (c) It prevents sample from drying. (b) photoresist cannot be heated in the oven (d) It makes thin films thicker. (c) *** solvent is not trapped by a crust at the (e) *** It makes thin-film deposition by evapora- surface which is formed when heated in the tion possible. oven 25. What is/are true for vacuum systems? (♡1) (d) photoresist is heated from inside (a) It is better to have a good pump than a better (e) air is not a good conductor of heat tube attached to the pump. 30. Which of the following sentences are correct to de- (b) *** The pressure is defined by the momentum scribe the photolithography resolution? (♡1) transfer during collisions of gas molecule with chamber walls. (c) Gas-transfer pump makes gas molecules to be absorbed at the developed surface area in the pump. (d) *** The higher the vacuum the lower the pres- sure so the longer the mean free path. (e) Pressure goes up only because of failed pump- ing system. 26. The speed of pattern writing by e-beam is limited by (♡2) (a) *** Resist sensitivity (b) Wafer thickness and its electrical conductivity (c) *** Bandwidth of deflection system (d) *** E-beam current density FIG. 7. To question27  7 (a) Higher resolution can be achieved by using (d) There is no difference longer wavelength. 36. If you compare thin-film deposition by evaporation (b) Thick photoresist normally improves pho- and sputtering, which statement(s) is(are) true? tolithography resolution. (♡1) (c) *** Resolution is limited by diffraction of light used for exposure. (a) *** Evaporated atoms generally have lower ki- netic energy than sputtered atoms. (d) *** Using high numerical aperture lenses to project the light can improve the photolithog- (b) For a lift-off process it is better to use sput- raphy resolution. tering than evaporation. 31. The thickness of the edge bead can be reduced if (c) *** Sputtered atoms generally experience (♡1) many collisions before reaching substrate, while evaporated atoms do not. (a) *** having smooth edges (d) *** Sputtering has better step coverage than (b) having sharp edges evaporation. (c) using rectangular wafers (e) In sputtering you have fewer grain orienta- (d) *** using circular wafers tions. 32. If we introduced some distance between a pho- 37. Which factor(s) does (do) improve the uniformity tomask and photoresist, (♡1) of thin-film thickness in PVD? (♡1) (a) *** it would decrease the resolution of pho- (a) Short source-to-substrate distance tolithography; (b) *** Long source-to-substrate distance (b) *** it would make the obtained pattern qual- (c) Static holder ity poorer; (d) Low deposition rate (c) it would give the obtained pattern more con- trast; (e) High deposition rate (d) it would increase the resolution; (f) Deposition at an angle ¿30 deg. (e) *** it would save the mask from contamina- 38. PVD by sputtering provides (♡1) tion; (a) *** Good adhesion of thin film to substrate. 33. In spin coating process, the resist thickness depends on? (♡1) (b) Spiral-like trajectories of atoms. (c) *** Substrate heating. (a) Moisture of the air. (d) Very poor coverage of steps and trenches. (b) *** Resist viscosity. (c) *** Spinning velocity. 39. In PVD method, a longer source-to-substrate dis- tance leads to : (♡1) (d) Illumination intensity. 34. Depth of focus can be made better without making (a) higher deposition rate resolution worse by (♡1) (b) *** lower deposition rate (a) increasing numerical aperture (c) *** better thin-film uniformity (b) decreasing numerical aperture (d) lower risk of contamination in low-vacuum chambers (c) *** using immersion photolithography (e) *** higher risk of contamination in low- (d) using masks with a semi-transparent pattern vacuum chambers 35. Which thin film deposition method gives the best step coverage? (♡1) 40. Do you always need a thickness monitor to know the thickness of a thin-film? (♡2) (a) Evaporation (a) *** No. You can measure the thickness after- (b) Sputtering wards, by e.g. AFM, profilometer, or other (c) *** Chemical vapor deposition suitable characterization method.  