JPH0556460B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cleanliness measuring method for measuring the cleanliness of the surface of a sample whose surface is partially covered with a contaminated layer.

Conventionally, the cleanliness of a sample surface, that is, the area of the sample surface that is not covered by a layer of contamination such as oil, fat, and dust, has been measured by an inspector through visual inspection. Ta. However, since such visual inspections have to rely on the inspector's intuition, problems arise when individual differences occur and cleanliness cannot be accurately measured.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a surface cleanliness measuring method that can accurately measure the cleanliness of the surface of a sample.

This purpose is to provide a cleanliness measurement method for measuring the cleanliness of a surface of a sample, a part of which is coated with a contaminated layer having a photoelectric work function larger than the photoelectric work function of the sample. Then, an energy higher than the photoelectric work function of the sample and lower than the photoelectric work function of the contamination layer is applied to emit electrons from the entire surface of the sample. This can be achieved by trapping electrons in the contamination layer while detecting electrons from the surface not covered by the contamination layer.

Here, the contaminated layer has a photoelectric work function larger than that of the sample, such as oil, fat, etc.
This applies to garbage, etc. The photoelectric work function is the energy difference from the Fermi level to the vacuum level in metals, and the energy difference from the top of the valence band to the vacuum level in semiconductors. In addition, the energy value given to the sample is greater than or equal to the photoelectric work function of the sample and less than the photoelectric work function of the contaminated layer, and as a result, electrons are generated from the entire surface of the sample, but electrons are not generated from the contaminated layer. Not released.
Among the electrons emitted from the sample surface, the electrons emitted from the surface covered with the contamination layer lose their kinetic energy in the contamination layer when passing through the contamination layer, and are all captured in the contamination layer. be done. On the other hand, electrons emitted from the surface not covered by the contamination layer continue to move as they are. Next, only the electrons that continued this movement are captured, and their number is measured or converted into a current and detected as a current value. Next, based on such detection results, the ratio of the surface area of the sample not covered with the contaminant layer to the total surface area of the sample is determined, and the cleanliness of the sample surface is measured. The atmosphere in which such measurements are performed may be various single gases, mixed gases, or the atmosphere.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows an air counter, in which numeral 1 is a case with windows 2 and 3 formed at the bottom, and this case 1 is grounded and serves as a cathode. A ring-shaped anode 4 is provided inside the case 1, and a high voltage power source 5 of, for example, 3.4 KV is connected to this anode 4. Between the anode 4 and the case 1,
For example, the first grid electrode 6 to which a voltage of 100V is applied
is installed, and a voltage of 80V, for example, is applied between the first grid electrode 6 and the sample 7 placed on the bottom of the case 1.
A second grid electrode 8 to which a voltage of is applied is installed. A part of the surface of the sample 7 has a contaminated layer 9,
For example, it is covered with a layer of oil. Reference numeral 10 denotes a light source, and the light from this light source 10 is made monochromatic by a spectroscope 11 and illuminates the sample 7 and the contaminated layer 9 through the window 2, and the reflected light exits through the window 3. Note that the intensity of the monochromatic light at this time is adjusted by two slits 12. Reference numeral 13 denotes an amplifier connected to the anode 4, and a first pulse generator 14 is provided between the amplifier 13 and the first grid electrode 6. When an electron pulse is generated at the anode 4, this first pulse generator 14 sends a 300V rectangular wave pulse to the first grid electrode 6 with a time width Te (5 ms), for example, to increase the voltage of the first grid electrode 6. The voltage is increased from 100V to 400V as shown in Figure 2b. Further, a second pulse generator 15 is provided between the amplifier 13 and the second grid electrode 8, and when an electron pulse is generated at the anode 4, the second pulse generator 15 generates a pulse with a time width Te (5ms). ), a rectangular wave pulse of -110V is supplied to the second grid electrode 8, and the voltage of the second grid electrode 8 is reduced from 80V to -30V as shown in FIG. 2c. The first and second pulse generators 1
Reference numerals 4 and 15 allow the time width and peak voltage of the generated rectangular wave pulse to be arbitrarily set. 16 is a counting means connected to the amplifier 13, and this counting means 16 counts the electron pulses generated at the anode 4. A calculating means 17 is connected to this counting means 16, and this calculating means 17 is composed of, for example, a microcomputer. Then, this calculating means 17 calculates the cleanliness T of the sample 7, that is, how much of the surface of the sample 7 is the output from the counting means 16, for example, when the number of counts of electron pulses per second (counting rate) is N. whether it remains uncovered by the contamination layer 9;
is the formula, T=N/N1 Here, N1 is calculated using the count number (counting rate) when the sample surface is completely clean and not covered with any contaminated layer, and the cleanliness T of sample 7 is calculated. seek. Next, the output signal from the calculation means 17 is sent to a display means 18 such as a CRT or a printer, and the calculation result, that is, the cleanliness T of the sample 7, is displayed on the display means 18.

Next, the operation of one embodiment of the present invention will be explained.

