RU2354007C1 - Method for manufacture of multiple-unit photoreceiving crystal based on mis structures - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: in method for manufacture of multiple-unit photoreceiving crystal based on MIS structures, InAs substrate is coated with SiO2 layer, in which through windows are formed lithographically to determine photosensitive area for photoreceiving crystals. Then substrate-gate insulator interface is formed on substrate in windows by means of anode oxidation. Area of window formed in SiO2 is specified with the possibility to cover area of all photosensitive elements of photoreceiving crystal. Then layer of gate insulator SiO2 is deposited onto layer of anode oxide with thickness of 1015 nm, and photosensitive elements are formed by creation of gates from ln2O3 on gate insulator. Conductive buses are made, which are withdrawn outside the limits of photosensitive area away from gates of photosensitive elements. ^ EFFECT: improved electro-optic isolation of elements due to suppression of photosensitivity in area of conductive buses. ^ 8 cl, 4 dwg

Description

The invention relates to microelectronics and can be used in the manufacturing technology of infrared (IR) radiation receivers, for example, of the line type.

A known method of manufacturing a multi-element photodetector based on MIS structures (G.L. Kuryshev, A.P. Kovchavtsev, N.A. Valisheva "Electronic properties of metal-insulator-semiconductor structures based on InAs", FTP, 2001, t .35, issue 9, pp. 1111-1119), which consists in the fact that a layer is formed on the semiconductor substrate that forms the interface between the substrate and the gate insulator, after which the gate insulator is deposited, then photosensitive elements are formed by creating gates on the gate insulator. As the substrate, n-type InAs auto-epitaxial structures with the concentration of the main charge carriers (1 ÷ 6) · 10 ¹⁵ cm ^-3 and a lifetime of 0.3 ÷ 1.8 μs on heavily doped n ⁺⁺ substrates (concentration of free carriers) are used charge order of 10 ¹⁸ cm ^-3 (111) a. The layer forming the boundary of the semiconductor-gate insulator section is produced by oxidation of a substrate in a fluorine-containing electrolyte (anodic oxidation). as a source of fluoride ions in the electrolyte which is a concentrated solution of am iaka in ethylene glycol in a ratio of 1: 5 by volume, was added ammonium fluoride oxidation is carried out at room temperature in a two-electrode cell in the galvanostatic mode at a current density of 0.5 mA / cm ² After the oxidation is deposited as gate dielectric silicon dioxide (SiO _2).. 140 nm thick at a temperature of 200 ÷ 240 ° C by oxidation of monosilane in oxygen in a low pressure reactor (SiO ₂ -RPD). Before oxidation, the surface is degreased. The shutter material of photosensitive elements is indium oxide 0.12 μm thick, deposited by ion-plasma spraying.

The reasons that impede the achievement of the following technical result include the presence of photosensitivity outside the area of the photosensitive elements - under the conductive busbars and contacts. Photosensitivity causes a slight difference in threshold voltages in the photosensitive region of the photodetector and in the field of conductive buses. The absence of a noticeable difference in the threshold voltage values under the conducting buses and photosensitive elements is due to the same values of the density of surface states and a fixed charge at the semiconductor substrate-insulator interface over the entire area of the photodetector: in the photosensitive region where the MIS structures are located and in the region conductive tires. In the technical solution there is no pronounced factor leading to the suppression of photosensitivity in the field of conductive tires.

The closest technical solution to the claimed invention is a method of manufacturing a multi-element photodetector based on MIS structures (Matrix photodetector devices of the infrared range. Edited by S.P.Sinitsa, Novosibirsk, Nauka, 2001, pp. 86-87) consisting in the fact that a layer is formed on the semiconductor substrate that forms the interface between the substrate and the gate insulator, after which the gate insulator is deposited, then photosensitive electrons are formed by creating gates on the gate insulator. cops. During the formation of the gates, a photoresist is applied and photolithography is performed, forming through windows in the photoresist, after photolithography, a conductive film in the windows is sprayed onto the gate dielectric and explosive photolithography is performed, creating a shutter. Next, the photoresist is removed and a protective dielectric layer is deposited, in which through-windows are lithographically created through the area of the photosensitive elements, and finally, lithographically conductive buses are made. Before creating a layer forming the interface between the substrate and the gate dielectric, a preliminary chemical treatment of the substrate is carried out. As the substrate, an InAs plate is used. The layer forming the substrate-gate dielectric interface is created by oxidizing the substrate in a fluorine-containing electrolyte (anodic oxidation). Immediately after oxidation, SiO ₂ -RPD is deposited as a gate dielectric at a temperature of 220 ° C. After photolithography, indium oxide with a thickness of 0.12 to 0.15 μm is sprayed as a conductive film.

