Online proceedings - EDA Publishing Association

7-9 October 2009, Leuven, Belgium
Devices fabricated on wafers with TSV interconnecting
elements are exposed to additional mechanical stress related to
the IC layout and wafer shape (Fig. 1). This paper discusses
various cases of stress distribution based on simulation results
performed by Coventor [5] and TCAD [6] packages.
A
Fig. 3. Mechanical design drawing (3D model), without and with
encapsulation [7].
Even if all standalone (non 3D) modules have been correctly
designed, simulated and would perfectly operate if assembled
as standalone devices, if the device profits from 3D integration
technique its functionality may be affected by various side
effects not taken into consideration during design. Such a
device not optimized for 3D integration during design process
– may fail. 3D integrated device comprises various modules.
Fig. 2. a) V T(P) - Threshold Voltage (V T) on Stress Tensor (P) sensitivity for
various Stress Tensor-Channel Angle (α). NMOS; L=130[nm]; Shallow S/D;
UDS=0.05[V] b) Threshold voltage variation for 350nm technology for
various mechanical stress levels and various angles between mechanical
force and source-drain direction
It is especially important for analogue blocks and low noise
amplifiers. Electrical simulations performed in TCAD show
that digital blocks are more resistant to the mechanical stress
then analogue ones. Sample simulations performed in TCAD
for MNOS and PMOS transistors show that mechanical stress
relative sensitivity of complementary MOS devices is
complementary as presented on Fig. 2b. Selected results of
TCAD simulations performed for simple digital blocks like
inverters and NAND digital gates also have been performed.
Simulated gates have been modeled for AMS 350nm
technology. Simulation results confirm that for moderate levels
of mechanical stress (mechanical stress level should not exceed
the level of 500MPa) parasitic stress does not significantly
affect transfer function of digital circuits.
Modeling and simulation results of the integrated, intelligent
health monitoring system 3D model [7] have been presented.
Such a system is the e-Cubes project demonstrator sample.
General idea is shown on the Fig. 3. Significant speedup and
improvements of product development stages will be the profit
of the project. From the reliability point of view thermomechanical
behavior of the whole system is the most important
parameter to be taken into consideration.
B
Fig. 4. 3D model of the e-Cubes demonstrator for health monitoring
designed in CoventorWare with the mesh ready for multidomain modeling
and simulation by FE methods.
Each of them affects neighboring modules in thermal,
mechanical, electrical, electromagnetic way. Probability that a
single module affects another in its neighborhood (e.g. by high
temperature transfer) is quite high. Therefore the module
arrangement and its complex multidomain simulation are so
important on each design stage.
For this simulation 3D model designed in CoventorWare have
been used (Fig. 4). 3D integration technique has been
simulated along with applied, real thermo-mechanical
boundary conditions like power dissipation present in different
modules. Also selected mechanical issues regarding the
encapsulation methodology have been done. Thermal
simulations results show that under assumed boundary
conditions temperature does not increase too much across the
whole demonstrator device structure Sample results of the
thermal investigation are shown on the Fig. 5.
The aim of this part of the simulation was verification of the
temperature distribution under high and low power operating
modes. 300 K ambient temperature has been assumed as one of
boundary conditions applied for this simulation as well as
convection and radiation on the bottom and upper surfaces. For
applied boundary conditions in the worst case temperature
increases to 325 K for high power mode and 310 K for low
power mode.
Apart from the thermal phenomena mechanical properties of
the device and used materials are important from reliability
point of view, especially under higher range device
temperatures. The main goal of performed simulation was to
©EDA Publishing/THERMINIC 2009 85
ISBN: 978-2-35500-010-2