JPS5963719A - Semiconductor device - Google Patents

Abstract

PURPOSE:To contrive to reduce the substrate component of a series resistor and the reverse recovery time by forming a recess in a low resistant semiconductor substrate and burying a metal into this recess. CONSTITUTION:Recesses are selectively formed on the other surface side of the low specific resistant substrate 1 provided with a high resistant semiconductor layer 2 on one surface. Next, contact metals 5 are vapor-deposited in these recesses, and the metal 4 is buried in these recesses. Then, an electrode layer 3 is vapor-deposited. Thereby, the substrate component of the series resistor and the reverse recovery time can be remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a semiconductor device, and more particularly to a semiconductor device in which a high resistivity layer is formed on a low resistivity substrate.

Conventional configurations and their problems In general, in semiconductor devices in which a high resistivity layer is formed on a low resistivity substrate, the low resistivity layer substrate is simply used to hold the high resistivity layer, and the semiconductor device It is unnecessary from the top of the operation. Conventionally, the entire low resistivity substrate was made uniformly thin to lower the resistance.

The cross-sectional structure of this conventional example is shown in FIG. In FIG. 1, 1 is a low resistivity substrate, 2 is a low resistivity layer, and 3 is a metal for ohmic contact. This structure is essential for reducing the high frequency series resistance rs value, for example in a band switch diode for U/V switching. However, in order to make the entire low resistivity substrate 1 uniformly thin, the semiconductor sea urchin...
- There is an upper limit for processing, and in semiconductor devices such as the above band switch diode, the reverse recovery time t determined by rs
There were still some areas where the values of rr etc. were still sufficiently reduced.

Purpose of the Invention The present invention eliminates the above-mentioned drawbacks, and makes it possible to reduce the series resistance by partially reducing the thickness of the low resistivity board, which is equivalent to the conventional one, and by filling these parts with metal. .

Structure of the Invention The semiconductor device of the present invention has a high resistivity substrate on one side of a low resistivity substrate, and a metal layer is embedded in a recess selectively formed on the other side of the low resistivity substrate. ``!!It's a semiconductor device.

DESCRIPTION OF THE EMBODIMENTS FIG. 2 is a cross-sectional view of a band switch diode pellet according to an embodiment of the present invention.

In the figure, the same numbers as in FIG. 1 indicate the same parts, 4 is a metal embedded in the recess of the low resistivity substrate 1, and 6 is an ohmic metal in the recess.

Specifically, in this semiconductor device, 1 is a silicon single crystal substrate doped with antimony and has a resistivity of 0.009 to 0, and a thickness of about 18Ω, and 2 is a silicon single crystal substrate doped with phosphorus and has a resistivity of 8 to 18Ω. The epitaxial silicon layer is 12Ω·C1rt and has a thickness of about 571η2. The size of the silicone pellet is O-357m:X:0.3
6ff1W. First, usual diffusion and electrode formation of a band switch diode are performed on the front side of a silicon substrate. Thereafter, the back side of the substrate 1 is uniformly thinned by etching as usual. From then on, using a positive photoresist and using this resist as a mask, the substrate 1 was selectively etched, for example, as shown in the hatched areas 4 in FIG. 3, using a well-known lift-off photolithography method. do. At this time, the etching depth is set so that the thickness of the etched region of the low resistivity substrate 1 is depressed by 30 to 60% in depth compared to the remaining region that has not been etched. It's warm. Furthermore, the resist remains in its casing,
Gold or AuSb@alloy 5 is deposited as a contact metal to a thickness of about 0.1 μm by sputter deposition. Then, only the recesses formed by the above etching are filled with nickel plating as the metal 4. At this time, care must be taken because if there are too many plating areas, curved portions of nickel may occur or Paris may become noticeable, making lift-off in the next process difficult. Nickel plating is performed so that the back surface of the wafer is flat. Thereafter, the resist is completely removed by a lift-off method. Then, AuSb y or the like is deposited as an electrode layer 3 on the back side of the sea urchin by vacuum deposition.

The cross-sectional structure of the band switch diode manufactured in this way is shown in FIG.

In the configuration shown in FIGS. 2 and 3, the thickness of the low resistivity substrate 1 is reduced by 41 area by A1, and the thickness is R' and the area is A.
′, the resistance of the low resistivity substrate when the back side is not processed is R1, and the resistance when the back side is processed is R′, then, since l/(1′>1, R′/R(1).

The low resistivity substrate 1 is, for example, A'/A = o, s
, l/l'=2 and n, R'/R=F-0,67
With T, it is possible to reduce the resistance by about 23 inches.

The series resistance r of the diode manufactured according to the previous example
The B value was determined by high frequency measurement in a reverse bias state. In order to eliminate the series resistance component of the epitaxial layer, a reverse bias was applied, and the high frequency resistance and capacitance -Ffi were determined at the time when the tip of the depletion layer reached the low resistance substrate. This high frequency resistance value was regarded as a low resistance substrate component of the series resistance rS.

FIG. 4 shows the distribution of resistance component values plotted against etching depth. In addition, etching 11. The structure is the same as the embodiment shown in FIGS. 2 and 3 except for the depth. Approximately 0.1 in case of substrate thickness 120/7772 with zero etching amount
After etching Ω and this by 60 μm, it becomes approximately o・0.
After etching by 7Ω, 70p and m, it is approximately 0.0.
An rg value substrate component of 6Ω was obtained.

In addition, the reverse recovery time trr value is 351S when the etching amount is zero, and 3Qn after etching by 60 μm.
It was reduced to S. Note that when etching is performed further than 70 μ772, the distribution widens and the silicon substrate becomes thinner.
The processing yield will decrease. Further, the resistance of the ohmic contact is a value that can be ignored compared to the value indicated by -F.

Effects of the Invention As described above, the present invention is achieved by forming a recess in a low resistance semiconductor substrate, plating these four parts with nickel, and making the thickness of these four parts 40 to 70% thinner than other areas. - The substrate component of the series resistor r5 and the reverse recovery time trr can be significantly improved, and this has immediate practical effects.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a pellet of a conventional semiconductor device, Fig. 2 is a cross-sectional view of a semiconductor pellet according to an embodiment of the present invention, and Fig. 3 is a pattern shape in which a low-resistance substrate on the back side of the semiconductor pellet is partially thinned. 4 are diagrams showing the relationship between the series resistance r3 and the etching depth of the diode according to the embodiment of the present invention. 1...Low resistance semiconductor substrate, 2...High resistance semiconductor layer, 3, 5...Metal for ohmic contact, 4...Metal.

Claims (1)

[Claims] A high resistivity layer is provided on one surface of the low resistivity substrate, four parts are selectively formed on the other surface of the low resistivity substrate, and metal is embedded in the recessed portions. Characteristic semiconductor devices.