RU2569551C2 - Boring of monocrystal silicon plates - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to semiconductor engineering, particularly, to production of microstructure elements of electronic devices. Production of bores in monocrystalline silicon plates comprises preparation of such plate by application on its surface of fine metal particles of catalyst to be coated with a thin film of sodium tetraborate (anhydrous). Plate is placed in radiant furnace and heated. Crosswise temperature gradient of 10-100 K/cm is created and directed from plate face to rear. Atomic silicon undersaturation is created in gas phase by feeding thereon the silicon tetrachloride to effect the gas-phase etching of the plate in crystal→liquid drop→vapour manner.

EFFECT: high-quality through bores in monocrystal silicon plates.

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Description

The invention relates to the field of microelectronics, in particular, to the technology of manufacturing semiconductor structures, which are the elemental base of functional microelectronics, and can be used in the technology of manufacturing silicon membrane filters, solar cells with vertical p-n junctions, silicon wafers of lightweight construction used in optical instrumentation.

Known methods for producing holes in single-crystal silicon wafers [Etching of semiconductors [collection of articles]. Per. from English S.N. Gorina. M .: Mir, 1965; Amirov I.I., Morozov O.V., Izyumov M.O., Kalnov V.A., Orlikovsky A.A., Valiev K.A. // Plasma-chemical etching of deep grooves in silicon with a high aspect ratio to create various elements of micromechanics. // Microsystem technology. 2004.V. 12. S. 15-18; Schetinin A.A., Dunaev A.I., Kosenkov O.D. On the etching of silicon single crystals through the liquid phase and the formation of conventional and “negative” nanocrystal systems // Voronezh, Polytechnic, Institute of Computer Science. Voronezh, 1981. 9 p. Dep. in VINITI 08.12.81, No. 5596-81]. Known technical solution [Etching of semiconductors [collection of articles]. Per. from English S.N. Gorina. M .: Mir, 1965], according to which holes in a silicon wafer are obtained by selective chemical isotropic etching of surface areas of the crystal unprotected by an oxide photomask in a buffer etchant based on nitric, hydrofluoric, and acetic acids. The disadvantages of this method are the low selectivity of the etching (the ratio of the etching rates of silicon and the material of the photomask), side etching under the mask and the inability to obtain holes with a high aspect ratio, depth / diameter.

There is a method of creating holes in single-crystal silicon wafers by selective plasma-chemical etching due to the chemical interaction of open areas of the silicon surface with chemically active charged particles and the formation of volatile compounds [Amirov II, Morozov OV, Izyumov M.O., Kalnov V. A., Orlikovsky A.A., Valiev K.A. // Plasma-chemical etching of deep grooves in silicon with a high aspect ratio to create various elements of micromechanics // Microsystem technique. 2004.V. 12. S. 15-18]. The disadvantages of the method are the low etching rate (2-10 nm / s), low etching anisotropy (the ratio of etching rates along the normal to the surface and in the tangential direction), the lack of hardware capabilities to provide etching of holes with a depth significantly exceeding 100 microns along the normal to the surface, and also the possibility of degradation and destruction of structures on the plate.

The closest analogue is a method of producing holes in semiconductor wafers by selective chemical gas-phase etching with the participation of finely dispersed metal particles according to the crystal → liquid drop → vapor scheme [Shchetinin A.A., Dunaev A.I., Kozenkov O.D. On the etching of silicon single crystals through the liquid phase and the formation of conventional and “negative” nanocrystal systems // Tomsk, 1981, pp. 2-9, Dep. in VINITI 08.12.81, No. 5596-81]. If there are metal particles on the plate at their locations, holes are formed in the form of cylindrical, prismatic or conical extended cavities and channels with diameters from 0.05 to 30 microns. The disadvantages of the method are the inability to create through holes passing through the entire thickness of the plate, a significant effect on the crystallographic orientation of the plate material and the formation of multifaceted etching figures, the possibility of splitting the drop and the formation of many holes in the form of narrow tunnels under the plate surface, the inability to control the direction of the spatial location of the hole in the plate.

The invention is directed to through holes in single-crystal silicon wafers.

This is achieved by the fact that before placing a silicon wafer with finely dispersed catalyst particles deposited on its surface in a radiation furnace and creating conditions for chemical gas-phase etching according to the crystal → liquid drop → vapor scheme, the catalyst is coated with a thin film of sodium tetraborate Na ₂ B ₄ O ₇ (anhydrous), in the silicon wafer a transverse temperature gradient grad T directed from the front to the back side of the wafer is created, the temperature gradient being selected from a range of 10 ≤ grad T ≤100 K / cm.