The reasons that impede the achievement of the following technical result include the presence of photosensitivity outside the area of the photosensitive elements - under the conductive busbars and contacts. Photosensitivity causes a slight difference in threshold voltages in the photosensitive region of the photodetector and in the field of conductive buses. The absence of a noticeable difference in the threshold voltage values under the conducting buses and photosensitive elements is due to the same values of the density of surface states and a fixed charge at the semiconductor substrate-insulator interface over the entire area of the photodetector: in the photosensitive region where the MIS structures are located and in the region conductive tires. In the technical solution there is no pronounced factor leading to the suppression of photosensitivity in the field of conductive tires.

The technical result of the invention is to improve the electro-optical isolation of the elements.

The technical result is achieved by the fact that in the method of manufacturing a multi-element photodetector based on MIS structures, which consists in creating a layer on the semiconductor substrate that forms the interface between the substrate and the gate dielectric, after which the layer of the gate dielectric is deposited, then by creating gates on the gate dielectric photosensitive elements are formed, and then conductive buses are made, before creating a layer forming the substrate-gate dielectric interface, on p an insulating layer is applied to the semiconductor substrate, in which lithographically through holes are formed defining a photosensitive region for each photodetector, after which a layer is formed on the semiconductor substrate in the through windows formed in the dielectric layer, and the substrate-gate dielectric interface is formed, and the area of the window formed in a dielectric layer, is set with the possibility of covering the area of all photosensitive elements of the photodetector, and the conductive bus from the shutter photo sensitive elements are taken outside the photosensitive area.

An InAs wafer is used as the semiconductor substrate.

In the method, a layer forming a substrate-gate dielectric interface is created by anodic oxidation of the substrate in a fluorine-containing electrolyte.

In the method anodic oxide is formed with a thickness of the order of 10-15 nm.

In the method, the formation of photosensitive elements by creating gates on a gate dielectric is carried out by applying a photoresist to the gate dielectric layer and performing photolithography, forming through windows in the photoresist, placing them in the field area of the layer forming the substrate-gate dielectric interface after forming the through windows in a photoresist with an area equal to the area of the photosensitive element, in the windows in the photoresist create gates by spraying a conductive film, then I remove the photoresist t and a protective dielectric layer is deposited, in which through each window of the photosensitive element lithographically through the windows to the shutter are created, and finally, lithographically conductive tires are made that are in contact with the shutters of the photosensitive elements.

As layers of a dielectric, a gate dielectric and a protective dielectric, SiO ₂ layers are used with thicknesses from 95 to 105 nm, respectively; from 135 to 155 nm; from 200 to 220 nm.

As a gate material with a thickness of 120 to 130 nm, In ₂ O _{3 is used} .

For the manufacture of conductive tires using titanium, with a layer thickness of 0.1 to 0.15 microns.

The invention is illustrated by the following description and the accompanying drawings. Figure 1 schematically shows the main stages of the manufacture of a multi-element photodetector based on MIS structures, where 1 is a semiconductor substrate (InAs), 2 is a dielectric layer (SiO ₂ -RPD), 3 is a layer (anode oxide) that forms the interface - gate insulator, 4 - gate insulator (SiO ₂ ), 5 - photosensitive element gate (In ₂ O ₃ ), 6 - protective dielectric layer (SiO ₂ -RPD), 7 - conductive busbars. Figure 2 schematically shows a top view of a line-type photodetector, where 7 are conductive buses, 8 are gate areas of photosensitive elements, 9 is the field of the layer forming the substrate-gate dielectric interface (photosensitive region). Figure 3 schematically shows an image of a semiconductor wafer with photodetector crystals located on it, where 10 is a photodetector crystal. The dotted line indicates the areas 9 of the location of the gates of the photosensitive elements 8. Figure 4 schematically shows the manufacturing process of the gates of the photosensitive elements, where 4 is a gate dielectric, 11 is a photoresist, 12 is a translucent conductive layer (In ₂ O ₃ ), 5 is a shutter of the photosensitive element .