8 (b) No. You can first weigh- and then evaporate (b) Large distance between electrodes all the material in the source. The relative (c) Electrodes should be parallel position of the source and substrate does not matter because the material is evaporated into (d) *** Some free electrons in the gas solid angle of 2π. 46. Which of the discharges is most commonly used in (c) *** No. You can first weigh- and then evapo- micro fabrication (♡1) rate all the material in the source. You have to know distance between the source and sub- (a) Townsend discharge strate. (b) Corona discharge (d) Yes. This is the must for thin-film deposition (c) *** Glow discharge systems. (d) Arc discharge 41. Which of the following statements about sputtering 47. Which of the following statements about sputter are true? (♡1) yield is not true? (♡1) (a) *** There is no melting of the material. (a) Sputter yield S is the number of sputtered (b) The method can only be used for metals. atoms per incident particle (c) *** High energy particles can damage the sub- (b) *** In sputtering of alloys, the composition in strate. the deposited thin film is not the same as in (d) *** Adhesion between the film and the sub- the target strate is usually good. (c) Sputter yields are different for various ele- (e) *** Gas atoms can be entrapped in the film. ments and materials (d) Sputter yield depends on the angle of ion in- 42. Which of the following describes Fick’s first law for cidence diffusion? (♡1) (e) Sputter yield depends on the energy of inci- (a) The time derivative of the concentration is dent ions proportional to the particle flux gradient. (f) *** Sputter yield does not depend on crystal- (b) *** The particle flux is directly proportional lographic orientation of the single - crystalline to the concentration gradient. target (c) The particle flux is inversely proportional to 48. How can Debye length be defined? (♡2) the concentration gradient. (d) The particle flux is inversely proportional to (a) Debye length is a measure of the time required the concentration time derivative. to restore charge equilibrium. 43. In a simplified atomistic model of diffusion process (b) *** Debye length is a measure of the size of a the main parameters are: (♡1) mobile electron cloud which is formed around positive ion when it is pushed into charge- (a) jump height neutral plasma. (b) *** attempt frequency (c) Debye length is a measure of the time re- (c) jump velocity quired by plasma electrons to neutralize posi- tive ion when positive ion is pushed into neu- (d) *** jump distance tral plasma. (e) *** activation energy (d) Debye length is an average distance between (f) flow rate charged particles in the plasma. 44. Estimation of the diffusion length can be done by 49. Sputtering yield as a function of the beam inci- using:? (♡1) dence angle (counted from the target-surface nor- (a) Dt0.5 (b) Dt−0.5 (c) (Dt)−0.5 (d) *** (Dt)0.5 mal) (♡1) (e) tD0.5 (f) tD−0.5 (a) first decreases, then increases. 45. What is most important for a discharge to occur? (b) decreases all the way up to nearly 90 degrees. (♡1) (c) *** first increases, then decreases. (a) Small distance between electrodes (d) increases all the way up to nearly 90 degrees.  9 50. What is/are not true about plasma? (♡1) (a) High substrate temperature and low deposi- tion rate (a) Plasma is a region of the gas discharge con- taining equal numbers of negative and positive (b) High substrate temperature and high deposi- charges. tion rate (b) The energies of the charge carriers and neu- (c) *** Low substrate temperature and high de- trals are randomized by collisions and interac- position rate tions. (d) Low substrate temperature and low deposition (c) *** In majority of cases, at least 10% of gas rate species are ionized. 56. Why do we use four probes in resistivity measure- (d) For stability of plasma, charge generation ments? (♡2) should replenish charge carrier loss due to re- combination and out-diffusion. (a) To measure the thickness of the thin film. 51. What is/are not true for RF plasma system? (♡2) (b) Because of historical reasons. (c) Because there are two physical quantities that (a) *** It is limited to conducting materials we actually measure: current and voltage, (b) Insulating materials can be sputtered with two probes for each. (c) *** The mobility of negative and positive (d) *** To eliminate the contribution from the charges are similar current flowing through an unknown contact (d) The mobilities of negative and positive charges resistance. are very different (e) To eliminate discharge between the contacts. 