RU2579546C1 - Method of detecting mechanical defects on the surface of solid materials - Google Patents

Abstract

FIELD: test equipment.

SUBSTANCE: invention relates to control of quality of high-grade surfaces. In disclosed method discharge used surface dielectric barrier discharge, localised on surface of one of two electrodes, simultaneously serving as table for investigated material sample; dielectric barrier is free and thoroughly polished which repeats configuration of surface of analysed sample, tightly pressed to sample, then brought into contact with sample pointed end of second electrode made in form of a rod of low-erosion conductive material; supply voltage of alternating current, electric strength of dielectric barrier selected exceeding maximum voltage power supply source is more than two times; for making a decision on suitability of surface of solid materials is used on surface of analysed sample in location places of defects of weak blue light air plasma in form of a bright blue luminous points; analysed surface is considered to be applicable at complete absence of luminous blue points.

EFFECT: high reliability of detecting defects and expansion of types of test specimens for increase in yield due to improved detection of defective materials before beginning of technological operations.

1 cl

Description

The invention relates to the field of quality control of high-class surfaces, transparent and opaque materials, including optical, single-crystal and metal surfaces in order to detect defects and chips on their surface.

A known method of flaw detection of surfaces [Patent No. 2069353 of the Russian Federation, IPC G01N 21/88. The method of surface inspection / Saprykina NN, Syromyatnikova T.Α .; Applicant and patent holder Institute for Problems of Engineering Science of the Russian Academy of Sciences. - No. 92015997/25; declared 12/28/1992; publ. November 20, 1996 - 4 pp.], In which the test surface is activated in a high-frequency arc discharge plasma by the cathode-free method in an argon atmosphere under conditions that prevent the material from being sprayed on the test surface. Immediately after activation, a layer of a liquid crystal 1 μm thick, protected by a coverslip, is applied to the surface and a planar texture is formed in the layer. When observing the test surface in polarized transmitted light or in reflected light, defects in machining, as well as defects in multiblockness, are invisible during ordinary optical observations.

The disadvantage of this method is the low reliability of detection of defects due to the need to form a planar texture in the layer of liquid crystal with the obligatory activation of the surface before its application, which is a necessary condition for ensuring good wettability of the sample surface with liquid crystal, and the effect of activation decreases with time, which reduces the reliability of detection of defects.

There is also known a method of electromagnetic acoustic non-destructive testing of products [Patent No. 2049328 of the Russian Federation, IPC G01N 29/04. Method of electromagnetic-acoustic non-destructive testing of products / Leshchenko A.S., Toropchin O.P., Kosmirova N.V .; applicant and patent holder A. Leshchenko, O. Toropchin, N.V. Kosmirova - No. 4954549/28; declared 05/05/1991; publ. November 27, 1995], in which, simultaneously with the control of the samples, they effect the product by the methods of plasma technology and metallurgy. When controlling the quality of a single crystal in the process of its production and control, the control and heating zone is moved along the product in the direction from the single crystal blank with a single crystal growth rate. Heated to the temperature of the melt and the movable control zone of the product actively interacts with the plasma and electromagnetic fields passed through it during the control process. Monitoring devices work like traps and plasma filters.

The disadvantage of this method is its high costs, since at the same time as the control of the samples, the product is impacted by the methods of two technologies at once - plasma technology and metallurgy, in addition, the product in the control zone is heated to the melt temperature, which is associated with additional energy costs.

A known method in which plasma processing is used to remove auxiliary or functional layers [Patent No. 2474918 C1 of the Russian Federation, IPC H01L 21/66, G01R 31/26. A method for detecting hidden electrical defects of matrix or linear silicon MOS multiplexes / Akimov V.M., Vasilieva L.A., Klimanov E.A., Liseikin V.P., Mikertumyants A.R .; applicant and patent holder of FSUE NPO Orion. - No. 20111134395/28; declared 08/16/2011; publ. 02/10/2013, Bull. No. 4 - 4 pp.: 5 ill.], In which to detect hidden electrical defects at one of the processing stages, plasmochemical photoresist removal in oxygen plasma is performed.

The disadvantage of this method is its high complexity associated with the need to conduct a whole cycle of technological processing of a product to decide on its suitability for further use as a raw material for manufactured products.

There is a method of quality control of diamond plates for the manufacture of ionizing radiation detectors [Patent No. 2525636 of the Russian Federation, IPC H01L 21/66. The method of quality control of diamond plates intended for the manufacture of ionizing radiation detectors / Mukhachev Yu.S., Ryabov E.V., Borzenko S.Yu .; Applicant and patent holder, Irkutsk State University. - No. 2013109788/28; declared 03/05/2013; publ. 08/20/2014, Bull. No. 23 - 7 pp.], In which weak radiation emanating from the plates is observed (injection electroluminescence in two bands with maxima at 520 nm and 420 nm). Luminescence is excited by an electric current passed through a diamond plate when an electric field is applied.

