JPH06120338A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a high breakdown voltage without deterioration of a passivation film in proximity to the bottom of trenches by removing the film through laser beam irradiation and cutting the area near the trench bottom by means of a dicing saw. CONSTITUTION:This method is for manufacturing a mesa diode. A p-type region 33 is formed on one surface of an n-type silicon substrate 30 by p-type impurity diffusion. Trenches 36 are formed in a grid pattern, and a passivation glass film 37 is deposited on the inner face of the trenches 36. The passivation glass film 37 is removed from the area in proximity to the bottom of the trenches 36 using a laser beam 45. The silicon substrate 30 is cut at the portion of the removal by means of a dicing saw 40. This prevents a dicing saw 40 from coming into contact with a passivation glass film 37 during the cutting of a silicon substrate 30, eliminating cracking in the film 37.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device such as a diode or a transistor having a mesa structure which is used when high withstand voltage is required, such as a rectifier for high power. .

[0002]

2. Description of the Related Art Conventionally, a rectifying element for high power uses a diode having a high breakdown voltage and having a mesa structure (hereinafter referred to as "mesa type diode"). An example of the structure of this mesa type diode is shown in FIG. Figure 2
In, the mesa portion 2 is formed on the one surface side of the N ⁻ type semiconductor substrate 1. A P-type region 3 in which P-type impurities are diffused is formed near the top surface of the mesa portion 2, and an anode electrode 5 is provided on the surface thereof. On the other hand, on the other surface side of the N ⁻ type semiconductor substrate 1, an N ⁺ type region 4 in which N type impurities are diffused at a high concentration is formed, and a cathode electrode 6 is provided on the surface thereof. The N ⁺ type region 4 is for obtaining ohmic contact. On the inclined surface 2a of the mesa portion 2, a glass-fired passivation glass film 7 is deposited mainly for the purpose of improving the withstand voltage of the PN junction portion against a reverse bias.

The manufacturing process of the mesa type diode as described above is shown in FIG. First, in FIG. 3 (a), N
N-type impurities are diffused in high concentration from the front surface and the back surface of the ⁻ type semiconductor substrate 1, and N ⁺ type regions 8 and 4 are formed. Then, as shown in FIG. 3B, the N ⁺ type region 8 is sliced and removed. Then, as shown in FIG. 3 (c), P-type impurities are diffused from the surface of the N ⁻ type semiconductor substrate 1 which has appeared by removing the N ⁺ type region 8 to form the P type region 3. It

Next, as shown in FIG. 3 (d), a resist 9 is provided as a mask for forming the mesa portion 2, and as shown in FIG. 3 (e), the grooves 10 are formed into a lattice by etching. It is formed. The portion surrounded by the groove 10 becomes the mesa portion 2. The groove 10 has a substantially semicircular cross section, and a passivation glass film 7 is deposited inside the groove 10 so as to cover the PN junction, as shown in FIG. 3 (f). Then, as shown in FIG. 3 (g), the anode electrode 5 is formed on the surface of the P-type region 3, and the cathode electrode 6 is formed on the surface of the N ⁺ -type region 4.
Each is formed by a vacuum deposition method or the like.

Next, as shown in FIG. 3 (h), the N ^-- type semiconductor substrate 1 is cut by a dicing saw 11 at the bottom 12 of the groove 10 to which the passivation glass film 7 is deposited. As a result, the mesa diode shown in FIG. 2 is obtained.

[0006]

Since the glass-fired passivation glass film 7 is a hard and brittle film, if it is directly cut with the dicing saw 11 as described above, cracks are likely to occur. Therefore, there is a problem that the breakdown voltage is deteriorated when a reverse bias is applied and a leak failure occurs.

For example, when the passivation glass film 7 is well formed, the change in the current I with respect to the voltage V between the cathode and the anode is as shown by the curve L1 in FIG. However, if cracks occur in the passivation glass film 7, the voltage-current characteristics between the cathode and the anode become characteristics like curves L2 and L3. That is, the breakdown voltage V _BD becomes smaller when the reverse bias is applied. Therefore, the withstand voltage against the reverse bias is lowered, and the leak failure is increased.

Therefore, an object of the present invention is to provide a manufacturing method capable of obtaining a semiconductor device having a high breakdown voltage without deteriorating a passivation film covering a mesa portion.

[0009]

In order to achieve the above object, a method of manufacturing a semiconductor device according to the present invention comprises a passivation film for covering the PN junction on an inclined surface of a mesa-shaped portion having a PN junction. A method of manufacturing a semiconductor device, the method comprising: forming a PN junction in a semiconductor substrate; and etching a surface of the semiconductor substrate to form a groove deeper than the PN junction in order to form the mesa-shaped portion. Step, a step of depositing a passivation film on the wall surface of the groove, a step of removing the passivation film near the bottom of the groove by irradiating a laser beam, and a dicing saw near the bottom of the groove of the semiconductor substrate And a step of cutting.

[0010]

According to the above manufacturing method, the passivation film near the bottom of the groove is irradiated with the laser beam to be removed, and the semiconductor substrate is cut from the removed portion with a dicing saw. Therefore, the semiconductor substrate can be cut without the dicing saw touching the passivation film.
Therefore, no crack is generated in the passivation film. Therefore, a high breakdown voltage semiconductor device can be obtained.