52. For a discharge to be ignited (♡3) 57. What is true regarding thin film versus bulk com- parison? (♡1) (a) ions should have high enough thermal energy (b) *** an electron should gain enough energy be- (a) Thin films have lower chemical reactivity tween collisions with neutrals (b) *** Thin film properties can be different from (c) electrons should have mean-free path compa- those of the bulk because of the size effects in rable with distance between electrodes thin films (d) an electron should gain enough energy while (c) *** Properties of thin film depend on deposi- freely propagating between electrodes tion methods (e) neutrals should have high enough thermal en- (d) High electrical fields are difficult to attain in ergy thin films 53. In thin-film deposition, which parameters should 58. How can one improve adhesion of thin films? (♡1) be used to have large grains in the thin film? (♡2) (a) *** By using reactive ion implantation (a) low substrate temperature (b) *** By using chemical pre-etching of the sub- (b) *** low deposition rate strate (c) high deposition rate (c) By adding thermal stress (d) *** high substrate temperature (d) *** By low energy pre-sputtering of the sub- strate 54. How do you see when a new epitaxial layer has been finished using RHEED? (♡1) (e) By increasing number of dislocations (a) When the RHEED signal is at minimum 59. Which is/are reason(s) for developing internal stress in thin films? (♡1) (b) When the RHEED signal is in the middle (c) *** When the RHEED signal is at maximum (a) a high nucleation density (d) None of the mentioned here (b) *** difference in lattice constants 55. For the case of Cu thin films on (111) NaCl, which (c) *** difference in thermal expansion coeffi- combination(s) would result in increased density of cients nuclei? (♡2) (d) long annealing times substrate  10 60. A customer wants you to measure the surface to- (a) you have to increase the width and length of pography of a sample. The sample is not electri- the transistor also cally conducting. Which method is the best for the (b) you have to use a low-k material instead of task? (♡1) silicon dioxide (a) SIMS (b) *** AFM (c) TEM (d) STM (e) SEM (c) *** you have to use a high-k material instead (f) XPS of silicon dioxide 61. What gives contrast in FIB microscopy and what (d) you have to use silicon trioxide instead of sili- is the corresponding feedback mechanism? (♡1) con dioxide (a) Conductivity contrast, insulators look bright 66. What kind of etching should be used to etch a v- while conductors are dark. groove in < 100 > oriented silicon? (♡1) (b) *** Orientational contrast, difference in yield of secondary particles depending on crystallo- (a) *** Anisotropic wet etching graphic orientation of grains. (b) Isotropic wet etching with forced agitation of (c) X-ray electron contrast, chemical composition the fluid spectroscopy. (c) Isotropic wet etching without agitation of the (d) *** Conductivity contrast, insulators look fluid dark while conductors are bright. (d) Plasma etching 62. Why FIB microscopy uses Ga ions? (♡1) 67. MEMS structures are based on ability to sculp- ture/machine silicon on micrometer scale. These (a) *** Gallium easily melts and remains liquid technologies can be divided into a few groups. for a long time even at temperature below the What are they? (♡1) melting one (b) Ga ions are light (a) *** Surface micro-machining (c) Ga is a cheap material (b) *** High-aspect-ratio electroplating (d) Ga readily diffuses into Si even at room tem- (c) Post processing perature (d) *** Bulk micro-machining 63. Which terminals do the MOS transistors have? (e) Hard baking (♡1) 68. Which of the methods below belong to the surface (a) Drain, Gate, Base, Source cleaning process ? (♡1) (b) *** Drain, Source, Gate, Bulk (a) photoresist pre-baking (c) Emitter, Base, Collector (b) *** soaking in acetone with ultrasonic agita- (d) Emitter, Gate, Collector tion (e) Drain, Gate, Bulk (c) *** oxygen plasma ashing (f) Drain, Gate, Bulk, Collector (d) primer coating 64. What is true about ion implantation? (♡1) 69. What happens to polymer e-resists exposed to elec- (a) *** The wafer can be held at ambient temper- tron beams? (♡2) ature during the process. (a) *** The molecule chains in the negative resist (b) *** The incoming energy can be controlled. become cross-linked (c) Only atoms with the same valency as the host (b) The molecule chains in the positive resist be- material can be implanted. come cross-linked (d) *** There is a good control of the incoming (c) The molecule chains in the negative resist are species and the dose. broken into shorter chains 65. Which of the following solutions is appropriate if (d) *** The molecule chains in the positive resist you want to increase the gate isolation thickness in are broken into shorter chains order to minimize the tunneling current but at the same time you do not want any changes of the gate 70. How do you call numbers used to describe plane electric field in the channel? (♡1) orientations in a crystal lattice? (♡1)  11 (a) Mollier indices. (b) Smaller numerical aperture (b) *** Miller indices. (c) *** Shorter wavelength (c) Mellow indices. (d) *** Usage of phase-shifting mask (d) Muller indices. (e) *** Larger numerical aperture 71. What factors do not affect photoresist adhesion? 75. Postbake is not needed for (♡1) (♡1) (a) *** Wet Etching. (a) Wetting characteristics of resist (b) *** Lift off. (b) *** Incorrect alignment (c) Ar-Ion Etching. (c) *** Time of post bake 76. Comparing to photolithography, electron-beam (d) Surface smoothness lithography (♡1) 72. Assuming one and the same particle energy, select (a) *** is characterized by a smaller beam spot the order of particles corresponding to a decreasing size de Broglie wavelength: (♡1) (b) *** can have raster- and vector modes of ex- (a) electrons, photons, protons. posure (b) electrons, protons, photons. (c) *** has a higher flexibility (c) protons, electrons, photons. (d) uses high-pressure mercury lamp to extract electrons by photo effect (d) *** photons, electrons, protons. (e) *** has a limited fabrication throughput (f) uses phase-shifting masks to compensate for diffraction effects 77. Which of the following statements are true? (♡1) (a) *** Prebake is used to evaporate the solvent from the resist after spin coating (b) Postbake is needed for lift-off processes (c) *** Longer and hotter postbake makes subse- quent resist removal more difficult (d) *** In negative photoresist exposed areas be- come insolvable in the developer 78. Which of the following pumping techniques is/are based on particle entrapment? (♡1) (a) *** Cryo-pump (b) *** Sputter ion pump FIG. 8. To question 73 (c) Diffusion pump 73. What is IBAD (see Fig. 8? (♡2) (d) Turbo-molecular pump (e) Rotary mechanical pump (a) *** Ion Beam Assisted Deposition (f) Roots pump (b) Ion Beam Angled Deposition (c) Ion Beam Atomic Deposition 79. Which valve(s) has(have) to be closed when main- (d) Ion Beam Accumulated Dose taining a high vacuum in the diffusion-pump vac- uum system shown in the picture (see Fig. 9? (♡2) (e) Ion Beam Angled Deposition 74. For projection printing, which option(s) can give (a) Foreline valve (b) Gate valve (c) *** Roughing improved resolution? (♡1) valve (d) *** Vent valve (a) *** Thinner photoresist 80. Which are the direct reading pressure gauges? (♡1)  12 83. Efficient way(s) of increasing pumping speed is(are): (♡2) (a) *** use of a more efficient pump, (b) use of a spiral pipeline, (c) use of a pipeline with a buffer volume in the middle, (d) *** decreasing the distance between the pump and chamber, (e) *** increasing diameter of a pipe between the pump and chamber. 