A method of producing holes in single-crystal silicon wafers is as follows. Finely dispersed metal particles of the catalyst deposited on the surface of the semiconductor wafer are coated with a thin film of sodium tetraborate Na ₂ B ₄ O ₇ (anhydrous). Then the plate is placed in a quartz reactor, purged with hydrogen, is heated to a predetermined temperature. Then, conditions are created for the undersaturation of atomic silicon in the gas phase by feeding silicon tetrachloride into the gas phase; the necessary transverse temperature gradient gradient T is created in the silicon wafer, directed from the front to the back of the wafer, the value of which is selected from the range 10 ≤ grad T ≤100 K / cm, and a chemical gas-phase etching is performed according to the crystal → liquid drop → ball scheme. The indicated range of the temperature gradient is determined by the fact that for catalytic particle sizes of 10 ^-2 -10 ^-3 cm, for the droplet to move, it is necessary to ensure a temperature drop in the metal droplet itself of at least 0.1 K / cm With a gradient of less than 10 K / cm, the drop does not deepen into the substrate, and with a gradient of more than 100 K / cm, the process of creating holes becomes uncontrollable: the drop can break into smaller drops, forming several holes oriented at different angles. Coating the metal particles of the catalyst with a thin film of sodium tetraborate Na ₂ B ₄ O ₇ (anhydrous) is carried out in order to reduce the surface tension of the liquid-phase catalyst particles.

Using the proposed method allows to obtain through (passing through the entire thickness) holes in single crystal silicon wafers, high selectivity and high anisotropy of the etching process of silicon. The proposed method allows to simplify the technology of creating silicon membrane filters, silicon wafers of lightweight construction, the manufacture of which provides for through holes in the membranes. The method allows to facilitate the creation of holes in the silicon wafers of solar cells with vertical p-n junctions, as well as to facilitate the creation of through holes when outputting collector contacts from the front to the back of the wafer in silicon single-sided photoelectric converters, and much more.

Examples of the method.

Example 1

Fine-dispersed Au particles having an average characteristic linear size of 20 μm were deposited on the front side polished single-crystal silicon wafers with a thickness of 350 μm and a {111} crystallographic orientation using photolithography processes. Then the particles were covered with a thin film of sodium tetraborate Na ₂ B ₄ O ₇ (anhydrous) preheated to a temperature of 335 K. Prepared plates were placed in a radiation furnace. The temperature of the furnace increased to 1300 (± 2) K with a simultaneous supply of hydrogen. A transverse temperature gradient of 10 K / cm was created in the silicon wafer, directed from the front to the back side of the wafer. Then, silicon tetrachloride was introduced into the gas phase at the molar ratio [SiCl ₄ ] / [H ₂ ] = 0.02, and a chemical gas-phase etching of silicon was carried out. The etching time was 10 minutes. The holes obtained were oriented perpendicular to the {111} plane of the plate, had a cylindrical shape and wore through, that is, a character passing through the entire thickness of the plate. The diameter of the holes was ~ 20 μm.

Example 2

The implementation of the invention was carried out analogously to example 1, but Pt particles were used as a catalyst. The results obtained are fully consistent with the results of example 1.

Example 3

The invention was carried out analogously to example 1, but the plate thickness was 250 μm, and Cu particles were used as a catalyst for the process. The etching time was 2 minutes. The results obtained were consistent with the results of example 1.

Example 4

The invention was carried out analogously to example 1, but single crystal silicon wafers with a thickness of 350 μm with a crystallographic orientation of {100} were used as substrates. The results obtained were consistent with the results of examples 1.

Example 5

The invention was carried out analogously to example 1, but the transverse temperature gradient was 100 K / cm The results obtained were consistent with the results of example 1, but the shape of the holes was conical, and the average diameter was 22 μm.

Claims (1)

A method for producing holes in single-crystal silicon wafers, including preparing a semiconductor wafer by depositing finely dispersed metal catalyst particles on its surface, followed by placing it in a radiation furnace and heating, creating conditions for the undersaturation of atomic silicon in the gas phase by feeding silicon tetrachloride into it and chemical vapor-phase etching scheme liquid crystal drop → → pairs, characterized in that the catalyst particles are coated with a thin film tetraborate Na ₂ B ₄ O _7, sodium (anh -stand), then the silicon wafer creates transverse directed from the front to the rear side of the plate the temperature gradient grad T, the temperature gradient value selected from a range of 10≤ grad T ≤100 K / cm.