RU2354009C1 - Method for manufacture of photoelectric transducers based on multilayer structure - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method consists in application of ohm contacts on back and front surfaces of multilayer semiconducting structure GalnP/Ga(ln)As/Ge grown on germanium substrate, structure division into chips, immunisation of chips side surface by dielectric, removal of some frontal contact layer of structure and application of anti-reflecting coat onto frontal part of structure. Structure division into chips is done via photoresist mask from the side of structure frontal surface at the depth of 15-50 mcm in two stages: at the first stage structure is etched down to germanium substrate by method of chemical etching, at the second stage germanium substrate is etched by method of electrochemical etching.

EFFECT: improved parameters of photoelectric transducers.

3 cl, 10 ex, 2 dwg

Description

The invention relates to solar energy, in particular to a method for manufacturing photovoltaic converters, and can be used in the electronics industry to convert light energy into electrical energy.

A known method of manufacturing cascade photoconverters (see "Features of the technology for producing solar cells based on AlGaPAs / GaAs heterostructures using the GLC method", Blagin A.V., Blagina L.V., Alfimova D.L., Sysoev I.A., Slutskaya OV Proceedings of the Ninth International Scientific and Technical Conference "Actual Problems of Solid-State Electronics and Microelectronics", settlement of Divomorskoye, Russia, 2004) based on AlGaPAs / GaAs heterostructures using gradient liquid-phase crystallization. As contact materials for the p-type layer, chromium-copper and nickel-copper alloys were used, the resistance of which does not exceed 0.23 Ohm / cm ² , for the n-type layer a combination of two metals - vanadium and aluminum, whose resistance is 0.105 Ohm / cm ² . The efficiency of the photoconverter based on the Al0.33Ga0.67P0.05As0.95 / GaAs heterostructure, measured on a solar radiation simulator, was 21.5%.

The disadvantage of this method of manufacturing cascade photoconverters is the high resistance of the ohmic contact, the complexity of manufacturing a semiconductor structure and low efficiency of the photoconverter.

A known method of manufacturing a photodetector element (see application RU No. 94021123, IPC H01L 31/18, published 04/20/1996) based on multilayer GaAs / AlGaAs heterostructures. The method consists in applying a sequence of layers on a semi-insulating gallium arsenide substrate: a conducting n ⁺ GaAs layer, a multilayer periodic structure of GaAs / AlGaAs and a second conducting n ⁺ GaAs layer, followed by etching of the upper conducting n ⁺ GaAs layer and a multilayer heterostructure in an aqueous solution of hydrogen peroxide containing organic acid. The method allows to increase the accuracy and precision of etching in the manufacture of photodetector elements, increase the yield of products and reduce the cost of photodetector elements.

The disadvantage of this method of manufacturing a photodetector element is the use of a gallium arsenide substrate, which leads to a deterioration of the parameters of the photoconverter.

A known method of manufacturing a solar cell (see application RU No. 93046763, IPC H01L 31/18, published September 20, 1995), consisting in the fact that at least one surface of the semiconductor substrate forms a structure of parallel grooves by mechanical removal or etching of the semiconductor material , separated from one another by hills, tapering to the tops. A passivating layer is applied to the entire structured surface, after which the tops of the hills are cut to the depth of the passivating layer, resulting in the formation of parallel plateau-shaped areas from which the brackets extend. On plateau-like regions, as well as on one of the bevels of each region, material is formed that forms electrically conductive contacts. The solar cell contains a semiconductor substrate, on one surface of which a structure of hills with plateau-like peaks and with side bevels is formed. Electrically conductive contacts are located on plateau-like peaks and partially on bevels. The surface of the semiconductor substrate in the region between the contacts is coated with a passivating material.

The disadvantage of this method of manufacturing a solar cell is the complexity of the process, the possible occurrence of structural defects in the process of cutting the tops of the hills, which leads to a deterioration of the parameters of the photoconverter.

The closest to the claimed technical solution in terms of essential features is a method of manufacturing photovoltaic cells (see "Research and development of GalnP / GaAs / Ge multi-junction solar cells", An Xinxin, Garnelly Dario Albino, Denisov Alexey, Di Lillo Luigi, Sacchetto Davide, Fisichella Salvatore, Reddy Pallavi, Zneng Liqiancg, Institut National Polytechnigue de Grenoble, Nanotech Labs Project, Grenoble, 2007) based on the AlGaPAs / GaAs / Ge heterostructure. In this method, the structure is grown on a germanium substrate, ohmic contacts are deposited by sequential deposition of layers of titanium and silver, the ohmic resistance of which is 10 ^-6 Ohm / cm ² , an antireflection coating is applied by successive deposition of ZnS and MgF ₂ layers.