84. Which pumps use gas transfer principle? (♡1) (a) Adsorption. (b) *** Diffusion. (c) Sputter ion. (d) *** Turbo-molecular. (e) *** Rotary mechani- cal. 85. In physical vapor deposition method by evapora- tion, the deposition rate depends on.... ? (♡1) (a) *** vapor pressure; (b) pumping speed; (c) *** distance between the source and sub- FIG. 9. To question 79. strate; (d) temperature of the chamber walls; (a) Energy Transfer. (e) *** substrate orientation; (b) *** Solid wall. (f) size of the chamber; (c) Charge generation. 86. The highest yield of sputtering takes place for (♡2) (d) *** Liquid wall. (a) particles propagating perpendicular to the 81. In Sputter-ion pump (♡1) surface; (a) *** Gases are ionized and accelerated by high (b) particles being implanted below the surface; voltage. (c) *** particles impinging the surface at some (b) Ions sputter Ta anode. acute angle of about 50-60 degrees from the surface normal; (c) *** New layer of Titanium buries gas molecules for good. (d) particles impinging the surface at a sliding angle less than five degrees from the surface (d) *** Titanium is deposited on the walls and plane; getters the gas molecules. (e) particles being reflected from the surface; (e) *** Ions sputter Ti cathode. (f) Gases are ionized and then electrostatically di- 87. What does the A.A.A. rule mean? (♡0) rected towards the pump exhaust. (a) Add amino acid to water. 82. Which of the following vacuum pumps need both (b) Acid always after water. active heating and cooling during continuous oper- (c) *** Always add acid to water. ation? (♡1) (d) Water always after acid. (a) Roots pump. 88. Which of the following sentences is(are) not cor- (b) Turbo-molecular pump. rect? (♡1) (c) Sputter ion pump. (a) Insulators can be deposited by CVD. (d) *** Diffusion pump. (b) Insulators and metals can be deposited by (e) Cryo pump. sputtering.  13 (c) *** Tungsten is usually deposited by evapora- (d) *** High substrate temperature promotes tion. growth of mono-crystals. (d) Metals can be deposited by evaporation. 94. Which are two main parameters governing thin-film (e) Metals can be deposited by sputtering. nucleation? (♡1) 89. The nucleation process is not affected much by: (a) Deposition rate and particle density. (♡1) (b) Particle mass and energy. (a) *** Optical transparency of the substrate. (c) Particle density and source temperature. (b) Roughness of the substrate. (d) Particle mass and deposition rate. (c) Deposition rate. (e) *** Substrate temperature and deposition (d) Surface temperature. rate. 90. To which kind of materials is RF-discharge plasma 95. In one of the methods used to find the film thickness systems limited to? (♡1) using acoustics, a laser pulse is used to: (♡2) (a) Electrically conducting materials. (a) Excite the thin film into emitting light that characterizes the thickness of the film. (b) *** None of the mentioned here. (b) None of the mentioned here. (c) Ceramic materials. (c) Burn a fine hole in the material which can be (d) Insulating materials. used to find the thickness. (e) Amorphous materials. (d) *** Create local heating resulting in a ma- 91. Which technique(s) is(are) commonly used to de- terial expansion. The sudden expansion pro- termine the quality of epitaxial growth of thin duces a pulse of acoustic wave. films? (♡1) 96. You want to grow a 100 nm thick layer of SiO2 on (a) XRR (X-ray reflection). top of Si by oxidation. Which of the following char- acterization techniques could you use to confirm the (b) THEED (Transmission high energy electron layer thickness without modifying or damaging the diffraction). sample? (♡1) (c) *** RHEED (Reflection high energy electron (a) *** Ellipsometry. (b) RBS. (c) RHEED. diffraction). (d) SIMS. (e) Quartz Crystal Microbalance. (d) RLEED (Reflection low energy electron (f) AFM. diffraction). 