TWI597853B - Shottcky diode structure and method for forming the same - Google Patents

Description

Xiaoji diode structure and its formation method

The present invention relates to a structure of a Schottky diode and a method of forming the same.

Schottky Diode uses Schottky Barrier to form a Schottky Barrier by contacting metal with a semiconductor. Since there are few carriers in the metal, the Schottky diode switches between conduction and non-conduction. The time delay, therefore, the Xiaoji diode is widely used in electronic devices, especially as a switch.

However, because the reverse bias of the Xiaoji diode is lower and the reverse leakage current is larger, and the leakage current is proportional to the temperature, that is, the higher the temperature of the environment in which the Xiaoji diode is operated. At the time, the shortcomings of the Xiaoji diode are more pronounced. Therefore, how to increase the breakdown voltage and reduce the leakage current (Leakage Current) is an inevitable problem when manufacturing the Schottky diode. Moreover, in the semiconductor manufacturing process, the lithography process greatly contributes to the overall manufacturing cost, including the process time cost and the cost of the reticle used in the process, and the conventional manufacturing method of the Schottky diode usually requires four. The reticle can be realized, which causes a significant increase in manufacturing costs.

In view of this, the present invention proposes a structure of a Xiaoji diode and a method of forming the same.

In one embodiment, the Schottky diode structure comprises a semiconductor substrate, an epitaxial layer, a metal layer, and an isolation structure. The semiconductor substrate has a first conductivity type and the semiconductor substrate includes a first upper surface, a side surface, and a second upper surface. Wherein the second upper surface is not coplanar with the first upper surface, and the second upper surface surrounds the first upper surface and is connected to the first upper surface via the side surface. The epitaxial layer has a first conductivity type and the epitaxial layer covers the first upper surface, and the surface of the epitaxial layer forms a guard ring structure having a second conductivity type. The metal layer comprises an upper surface and a lower surface, the lower surface of which covers the epitaxial layer. The isolation structure covers the second upper surface of the semiconductor substrate, the side surface of the semiconductor substrate, the side surface of the epitaxial layer and the side surface of the metal layer, and the isolation structure protrudes from the upper surface of the metal layer.

In an embodiment, the isolation structure covers a portion of the lower surface of the metal layer.

In an embodiment, the isolation structure covers a portion of the upper surface of the metal layer.

In one embodiment, the method for forming a Schottky diode structure includes forming an epitaxial layer on a semiconductor substrate, the epitaxial layer and the semiconductor substrate having a first conductivity type; forming a guard ring structure on the surface of the epitaxial layer The guard ring structure has a second conductivity type; forming a metal layer on the epitaxial layer; forming a trench through the metal layer, the guard ring structure, the epitaxial layer, and extending into the local semiconductor substrate; and filling the isolation material in the trench To form an isolation structure that protrudes from the surface of the metal layer.

In one embodiment, before performing the step of filling the isolation material, the ring structure, the epitaxial layer and the semiconductor substrate in the dry etching trench are further included to partially expose the metal layer toward the surface of the epitaxial layer.

In one embodiment, the step of filling the isolation material in the trench to form the isolation structure comprises covering the isolation material to the surface of the metal layer toward the epitaxial layer.

In one embodiment, the step of filling the isolation material in the trench to form the isolation structure Further comprising covering the isolation material on a partial upper surface of the metal layer.

In summary, according to an embodiment of the Schottky diode structure of the present invention, the isolation structure protrudes from the upper surface of the metal layer, and the isolation structure covers the lower surface of the local metal layer and the upper surface of the metal layer. Therefore, the aforementioned Schottky diode has a small leakage current and a relatively stable breakdown voltage, thereby improving its reliability and antistatic capability and greatly reducing the cost of the mask.

1‧‧‧Xiaoji diode

11‧‧‧Semiconductor substrate

11A‧‧‧First upper surface

11B‧‧‧Second upper surface

11C‧‧‧ lower surface

11D‧‧‧ side surface

11E‧‧‧ side surface

12‧‧‧ epitaxial layer

12A‧‧‧ side surface

12B‧‧‧ upper surface

121‧‧‧Guard ring structure

13‧‧‧First metal layer

131‧‧‧Protruding

13A‧‧‧Upper surface

13B‧‧‧ lower surface

13C‧‧‧ side surface

14‧‧‧Isolation structure

15‧‧‧Oxide layer

15A‧‧‧ Groove

15B‧‧‧ Groove

16‧‧‧ditch

17‧‧‧Second metal layer

18‧‧‧Protective layer

Fig. 1 is a cross-sectional view showing an embodiment of a Schottky diode structure according to the present invention.

FIG. 2 is a cross-sectional view showing an embodiment of the Schottky diode of FIG. 1. FIG.