The disadvantage of this method of manufacturing photovoltaic converters are quite significant leakage pn junctions.

The objective of the proposed technical solution is to improve the parameters of photovoltaic converters.

This object is achieved in that a method of manufacturing photoelectric converters based on a multilayer semiconductor structure GalnP / Ga (ln) As / Ge grown on a germanium substrate includes applying ohmic contacts to the back and front surfaces of the structure, separating the structure into chips, passivation of the side surface of the chips dielectric, removing part of the frontal contact layer of the structure by chemical etching and applying an antireflection coating to the frontal surface of the structure. In this case, the structure is divided into chips through a photoresist mask from the front of the structure surface to a depth of 15-50 μm in two stages: at the first stage, the structure is etched to the germanium substrate by chemical etching, and at the second stage, the germanium substrate is etched by electrochemical etching.

Etching of the structure to a germanium substrate can be carried out at a temperature of 19-23 ° C in an etchant containing components in the following ratio, parts by weight:

K ₂ Cr ₂ O ₇ 80-110 HBr 80-110 H ₃ PO ₄ 150-180 water rest.

The etching of the germanium substrate can be carried out at a temperature of 19-23 ° C in an electrolyte containing components in the following ratio, parts by weight:

glycerol 30-50 Koh 1-4 water rest at external voltage 9-15 V.

The inventive method provides a smooth vertical wall of the separation mesa to the depth of all pn transitions of the structure, allows the best passivation of the side surface of the chips, eliminates leakage of the pn junction, which leads to the parameters of the photoelectric converters.

With a separation etching depth of less than 15 μm, it is not possible to separate the structure into individual solar cells. With an etching depth of more than 50 μm, further work with the semiconductor structure is impossible due to its fragility.

When the content of K ₂ Cr ₂ O _{7 is} less than 80 g / l or more than 110 g / l, with the content of HBr less than 80 g / l or more than 110 g / l, with the content of H ₃ PO ₄ less than 150 g / l or more than 180 g / l in the etchant used to etch the semiconductor structure, and when the etching temperature is less than 19 ° C or more than 23 ° C, the etching rates of the layers of the structure change. Due to the difference in the compositions of these layers, the etching rates of some layers decrease, which leads to the formation of “peaks” on the side wall of the separation mesa. Etching rates of other layers increase, which leads to etching of the structure. As a result, it is impossible to obtain an even vertical wall of the separation mesa and, therefore, it is impossible to achieve the best passivation of the lateral surface of the chips, which leads to leakage of pn junctions.

The use of the etchant of the above composition for etching a semiconductor structure is also due to the fact that it does not have strict selectivity with respect to germanium, which allows etching the germanium substrate to a small depth at the first etching stage and, therefore, to create an even vertical separation mesa to the depth of all pn junctions, which provides the best passivation of the side surface of the chips.

When the glycerol content is less than 30 g / l, when the KOH content is less than 1 g / l in the electrolyte used to etch the germanium substrate, the etching rate of germanium decreases, the morphology of the etching surface worsens and, therefore, the conditions for the best passivation of the chip side surface are worsened, which increases the etching time and, consequently, the labor required to manufacture the photoconverter. When the glycerol content is more than 50 g / l, the etching surface morphology worsens. When the KOH content is more than 4 g / l, etching occurs under the photoresist mask, through which etching is performed, and, therefore, the photosensitive surface of the photoconverter is etched, which leads to a sharp deterioration in its parameters. At an external voltage of less than 9 V, etching is uneven and slow; an oxide layer is formed on the surface that prevents etching. At voltages greater than 15 V, etching under the mask of the photoresist occurs and, therefore, the photosensitive surface of the photoconverter is etched. At temperatures below 19 ° C, the etching rate of germanium decreases, which leads to a deterioration in the surface morphology and to an increase in labor costs for the manufacture of a photoconverter. At temperatures above 23 ° C, the etching rate of germanium increases, which leads to etching under the photoresist mask.

