Microelectronics Technology Mustafa Arikan University of Iceland.

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  • Slide 1
  • Microelectronics Technology Mustafa Arikan University of Iceland
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  • Contact info Mustafa Arkan (Musti) arikan@raunvis.hi.is ; mustafa.arikan@gmail.com arikan@raunvis.hi.is mustafa.arikan@gmail.com Tel : 525-4751 (Ingvarsson Lab., VR-III) Office hours ???
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  • In this course Two parts: Semiconductor processing (from raw material to microelectronic components) Semicondcutor characterization methods (physical & electrical-optical) Lectures & Labs Two lectures on 07.02.2008 and 07.03.2008 Two labs in two groups on 14.02, 21.02 and 14.03, 21.03.2008
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  • Goal of this lectures Overview of the fundamentals of microelectronics technology Fast & quick The tools we employ to produce and characterize electronic components Complexity and beauty of the technology Desired outcome Understanding of whole process Big picture Different approaches
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  • What is microelectronics? What is it about? Microelectronics is a subfield of electronics study and manufacture of electronic components which are very small (i.e. transistors, diodes) Semiconductors, metals, organic & plastic
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  • Real smalland impressive
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  • But very complex sometime
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  • What takes to achieve it?
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  • Different approaches
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  • The basics of semiconductor device fabrication Proper material for the purpose Geometry Material growth and removal (over and over again) by the help of lithography
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  • Simple example : MESFET Metal-Semiconductor Field Effect Transistor
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  • MESFET fabrication & The idea of lithography A real device from substrate to final form MESFET is relatively simple but not all the devices can be fabricated this easily Inverter fabrication
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  • CMOS Inverter
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  • Fabrication of a cmos inverter : Silicon technology Includes many steps Many different tools & technologies Crystal (substrate) growth Oxidation Diffusion & implantation Material growth (metal evaporation, sputtering, vapor deposition, epitaxy) Lithography & etching
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  • We need a substrate ! How do we get single crystalline Si? Czochralski Majority of the wafers Floating zone (high purity) High purity low oxygen & carbon impurity More complex w.r.t. Czochralski Bridgman Easy (melting & cooling) Low quality Drip melting, strain annealing and others
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  • Czochralski growth
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  • Ingot by Czochralski method
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  • Czochralski growth Typically used for Silicon but also Single crystal semiconductors (Si, Ge, GaAs) Metals (Pd, Pt, Ag, Au) Salts etc Requires seed crystal Fast (1-2 mm/min) Oxygen contamination from crucible Uniformity of axial resistivity is poor Segregation problems for dopants
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  • We have Si substrate Next Lets focus on individual steps and technologies from now on
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  • Oxidation CVD LPCVD (chemical vapor deposition (film growth) Thermally grown oxide (Oxidation) Photoresist (Lithography & etching)
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  • Oxidation One of the two main advantages of Si Ge is superior to Si (mobility, power consumption) SiGe (MOSFET channel), Gd 2 O 3 Dry oxidation : Si + O 2 SiO 2 Wet oxidation : Si + 2H 2 O SiO 2 + 2H 2 oxygen must diffuse through the oxide to react at the Si/SiO2 interface, so rate depends on the thickness of the oxide and reduces as the oxidation progresses.
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  • Oxidation thermal oxidation is performed in furnaces at temperatures between 800 and 1200C Many wafers on the boat (a quartz rack) at the same time Variants : RTO
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  • Oxidation : dry vs. wet Dry (molecular oxygen) : better oxide but slow (gate oxide) Wet (steam water vapor) : fast but porous (isolation) Deal-Grove model : thickness vs. time - theory
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  • Oxidation Thickness vs. time practice : Charts !
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  • Oxidation
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  • Lithography & Pattern Transfer Used for pattern transfer into metals, oxides and semiconductors Thin film deposition and lithography (including photo and e-beam, wet etching and lift-off) are the most frequently used method in our labs 2 types of resists: Positive : PR pattern is same as mask. On exposure to light, light degrades the polymers resulting in the photoresist being more soluble in developers. The PR can be removed in inexpensive solvents such as acetone. Negative : PR pattern is the inverse of the mask. On exposure to light, light polymerizes the rubbers in the photoresist to strengthen its resistance to dissolution in the developer
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  • Lithography & Pattern Transfer Black areas (PR) are the openings after development of PR
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  • Lithography & Pattern Transfer How do we perform this lithography thing? Dehydration bake or pre-bake Adhesion promoter (i.e. HMDS) Apply resist spinner Soft bake UV-exposure with mask Post-bake Post processing such as development & etching & lift-off Other processes required by specific needs (MEMS)
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  • Lithography & Pattern Transfer Baking spinner
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  • Lithography & Pattern Transfer Expose Develop
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  • Lithography & Pattern Transfer : Uses of lithography Etching Processes: open windows in oxides for diffusion, masks for ion implantation, etching, metal contact to the semiconductor, or interconnect.
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  • Lithography & Pattern Transfer Lift off Processes: Metalization
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  • Lithography & Pattern Transfer Issues with photolithography Resolution : feature size (~0.5 micron usually) Shorter wavelength = better resolution Registration : alignment of different layers on the same wafer (~ 1/3 of the resolution or 0.06 micron) Throughput : effective cost and time Resist thickness ~ 1/spin speed
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  • Lithography & Pattern Transfer Photolithography systems
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  • Lithography & Pattern Transfer Contact Resist is in contact with the mask: 1:1 magnification Inepensive, relatively high resolution (~ 0.5 micron), contact with the mask (scratches, particles and dirt are imaged in the wafer) Proximity Resist is almost but not in contact with the mask: 1:1 magnification Inexpensive, low resolution (~ 1-2micron), diffraction effects limit accuracy of pattern transfer. Less repeatable than contact methods, Projection Mask image is projected a distance from the mask and de-magnified to a smaller image: 1:4 -1:10magnification Can be very high resolution (~0.07 um or slightly better), No mask contact results in almost no mask wear (high production compatible), mask defects or particles on mask are reduced in size on the wafer. Extremely expensive and complicated equipment, Diffraction effects limit accuracy of pattern transfer
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  • Lithography & Pattern Transfer
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  • Lithography & Pattern Transfer : Light sources Typically mercury (Hg)- Xenon (Xe) vapor bulbs are used as a light source in visible (>420 nm) and ultraviolet (>250-300 nm and