JPH0352219B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for calibrating the sensitivity of an automatic foreign matter inspection apparatus for semiconductor wafers, masks, etc.

[Background of the invention]

The most common foreign particle inspection equipment on semiconductor wafers is
As shown in the figure, it is composed of a light source 3, a sample wafer 1, a photoelectric conversion section 6, and a voltage amplifier 7.

However, if the illuminance of the illumination light 4 changes due to deterioration of the light source 3 or the sensitivity of the photoelectric conversion unit 6 or voltage amplifier 7 changes (change over time), the apparent intensity of the reflected light 5 from the foreign object 2 will change. Periodic sensitivity calibration is required.

In other words, the sensitivity calibration of foreign object inspection equipment is the first step.
The result will be as shown in the figure. Device detection output value V of foreign object 2
8 (the value outputted by the photoelectric converter 6 of the intensity of the reflected light 5 from the specific foreign object 2 with respect to the illumination light 4). but,
It is difficult to apply a very small amount of specific foreign matter 2 of about 1 μm onto a sample and maintain it for a long time. In addition, there are various types of actual foreign matter 2 such as metal powder, dust, etc., but even if they are the same size, the reflected light intensity is significantly different. Therefore, if the actual foreign matter 2 is used as the specific foreign matter 2, It is also difficult to make the sensitivities of multiple foreign object inspection devices the same.

Therefore, there is a method of using bead-shaped latex standard particles, whose size is clearly measured in advance and whose reflected light intensity with respect to the reference illumination light 4a is almost equal to that of the actual foreign matter defect, in place of the specific foreign matter 2 as a reference for the foreign matter defect in calibration. Common. Also, at production sites, the actual size of foreign particles is determined by a specific foreign particle inspection device as ``a foreign particle equivalent to the reflected light intensity equivalent to several micrometers of a standard particle,'' and is replaced by the standard particle diameter.

Here, the reference illumination light 4a is obtained by a method as shown in Japanese Patent Laid-Open No. 138983/1983. That is, the illumination light 4 illuminance is measured by the second photoelectric converter 30 (illuminance meter) with no sensitivity change, and the output of the photoelectric converter 30 is measured.
This is a method of changing the input of the light source 3 so that Vc becomes a preset value _V0 . This method is illustrated in FIG. A part of the illumination light 4 is incident on the photoelectric converter 30 by the semi-transparent mirror 33 . Photoelectric converter 30 measured in advance at an early stage when the light source 3 has not deteriorated
A comparator circuit 31 compares the output V ₀ of the output V 0 and the output Vc at the time of calibration. The electric circuit 32 controls the illumination brightness of the light source 3 based on the comparison result until the output reaches V ₀ .
At this point, the semi-transparent mirror 33 is removed and the reference illumination light 4 is
a is obtained, and the detection output 8 of the intensity of reflected light from a standard particle of a specific diameter is called the initial device sensitivity.

Next, a method using standard particles will be explained below.
As shown in Figures 3 and 4, on a smooth and clean sample surface 1,
Standard particles 9 are stirred in pure water 10 (clean without any foreign substances), and dried by spraying 12 with clean air 11 and applied. Standard particle size D _s of a specific diameter (e.g. 1 μm
Record the initial correlation function (initial device sensitivity) of the device detection output of 8 V _s (diameter) in a notebook. To calibrate the device sensitivity due to changes over time, apply standard particles 9' of the same diameter again at the time of calibration, and adjust the light source 3 or photoelectric conversion voltage amplifier 7 each time to maintain the initial correlation between D _s and V _s . This is done through adjustment.

However, this method takes time and effort to spray, and since the application is performed in a clean room such as a clean room, the room is likely to get dirty. In addition, it is difficult to preserve early standard particle coating samples because the standard particles fall off and other foreign substances such as operator's fingerprints adhere to them. Furthermore, this sample has drawbacks such as not being able to be washed (standard particles fall off).

In addition, as a conventional calibration method for changes over time, as shown in FIG. 5, a sample 1 whose surface is made uneven by laser melting 13 or etching chemical treatment 14 is used. That is, the initial calibration correlation is recorded as the initial device sensitivity of the device detection output values of the unevenness 13 and 14, and if a change occurs over time,
For this reason, this method compares the intensity of the reflected light 5 from the unevenness 13 and 14 with the initial device sensitivity to adjust the illumination light source 3 or the voltage amplifier 7 for photoelectric conversion.