The claimed technical solution is illustrated by illustrations, where

figure 1 shows a photograph of the separation mesa after etching the structure to a germanium substrate;

figure 2 shows a photograph of the separation mesa after etching of the structure and the germanium substrate.

Figure 1 and figure 2 shows the following notation: 1 - mask photoresist; 2 - semiconductor structure; 3 - germanium substrate.

The inventive method of manufacturing photoelectric converters is carried out on the basis of a multilayer semiconductor structure GalnP / Ga (ln) As / Ge grown on a germanium substrate. The process of manufacturing solar cells is carried out in several stages: they carry out chemical etching of the back side of the structure to a depth of 20-30 microns in the etchant CP4, spraying the rear ohmic contact with a thickness of 0.4-0.5 microns by vacuum thermal evaporation at the universal post-vacuum unit VUP- 5M. The front surface of the structure is cleaned by ion-beam etching at the Rokappa IBE ion-beam etching unit to a depth of 0.005-0.1 μm. An ohmic contact is deposited with a thickness of 0.2-0.4 μm on the front surface of the structure through a photoresist mask by vacuum thermal evaporation on a post-vacuum universal unit VUP-5M. The ohmic contacts are burned at a temperature of 360-370 ° C for 10-60 seconds. The ohmic contacts are thickened by electrochemical deposition of successive layers of gold, nickel and again gold with a total thickness of 1.6-3.5 μm through a photoresist mask. Separate etching of the structure to a depth of 15-50 μm is carried out through the mask of photoresist 1 (see Fig. 1) in two stages: at the first stage, the semiconductor structure 2 is etched to the germanium substrate 3 (see Fig. 1) at a temperature of 19-23 ° C in the etchant containing the components in the following ratio, parts by weight:

K ₂ Cr ₂ O ₇ 80-110 HBr 80-110 H ₃ RO ₄ 150-180 water rest.

At the second stage, the germanium substrate 3 is etched (see FIG. 2) at a temperature of 19-23 ° C. in an electrolyte containing components in the following ratio, parts by weight:

glycerol 30-50 Koh 1-4 water rest at external voltage 9-15 V.

Passivation of the side surface of the chips is carried out by applying a layer of silicon nitride by plasma-chemical deposition under reduced pressure using high-frequency plasma on a plasma-chemical deposition of dielectrics Rokappa PCVD. Local chemical etching of the contact layer of the structure is carried out in places free of ohmic contact in order to open the photosensitive surface of the solar cell in two stages: at the first stage, oxides are removed in the etchant containing the components in the following ratio, parts by weight:

NH ₄ OH 2-3 H ₂ O ₂ 6-7 water rest;

in the second stage, the contact layer of the structure is completely etched to the GalnP stop layer in the etchant containing the components in the following ratio, parts by weight:

lemon acid 550-570 H ₂ O ₂ 60-70.

The antireflection coating is sprayed by vacuum-thermal evaporation at the universal post-vacuum unit VUP-5M by successive spraying of ZnS layers 0.045 μm thick and 0.095 μm thick MgF ₂ in places free of ohmic contacts through windows in a magnetic mask.

Example 1

A photoelectric converter was fabricated based on the GalnP / Ga (ln) As / Ge multilayer semiconductor structure grown on a p-type germanium substrate. The manufacturing process of photovoltaic converters was carried out in several stages. We carried out chemical etching of the back side of the structure to a depth of 20 μm in the CP4 etchant, sprayed the rear ohmic contact with a thickness of 0.5 μm at the universal vacuum unit VUP-5M, which consisted of a successively arranged alloy layer containing 95 wt.% Silver and 5 wt. Manganese. %, layers of nickel and gold. The frontal surface of the structure was cleaned on a Rokappa IBE ion-beam etching unit to a depth of 0.005 μm. An ohmic contact with a thickness of 0.2 μm was sprayed onto the front surface of the structure through a photoresist mask on a VUP-5M universal postvacuum installation consisting of a successively arranged alloy layer containing 90 wt.% Gold and 10 wt.% Germanium, nickel and gold layers. The ohmic contacts were incinerated at a temperature of 370 ° С for 10 s. The ohmic contacts were thickened by electrochemical deposition through a photoresist mask of successive layers of gold, nickel and again gold with a total thickness of 3.5 μm. Separate etching of the semiconductor structure to a depth of 15 μm was carried out through a photoresist mask in two stages: in the first stage, the semiconductor structure was etched to a germanium substrate at a temperature of 19 ° C in an etchant containing components in the following ratio, parts by weight:

K ₂ Cr ₂ O ₇ 80 HBr 80 H ₃ PO ₄ 150 water rest;

at the second stage, the germanium substrate was etched at a temperature of 19 ° C in an electrolyte containing components in the following ratio, parts by weight:

glycerol fifty Koh four water rest at external voltage 9 V.

