Control for Epitaxial Growth Cycles of Wafers

Introduction

Many years ago, at the beginning of CJB’s hardware and software design activities, we were contacted by a well-known Italian company operating (and still operating) in the field of equipment for Silicon Wafer production.

The request, in light of the technology available at the time, was to design the automation of the chemical deposition process of various substances (doping) on silicon wafers, thus producing wafers ready for the “screen printing” of electronic components and their subsequent production.

How an Epitaxial Reactor Works

Simplifying the description, the reactor consists of a robot that picks up virgin silicon wafers and places them on a graphite support, which is inside a hermetically sealed reaction chamber.

Inside the chamber, the desired doping reaction takes place.

The reaction chamber reaches very high temperatures, depending on the support: 1300ºC for silicon wafers and up to 1700ºC for silicon carbide wafers.

Following specific recipes, with precise injection quantities and timing, doping chemical substances are dosed and injected into the reaction chamber. These substances, also due to the extremely high temperatures, diffuse in a controlled manner into the wafers.

In some cases, these processes are carried out under high vacuum conditions.

At the end of the process, the reaction chamber is cooled, and a robot picks up the doped wafers.

These wafers can then proceed to the next steps (screen printing, etching, etc.) for the production of integrated circuits, which will eventually be cut from the silicon/silicon carbide wafer.

The Beginning of the Project

Twenty-five years ago, automation systems were based on large-format boards inserted into racks equipped with a dedicated backplane for board-to-board communication.

The chosen format was VMEbus, with CPU boards mainly based on Motorola processors (68020, 68030), which were among the most widely used in industrial control systems at the time.

CJB’s Role

CJB designed the VMEbus I/O hardware, using Motorola boards as CPUs (the well-known MVME162).

CJB also developed the management software, based on a proprietary real-time operating system.

Evolution and Current Status

Over the years, VMEbus systems have become obsolete, replaced by PC-based systems incorporating appropriate Fieldbus boards such as CANbus, DeviceNet, etc.

However, process control must remain real-time. Therefore, CJB has continuously updated its software using the latest real-time operating system technologies.

The current choice is QNX, a widely used Hard-Real-Time Operating System, in which CJB has gained significant expertise in developing software applications.

Acquired Expertise

Knowledge of wafer production & doping processes at the automation control level, both for Silicon and Silicon Carbide.

Optimization of software in a hard-real-time environment with the QNX Operating System.

Management of fieldbus networks for critical applications (CANbus, DeviceNet, etc.) and control of motors and robots.