97. What is correct in general? (♡2) (e) XRD (X-ray diffraction). (a) *** the thinner the thin film, the higher the 92. What are the basic modes of thin film growth? resistance; (♡1) (b) the thicker the thin film, the higher the re- (a) Kinetic. sistivity, when the mean-free path is shorter (b) Diffusional. than the film thickness; (c) Thermodynamic. (c) *** the thinner the thin film, the higher the (d) *** Layer-by-layer. resistivity, when the mean-free path is compa- rable with the film thickness; (e) *** Island. (d) the thicker the thin film, the higher the resis- (f) *** Stransky-Krastanov. tance; 93. Which is/are true regarding thin film growth? (♡1) 98. ZnO has a wide direct band gap. Its most com- (a) Low substrate temperature promotes growth mon applications are powerful laser diodes and light of mono-crystals. emitting diodes. Which common metals would you (b) *** High deposition rate promotes growth of prefer for making contacts to ZnO, among those poly-crystals. present in the Figure 10? (♡2) (c) Low deposition rate promotes growth of poly- (a) *** Cu or Ni, because they would not reduce crystals. ZnO at elevated temperature.  14 (b) Al, because it would not reduce ZnO and is 101. How to increase photolithography resolution? Use: cheap. (♡2) (c) Ti, because it would not reduce ZnO and has (a) thicker photoresist and shorter wavelength; a good adhesion. (b) *** thinner photoresist and shorter wave- 99. Which of the following methods can be useful in length; avoiding the effects of standing waves in photore- (c) thicker photoresist and longer wavelength; sists? (♡2) (d) *** thinner photoresist and larger aperture; (a) *** using thinner photoresists; (e) more sensitive photoresist and shorter expo- (b) decreasing the numerical aperture of the opti- sure time; cal system involved; (f) more sensitive photoresist and shorter devel- (c) using monochromatic incident light; oping time; (d) defocussing the optical system; 102. Which of the following steps in Photolithography (e) using thicker photoresists; should not be used for the lift-off method? (♡1) (f) *** using a broadband illumination; (a) Soft bake. (g) using immersion photolithography; (b) *** Hard bake. (c) Developing. 100. Which light wavelength(s) can be used for making grating with the period of 1.5 µm if a contact mode (d) Post processing cleaning. mask aligner and a photoresist with typical thick- (e) Exposure. ness of 1.3pµm are employed? Hint:Use equation 2bmin = 3 λ(a + d/2) (♡2) 103. What is(are) the difference(s) between AFM and STM? (♡0) (a) *** 193 nm; (b) *** 335 nm; (c) *** 248 nm; (d) *** 365 nm; (e) 405 nm; (a) In AFM the tip scans surface of samples but not in STM. (b) In STM the tip scans surface of samples but not in AFM. (c) *** The STM is based on electron tunnelling between the tip and surface of a sample while the AFM is based on detecting the attraction force between the tip- and surface. (d) Electrically conducting materials can only be studied in STM. 104. The energy which is required to remove an electron from a metal into free space is called (♡1) (a) Fermi energy. (b) Activation energy. (c) Planck energy. (d) Gibbs-Helmholtz energy. (e) *** Work function. (f) Free energy. 105. The temperature is a measure of (♡1) (a) the number density of gas molecules; (b) *** the kinetic energy of gas molecules; (c) the mean-free path of molecules; (d) the inter-atomic forces, FIG. 10. To question 98 (e) the potential energy of gas molecules;  15 106. Which deposition technique is the most suitable for 111. The thickness monitor is situated 60 cm away from a lift-off process? (♡1) the evaporation source. The wafer is 85 cm away. Both are equally tilted towards the source. What (a) CVD. is the tooling factor for this arrangement, i.e., how (b) *** Evaporation. different is the real thickness of the thin film com- pared to the one deposited onto the thickness mon- (c) Electroplating. itor? (♡3) (d) Atomic Layer Deposition. (a) 0.75 (b) *** 0.5 (c) 0.44 (d) 2.3 (e) 1.5 (e) Sputtering. 