JPS592375B2 - Manufacturing method of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of manufacturing a mesa-type semiconductor device having a glass passivation layer.

In mesa type semiconductor devices such as transistors, thyristors, diodes, etc., it is well known that the end portion of a PN junction exposed in a mesa groove is covered and protected with a glass passivation layer.

For example, to explain a mesa diode, in FIG. 1, 1 is a P-type region, 2 is an N-type region, 3 is a PN junction at the boundary between P-type region 1 and N-type region 2, and 4 is a thermal oxide film. 5 is a glass passivation layer covering and protecting the end of the PN junction 3, 6 is a cathode electrode formed in the window hole 4a of the insulating film 4, and 7 is an anode formed in the P-type region 1. It is an electrode. However, in the mesa-type semiconductor device having such a structure, the glass passivation layer 5 was insufficiently formed, resulting in poor characteristics and low reliability.

This is due to the manufacturing method, so below:
The conventional manufacturing method and causes will be explained using FIGS. 2A to 2E. First, as shown in FIG. 2A, a semiconductor substrate 10 having a PN junction 3 in which a P-type region 1 is completely diffused on one side of an N-type silicon substrate 2 is prepared, and an insulating film 4 is formed on the entire surface of the N-type region 2. A photoresist film 11 is formed on the insulating film 4, and exposed and developed to form an opening 11a in the photoresist film 11. Although a wax layer was actually formed on the entire surface of the P-type region 1, this will be omitted below since the explanation will be complicated. Next, as shown in FIG. 2B, the insulating film 4 exposed through the opening Ila of the photoresist film 11 is removed by etching, and then the semiconductor substrate 10 exposed through the opening is etched to remove the PN junction 3.
A mesa groove 12 having a depth exceeding 1 is formed, and the photoresist film 11 is removed. Next, as shown in FIG.
The exposed end face of the PN junction 3 is covered and protected. continue,
As shown in FIG. 2D, an aluminum vapor deposition layer 13 is formed on the entire surface U, and a photoresist film 14 is further laminated, and exposed and developed to form the cathode electrode 3 and the portion where the electrode 6 is to be formed. The photoresist film 14 is left only on.
Next, as shown in FIG. 2E, the exposed aluminum deposited layer 13 is removed by etching, and the photoresist film 14 is removed, thereby forming a cathode electrode 6 in a predetermined pattern. Thereafter, an anode electrode 7 is formed on the P-type region 1, and the anode electrode 7 is cut and separated from the position indicated by the dashed line shown in the figure, thereby obtaining a mesa diode as shown in FIG. Said Figure 2C
When forming the glass passivation layer 5, the glass passivation layer 5 tends to be thicker at the bottom of the mesa groove 12 and thinner at the side closer to the main surface.

If the glass passivation layer 5 at the bottom becomes too thick, it will become difficult to cut and separate the material later, so if the glass passivation layer 5 at the bottom of the mesa groove 12 is made to have an appropriate thickness,
The thickness of the glass passivation layer 5 near the main surface may be insufficient. Further, the aluminum vapor deposited layer 13 shown in FIG. 2D is also thick at the bottom of the glass passivation layer 5 and tends to be thin at the shoulder of the insulating film 4.

Therefore, when etching the aluminum evaporated layer 13, the thin shoulder portion is removed first, and when the thick bottom portion is removed, the glass passivation film 5 may also be etched. As a result, the vibration effect becomes insufficient, resulting in deterioration of characteristics and lower reliability. Therefore, as shown in FIG. 3, the applicant provided a shallow step 24 that does not reach the PN junction 3 around the mesa groove with a depth exceeding the PN junction 3, so that the glass passivation layer 5 is sufficiently deep. We have proposed a semiconductor device that can be formed to a certain thickness.

This type of semiconductor device is illustrated in FIGS. 4A to 4G, for example.
It is manufactured through the manufacturing process shown below.

That is, first, as shown in FIG. 4A, P type regions 1, N
A semiconductor substrate 10 having a type region 2 and a PN junction 3 is prepared, an insulating film 4 is formed on the entire surface of the N-type region 2, and the insulating film 4 is
A photoresist film 15 is formed thereon, and an opening 1 with a width larger than the width of the mesa groove to be formed by exposure and development is formed.
5a is formed. Next, as shown in FIG. 4B, the opening 1
The insulating film 4 exposed from the insulating film 5a is removed by etching, and the semiconductor substrate 10 exposed from the opening of the insulating film 4 is further etched to form a shallow step 16 in the PN junction 3), and the photoresist film 15 is removed. Next, a photoresist film 17 is formed again on the entire surface, exposed and developed, and as shown in FIG.
As shown in FIG. 1, an opening 17a smaller than the width of the step 16 is formed on the step 16. Then, as shown in FIG. 4D, the semiconductor substrate 10 exposed from the opening 17a is etched to form a mesa groove 18 with a depth exceeding the PN junction 3.
Photoresist film 17 is removed. Next, as shown in FIG.
A glass passivation layer 5 is formed by applying glass powder to the substrate and heating and sintering it. At this time, since the shallow step 16 is formed around the mesa groove 18, the glass passivation layer 5 is formed to have a sufficient thickness. After this, Figure 4 F
As shown in FIG. 2, an aluminum vapor deposition layer 19 is formed on the entire surface, a photoresist film 20 is formed, and the photoresist film 20 is left only on the portion where the cathode electrode 6 is to be formed by exposure and development. Subsequently, the aluminum vapor deposited layer 19 that is not covered with the photoresist film 20 is etched away, and when the photoresist film 20 is removed, the cathode electrode 6 is formed as shown in FIG. 1
An anode electrode 7 is formed on the substrate, and the semiconductor device as shown in FIG. 3 is obtained by cutting and separating from the position indicated by the dashed dot line in the figure. According to such a manufacturing method, the above-mentioned problems are eliminated, but in order to form the shallow step 16 and the mesa groove 18, the formation, alignment, exposure, and development of the photoresist films 17 and 20 are required, respectively. It is troublesome as it requires complicated processes. In addition, the photoresist films 15 and 17 are generally prone to pinholes due to scratches on the glass mask, dust, etc., and if there are pinholes in the photoresist film 15, the photoresist films 15 and 17 will be damaged during etching of the insulating film 4. The insulating film 4 below the resist film 15 is easily etched and pinholes are easily formed. If there is a pinhole in an undesired part of the insulating film 4, the undesired part of the semiconductor substrate 10 will be etched 7 when the step 16 is formed later, and the undesired part will be etched when the mesa groove 18 is formed. In some cases, the process progressed to reach the PN junction 3. Therefore, the main object of the present invention is to provide a method for easily manufacturing a semiconductor device having the structure shown in FIG.