Passivation of the side surface of the chips was carried out by applying a layer of silicon nitride by plasma-chemical deposition under reduced pressure using high-frequency plasma on a plasma-chemical deposition of dielectrics Rokappa PCVD. Local chemical etching of the contact layer of the structure in places free of ohmic contact was carried out in two stages: at the first stage in the etchant containing the components in the following ratio, parts by weight:

NH ₄ OH 3 H ₂ O ₂ 7 water rest;

at the second stage in the etchant containing components in the following ratio, parts by weight:

lemon acid 570 H ₂ O ₂ 70 water rest.

The antireflection coating was sprayed on the universal post-vacuum unit VUP-5M by successive spraying of ZnS layers 0.045 μm thick and 0.095 μm thick MgF ₂ in places free of ohmic contacts through windows in a magnetic mask.

Example 2

A photoelectric converter was manufactured by the method described in example 1, with the following distinctive features: separation etching of the semiconductor structure was carried out to a depth of 50 μm in two stages. At the first stage, the semiconductor structure was etched to a germanium substrate at a temperature of 23 ° C in an etchant containing components in the following ratio, parts by weight:

K ₂ Cr ₂ O ₇ 110 HBr 110 H ₃ PO ₄ 180 water rest;

at the second stage, the germanium substrate was etched at a temperature of 23 ° C in an electrolyte containing components in the following ratio, parts by weight:

glycerol fifty Koh four water rest at external voltage 9 V.

Example 3

A photoelectric converter was manufactured by the method described in example 1, with the following distinctive features: separation etching of the semiconductor structure was carried out to a depth of 50 μm in two stages. At the first stage, the semiconductor structure was etched to a germanium substrate at a temperature of 23 ° C in an etchant containing components in the following ratio, parts by weight:

K ₂ Cr ₂ O ₇ 80 HBr 80 H ₃ PO ₄ 150 water rest;

at the second stage, the germanium substrate was etched at a temperature of 19 ° C in an electrolyte containing components in the following ratio, parts by weight:

glycerol fifty Koh four water rest at external voltage 15 V.

Example 4

A photoelectric converter was manufactured by the method described in example 1, with the following distinctive features: separation etching of the semiconductor structure was carried out to a depth of 15 μm in two stages. At the first stage, the semiconductor structure was etched to a germanium substrate at a temperature of 19 ° C in an etchant containing components in the following ratio, parts by weight:

K ₂ Cr ₂ O ₇ 110 HBr 110 H ₃ PO ₄ 180 water rest;

at the second stage, the germanium substrate was etched at a temperature of 23 ° C in an electrolyte containing components in the following ratio, parts by weight:

glycerol thirty Koh one water rest at external voltage 15 V.

Example 5

A photoelectric converter was manufactured by the method described in example 1, with the following distinctive features: separation etching of the semiconductor structure was carried out to a depth of 15 μm in two stages. At the first stage, the semiconductor structure was etched to a germanium substrate at a temperature of 23 ° C in an etchant containing components in the following ratio, parts by weight:

K ₂ Cr ₂ O ₇ 80 HBr 80 H ₃ PO ₄ 150 water rest;

at the second stage, the germanium substrate was etched at a temperature of 19 ° C in an electrolyte containing components in the following ratio, parts by weight:

glycerol thirty Koh one water rest at external voltage 15 V.

Example 6

A photoelectric converter was manufactured by the method described in example 1, with the following distinctive features: separation etching of the semiconductor structure was carried out to a depth of 15 μm in two stages. At the first stage, the semiconductor structure was etched to a germanium substrate at a temperature of 23 ° C in an etchant containing components in the following ratio, parts by weight:

K ₂ Cr ₂ O ₇ 80 HBr 80 H ₃ PO ₄ 150 water rest;

at the second stage, the germanium substrate was etched at a temperature of 19 ° C in an electrolyte containing components in the following ratio, parts by weight:

glycerol thirty Koh four water rest at external voltage 15 V.

