Semiconductor devices - Mobile ion tests for metal-oxide semiconductor field effect transistors (MOSFETs)

IEC 62417:2010 provides a wafer level test procedure to determine the amount of positive mobile charge in oxide layers in metal-oxide semiconductor field effect transistors. It is applicable to both active and parasitic field effect transistors. The mobile charge can cause degradation of microelectronic devices, e.g. by shifting the threshold voltage of MOSFETs or by inversion of the base in bipolar transistors.

Dispositifs à semiconducteurs - Essais d'ions mobiles pour transistors à semiconducteurs à oxyde métallique à effet de champ (MOSFETs)

La CEI 62417:2010 fournit une procédure d'essai au niveau de la plaquette pour déterminer la quantité de charge positive mobile à l'intérieur des couches d'oxyde dans les transistors à semiconducteur à oxyde métallique à effet de champ. Elle s'applique aux deux transistors à effets parasites et effets actifs. La charge mobile peut causer des dégradations des dispositifs microélectroniques, par exemple en décalant la tension de seuil des MOSFETs ou par inversion de la base dans les transistors bipolaires.

General Information

Status
Published
Publication Date
21-Apr-2010
Technical Committee
Current Stage
PPUB - Publication issued
Start Date
22-Apr-2010
Completion Date
22-Apr-2010
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IEC 62417
Edition 1.0 2010-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Semiconductor devices – Mobile ion tests for metal-oxide semiconductor field
effect transistors (MOSFETs)
Dispositifs à semiconducteurs – Essais d’ions mobiles pour transistors à
semiconducteur à oxyde métallique à effet de champ (MOSFETs)
IEC 62417:2010
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 62417
Edition 1.0 2010-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Semiconductor devices – Mobile ion tests for metal-oxide semiconductor field
effect transistors (MOSFETs)
Dispositifs à semiconducteurs – Essais d’ions mobiles pour transistors à
semiconducteur à oxyde métallique à effet de champ (MOSFETs)
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX
ICS 31.080 ISBN 978-2-88910-696-7
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – 62417 © IEC:2010
CONTENTS

FOREWORD...........................................................................................................................3

1 Scope...............................................................................................................................5

2 Abbreviations and letter symbols ......................................................................................5

3 General description ..........................................................................................................5

4 Test equipment.................................................................................................................6

5 Test structures .................................................................................................................6

6 Sample size......................................................................................................................6

7 Conditions ........................................................................................................................6

8 Procedure ........................................................................................................................7

8.1 Bias temperature stress...........................................................................................7

8.2 Voltage sweep.........................................................................................................7

9 Criteria .............................................................................................................................7

10 Reporting .........................................................................................................................8

---------------------- Page: 4 ----------------------
62417 © IEC:2010 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SEMICONDUCTOR DEVICES –
MOBILE ION TESTS FOR METAL-OXIDE
SEMICONDUCTOR FIELD EFFECT
TRANSISTORS (MOSFETs)
FOREWORD

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International Standard IEC 62417 has been prepared by IEC technical committee 47:

Semiconductor devices.
The text of this standard is based on the following documents:
FDIS Report on voting
47/2042/FDIS 47/2049/RVD

Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

---------------------- Page: 5 ----------------------
– 4 – 62417 © IEC:2010

The committee has decided that the contents of this publication will remain unchanged until

the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
---------------------- Page: 6 ----------------------
62417 © IEC:2010 – 5 –
SEMICONDUCTOR DEVICES –
MOBILE ION TESTS FOR METAL-OXIDE
SEMICONDUCTOR FIELD EFFECT
TRANSISTORS (MOSFETs)
1 Scope

This present standard provides a wafer level test procedure to determine the amount of

positive mobile charge in oxide layers in metal-oxide semiconductor field effect transistors. . It

is applicable to both active and parasitic field effect transistors. The mobile charge can cause

degradation of microelectronic devices, e.g. by shifting the threshold voltage of MOSFETs or

by inversion of the base in bipolar transistors.
2 Abbreviations and letter symbols
This standard uses the following abbreviations and letter symbols:
CV test capacitance-voltage measurement
HFCV test high frequency capacitance-voltage measurement
V gate voltage
t oxide thickness
I drain-source current
V positive power supply voltage
V maximum supply voltage
dd,max
V transistor threshold voltage
V the absolute value of the threshold voltage before the test
t,initial
V the absolute value of the supply voltage
supply
ε dielectric constant of the oxide
3 General description

The stress applied is on test structures at an elevated temperature where mobile ions can

overcome the energy barriers at the interfaces and the ion mobility in the oxide is sufficiently

high. Two test methods are described in this document.
• Bias temperature stress (BTS)
• Voltage sweep (VS).

The bias temperature stress test is done on transistors. The threshold voltage is determined

from an I - V measurement at room temperature on fresh structures. The threshold voltage

ds gs

is defined as the gate voltage needed to force a fixed drain current through the transistor.

