JPS5848920A - Preparation of semiconductor device - Google Patents

Abstract

PURPOSE:To simplify the groove forming process by selectively providing the etching mask material on the surface of semiconductor base material, forming the mask by removing the mask material after irradiating the laser beam to the groove forming area and etching said mask. CONSTITUTION:The both sides of semiconductor base material 41 having completed the diffusion is covered with the oxide film 42 and it is removed and simultaneously the groove 16 is formed by irradiating the laser beam to the groove forming area. Thereafter, the groove 45 is formed by etching process using the mixed acidic solution of the fluoric acid + nitric acid + acetic acid, thereby uneven surface of affected layer generated by irradiation of laser beam and pattern edges can be removed. Succeedingly, when the groove surface is covered with the insulating layer, the specified rejection characteristic can be obtained. According to this method, the groove can be selectively formed only with two processes, attaining reduction in cost.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, which includes a step of forming a groove in a semiconductor substrate.

In semiconductor devices, particularly high voltage semiconductor devices, grooves are formed in the main surface of a semiconductor substrate on which a pn junction is formed.

A widely used method is to expose a pn junction within the trench and then deposit an insulating film on the surface of the trench. Although this structure has the advantage that a higher withstand voltage can be easily obtained than the planar structure, it requires an extra step of forming the grooves. Generally, the method shown in FIG. 1 is widely used to form grooves. (
a) An oxide film 2 is formed on the amphibodi surface of the semiconductor substrate 1. This step is usually performed simultaneously with diffusion. (b) A photoresist 3 is applied to the surface of the oxide film 2 and prebaked. (C
-) Perform exposure and development to remove the photoresist at one location 4 where a groove is to be formed. Next, post-baking is performed.

(d) The oxide film 2 is selectively removed by immersing it in a solution containing hydrofluoric acid as a main component and using the photoresist 3 as a mask.

(e) immersed in a mixed acid consisting of hydrofluoric acid, nitric acid, and lead acid;
Using the photoresist 3 and the oxide film 2 as a mask, the semiconductor substrate 1 is etched to form a deep trench 5 beyond the pn junction.

As described above, the conventional trench forming method requires many steps and has the problem that the cost of the semiconductor device is high.

An object of the present invention is to provide a method for manufacturing a semiconductor device that simplifies the trench forming process.

In the present invention, after a material serving as an etching mask is formed on the surface of a semiconductor substrate, a laser beam is irradiated to a location where a groove is to be formed, and the etching mask material at that location is removed. When forming deep trenches, it is preferable to also remove a portion of the semiconductor body under the etch mask material.

Next, etching is performed using the A-shaped etching mask material as a mask to form grooves. In this case, if a deteriorated layer caused by the laser beam irradiation remains, the leakage current of the semiconductor device will be large and the withstand voltage will be low. FIG. 2 shows the two-sorting time after laser beam irradiation and the current-voltage characteristics of the semiconductor device. Song JA has an etching time of 0 seconds, B has an etching time of 5 seconds.
seconds, C is data for 30 seconds, and D is data for 60 seconds. When the etching time is short, there is a lot of leakage current and the waveform is so-called soft, but as the etching time increases, the leakage current decreases, and good characteristics are obtained when the etching time is longer than 60 seconds. In this case, the altered layer caused by laser beam irradiation has been completely removed. In addition, since the laser is a pulse, the edges of the laser irradiation pattern are uneven as shown in Figure 3 (a), and the grooves have such unevenness, especially acute-angled protrusions as circled in the figure. If there is, the electric field will concentrate in that area and the withstand voltage will drop.

Furthermore, it has been empirically confirmed that when the radius of curvature of the convex portion is 300 μm or less, the breakdown voltage decreases.

If this material is etched for an appropriate time, the unevenness will be eliminated by side etching, and the desired withstand pressure will be obtained. Therefore, it is necessary to perform etching after laser irradiation until the laser irradiation-altered layer is eliminated and the irregularities with a small radius of curvature that would affect the breakdown voltage are eliminated.

Next, an example in which the present invention is applied to forming grooves in a diode will be described with reference to FIG. (a) shows a semiconductor substrate 41 that has been completely diffused. The amphibian surface of the semiconductor substrate 41 is covered with an oxide film 42 formed in a diffusion process. (G) Laser light is irradiated onto the portion where the groove is to be formed to remove the oxide film 42 and form a groove 4σ with a depth of 30 μm. (C) Hydrofluoric acid, nitric acid.

Etching is performed for 120 seconds using a mixed acid with a lead acid capacity ratio of 5:8:5 to form a groove 45 with a depth of 80 μm. This etching removes the altered layer and unevenness at the edge of the pattern caused by laser irradiation. Thereafter, the groove surface is coated with an insulating film to obtain a predetermined blocking characteristic.

As described above, according to the present invention, grooves can be selectively formed in just two steps, thereby reducing the cost of groove formation.

In the above embodiment, an oxide film is used as the etching mask material, but any material such as nitride/recon, phosphor glass, alumina, oxygen-doped polycrystalline silicon, tantalum oxide, etc. may be used.

According to the present invention, the number of steps is small and simple, so that grooves can be formed at low cost.

[Brief explanation of the drawing]

FIG. 1 is a process diagram explaining the conventional 14 forming method, FIG. 2 is a current-voltage characteristic diagram of a semiconductor device explaining the present invention, and FIG.
The figure is a plan view of the groove, and FIG. 4 is a process diagram illustrating the groove forming method according to the present invention. 41... Semiconductor base, 42... Oxide film, 45...
groove. Kudzu 1m 82m /l /L(r)

Claims (1)

[Claims] 1. In a method for forming grooves on the main surface of a semiconductor substrate,
A process of forming an etching mask material in advance on a selected surface of a semiconductor substrate, a process of irradiating a laser beam to the location where a groove is to be formed and removing at least the etching mask material, and a process of removing at least the etching mask material using the etching mask material as a mask. 1. A method of manufacturing a semiconductor device, comprising the step of selectively etching to form a groove in a selected main surface of a semiconductor substrate. 2. A semiconductor device according to claim 1, wherein the etching is carried out for a sufficient time to remove at least the altered layer caused by laser beam irradiation and at the same time eliminate the unevenness of the groove pattern. manufacturing method.