Marvell NanoLab
Member login
Lab Manual Contents
MercuryWeb
Berkeley Microlab
Chapter 8.34
Nanometrics 210 XP Scanning UV
Nanospec/DUV Microspectrophotometer
(nanoduv - 380)
1.0
T it le
Nanospec/DUV Microspectrophotometer (NanoDUV)
2.0
Pu rp ose
The Nanospec®/210 XP Scanning UV is a computerized film thickness measurement system. It is an
old generation of NanoSpec (Chapter 8.33). The monochromator is mechanical and the software runs
on DOS environment. However, there are some features that NanoSpec does not provide.
► Deep UV light source that extends the measurement limit down to 100Å.
► The refractive index can be entered by user as an option.
► Capable of measuring underlayer film thickness.
► Wafer stage that accommodates 6” wafer.
3.0
Sc ope
This manual covers the operating procedure of film thickness measurement, system re-initialization, and
user level trouble-shooting guide. The available measurement programs for various film stacks are listed
in Appendix 12.1.
4.0
Ap p lic ab le Documents
Revision History
4.1
Nanometrics AFT Operations Manual (copy in Office)
4.2
NanoSpec Film Thickness Measurement System, Microlab Online Manual Chapter 8.33.
5 .0 De f in it ions & Proc es s T er mino log y
N/A
6.0
Saf ety
6.1
Burn Hazard: The light source is hot. Be careful when aligning the light bulb.
6.2
Strong Light Hazard: Do not look into the light source directly for a long period of time.
6.3
UV Light Hazard: Do not look into the UV light source.
7 . 0 S t a t i st ic a l/ P r oce ss D a t a
N/A
8 . 0 A v a i lab l e P r oc ess es, G ase s P ro ce ss N o t e s
8.1
Standard programs provided by the instrument vendor are listed in Appendix 12.1.
8.2
In order to measure the film thickness, the refractive index of the film is needed. A user can use
the default value stored in the computer or enter it before the measurement.
nanoduv
Chapter 8.34
8.3
NanoDUV can only measure transparent film. Metal film and thick Germanium/Silicon film can not
be measured.
9 . 0 E q u ip me nt O pe rat i on
System Description
9.1
The Nanospec system consists of a customized optical microscope and a personal computer with
DOS OS. The optical microscope has a mechanical spectrophotometer head and a dual wafer
stage, left side for the reference wafer and right side for the sample to be measured. The
microscope has three objective lenses: 5X, 10X, 15X (for UV measurement ONLY), and 50X
magnifications.
9.2
All the system operations are controlled by the specially labeled keys on the computer keyboard.
The functions of these keys are as follows:
CALIB
Stops any measurement in progress and returns to the Available Programs screen.
This gives the operator an opportunity to choose another program, objective lens or
to run a new reference scan.
NEW TEST Initiates a new measurement sequence with a new sample using a previously
selected film program. A zero check is generally made and new sample
identification, which can be blank, must be entered.
ENTER
Terminates an alphanumeric entry. The computer has not received the data until
<Enter> is pressed.
MEAS
Initiates a measurement. It can also be used to respond to a prompt requiring a
"YES" answer. Holding down the <MEAS> key causes the system to make continue
measurements.
YES/0
Is used to respond "YES" to certain prompts ending with a question mark, or as the
zero key in a numerical entry.
NO/+
Is used to respond "NO" to certain prompts ending with a question mark, or as a
decimal point in a numerical entry.
HELP
Explains what the commands are and assist you answering the questions.
R/I ON/OFF Toggles on and off the instrument's option to measure the refractive index of a single
layer film. The Refraction Index Option must have been enabled (Section 9.9.3)
during the initialization for this function to work.
DUAL
Measures the thickness of both layers of films with a single measurement. The
estimated underlayer thickness needs to be entered for each sample.
GRAPH
Displays an interference spectrum (Reflectance versus Wavelength) for both the
measured sample and the mathematical model corresponding to the measured
thickness. When pressed, the screen shows the previous stored spectrum. Follow
the computer instruction to clear it and display the current measurement.
DISPLAY
STATISTICS is used to display statistics for measurements taken on an individual sample during
a measurement session.
Measurement Procedures
9.3
Enable NanoSpec on the WAND. Turn on the LCD screen and press any key to stop the screen
saver program. Make sure the light source is on. If there is no light in the microscope, report on
the WAND.
9.4
If need UV light for thin film measurement (program 17 to 20), turn on the UV light source on the
wall shelf to the left of the system. Wait at least 20 minutes for the UV light source to stabilize.
