SU320228A1 - Method for obtaining fusion-diffusion pneumatic junction - Google Patents

Description

(21) 1400378 / 26-25

(22) 12.02.70

(46) 03/30/84. Bksh. № 12 (72) O.F. Astakhov, A.A. Galaev, S.S.Gorelik, V.D.Ermoshin, S.K.Korovin, I.I. Kruglov, K.A. Preobrazhentsy, M.M. Samokhvalov and S.V.Fronk (53) 621.382.002 (088.8) (54) (57) METHOD FOR OBTAINING USH1AVNOFFOOR P-P TRANSITION by applying a layer of active metal, for example, titanium, an electrode metal and heating the resulting structure to a temperature not lower than the eutectic temperature of the electrode metal - semiconductor, followed by diffusion annealing and crystallization, characterized in that, in order to Increasing the capacitance overlap factors and making transitions of any given area, an acceptor and donor impurity layers are placed between the layers of the electrode carrier metal. 1 The invention relates to a process for the manufacture of semiconductor devices, preferably non-linearly controlled capacitances, for example, varicaps. A method is known for obtaining a contact of an electrode metal with a semiconductor nick when a layer of active metal, for example, titanium, not more than 1000 A thick and a layer of metal protecting the active metal from oxidation by the environment, eg silver, is applied to the surface of the nprf semiconductor material. . An electrode metal layer, lightly doped with appropriate impurities, is placed on this layer, with its subsequent fusion into the bulk of the semiconductor material at a temperature not lower than the eutectic temperature of the electrode metal — semiconductor. The reverse gradient of the impurity concentration in the p – n junction base can be formed by melting the electrode metal (alloy in the form of a tablet or ball) doped with the appropriate impurities into a semiconductor material of the appropriate conductivity type through a layer of active metal with a thickness of less than 1000 A followed by diffusion of these dopants into the bulk of the semiconductor material and crystallization. For example, the electrode, metal (alloy) agaominium-antimony-tin is melted into a conduction silicon through a thin layer of titanium and silver at 1000 C. At the same time, a layer of active titanium metal restores and destroys surface oxides, an acceptor impurity — aluminum ensures the creation of a reverse gradient — the impurity concentration in the baster-p-junction, the donor impurity — antimony forms the pn-p-junction itself, and tin is the electrode carrier metal . The known method has a number of disadvantages: firstly, due to the formation of deep recrystallized layers obtained as a result of the melting of the electrode metal and the fluctuation of the melting front, it is difficult to obtain thin base structures (24 µm) and high Q-factors of the instruments; secondly, the method does not provide the possibility of obtaining p – tt transitions with an inverse impurity concentration gradient over sufficiently large areas (2 mm), since this is due to an increase in the amount (mass) of the melted electrode metal, which leads to anomalous distortion of the melting-in front and the rise of significant mechanical stresses in a semiconductor chip; thirdly, since the concentration of the ligature in the electrode metal (alloy) uniquely determines the parameters of the inverse gradient, and it is not possible to ensure sufficient chemical homogeneity of the alloy during its preparation, a certain variation in the parameters of the volt-fade characteristic of the varicap is inevitable during its manufacture. The purpose of the invention is to obtain alloy-diffusion p-n junctions on any area with an inverse gradient of impurity concentration in the base, providing a high coefficient of overlap in capacitance (C of order 25-50) in the voltage range of 0.110 V, improving the chemical homogeneity of the alloy and reducing variations in the volt-farad characteristic of varicap, the realization of thin bases (on the order of 2–4 µm) and high Q-values of the instrument. This is achieved by applying layers of active metal (with a thickness of less than 1000 A) and layers of an electrode metal carrier, between which layers of acceptor and donor impurities are deposited on the surface of a plate of a semiconductor material of the appropriate conductivity. . The multilayer film structure of the electrode metal carrier and dopants thus obtained on the surface of the plate is fused into the bulk of the semiconductor material at a temperature not lower than the eutectic temperature of the electrode carrier metal — semiconductor. In this case, a multicomponent homogeneous layer of the melt is formed semiconductor, and a vodnik is an electrode metal-carrier impurity, from which doping impurities diffuse into the bulk of the semiconductor.

melting, high chemical homogeneity of the melt and minor mechanical stresses in the area of the coats. The method is implemented on semiconductor materials such as germanium and silicon, where metals, such as titanium, niobium, zirconium, chromium, etc., capable of reducing the surface oxides of the semiconductor and providing high-quality subsequent metals, are used as the active metal applied to the surface of the semiconductor material. layers of electrode carrier metal in a semiconductor material.

The electrode metal carrier must ensure the possibility of the controlled introduction of dopants into the melt of the electrode metal carrier — the semiconductor material and the corresponding formation of the reverse gradient of the impurity concentration of the ir – n junction. Electrode metals, electrically neutral, or electrode metals that do not alter the basic characteristics of a semiconductor material and form simple eutectic systems with it, for example silver, gold, etc., meet these requirements most fully.

Between the layers of the electrode metal carrier there are at least two layers of dopant acceptor, which is used, for example, boron, aluminum, gallium, indium, and the donor layer — phosphorus, mouse, antimony, bismuth.

