Carrier concentration gallium-based liquid metal measurement probe and apparatus

Abstract

The application discloses a carrier concentration gallium-based liquid metal measuring probe, a conductive wire is connected with a tungsten carbide rod, one end of the tungsten carbide rod is inserted into a liquid metal container made of a corrosion-resistant material, the liquid metal container is provided with a through cavity and a capillary, and the cavity is communicated with the capillary; the cavity is filled with gallium-based liquid metal, the gallium-based liquid metal is immersed in the tungsten carbide rod, and a measuring probe is formed by using the gallium-based liquid metal in the capillary, so that the safety and environmental protection of the probe are solved; the measuring probe is in surface contact with a measuring sample, compared with point contact of a traditional probe, the contact area is increased, the repeatability of the measuring data is good, and the accuracy of the measuring data is improved; the container and the capillary of the liquid metal made of a corrosion-resistant material such as polytetrafluoroethylene are not corroded by the gallium-based alloy and are not adhered to the gallium-based liquid metal, the flowability of the gallium-based liquid metal is improved, and therefore the measuring precision is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to semiconductor measurement, in particular to a gallium-based liquid metal measurement probe for measuring carrier concentration of semiconductor polished wafer by using capacitance-voltage (CV) method and a device thereof. BACKGROUND

[0002] Silicon polished wafer and gallium arsenide polished wafer are important basic materials in semiconductor devices, and they are doped with different impurities to control the resistivity, type and other properties of the materials, so as to form PN junction, MOS junction and other devices. The carrier concentration in semiconductor single crystal is closely related to the resistivity and doping distribution, and is an important quality parameter that must be mastered in material and device process.

[0003] The measurement of carrier concentration generally uses CV (capacitance-voltage) method, and if a general probe is used for measurement, a very sharp needle is used, and the contact diameter is measured in microns (tens of microns), which belongs to point contact. Since the junction capacitance C measured in the CV method is proportional to the contact area, the contact area of point contact is small and unstable, and stable measurement results cannot be obtained, and the polished wafer will be damaged, so a sharp needle cannot be used as a probe. Therefore, related technologies and equipment that can realize surface contact measurement must be found (since the contact area of surface contact is large and stable, and because only metal directly contacts the measurement sample to form a good metal-semiconductor junction, and the junction is necessary for CV measurement).

[0004] Considering that liquid metal mercury has excellent fluidity, will not have any adhesion to the capillary tube (i.e. mercury will not adhere to the capillary tube), and has no corrosive effect on metal, various conductive metals can be used as electrode leads, the contact area between the mercury probe and the semiconductor polished wafer is stable, and the repeatability is also good, therefore, for many years, mercury has been used as a measurement medium (one pole of capacitance) in this field at home and abroad, but because mercury is highly toxic, it brings hidden dangers to the health of users, brings many difficulties to protection, and also inhibits the popularization of this method.

[0005] In the existing carrier concentration measuring device (SSM495, MCV530L, MCV-3000), the probe is mercury, and the mercury is controlled by the pressure of the gas distributor in the capillary (connected with the gas circuit). When the air pressure is negative, the mercury retracts into the capillary and is separated from the measuring sample. When the air pressure is positive, the mercury extends to the capillary port and contacts the semiconductor measuring sample in the air to form a metal-semiconductor junction (Schottky junction). At this time, the mercury is exposed to the air. In order to prevent the harm of mercury, the collection, discharge and analysis of mercury vapor, the treatment of contaminated wafers occupy a very important part in the device, which increases the cost and complexity of the device, and also increases the difficulty of use, and brings trouble to the later mercury treatment. In short, due to the high cost of the device and the high protection requirement of mercury, it is especially not suitable for small and medium-sized enterprises and colleges to do measurement or experimental equipment.