Fig. 3 is an exploded perspective view (1) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

Fig. 4 is an exploded perspective view (2) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

Fig. 5 is an exploded perspective view (III) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

Fig. 6 is an exploded perspective view (4) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

Fig. 7 is an exploded perspective view (5) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

Fig. 8 is an exploded perspective view (6) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

Fig. 9 is an exploded perspective view (7) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

Fig. 10 is an exploded perspective view (8) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

Fig. 11 is an exploded perspective view (9) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

Fig. 12 is an exploded perspective view (10) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

Fig. 13 is an exploded perspective view (11) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

Fig. 14 is an exploded view (12) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view showing an embodiment of a Schottky diode structure in accordance with the present invention. It should be understood that the ratios in the drawings are merely schematic and the invention is not limited thereto.

Referring to FIG. 1 , a Schottky diode 1 is disclosed, including a semiconductor substrate 11 , an epitaxial layer 12 , and two metal layers (referred to as a first metal layer 13 and a second metal layer 17 for convenience of description) and isolation. (passivation) structure 14. The semiconductor substrate 11 includes two upper surfaces (referred to as a first upper surface 11A and a second upper surface 11B, respectively for convenience of description), a lower surface 11C, and both side surfaces 11D, 11E. Wherein, the second upper surface 11B is not coplanar with the first upper surface 11A, the second upper surface 11B surrounds the first upper surface 11A, and the second upper surface 11B is connected to the first upper surface 11A via the side surface 11D. In other words, the side surface 11E, the second upper surface 11B, the side surface 11D, and the first upper surface The surface 11A forms a mesa structure of the intermediate protrusions. In the present embodiment, the semiconductor substrate 11 has a first conductivity type. For example, the semiconductor substrate 11 may be a heavily doped N-type germanium substrate.

The epitaxial layer 12 covers and contacts the first upper surface 11A of the semiconductor substrate 11, and the upper surface 12B of the epitaxial layer 12 has a guard ring structure 121 for avoiding the Schottky diode and the adjacent Electrical interference between components causes leakage. In this embodiment, the epitaxial layer 12 is homoepitaxial, that is, the epitaxial layer 12 also has a first conductivity type. For example, the material of the epitaxial layer 12 may be a lightly doped N-type. Hey. On the other hand, the grommet structure 121 has a second conductivity type, for example, a P-type, and its concentration is greater than the dopant concentration of the adjacent epitaxial layer 12.

The first metal layer 13 has an upper surface 13A and a lower surface 13B, the lower surface 13B of which contacts and covers the epitaxial layer 12 to form a schottky contact. The second metal layer 17 contacts and covers the lower surface 11C of the semiconductor substrate 11 to form an ohmic contact. The material of the first metal layer 13 and the second metal layer 17 may be any electrically conductive metal such as Ti, Ni, Ag, Al or the like and a combination of the foregoing items. In some embodiments, the first metal layer 13 and the second metal layer 17 may include a barrier region, and the surfaces of the first metal layer 13 and the second metal layer 17 may be coated with a protective layer to improve surface resistance.

The isolation structure 14 contacts and covers the second upper surface 11B of the semiconductor substrate 11, the side surface 11D, the side surface 12A of the epitaxial layer 12, and the side surface 13C of the first metal layer 13. In other words, the isolation structure 14 extends through the first metal layer 13 and the epitaxial layer 12 to the semiconductor substrate 11 to penetrate the local semiconductor substrate 11 , and the isolation structure 14 shields the second upper surface 11B and the side surface 11D of the semiconductor substrate 11 . The side surface 12A of the epitaxial layer 12 and the side surface 13C of the first metal layer 13. Further, the isolation structure 14 protrudes from the extending direction of the semiconductor substrate 11 to the metal layer 13 The upper surface 13A of the first metal layer 13 makes it less likely to pass over the isolation structure 14 when the electrons move on the upper surface 13A to reduce the leakage current effect. The material of the isolation structure 14 may be polyimide (PI). Compared with the conventional Xiaoji diode, the Xiaoji diode 1 has a small leakage current and a relatively stable breakdown voltage, which has better reliability and better performance. Antistatic (ESD) capability. Preferably, the antistatic force is up to 30 kV.

In some embodiments, as shown in FIG. 2, the first metal layer 13 protrudes from the epitaxial layer 12 on both sides of the guard ring structure 121 to form a protrusion 131, that is, the first metal layer 13 A portion of the lower surface 13B is not covered by the epitaxial layer 12 and faces the second upper surface 11B of the semiconductor substrate 11. At this time, the isolation structure 14 contacts and covers the partial lower surface 13B of the first metal layer 13, and the isolation structure 14 contacts and covers the upper surface 13A of the first metal layer 13. Therefore, compared with the isolation structure 14 of FIG. 1, the isolation structure 14 illustrated in FIG. 2 surrounds the protrusion 131 and is engaged with the first metal layer 13, so that the isolation structure 14 can be prevented from falling off due to the force. In turn, the durability of the Xiaoji diode 1 is improved.

