JP5880839B2 - Method for manufacturing trench diode - Google Patents

Description

  The present invention relates to a trench diode having a high aspect ratio trench formed in a direction substantially perpendicular to a silicon substrate and a method for manufacturing the same, and in particular, a near red having a wavelength of 1100 nm or less that can be directly detected by a silicon semiconductor device. The present invention relates to a trench diode capable of efficiently collecting charges such as electrons and holes generated by external light and a method for manufacturing the same.

  Conventionally, semiconductor image sensors such as CCD and CMOS imagers used in video cameras and digital cameras are inexpensive and low power consumption image sensors for converting optical signals of captured images into electrical signals. As widely used. Many of them are aimed at realizing image detection characteristics similar to those of the human eye, and are mainly made of silicon semiconductors in order to make sensing such as visible light highly sensitive and efficient.

  On the other hand, silicon solar cells are expected to be a green energy source because they can convert light energy into electric energy with high efficiency, and are being installed in various places. In the internal photoelectric effect that can convert an optical signal (optical energy) into an electrical signal (electric energy) with high efficiency, the wavelength of light that can be converted is determined by the band gap of the semiconductor. A wavelength range (400 nm to 1100 nm) can be detected (converted).

  By the way, since near infrared rays have a wavelength longer than that of visible light, the absorption coefficient in the silicon semiconductor is small, so that the penetration length into the semiconductor substrate ranges from several tens of μm to several hundreds of μm. It is the depletion layer region of the PN junction that can efficiently collect charges such as electrons and holes generated by the internal photoelectric effect. Charge generated by the internal photoelectric effect inside the semiconductor substrate is carried to the depletion layer region by diffusion, but when the distance to the depletion layer region is long, it recombines and disappears before reaching the depletion layer region. Therefore, it is impossible to efficiently collect charges generated by near infrared absorption. Therefore, in order to increase the near-infrared light receiving sensitivity and energy conversion efficiency, a pn junction is formed deeply inside the substrate substantially parallel to the incident direction of light, that is, in a direction substantially perpendicular to the light receiving surface of the substrate surface. A trench diode has been proposed in which a pn junction is formed along the inner wall of a trench to be formed.

JP 2010-219089 A

  However, in such a conventional trench diode, since the electrode manufactured by the planar technology which is the conventional LSI manufacturing technology exists on the substrate surface, the charges generated in the deep part of the substrate move through the diffusion layer having high resistance. However, due to the high resistance in this diffusion layer, the charges generated in the deep part of the substrate cannot be efficiently collected by transporting to the electrode, and the near-infrared light receiving sensitivity In addition, there is a problem that the energy conversion efficiency cannot be improved.

  Accordingly, the present invention provides a trench diode that can efficiently collect charges generated in the deep part of a semiconductor substrate with an electrode, and can greatly improve near-infrared light receiving sensitivity and energy conversion efficiency, and a method for manufacturing the same. The purpose is to do.

  According to the present invention for solving the above-described problems, a light receiving surface is formed on a surface of a semiconductor substrate, and a part of the light receiving surface is formed as an opening and extends into the substrate in a direction substantially perpendicular to the light receiving surface. A trench diode in which a trench is formed and a pn junction is formed on the inner wall side of the trench along the inner wall of the substrate, the light beam from the light receiving surface being applied to substantially the entire inner wall of the trench. A low-resistance film or a metal film that collects the charges generated therein through the pn junction is formed. In the present invention, the low resistance film means a film made of a material having conductivity or low resistance which can be an electrode or a wiring.

  In the method of manufacturing a trench diode according to the present invention, an electrode that collects charges generated in the substrate by light from the light receiving surface through the pn junction may be formed on substantially the entire inner wall of the trench and the surface of the substrate. And a step of forming a low resistance film or metal film having a thickness of about 100 nm or more for forming a wiring.

