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Section Ill
OPERATION
3.1 GENERAL
This section contains the operating procedures for the FPP-5000, including the function of a l l front panel controls and indicators, procedures for adjusting probe heads, and wafer measurement procedures.
3.2 CONTROLS AND INDICATORS
The following paragraphs describe each control and indicator on the FPP-5000 front panel, Figure 3-1.
3.2.1 Display Select Switches
Each of the following four monetary switches electronically interlock. Each switch has an integral indicator light that illuminates when a selection is made. When selected, FPP-5000 displays measurement described below. Depressing the switch a second time, causes the test to bede-selected.
a. V/I switch - Displays measured V/I multiplied by programmed GEOM constant.
b. SHEET resistance switch - Displays sheet resistivity based on measured VII.
c. SLICE resistivity displays switch - Calculates the bulk resistivity of a slice or layer whose thickness is entered by means of the PRGM mode keyboard switches.
d. THICK switch - Calculates the thickness of a layer or slices whose slice resistivity is entered on the PRGM mode keyboard switches.
3.2.2 TYPE Switch
When selected a type test is performed on each probing.
3.2.3 PEN Select Switch
When selected a penetrate pulse is applied to the sample on each probing.
I f the penetrate function is internally disabled the display will indicate E 05. PRGM mode select switch - A momentary switch that when depressed places the unit into the program mode. The PRGM indicator will illuminate when this mode is selected.
Table 3-1 shows the relationship between the display select switches and their constants.
Figure 3-1. Operating Controls and Indicators
Table 3-1. Display Selected and Associated Constants
3.2.4 SELF TEST
A momentary switch that when depressed places the unit into the self test mode. Programmed constants are retained a t the conclusion of self test (units serial number 330 and less require soft- ware update). A complete digital checkout is performed. I f a failure is detected, the display will display an error code which corresponds to the failure detected. I f the test is successful then all indicators, with the exception of the FAIL indicator, will illuminate and the display will indicate 888 X 10'. The clear button in the keyboard section must be depressed to resume normal operation.
Power On Default Value
1 .OOO X 1 0°
1 .OOO X 10" 1 .OOO X 10" MIL
1.000 X 10" OHM-CM -
Display Select
V/ I Sheet
Slice
Thick
Constant
GEOM
GEOM
Thickness in A, MIL, u
Slice Resistance in OHM-CM
3.2.5 RETEST Switch
A momentary switch that causes the unit to enter a measurement cycles i f the Probe interlock switch is closed. If the Probe interlock switch is not closed the display will indicate EO 1.
3.2.6 CONST Switch
A momentary switch that when depressed causes the display to indicate the programmed constant which corresponds to the display mode selected as shown in Table 3-2.
Table 3-2. Selected Programmed Constants - - - -
3.2.7 Keyboard Programming Switches
Display select
VII
Sheet
Slice
Thickness
All switches are momentary and are described below.
Constant
G EOM
GEOM
Thickness, in A. U, MIL
>
Slice Resistivity in OHM-CM
a. 0-9 buttons - used in programming the mantissa and exponent display digits.
b. +I- button - changes the exponent sign from + to - and vice versa.
c. CE button - deletes last keyboard entry.
d. STORE button - stores programmed constant. Display indicates E 04 if the STORE button was pressed prior to entering all necessary digits.
e. CLEAR button - a multi-function button that clears an entire entry up to the last digit entered. I t does not erase the previously stored constant. In addition, it clears certain error codes from the display. The following error codes cannot be cleared with the CLEAR button:
The CLEAR button also is used to exit from the SELF TEST mode.
f. u, A, MIL buttons - these three buttons are multifunctions keys that are used to select the units of thickness when programming the SLICE resistivity constant.
They are also used to change the thickness units when the THICK display select indicator is illuminated. The unit automatically recalculates the THICK display based on the units selected. I f the thickness units are out of range the display will indicate E 03. For example, E 03 will be displayed if the display is currently reading 1.000 X lo-' u and the operator presses the A button. I f the operator were permitted to do so the display exponent digit would overflow and thus the results would be meaningless.
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3.2.8 Digital Display
The digital display consists of five digits. The display is a scientific notation display with the digits broken into four mantissa digits and one signed exponent digit. The four digit mantissa display is a 3% digit display. Numbers less than two are displayed with a l l four digits, while numbers greater than 1.999 are displayed with three digits. For example, 2.54 X 10.' would be displayed as .254 X 10.' .