-2-
nanoduv
Chapter 8.34
9.5
Place the reference wafer (clean bare silicon wafer) on the left side and the sample to be
measured on the right side of the stage.
9.6
Press the CALIB key to display all available programs on the screen. Select the program for the
measurement by entering the program number. Enter the objective lens magnification, and
refractive index when prompted. To use the default refractive index, just press Enter key.
9.7
The computer will prompt you to do a reference calibration. Follow the screen instructions.
9.8
9.7.1
Depends on the program used, it may ask to open or close UV light shutter. The shutter
is located on the black box behind the wafer stage.
9.7.2
Use the tab at the front center of the wafer stage to move the stage to the right end, so
that the reference wafer is under the objective lens.
9.7.3
Use the coarse (large) and fine (small) knobs at the base of the microscope to focus on
the reference wafer. Since there is no pattern on the reference wafer, focus on the
octagon in the field of view.
After the reference calibration, the tool is ready to make measurements.
9.8.1
Use the tab on the front center of the wafer stage to move the stage to the left end, so
that the sample is under the objective lens.
9.8.2
Focus on the sample. Move the wafer stage using the X-Y axis knobs under the stage.
9.8.3
When measuring patterned sample, make sure the black dot, which marks the active
optical area, in the center of the objective lens is well within the center of the patterned
feature to be measured. The actual dot size depends on the magnification of the
objective lens.
Objective
Magnification
Meas. Dot Size
(μm)
5X
30
10X
15
15X (UV only)
10
50X
3
If you need to change the objective magnification now, you have to redo the reference
calibration again. Use the same magnification for the calibration as for the sample
measurement.
9.8.4
Press the MEAS key to make a measurement. To ensure the sanity of the measurement,
you should press the GRAPH key to see how the measurement algorithm fit with the
actual spectrum. The rule of thumb is when the peaks and valleys of the spectrum fit well,
the measurement should be correct.
9.8.5
Write down the data since there is no printer attached to the tool. Disable the tool on the
WAND when done.
System Initialization
9.9
The NanoDUV needs be initialized only when it does not work properly, or the user wants to
change the Refractive Index Option. To start the initialization procedure, hold down the control
key, and type r-e-s-e-t (reset).
9.9.1
A startup message will appear on the screen, along with the question: Enable Datalink?
Answer <NO> because this function is no longer supported.
-3-
nanoduv
Chapter 8.34
9.9.2
The next prompt asks “Is WAVELENGTH 480?” Check the wavelength displayed on the
spectrophotometer head. If the wavelength is 480, simply press the <YES/0> key.
Otherwise, press <NO/+> and then enter the current wavelength shown on the display (3
digits only) at the "Enter Wavelength" prompt. The instrument will adjust the wavelength,
and prompt you again. Another repetition of this process may necessary to set the
wavelength at 480 nm. Once the wavelength is 480 and you have answered "YES" to the
prompt, the question
9.9.3
The next prompt asks “Refractive Index Option?” Answer <YES> to enable this feature,
giving users the option of entering a refractive index for a given film other than the
default. Answer to disable the R/I ON/OFF key and use the system default values.
9.9.4
The last question is “Enable Printer?” Answer <NO> since there is no printer
connected.
9.10
Then follow the screen instructions to adjust the Gain controls. The Zero and Gain controls are
both located inside the cover under the spectrophotometer head. Adjust these by inserting a
forefinger in the open left end of the cover. The first knob (small metallic) is for the Zero and the
second (bigger plastic) is for the Gain.
9.11
When initialization is complete, the list of available programs will appear on the screen. The
system is ready for measurement.
Special Instructions for UV Programs
9.12
Turn on the DUV lamp power supply. It locates on the back shelf of the tool. It needs 20 to 30
minutes to stabilize. You can feel by touch that the lamp case is warm afterwards. If not, the lamp
is not working and needs to be replaced.
9.13
The native oxide on the reference wafer will affect your measurements. For consistent results,
you should dip the reference wafer in HF to get rid of the native oxide. Follow the sink operation
procedures to rinse and dry the reference wafer before put it on the stage.
9.14
Use only 15X (UV) objective lens to do your measurements.
1 0 .0 T ro ub l es ho ot i ng G u id e l in es
10.1 Problem: Computer does not respond to the keyboard.
Cause:
Computer OS/hardware problem.
Solution: Reset the computer by switching it off/on.
10.2
Problem:
Cause:
Solution:
The measurement spectrum does not agree with the computer algorithm.
The reference calibration was not done correctly.
Press the Calibrate key and re-start the calibration.