  In addition, the method of manufacturing a trench diode according to the present invention may include a step of etching the low resistance film or metal film on the substrate surface after the low resistance film or metal film is formed on substantially the entire inner wall of the trench and the substrate surface. And a step of applying a photoresist having a viscosity of about 10 Pa · s or more to the opening of the trench and its periphery to close the opening of the trench.

  Further, in the method of manufacturing a trench diode according to the present invention, the low resistance film or the metal film on the substrate surface is removed by vertical etching, except for the portion connected to the low resistance film or the metal film on the inner wall of the trench. And connecting the low-resistance film or metal film on the light-receiving surface that has not been removed in the vertical etching process by isotropic etching with the low-resistance film or metal film on the inner wall of the trench therein It is desirable to include a step of removing except for a necessary part.

  In the method of manufacturing a trench diode according to the present invention, after the low resistance film or metal film is formed on substantially the entire inner wall of the trench and the substrate surface, the low resistance film or metal film on the substrate surface is etched. Before, a step of applying a photoresist having a viscosity of about 10 Pa · s or more to the opening of the trench and its periphery to cover the opening of the trench, and a vertical etching, a low resistance film on the surface of the substrate or The step of removing the metal film except for the portion of the inner wall of the trench that is connected to the low resistance film or the metal film, and the low on the light receiving surface not removed in the vertical etching step by isotropic etching. Removing a resistance film or a metal film except a portion necessary for connection with a low resistance film or a metal film of the inner wall of the trench therein. Desirable.

  Further, in the method of manufacturing a trench diode according to the present invention, the trench has an opening having a diameter of about 10 μm or less and an aspect ratio of about 5 or more, and the vertical etching is performed by RIE (Reactive Ion Etching), Isotropic etching is desirably performed using a solution containing phosphoric acid.

  In the trench diode according to the present invention, a low-resistance film or a metal film for collecting charges generated in the substrate by light from the light receiving surface through the pn junction is formed on substantially the entire inner wall of the trench. Therefore, the charge generated in the depletion layer region of the pn junction or reaching the depletion layer region is collected very efficiently by the low resistance film or metal film formed in the vicinity of the depletion layer region. (On the other hand, conventionally, since the electrode is formed on the substrate surface and the distance between the depletion layer region and the electrode is long, the electrode is generated in the depletion layer region of the pn junction or reaches the depletion layer region. The collected charges disappeared by being recombined before being carried to the electrodes on the substrate surface, and thus the charges could not be collected efficiently). Therefore, according to the present invention, charges generated in the deep part of the semiconductor substrate can be efficiently collected by the electrodes, and the near-infrared light receiving sensitivity and energy conversion efficiency of the trench diode can be greatly improved.

  In the method of manufacturing a trench diode according to the present invention, a low resistance film or metal film having a thickness of about 100 nm or more is formed on substantially the entire inner wall of the trench and the surface of the substrate. The effect that the electrode which collects the electric charge generated in the substrate by light through the pn junction and the wiring on the surface of the substrate can be formed simultaneously is obtained.

  In the method for manufacturing a trench diode according to the present invention, a low resistance film or a metal film is formed on substantially the entire inner wall of the trench and the surface of the substrate, and then the low resistance film or the metal film on the surface of the substrate is etched. Since a photoresist having a viscosity of about 10 Pa · s or more is applied on and around the opening of the trench to cover and close the opening of the trench, the low resistance film or metal film on the substrate surface is etched. In this case, it is possible to effectively prevent the low resistance film or metal film on the inner wall of the trench from being etched. Therefore, according to the present invention, a low resistance film or a metal film can be formed on substantially the entire inner wall of the trench to collect charges generated inside the substrate with high efficiency. Sensitivity and energy conversion efficiency can be greatly improved.