Then, a positive gate stress is applied at a high temperature, to sweep the mobile ions

towards the substrate. After the stress the test structure is cooled to room temperature with

the bias still applied. A second I - V curve is measured at room temperature. The

ds gs

sequence is completed with a negative gate stress at high temperature followed by an I -

V measurement at room temperature. Mobile charge causes a shift in the I - V curve.

gs ds gs

The distance over which the curve is shifted is a measure of the amount of mobile charge in

the insulator.
---------------------- Page: 7 ----------------------
– 6 – 62417 © IEC:2010

Edge effects of the transistor structure can be taken into account by applying a negative gate

bias for 2 minutes duration at the elevated temperature prior to the BTS measurement.

NOTE Mobile charge in dielectric layers above a large area polysilicon or metal-plate cannot be detected,

because there is no electric field which drives the ions towards the underlying oxide. To overcome this problem

special edge sensitive test structures can be used, that have a large edge/area value, e.g. structures with fingers.

The voltage sweep measurements are done on capacitors. A quasi-static C-V curve is

measured and compared with a low-frequency C-V curve. The ionic displacement current,

which appears as a peak in the quasi-static C-V curve, is indicative of the mobile ion

concentration.
4 Test equipment

The hot chuck shall be capable of maintaining a temperature of 250 °C. A capacitance (LCR)

meter is needed for HFCV measurements and quasi-static C-V measurements. A pA-meter is

needed for low-frequency C-V (typical frequency = 1 kHz) measurements. The frequency for

low-frequency C-V measurements may differ from 1 kHz as long as the accumulation and

inversion capacitances differ no more than 10 %.
5 Test structures

The test structures for bias temperature stress are transistors and, for voltage sweep,

capacitors are used. The minimum area A of this capacitor is calculated from the voltage

min

sweep rate dV/dt and the lowest measurable current I (determined by the resolution of the

min
test equipment) according to the following equation:
I ⋅t
min ox
A = (1)
min
ε ⋅ ε ⋅ dV / dt
ox 0
where
ε is the permittivity of vacuum.
6 Sample size
The recommended sample size is 5.
7 Conditions
The electric field during stress is as follows:
±1,0 MV/cm with a minimum of (operating voltage +10 %) for gate oxide;
±0,2 MV/cm for polysilicon gates on field oxide;
± 0,3 MV/cm for metal gates on field oxide.
The electric field is calculated as V /t .
g ox
---------------------- Page: 8 ----------------------
62417 © IEC:2010 – 7 –
8 Procedure
8.1 Bias temperature stress
The test structures are subsequently subjected to the following procedures:
• measure the first I - V (or HFCV) characteristic at room temperature;
ds gs

• apply a positive gate bias to collect mobile ions at the silicon/oxide interface;

• ramp the temperature to 250 °C;
• hold 5 min;
• ramp down to room temperature;
• remove bias;
• measure the second I - V (or HFCV) characteristic;
ds gs
• apply a negative gate bias to collect mobile ions at the gate/oxide interface;
• ramp the temperature to 250 °C;
• hold 5 min;
• ramp down to room temperature;
• remove bias;
• measure the third I - V (or HFCV) characteristic.
ds gs
I - V characteristics may be measured at 250 °C (fast tests). HFCV and I - V
ds gs ds gs

measurements shall be started with the polarity used in the preceding high temperature stress.

NOTE Reporting of correlation data is required if the stress temperature deviates from 250 °C by more than 10 ºC.

8.2 Voltage sweep

The device temperature is 250 °C. The start/stop values of the gate bias are calculated from

the oxide thickness, so that the maximum electric field is ±1 MV/cm. The stress field is

±1 MV/cm.
The capacitors are subsequently subjected to

• a positive gate stress of 1 MV/cm for 5 seconds duration to collect mobile ions at the

silicon/oxide interface,
• a low-frequency C-V measurement,
• a positive gate stress of 1 MV/cm for a period of 20 s,
• a quasi-static C-V measurement with a negative gate voltage ramp of 100 mV/s.
The electric field is defined as V /t .
g ox

For thick oxides the electric field is limited by the supply voltage of the equipment. The values

for the stress field and the start/stop values may then be reduced, but shall be at least

2 × 10 V/cm.

NOTE Reporting of correlation data is required if the temperature deviates from 250 °C by more than 10 ºC.

9 Criteria
The shift in the threshold voltage shall be less than
• 0,02 × V with a minimum value of 100 mV for gate oxides, where V is the
dd,max dd,max
maximum voltage difference between V pins and ground;
---------------------- Page: 9 ----------------------
– 8 – 62417 © IEC:2010
• V – 1,5 × V for polysilicon and metal gates on field oxide, where V is the
t,initial supply t,initial

absolute value of the threshold voltage before the test, and V is the absolute value of

supply
the supply voltage. If V – 1,5 × V ≤ 0, then the shift shall b
...

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