10.3
Problem:
Cause:
Solution:
No light in the microscope
Light bulb burned down or power source turned off.
Report the problem on the WAND.
1 1 .0 F i gu re s & S c he mat i cs
N/A
-4-
nanoduv
Chapter 8.34
12.0 Appendices
12.1
Program Descriptions
The system holds 20 predefined standard programs, and 32 user-defined programs:
Prg. #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
252
253
254
255
Type of Film
Standard R.I.
Wavelength Range (nm)
Oxide on Silicon
Nitride on Silicon
Negative Resist on Silicon
Polysilicon on Oxide
Negative Resist on Oxide
Nitride on Oxide
Thin Oxide on Silicon
Thin Nitride on Silicon
Polyimide on Silicon
Positive Resist on Silicon
Positive Resist on Oxide
Reflectance Mode
Thick Films
EPA914EZ Resist on Silicon
Very Thin Oxide on Silicon
Very Thin Nitride on Silicon
UV Thin Oxide on Silicon
UV Thin Nitride on Silicon
UV Oxide on Polysilicon
UV Oxide on Aluminum
OxiNitride on Silicon
OxiNitride on Oxide
Special Substrate
Non-Standard Dual Layer
Single Layer Films
Special Program
1.456
2.001
1.550
3.973
1.550
2.001
1.456
2.001
1.781
1.631
1.631
480 – 800
480 – 800
480 – 800
480 – 800
480 – 800
480 – 800
520 only
520 only
480 – 800
480 – 800
480 – 800
Choose 1-3 wavelengths
720- -760
480 – 800
Not Available
Not Available
200 – 280
200 – 280
220 – 280
210 – 280
480 – 800
480 – 800
1.600
1.631
1.447
1.932
1.447
1.447
1.770
1.770
1.
Oxide on Silicon
This program measures silicon dioxide on silicon prepared by thermal oxidation. Measuring
highly doped silicon dioxide may affect accuracy, because heavy doping changes the film's
optical properties. The instrument will display "Under-range" when measuring silicon dioxide
less than 100 A thick.
2.
Nitride on Silicon
Use for measuring silicon nitride that has been chemically deposited on silicon. Measuring
plasma nitrides may be less accurate than measuring chemically deposited nitrides because
the varying stoichiometry of plasma films can cause measurement error. Frequently, the
refractive index (if known) can be used to scale results obtained from plasma nitride samples.
For films under 500 Å, use program 8. The instrument will display "Under-range" when
measuring silicon nitride of less than 100 Å.
-5-
nanoduv
Chapter 8.34
3.
Negative Resist on Silicon
Measurements made with this program are in the range 500 - 40,000Å. The refractive index
(RI) for the particular negative resist must be known. The default RI is 1.55.
4.
Undoped Polysilicon on Oxide
Undoped polysilicon in the range of 550 - 10,000 Å can be measured using this program.
When used on polysilicon films less than about 300 Å the message "under-range" is
displayed. Research indicates that measurements of thick polysilicon (approximately 3,000 10,000 Å) are highly accurate when the range of underlying silicon dioxide thickness is
between 300 - 1,200 Å. Measurement for thin polysilicon (less than 3,000 Å) is most accurate
when the underlayer thickness is in the range of 800 - 1,200 Å. The instrument will display
"Under-range" when measuring oxide of less than 10 Å.
5.
Negative Resist on Oxide
A resist film between 4,000 - 30,000Å on an oxide film between 500 - 15,000 Å can be
measured with this program. The program contains an extra prompt for the operator
requesting that the oxide thickness be typed in. The refractive index (RI) for the particular
negative resist must be known. The default RI is 1.55. It is important to enter an accurate,
premeasured oxide thickness. Any error entered in the thickness results in an error in resist
thickness readout. The instrument will display "Under-range" when measuring oxide of less
than 10 Å.
6.
Nitride on Oxide
This program measures the thickness of chemically deposited silicon nitride. The silicon
nitride thickness must be greater than 100 Å. The instrument will display "Under-range" when
measuring silicon oxide of less than 10 Å.
7.
Thin Oxide on Silicon
This program averages data at 520 nm rather than scanning through a wavelength range. A
new reference should be taken whenever selecting this program. When measuring very thin
films, take a new reference every 30 minutes or more often. For increased confidence in very
thin film measurements, repeat measurements. The instrument will display "Under-range"
when measuring thin oxide of less than 20 Å.
