JPS6089981A - Impatt diode - Google Patents

Abstract

PURPOSE:To prevent the manufacturing yield from decreasing in an IMPATT diode formed in a mesa structure by coating the surface of a substrate formed when chemical etching is performed from a contact layer side with a metal film. CONSTITUTION:The substrate side of an Si epitaxial wafer on which an N<-> type operation layer 2 and a P<+> type contact layer 3 are sequentially formed on an N<+> type Si is cut by mechanical or chemical etching, and circular electrodes 4, 4' made of multilayer structure of Ti-Pt-Au are formed on both side surfaces. Then, with the electrode 4 of the layer 3 side as a mask a mesa structure is formed at the junction by chemical etching, and a gold film 5 is then deposited on the mesa side. This gold film is formed on the electrode 4 and the substrate 1, but becomes a shade at the P-N junction in which the electrode 4 is projected from the mesa, and the gold film is not formed on the portion. After the gold film 5 is then cut, with the electrode 4' from the substrate 1 side as a mask the substrate is cut by chemical etching to obtain a pellet.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention mainly relates to a pellet structure of an invat diode operated in a millimeter wave band.

Traditionally, in-butt diodes have required low thermal resistance to improve oscillation characteristics and reliability, and are assembled in a so-called upside-down structure in which the P-N junction is close to the heat sink side of the package. It is being Therefore, in order to facilitate its assembly, a pellet structure is also used as shown in FIG.
The structure has electrode metal layers 4, 4' made of a Ti--Pt--Au multilayer structure with excellent heat resistance at both ends of a disk-shaped silicon chip made of the P3 contact layer 3.

Figure 2 shows the method for producing the above pellets, and shows the method for producing the pellets.
+ A shrimp wafer in which an N- operation layer 2 and a P1 contact layer 3 were sequentially formed on a silicon substrate 1 was ground to a thickness of about 50 μm, and a circular electrode 4 having a multilayer structure of ':['1-Pt-Au was formed on both sides. .4' are formed facing each other (Fig. 2(a)). Next, using the electrode 4 on the P-N junction side as a mask, a mesa portion is formed by chemical etching (in Fig. 2).
Finally, the substrate is cut into individual pellets by chemical etching using the electrode 4' on the substrate side as a mask (FIG. 2(C)).

Figure 3 is a general structural diagram of an invat diode, in which a pellet 11 is thermocompression bonded to the pedestal 12 of the package in an upside-down method, and a gold tape 13 for electrode is thermocompression bonded to the pellet 11 and the flange 14 of the package. death,
Finally, the cap 15 is sealed to complete the assembly.

Now, the high-frequency current generated when the invat diode is in operation flows vertically through the pellet, but when the operating frequency reaches the millimeter wave region, the current begins to flow along the surface of the pellet substrate due to the skin effect. As a result, the resistance of the silicon substrate cannot be ignored. This has a great negative effect on the high frequency output characteristics. On the other hand, by making the silicon substrate thinner, it is possible to reduce the resistance of the silicon substrate, but even so, the thickness of about 50 μm is the limit for 1L.
If the wafer was made thinner than this, wafer cracking would occur during pellet production, resulting in a significant decrease in yield.

An object of the present invention is to provide an invat diode with excellent oscillation operation characteristics without reducing the production yield of an invat diode pellet that operates mainly in the millimeter wave band.

The in-bat diode of the present invention is manufactured by forming an electrode metal layer on both sides of a silicon wafer in which an active layer and a contact layer are sequentially formed on a silicon substrate, and then forming this metal layer into a predetermined pattern.

It has a silicon chip formed by cutting a silicon shrimp wafer into a mesa structure and cutting the substrate using chemical etching from both the contact layer side and the substrate side. It is characterized in that the surface of the substrate formed by etching is covered with a highly conductive metal film.

Next, the present invention will be explained using several examples.

FIG. 4 shows a method for manufacturing an in-vat diode pellet according to the present invention. First, an N- active layer 2 and a P+ contact layer 3 are placed on a N-silicon substrate 1 with a thickness of about 300 μm.
The substrate side of the silicon shrimp wafer on which the wafers were sequentially formed was ground to a thickness of about 50 μm using mechanical etching or chemical etching, and circular electrodes made of a multilayer structure of 'Pi-Pt-Au were formed on both sides. 4.4' are formed facing each other (Fig. 4(a)). Next, using the electrode 4 on the contact layer 3 side as a mask, a mesa structure is formed at the junction by chemical etching (see Fig. 4), and then a gold film 5 is deposited on the mesa side (
Figure 4(C)). This gold film is formed on the electrode 4 and the silicon substrate, but since the electrode 4 protrudes from the mesa portion, the P-N junction is not in the shadow and no gold film is formed on that part. Next, after cutting the gold film 5 on the silicon substrate using mechanical or chemical etching (FIG. 4(d)),
By cutting the substrate from the silicon substrate side by chemical etching using the stain electrode 4' as a mask and separating it into individual pieces, the desired pellet can be manufactured (FIG. 4(e)).

According to the present invention, even if the high-frequency current that flows through the pellet during operation of the invat diode flows on the surface of the pellet due to the skin effect, the silicon substrate is partially covered with a gold film that is a good conductor. The resistance component is reduced and the loss is accordingly reduced, resulting in excellent oscillation output characteristics. Furthermore, from the perspective of pellet manufacturing, in the past, in-butt diodes used in the mid-IJ wave region were made to have a thickness of about 15 μm in order to prevent characteristic deterioration; On the other hand, sea urchin/S-cracks occurred frequently and the yield decreased significantly, but according to the present invention, it is possible to prevent the decrease in manufacturing yield because it can be processed while keeping the thickness thicker than before. There are advantages.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional pellet, and Figures 2 (a) to (
C) is a cross-sectional view of each process showing the conventional pellet manufacturing method, Figure 3 is the structure of the in-butt diode, and Figure 4 (a)
-(e) are cross-sectional views of each process based on the manufacturing method of a pellet according to an embodiment of the present invention. 1... Silicon substrate, 2... Operating layer,
3...Contact layer, 4.4'...T
i-P t-Au multilayer metal film, 5...gold coating, 11...invat diode pellet,
12...Pedestal of the package. 13...Gold tape 514...Package flange 6-ji, 15...Cap. -7- Atsushi / Figure ＾ Gonor thing 3 Figure

Claims (1)

[Claims] A metal layer for electrodes is attached to both sides of a wafer on which an active layer and a contact layer are sequentially formed on a silicon substrate, and after forming the metal layer into a predetermined shape, chemical treatment is applied from both the contact layer side and the substrate side. In an in-bat diode formed into a mesa structure using an etching method, the substrate surface created when chemical etching is applied from the contact layer side is covered with a metal film. Invat diode.