However, since this method shows a relative relationship with the initial sensitivity (not absolute calibration), it becomes impossible to recalibrate the device due to damage to the sample. Further, even if the laser processing time, etching time, etc. are controlled, the same shape cannot be obtained (that is, there is no reproducibility), so there are drawbacks such as the need to calibrate each processed sample.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for calibrating the sensitivity of an automatic foreign matter inspection device, which eliminates the drawbacks of the prior art and allows the absolute sensitivity calibration of the automatic foreign matter inspection device to be carried out stably and easily.

[Summary of the invention]

As mentioned above, in the conventional calibration method, the sample coated with standard particles requires a laborious spraying operation and is difficult to store, and if other foreign matter adheres to the calibration sample, it is impossible to clean it. Furthermore, since the etched and laser-processed sample is a relative calibration sample of the initial value, the sensitivity of the initial device cannot be reproduced due to damage.

Therefore, in the present invention, uneven scratches corresponding to the standard particle diameter are formed on the surface by processing, and the uneven scratches are further irradiated with reference illumination light by an illumination means and the reflected light intensity detected by the detection means is measured. Prepare a standard sample for absolute sensitivity calibration in which the intensity of reflected light from the lever is specified, and then use the prepared standard sample for absolute calibration in an actual foreign matter inspection device to apply illumination light to the uneven scratches on the standard sample using an illumination means. This is a method for calibrating the sensitivity of an automatic foreign substance inspection apparatus, which is characterized by illuminating the standard sample and calibrating the absolute sensitivity so that the intensity of reflected light specified in the standard sample is obtained from the detection means. Specifically, the following is the standard sample for the above absolute sensitivity calibration.
Shown in (1) to (4).

(1) An uneven scratch is formed on the sample surface by processing such as mechanical processing, laser melting processing, or etching chemical treatment, and the uneven scratch is irradiated with reference illumination light by the illumination means in advance and detected by the detection means. A standard sample for absolute sensitivity calibration in which the reflected light intensity (value converted to an output voltage value) is measured and this reflected light intensity is displayed on the sample surface, or this reflected light intensity is clearly written on paper such as a plastic sheet and recorded. Standard sample for absolute sensitivity calibration.

(2) In (1) above, a standard sample for absolute sensitivity calibration in which the reflected light intensity for the reference illumination light from the uneven scratches is replaced with a standard particle size having the same reflected light intensity.

(3) In (1) and (2) above, for the purpose of easily attaching the absolute calibration standard sample to the actual foreign matter inspection device to be calibrated, the test object is the object to be inspected with the actual foreign matter inspection device. , that is, a standard sample for absolute calibration based on a photomask or silicon wafer,
Or a standard sample for absolute sensitivity calibration made of a smooth metal plate having the same shape and thickness as a photomask or silicon wafer.

(4) In (1), (2), and (3) above, the uneven scratches to be processed are formed into a base pattern (matrix pattern), a pattern such as equally spaced circles (ring pattern), or numbers or letters. The placed standard sample for absolute sensitivity calibration.

The purpose of this is to use the function of displaying the inspection results of the actual foreign matter inspection device in the form of a map of the distribution of foreign matter, to clearly distinguish uneven scratches from other adhered foreign matter, and to easily adjust the sensitivity (sensitivity calibration). This is to ensure that.

By preparing the standard sample for absolute sensitivity calibration as described above, it becomes possible to stably and easily calibrate the absolute sensitivity in the actual foreign matter inspection device to be calibrated.

[Embodiments of the invention]

As a specific embodiment of the present invention, standard samples for absolute sensitivity calibration for semiconductor automatic foreign matter inspection equipment are
This will be explained based on FIG.

FIG. 6a shows a calibration silicon wafer 15 which is an embodiment of the standard sample for absolute sensitivity calibration according to the present invention.
FIG. That is, the calibration silicon wafer 15 is prepared by forming scratches 13 on the silicon wafer in advance by laser processing so as to correspond to the standard particle diameter, and then using the silicon wafer with the scratches 13 formed in advance in the initial apparatus shown in FIG. and illuminates the scratch 13 with the reference illumination light 4a from the controlled light source 3 to illuminate the scratch 1.
The intensity of the reflected light from 3 is measured by the photoelectric converter 30, and the detected output value 16 and the converted standard particle diameter size 17 obtained by replacing it with a standard particle diameter having the same detection output value as the detected output value are determined by the laser pen, Alternatively, it can be manufactured by clearly marking it by etching or the like.