The disadvantage of this method is its narrow focus in relation to the varieties of the samples. The method is applicable mainly only for quality control of specific types of diamond plates intended for the manufacture of ionizing radiation detectors.

Closest to the claimed is a method for controlling the quality of diamond plates intended for the manufacture of ionizing radiation detectors [Patent No. 2525641 of the Russian Federation, V07C 5/00. The method of quality control of diamond plates intended for the manufacture of ionizing radiation detectors / Mukhachev Yu.S., Ryabov E.V., Borzenko S.Yu .; Applicant and patent holder, Irkutsk State University. - No. 20133110276/28; declared 03/07/2013; publ. 08/20/2014, Bull. No. 23 - 7 pp.], Which consists in registering a band with a maximum at 520 nm, deciding on the results of recording the glow, applying an electrode to the lower surface of the diamond plate, installing the plate on a metal electrode electrically connected to the ground. A corona discharge is ignited above the surface of the diamond plate, which is free from the electrode, the luminescence of the diamond plate is recorded in the green region of the spectrum, and the spatial distribution of the green glow leads to the conclusion that the diamond plate is suitable for the manufacture of diamond detectors. The glow pattern of diamond plates is interpreted under conditions of injection electroluminescence excited by a corona discharge. A diamond plate is considered conditionally suitable for the manufacture of detectors of medium quality in the presence of a green glow in the form of several points occupying a small part of the surface of the diamond plate.

The disadvantages of this method are, firstly, the high complexity associated with the need for preliminary preparation of samples before measurements, which consists in applying temporary electrodes from aquadag or contactol on their surface, which, on the one hand, pollute the samples, and on the other, lead to additional costs; secondly, the low reliability of the method for determining defects due to the volume glow of the discharge at the end of the needle located above the sample surface at a distance of 2-5 mm, which falls on the image of the investigated surface, making it difficult to control the quality of the plates.

The technical result of the invention is to increase the reliability of detection of defects, reducing the complexity, while reducing the cost of it and expanding the types of controlled samples, in order to further increase the yield of products by improving the identification of defective materials before starting technological operations.

This result is achieved by the fact that in the method for detecting mechanical defects on the surface of solid materials, which consists in igniting a discharge, registering a glow and making a decision on it, according to the invention, a surface dielectric barrier discharge localized on the surface of one of two electrodes and simultaneously serving as a table for the material sample under study, while the dielectric barrier is made defect-free and carefully polished, repeating the configuration the surface of the test sample, the sample is pressed tightly against it, then the pointed end of the second electrode made in the form of a rod of a low-corrosion conductive electric current material is brought into contact with the sample and the supply voltage of the alternating electric current is connected, while the dielectric barrier is selected to exceed the maximum voltage more than double the power supply; To make a decision about the suitability of the surface of solid materials, use the weak blue glow of the air plasma in the form of bright luminous blue dots that appears on the surface of the test sample at the locations of the defects, and recognize the test surface as suitable in the complete absence of luminous blue dots.

The technical result is achieved due to the fact that the pointed electrode, tightly pressed to the sample, distributes the electric field of the discharge over the surface of the sample, and the highest electric field will be on the surface areas with defects, since all defects are characterized by a change in the electrical conductivity compared to not defective materials.

Due to the presence of a defect-free dielectric barrier that repeats the shape of one of the electrodes, which simultaneously serves as a table for the sample, and the absence of a gap between the pointed electrode and the sample, the discharge is completely localized on the surface of the studied sample in the form of luminous dots attributable to defects. The recommended requirements for the dielectric barrier dielectric strength ensure a stable glow of points on the surface, their color does not depend on the type of sample material, which provides an extension of the types of controlled samples (from metals, their alloys, semiconductor crystalline materials to dielectric) and the nature of the defects on its surface and will always blue, since the surface barrier discharge in the method is an air plasma, the main emitting component of which is in the visible region of the spec Tra is nitrogen. Due to these features of the method, reliable detection of mechanical defects on the surfaces of solid materials is achieved with a simultaneous reduction in the cost of the control process and an increase in the yield of suitable products in the future by improving the identification of defective materials before starting technological operations with them. In addition, the method allows you to control mechanical defects on the surface of samples from various technological batches of products, without changing its essence and without requiring sample preparation, which reduces the complexity when using the method at the scale of operating enterprises that produce products with different nomenclature. The method is as follows.