The digital display is also used to display error code information. Under most circumstances the error code display can be cleared however under certain conditions it cannot be cleared. Table 3-3 is a list of error codes that could be displayed along with the resultant display after the CLEAR button is pressed.
In addition, the display will flash if a Geometric Correction Measurement is not within a range of 4.18 and 4.82. The display will only flash if the display select indicators SHEET, SLICE, or THICK are illuminated and will continue to flash as long as the calculated geometric correction factor is not between 4.18 and 4.52. Flashing on the next reading can be terminated by disabling the Geometric Correction mode internally.
Table 3-3. Error Codes
3.2.9 Units Indicators
Error Code
E 01
E 02
E 03
- - E 04
- E 05
E 06
E 07
E 21 Thru E 40 --- E 51 Thru E 57
The unit indicators 52, 52/SQ, a-CM, A, u, MIL, GEOM are not visible unless the indicator is illuminated. These indicators are located to the right of the digital display. Upon power turn-on the OHM indicator and V/I display select indicators illuminate.
Description
Retest Attempted while probe interlock is open
Probe interlock is opened while a measurement in progress
Display Exponent overflow or underflow exponent greater 9 or exponent less 9
Store attempted without completing entry of the new constant in PRGM mode
Penetrate Switch Depressed while Penetrate Mode internally disabled
Normal and Reverse V/I Disagree by more than 10%
Arithmetic Error produced as a result of a geometric correction measurement
Electron~c Failure while attempting to make a measurement
Self Test Errors
Display After Clear
Previous Reading
Display read five 8's
Cannot Clear Error Code
Previously programmed constant
Previous Reading
Normal V/I Sheet, Slice, and Thickness
Cannot Clear Error Code
Display reads five 8's
Display reads five 8's
3.3 OPERATING INSTRUCTIONS
3.3.1 Basic Test Station
The FPP-5000 is a compact integrated four point probe test station incorporating easily replaceable probe head adaptor assembly, moveable platen, pre-indexed wafer carrier. RFI light shield, microprocessor based electronics and LED readout. As shipped, the FPP-5000 is ready to plug in. turn one, and test your 2, 3, 4, 5, or 6 inch or frap mented wafers, epitaxial diffused, ion implanted and metalized layers..
3.3.2 Adjustment of Probe Form
The unique probe up design with fixed probe head and moveable platen assures constant probe pressure inde- pendent of operator force. The wafer i s moved a constant distance, for each probing independent of substrate thickness. First adjust the platen travel, then if required, adjust the probe head pressure.
3.3.3 Adjustment of Platen Travel
To adjust the platen for proper travel, use the circular platen travel setting tool provided with accessories received. The circular tool has two surfaces. The inner surfaces rests on the platen while the outer surface is used as the guide to set the proper platen travel. Adjustment is as follow:
a. Place the appropriate platen adjustment tool on the platen so that i t s outer surface is over the platen apperture.
b. Close cover to approximately 45 degrees while pressing down on the platen until the platen lock is re- leased and the platen fully descends.
c. While holding down the platen so it i s resting against its stop, turn the adjustment screw, accessible through a hole in the platen marked INCREASE, clockwise to increase the platen travel or counter- clockwise to decrease the platen travel. Adjust this screw until the probe pin just touches the outer surface of the circular tool. (See Figures 3-1A and 3-3)
Failure to set the platen adjustment and consequently, probe height in this fashion will result in poor probe to wafer contact, and error codes E01 and1 or E30.
d. Repeat procedures in paragraph 2.3.
3.3.4 Adjustment of Alerri Probe Head Preuure
The probe force is adjustable from 40 to 70 or 70 to 180 grams per pin when using the Alessi probe head. It is not adjustable when using the K & S Fell head which is preset at predefined pressures of 20 to 200grams per pin.
Adjustment of the probe head should only be made i f after a measurement display reads E 06, signifying that the normal V/I disagrees with the reverse VII by more than 10%. In addition, to optimize the life of the probe head (the Aleni head is specified to operate for a minimum of 20,000 probings) the user should always start out with the lightest prenure possible, and increase the pressure only if there is a large amount of random error or i f an E 06 error code is displayed.
