EA026882B1 - Schottky diode - Google Patents

Abstract

The invention is related to electronic engineering, in particular, to design of a chip of powerful Schottky diodes, and can be used, e.g., as rectifiers in products of power electronics. The present invention is based on the task of reduction of reverse current in a Schottky diode and a decrease in specific rhenium consumption. The essence of the invention is that in a Schottky diode comprising a highly-doped silicon substrate of n-type conductivity with an oxidated, lightly doped epitaxial layer of the same conductivity type and a guard ring of p-type conductivity forming a p-n junction, a window opened in silicon oxide, a 0.05-0.5 μm recess made in the window, a Schottky diode barrier layer and a contact electrode, the Schottky diode barrier layer consists of two layers: the lower layer is made of rhenium having a thickness of 5.0 to 15.0 nm, and the upper layer is formed of molybdenum 100 to 300 nm thick.

Description

The invention relates to electronic equipment, and more specifically to the design of a crystal of powerful Schottky diodes, and can be used, for example, as rectifiers in power electronics products.

Known Schottky diode [1], containing a heavily doped silicon substrate of η-type conductivity with a formed lightly doped epitaxial layer of the same type of conductivity, on the surface of which contains a film of silicon oxide, a window opened in silicon oxide, a Schottky electrode barrier layer in the window and adjacent to the window silicon oxide surface.

However, due to the lack of a guard ring, the Schottky diodes of this design are characterized by high edge reverse currents around the periphery of the Schottky electrode at the reverse bias of the diode, which causes a low percentage of the output of suitable Schottky diodes.

Known Schottky diode [2], containing a heavily doped silicon substrate of η-type conductivity with the formed oxidized lightly doped epitaxial layer of the same type of conductivity and a guard ring of the opposite type of conductivity, forming a p-η junction, an open window in the oxide, a Schottky barrier layer of molybdenum to a window made with a gap with respect to silicon oxide above the guard ring, and a contact electrode.

The presence of a guard ring allows you to reduce the level of reverse current due to the elimination of edge currents. However, the barrier layer of a molybdenum Schottky electrode is characterized by a relatively high level of reverse current.

The closest technical solution to the proposed device is the Schottky diode [3], which contains a heavily doped η-type silicon substrate with a formed oxidized lightly doped epitaxial layer of the same conductivity type and a p-type conductivity guard ring forming a p-η junction exposed in silicon oxide a window, a recess formed in the window, a barrier layer of a Schottky electrode of a molybdenum-rhenium alloy with a rhenium content of 250 wt.

In this device, the presence of rhenium in the barrier layer increases the height of the Schottky barrier and reduces the reverse current of the Schottky diode. However, reducing the reverse current of the Schottky diode is not enough and this is achieved by increasing the specific consumption of rhenium.

The present invention is based on the task of reducing the reverse current of a Schottky diode and reducing the specific consumption of rhenium.

The essence of the invention lies in the fact that in a Schottky diode containing a highly doped silicon substrate of η-type conductivity with a formed oxidized lightly doped epitaxial layer of the same type of conductivity and a protective ring of p-type conductivity, forming a p-η junction, a window formed in silicon oxide, formed in the window, a depression of 0.05-0.5 μm, a barrier layer of a Schottky electrode, a contact electrode; The Schottky electrode barrier layer is bilayer: the lower layer is formed from rhenium with a thickness of 5.0 to 15.0 nm, and the upper layer is formed of molybdenum with a thickness of 100 to 300 nm.

A comparative analysis of the invention with the prototype showed that the claimed device differs from the known one in that the Schottky barrier layer is double-layer: the lower layer is formed from rhenium from 5.0 to 15.0 nm thick, and the upper layer is formed from molybdenum from 100 to 300 thickness nm

The solution of the problem set in the invention is explained as follows. At a given temperature, the reverse current of the Schottky diode is the inverse exponential function of the height of the Schottky barrier. The Schottky barrier height of η-type molybdenum-silicon is of the order of 0.68 eV [1]. The barrier layer of the Schottky electrode of the molybdenum-rhenium alloy (in accordance with the prototype) provides a Schottky barrier height of about 0.7 eV, which leads to a 3-fold decrease in the reverse current of the Schottky diode. The implementation of the Schottky barrier layer of the electrode as a two-layer rhenium-molybdenum structure allows one to obtain a Schottky barrier height of the order of 0.75 eV, which leads to a decrease in the reverse current relative to the Schottky barrier made of pure molybdenum.

With a rhenium thickness of less than 5.0 nm and a molybdenum thickness of less than 100 nm, the formation of a continuous Schottky barrier is not ensured and the solid-phase interaction of the material of the contact electrode with the barrier layer of the Schottky electrode occurs, which reduces the height of the Schottky barrier and increases the reverse current.