8. Thin Nitride on Silicon
Programs 7 and 8 average data at one wavelength, 520 nm, for about 3 seconds, instead of
scanning through the visible wavelength range (480 - 800 nm). When either Program 7 or 8 is
selected, the NanoSpec's wavelength counter display changes from 480 to 520 nm. A new
reference check must be run on a bare silicon wafer. The reference measurement takes data
at 520 nm for about 3 seconds, and stores it in memory.
Note: Critical Focusing for Optimum Results on Thin Films Programs 7 and 8 require very
careful focusing on the wafer surface.
To measure a sample, the instrument takes reflectance data for the sample at 520 nm and
compares it with the reflectance of the bare silicon reference. Film thickness is calculated
from this comparison.
When measuring very thin films in this way, the calculation depends strongly on the
reflectivity from the bare silicon. For this reason, use silicon from the same manufacturer with
the same crystal orientation, doping and so on, as that used in the samples. Although these
programs are specified up to 800 Å Programs 1 and 2 are better for films above 500 Å.
Because data are taken at a single wavelength, this algorithm can mistake a thick film for a
thin film of measurements, measure only films that are known to be less than approximately
800 Å on oxide and less than approximately 600 Å on nitride. If unsure of the correct
thickness, check the range with Program 1 or 2.
-6-
nanoduv
Chapter 8.34
When the computer calculates a thickness less than 20 Å, the message: LESS THAN 20 Å
appears. For increasing confidence in measurements of very thin films, repeat the
measurements. For very thin films, a new reference should be run at least every thirty
minutes.
9.
Polyimide on Silicon
Measurements made with this program are in the range 500 - 30,000 Å.
10.
Positive Resist on Silicon
Measurements made with this program are in the range 500 - 40,000 Å. The refractive index
(RI) for the particular positive resist must be known. The default RI is 1.63.
11.
Positive Resist on Oxide
The sum of the positive resist thickness and the underlaying silicon dioxide thickness must
not exceed 30,000 Å. It is important to enter an accurate, premeasured oxide thickness. Any
error in the oxide thickness entered results in an error in the resist thickness measurement.
The refractive index (RI) for the particular positive resist must be known. The default RI is
1.63. The instrument will display "Under-range" when measuring oxide of less than 10 Å.
12.
Reflectance Mode
The reflectance program, unlike the direct film thickness programs, measures the amount of
light reflected from a sample at up to three wavelengths specified by the user. Repeatability is
± 2%. The wavelengths to be specified depend on the type of light to which the sample will be
subjected in later processing. For example, in a process using mercury vapor lamps to
expose photolithographic resist, wavelengths of 405, 436 and 546 nm should be specified.
Mercury vapor emits strongly at these wavelengths and the reflectance of the resist is low
since it absorbs light rather than reflecting it. If incandescent light is to be used, wavelengths
of 410, 530 and 650 nm might be suitable. Such light emits on a continuous spectrum with
representative wavelengths at the violet, yellow-green and red portions of the spectrum.
Use program 12 with any lens, however, measuring film under 380 nm requires the UV option
with the 15X lens.
When program 12 is specified, the computer requests sample identification. After the
operator has focused on the sample, the computer asks the operator for the number of
wavelengths to be used (1-3) and then for their values. These are to be specified by a threedigit number in the range 200 - 800 nm.
Measurement time may be varied between 0.1 second and 6.8 seconds in steps of 0.1
seconds. Repeatability is substantially improved when measurement times are longer than 3
seconds. Longer times can be used at any wavelength but are particularly recommended
when measuring wavelength below 400 nm.
When a measurement is taken with this program, the reference reflectance at each specified
wavelength is measured and stored.
Attention: If the yellow filter is removed, be sure to replace it after completing reflectance
measurements.
If results of the reflectance measurements are question- able for any reason, better results
may be obtained by varying the standard measurement time of 2.5 seconds for program 12.
For example, if one or more of the wavelengths is 400 nm or less, the accuracy of the
measurement may be reduced by the low signal-to-noise ratio at these short wavelengths. To
vary the measurement time, request program 120 instead of 12; the two programs are
identical, except that 120 asks for a sample time, which can be between 0.1 - 25.5 seconds,
in steps of 0.1 second. The reflectance is measured for the length of time specified.
Repeatability of the measurements is substantially improved with measurement times longer
-7-
nanoduv
Chapter 8.34
than 3 seconds. Longer times can be used at any wavelength but are recommended below
400 nm.
Dopants in the film tend to change its color, and therefore its reflectance at particular
wavelengths. Such factors should be taken into account in evaluating the results of
reflectance measurements.
13.