Dopant concentration. in the melt, which specifies the inverse gradient depending on the specific parameters of the voltfarad characteristic, is determined by an interval of 10 cm, and impurities, 06 by p - “- transition - a concentration of at least 5-10 cm, the thickness of the layers of dopants - first , the total thickness of the layers of the electrode carrier metal and the physicochemical nature of the selected impurities. The thickness of the layers of the electrode metal carrier should ensure that such an amount of dopant is introduced into the melt that is sufficient to maintain the desired the concentration of ligatures in the melt in the process of diffusion annealing, therefore

the minimum thickness of the layer of the electrode carrier metal is 1000 A.

The described β-method is implemented, for example, for varicaps with an overlap ratio of 30 in the range of voltages and a displacement of 0.1-10 V, with breakdown voltages of 20 V, reverse currents of .5 µA and a quality factor of 100 when the bias voltage is 2 In at a frequency of 10 MHz.

A p-type silicon doped boron with a specific resistance of 0.01, with a suitably prepared surface of 180 ± 5 µm thick, on which the p-type silicon epitaxial film is deposited (increased) by any known method boron doped to the resistivity is 20 + 20% ohm "cm. 6i.0.5 microns thick.

At the same time, a silicon and -type technological substrate, alloyed with antimony, with a specific resistance of 0.5 Ω "cm, 180 + 5 microns thick, is being prepared at the same time to ensure the cleanliness of the surface of which the plates are pre-polished with M5 powder and then partially removed the broken layer by known methods of chemical treatment .

On the working plate of silicon of p-type conductivity by the method of vacuum evaporation at a pressure of 1-10 -10 mm Hg. and a substrate temperature of 200-600 ° C are sequentially deposited with layers of titanium with a thickness of about 300 A. and silver, 500–1500 A thick, silver (electrode carrier metal) about 2 microns thick, which provides high-quality silver-silicon aluminum alloying, about 1000 A thick, an acceptor additive that provides the formation of a reverse gradient, and silver, about 2 microns thick, layer which eliminates the drop forming of alcmini both in the process of melting and in subsequent spraying operations of another impurity; antimony

about 1500 A thick — a donor additive that provides a p-N junction, and silver about 2 microns thick, a layer of which eliminates the formation of an antimony film during the fusion process,. titanium and silver are sprayed according to the described technological cycle. The Ir-type silicon platinum prepared in this way, carried out by type, are folded with surfaces having sprayed layers, and silver-antimony-aluminum is fused with the simultaneous formation of a homogeneous melt, from which, in a temperature range of 950-1200 ° C, the silicon epitaxial film is type diffuse aluminum and: SB. The cake-like structure obtained after fusion and diffusion annealing is polished on the side of silicon of the L-type to a plate thickness of 4050 µm (the total cake thickness after grinding is 220 + 10 µm) and subjected to 30 etches in a mixture of hydrofluoric, nitric and acetic acids in a ratio of 2 : 9: 4 to remove contaminants from the surface of the plates before metallizing and applying the Omich contact. Ohmically contact is obtained by lysadium metal on both sides of the structure obtained by successive sputtering in a vacuum of 5.10 mm Hg. at a substrate temperature not lower than the layers of titanium and nickel with a total thickness of about 1000. The plate is applied to the crystals by chemical etching of an unprotected semiconductor material to form messes. For this, the cake is glued with a p-type plate on a fluoroplastic disk, and from the opposite side a layer of bitumen is applied through a mask with round holes 1 mm in diameter to protect the surface of the crystal. The structure is etched in a mixture of liquors, nitric and acetic acids in a ratio of 2: 9: 4 until complete removal of n-type silicon and the release of etchant for silver, which is removed by successive oxidation of it in nitric acid and dissolution of silver nitrate in water. Then, the p-type silicon wafer is additionally trimmed to a depth of 5-10 MKti in the mixture of these acids, washed in water, toluene, and dried. After drying by scribing, the plates are finally separated into crystals, which are fused in the next operation with flat-plate type electrodes. Outlet electrodes with a size of 13 X 0.8 X 0.1 mm, made of a nickel strip with a layer of gold 5-6 microns thick galvanically deposited on it, using a cassette assembly in a vacuum of 10 mm Hg. and at 480-500 ° C, they fuse with a crystal, where as a result of melting a gold coating into silicon, fused contact is obtained over the entire transition area. The assembled diode is etched for 1 min in a mixture of acids of the indicated composition and thoroughly washed in deionized water, after which the structure is silanated with organosubstituted hydrolyzed} silane, dried and protected with a thin layer of silicone rubber. At the end of the rubber polymerization, the diode is covered with a drop of epoxy-oxane compound, followed by polymerization at 200 C. As a result of the technological operations, we obtain a varicap with the required electrical parameters.

Claims (1)

METHOD FOR PRODUCING ALLOY-DIFFUSIVE p – P-TRANSITION by depositing a layer of an active metal, for example titanium, on the wafer surface of the wafer, depositing the electrode metal on it and heating the resulting structure to a temperature not lower than the temperature of the eutectic electrode metal – semiconductor, followed by diffusion annealing and crystallization, characterized in that, in order to increase the coefficients of overlap in capacity and making transitions of any given area, between the layers of electrode metal, wear They have a layer of acceptor and donor impurities.