STUDY of an ELLIPSOMETER

Summer Internship work

By CHION RomainUnder the guidance of Professor Kimani Toussaint

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SynopsisBasic information about Ellipsomettry

Possible causes of defect

Testing the optical componentsPolarizer

Compensator

Analyzer

Testing the electronic componentsLogic board

Jacks

Photodetector

SoftwareSamples data

Acknowledgment

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Basic information (1/4)

• The ellipsometry allows us, by studying the polarization of the reflexion of a LASER beam on a sample, to know the thickness of the different layer of this sample as well as their refraction index or composition…

Synopsis

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Basic information (2/4)

• The ellipsometer studied here is fromGaertner Scientific Corporation

• It is composed of:• Input:

• LASER (1)

• Polarizer (1)

• Compensator or QWP (ON or OFF) (1)

• Sample stage (2)

• Output:• Analizer (3)

• Motor (4)

• Photodetector (4)

Synopsis

(1)Should be here

(2)

(3)

(4)

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Basic information (3/4)

• The ellipsometry measurement consists in two series of measure:• For the first one, the compensatoris OFF, the incoming light beam istherefore lineary polarized and isreflected elliptically

• Then, the compensator is ON,the incoming light beam is circularlypolarized by rotating the analyzerwe can then get two series of data

Synopsis

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Basic information (4/4)

• The data measured is then processed through an original software that gives us the information required.

• The user manual describes perfectly the methods to make the ellipsometer and the software work properly.

Synopsis

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Possible problems

• The different problems that can occure with an ellipsometer can be divided among the different types of components:• Mechanical: not much to do, it's broken. Though some small problems

and mistakes are listed in the user manual.• Optical: Problems with the path of the beam, with it's polarization,

with the input wavelength…• Electric & Electronic: Photodetector giving a wrong output, row data

are not processed well, computer and ellipsometer not talking the right way…

• Software

• While many problems can be detected easily, some of them need an accurate checking through tests.

Synopsis

• Polarizer• Compensator• Analyzer

Optical Components

Synopsis

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Polarizer (1/3)

• The polarizer is part of the income device, we can't dismantle it without decreasing the acuracy of the ellipsometer.

• Therefore to test it we have to use the whole income of the ellipsometer.

Synopsis

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Polarizer (2/3)

• Hypothesis: If a light beam passing through the polarizer is linearly polarized then this polarizer is working.

• Method:• Dismantle all the output (explained in user's manual)

• Put back the lense• Put the two arms of the ellipsometer on 90°• Put a second polarizer (analyzer) and a powermeter instead of the

missing output in the light beam path.• By rotating the analyzer search for the highest intensity• Measure the intensity for a set of angles of polarization for the analyzer• Compare the experiment data with Malus Law theory

Synopsis

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Rotation (°) Measured Intensity (µA) Malus Law (µA)0 114,6 114,6

15 109,9 106,923255630 96,9 85,9545 69,7 57,360 35 28,6575 7 7,67674436390 0,015 0

105 7,7 7,676744363120 34,1 28,65135 71,1 57,3150 96,3 85,95165 107,9 106,9232556180 114,3 114,6195 109 106,9232556210 96,8 85,95225 70,3 57,3240 35,4 28,65255 7,9 7,676744363270 0 0

0 50 100 150 200 250 3000

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60

80

100

120

140

Measured Intensity (µA)

Malus Law (µA)

Rotation (°) Measured Intensity (µA) Malus Law (µA)0 114,6 114,6

15 109,9 106,923255630 96,9 85,9545 69,7 57,360 35 28,6575 7 7,67674436390 0,015 0

105 7,7 7,676744363120 34,1 28,65135 71,1 57,3150 96,3 85,95165 107,9 106,9232556180 114,3 114,6195 109 106,9232556210 96,8 85,95225 70,3 57,3240 35,4 28,65255 7,9 7,676744363270 0 0

Rotation (°) Measured Intensity (µA) Malus Law (µA)0 114,6 114,6

15 109,9 106,923255630 96,9 85,9545 69,7 57,360 35 28,6575 7 7,67674436390 0,015 0

105 7,7 7,676744363120 34,1 28,65135 71,1 57,3150 96,3 85,95165 107,9 106,9232556180 114,3 114,6195 109 106,9232556210 96,8 85,95225 70,3 57,3240 35,4 28,65255 7,9 7,676744363270 0 0

Polarizer (3/3)

Results:• Maximum intensityevery 180°

• Near to zero intensity90° after each maximum

• Average distanceof 5%

• Linearly polarized

Synopsis Measurement Calculus and Stats

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Compensator (1/3)

• The compensator is activated thanks to the little spring above the polarizer.