Alessi probe force is adjusted by turning a 1116 inch Allen head screw, located inside the aperature on the underside of the probe block. Turning the screw clockwise will increase the probe force.
NOTE - The proper selection of the probe head for application is critical to insure reliable and repeatable results. Refer to the specification section for the recommended probe head pressure and tip radii. .
3.4 DISPLAY SELECTION
Proper mode selection should be determined prior to programming of constants and1 or probing. The mode selection is described in paragraph 3.2.1.
3.5 PROGRAMMING OF CONSTANTS
The constants GEOM, thickness in MIL, u, or A, and slice resistivity can be programmed via the keyboard programming switches on the front panel. The constant to be programmed is directly dependent of the display select mode chosen. The constant presently programmed can be viewed at any time by pressing the CONST switch on the front panel. Table 3-1 lists the display select mode and the constant used in calculating the display.
The following procedure should be used to program a constant:
a. Select the appropriate display select mode.
b. Press the PRGM switch and observe that the indicator on the PRGM switch illuminates. Also observe that the constant is displayed along with i ts appropriate units.
c. First, enter the new mantissa with keyboard switches labeled 0-9 four digits for numbers less than 2 and 3 digits for numbers greater than 1.999.
d. Next, enter the sign of the exponent by pressing the +/- key. I f the desired exponent is positive, then no entry need be made.
e. Enter the exponent by pressing one of the keyboard switches labeled 0-9.
f. Observe that the number of the display is correct. If not, then either clear the entiredis- play by pressing the CLEAR key, or delete one digit a t a time by pressing the clear entry key labeled CE.
g. Press the STORE key and observe that the display winks indicating that the information is acceptable. The display will indicate E 04 if an insufficient number of digits were entered. If this happens, then press CLEAR and start over from the beginning; this time be careful to enter al l the necessary information including the exponent.
The following examples will clarify the procedure:
Example 1
The operator wishes to measure the slice resistance of a 7.3 (.73 X 10') micron thick epitaxial layer. Proceed as follows:
a. Press the SLICE switch and observe that the SLICE indicator illuminates.
b. Press the PRGM switch to put the instrument in the program mode. Observe that the PRGM indicator and the units indicator MIL are illuminated.
c. Enter 7 and observe that the display indicates .7 with all trailing digits blanked.
d. Next, enter 3 and observe that the display indicates .73 with all trailing digits blanked.
e. Enter 0 and observe that the display indicates .730 with the exponent digit blanked.
f. Enter the exponent digit 1 and observe that the display reads .730 X 10'
g. Press the u (micron) key to change the units from MILS to microns. Observe that the u indicator illuminates.
h. Press STORE and observe that the display winks.
i. Press the PRGM switch to exit from the program mode. Observe that the PRGM mode indicator extinguishes.
Example 2
The operator wishes to measure the slice, resistance of an 11.7 MIL (1.17 X 10' ) thick slice. Proceed as follows:
a. Press the SLICE switch and observe that the SLICE indicator illuminates.
b. Press the PRGM switch to put the instrument in the program mode. Observe that the PRGM indicator and the units indicator MIL are illuminated.
c. Enter 1 by pressing the 1 key. The display should indicate 1 with a l l trailingdigits blanked.
d. Next enter 1 and observe that the display indicates 1. 1 with all trailing digits blanked.
e. Next enter 7 and observe that the display indicates 1.17 with the remaining digits blanked.
f. Enter 0 and observe that the d~splay indicates 1.170 with theexponent digit blanked.
g. Enter an exponent of 1 and observe that the display indicates 1.170 X 10'
h . Press STORE and observe that the display winks.
i. Press the PRGM switch to exit from the program mode. Observe that the PRGM mode indicator extinguishes.
Example 3
The operator wishes to measure the metallization layer thickness of pure aluminum with a slice resistance of 2.65 micro ohm-cm (.265 X ). Proceed as follows:
a. Press the THICK switch and observe that the THICK indicator illuminates.
b. Press the PRGM switch to put the instrument in the program mode. Observe that the PRGM indicator and units indicator h-2 - cm are illuminated.
c. Enter 2 by pressing the 2 key. Observe that the display indicates .2 with all trailing digits blanked.
d. Next enter 6 and observe that the display indicates .26 with a l l trailingdigitsblanked.
e. Enter 5 and observe that the display indicates .265 X 10 with the exponent digit blanked.
f. Press the +/- key and observe that the sign digit adjacent to the X 10 illuminates.
g. Enter 5 and observe that the display reads .265 X lU5.
h. Press STORE and observe that the display winks.
i. Press the PRGM switch to exit from the program mode. Observe that the PRGM indicator extinguishes.