112. Which of the following statement(s) is/are not cor- 107. Sheet resistance is related to the bulk resistivity rect; (♡1) (ρ). Let w, l, and t be the width, length, and thick- ness of the thin-film sample, respectively. The sheet (a) Materials with low surface energy wet sub- resistance is (♡1) strates with a higher surface energy (a) ρ · w; (b) ρ/l; (c) ρ · t/w; (d) *** ρ/t; (e) ρ · t; (b) Both diffusion and desorption are determined by the temperature of substrate 108. In sputter-deposition of alloys, which of the flow- (c) Epitaxy is extended formation of single- ing is true about composition of the deposited thin crystal thin film on a single-crystalline sub- films? (♡1) strate (a) The composition of deposited thin film is dif- (d) *** Nucleation rate is unaffected by deposi- ferent from the target alloy material. tion rate and temperature of the substrate (b) *** The composition of deposited thin film is 113. What does ”critical thickness” mean in epitaxial the same as the target alloy material. films? (♡1) (c) The composition of deposited thin film de- (a) The minimum thickness of defect-free layer pends on the plasma and sputtering condi- tions. (b) *** The maximum thickness of the defect-free layer 109. What is the sputter yield? (♡1) (c) Thickness of substrate needed for epitaxial growth of film on it (a) *** The number of sputtered atoms per inci- dent particle. (d) The film lattice would compensate for dislo- cation defects above this thickness. (b) The number of sputtered atoms per second. (c) The number of sputtered atoms per minute. 114. Which statement(s) is(are) true regarding nucle- ation of a thin film? (♡2) (d) The amount of energy which is dissipated after the collision with target (per particle). (a) *** A high substrate temperature results in (e) The number of sputtered atoms per unit solid larger- but fewer nuclei angle. (b) *** At higher temperatures the nucleation barrier is higher 110. The residual resistivity of a metal thin film at low temperature (♡3) (c) A high deposition rate encourages formation of a coarse-grained structure in thin film (a) *** is proportional to the density of defects; (d) A high nucleation rate encourages formation (b) is inversely proportional to the density of de- of a coarse-grained structure in thin film fects; 115. One of the evaporation geometries to achieve uni- (c) *** depends on the thickness for high-purity form deposition is shown in the right part of Fig- and low-defect thin films; ure 11 (Fig. 3-9 of Ohring’s book). Referring to (d) depends on the specimen length and width that Figure, assume that the wafers are r0 in diam- (larger than the thin film thickness); eter, where r0 is the radius of the spherical dome (e) *** depends neither on the specimen length holding the wafers. How non-uniform is a thin film nor its width (larger than the thin film thick- deposited on the topmost wafer? (♡5) ness); (a) The geometry assures a uniform deposition, (f) *** depends on the metal; d/d0 = 1. That is exactly its purpose.  16 (b) d/d0 ≈ 29/32 = 0.91 (e) *** Thin film can have some contamination (c) *** d/d0 ≈ 7/8 = 0.88 in the beginning of deposition process if the shutter is not used (d) d/d0 ≈ 3/4 = 0.75 (e) d/d0 ≈ 31/32 = 0.97 118. A horizontal 3” wafer is quickly rotated around its center (=1100 rpm). A surface evaporation source 116. The photolithography resolution does not depend is 4” below the center of the wafer. What is the on: (♡1) ratio of the thin-film thickness at the edge to that in the center? (♡3) (a) Diffraction of light (a) 1 (b) 0.63 (c) 1.15 (d) *** 0.77 (e) 0.86 (b) *** Density of photoresist (c) Mask-to-photoresist distance 119. Henri-Louis Le Chateliers principle states that (♡2) (d) Thickness of photoresist (a) If the conditions of a system, once in equi- librium, are changed, the system will stay in 117. A simple evaporation-type thin-film deposition sys- equilibrium because it corresponds to the min- tem has a shutter. Is it needed? (♡2) imum of the free energy. (a) *** Thin films can be deposited even without (b) If the conditions of a system, initially in equi- shutter librium, are changed, the new state will be the (b) It is virtually impossible to deposit thin films new equilibrium. without shutter (c) If the conditions of a system, initially at equi- (c) It is needed for periodical termination of the librium, are changed, the equilibrium will shift deposition for better uniformity of the thin in such a direction as to amplify the changes. film Indeed, an explosive, if heated, will be set off (d) The thin film thickness can not be measured instantly thereby further increasing the tem- without first adjusting and stabilizing the de- perature. position rate and then opening the shutter (d) *** If the conditions of a system, initially at equilibrium, are changed, the equilibrium will shift in such a direction as to tend to restore the original conditions. 