JP2007158287A - Schottky barrier diode and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent stepped cut of a metal by inhibiting formation of a protruding form right under a resist to improve adhesiveness between a surface protective film and a metal film. <P>SOLUTION: By making the surface protective film 3 have a laminate structure of insulators in which etching rates get higher in sequence from an epitaxial layer 2 side, the etching rate of the insulator in the region right under a resist film, where the protruding form is easy to when an opening part 4 is formed, becomes the highest, so that formation of the protruding form right under the resist is inhibited and adhesiveness between the surface protective film 3 and the metal film 5 is improved to prevent stepped cut of the metal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a Schottky barrier diode in which an electrode is formed in an opening of a surface protective film via a metal film, and a method for manufacturing the Schottky barrier diode.

  As a conventional Schottky barrier diode manufacturing method, a first conductive type epitaxial layer is formed on a first conductive type semiconductor substrate, a protective film is formed on the surface of the epitaxial layer, and an epitaxial layer is formed on the surface protective film. There was a method of forming a reaching opening (for example, see Patent Document 1).

  Hereinafter, a conventional Schottky barrier diode will be described with reference to FIGS.

  FIG. 5 is a cross-sectional view showing a conventional Schottky barrier diode, FIG. 6 is a cross-sectional view for explaining a conventional method for manufacturing a Schottky barrier diode, and FIGS. 6 (a) to 6 (d) show the manufacturing method. Process sectional drawing along a process flow, Drawing 6 (e) is the B section enlarged view of Drawing 6 (c).

  In FIG. 5, in the conventional Schottky barrier diode, an epitaxial layer 102 is formed on a first main surface of a highly doped N-type semiconductor substrate 101, and a silicon oxide film 103a and a PSG (PSG) are formed on the surface of the epitaxial layer 102. A surface protective film 103 made of a phosphosilicate glass (103) film 103b is formed, and an opening 104 reaching the epitaxial layer 102 is formed in the surface protective film 103. At least on the opening 104 and on the surface protective film 103 in the peripheral portion thereof The patterned metal film 105 is formed, and the electrode 106 is formed on the metal film 105 and on the second main surface of the N-type semiconductor substrate 101.

As shown in FIGS. 6A to 6E, a conventional Schottky barrier diode manufacturing method is first performed by vapor phase growth on the first main surface of a highly doped N-type semiconductor substrate 101. An epitaxial layer 102 is formed (FIG. 6A). Next, a silicon oxide film 103a is formed on the surface of the epitaxial layer 102 using a thermal oxidation method, and a PSG (Phosphorus Silicon Glass) film 103b is formed on the silicon oxide film 103a using a CVD (Chemical Vapor Deposition) method. Thereby, the surface protective film 103 is formed (FIG. 6B). A resist film 107 patterned by photolithography is formed on the surface protective film 103, and an opening 104 of the surface protective film 103 reaching the epitaxial layer 102 is formed by etching using the resist film 107 as a mask (FIG. 6C). )). Next, patterning is formed on the opening 104 and the surface protective film 103 in the periphery thereof, and a metal film 105 is formed by a CVD method (FIG. 6D). Finally, an electrode 106 is formed on the metal film 105 and on the second main surface of the N-type semiconductor substrate 101 using the CVD method.
JP 2003-347540 A

  However, in the conventional configuration, a resist film 107 patterned by photolithography is formed on the surface protective film 103, and the opening 104 of the surface protective film 103 reaching the epitaxial layer 102 is etched using the resist film 107 for masking. Therefore, in the vicinity of the resist film 107, as shown in FIG. 6E, a region that cannot be uniformly etched is generated because the etching reaches the lower part of the resist film 107, and the surface protective film 103 is formed. There is a problem that the protrusion shape 108 is generated in part. In addition, the protrusion shape 108 affects the adhesion with the metal film 106, and the metal is disconnected due to a decrease in coverage.

  The Schottky barrier diode and the manufacturing method of the Schottky barrier diode of the present invention solve the above-mentioned conventional problems, suppress the formation of the protrusion shape immediately below the resist, and adhere to the surface protective film and the metal film. The purpose is to prevent breakage of the metal by increasing the height.

