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SEMI MF2139-1103 © SEMI 2003 7 NOTICE: SEMI makes no warranties or representations as to the suitability o f the standards set forth herei n for any pa rticular application. The determination of the suitability o f the s…

SEMI MF2139-1103 © SEMI 2003 6

12.5 If a cryopanel is used, fill the liquid nitrogen or

helium cold trap.

12.6 For the calibration specimen use a cesium primary

ion beam and detect the negative ion of

Si or

Si, depending upon the nitrogen isotope used in

the ion implantation; detect during or at the end of the

profile a matrix negative ion (

Si,

Si, or

Si). After

the entire sample load is analyzed, measure the SIMS

crater depth in this sample using a profilometer.

12.7 Position the specimen holder to sputter a crater in

a test specimen near the center of the window. Without

detecting secondary ion intensities, begin a SIMS

profile.

12.8 Repeat Section 12.7 for each test specimen.

12.9 If the boron level in the test specimen is below 1

× 10

/cm

, detect the negative ions of

Si,

and a matrix signal (

Si,

Si, or

). If the

boron level is at or above 1 × 10

/cm

, include the

detection of the negative ion of

Si.

12.10 For the analysis of the test specimens, select two

raster conditions, one to maximize the sputter rate, and

one that provides a slower sputter rate. Choose

apertures or other means to maintain the analysis area

under raster change and to keep the negative ion count

rates on the electron multiplier detector below 1 × 10

counts/s for the test specimen.

12.11 Position the specimen holder to sputter a new

crater near the crater created in Section 12.7 or Section

12.8 . Do not make the second crater in the same crater

created in Section 12.7 or Section 12.8 .

12.12 Center the primary ion beam and begin a SIMS

profile with the raster area that produces the lower

sputter rate. Continue the profile until all signals

provide relatively constant intensity for at least 20 data

points.

12.13 Change the raster area to maximize the signal

intensity. Continue the profile under this raster

condition for at least 20 data points.

12.14 Reduce the raster area back to the original

condition.

12.15 If the boron content is less than 1 × 10

/cm

subtract 0.0341 times the measured mass 40 signal

(counts/s) from the measured mass 42 signal (counts/s)

to obtain the corrected mass 42 signal corresponding to

real nitrogen (

Si).

NOTE 2: If mass 40 carbon (

Si) is defined = 1, mass 42

(

Si +

Si) = 0.0335 + 0.0006 = 0.0341.

NOTE 3: A hydride correction should be negligible for H on

the order of 10

atoms/cm

or less.

12.16 If the boron concentration is at or greater than 1

× 10

/cm

, subtract 0.0583 times the mass 39 signal

from the carbon correction to correct for the boron

interference.

NOTE 4: The mass 39 boron (

Si +

Si) is defined =

1, and mass 40 (

Si +

Si) = 0.0583.

12.17 Calculate the bulk nitrogen concentration [N]

and the background nitrogen concentration [N

] for

each test specimen using Equations 5 and 6.

12.18 Record the specimen identification.

13 Report

13.1 Report the following information:

13.2 The instrument used, the operator, and the date of

the measurements,

13.3 Identification of the test and calibration

specimens,

13.4 The bulk nitrogen concentration values for the test

specimens,

13.5 The nitrogen instrumental background concentra-

tion during the faster sputter rate, and

13.6 Whether anomalous nitrogen spikes were present,

and if so, whether the averaging included or excluded

these spikes.

14 Precision and Bias

14.1 The precision of the nitrogen determination has

not yet been determined either by pilot study or by

interlaboratory test.

14.2 There is no accepted reference material for

determining the bias for the procedure in this test

method. Therefore, no statement on bias can be made.