3.6 PENETRATE FUNCTION
A high-voltage low-energy pulse is applied to the probe tips in order to breakdown any thin oxide growth (approximately 700 Angstroms of SiO, or 2200 Angstroms of AIO,) on the sample under test. Press the PEN switch to enable the penetrate function to apply the high voltage pulse on each probing. E 05 is displayed if the penetrate function is internally disabled. To enable the penetrate function set switch S1-1 on the digital PC board to the ON position. This switch is acces- sible from the top of the instrument with the cover removed. (Refer to Section VI.)
3.7 TYPING FUNCTION
A type test can be made for each measurement by pressing the TYPE switch. Observe that the TYPE indicator illuminates. The substrate type will be indicated as N-type by illuminating the N indicator adjacent to the display of P-type by illuminating the P indicator adjacent to the display. Both P and N indicators are simultaneous illuminated if the results of the type test are inconclusive. To disable the type test press the TYPE switch. Observe that the TYPE indicator extinguishes.
NUIt
The FPP-5000 employs both rectification and thermal type tests. However, some materials that l ie within the practical limits of the type mode may not be able to be typed tested reliably.
3.8 AUTOMATIC COMPUTATION OF GEOMETRIC CORRECTION FACTOR
The geometric correction factor of 4.53 (nIln2) is used by the unit to compute SHEET resistance from a V/I measurement. Automatic geometric correction computation can be used to reduce probe errors due to probe tip spacing variations and edge effects. This is particularly useful when checking the uniformity of ion implanted layers.
The FPP-5000 computes the geometric correction by incorporating both the hardware and software necessary to employ the Two Configuration Technique.' Generally, the two configuration technique is recommended for those layers with doses greater than loL3 ions/cm2.
The auto geometric correction mode does not eliminate the necessity for the constant GEOM which can be used to compensate for thickness and temperature effects (See reference section 1.4).
'D.S. Perloff, N.J. Gan, F.E. Wahl, "Dose Accuracy and Coping Uniformity of Ion Implantation Equipment", Solid State Technology, February 1981.
The auto geometric correction factor computation can be enabled by setting switch S1-2, on the digital PC board to the ON position. The display will flash in SHEET, SLICE, and THICK if the computed geometric correction is not between 4.18 and 4.82. Thedisplay will indicate E 07 if the geometric correction factor cannot be calculated. This error cannot be cleared with the CLEAR button.
3.9 PROBING
Make wafer measurements as follows:
a. Adjust the rear stop by loosening thethumb screw and moving the position of the Sop to the appropriate wafer size position. (100 mm, 125.mm, 150 mm, 2 inch and 3 inch positions are in accordance with SEMI STD MI. 1 .)
The FPP-5000 is now set up to probe in the R/2 locations on the wafer.
b. Place the wafer you wish to probe in the wafer holder.
c. Place the appropriate size backing plate with the spiral side facing the wafer.
d. Slide the wafer holder forward so that it is "banking" on the front stop. The wafer is now positioned to be probed in the center.
e. With power on, select the proper display mode as described in paragraph 3.2.1.
f. Close the cover and hold it down to initiate a test. The display will go blank and the TEST indicator adjacent to the display will illuminate for not more than 2 seconds at which time the display will reappear. E 02 will appear on the display if the cover is re- leased before a measurement is completed.
By depressing the RETEST button, with the cover down, you can reinitiate the test. The display will indicate E 01 if the cover is not held down while pressing the retest button.
It is recommended that al l measurements be performed with the cwer closed to elimin- ate effects due to light and RFI.
g. Open the cover.
h. Slide the wafer holder so that it "banks" against the rear stop and rotate it SO that the location marked "2" is facing you (90').
i. Probe this location as was done in step f.
j. Repeat steps g through i for locations marked "3", "4" and "5".
k. Remove the wafer backing plate and remove the wafer.