3 to 14 are exploded perspective views of an embodiment of a method for forming a Schottky diode according to the present invention. Referring to FIG. 3 to FIG. 14 simultaneously, first, as shown in FIG. 3, a heavily doped semiconductor substrate 11 of the first conductivity type, for example, the aforementioned N+ germanium substrate, is provided. Next, one epitaxial layer 12 of the first conductivity type is formed on the first upper surface 11A of the semiconductor substrate 11 by a conventional epitaxial process, and the doping concentration of the epitaxial layer 12 is smaller than that of the semiconductor substrate 11.

Next, as shown in FIGS. 4 and 5, an oxide layer 15 is formed on the upper surface 12B of the epitaxial layer 12 by a dry or wet oxidation process. And, the oxide layer 15 is patterned by a lithography and etching process to form the two grooves 15A, 15B. As shown in FIG. 5, the partial upper surface 12B of the epitaxial layer 12 is exposed through the two grooves 15A, 15B, so that the area where the guard ring structure 121 is to be formed can be defined. In the present embodiment, the material of the oxide layer 15 may be cerium oxide (SiO ₂ ).

Then, the surface of the epitaxial layer 12 is doped with impurities, such as boron (Boron), by a diffusion method or ion implantation by the two grooves 15A, 15B to be adjacent to the epitaxial layer. The region of the upper surface 12B of 12 forms a guard ring structure 121 having a second conductivity type, as shown in FIG.

Next, as shown in FIG. 7, the oxide layer 15 is completely removed to expose the entire upper surface 12B of the epitaxial layer 12. As shown in FIG. 8, a first metal layer 13 is formed on the upper surface 12B to form a Schottky junction, and a second metal layer 17 is formed on the lower surface 11C of the semiconductor substrate 11 to form an ohmic junction. In some embodiments, the upper surface 12B of the epitaxial layer 12 and the lower surface 11C of the semiconductor substrate 11 are planarized before the first metal layer 13 and the second metal layer 17 are formed, for example, using aqua (aqua) Regia) to the chemical mechanical polishing (CMP) process, and then through the deposition process of chemical vapor deposition (CVD) or physical vapor deposition (PVD) to form the first metal Layer 13 and second metal layer 17. Further, after the first metal layer 13 and the second metal layer 17 are formed, an annealing treatment is performed.

A trench 16 is then formed. As shown in FIG. 10, the trench 16 extends through the first metal layer 13, the guard ring structure 121, and the epitaxial layer 12 to extend into the local semiconductor substrate 11 to expose the second upper surface 11B and the side surface 11D of the semiconductor substrate 11. The side surface 12A of the epitaxial layer 12, the side surface of the guard ring structure 121, and the side surface 13C of the first metal layer 13. Here, the aforementioned platform structure is formed between the two trenches 16. In some embodiments, the trench 16 can be formed by mechanical cutting, for example, The trench 16 is formed along a pre-formed scribe line via a Diamond Blade. Alternatively, the trench 16 may be formed by laser cutting; and before the cutting process is performed, a tape (for example, a blue tape) is attached to the lower surface 11C of the semiconductor substrate 11, and the tape is removed after the trench 16 is formed.

Next, the isolation material may be filled in the trench 16, as shown in FIG. 12, and filled to protrude from the upper surface 13A of the first metal layer 13 to form the isolation structure 14. In this case, the isolation structure 14 contacts and covers the second upper surface 11B of the semiconductor substrate 11, the side surface 11D, the side surface 12A of the epitaxial layer 12, the side surface of the guard ring structure 121, and the side surface of the first metal layer 13. 13C. Further, as described above, in order to increase the durability of the isolation structure 14, as shown in FIG. 11, the trench 16 is subjected to a dry etching process to etch the adjacent guard ring structures on both sides of the trench 16 before filling the isolation material. 121, the surface of the epitaxial layer 12 and the semiconductor substrate 11. Here, the protruding portion 131 of the metal layer 13 is formed, thereby partially exposing the metal layer 13 toward the surface of the epitaxial layer 12 (i.e., the lower surface 13B). In this case, as shown in FIG. 12, the isolation structure 14 more contacts and covers a portion of the lower surface 13B of the metal layer 13. As a result, the durability of the isolation structure 14 is improved.