[0011]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. 1A to 1D are sectional views showing a method of manufacturing a mesa type diode according to an embodiment of the present invention in the order of steps. First, as shown in FIG. 1A, N-type impurities (for example, phosphorus) are diffused at high concentrations from the front surface 30a and the back surface 30b of the N ⁻ type silicon substrate 30, respectively, and N ⁺
Mold regions 31 and 32 are formed. The N ⁺ type region 32 is for obtaining ohmic contact between the cathode electrode described later and the substrate 30.

Thereafter, as shown in FIG. 1B, the N ⁺ type region 31 is sliced and removed by the polishing method.
Then, as shown in FIG. 1C, a P-type impurity (for example, boron) is diffused from the surface 30c of the substrate 30 which appears by removing the N ⁺ -type region 31 to form a P-type region 33. To be done. As a result, a PN junction is formed.

Next, as shown in FIG. 1 (d), the resist 3
5 are patterned. The resist 35 is formed with a lattice-shaped window 35a. Next, as shown in FIG. 1 (e), the substrate 30 is etched by etching with hydrofluoric nitric acid (HF, HNO ₃ ) or the like using the resist 35 as a mask. By this etching, the grid-shaped grooves 36 are formed on the substrate 30. The groove 36 is formed deeper than the PN junction portion, and its cross section has a substantially semicircular shape. The portion surrounded by the groove 36 becomes the mesa portion 34.

Next, as shown in FIG. 1 (f), the P-type region 3
A passivation glass film 37 having a film thickness of about 20 to 30 μm is formed so as to cover the surface of No. 3 and the inner wall surface of the groove 36. To form the passivation glass film 37, for example, a method of dissolving powdered low melting point glass in a mixed liquid of ethyl acetate and isopropyl alcohol, applying the solution on the surface of the substrate 30 and sintering the solution is adopted.

Then, as shown in FIG. 1 (g), the passivation glass film 37 in the other region is mechanically cut by, for example, a cylindrical blade so that the passivation glass film 37 remains only on the inner wall surface of the groove 36. It By thus forming the passivation glass film 37 on the inner wall surface of the groove 36, contact of the PN junction with the outside air can be prevented.

A conductive metal such as aluminum (Al) is vacuum-deposited on the surface of the P-type region 33 from which the passivation glass film 37 has been removed, whereby an anode electrode 38 is formed. In addition, a metal such as aluminum is vacuum-deposited on the surface of the N ⁺ type region 32 to form the cathode electrode 3.
9 is formed. Next, as shown in FIG. 1H, the passivation glass film 37 near the bottom of the groove 36 is removed by the laser beam 45. At this time, the width w of the passivation glass film 37 to be removed is about 80 μm, for example. The width w may be set sufficiently large so that the dicing saw 40 described later does not come into contact with the passivation glass film 37 which has not been removed.

Next, as shown in FIG. 1 (i), the dicing saw 40 is removed from the portion removed by the laser beam 45.
Thus, the substrate 30 is cut along the line 46. The width of the dicing saw 40 is, for example, about 40 μm.
That is, since this width is smaller than the width w (about 80 μm) of the passivation glass film 37 removed by the laser beam 45, the dicing saw 40 does not touch the passivation glass film 37 when the substrate 30 is cut. Therefore, the passivation glass film 37 is not cracked.

As described above, in the mesa diode manufacturing method of this embodiment, the passivation glass film 37 is removed by the irradiation of the laser beam 45 near the bottom of the groove 36 for forming the mesa portion 34. Then, the substrate 30 is cut from the removed portion with the dicing saw 40, and the mesa type diode is manufactured. Therefore, in the present embodiment, the dicing saw 40 cuts only the substrate 30 in contrast to the conventional technique in which the passivation glass film and the substrate are directly cut by the dicing saw to manufacture the mesa type diode. Never touch. Therefore,
No cracks or the like occur in the passivation glass film 37 that covers the PN junction. As a result, a high breakdown voltage mesa diode can be manufactured.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, although the above-mentioned embodiment has explained the mesa type diode, the present invention can be widely applied to the semiconductor device having the above mesa structure such as a power transistor and a thyristor. In addition, various design changes can be made without changing the gist of the present invention.

[0020]

As described above, according to the semiconductor device manufacturing method of the present invention, the semiconductor substrate can be cut without the dicing saw coming into contact with the passivation film. Therefore, a crack or the like does not occur in the passivation film, so that a high breakdown voltage semiconductor device can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method of manufacturing a mesa diode according to an embodiment of the present invention in the order of steps.

FIG. 2 is a cross-sectional view showing the structure of a mesa diode.

FIG. 3 is a cross-sectional view showing a method of manufacturing a conventional mesa diode in the order of steps.

FIG. 4 is a characteristic diagram showing voltage-current characteristics of a mesa diode.

[Explanation of symbols]

30 N ⁻ type silicon substrate 33 P type region 34 mesa section 36 groove 40 dicing saw 45 laser beam

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H01L 21/316 G 7352-4M 29/06 21/329

Claims (1)

[Claims] 1. A method of manufacturing a semiconductor device having a passivation film for covering the PN junction on an inclined surface of a mesa-shaped portion having a PN junction, the method comprising: forming a PN junction on a semiconductor substrate; Etching the surface of the semiconductor substrate to form a groove deeper than the PN junction in order to form the mesa-shaped portion; depositing a passivation film on the wall surface of the groove; A method of manufacturing a semiconductor device, comprising: a step of irradiating a laser beam to remove a passivation film near a bottom portion; and a step of cutting the bottom portion of the groove of the semiconductor substrate with a dicing saw.