  Further, in the method of manufacturing a trench diode according to the present invention, after a low resistance film or a metal film is formed on substantially the entire inner wall of the trench and the surface of the substrate (and the viscosity is about about the opening of the trench and the periphery thereof). After applying a photoresist of 10 Pa · s or more to close the opening of the trench, the low resistance film or metal film on the substrate surface is formed by vertical etching into the low resistance film or metal on the inner wall of the trench. The low resistance film or metal film on the light-receiving surface that is not removed in the vertical etching is removed by isotropic etching after removing the portion connected to the film, and the low resistance film on the inner wall of the trench therein Alternatively, since it is removed except for a portion necessary for connection to the metal film, the etching is performed when the low resistance film or the metal film on the substrate surface is etched. It is possible to effectively prevent the up low resistance film or the metal film Ji inner wall etches. Therefore, according to the present invention, while forming a low resistance film or a metal film (electrode) on substantially the entire inner wall of the trench, a portion covered with the low resistance film or metal film (wiring) on the light receiving surface is minimized. Since the light receiving area can be secured widely by suppressing, the near-infrared light receiving sensitivity and energy conversion efficiency of the trench diode can be greatly improved.

  In particular, the method of forming the electrodes and wirings of the trench diode employed in the present invention is a manufacturing method having a high affinity with the silicon integrated circuit manufacturing, so that the signal processing circuit and the light receiving portion can be manufactured on the same substrate. It becomes easy. Therefore, according to the present invention, for example, a vehicle-mounted near-infrared sensor, a high-sensitivity dark place monitoring sensor, and the like that require high-speed response can be provided at a relatively low cost.

It is sectional drawing which shows the trench diode suitable for the highly efficient light reception by embodiment of this invention. It is an electron micrograph of a substrate cross section showing a state when an Al film is formed on the inner wall of a high aspect ratio trench and the substrate surface in the method according to the present embodiment. It is an electron micrograph of the substrate cross section which shows the state which coat | covered the opening part of the trench with the high viscosity photoresist before the etching process in the method which concerns on this embodiment. 4 is an electron micrograph of a substrate plane showing a state in which a wiring (Al film) with an Al film on the inner wall of a trench is formed on the substrate surface by etching in the method according to the present embodiment. It is a schematic diagram for demonstrating the method to form Al film in the trench inner wall and board | substrate surface in the method which concerns on this embodiment, the upper side is the fragmentary top view of a board | substrate, and the lower side is the sectional drawing.

  In order to increase the sensitivity of a near-infrared image sensor using a silicon semiconductor and increase the conversion efficiency of a solar cell, the present inventor, that is, a charge generated inside a semiconductor substrate and reaching a depletion layer region of a pn junction. The present invention has been devised on the assumption that it is necessary to produce a low-resistance film or a metal film as wide as possible in the vicinity of the inner wall of the trench diode in order to collect them efficiently with electrodes. In order to improve the charge collection efficiency of the trench diode, the inventor prevents the near-infrared light from entering the semiconductor substrate from the light receiving surface on the substrate surface so that the wiring layer on the substrate surface does not hinder it. The present invention has been devised in view of the necessity (to ensure a wide effective light receiving area).

  FIG. 1 shows a trench diode suitable for high-efficiency reception of near-infrared light devised from such a viewpoint, in particular, a trench diode having a high aspect ratio trench with an opening of several μm and an aspect ratio of 5 to 10 or more. It is sectional drawing which shows an example typically. In FIG. 1, 1 is a p-type silicon substrate, 2 is a silicon oxide film formed on the silicon surface of the substrate 1, 3 is a light-receiving surface disposed on the surface of the substrate 1 (on the silicon oxide film 2), 4 is A substantially hole-shaped or substantially groove-shaped trench 5 is formed so that a part of the light-receiving surface 3 is an opening portion and extends in the substrate 1 from the opening portion in a direction substantially perpendicular to the light-receiving surface 3. An n-type layer (n-type region) formed on the inner part of the trench 4 (around the inner wall) along the inner wall surface of the trench 4 (substantially parallel to the inner wall surface of the trench 4), 6 is the substrate 1 ( a depletion layer formed in the vicinity of a boundary surface of a pn junction formed by the p-type region) and the n-type layer 5; A metal film integrally formed on the film 2), for example, an Al layer. . A light receiving portion (not shown) is formed below the light receiving surface in FIG.