Example 7

A photoelectric converter was manufactured by the method described in example 1, with the following distinctive features: separation etching of the semiconductor structure was carried out to a depth of 50 μm in two stages. At the first stage, the semiconductor structure was etched to a germanium substrate at a temperature of 19 ° C in an etchant containing components in the following ratio, parts by weight:

K ₂ Cr ₂ O ₇ 110 HBr 110 H ₃ PO ₄ 180 water rest;

at the second stage, the germanium substrate was etched at a temperature of 23 ° C in an electrolyte containing components in the following ratio, parts by weight:

glycerol fifty Koh one water rest at external voltage 9 V.

Example 8

A photoelectric converter was manufactured by the method described in example 1, with the following distinctive features: separation etching of the semiconductor structure was carried out to a depth of 50 μm in two stages. At the first stage, the semiconductor structure was etched to a germanium substrate at a temperature of 19 ° C in an etchant containing components in the following ratio, parts by weight:

K ₂ Cr ₂ O ₇ 80 HBr 80 H ₃ PO ₄ 150 water rest;

at the second stage, the germanium substrate was etched at a temperature of 19 ° C in an electrolyte containing components in the following ratio, parts by weight:

glycerol thirty Koh one Water rest at external voltage 9 V.

Example 9

A photoelectric converter was manufactured by the method described in example 1, with the following distinctive features: separation etching of the semiconductor structure was carried out to a depth of 40 μm in two stages. At the first stage, the semiconductor structure was etched to a germanium substrate at a temperature of 20 ° C in an etchant containing components in the following ratio, parts by weight:

K ₂ Cr ₂ O ₇ 90 HBr 90 H ₃ PO ₄ 170 water rest;

at the second stage, the germanium substrate was etched at a temperature of 20 ° C in an electrolyte containing components in the following ratio, parts by weight:

glycerol 40 Koh 2 water rest at external voltage 10 V.

Example 10

A photoelectric converter was manufactured by the method described in example 1, with the following distinctive features: separation etching of the semiconductor structure was carried out to a depth of 25 μm in two stages. At the first stage, the semiconductor structure was etched to a germanium substrate at a temperature of 22 ° C in an etchant containing components in the following ratio, parts by weight:

K ₂ Cr ₂ O ₇ 80 HBr 80 H ₃ PO ₄ 150 water rest;

at the second stage, the germanium substrate was etched at a temperature of 22 ° C in an electrolyte containing components in the following ratio, parts by weight:

glycerol 35 Koh one water rest at external voltage 10 V.

Carrying out the manufacturing process of photovoltaic converters in compliance with the above parameters made it possible to obtain an even vertical wall of the separation mesa to the depth of all pn transitions of the structure, to obtain a passivating coating that ideally covers the entire side surface of the chips without defects and tears, to eliminate leakage of pn junctions, which led to an improvement parameters of photovoltaic converters: the FF factor increased to 84%, the yield of useful elements increased from 60% to 80%.

Claims (3)

1. A method of manufacturing photoelectric converters based on a multilayer GalnP / Ga (ln) As / Ge structure grown on a germanium substrate, including applying ohmic contacts to the back and front surfaces of the structure, separating the structure into chips, passivating the side surface of the chips with an insulator, removing part of the front the contact layer of the structure by chemical etching and applying an antireflection coating on the front surface of the structure, characterized in that the separation of the structure into chips is carried out through ascus photoresist from the front surface of the structure to a depth of 15-50 microns in two stages: the first stage is carried out to etch the structure germanium substrate by chemical etching in the second etching step is carried germanium substrate by electrochemical etching. 2. The method according to claim 1, characterized in that the etching of the structure to a germanium substrate is carried out at a temperature of 19-23 ° C in an etchant containing components in the following ratio, parts by weight:
K ₂ Cr ₂ O ₇ 80-110 HBr 80-110 H ₃ PO ₄ 150-180 water rest. 3. The method according to claim 1, characterized in that the etching of the germanium substrate is carried out at a temperature of 19-23 ° C in an electrolyte containing components in the following ratio, parts by weight:
glycerol 30-50 KOH 1-4 water rest,
with an external voltage of 9-15 V.

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