• The method is the same than for the former experience.

Synopsis

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Compensator (2/3)

Synopsis

• Hypothesis: If a light beam passing through the working polarizer with compensator (Quarter Wave Plate) is circularly polarized then the compensator is working.

• Method:• Dismantle all the output (explained in user's manual)

• Put back the lense• Put the two arms of the ellipsometer on 90°• Put a second polarizer (analyzer) and a powermeter instead of the

missing output in the light beam path.• Maintain the spring of the compensator ON• Measure the intensity for a set of angles of polarization for the analyzer• The data should be constant

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Results:

• Almost always the samevalue

• Independent of the angleof polarization

• Circularly polarized.

Compensator (3/3)

Synopsis

Rotation (°) Intensity (µA)0 52

15 5230 5145 50,560 5175 4990 52

105 51,5120 50135 50,5150 51165 51180 52

0 20 40 60 80 100 120 140 160 180 2000

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30

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50

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Measured Intensity (µA)

Measurement Calculus and Stats

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Analyzer

• The analyzer is the output polarizer of the ellipsometer. It can't be took apart from the motor.

• The method is the same as before but the only part taken off shall be the photodetector.

• The results are similar to those before.

Synopsis

•Logic board•Jacks•Photodetector

Electronic Components

Synopsis

17Synopsis

Logic board

• The logic board, counter, and PCI board are accessible through manipulations explained in the "Logic board upgrade" manual

• They all can be tested through the side jacks

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Jacks (1/2)

• The ECE store did not have the compatible male jacks so we used a simple voltmeter to measure the different output of the jacks:• Red: Photodetector output• Orange: Reference pulse at the begining of the automatic

measurement• Yellow: Count pulse each 5°• Black: Ground• Green: Signal that a reading is ready for the computer• Blue: Signal that the computer is ready for the reading• Brown: Count pulse but for the motor

Synopsis

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• Finally the computer and boards are ready only while taking measurements.

Jacks (2/2)

• Results:

Synopsis

Jacks AS Mode (mV) AM Mode N/M (mV) AM Mode W/M (mV)Red 70 72 ~ 120 75 ~ 121Orange 51 55 55 ~ 225Yellow 50 1600 1600Green 55 49 1600Blue 56 45 1600Brown 56 1600 1600

Measurement Calculus and Stats

• We can notice that the output vary with the analyzer rotating whether we take measures or not, the logical board therefore receive data

• The measurement pulse appears only while taking measurements

• Count pulse appears only when the output part is rotating as well as for motor pulse

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Photodetector (1/3)

• The photodetector is part of a photodetector board. It's easy to take it off thanks to the user's manual instructions

• By looking at the different components datasheets we have been able to create a dynamic map of the board

Synopsis Dynamic Photodetector Map

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Photodetector (2/3)

• Hypothesis: Following the datasheet of the photodetector we can follow a similar patern with the intensity curves in function of the wavelength and our measures.

• Method:• Dismantle the photodetector• Connect the power supply (V+ on PIN, V- on PIN)• Take measurement of the different outputs (row output on

PIN, amplified output on PIN) • Repeat for different wavelength LASER

Synopsis

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Photodetector (3/3)

• Results:

• If we compareexperimental andtheoretical data we findthe same ratiosbetween green andred lights

Synopsis Measurement Calculus and Stats

PIN White light (mV) Green Laser (mV) Red Laser (mV) Ellipsometer (mV)H 260 7200 ? 9300O 250 6300 ? 7900

•Datas

Software

Synopsis

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Data (1/2)

• The data are collected after different samples with the ellipsometer.

• With enough data, an offset might be found. We can then calculate the true values from the results given by the software

Synopsis

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Datas (2/2)

• If we compare theexpected and measureddata, we find similareresults, which is good,But the acuracy is notenough for such acomplex device as anellipsometer

Synopsis

Samples Expected (Å et Ø) Calculated (Å et Ø)SiO2 1156,6 1155,3Substrate: 2,5 1,437 1,469

SiN 4060 3038Substrate: 3,6 1,754 1,753

SiN 4060 3038Substrate: 3,4 1,754 1,753

Training * 2 490 ±5% 927Substrate: 3,4 ? 1,71

No LASER 0 010000 9172

Substrate: 1 1 1,001

LASER alone 0 010000 9172

Substrate: 1 1 1,001

Measurement Calculus and Stats

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Acknoledgement

• I would like to thank Santosh Tripathi for all the help he gave me this summer

• I thank also the whole ProbeLab for their support and company.

• Finally I thank Professor Toussaint for the opportunity he gave me to work here and for the experience it gave me.

Synopsis

THANKS FOR YOUR ATTENTION