[0006] In order to replace the use of mercury, research shows that gallium-based liquid alloy which is basically harmless to human body is the best choice. For example, the prior art: Chinese patent document CN106381434 (a gallium-based liquid alloy with low temperature fluidity, preparation process and body thermometer) can reduce the "pre-solidification" temperature of the liquid alloy, improve the low temperature viscosity, and ensure the normal use and storage of the liquid alloy device in low temperature environment. The gallium-based liquid alloy with low temperature fluidity is composed of the following components by weight percentage: gallium 60-80%, indium 9-10%, tin 5-2%, bismuth 0.5-4% and silver 0.2-1.5%. The technology has wide application in the fields of mercury replacement in medical devices, key refrigeration medium in advanced refrigeration field, etc. The gallium-based liquid alloy thermometer solves the problem of adhesion of alloy and glass capillary. It is heated and expanded in volume at body temperature. This kind of gallium-based thermometer can only be used in temperature change measurement environment, and the liquid metal in the thermometer is sealed in the glass tube. This kind of thermometer structure cannot be applied to semiconductor measurement (the gallium-based liquid alloy cannot be directly contacted with the surface of the measured object, and cannot rely on thermal expansion and contraction to change the liquid column height).

[0007] Although the gallium-based alloy is non-toxic, it is corrosive to most metals, adheres to glass capillary, and is oxidized, so the contact area with the polished wafer may be unstable, which seriously affects the measurement accuracy. If gallium-based alloy is used to replace mercury, the adhesion to capillary and poor fluidity must be solved. SUMMARY

[0008] In order to overcome the above technical defects, the present application proposes a gallium-based liquid metal measuring probe and device for carrier concentration measurement, which has good fluidity and non-toxicity in the capillary, and directly contacts the measured sample sheet with a certain diameter of plane.

[0009] In order to achieve the above object, the technical scheme adopted by the present application is: a carrier concentration gallium-based liquid metal measuring probe, comprising a conductive wire, the conductive wire is connected with a tungsten carbide rod, one end of the tungsten carbide rod is inserted into a liquid metal container made of corrosion-resistant material; the liquid metal container is provided with a through cavity and a capillary, the cavity is communicated with the capillary; the cavity is filled with gallium-based liquid metal, the gallium-based liquid metal is immersed in the tungsten carbide rod, and the gallium-based liquid metal can flow in the capillary under the action of external force.

[0010] Further, the cavity is communicated with the capillary, the capillary is provided with a guide column, and the guide column is made of corrosion-resistant material.

[0011] Further, the bottom end of the capillary is sealed by a cover.

[0012] Further, the gallium-based liquid metal comprises EGaIn, GaIn10, GaIn20 or GalnSn.

[0013] Further, the opening of the cavity is provided with a cover plate, the cover plate penetrates the tungsten carbide rod, and the other end of the tungsten carbide rod is exposed outside the cover plate.

[0014] Meanwhile, the technical scheme adopted by the present application is: a carrier concentration gallium-based liquid metal measuring device, comprising a conductive wire, the conductive wire is connected with a tungsten carbide rod, one end of the tungsten carbide rod is inserted into a liquid metal container made of corrosion-resistant material; the liquid metal container is provided with a through cavity and a capillary, the cavity is communicated with the capillary; the cavity is filled with gallium-based liquid metal, the gallium-based liquid metal is immersed in the tungsten carbide rod; the opening of the cavity is provided with a cover plate, the cover plate penetrates the tungsten carbide rod, and the other end of the tungsten carbide rod is exposed outside the cover plate; the cover plate is provided with a plurality of air holes; the liquid metal container and the cover plate are packaged by a cylinder and a cylinder seat, the cylinder and the cylinder seat are threadedly connected into one body, the internal space formed by the cylinder and the cavity is used for introducing inert gas or air, and the internal space formed by the cylinder seat and the outer side of the liquid metal container is used for introducing inert gas or air; the conductive wire is led out of the cylinder, and the cylinder is communicated with an air pipe quick connector; the cylinder seat is communicated with a nitrogen protection quick connector.

[0015] Further, the back of the cover plate is pasted with a waterproof and breathable film.

[0016] The application is implemented by filling the gallium-based liquid metal in the liquid metal container, using the tungsten carbide rod which cannot be corroded by the gallium-based liquid metal as the conductive medium, and using the gallium-based liquid metal in the capillary to form the measuring probe. The non-toxic gallium-based liquid metal completely replaces the traditional toxic mercury as the measuring probe, and the safety and environmental protection of the probe are solved. The measuring probe is in surface contact with the measuring sample, and compared with the point contact of the traditional probe, the contact area is increased, the repeatability of the measurement data is good, and the accuracy of the measurement data is improved. The liquid metal container and the capillary made of corrosion-resistant materials such as polytetrafluoroethylene cannot be corroded by the liquid metal and cannot be adhered to the gallium-based liquid metal, the adhesion between the measuring medium and the capillary is solved, the flowability of the gallium-based liquid metal is improved, and the measurement precision is improved. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 FIG. 1 is a structural schematic diagram of a gallium-based liquid metal measuring probe.