The achievement of the technical result in the present invention is based on the creation of a significant difference in threshold voltages in the photosensitive region of the photodetector and in the field of conductive buses. A significant difference in threshold voltage values under the conductive buses 7 and photosensitive elements and the suppression of photosensitivity outside the region of the photosensitive elements, under the conductive buses 7, is achieved due to the formation of regions with different values of the density of surface states and a fixed charge at the semiconductor-dielectric interface during manufacturing MIS structures for photodetectors (see Figure 1 and Figure 2). So, in the photosensitive region located in the field of layer 3, forming the substrate-gate dielectric interface (see Figure 1), in which the photosensitive elements are concentrated (Figure 2), the density of surface states (Nss) at the substrate-gate gate interface the dielectric reaches a value of less than 5 · 10 ¹² cm ^-2 eV ^-1 , and the voltage of the flat zones (U _FB ) from -3 to 5 V. In the area of the conductive busbars 7, lying outside the field of layer 3, forming the substrate-gate interface dielectric characterized by the presence of more of the protective dielectric layer 6, the density of surface states at the substrate – dielectric interface reaches 10 ¹² cm ^–2 eV ^–1 , and the voltage of the flat zones is about –20 V. The difference in the values of these parameters suppresses photosensitivity in the field of conducting buses.

Technologically, the difference in threshold voltages and the suppression of photosensitivity in the field of conductive buses is achieved by creating a layer that forms the substrate-gate dielectric interface, whose function is to ensure the minimum density of surface states and a fixed charge only in the photosensitive region of the photodetector. To do this, additional operations are introduced into the well-known list of operations: before creating a layer forming the interface between the substrate and the gate insulator, a dielectric layer 2 is deposited on the semiconductor substrate 1, then lithographic through windows are formed in it (Fig. 1). Further, the layer 3 forming the substrate-gate dielectric interface is not created on the entire semiconductor substrate, including under the conducting buses, as is the case in the above-mentioned closest technical solution, but only in the window formed in the dielectric layer 2. The formed window (Fig. 1) defines the photosensitive region of the photodetector (see Figs. 2 and 3) in which the photosensitive elements will be located (Fig. 2), and sets the boundary beyond which the conductive buses 7 from the areas of the photosensitive elements will be taken out.

Thus, the claimed method includes the following sequence of actions (Figure 1).

InAs wafers, which are semiconductor substrates 1, are rejected in appearance, lifetime of minority charge carriers, and thickness.

Then the semiconductor substrate 1 is subjected to pre-treatment, degreased in a mixture of monoethalomine with hydrogen peroxide. After carrying out this generally accepted procedure, a dielectric layer 2 is deposited on a semiconductor substrate 1. SiO ₂ 95–105 nm thick is used as a dielectric, which is deposited in a reduced pressure reactor from a mixture of monosilane and oxygen in argon at a temperature of 220 ° C. Dielectric layer 2 serves as a mask that ensures the formation of an interface with a minimum density of surface states and a fixed charge only in the photosensitive region of the crystal, where, through subsequent technological operations, gates of a multi-element photodetector crystal based on MIS structures are formed: windows are opened in the dielectric layer 2 by lithography for all photodetector crystals (see Figure 3), in which a layer 3 is formed on the semiconductor substrate 1, forming the interface and the substrate is a gate dielectric (see Fig. 1a).