  In order to achieve the above object, a Schottky barrier diode according to the present invention includes an epitaxial layer formed on a first main surface of a semiconductor substrate, a surface protective film formed on the surface of the epitaxial layer, and the surface. An opening reaching the epitaxial layer formed in the protective film, at least a metal film formed in the opening, and an electrode formed on the metal film and on the second main surface of the semiconductor substrate; The surface protective film is made of at least three layers of insulators whose etching rate increases in order from the epitaxial layer side.

  The method for manufacturing a Schottky barrier diode according to the present invention includes a step of forming an epitaxial layer on a first main surface of a semiconductor substrate, and an etching rate increasing at least 3 in order from the epitaxial layer side to the surface of the epitaxial layer. A step of forming a surface protection film made of a layer insulator, a step of forming an opening reaching the epitaxial layer in the surface protection film, a step of forming a metal film at least in the opening, and on the metal film And forming an electrode on the second main surface of the semiconductor substrate.

  As described above, the formation of the protrusion shape immediately below the resist can be suppressed, the adhesion between the surface protective film and the metal film can be improved, and the disconnection of the metal can be prevented.

  The Schottky barrier diode and the manufacturing method of the Schottky barrier diode according to the present invention have a structure in which an opening is formed by forming a surface protection film in an insulating laminated structure in which an etching rate is increased in order from the epitaxial layer side. The etching rate of the insulator directly under the resist film where the protrusion shape is easily formed becomes the fastest, so the formation of the protrusion shape immediately below the resist is suppressed, and the adhesion between the surface protective film and the metal film is improved to prevent the metal from being cut off. Can be prevented.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a sectional view showing a Schottky barrier diode according to Embodiment 1 of the present invention.

  In FIG. 1, an epitaxial layer 2 is formed on a first main surface of a semiconductor substrate 1 of a first conductivity type doped at a high concentration, and a silicon oxide film 3a and a first PSG (Phospho Silicate) are formed on the surface of the epitaxial layer 2. (Glass) film 3b and second PSG film 3c are formed, and surface protection film 3 is formed with opening 4 (see FIG. 2C showing the manufacturing process) reaching epitaxial layer 2. Then, a patterned metal film 5 is formed on at least the opening 4 and the surface protective film 3 in the periphery thereof, and an electrode 6 is formed on the metal film 5 and the second main surface of the semiconductor substrate 1.

  At this time, the surface protective film 3 is selected and formed in the order of the silicon oxide film 3a, the first PSG film 3b, and the second PSG film 3c so as to increase the etching rate.

  In this way, by forming the surface protective film 3 in an insulating laminated structure in which the etching rate increases in order from the epitaxial layer 2 side, a resist film 7 (manufactured easily in the form of a protrusion when the opening 4 is formed) (See FIG. 2 (c) showing the process) Since the etching rate of the insulator in the region immediately below becomes the fastest, the etching residue of the protective film 3 does not occur in the opening 4, and a protrusion-shaped portion is formed in the vicinity of the resist film 7. Since there is no continuous taper shape, the adhesion between the surface protective film 3 and the metal film 5 can be improved to prevent the metal from being disconnected.

  Here, as the two types of PSG films formed on the silicon oxide film 3a, two layers of PSG films having different concentrations (for example, 4 mol and 7 mol) may be formed.

  Although the case where the surface protection film 3 has a three-layer structure has been described, the etching rate increases in order from the epitaxial layer 2 side, and the insulating film having the highest etching rate is formed in a region where the protrusion shape is most likely to occur. A laminated structure of three or more layers may be used.

  FIG. 2 is a cross-sectional view for explaining a Schottky barrier diode manufacturing method according to Embodiment 1 of the present invention, and FIGS. 2 (a) to 2 (d) show the process flow of the Schottky barrier diode manufacturing method. FIG. 2E is an enlarged view of a portion A in FIG. 2C.

  2A to 2E, first, a thin film crystal is grown on the first main surface of the first conductivity type semiconductor substrate 1 to form an epitaxial layer 2 (FIG. 2A).

  Next, a silicon oxide film 3a is formed on the surface of the epitaxial layer 2 by a thermal oxidation method, a first PSG film 3b is formed on the surface of the silicon oxide film 3a by a CVD method, and a surface of the PSG film 3b is formed by a CVD method. A second PSG film 3c is formed, and a surface protective film 3 composed of a silicon oxide film 3a, a first PSG film 3b, and a second PSG film 3c is formed (FIG. 2B).

