Thin Film Deposition Prof. Dr. Ir. Djoko Hartanto MSc Electrical Engineering Department Faculty of Engineering University of Indonesia February 14, 2003 1

Introduction The need of layers of semiconductor, dielectrics, and conductors to complete the device Beside the circuits have shrunk, they also have grown in the vertical direction. Through increased numbers of deposit layers.

Overview List of common deposition systems Atmospheric Pressure (AP) Horizontal Vertical Barel Vapor phase epitaxy

List of common deposition systems Overview List of common deposition systems Low Pressure (LP) and Ultra High Vacuum (UHV) Horizontal Vertical Barel Vapor phase epitaxy

Overview There two primary techniques for layer deposition : Physical Vapor Deposition (PVD) Chemical Vapor Deposition (CVD)

Physical Vapor Deposition (PVD) Physical vapor deposition (PVD) refers to a family of processes in which a material is converted to its vapor phase in a vacuum chamber and condensed onto a substrate surface as a thin film. PVD can be used to produce coatings of a wide variety of materials: metals G alloys ceramics G glasses semiconductors G polymers

Physical Vapor Deposition (PVD) All PVD processes consist of the following steps: synthesis of coating vapor, vapor transport to the substrate, condensation of vapors onto the substrate surface to form a thin film. These steps are carried out inside a vacuum chamber, so evacuation of the chamber always precedes the PVD process.

Physical Vapor Deposition (PVD) Pressure Units: 1 atm = 14.7 psia = 29.92 inches Hg = 760 mm Hg = 760 torr = 1.013 bar = 1.013 x 105 Pa 1 Pa = 1 N/m2 = 7.5 x 10-3 torr

Physical Vapor Deposition (PVD) The two most common PVD processes are: evaporation sputtering We have already covered the basics of evaporation. For evaporation, the background pressure in the vacuum chamber is typically ~10-6 Torr (~10-4 Pa) or lower. For sputtering, the background pressure in the vacuum chamber is typically 10-3 to 10-2 Torr (~1 Pa).

Evaporation In order to evaporate a material, it must be heated to a temperature at which its vapor pressure is 10-3 Torr or higher. E.g., aluminum must be heated to 1000°C or more.

Evaporation There are two common ways to heat the source material : resistive heating electron-beam heating. Resistive heating uses electric current flow through a tungsten filament to heat the source material. The source material can be placed directly on the tungsten filament, or it can be put in a crucible that is heated by the filament.

Evaporation Evaporation from a filament-heated crucible. Aluminum Vapor Aluminum Film Silicon Wafer

Evaporation In electron-beam (e-beam) evaporation systems, a high intensity beam of electrons, with energy up to 15 keV, is focused on the source material. Electron bombardment heats the source material to the temperature required for evaporation. Heating can be restricted to the source material itself . Þ The surroundings stay cool. Because pressure is so low in the vacuum chamber, in evaporation the source material travels in a straight line from the source to the substrate Þ shadowing

Physical Vapor Deposition (PVD) The mean free path, l of atoms or molecules in a chamber at pressure P is given by T is the absolute temperature, k is Boltzmann’s constant, and d is the diameter of the gas atoms or molecules The mean free path is the average distance between collisions in the chamber.

Physical Vapor Deposition (PVD) At room temperature and for a typical atom/molecule diameter of 4 Å, the previous equation becomes The pressure P is in pascals (Pa). 1 Pa = 1 N/m2 = 7.5 ´ 10-3 Torr What is the mean free path for typical evaporation and sputtering conditions?

Sputtering In sputtering, the source material is usually in the form of a sheet or plate, called a target. Sputtering is achieved by bombarding the target with energetic ions, typically Ar+. Atoms on the surface of the target are dislodged by this bombardment and fly off . These atoms then impinge on the substrate, resulting in deposition of a thin film.

Chemical Vapor Deposition Chemical Vapor Deposition (CVD) is the formation of a solid material (insulator, metal, or semiconductor) from the reaction of source gases (or vaporized liquids). The solid material is usually in the form of coating (a “thin film”) 20-5000nm thick (200-50,000Å or 0.02-5mm).

CVD of Zinc Oxide (ZnO) A simple Chemical Vapor Deposition system for the preparation of thin film coatings of ZnO on a substrate (e.g., a Si or GaAs wafer) is shown: Exhaust N2 + H2O + Zn(OOCCH3)2 Air Furnace Wafer

Chemical Vapor Deposition Materials deposited by CVD are usually amorphous or polycrystalline. If a “clean” crystalline substrate is used, it can sometimes act as a seed, resulting in a single crystal deposited layer. A crystalline layer deposited on a crystalline substrate is called an epitaxial layer.

Chemical Vapor Deposition Examples in microelectronics -- insulators (dielectrics) Silica (SiO2) deposition (400-500ºC) SiH4 + O2 ® SiO2 + 2H2 Silicon Nitride (Si3N4) deposition (700-800ºC) 3SiH4 + 4NH3 ® Si3N4 + 12H2

LPCVD Systems