In some embodiments, the isolation structure 14 can be formed by chemical vapor deposition or physical weather deposition.

In some embodiments, in order to avoid inadvertently destroying the first metal layer 15 during the cutting process, as shown in FIGS. 9 to 12, the protective layer may be coated on the upper surface 13A of the first metal layer 13 before the cutting process is performed. 18. Also, the protective layer 18 is completely removed after the isolation structure 14 is formed. Before the protective layer 18 is removed, as shown in FIG. 12, the isolation structure 14 does not contact the upper surface 13A of the first metal layer 13; after the protective layer 18 is completely removed, as shown in FIG. 13, the isolation structure 14 contacts And covering a portion of the upper surface 13A of the first metal layer 13 to increase the resistance of the isolation structure 14 Use sex.

Finally, as shown in FIG. 14, the semiconductor substrate 11 and the second metal layer 17 are diced along the isolation structure 14 to perform a separation process, thereby forming a plurality of separated Schottky diodes 1. As shown in FIG. 14, after the separation process is performed, a plurality of separated Schottky diodes 1 are formed. Compared with the conventional Xiaoji diode, the Xiaoji diode 1 has a small leakage current and a relatively stable breakdown voltage, thereby improving the reliability and antistatic of the Xiaoji diode 1 . Ability (ESD). Further, in the process of forming the Schottky diode 1 , only the photomask is used for patterning the oxide layer 15 , which requires four masks compared to the conventional method of forming the Schottky diode. Significant savings in mask costs.

In summary, according to an embodiment of the Schottky diode structure of the present invention, the isolation structure protrudes from the upper surface of the metal layer, and the isolation structure covers the lower surface of the local metal layer and the upper surface of the metal layer. Therefore, the aforementioned Schottky diode has a small leakage current and a relatively stable breakdown voltage, thereby improving its reliability and antistatic capability and greatly reducing the cost of the mask.

The present invention has been disclosed in the above embodiments, and it is not intended to limit the present invention. Any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended patent application.

1‧‧‧Xiaoji diode

11‧‧‧Semiconductor substrate

11A‧‧‧First upper surface

11B‧‧‧Second upper surface

11C‧‧‧ lower surface

11D‧‧‧ side surface

11E‧‧‧ side surface

12‧‧‧ epitaxial layer

12A‧‧‧ side surface

12B‧‧‧ upper surface

121‧‧‧Guard ring structure

13‧‧‧First metal layer

131‧‧‧Protruding

13A‧‧‧Upper surface

13B‧‧‧ lower surface

13C‧‧‧ side surface

14‧‧‧Isolation structure

17‧‧‧Second metal layer

Claims (6)

A Schottky diode structure comprising: a semiconductor substrate having a first conductivity type, the semiconductor substrate comprising a first upper surface, a side surface and a second upper surface, the second upper surface and the first The upper surface is not coplanar, the second upper surface surrounds the first upper surface and is connected to the first upper surface via the side surface; an epitaxial layer having the first conductivity type, the epitaxial layer covering the first surface On the upper surface, a surface of the epitaxial layer is formed with a guard ring structure having a second conductivity type; a metal layer including an upper surface, a protrusion and a lower surface, the lower surface covering the epitaxial layer The protrusion protrudes from the epitaxial layer; and an isolation structure covers the second upper surface, the side surface, a side surface of the epitaxial layer and a side surface of the metal layer, and the isolation structure protrudes the metal layer The upper surface, the isolation structure surrounds the protrusion. The Schottky diode structure of claim 1, wherein the isolation structure covers the lower surface of the portion of the metal layer. The Schottky diode structure of claim 1 or 2, wherein the isolation structure covers the upper surface of a portion of the metal layer. A method for forming a Schottky diode structure includes: forming an epitaxial layer on a semiconductor substrate, the epitaxial layer and the semiconductor substrate having a first conductivity type; forming a guard ring structure on a surface of the epitaxial layer The guard ring structure has a second conductivity type; forming a metal layer on the epitaxial layer; Forming a trench extending through the metal layer, the guard ring structure, the epitaxial layer, and extending into the local semiconductor substrate; dry etching the guard ring structure, the epitaxial layer, and the semiconductor substrate in the trench Exposing the metal layer to the surface of the epitaxial layer; and filling the trench to the trench to form an isolation structure that protrudes from the surface of the metal layer. The method for forming a Schottky diode structure according to claim 4, wherein the step of filling the isolation material in the trench to form the isolation structure comprises covering the isolation material on the surface of the metal layer toward the epitaxial layer. The method for forming a Schottky diode structure according to claim 4, wherein the step of filling the isolation material in the trench to form the isolation structure further comprises covering the isolation material on a portion of the upper surface of the metal layer.