Before creating layer 3, the treatment is repeated by degreasing in a mixture of monoethalomine with hydrogen peroxide. Layer 3 is created by anodic oxidation of the substrate in an acid fluorine-containing electrolyte in the galvanostatic mode. Anodic oxide is formed with a thickness of about 10 ÷ 15 nm, while the molding voltage, depending on the concentration of the fluorine-containing additive (NH ₄ F) 0.05 ÷ 15 g / l, is for a thickness of 10 nm from 6.6 to 14 V, and for a thickness of 15 nm from 7.9 to 16 V. The purpose of layer 3 obtained on substrate 1 by anodic oxidation in SiO ₂ through-holes is to form an interface with a density of surface states of the order of or less than 5 · 10 ¹⁰ cm ^-2 eV ^-1 and an internal charge of the order of 10 ¹⁰ cm ^-2 , while under the dielectric layer 2 (layer - mask SiO ₂ ) the values of these parameters are t respectively of the order of or more than 10 ¹² cm ^-2 eV ^-1 and of the order of 10 ¹² cm ^-2 .

At the above-described stage (see Fig. 1a), the method is set to the geometrically photosensitive region of the photodetector crystals, for example, a line photodetector, the physical parameters of the substrate-gate dielectric interface are set in the photosensitive region and in the field of conductive buses, which determine the possibility of increasing the difference in threshold voltage values and improving electro-optical isolation of the elements. The result of this stage is an increase in the difference in the threshold voltage values under the conductive buses, compared with photosensitive elements, by 10 ÷ 15 V.

After the anodic oxidation of the substrate 1 in the windows of the dielectric mask (dielectric layer 2), they proceed to the step of deposition of the gate dielectric 4 and the creation of gates 5 (see Fig. 1b). A gate insulator 4, which is used as a SiO ₂ -RPD with a thickness of 135 ÷ 445 nm, is deposited over the entire area of the semiconductor substrate 1, using a mixture of monosilane with oxygen in argon and a temperature of 220 ° C for deposition. The gate insulator 4 is designed to provide the required dielectric properties of the MIS structures necessary for the proper operation of the photodetectors.

The creation of the shutters 5 is carried out in the photosensitive region of the photodetector crystals. For the manufacture of gates using, for example, the method of explosive photolithography (see Figure 4).

A photoresist is applied to the precipitated gate dielectric 4 and photolithography is performed (Fig. 4a). After opening the windows in the photoresist, In ₂ O _{3 is} sputtered by cathodic sputtering with a thickness of 120 ÷ 130 nm (Fig. 4b). Then, by means of explosive photolithography along In ₂ O ₃ , gates 5 of photosensitive elements are formed (Fig. 4c).

Next, on the semiconductor substrate 1 on top of the MIS structures formed on it, a protective dielectric layer 6 is applied and windows are formed in it for contacts to the gates 5 (Fig. 1c). As a protective dielectric, a SiO ₂ layer with a thickness of 200 ÷ 220 nm is used, which is obtained by the above method at a temperature of 195 ° C. The purpose of this layer is: firstly, to provide electrical isolation of the gates of the MIS structures with conductive buses 7 and a screen (not shown) and, secondly, to protect the MIS structures from the negative effects of subsequent technological operations.

Then, to ensure contact between the conductive busbars 7 and the gates 5 by lithography on the SiO ₂ protective layer, windows are opened to the gates 5 of In ₂ O ₃ . Then proceed to the final stage (see Fig.1g).

For this, pre-treatment is carried out in order to improve adhesion. The final stage of production includes the creation of conductive buses 7 in contact with the shutters 5 of the photosensitive elements (Fig. 1d) and a screen (not shown), as well as the operation of manufacturing indium poles for the Flip-Chip assembly with a silicon multiplexer. To create conductive tires 7, titanium is sprayed by cathodic sputtering with a thickness of the order of 0.1 ÷ 0.15 μm. Then conduct lithography on titanium. These two operations provide the manufacture of conductive tires 7 and located between the shutters of the screen, which provides protection against stray light.

After the manufacture of the conductive buses 7 and the shield is completed, an indium pole is formed on each conductive bus intended for connecting the photodetector crystal (chip) with a device for reading signals from photosensitive elements. For this purpose, indium is sprayed with an adhesive nickel sublayer. The thickness of indium is about 5–6 μm. Then carry out photolithography on indium-nickel.

In conclusion, indium with a thickness of the order of 0.3 μm is sprayed onto the non-planar side of the plate in order to create contact. After testing, the plate is divided into crystals. Each photodetector crystal 10 (FIG. 3) may contain a different number of photosensitive elements, for example 2 × 192, or 2 × 128, or 1 × 68, with different steps and shutter sizes.