In addition, in order to avoid writing with a laser pen and the etching process, the converted standard particle diameter is 17.
and its detection output value (reflected light intensity) 16 on paper 1.
8 may also be used. However, in this case, it is desirable that the scratch 13 corresponds to the recording position on the paper, as shown in FIG. 6b. The right diagram of FIG. 6b is a sheet 18 on which the detection output value (reflected light intensity) 16 and the size 17 of the converted standard particle diameter are specified.

In order to easily attach the standard sample for absolute sensitivity calibration according to the present invention to a foreign matter inspection device, the same base material as the object to be inspected, that is, the silicon wafer 15 shown in FIG.
FIG. 7b shows a photomask 19 with calibration scratches 13 formed thereon. In addition, in order to easily attach it to the foreign object inspection device and prevent it from being damaged, Figure 7c shows a calibration scratch 1 on a smooth iron plate 20 that has the same shape as the photomask.
The standard sample for absolute sensitivity calibration processed from 3 is shown.

By using the above standard sample for absolute sensitivity calibration when calibrating the foreign object inspection device, a flaw 13 whose reflected light intensity is always constant is provided, and the reflected light intensity from this flaw 13 is detected by a photoelectric converter. By matching the detected output value to the specified detection output value (reflected light intensity) (sensitivity by the initial device) 16, the foreign matter inspection device can be easily calibrated.

However, the scratch 13 was about 1 to 3 μm in size, and the foreign object inspection equipment was equipped with a magnifying microscope (Hitachi Hyoron Showa).
(November 1955, Vol. 62, No. 11, Volume 706, Page 791) is not included, it will be difficult to find scratches 13, and when calibrating, as shown in Figure 1. It takes a long time to illuminate the scratch 13 with the illumination light 4 and measure the detection output of 8V from the photoelectric converters 6 and 7.
Therefore, during calibration, there is a function (mapping function) that displays the foreign material distribution of the inspection results of the foreign material inspection device in a map form.
Use a method that utilizes.

Figures 8a and b show scratches 1 on the calibration standard sample mentioned above.
3 are processed at clearly known processing positions in advance, for example (a) is an example in which they are arranged in a matrix shape 21, and (b) is an example in which they are processed in radial arrangement.
In addition, Fig. 8 b and c show the size of the scratches arranged in order of size 2.
This is an example of processing and arrangement according to 2. In this case, it is necessary to make the size of the scratches uniform in an annular shape or in a horizontal line, which may be difficult with conventional laser machining or etching processing.

Therefore, it is necessary to use a process technique for forming fine and stable irregularities by light or X-ray lithography of the photoresist coated on the wafer, or development treatment or etching treatment after electron beam lithography.

These embodiments allow absolute sensitivity calibration to be performed easily, stably, and in a short time, and the storage conditions for the calibration standard sample 15 are also facilitated. The reason for this is that, as shown in FIGS. 9a and 9b, if a calibration standard sample with scratches arranged in a matrix is used, the foreign substance distribution map 34 obtained from the foreign substance inspection device can be displayed on the calibration standard sample 15. This is because it is possible to clearly distinguish between the scratches 13 and the adhesion of other foreign matter 35, and the sensitivity calibration can be easily performed. Furthermore, instead of adjusting the light source 3 or voltage amplifier 7 in the foreign matter inspection apparatus shown in FIG. 1 by attaching a calibration standard sample during calibration, a method of adjusting the slice level may be used. In other words, even if calibration is performed by adjusting the slice level VL shown in Fig. 8d (in the figure, for example, an output exceeding a diameter of 2 μm), the detection level of the detected particle (detected foreign object) diameter cannot be easily calibrated. Ru. Using the calibration standard sample shown in Figure 8c, the slice level VL is 2μ.
When the calibration is completed to a level exceeding 2 μm, scratches smaller than 2 μm are not displayed in the foreign matter distribution map 34 shown in FIG. Even an expert can easily check the calibration work by easily adjusting the slice level appropriately.

Further, the processing positions of the scratches may be arranged so as to form letters, numbers, etc. For example, Figure 10a
is a flaw of the same size, and the character 38 indicating the size of the flaw (the size of the converted standard particle diameter obtained by replacing the detection output value detected by the initial flaw device with a similar standard particle diameter) It is processed and arranged so as to form. As a result, according to the calibration method using the slice level VL adjustment described above,
With the foreign matter distribution map output display function, Fig. 10b
As shown in the figure, the letters 3 μm are displayed, indicating scratches larger than the slice level. Thereby, the slice level can be clearly understood and the calibration work can be easily performed.