120. Which type of thin film growth can be expected in case when there is no wetting between the de- posited material and the substrate? (♡1) (a) *** Only ”island” type, no ”layer” (b) Only ”layer” type, no ”island” (c) Both ”island” and ”layer” are possible FIG. 12. To question 121. 121. Calculate the diffusion coefficient for As at 1000◦ C (in [cm2 /s] see Table in Fig. 12(♡3) FIG. 11. To question 115 (a) 3.5E-13 (b) 1.3E-14 (c) 3.1E-17 (d) *** 2.6E-15  17 122. Which effect makes the depth control of ion im- (c) Master of Science Directives System plantation difficult? (♡1) (d) *** Material Safety Data Sheet (a) tunneling effect 128. What do you do if you have evacuated the building (b) parasitic effect and the alarm has stopped, but the red light is still (c) charging effect flashing? (♡1) (d) *** channeling effect (a) Go back in the building and continue working. (e) electrical field effect (b) Go back and assess the situation. 123. In the constant-source diffusion, the dose is (c) *** Stay away. Do not go back in until the 2N0 (Dt/π)0.5 , where N0 , D, t are the concentra- lights have stopped flashing. tion at the surface, the diffusion coefficient, and (d) Go back into the building and rescue your the time, respectively. A 15-nm boron thin film on work. silicon wafer is annealed at 1100 C. Calculate the thickness of the film after one hour of the anneal- 129. In the case of spilling chemicals on the clean-room ing. The solubility limit of boron in silicon at this floor, which of the following activities should we temperature is 3.2E20 [1/cm3 ]. Take the density do? (♡1) and molar weight of boron to be 2.34 [g/cm3 ] and (a) Try to clean the chemical with the water as 10.8 [g/mol], respectively. The diffusion coefficient soon as possible of boron in silicon obeys the Arrhenius law with the prefactor D0 = 10.5 [cm2 /s] and the activation en- (b) *** Isolate the area ergy Ea = 3.69 eV (1 eV = 11605 K). The thickness (c) *** If possible use absorbing materials (in nm) is: (♡6) (d) Just ignore it and do your your job; the lab (a) 0.0; (b) 7.1; (c) 4.3; (d) 8.4; (e) 10.2; (f) *** staff will clean the chemical in due time 14.1; (e) *** Call the lab staff 124. You are to evacuate the lab when either the gas or 130. RHEED in MBE (♡1) fire alarms are active. What colors do these alarms have? (♡1) (a) *** Can be used to monitor the layer by layer growth. (a) both are blue (b) *** Has the maximum intensity when the (b) fire is red and gas is blue growth of one atomic layer finishes. (c) *** both are red (c) Has the minimum intensity when the growth (d) gas is red and fire is blue of one atomic layer finishes. 125. In the event of fire, personnel should first of all (d) Has the medium intensity when the growth of consider to leave the clean room using (♡1) one atomic layer finishes. (a) the quickest route 131. In Colloidal Lithography, which factor could have effect on the distance between the particles? (♡1) (b) following other personnel (c) *** by following well-rehearsed evacuation (a) Van der Waals force. procedures (b) *** Surface charge of the particles. (d) going in whichever direction seems safest (c) Surface tension of the solution. 126. The manual alarm station is normally situated? (d) *** Ionic strength of the solution. (♡1) (e) Temperature. (a) in the middle of the clean room 132. A cylindrical chimney with the radius r0 is intro- (b) *** near an exit duced to protect lower parts of chamber from thin- (c) close to chemical storage cabinets film depositions (see Fig. 13). Find the ratio of the (d) outside the building thin-film thicknesses on chimney’s inner surface at z = 3r0 and z = r0 assuming the surface source 127. What does the commonly-used in the clean room (hint: the deposition rate Ṁ ∝ cos(ϕ) cos(ψ)/R2 ). abbreviation ’MSDS’ stand for? (♡1) (♡4) (a) Molybdenum Sulphate Diluted Solution (a) 0.08 (b) 0.12 (c) 0.19 (d) 0.32 (e) 0.47 (b) Material Science and Data Structures  18 FIG. 13. To question 132.