The inventor has devised and developed the following three techniques as a technique for realizing a trench diode capable of efficiently receiving near-infrared light as shown in FIG.
(1) Production of low resistance film or metal film on inner wall of high aspect ratio trench (2) Lithography technology for substrate surface without etching low resistance film or metal film on inner wall of trench (3) Near infrared light is inside silicon Etching technology to form a light-receiving surface that can efficiently penetrate

  Various methods have been devised so far for (1) among the above three techniques. For example, a low resistance polysilicon film by LP-CVD, a W film by MOCVD, a Cu film by plating, and various metal films (Al film, Cu film, etc.) by sputtering. In consideration of the manufacturing cost and the diffusion of the metal film due to heat at the time of film formation, the sputtering method is advantageous. Therefore, in this embodiment, Al atoms or particles are attached and deposited using the sputtering method, and the Al film is obtained. Formed. In the step of forming the Al film, the Al film was integrally formed on both the substantially entire inner wall of the trench and the substrate surface at the same time.

  FIG. 2A shows a substrate in the present embodiment in which a plurality of trenches are formed at a predetermined pitch on a semiconductor substrate, and an Al film is formed on the inner wall and substrate surface of each trench. It is an electron micrograph of a cross section. FIG. 2B is an electron micrograph showing an enlarged Al film formed on the inner wall of the trench. As shown in FIG. 2, in this embodiment, an Al layer is formed over substantially the entire inner wall of the trench as an electrode for collecting charges generated inside the substrate with high efficiency. .

  Regarding (2) in the above three technologies, the following is performed. Photoresist is used for patterning and etching of the metal film. However, when a photoresist having a viscosity of about 1 Pa · s, which is generally used, is used, the photoresist flows down into the trench. When patterning the film, the metal film on the inner wall of the trench is etched together. Therefore, in this embodiment, the substrate surface is applied using a photoresist having a high viscosity of 10 Pa · s or more. In this case, since the opening of the trench is covered and blocked by the surface tension of the photoresist, the inconvenience of etching the metal film on the inner wall of the trench together when patterning the metal film on the substrate surface is avoided. . FIG. 3 is an electron micrograph showing the situation, and shows the result of covering the opening of the trench with a high-viscosity photoresist.

  Regarding (3) in the above three techniques, vertical etching and isotropic etching were combined. That is, first, the Al film on the substrate surface is vertical except for a wiring portion (including a portion covering all or part of the light receiving surface around the trench opening) that connects the Al film on the inner wall of the trench. It was removed by etching. Next, in the AL film on the light-receiving surface that has not been removed by the vertical etching (Al film covering all or part of the light-receiving surface), wiring necessary for connection with the Al film on the inner wall of the trench; Except for this part, it was removed by isotropic etching (especially by lateral etching so as not to etch the Al film on the inner wall of the trench). By combining such vertical etching and isotropic etching, the area of the Al film (wiring) covering the light receiving surface is minimized while forming an Al film (electrode) on substantially the entire inner wall of the trench. Thus, a wide effective light receiving area on the light receiving surface can be secured. FIG. 4 shows a wiring Al film for connecting to the Al film on the inner wall of the trench as described above (a wiring Al film formed to minimize the area occupied on the light receiving surface in order to ensure a large effective light receiving area). ) Is an electron micrograph showing a state in which is formed on the substrate surface.