The materials presented for creating the structural elements of multi-element photodetector crystals based on MIS structures and methods for forming layers from them are known, and the layer thicknesses, the materials and equipment used during lithographic processes are typical of the existing technology.

As information confirming the possibility of carrying out the invention with the achievement of a technical result, we give the following implementation examples.

Example 1

A dielectric layer is applied to a pre-defatted semiconductor substrate, in which lithographically through windows are formed that define the photosensitive region for each photodetector. Then, on the semiconductor substrate in the through windows formed in the dielectric layer, a layer is formed that forms the substrate-gate dielectric interface. Moreover, the area of the window formed in the dielectric layer is set to cover the area of all photosensitive elements of the photodetector.

A layer of the gate insulator is subsequently deposited, photosensitive elements and conductive busbars are formed by creating gates on the gate insulator. In this case, the conductive buses from the gates of the photosensitive elements are taken outside the photosensitive region.

An InAs wafer is used as the semiconductor substrate.

The layer forming the substrate-gate dielectric interface is created by anodic oxidation of the substrate in a fluorine-containing electrolyte. An anodic oxide with a thickness of about 15 nm is formed.

The formation of photosensitive elements by creating gates on the gate dielectric is carried out by sequentially performing the following operations. A photoresist is applied to the gate dielectric layer. Lithography is carried out, forming through windows in the photoresist, placing them in the field of the area of the layer forming the interface between the substrate and the gate insulator. In the windows formed in the photoresist, gates are created by spraying a conductive film and then removing the photoresist. A layer of protective dielectric is precipitated. Through a layer of a protective dielectric relative to each photosensitive element, through windows are formed lithographically to the shutter. In conclusion, lithographic conductive tires are made that are in contact with the shutters of the photosensitive elements.

As layers of a dielectric, a gate dielectric, and a protective dielectric, SiO ₂ layers are used with a thickness of 100 nm, 140 nm, and 200 nm, respectively.

As the material of the conductive film to create the gates using In ₂ O ₃ , which is sprayed with a thickness of 130 nm.

For the manufacture of conductive tires using titanium, sprayed with a layer of a thickness of the order of 0.1 microns.

Example 2

A dielectric layer is deposited on a pre-defatted semiconductor substrate, in which lithographically through windows are formed that define the photosensitive region for each photodetector. Then, on the semiconductor substrate in the through windows formed in the dielectric layer, a layer is formed that forms the substrate-gate dielectric interface. Moreover, the area of the window formed in the dielectric layer is set to cover the area of all photosensitive elements of the photodetector.

A layer of the gate dielectric is subsequently deposited, by creating gates on the gate dielectric, photosensitive elements are formed and conductive buses are made. In this case, the conductive busbars from the metal electrodes of the photosensitive elements are carried outside the photosensitive region.

An InAs wafer is used as the semiconductor substrate.

The layer forming the substrate-gate dielectric interface is created by anodic oxidation of the substrate in a fluorine-containing electrolyte. An anodic oxide with a thickness of about 13 nm is formed.

The formation of photosensitive elements by creating gates on the gate dielectric is carried out by sequentially performing the following operations. A photoresist is applied to the gate dielectric layer. Lithography is carried out, forming through windows in the photoresist, placing them in the field of the area of the layer forming the interface between the substrate and the gate insulator. In the windows formed in the photoresist, gates are created by spraying a conductive film and then removing the photoresist. A layer of protective dielectric is precipitated. Through a layer of a protective dielectric relative to each photosensitive element, through windows are formed lithographically to the shutter. In conclusion, lithographic conductive tires are made that are in contact with the shutters of the photosensitive elements.

As layers of a dielectric, a gate dielectric and a protective dielectric, SiO ₂ layers are used with thicknesses of 95 nm, 130 nm, and 220 nm, respectively.

As the material of the conductive film to create the gates using In ₂ O ₃ , which is sprayed with a thickness of 120 nm.

For the manufacture of conductive tires using titanium sprayed with a layer of a thickness of the order of 0.15 microns.

