RU1784868C - Method for substrate surface purity determining - Google Patents

Abstract

The method relates to the field of measurement technology and can be used in microelectronics in the manufacture of integrated circuits on passive and active substrates. The method consists in measuring the spreading rate of a drop of liquid falling on the surface of a substrate. The spreading rate is determined by the change in the intensity of the light flux passing through a transparent substrate and a liquid drop or reflected from the surface of a drop when a liquid drop is illuminated by a stream of light. 2 C.p. f-ly, 2 ill.

Description

The invention relates to the field of measurement technology and can be used in microelectronics in the manufacture of integrated circuits on passive and active substrates.

A known method for determining the surface cleanliness of substrates by the wetting angle is by measuring the volume of a drop placed on a flat substrate. However, this method of determining the surface cleanliness is very laborious, since it is first necessary to measure the geometric parameters of the droplet, and only then the desired value of the contact angle, which determines the surface cleanliness of the substrates, is determined.

The closest in technical essence to the proposed method for determining the cleanliness of the surface of the substrate by the wetting angle lies in the fact that a drop of liquid is illuminated with a parallel beam of light towards the substrate. In this case, the droplet is a collecting lens. Deviation of light rays at the edges of a drop

determines local values of the contact angle.

The disadvantages of the method include the long measurement time determined by the time it takes to establish the static state of a liquid drop on the surface of the substrate and the fixation time of a large number of points, as well as the difficulty of determining the contact angle of substrates with a slightly soiled surface, i.e. the sensitivity of the method decreases with increasing surface cleanliness of the substrates and the technical complexity of the quantitative recording of the wetting angle and a larger error in its measurement due to the high sensitivity to vibration of the substrate. All this significantly reduces the performance of the method.

An object of the invention is to increase the productivity of a process.

The method for determining the surface cleanliness of the substrate consists in using

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the rate of liquid droplet spreading over the surface of the substrate, falling from a height h, with 1.40, where K

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p is the density of the liquid; g is the acceleration of free fall; EC in the binding energy of liquid molecules; D is the diameter of the droplet, and the rate of droplet spreading over the surface of the substrate is determined by measuring the intensity of the light flux passing through the liquid droplet on the substrate or reflected from the surface of the droplet.

If the height h exceeds the KDf value, then upon impact on the surface, a drop of energy will be released in the drop, the value of which will exceed the binding energy of the liquid molecules, and the drop will fly apart into several parts, i.e. purity measurement process will become impossible.

If the drop height of the drop on the test surface is less than 1.4D, then the drop either touches the surface of the substrate or is so small that the forces of the surface potential will bend the drop and affect the size of the drop, distorting the measurement.

Fig. 1 is a diagram of an apparatus for determining the surface cleanliness of a substrate; Fig. 2 shows a calibration dependence of the spreading rate of a water droplet on a substrate surface on the concentration of impurity atoms on the substrate surface.

The device (Fig. 1) comprises a photodetector 1 detecting the amount of luminous flux transmitted through the transparent substrate 2 and the DROP 3 of the liquid or photodetector 4 if the substrate or liquid is opaque to measure the amount of light reflected from the surface of the droplet; a lightproof chamber 5, a light source 6, a drop former consisting of a hollow needle 7, a cylinder 8 of quartz filled with liquid, a piston 9 and an electronic circuit 10 consisting of a differential amplifier 11, a peak voltmeter 12 and an indicator device 13.

The method is carried out as follows.

In the measuring opaque chamber 6, a substrate 2 is installed and its surface is illuminated with a light flux. The piston 9 pushes the liquid from the cylinder 8 into the hollow needle 7 until a drop of liquid forms and breaks away from the end of the needle. The photodetector 1 (or 4) records a change in the intensity of the light flux, which is rigidly related to the spreading rate of the droplet on the surface of the substrate.

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The differential amplifier 11 converts this change into a function of speed, the value of which is fixed by a peak voltmeter 12 and an indicator device 13,

PRI me R. As the investigated substrates, substrates of the Polycor type are used, and distilled water as the liquid. The diameter of the drop is 4.2 mm. Controlled contamination on the surface of the substrate is applied by vacuum spraying on a UVN-2M-1 type apparatus. Surface cleaning of the substrates is carried out in air plasma on a 08PHO-100T-001 type apparatus. The luminous flux intensity is measured with an FD-1 type photodetector. The drop drop height is varied from 4.9 to 30 mm. At h 5.9 mm and h 25 mm, the amplitude of the signal being monitored, recorded by the peak voltmeter 12 and the indicator device 13, and, consequently, the rate of spreading of the droplet on the substrate practically do not change. Therefore, measurements are taken at 5.9 h 25 mm, where the change in signal amplitude has a linear relationship. From the calibration curve (Fig. 2), the concentration of impurity atoms on the surface of the substrate is determined, which determines the purity of the substrate.

Claims (1)

1. A method for determining the cleanliness of the surface of a substrate, including applying a drop of liquid to a transparent substrate, illuminating the drop with a light stream and measuring the intensity of the light flux, characterized in that, in order to increase the productivity of the method, a drop of liquid is applied to the surface of the substrate by dropping it from a height h which is selected from condition 1, KD 3, where K Gece / lgrd, D is the diameter of the incident droplet, and ecb is the binding energy of the liquid molecules; p is the density of the liquid, g is the acceleration of gravity, determine the rate of change of the intensity of the light flux passing through the drop on the substrate, and its maximum value, which determines the maximum spreading rate of a liquid drop on the surface of the substrate, and the purity of the surface of the substrate is determined t according to the previously measured dependence of the spreading rate of a liquid drop on the surface of the substrate on the concentration of atoms and impurity molecules adsorbed on the surface. 2, The method of claim 1, characterized in that the rate of change in the intensity of the light flux reflected by the surface of the droplet on the substrate is determined. uchchuchuzhuu4 . K VSXVOs4 to I., 1 I t P t 7 n 6 5 4 FIG. i