  FIG. 5 is a schematic diagram showing a method for forming the electrode Al film on the inner wall of the trench and the Al film for wiring on the substrate surface in the present embodiment described above, the upper side is a partial plan view of the substrate, and the lower side is a plan view thereof. It is sectional drawing. In this embodiment, first, as shown in FIG. 5A, Al atoms or particles are deposited and deposited on substantially the entire inner wall of the trench 4 and the surface of the substrate 1 by sputtering, for example, to form an Al film. Form. Next, as shown in FIG. 5B, a part of the surface of the substrate 1 including the opening of the trench 4 and its periphery is applied using a photoresist 11 having a high viscosity of 10 Pa · s or more, The opening of the trench 4 is covered and closed.

  Next, as shown in FIG. 5C, a wiring portion (opening portion of the trench 4) for connecting the Al film 7 on the surface of the substrate 1 to the Al film 7 on the inner wall of the trench 4 by vertical etching by RIE. (Including a portion covering all or a part of the light receiving surface 3 around the periphery). Next, as shown in FIG. 5D, in the AL film 7 (the Al film 7 covering all or part of the light receiving surface 3) on the light receiving surface 3 that has not been removed by the vertical etching, By isotropic etching with a solution containing phosphoric acid except for a portion that becomes a wiring necessary for connection to the Al film 7 on the inner wall of the trench 4 (particularly in order not to etch the Al film on the inner wall of the trench) (This etching also removes the Al film 7 below the photoresist 11 as shown in FIG. 5D). Finally, as shown in FIG. 5E, the photoresist 11 is removed (note that the wiring Al film on the surface of the substrate 1 is not shown in the sectional views of FIG. 5E, etc.). .

  As mentioned above, although each Example of this invention was described, this invention is not limited to what was described as said embodiment, A various correction and change are possible. For example, in the embodiment, the Al film is formed as the electrode on the inner wall of the trench 4 and the wiring on the surface of the substrate 1, but the present invention is not limited to this, for example, a Cu film, an Ag film, etc. May be formed.

  The present invention realizes a trench diode capable of efficiently collecting charges such as electrons and holes generated by near-infrared light having a wavelength of 1100 nm or less that can be directly detected by a silicon semiconductor element. Therefore, it can be used for high-sensitivity near-infrared imaging devices, silicon solar cells, and the like.

1 p-type silicon substrate 2 silicon oxide film 3 light-receiving surface 4 trench 5 n-type layer 6 depletion layer 7 Al film 7a Al wiring film 11 photoresist

Claims (3)

A light receiving surface is formed on the surface of the semiconductor substrate, and a trench extending into the substrate in a direction substantially perpendicular to the light receiving surface with a part of the light receiving surface as an opening is formed on the inner wall side of the trench of the substrate. A pn junction is formed along the inner wall, and for collecting charges generated in the substrate by light from the light receiving surface on the substantially entire surface of the trench inner wall and the substrate surface via the pn junction. A method of manufacturing a trench diode in which a low resistance film or metal film having a thickness of about 100 nm or more serving as an electrode and wiring is formed,
After the low resistance film or metal film is formed on substantially the entire inner wall of the trench and the substrate surface, and before etching the low resistance film or metal film on the substrate surface, in the opening of the trench and its periphery, A method for manufacturing a trench diode, comprising: applying a photoresist having a viscosity of about 10 Pa · s or more to close the opening of the trench. After the step of closing the opening of the trench, the step of removing the low resistance film or metal film on the surface of the substrate by vertical etching, except for the portion connected to the low resistance film or metal film on the inner wall of the trench. When,
A portion of the low resistance film or metal film on the light-receiving surface that has not been removed in the vertical etching process by isotropic etching, which is necessary for connection with the low resistance film or metal film on the inner wall of the trench therein A step of removing,
The method of manufacturing a trench diode according to claim 1, further comprising: The trench has an opening having a diameter of about 10 μm or less and an aspect ratio of about 5 or more, the vertical etching is performed by RIE (Reactive Ion Etching), and the isotropic etching uses a solution containing phosphoric acid. The method for manufacturing a trench diode according to claim 2, wherein the method is performed.