In summary, the present invention involves forming a wax layer with a smaller area than the insulating film on an insulating film having an opening, and first forming a mesa groove with a depth exceeding the PN junction using the insulating film and the wax layer as a mask. Then, using the wax layer as a mask, the insulating film protruding from the wax layer is etched away, and then a shallow step that does not reach the PN junction is formed around the mesa groove.

The above objects and other objects and features of the present invention will become more apparent from the following detailed description taken in conjunction with the drawings.

First, as shown in FIG. 5A, P type region 1, N type region 2
} and a semiconductor substrate 10 having a PN junction 3 is prepared,
An insulating film 4 is formed on the entire surface of the type 1 region 2, and a photoresist film 21 having an opening 21a is formed on the insulating film 4.

Next, as shown in FIG. 5B, the insulating film 4 exposed through the opening 21a of the photoresist film 21 is removed by etching. A wax layer 22 is formed. Thereafter, as shown in FIG. 5C, the semiconductor substrate 10 is etched using the wax layer 22 and the insulating film 4 as a mask to form a mesa groove 23 with a depth exceeding the PN junction 3. At this time, even if there is a pinhole in the center of the insulating film 4, the desired portion will not be etched because the wax layer 22 covers it. Next, as shown in FIG. 5D, the wax layer 22
Using as a mask, the insulating film 4 protruding from the wax layer 22 is etched away, and then the area around the exposed mesa groove 23 is etched to form a PN around the mesa groove 23.
A shallow step 24 is formed that does not reach the junction 3, and the wax layer 22 is removed. Thereafter, as shown in FIG. 5E, a glass passivation layer 5 is formed on the mesa groove 23 and the steps 24 around it. Next, as shown in FIG. 5F, an aluminium-deposited layer 25 is formed on the entire surface, a photoresist film 26 is formed thereon, and only the portion where the cathode electrode 6 is to be formed is exposed and developed. A photoresist film 26 is left behind. Subsequently, as shown in FIG. 5G, the exposed aluminum deposited layer 25 is etched and the photoresist film 26 is removed, thereby forming the cathode electrode 6. Finally, an anode electrode 7 is formed in the P-type region 1, and the semiconductor device as shown in FIG. 6 is obtained by cutting and separating from the position indicated by the dashed line shown in the figure. According to the manufacturing method of the present invention, as shown in FIGS. 5B to 5D, the insulating film 4
A wax layer 22 having a smaller area than this insulating film 4 is formed on top of the insulating film 4, and using the wax layer 22, shallow steps 24 are formed around the periphery.
The mesa groove 23 having a deep mesa groove 23 can be formed much more easily than using the conventional photoresist film 17, and since the deep mesa groove 23 is formed with the insulating film 4 covered with the wax layer 22, the insulating film 4 When the undesired portion is etched by the pinhole, it is effective in eliminating scratches.

Note that although the above embodiments have been explained using diodes, they can be similarly implemented using transistors, thyristors, and the like.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a conventional glass passivation type diode, FIG. FIGS. 4A to 4G are vertical cross-sectional views of a glass passipation type diode, which are the premise of the present invention, and FIG.
5G to 5G are longitudinal sectional views of a semiconductor substrate at each step of the method of the present invention. 3...PN junction, 4...insulating film, 5...
...Glass passivation layer, 10...
Semiconductor substrate, 21, 26... Photoresist film, 22... Wax layer, 23... Mesa groove, 24... Step portion, 25... ...Aluminum vapor deposited layer.

Claims (1)

[Claims] 1. Forming an insulator having an opening on the main surface of the semiconductor substrate, forming a wax layer having a smaller area than the insulating film on this insulating film, and etching the semiconductor substrate exposed from the opening in the insulating film. forming a mesa groove, and removing the insulating film protruding from the wax layer;
A step of etching the main surface of the semiconductor substrate after removing the insulating film to form a step shallower than the mesa groove around the mesa trench, and a step of forming a passivation film in the mesa trench and the shallow step around the mesa trench. A method for manufacturing a semiconductor device, comprising: