608
6 Reverse Engineering of Microcircuits
with standard reverse engineering tools and methods but serve as active elements
performing specific logic functions. The disadvantage of such methods of protection
from reverse engineering is an increase in the development cost due to complication of
the IC production process, increased number of process operations, and the necessity
to alter masks or use additional masks. At the same time, the use of these methods
does not ensure complete protection, even though it significantly increases the time
and stability of the process of restoring circuitry solutions.
As a rule, both of these groups of methods are used simultaneously, which
increases the IC protection level.
In order to ensure reliable protection from reverse engineering, the development of
the technology for prevention of recovery of the circuit and IC functioning algorithms
shall include two stages:
1st stage—structural and technological modification of the structure of functional
elements of the IC chip;
2nd stage—circuitry transformations.
Let us consider the main technical solutions used to modify the structure of
functional elements and blocks of the chip for the purpose of countering reverse
engineering.
6.7.2.1 Structural and Technical Methods of Countering Microcircuit
Re-engineering
As indicated above, the stage of modifying IC functional elements, which is additionally introduced in the design route, is based on applying structural and process
methods of countering reverse engineering on the level of the IC chip, including
various approaches to creating hidden (masked) elements and connections, false
additional traces and interconnects, non-functioning (stuck-open and stuck-closed)
transistor structures, etc.
6.7.2.2 Methods of Introducing Hidden (Masked) Interconnections
into Microcircuit Designs
The role of hidden (masked) connections is most commonly performed by ionimplanted connections—ohmic connections between doped regions of n-type or ptype of conductivity (e.g., transistor sources/drains) formed with the help of a recessed
ion-implanted conductive channel; electrical connections of integrated elements with
the help of a metal silicide layer, etc.
We will consider the features of using hidden connections on the example of
using ion-implanted connections to replace metallization buses, which were used
in the original design not to connect doped regions of integrated elements [24].
Since the connections formed by ion implantation are nearly impossible to identify
using optical microscopy means, they cannot be identified by a reverse engineering
6 Reverse Engineering of Microcircuits
with standard reverse engineering tools and methods but serve as active elements
performing specific logic functions. The disadvantage of such methods of protection
from reverse engineering is an increase in the development cost due to complication of
the IC production process, increased number of process operations, and the necessity
to alter masks or use additional masks. At the same time, the use of these methods
does not ensure complete protection, even though it significantly increases the time
and stability of the process of restoring circuitry solutions.
As a rule, both of these groups of methods are used simultaneously, which
increases the IC protection level.
In order to ensure reliable protection from reverse engineering, the development of
the technology for prevention of recovery of the circuit and IC functioning algorithms
shall include two stages:
1st stage—structural and technological modification of the structure of functional
elements of the IC chip;
2nd stage—circuitry transformations.
Let us consider the main technical solutions used to modify the structure of
functional elements and blocks of the chip for the purpose of countering reverse
engineering.
6.7.2.1 Structural and Technical Methods of Countering Microcircuit
Re-engineering
As indicated above, the stage of modifying IC functional elements, which is additionally introduced in the design route, is based on applying structural and process
methods of countering reverse engineering on the level of the IC chip, including
various approaches to creating hidden (masked) elements and connections, false
additional traces and interconnects, non-functioning (stuck-open and stuck-closed)
transistor structures, etc.
6.7.2.2 Methods of Introducing Hidden (Masked) Interconnections
into Microcircuit Designs
The role of hidden (masked) connections is most commonly performed by ionimplanted connections—ohmic connections between doped regions of n-type or ptype of conductivity (e.g., transistor sources/drains) formed with the help of a recessed
ion-implanted conductive channel; electrical connections of integrated elements with
the help of a metal silicide layer, etc.
We will consider the features of using hidden connections on the example of
using ion-implanted connections to replace metallization buses, which were used
in the original design not to connect doped regions of integrated elements [24].
Since the connections formed by ion implantation are nearly impossible to identify
using optical microscopy means, they cannot be identified by a reverse engineering