With a rhenium thickness of more than 15.0 nm and a molybdenum thickness of more than 300 nm, a further effect in reducing the reverse current is not observed, but the specific consumption of rhenium increases.

The invention is illustrated in the figure, which shows a cross section of a Schottky diode in accordance with the proposed technical solution, containing a highly doped silicon substrate of η-type conductivity (1) with a formed oxidized lightly doped epitaxial layer of the same type of conductivity (2) and a protective ring of p-type conductivity (3) forming the pη junction, a window opened in silicon oxide (4), a recess under the barrier layer of a Schottky electrode of 0.05-0.5 μm in size, a contact electrode (7), a barrier layer of a Schottky electrode flax is bilayer: the lower layer is formed from rhenium (5) with a thickness of 5.0 to 15.0 nm, and the upper layer is formed from molybdenum (6) with a thickness of 100 to 300 nm.

- 1,026882

This structure can be made as follows. In the initial epitaxial n + / structure, the region of the p-type conduction ring is formed by standard methods of photolithography and diffusion (3). Then, using photolithography and subsequent liquid etching, the contact window of the desired configuration is opened. Then, after appropriate surface preparation, rhenium (5) from 5.0 to 15.0 nm thick is applied by magnetron sputtering, molybdenum (6) from 100 to 300 nm thick is applied by magnetron sputtering, and a barrier layer configuration is formed by subsequent photolithography Schottky electrode. After that, the metallization of the contact electrode is applied to the resulting structure by magnetron sputtering followed by photolithography, which forms its configuration.

The proposed Schottky diode operates as follows. The layer of rhenium contacting silicon (5), which forms a Schottky barrier, provides the specified electrical properties of the Schottky diode, such as the height of the Schottky barrier, the shape of the current – voltage characteristic, the reverse current, and the voltage drop under forward bias. The molybdenum layer (6) prevents the solid-state interaction between rhenium and the contact electrode material and thus stabilizes the electrical properties of the Schottky diode. The guard ring (3) serves to eliminate the edge leakage currents around the perimeter of the barrier electrode. Since molybdenum has poor adhesion to δίθ ₂ , there is a gap between the edges of the barrier electrode and the window in silicon oxide (4) located above the guard ring. The contact electrode (7) is used to create a field lining along the outer perimeter of the guard ring (3), which prevents surface breakdown of the pn junction during reverse bias, ensures a uniform distribution of current over the entire Schottky contact area, and to create the necessary conditions for connecting an external output to the planar sides of the crystal.

The table shows a comparative characteristic of the reverse currents of Schottky diodes and the specific consumption of rhenium per one plate of Schottky diodes made in accordance with the present invention with respect to the prototype.

Comparative characteristics of the reverse leakage currents of Schottky diodes and the specific consumption of rhenium per one plate of Schottky diodes

No. p / p Type of Schottky barrier layer Ke layer thickness, nm Thickness layer Mo, nm 1obr / 1obr pr R "A Pr one rhenium 3 70 0.270 0,088 2 rhenium 5 one hundred 0,097 0.146 3 rhenium 10 200 0,055 0.291 4 rhenium fifteen 300 0,073 0.437 5 rhenium twenty 500 0,093 0.582 6 Alloy molybdenum-rhenium with a rhenium content of 10.0 mass. % (prototype) 150 1,0 1,0

Note:

1 obr / 1 obr pr is the ratio of the reverse leakage current of a Schottky diode manufactured in accordance with the present invention to the leakage current of a Schottky diode - prototype.

Rke / Rke pr - the ratio of the specific consumption of rhenium per one plate of a Schottky diode made in accordance with the present invention to the consumption of rhenium per one plate of a Schottky diode - prototype.

Thus, the proposed design in comparison with the prototype allows us to solve the problem of reducing the reverse leakage current of the Schottky diode by 10.3-13.7 times and reducing the specific consumption of rhenium by 2.3-6.8 times.

Information sources.

Zi S. Physics of semiconductor devices: Kn. 1 / Per. from English - M .: Mir, 1984. - S. 456.

U.S. Patent 4,899,199, IPC H01 29/47, 29/66, publ. 02/06/1990.

Patent RB 8380, IPC Н01Ь 29/872, 29/47, publ. 08/30/2006.

Claims (1)

CLAIM A Schottky diode containing a heavily doped p-type silicon substrate with a formed oxidized lightly doped epitaxial layer of the same type of conductivity, a p-type protective ring, forming a p-n junction, a window opened in silicon oxide, a recess formed in the window of 0.05- 0.5 μm, the Schottky electrode barrier layer and a contact electrode, characterized in that the barrier Schottky electrode layer is bilayer: the lower layer is formed from rhenium with a thickness of 5.0 to 15.0 nm, and the upper layer is formed from mo ibdena thickness from 100 to 300 nm.