〔Effect of the invention〕

As explained above, according to the present invention, uneven scratches corresponding to the standard particle diameter are formed on the surface by processing, and the uneven scratches are further irradiated with reference illumination light by the illumination means in advance and detected by the detection means. Since we have prepared a standard sample for absolute sensitivity calibration that measures the intensity of reflected light and specifies the intensity of reflected light, it is easy to store and clean the standard sample for absolute sensitivity calibration, and it is also easy to use in automatic foreign matter inspection equipment. Even if the illumination brightness or detection sensitivity changes due to changes over time, etc., the absolute sensitivity calibration can always be easily and accurately performed in a short time.

The calibration time was reduced to about 1/10 compared to the conventional calibration method for automatic foreign substance inspection equipment and the calibration method of the present invention. This is because the calibration sample is equivalent to the object to be inspected by the inspection device, and also because it is an absolute calibration (relative to the standard particle diameter).

The calibration sample of the present invention is a material that can be easily stored and cleaned, and is difficult to damage. (When the metal plate sample according to claim 3 is used) Even if it is damaged, it is an absolute calibration sample, so recalibration can be performed with another sample.

In addition, as a method to shorten the calibration time, by arranging the flaws in a matrix, there is no need to calibrate the peak value of the detection output waveform of each flaw using a synchroscope, etc., and the foreign matter distribution map can be output and displayed. Sensitivity adjustment can be done easily and quickly depending on the function.

Further, according to the present invention, by utilizing the advantage of absolute calibration, it is possible to easily make the sensitivities of a plurality of foreign object inspection devices the same.

Further, the standard sample of the present invention may be a photomask in addition to a semiconductor wafer.

[Brief explanation of drawings]

Figure 1 shows a general foreign matter inspection device on semiconductor wafers, Figure 2 shows an example of a conventional sensitivity calibration method, and Figures 3 and 4 show sensitivity calibration using standard particles. Figures 5a and 5b are diagrams showing the calibration method, Figures 5a and b are diagrams showing the case of initial sensitivity calibration using a sample processed with unevenness, Figures 6a and b are calibration samples for the automatic foreign substance inspection device according to the present invention. Figure 7 a~
c is a diagram showing another calibration sample for an automatic foreign matter inspection device different from FIGS. 6a and b, FIGS. FIGS. 10A and 10B are diagrams showing still another calibration sample for an automatic foreign substance inspection apparatus, and FIGS. 10A and 10B are diagrams showing still another calibration sample for an automatic foreign substance inspection apparatus. 1; Calibration sample, 2; Foreign object, 3; Light source, 4; Illumination light, 4a; Reference illumination light, 5; Reflected light from foreign object, 6; Photoelectric converter, 7; Amplifier, 8; Detection output value, 9 ; Standard particles, 10; Pure water, 11; Clean air, 12; Spraying, 13; Scratches caused by laser processing, 14; Scratches caused by etching processing, 15; Silicon wafer, 16; Specified detection output value, 1
7; Specified standard particle size, 18; Paper, 19;
Photomask, 20; Iron plate, 21; Arranged in matrix, 22; Arranged in order of size, 30; Photoelectric converter (illuminance meter), 31; Comparison circuit, 32; Electric circuit, 3
3; Half mirror, 34; Foreign matter distribution map display on monitor, 35; Adhering foreign matter, 36; Foreign matter distribution map display of processing scratches, 37; Foreign matter distribution map display of attached foreign matter, 3
8; A group of scratches arranged to form letters.

Claims (1)

[Claims] 1. Forming uneven scratches corresponding to the standard particle diameter on the surface by processing, and further irradiating the uneven scratches with reference illumination light using illumination means to measure the reflected light intensity detected by the detection means. Prepare a standard sample for absolute sensitivity calibration in which the reflected light intensity has been measured, and then use the prepared standard sample for absolute sensitivity calibration in an actual foreign matter inspection device to illuminate the uneven scratches on the standard sample using illumination means. 1. A method for calibrating the sensitivity of an automatic foreign substance inspection device, which comprises illuminating the illumination light and calibrating the absolute sensitivity so that the intensity of reflected light specified on the standard sample is obtained from the detection means. 2. The method for calibrating the sensitivity of an automatic foreign substance inspection device according to claim 1, wherein the standard sample for calibrating absolute sensitivity further includes a standard particle diameter dimension.