[0018] Figure 2 FIG. 2 is an internal structure diagram of the gallium-based liquid metal measuring probe.

[0019] Figure 3 FIG. 3 is a structural schematic diagram of a liquid metal container.

[0020] Figure 4 FIG. 4 is a structural schematic diagram of a nitrogen cylinder.

[0021] Figure 5 FIG. 5 is an assembly diagram of the gallium-based liquid metal measuring probe and the nitrogen cylinder.

[0022] Figure 6 FIG. 6 is a working state schematic diagram of a gallium-based liquid metal measuring device.

[0023] In the figure, A is a gallium-based liquid metal measuring probe, B is a nitrogen cylinder, C is a lifting device, 1 is a waterproof air permeable film, 2 is an SMA joint, 3 is a conductive wire, 4 is a liquid metal container, 5 is a cover plate, 6 is a guide column, 7 is gallium-based liquid metal, 8 is a bracket, 9 is a tungsten carbide rod, 10 is an O-shaped sealing ring, 11 is a cylinder body, 12 is a nitrogen protection quick connector, 13 is a cylinder seat, 14 is a metal lead, 15 is an SMA joint, 16 is a gas pipe quick connector, 17 is a measuring sample, and 18 is a cover. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0025] Referring to Figures 1 to 3 The gallium-based liquid metal measurement probe A mainly comprises a gallium-based liquid metal 7, a liquid metal container 4, a tungsten carbide rod 9, a guide column 6 and a waterproof air-permeable film 1.

[0026] The inside of the container body 4.1 of the liquid metal container 4 is sequentially provided with a groove 4.3, a cavity 4.2, a capillary tube 4.4 and an embedding groove 4.5, the cavity 4.1 is used to fill the gallium-based liquid metal 7, the volume of the gallium-based liquid metal is equivalent to about 2 / 3 of the volume of the cavity 4.1, and the capillary tube 4.4 is used to pass through the gallium-based liquid metal 7.

[0027] The gallium-based alloy formula belongs to the prior art, and can be seen from CN106381434A (gallium-based liquid alloy with low temperature fluidity) and CN110129592A (gallium-based liquid alloy). One of EGaIn, GaIn10, GaIn20 or GalnS can be selected.

[0028] The waterproof air-permeable film 1 and the cover plate 5 are arranged at the groove 4.3 of the liquid metal container 4, the waterproof air-permeable film is located between the groove 4.3 and the cover plate 5, and the back surface of the cover plate 5 is pasted with the waterproof air-permeable film 1. The waterproof air-permeable film (also called hydrophobic film) is a kind of high molecular film through which fluid cannot pass, and gas can freely pass through. It can make the gallium-based liquid metal in the perfectly closed probe not overflow.

[0029] The cover plate 5 is provided with a plurality of air holes 5.1, the air holes are used for transmitting nitrogen or air with a certain pressure (positive pressure or negative pressure) into the liquid metal container, so that the height of the liquid metal is variable, the position of the liquid metal is controlled, and the liquid metal can press or separate from the surface of the measurement sample.

[0030] The waterproof air-permeable film 1 and the cover plate 5 are inserted (hoisted) with the tungsten carbide rod 9, one end of the tungsten carbide rod 9 extends out of the cover plate 5, and the other end of the tungsten carbide rod 9 extends into the cavity 4.2 of the liquid metal container 4 and contacts with the gallium-based liquid metal 7 (the tungsten carbide rod is immersed in the gallium-based liquid metal).

[0031] The cover plate 5 is installed with a vertical support 8, the support 8 is installed with an SMA (interface) joint 2, the SMA joint (interface) 2 is connected with the tungsten carbide rod 9 through a conductive wire 3, the conductive wire is used for conducting the potential of the gallium-based liquid metal, and plays a role of transmitting the voltage of the probe.