A surface barrier discharge localized on the surface of one of the two electrodes and simultaneously serving as a table for the material sample under study is used as a discharge. The dielectric barrier is made defect-free and carefully polished, repeating the configuration of the surface of the test sample and the electrode on which it is located. The studied sample, for example, a round single-crystal silicon wafer, is placed in the zone of action of a surface barrier discharge realized at atmospheric pressure in air between two electrodes. In this case, the test sample should be completely placed on the electrode with a dielectric barrier, and the electrode with the dielectric barrier is grounded. If there is a space between the grounded electrode and the barrier, visual observation of defects in the test sample will be difficult due to the effect of background illumination. Then, the pointed end of the second electrode is tightly pressed against the sample, while it is made in the form of a rod of low-corrosive, conductive electric current, material. The choice of material of the first electrode is not critical, it is only important that it is easily processed and conductive. In this case, both electrodes are made of stainless steel. To ensure reliable contact of the pointed electrode with the sample, a thread is cut on its surface, which is an element of its movement system in the direction of the dielectric barrier in the form of a screw pair. To control defects on the surface of the sample, the supply voltage of an alternating electric current is connected to the electrodes to ignite the dielectric barrier discharge (defects in the form of chips on silicon semiconductor wafers with a diameter of 120 mm were controlled at a power source voltage of 8 kV), while the dielectric barrier was selected to exceed the maximum strength more than two times the voltage of the electric power source (to control defects in semiconductor wafers, S-49 grade molybdenum glass). On the surface of the test sample at the locations of mechanical surface defects, a blue glow of the air plasma appears in the form of bright luminous blue dots, which are visually recorded and used to decide on the suitability of the surface of solid materials. The investigated surface is considered suitable in the complete absence of luminous blue dots. If there are luminous dots on the sample, then its surface is recognized as defective and these samples are rejected.

The studied samples can be of any geometric shape, however, one should take into account the fact that luminous points can also be observed on the peaks of sharp protrusions and sharp edges. If, in accordance with the technological regulations, such should not be, then the latter should be identified as defects.

For reliable visual observation of defects in the absence of direct illumination of the sample, the high-voltage AC power source is selected according to the following parameters:

- output voltage - not less than 8 kV,

- frequency - not less than 6 kHz,

- load current - not less than 10 mA.

The indicated minimum requirements for a power source are suitable for observing defects in single-crystal substrates (semiconductor wafers) in microelectronics technology. To study bulk samples, the output voltage and frequency are increased.

In industry, the identification of defective materials before the start of technological operations increases the yield of products, which reduces the economic costs of production and improves the quality of the final product.

The proposed method in microelectronics is express oriented and is intended for non-destructive testing of the presence on the surface and end faces of semiconductor materials (ingots, washers, plates) of chips, scratches and microcracks (about several tens of micrometers in size) that are formed during their processing, for example, grinding or polishing. The absence of the need for special preparation of samples before measurements, for example, the application of temporary electrodes and activation of samples on them, reduces the complexity, and a wide range of materials of the analyzed samples makes it possible to apply this method at various stages of related technological processes.

In mechanical engineering, the proposed method can detect violations of the continuity or homogeneity of the material, in metallurgy - to identify defects formed during the melting and casting process, such as shells, pores, zones of loosening, inclusions, cracks, as well as delamination, press-pulls, flaws, zakova, sunsets. The method also allows to detect defects in thermal and chemical-thermal treatment, for example, coarse-grained structure zones, overheating and burnout, welding and soldering defects (cracks, non-solder).

The proposed method for detecting mechanical defects will significantly reduce production costs during the rejection of defective parts and samples.

Claims (1)

A method for detecting mechanical defects on the surface of solid materials, which consists in igniting a discharge, registering a glow and making a decision on it, characterized in that the discharge is a surface dielectric barrier discharge localized on the surface of one of two electrodes, which simultaneously serves as a table for the sample of material while the dielectric barrier is defect-free and carefully polished, repeating the configuration of the surface of the test sample, tightly they press the sample against it, then bring into contact with the sample the pointed end of the second electrode, made in the form of a rod of a low-corrosive material conducting electric current, and connect the supply voltage of the alternating electric current, while the electric strength of the dielectric barrier is chosen to exceed the maximum voltage of the electric power source by more than twice; To make a decision about the suitability of the surface of solid materials, use the weak blue glow of the air plasma in the form of bright luminous blue dots that appears on the surface of the test sample at the locations of the defects, and recognize the test surface as suitable in the complete absence of luminous blue dots.