Thick Films
This program is for measurement on thick films (4 – 25 μm). It scans the sample from 720 760 nm at a slower speed. The operator should be told that this slower scan speed will make
a different sound, which does not indicate a malfunction. Best results are obtained with the
5X lens; however, the 10X lens may be used with films of lower refractive index value in the
thinner portion of the thickness range. The instrument will display "Under-range" when
measuring thick films of less than 0.01μm.
14.
EPA914EZ Resist on Silicon
This program was specifically designed for use with Mac Dermid's EPA914-EZ positive dyed
resist. The instrument will display "Under Range" when measuring thicknesses less than
100Å.
15.
Very Thin Oxide on Silicon
Not available at this time.
16.
Very Thin Oxide on Silicon
Not available at this time.
17.
UV Thin Oxide on Silicon
Program 17 measures very thin silicon dioxide on silicon in the range of 25 – 175 Å. To
ensure accurate measurements, use an ellipsometer calibrated 0- 60 A oxide sample.
18.
UV Thin Nitride on Silicon
Program 18 measures very thin nitride on silicon in the range of 25 – 500 Å. To ensure
accurate measurements, use a bare silicon reference wafer.
19.
UV Oxide on Polysilicon
Program 19 measures silicon dioxide on polysilicon in the range of 150 – 10 kÅ. This
program reduces measurement errors, caused by polysilicon scattering the UV light by
requiring two reference scans. The 1st reference scan is made on a bare silicon reference
wafer. The 2nd reference scan is made on a sample of your bare polysilicon on oxide, or an
oxide on polysilicon sample where the oxide thickness is known.
20.
UV Oxide on Aluminum
Program 20 may be used to measure silicon dioxide on aluminum in the range 500A-20 KA.
This program reduces measurement errors, caused by aluminum scattering the UV light, by
requiring two reference scans. The 1st reference scan is made on a bare silicon reference
wafer. The 2nd reference scan is made on a sample of your bare aluminum, or an oxide on
aluminum sample where the oxide thickness is known.
Note: Programs 17 to 20 require the DUV lamp be turned on 15 minutes prior to any
measurement (including the reference wafer). A reference must be taken every time a
UV test is run also.
-8-
nanoduv
Chapter 8.34
21.
Oxi-Nitride on Silicon
Program 21 measures the thickness of a single layer Oxi-Nitride film on silicon. The
instrument will display "Under Range" when measuring thicknesses less than 100Å.
22.
Oxi-Nitride on Silicon Dioxide
Film type 22 measures the thickness of an Oxi-Nitride film on silicon dioxide. This program
measures top layer only or both layers simultaneously. The instrument will display "Under
Range" when measuring oxide of less than 100Å.
252. Special Substrate
Program 252 measures films on non-standard substrates. For example, this program can be
used to measure resist on glass, carbon on magnetic media, etc.
253. Dual Layer Films
Program 253 measures non-standard dual layer films by entering Cauchy** values for both
layers. This program can measure the top layer only or both layers simultaneously.
**Caushy Formula: n = A + B/sq.L (See Nanometric Operation Manual, Model 210XP,
Chapter 4, pages 4-7)
254. Single Layer Films
Program 254 allows you to measure non-standard single layer films by entering Cauchy
values for your film. When you define a test that uses program 254, you are prompted to
enter numerical values, for two parameters, that describe the refraction and dispersion of the
film.
255. Special Program
Program 255 may be used to measure the thickness of single layer films such as resists or
oxides on non-standard substrates like metals. To use this program, you must enter the
maximum and minimum reflectances obtained by scanning the sample. This program utilizes
the reflectance values you enter to normalize the interferogram.
Note: To use program #17 to #22, turn on deuterium lamp power supply and let it warm up
for 15 minutes before use. Please refer to page 4-13 to 4-15 on the NanoSpec/AFT
Model 210XP operations manual for details.
12.2 Additional Keyboard Functions
Special commands are described below; these are executed by holding down the control key and
typing the letters as follows:
Ctrl nano
Enter Engineering Menu-displays, print data and statistics, exit to DOS. Toggle
logging Enable/Disable. Set up log files.
Ctrl reset
To reinitialize system.
Ctrl setup Enter setup mode for creating, changing, and etc. user tests.
Ctrl stats
Enter global stats mode.
Ctrl sltpa,
c,d,e, or f Go to slit position a, c, d, e or f.
Ctrl prntr
Will toggle the line printer on/off.
Ctrl goodf Display a numerical fit value in lower right corner of screen. This fit number is a value
for the quality of the fit between theoretical model and the actual film measured. The
closer this number is to zero the better the fit.
-9-