Example 3

A dielectric layer is deposited on a pre-defatted semiconductor substrate, in which lithographically through windows are formed that define the photosensitive region for each photodetector. Then, on the semiconductor substrate in the through windows formed in the dielectric layer, a layer is formed that forms the substrate-gate dielectric interface. Moreover, the area of the window formed in the dielectric layer is set to cover the area of all photosensitive elements of the photodetector.

A layer of the gate dielectric is subsequently deposited, by creating gates on the gate dielectric, photosensitive elements are formed and conductive buses are made. In this case, the conductive buses from the sites of the photosensitive elements are taken outside the photosensitive region.

An InAs wafer is used as the semiconductor substrate.

The layer forming the substrate-gate dielectric interface is created by anodic oxidation of the substrate in a fluorine-containing electrolyte. An anodic oxide is formed with a thickness of the order of 10 nm.

The formation of photosensitive elements by creating gates on the gate dielectric is carried out by sequentially performing the following operations. A photoresist is applied to the gate dielectric layer. Lithography is carried out, forming through windows in the photoresist, placing them in the field of the area of the layer forming the interface between the substrate and the gate insulator. In the windows formed in the photoresist, gates are created by spraying a conductive film and then removing the photoresist. A layer of protective dielectric is precipitated. Through a layer of a protective dielectric relative to each photosensitive element, through windows are formed lithographically to the shutter. In conclusion, lithographic conductive tires are made that are in contact with the shutters of the photosensitive elements.

As layers of a dielectric, a gate dielectric, and a protective dielectric, SiO ₂ layers are used with thicknesses of 105 nm, 145 nm, and 209 nm, respectively.

As the material of the conductive film to create the gates using In ₂ O ₃ , which is sprayed with a thickness of 124 nm.

For the manufacture of conductive tires using titanium, sprayed with a layer of a thickness of the order of 0.12 microns.

Claims (8)

1. A method of manufacturing a multi-element photodetector crystal based on MIS structures, which consists in creating a layer on the semiconductor substrate that forms the interface between the substrate and the gate dielectric, and then depositing a layer of the gate dielectric, then creating photosensitive elements by creating gates on the gate dielectric, after what is made of conductive bus, characterized in that before creating a layer forming the interface between the substrate-gate dielectric, on a semiconductor a dielectric layer is applied to the spoon, in which lithographically through holes are formed that define the photosensitive region for each photodetector, after which a layer is formed on the semiconductor substrate in the through windows formed in the dielectric layer, and the surface of the window is formed in the layer dielectric, is set to cover the area of all photosensitive elements of the photodetector crystal, and conductive buses from the gates of the photosensitive elements ntov endure beyond the photosensitive area. 2. The method according to claim 1, characterized in that the InAs wafer is used as the semiconductor substrate. 3. The method according to claim 1, characterized in that the layer forming the substrate-gate dielectric interface is created by anodic oxidation of the substrate in a fluorine-containing electrolyte. 4. The method according to claim 3, characterized in that anodic oxide with a thickness of about 10-15 nm is formed by oxidation. 5. The method according to claim 1, characterized in that the formation of photosensitive elements by creating gates on the gate dielectric is carried out by applying a photoresist to the gate dielectric layer and performing photolithography, forming through windows in the photoresist, placing them in the field area of the layer forming the interface gate-dielectric substrate, after the formation of through windows in the photoresist with an area equal to the area of the photosensitive element, gates are created in the windows in the photoresist by spraying a conductive film and further, the photoresist is removed and a protective dielectric layer is deposited, wherein with respect to each pad photosensitive member lithographically created through until the gate window, in conclusion lithographically produced conductive tire contacting the gate electrodes of the photosensitive elements. 6. The method according to claim 1 or 5, characterized in that as layers of a dielectric, a gate dielectric and a protective dielectric, SiO ₂ layers are used with thicknesses, respectively, from 95 to 105 nm; from 135 to 155 nm; from 200 to 220 nm. 7. The method according to claim 5, characterized in that In ₂ O _{3 is} used as a gate material with a thickness of 120 to 130 nm. 8. The method according to claim 1 or 5, characterized in that for the manufacture of conductive tires using titanium, with a layer thickness of from 0.1 to 0.15 microns.

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