First, a constant thickness, e.g. mean free path of electrons,
A sample 7 made of, for example, silicon and having a contaminant layer 9 made of the oil or fat adhered to a part of its surface is placed on the bottom surface of the case 1. Next, a high voltage of, for example, 3.4 KV is applied from the high voltage power supply 5 to the anode 4 as shown in FIG. 2a. Next, the light from the light source 10 is turned into monochromatic light by the spectroscope 11, and the slit 1
The intensity is adjusted by 2 and the sample 7 is irradiated. As the monochromatic light that gives energy to the sample 7 , light having energy that is greater than or equal to the photoelectric work function of the sample 7 and less than the photoelectric work function of the contamination layer 9 is used. The monochromatic light irradiated onto the sample 7 passes through the contamination layer 9 and then imparts light energy to the surface of the sample 7.
The entire surface of this sample 7, that is, both the part covered with the contamination layer 9 and the part not covered,
emit photoelectrons with low energy of less than 10 eV. At this time, since the optical energy of the monochromatic light is less than the photoelectric work function of the contamination layer 9, no electrons are emitted from the contamination layer 9. Next, when the electrons emitted from the contaminated surface covered by the contaminated layer 9 pass through the contaminated layer 9, they lose their kinetic energy and are captured by the contaminated layer 9. Therefore, it cannot appear externally. On the other hand, electrons emitted from the clean surface not covered by the contamination layer 9 continue to move. In this way, electrons from the contaminated surface covered by the contaminated layer 9 do not appear outside, while electrons from the clean surface not covered by the contaminated layer 9 move as they are and appear outside. If you check the number of electrons that appeared, sample 7
It is possible to know how much of the surface remains uncovered by the contamination layer 9.
Electrons from the clean surface pass through the second grid electrode 8 and the first grid electrode 6 and are attracted to the anode 4. Then, when the electrons reach the vicinity of the anode 4,
Since a strong electric field is generated near the anode 4 due to the high voltage, electrons are accelerated by this electric field, causing a gas discharge. Due to this gas amplification effect, the potential of the voltage applied to the anode 4 decreases as shown in FIG. 2a, and an electron pulse is generated. The electron pulse generated at the anode 4 is sent to a first pulse generator 14 and a second pulse generator 15 via an amplifier 13. The first pulse generator 14 has a voltage
A rectangular wave pulse of 300V and a time width of Te is generated and sent to the first grid electrode 6 to increase the voltage of the first grid electrode 6.
Increase Te time from 100V to 400V. As a result, the potential difference between the anode 4 and the first grid electrode 6 increases.
The voltage drops by 300V, and as a result, secondary electrons generated by light and positive ions generated by gas amplification cannot reach the discharge voltage, and continuous discharge is prevented. On the other hand, the second pulse generator 15 has a time width of Te
A square wave pulse with a voltage of -110V is sent to the second grid electrode 8, and the voltage of the second grid electrode 8 is changed from 80V to -
Reduce to 30V. As a result, the positive ions generated by the gas amplification effect are transferred to the second grid electrode 8.
captured and neutralized. This prevents positive ions from reaching the contaminated layer 9 and the sample 7 and affecting them. Then, after a period of time Te has elapsed, the voltages of the first and second grid electrodes 6 and 8 are restored to their original voltages, and the air counter is in a state where it can detect electrons again. The electron pulses generated at the anode 4 are simultaneously sent to a counting means 16 via an amplifier 13, which counts the number of electron pulses emitted from the clean surface not covered by the contamination layer 9. The number of electrons is counted, and the counting result, for example, the counting rate, is output to the calculation means 17. The calculation means 17 calculates the cleanliness of the sample 7 by calculating based on the above-mentioned formula, and sends the calculation result to the display means 18. Here, when the surface of the sample 7 is a completely clean surface, that is, when it is not covered with the contaminated layer 9 at all, the counting rate becomes equal to the above-mentioned N1 and the calculation result (cleanliness) becomes 1, In addition, as the surface of the sample 7 is covered with the contamination layer 9, the counting rate decreases and the calculation result (cleanliness)
approaches 0 from 1 and is a completely contaminated surface, that is, when it is completely covered by the contaminated layer 9, the counting rate becomes 0 and the calculation result (cleanliness) becomes 0. When the calculation result is input to the display means 19, the display means 18 displays the cleanliness T of the sample 7.

In the above embodiment, the air counter for detecting low-speed electrons, the counting means 16, the calculating means 17, and the display means 18 were integrated into one device, but in this invention, For example, the air counter and counting means 16, the calculation means 17 and the display means 18 may be separated, and the detection of the number of electrons and the calculation display may be performed at separate locations.

As explained above, in the present invention, the number of photoelectrons from the sample is detected by irradiating light with an energy larger than the work function of the sample and smaller than the work function of the contaminant attached to the surface of the sample. However, since the amount of contaminants is detected based on the difference between this number and the number of photoelectrons based on a clean sample, there is no need to consider the energy of the photoelectrons itself as a problem. This enables on-line measurement of the cleanliness of industrial products.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view, partially shown in blocks, showing an embodiment of an apparatus for carrying out the present invention, and FIG. 2 is a graph showing voltage changes of an air counter. 4...Anode, 7...Sample, 9...Contaminated layer, 10
... light source, 16 ... counting means, 17 ... calculation means, 18 ... display means.

Claims (1)

[Claims] 1. Detect the number of photoelectrons from the sample by irradiating light with an energy larger than the work function of the sample and smaller than the work function of the contaminants attached to the surface of the sample, and compare the number with the clean one. A surface cleanliness measurement method that detects the amount of contaminants based on the difference in the number of photoelectrons based on the sample.