15 Keywords

15.1 nitrogen concentration; secondary ion mass

spectrometry; silicon; SIMS

SEMI MF2139-1103 © SEMI 2003 7

NOTICE: SEMI makes no warranties or

representations as to the suitability of the standards set

forth herein for any particular application. The

determination of the suitability of the standard is solely

the responsibility of the user. Users are cautioned to

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respecting any materials or equipment mentioned

herein. These standards are subject to change without

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SEMI MF2166-0304 © SEMI 2004 1

SEMI MF2166-0304

PRACTICES FOR MONITORING NON-CONTACT DIELECTRIC

CHARACTERIZATION SYSTEMS THROUGH USE OF SPECIAL

REFERENCE WAFERS

This standard was technically approved by the Global Silicon Wafer Committee and is the direct

responsibility of the North American Silicon Wafer Committee. Current edition approved for publication by

the North American Regional Standards Committee on October 16, 2003. Initially available at

www.semi.org February 2004; to be published March 2004. Originally published by ASTM International as

ASTM F 2166-02. Last previous edition SEMI MF2166-02.

1 Purpose

1.1 Non-contact dielectric characterization systems

(NCDCS) that supply surface charge by means of a

corona instead of an electrode are frequently used to

determine the oxide characteristics of MOS device

structures. These instruments can measure a number of

characteristic parameters, including:

1.1.1 initial surface voltage (V

surf

or V

cpd

1.1.2 flatband voltage (V

1.1.3 effective charge (Q

eff

1.1.4 density of interface traps (D

1.1.5 mobile charge (Q

), and

1.1.6 electrical dielectric thickness (T

1.2 To determine that the NCDCS is performing

correctly, it is necessary to test the tester. This practice

provides procedures for testing these systems with the

use of special reference wafers with specified

characteristics.

1.3 The procedures in these practices are designed to

ensure that the NCDCS being evaluated provides

reliable data for selected device-related parameters.

1.4 Flatband voltage is an important parameter in the

fabrication of MOS devices. Its value is dependent on

the charge structure within and on the dielectric as well

as at the silicon-dielectric (Si-SiO

) interface. These

charges consist of interface and bulk trapped and fixed

charge, mobile charge distributed within the dielectric,

and charge residing on the top of the dielectric.

Although the total charge in and on the oxide

determines flatband voltage, the charge near the silicon

has the greatest effect.

1.4.1 Most device applications require that the mobile

charge be minimized to provide stable threshold

voltage. Stability of the charges at elevated

temperatures is a measure of mobile charge density

within the dielectric. The mobile charge changes

location under temperature and electric field stress.

The mobile charge density can be calculated from the

resulting change in flatband voltage.

1.4.2 Equipment used to produce dielectrics can

become contaminated in various ways. When such

equipment becomes contaminated, it usually introduces

an increased level of mobile ions into the dielectric.

1.4.3 Measuring V

surf

or V

cpd

, the contact potential

between the probe and the semiconductor, with a

Kelvin or Monroe probe allows a quantitative

measurement of the charges associated with the

semiconductor surface and the dielectric, independent

of top (contact) electrode variations as in MOS C-V

measurements. A special reference wafer has the

mobile ions confined to the top half of the dielectric. It

is therefore a good check of the Kelvin or Monroe

probe, which is most sensitive to charges near the top of

the dielectric.

1.5 The procedures in this practice can be used to

ascertain that the dielectric characterization system(s)

meet quality control requirements. They can be used as

a training tool for tester applications.

1.6 The results obtained by these measurements can

also be used to expose and troubleshoot tester problems

including wafer handling and software issues.

2 Scope

2.1 These practices describe the use of wafers with

special electrical and physical characteristics for

controlling and monitoring performance of non-contact

dielectric characterization systems (NCDCS) that

employ corona. They apply in general to dielectrics

with charge structure that can be measured by the

characterization system. Their applicability to

dielectrics of less than 3-nm electrical oxide thickness

depends on the capability of the NCDCS. A thickness

correlation between the reference wafer(s) and thin-

dielectric monitor wafers must be established.

2.1.1 The reference wafers must be designed to check

the repeatability and functionality of all the parts and

subsystems of the characterization system. Thermally

oxidized wafers are not sufficient for this purpose

because of parametric drift due to temperature-bias

stressing and exposure to the atmosphere.