[0032] The slot 4.5 of the liquid metal container 4 is embedded with a guide post 6, both of which are made of polytetrafluoroethylene material, to maintain the full contact and sealing between the lower end of the probe and the surface of the sample, and to keep the contact area between the liquid metal and the sample unchanged. A capillary hole 6.1 is formed on the axis of the guide post 6, which is in communication with the capillary tube 4.4. The diameters of the capillary hole 6.1 and the capillary tube 4.4 are 1-3 mm, and the total length of the capillary hole 6.1 and the capillary tube 4.4 is 7-9 mm. The descending and ascending stroke of the liquid metal column is 5-7 mm. The gallium-based liquid metal in the capillary tube 4.4 and the capillary hole 6.1 forms a liquid metal column. The guide post is elastic (can produce flexible deformation), which can better prevent the gallium-based liquid metal from overflowing from the capillary tube when the liquid metal column is pressed on the surface of the measured sample.

[0033] When not measuring, the guide post 6 needs to be sealed with the cover 18 to prevent oxygen from entering the liquid metal container and contacting the gallium-based liquid metal.

[0034] As shown in Figure 4 The nitrogen cylinder B is mainly composed of a cylinder body 11 and a cylinder base 13. The cylinder body has an opening, and the open end of the cylinder body 11 is threadedly connected to the cylinder base 13. The cylinder base 13 is provided with a through hole 3.1. The cylinder body 11 is connected to the gas pipe quick connector 16 and the SMA connector 15, and the cylinder base 13 is connected to the nitrogen protection quick connector 12. The cylinder body 11 and the cavity 4.2 form an internal space, and the cylinder base 13 and the outer side of the liquid metal container 4 form another internal space. One way of nitrogen gas enters or exhausts through the gas pipe quick connector 16, and the pressure makes the liquid metal in the probe descend to contact the surface of the sample, and the negative pressure makes the liquid metal rise to leave the surface of the sample. Another way of nitrogen gas is connected to a nitrogen source with a certain pressure through the nitrogen protection quick connector 12, so that nitrogen gas is always sprayed out of the lower end of the probe, which isolates the outside humid air and avoids the oxidation of the liquid metal by the outside air, and avoids the formation of an oxide film on the surface of the gallium-based liquid metal.

[0035] As shown in Figure 5 The nitrogen cylinder is internally assembled with the gallium-based liquid metal measurement probe. The cylinder body 11 and the liquid metal container 4 are sealed by the O-shaped sealing ring 10. The SMA connector 2 and the SMA connector 15 are connected by the metal lead 14. SMA refers to a radio frequency coaxial connector. The nitrogen cylinder B and the gallium-based liquid metal measurement probe A are assembled into a carrier concentration measurement device.

[0036] The measurement principle of the liquid metal probe (head) can be seen from GB14146-709-T Silicon Epitaxial Layer Carrier Concentration Measurement Mercury Probe Capacitance-Voltage Method and GB-T268-706 Gallium Arsenide Epitaxial Layer Carrier Concentration Capacitance-Voltage Measurement Method. In the actual measurement process, the liquid metal column in the capillary needs to be moved as a whole, and the bottom end is tightly pressed against the surface of the measurement sample to form a Schottky junction. When the negative bias is changed, the change of the capacitance is measured, and the distribution of the carrier concentration along the depth of the sample is calculated. As shown in the embodiment of the present application, Figure 6 The working principle of the carrier concentration measurement device is as follows. The sample to be measured 17 is placed directly below the carrier concentration measurement device in advance, the cover 22 is removed, the lifting device C drives the carrier concentration measurement device to descend to a position close to the surface of the measurement sample, the lifting device C removes the descending driving force, and the gallium-based liquid metal measurement probe fully contacts the surface of the measurement sample under the action of gravity. Then, the nitrogen gas with a positive pressure (10 KPa) is input from the gas pipe quick connector 16 of the nitrogen cylinder B, the nitrogen gas enters the cavity 4.2 of the liquid metal container 4 through the gas hole 5.1 of the cover plate 5 and then through the waterproof air permeable film 1, the gallium-based liquid metal 7 in the cavity 4.2 produces a downward movement under the action of the nitrogen gas pressure, and the gallium-based liquid metal 7 then produces a downward movement in the capillary tube 4.1 and the capillary hole 6.1 until the gallium-based liquid metal is exposed outside the guide column 6 so that the gallium-based liquid metal contacts the surface of the sample 17 in a surface manner. At this time, the nitrogen gas is input from the nitrogen gas protection quick connector 12 of the nitrogen cylinder B, and the nitrogen gas is sprayed out through the through hole 13.1 of the cylinder seat 13, so that the exposed gallium-based liquid metal is surrounded by the nitrogen gas, thereby avoiding the oxidation of the gallium-based liquid metal due to contact with air. After the measurement is completed, the nitrogen gas is extracted from the gas pipe quick connector 16 with a negative pressure, the gallium-based liquid metal produces an upward movement, the exposed gallium-based liquid metal is retracted into the capillary hole 6.1, all the gallium-based liquid metal rises (returns) to the cavity for storage, and finally the guide column is sealed by the cover.