  Next, a resist film 7 patterned by a photolithography technique is formed on the surface protective film 3, and an opening 4 of the surface protective film 3 reaching the epitaxial layer 2 is formed by etching using the resist film 7 as a mask ( FIG. 2 (c)).

  At this time, the surface protective film 3 is configured such that the etching rate increases in the order of the silicon oxide film 3a, the PSG film 3b, and the high-concentration PSG film 3c by thermal oxidation. For example, there is a method of forming two types of PSG films (for example, 4 mol and 7 mol) 3b and 3c having different concentrations on the silicon oxide film 3a.

  In this way, the surface protective film 3 is made of an insulating laminated structure in which the etching rate is increased in order from the epitaxial layer 2 side, and the opening 4 is formed by etching, so that the region immediately below the resist film 7 where the protrusion shape can be easily formed. As shown in FIG. 2E, the etching residue of the protective film 3 is not generated in the opening 4 and the projection film is not continuously formed in the vicinity of the resist film 7 as shown in FIG. Because of the tapered shape, the adhesion between the surface protective film 3 and the metal film 5 can be improved to prevent metal breakage.

  Next, patterning (not shown) is formed on at least the opening 4 and the surface protective film 3 including the peripheral portion, the metal film 5 is formed by the CVD method, and the metal film 5 and the second of the semiconductor substrate 1 are formed. An electrode 6 is formed on the main surface by CVD (FIG. 2D).

(Embodiment 2)
FIG. 3 is a sectional view showing a Schottky barrier diode according to the second embodiment of the present invention.

  In FIG. 3, the same components as those in FIGS. An epitaxial layer 2 is formed on the first main surface of the first conductivity type semiconductor substrate 1 doped at a high concentration, and a surface comprising the silicon oxide film 3a, the PSG film 3b, and the silicon nitride film 3d is formed on the surface of the epitaxial layer 2. A protective film 3 is formed, and an opening 4 (see FIG. 4 (c) showing a manufacturing process) reaching the epitaxial layer 2 is formed in the surface protective film 3, and at least the opening 4 and the surface protective film around the opening 4 A patterned metal film 5 is formed on 3, and an electrode 6 is formed on the metal film 5 and on the second main surface of the semiconductor substrate 1.

  At this time, the surface protective film 3 is formed by selecting the silicon oxide film 3a, the PSG film 3b, and the silicon nitride film 3c in order of increasing the etching rate.

  In this way, by forming the surface protective film 3 in an insulating laminated structure in which the etching rate increases in order from the epitaxial layer 2 side, a resist film 7 (manufactured easily in the form of a protrusion when the opening 4 is formed) (See FIG. 4 (c) showing the process) Since the etching rate of the insulator in the region immediately below becomes the fastest, the etching residue of the protective film 3 does not occur in the opening 4, and a protrusion-like shape is formed in the vicinity of the resist film 7 Since there is no continuous taper shape, the adhesion between the surface protective film 3 and the metal film 5 can be improved to prevent the metal from being disconnected.

  Further, by forming the silicon nitride film 3d on the outermost surface layer of the surface protective film 3, even when the electrode 6 formed on the metal film 5 is formed of aluminum, the PSG film 3b and aluminum are not in direct contact with each other. Corrosion of aluminum can be prevented.

  FIG. 4 is a cross-sectional view illustrating a method for manufacturing a Schottky barrier diode according to the second embodiment of the present invention, and FIGS. 4A to 4D are Schottky barrier diodes according to the second embodiment of the present invention. It is process sectional drawing along the process flow of this manufacturing method.

  4A to 4D, first, a thin film crystal is grown on the first main surface of the first conductivity type semiconductor substrate 1 to form an epitaxial layer 2 (FIG. 4A).

  Next, a silicon oxide film 3a is formed on the surface of the epitaxial layer 2 by thermal oxidation, a PSG film 3b is formed on the surface of the silicon oxide film 3a by CVD, and LPCVD (Low Pressure CVD) is formed on the surface of the PSG film 3b. A silicon nitride film 3d is formed by the method, and a surface protective film 3 composed of the silicon oxide film 3a, the PSG film 3b, and the silicon nitride film 3d is formed (FIG. 4B).

