Thermal process Part 1 Objective Identify two types

Thermal process Part 1

Objective • Identify two types of thermal process • Ability to describe, explain and discuss, evaluate on oxidation (wet and dry oxidation and include cleaning process) • Ability to describe and write on Diffusion and Drive-in, Annealing, Rapid thermal process (RTP).

Definition • Thermal processes are the processes operate at high temperature, which is usually higher than melting point of aluminum. • They are performed in the front-end of the semiconductor process, usually in high temperature furnace commonly called diffusion furnace.

THERMAL PROCESSES IN IC FABRICATION - OXIDATION

2 TYPES OF FURNACE: HORIZONTAL FURNACE VERTICAL FURNACE

HORIZONTAL FURNACE • Commonly used tool for thermal processes • Often be called as diffusion furnace • Quartz tube inside a ceramic liner called muffle • Multi-tube system

LAYOUT OF A HORIZONTAL FURNACE

HORIZONTAL FURNACE

OXIDATION: INTRODUCTION

OXIDATION: INTRODUCTION

OXIDATION: APPLICATION

OXIDATION: APPLICATION – DIFFUSION BARRIER

OXIDATION: APPLICATION – PASSIVATION SURFACE

OXIDATION: APPLICATION – SCREEN OXIDE

OXIDATION: APPLICATION – PAD & BARRIER OXIDES IN STI PROCESS

OXIDATION: APPLICATION – PAD OXIDE

Oxidation: Application – Device Isolation

Oxidation: Application – Blanket Field Oxide Isolation

Oxidation: Application – Local Oxidation of Silicon (LOCOS)

Oxidation: Application – LOCOS Process

Oxidation: Application – Sacrificial Oxide

Oxidation: Application – Device Dielectric

Oxidation: Application – Device Dielectric

RCA CLEAN

Oxidation: Mechanisms

Oxidation: Oxide Growth Rate Regime

Oxidation Rate Temperature

Oxidation Rate Wafer Orientation

Oxidation Rate Dopant Concentration

Pre-oxidation Clean

Oxidation Process

Dry Oxidation System

Dry Oxidation

Wet Oxidation Process vs Dry Oxidation Process

Boiler System

Diffusion Stopped here…

Illustration of Diffusion Doping

Diffusion • Replaced by ion implantation due to the less process control • Still being used in drive-in for well formation

Diffusion Doping Process

Wafer Clean Oxidation Doped Area Patterning Etch Silicon Dioxide Strip Photoresist Wafer Clean

Wafer Clean Drive-in Oxidation Strip Photoresist Doped Area Patterning Wafer Clean Etch Silicon Dioxide

Drive-in

Phosphorus Drive-in

Limitations and Applications

Application of Diffusion: Drive-in

Four-Point Probe Measurement

Annealing and Rapid Thermal Process (RTP)

Rapid Thermal Processing (RTP)

Rapid Thermal Processing (RTP)

Schematic of RTP Chamber

Annealing & Dopant Diffusion

Annealing and Dopant Diffusion

Anneal Rate and Diffusion Rate Dopant Diffusion After Anneal

Advantage of RTP over Furnace

RTP Temperature Change

Summary of Thermal Process 1. Oxidation, diffusion, annealing, and deposition 2. Wet oxidation is faster, dry oxidation has better film quality. Advanced fab: mainly dry oxidation. 3. Diffusion doping with oxide mask, used in lab 4. Annealing recovers crystal and activates dopants 5. RTP: better control, faster and less diffusion 6. Furnaces: high throughput and low cost, will continue to be used in the future fabs

‘It does not matter how slowly you move, as long as you do not stop’ - Confucius