3.10 SELF TEST MODE
A self test of the microprocessor circuitry can be performed by pressing the SELF TEST switch. The test is successful if the display indicated all eights and all indicators, with the excep- tion of FAIL, illuminate. One of the following error codes will be displayed if the self test is not successful:
a. E 51 - CPU readlwrite memory error
b. E 52 - IC4 readlwrite memory error
c. E 53 - Peripheral interface adaptor (IC 6) readlwrite error
d. E 54 - EPROM (IC 2 & IC 3) checksum error
e. E 55 - Real time interrupt clock frequency too high or too low
f. E 56 - Read only buffer (IC 10) error
g. E 57 - Front panel switch shorted
These errors are discussed in detail in Section VI.
The self test erases all pre-programmed constants. The CLEAR switch must be pressed to resume normal operation after a self test.
3.1 1 GEOM. CORR. (GEOMETRIC CORRECTION)
In some extreme cases it might be desirable to multiply the measured result times a geo- metric correction. This correction, as discussed in Technical Papers,'12 generally has to do with the ratio of the diameter of the wafer (D) divided by the probe spacing (S). I f the resultant number (DIS) is greater than 40, no correction is necessary. For DIS values less than 40 typical configura- tion of wafer diameter (Dl and probe spacing (S) are indicated in Table 3-4 along with a plot of the same information on Figure 3.2. For sheet and VII measurements you input the correction by programming the Geometric Correction factor using the keyboard.
Example: If the probe spacing is 62.5 mils, and the wafer is 1.0 in. in diameter then
- looO - 16. From Figure 3.2 or Table 3.4 the correction factor for 16 is .967. Enter s-62.5- .967 X l o 0 using the keyboard switches. The resultant display will be multiplied by .967 thus compensating for the geometry error. Once programmed, all readings of VII, slice, sheet and thickness will be multiplied by the inputted geometric correction factor.
3.12 RS-232 OPTION OPERATION
3.12.1 RS-232 Output OnlOff Control
The RS-232 output is activated from the FPP-5000 front panel by pressing the STORE button. Pressing STORE during PROGRAM mode or while an Error is being displayed will not activate the output.
Once the RS-232 output mode is activated it will remain so until the front panel CE button is pressed. Pressing CE button during PROGRAM mode, however, will not deactivate the RS-232 output.
While the RS-232 output mode is active, any new measurement will automatically initiate a transmission of data in the specified format.
'~aldes, L.B., Resistivity Measurements on Germanium for Transistors, Proc. of I.R.E., 42, February 1954, p. 420. '~rnits. F.M., Measurement of Sheet Resistivities with the Four Point Probe. The Bell System Technical Journal, May 1958.p.711.
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Table 3-4. Geometric Corrections
25 MIL PROBE SPACING (S)
40 MIL PROBE SPACING (S)
DIA (Dl
1.00 1.5 2.0 3.0
62.5 MIL PROBE SPACING (S)
D/S
40 60 80
120
DlA (D)
1 .O 1.5 2.0 3.0
Any time a measurement display mode is changed (i.e., from V/I to SH'EET) a new trans- mission is initiated.
CORRECTION
.995 1 .OO 1 .oo 1 .OO
D/S
25 37.5 50 75
Exit from PROGRAM Mode will also initiate a transmission.
% ERROR
+ .5% 0 0 0
-
% ERROR
+2.3% +1.5% + .9% 0
DIA (D)
1 .O 1.5 2.0 3.0
3.12.2 WAFER and LOT Number Entry
CORRECTION
.985
.994 1 .OO 1 .OO
Four digit Wafer and Lot numbers are entered via the front panel by first pressing the +/- bunon. The display will now read the last LOT number entered. The exponent digit reads "u" to indicate that you are in LOT number entry mode.
% ERROR - +1.5% + .6% 0 0 -
DIS
16 24 32 48
The flashing digit points to the one that can be altered by pressing the desired front panel number button (0-9). After you enter a digit, the next digit to the right will flash.
CORRECTION
,967 .985 .99 1
1.00
Press the +/- button again and the display will now read the last WAFER number entered. The exponent digit reads "c" to indicate that you are in the WAFER number entry mode.
The Wafer number can be changed in the same manner as was the LOT number.
Pressing the +/- bunon again will put you back into the LOT number entry mode and so on.
To leave this mode, press the CLEAR bunon.
See sample operation.