[0037] It is apparent for those skilled in the art that the present application is not limited to the details of the foregoing exemplary embodiments, but can be implemented in other concrete forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, the scope of the present application being defined by the appended claims rather than the foregoing description, and it is intended to embrace all changes and modifications that fall within the meaning and scope of equivalents of the claims.

Claims

1. A carrier concentration gallium-based liquid metal measuring device comprising a conductive wire, characterized in that: the conductive wire is connected to a tungsten carbide rod, one end of the tungsten carbide rod extending into a liquid metal container made of corrosion-resistant material; the liquid metal container is provided with a through cavity and a capillary tube, the cavity being connected to the capillary tube; wherein the liquid metal container is made of polytetrafluoroethylene material; the cavity is filled with gallium-based liquid metal, and the gallium-based liquid metal immerses the tungsten carbide rod; the cavity is connected to the capillary tube, and the capillary tube is provided with a guide column made of corrosion-resistant material; a capillary hole is formed on the center line of the guide column, the capillary hole being connected to the capillary tube, the diameter of the capillary hole and the capillary tube being 1-3 mm, the total length of the capillary hole and the capillary tube being 7-9 mm, the falling and rising stroke of the liquid metal column being 5-7 mm, and the gallium-based liquid metal in the capillary tube and the capillary hole forming a liquid metal column; the guide column is elastic and can produce flexible deformation, which can better prevent the gallium-based liquid metal from overflowing from the capillary tube when the liquid metal column presses on the surface of the measurement sample; the gallium-based liquid metal comprises GaIn10, GaIn20 or GalnSn; the opening of the cavity is provided with a cover plate, the cover plate penetrating the tungsten carbide rod, and the other end of the tungsten carbide rod being exposed outside the cover plate; the cover plate is provided with a plurality of air holes; the liquid metal container and the cover plate are packaged by a cylinder body and a cylinder base, the cylinder body and the cylinder base being threadedly connected into one body, the internal space formed by the cylinder body and the cavity being used for introducing inert gas or air, and the internal space formed by the cylinder base and the outer side surface of the liquid metal container being used for introducing inert gas or air; the conductive wire is led out of the cylinder body, and the cylinder body is connected to an air pipe quick connector; the cylinder base is connected to a nitrogen protection quick connector; the cylinder body and the cylinder base form a nitrogen cylinder B, the cylinder body has an opening, the opening end of the cylinder body is threadedly connected to the cylinder base, the cylinder base is provided with a through hole, the cylinder body is connected to an air pipe quick connector and an SMA connector, and the cylinder base is connected to a nitrogen protection quick connector, wherein 10 KPa of nitrogen gas is input from the air pipe quick connector of the nitrogen cylinder B; the cylinder body and the cavity form an internal space, and the cylinder base and the outer side surface of the liquid metal container form another internal space; one way of nitrogen gas is input or exhausted through the air pipe quick connector, and the liquid metal in the probe is caused to fall to contact the surface of the sample under pressure, and the liquid metal is caused to rise to leave the surface of the sample under negative pressure; another way of nitrogen gas is connected to a nitrogen source of a certain pressure through the nitrogen protection quick connector, so that nitrogen gas is continuously sprayed from the lower end of the probe, the outside humid air is isolated, the liquid metal is prevented from being oxidized by the outside air, and the gallium-based liquid metal is prevented from generating an oxide film on the surface. The back of the cover plate is pasted with a waterproof and breathable film. The bottom end of the capillary tube is sealed by a cover. The opening of the cavity is provided with a cover plate, the cover plate penetrating the tungsten carbide rod, and the other end of the tungsten carbide rod being exposed outside the cover plate. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The carrier concentration gallium-based liquid metal measuring device of claim 1, wherein: ​ 3. The carrier concentration gallium-based liquid metal measuring device of claim 1, wherein: ​ 4. The carrier concentration gallium-based liquid metal measuring device of claim 1, wherein: ​

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