Measuring Al Thin Film Thickness Using Reflectance Spectrometer (EQ-TFMS-LD)

This application note shows the operation procedures of a typical metal thin film measurement using Reflectance

Spectrometer (EQ-TFMS-LD). The sample used is DC magnetron sputtered Al metal thin film on a glass coverslip.

1. Plug the power cord and USB cable to the back panel of measurement system (Pic. 1). Connect the reflectance

cable to the reflectance probe. On the front panel of the measurement system (Pic. 2), connect the SAM

connector on the end marked “Read” to the spectrometer port, and the SMA connector on the “illumination” end

to the illumination port. Assemble the sample table, and mount the reflectance probe above the table as shown in

Pic 3. Switch on the power of the measurement system from the back panel.

Pic 1. Measurement system back panel. Pic 2. Measurement system front panel.

USB Cable to Laptop Power Switch

Power Inlet

Illumination Port Power Indicator

Read Port

Pic 3. Sample table setup.

Attention:

Never look directly in the light source or in the probe to avoid eye damage.

2. Plug both the USB cable and the hardware license USB drive to the laptop (Pic 4). Start TFCompanion software

using the default account (User - Admin_hdw. Password - psw). Place the included reference sample – bare Si

wafer on the sample table with the polished side facing up, and slide it under the reflectance probe. Adjust the

height of the probe to be around 5 - 10 mm above the silicon wafer. User can also move probe higher to get a

smaller spot size for local area measurement on the sample.

Pic. 4. Connect USB cable and hardware license USB drive to the laptop.

3. First use the included verification samples to test the reflectance spectrometer. Follow the steps below.

Hardware License USB Drive

USB Cable to Measurement System

Pic. 5. Set up calibration for the verification samples.

Pic 6. Calibration with the included bare Si wafer and black pad.

c. Check and make sure the film stack is the default

- Sio2.mat / Substrate: Si.mat

b. Select the measurement recipe – Refl_Vis_Calc

a. Click “Measure” and select “Calibrate Now” in the popup window

d. Follow the prompt to calibration step 1: measurement of reference sample. Use the included bare Si wafer as

the reference sample. The light intensity will be automatically adjusted during the measurement. Wait for

measurement to finish.

e. Follow the prompt to calibration step 2: measurement of dark current. Remove the reference sample, and use

the included black pad as the sample. Wait for measurement to finish.

4. After calibration is completed, click “Continue” to proceed. Place the included bare Si wafer under the probe.

Click “Measure” on the left sidebar to measure the reflectance and calculate the thickness. The measured

thickness of SiO2 should be 0 Å, as the measured reflectance result is the same as the saved reference sample.

Then place the included 202 nm SiO2 / Si sample under the probe with the SiO2 side facing up, and click

“Measure”. The measured thickness of SiO2 is 203 nm, which is close to the 202 nm reference value.

Pic. 7 Verification sample measurement result.

5. Next set up the measurement film stack of Al metal film on glass substrate. Click on the “Substrate: Si.mat”,

find “Glass (microscope slide).mat” in the material library, right click and click “Set to Table” to change the

substrate layer. Click “OK” to proceed. Similarly, change the film layer from “Sio2.mat” to “Al.mat”

0 Å measured thickness of SiO2 on

bare Si wafer

2030 Å measured thickness of

SiO2 on 202 nm SiO2 / Si sample

Pic 8. Configure the measurement film stack.

6. Go to “Measure” on the top menu, and select “Clear” to clear the bare Si wafer calibration. Re-do the

calibration with a bare glass coverslip and the included black pad. After calibration, place the Al metal film

sample under the probe with the film side facing up, and click “Measure” on the left sidebar. The thickness

of Al metal is measured to be 28 nm (Pic 10).

Pic 9. Al metal film measurement steps.

b. Measurement – Al metal film

sputtered on glass coverslip

a. Calibration Step 2 – Black

pad

c. Calibration Step 1 – Bare

glass coverslip

Pic 10. Al metal film measurement result.

7. If using a small spot size for measurement, user can move the sample around on the sample table, and

measure several points on the film for thickness distribution measurement.

8. After the measurement, close off the TFCompanion software and shut down the laptop. Power off the

measurement system.

Appendix

Metal Thin Film Measurement:

Only metal films below 40 or 50 nm thicknesses can be measured. Thicker metal films are opaque and thus

cannot be measured by EQ-TFMS-LD. The actual measurable thickness depends on the type of the metal.

The Table 1 below shows the measurable thicknesses for several metals. It assumes that metal surface is

smooth (mirror) – surface roughness will cause scattering and decrease of the measurable thickness.

Table 1. Measurable thickness of various metal thin films using EQ-TFMS-LD.

Please refer to Table 2 for estimated precision of W thin film measurement.

Table 2. Estimated precision of W film measurement depending on the thickness.

Sample Information:

Substrate – Microscope coverslip. 18 mm x 18 mm. ~0.2 mm thickness

Sputter Target – 2” Al target, 2 mm thickness

Sputter Tool – High Power DC Magnetron Sputtering Coater (VTC-16-SM)

Sputter Power – 208 W. 130 mA current, 1600 VDC voltage

Sputter Distance – 60 mm

Sputter Base Vacuum – 1.0E-4 Torr

Sputter Pressure – 1.0E-3 Torr

Sputter Time – 100 second. Pre-sputter time: 100 second

TFCompanion Software Installation and Setup.

a. There are two USB drives: installation USB drive and hardware key USB drive. Plug the installation USB

drive to the laptop.

b. Open the USB drive. Click StartCD.htm, and a welcome page will be opened in web browser.

c. Select “Install MProbe Version of TFCompanion” and choose from 32 bit and 64 bit versions based on the

operating system. Install the software as administrator, otherwise the spectrometer drivers will not install

properly.

d. Go to /CDCdriver folder in the USB drive. Follow the “CDC_driverInstallation.pdf” instruction to install the

driver. For Windows 8 and Windows 10, there may be an error of “The hash for the file is not present in the

specified catalog file” during driver installation. Please temporarily disable the digital signature enforcement

to properly install the CDC driver.

e. Go to /HardwareConfiguration folder in the USB drive. Copy file “PICConfigurations.properties” to

C:\TFCompanion\init folder.

f. Plug the hardware license USB to the laptop. Start TFCompanion software using the default account (User -

Admin_hdw. Password - psw). Go to Help/Check Update and update the software to the latest release.