  Next, a resist film 7 patterned by a photolithography technique is formed on the surface protective film 3, and an opening 4 of the surface protective film 3 reaching the epitaxial layer 2 is formed by etching using the resist film 7 as a mask ( FIG. 4 (c)).

  At this time, the surface protection film 3 is configured such that the etching rate increases in the order of the silicon oxide film 3a, the PSG film 3b, and the silicon nitride film 3d by thermal oxidation.

  Thus, by forming the opening 3 by etching with the surface protective film 3 having an insulating laminated structure in which the etching rate becomes higher in order from the epitaxial layer 2 side, a region immediately below the resist film 7 where the protrusion shape can be easily formed. Since the etching rate of the insulator is the fastest, the etching residue of the protective film 3 does not occur in the opening 4, and the surface protective film has a continuous tapered shape with no protrusions in the vicinity of the resist film 7. 3 and the metal film 5 can be improved to prevent metal breakage.

  Next, patterning (not shown) is formed on at least the opening 4 and the surface protective film 3 including the peripheral portion, the metal film 5 is formed by the CVD method, and the metal film 5 and the second of the semiconductor substrate 1 are formed. The electrode 6 is formed on the main surface using the CVD method (FIG. 4D).

  In order to prevent the formation of the protrusion shape immediately below the resist by making the oxide film into three layers, a method of forming two types of PSG films having different concentrations on the silicon oxide film by the thermal oxidation method described above. Not only, but also a method of forming a PSG film (for example, 7 mol) after forming an NSG (nonphosphosilicate glass) film on a silicon oxide film by a thermal oxidation method, or a PSG on a silicon oxide film by a thermal oxidation method. After forming a film (for example, 4 moles) and annealing, and further forming a PSG film (for example, 4 moles) having the same concentration and performing annealing, three or more oxide films having different etching rates are used. As long as it is a method to form, it can change suitably, unless it deviates from the thought of this invention.

  The present invention suppresses the formation of the protrusion shape immediately below the resist, improves the adhesion between the surface protective film and the metal film, and prevents metal disconnection. The metal protective film is interposed in the opening of the surface protective film. This is useful for a Schottky barrier diode for forming an electrode and a method for manufacturing the Schottky barrier diode.

Sectional drawing which shows the Schottky barrier diode in Embodiment 1 of this invention Sectional drawing explaining the manufacturing method of the Schottky barrier diode in Embodiment 1 of this invention Sectional drawing which shows the Schottky barrier diode in Embodiment 2 of this invention Sectional drawing explaining the manufacturing method of the Schottky barrier diode in Embodiment 2 of this invention Sectional view showing a conventional Schottky barrier diode Sectional drawing explaining the manufacturing method of the conventional Schottky barrier diode

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Epitaxial layer 3a Silicon oxide film 3b PSG film 3c PSG film 3d Silicon nitride film 3 Surface protective film 4 Opening part 5 Metal film 6 Electrode 7 Resist film

Claims (4)

An epitaxial layer formed on the first main surface of the semiconductor substrate;
A surface protective film formed on the surface of the epitaxial layer;
An opening reaching the epitaxial layer formed in the surface protective film;
A metal film formed at least in the opening;
An electrode formed on the metal film and on the second main surface of the semiconductor substrate;
The Schottky barrier diode is characterized in that the surface protective film is made of at least three layers of insulators whose etching rate increases in order from the epitaxial layer side.   2. The surface protection film includes an insulator in which an oxide film is stacked on at least the epitaxial layer, a PSG film on the oxide film, and a nitride film on the PSG film in this order. Schottky barrier diode. Forming an epitaxial layer on the first main surface of the semiconductor substrate;
Forming on the surface of the epitaxial layer a surface protective film made of at least three layers of insulators whose etching rate increases in order from the epitaxial layer side;
Forming an opening reaching the epitaxial layer in the surface protective film;
Forming a metal film at least in the opening;
And a step of forming an electrode on the metal film and on the second main surface of the semiconductor substrate. The surface protective film forming step includes a step of forming an insulator in which at least an oxide film on the epitaxial layer, a PSG film on the oxide film, and a nitride film on the PSG film are sequentially stacked. A method for manufacturing a Schottky barrier diode according to claim 3.

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