JP2011129738A - Schottky barrier diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the lowering of a forward direction voltage, and to make element breakage hardly occur even at a surge voltage not lower than a Zener voltage which is instantaneously generated by increasing rated surge inverter power (PRSM) on the assumption of that a desired Zener voltage is designed. <P>SOLUTION: A first region t1-1 where the logarithm of resistivity corresponding to a depth from a surface of an N<SP>-</SP>layer 2 toward an N<SP>+</SP>substrate 3-side is linearly reduced in accordance with an increase of the depth, a second region t1-2 in which the logarithm is constant even if the depth is increased, and a third region t2 in which the logarithm is steeply reduced as the depth is increased are sequentially formed. A reducing rate of the logarithm of resistivity in the third region t2 is larger than that of the logarithm of resistivity of the first region t1-1. A position X1-1 of the deepest part of the first region is deeper than a junction face Xj of a guard ring 1 and the N<SP>-</SP>layer 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a Schottky barrier diode (SBD) using a guard ring, and more particularly to a Schottky barrier diode having a Zener diode function.

  Schottky barrier diodes using the rectifying action of the potential barrier caused by the contact between metal and semiconductor can operate at high speed because the conduction phenomenon is due to majority carriers, and the height of the potential barrier depends on the metal. The voltage drop can be reduced, and it is widely used in high frequency signal circuits, power supply rectifier circuits, reverse connection prevention circuits, and the like.

  In a Schottky barrier diode, the potential barrier is lowered when a forward voltage is applied, electrons flow from the N-type silicon to the metal (forward characteristics), and electrons that move from the N-type silicon to the metal when a reverse voltage is applied. There is no flow (reverse characteristics).

  By the way, when the applied voltage in the reverse direction is increased, there is a possibility that the leakage current increases and the device is locally destroyed. Therefore, a configuration in which a guard ring is provided in the Schottky barrier diode in order to obtain a reverse characteristic that has a higher reverse blocking voltage (withstand voltage) and can suppress a leakage current in a state where a high reverse voltage is applied. It has been known.

FIG. 3A is a diagram showing a cross-sectional structure of a conventional Schottky barrier diode with a guard ring, where 1 is a P layer constituting the guard ring, 2 is an N ⁻ epitaxial layer, 3 is an N ⁺ substrate, 4 Is an anode electrode metal, 5 is a cathode electrode metal, and 6 is an oxide film (SiO 2 film).

In this conventional Schottky barrier diode with a guard ring, as shown in FIG. 3A, a guard ring 1 is provided around the active region of the N ⁻ layer on the device surface side. By providing the guard ring 1 in this way, the guard ring 1 breaks down before the edge effect at the end of the active region and the breakdown due to the high electric field formed at the Schottky barrier diode interface occur. Thus, the Schottky barrier diode body can be protected.

However, even the Schottky barrier diode with a guard ring has the following problems that cannot be solved sufficiently.
(1) Depending on the application circuit in which the Schottky barrier diode is incorporated, an avalanche state is generated due to an unexpected surge voltage, which causes element destruction.

(2) As a countermeasure, the reverse blocking voltage must be set higher than the steady voltage. For this reason, the resistivity-depth product of the semiconductor substrate of the Schottky barrier diode (integral value of resistivity in the depth direction, hereinafter referred to as ρt product) must be increased. Therefore, when the ρt product is increased, the resistance component increases, so the forward loss of the Schottky barrier diode increases, and the loss of the entire circuit including the Schottky diode increases.

(3) A snubber circuit for absorbing the surge voltage is necessary as a measure for preventing the adverse effect of the surge voltage on the Schottky barrier diode, and the application circuit itself is complicated and expensive.

  Therefore, in order to solve such a problem, the applicant of the present application has a structure having a cross-sectional view shown in FIG. 4A and a Schottky having a Zener function having a resistivity profile shown in FIG. A barrier diode (Schottky barrier diode with a Zener diode) has been proposed (see Patent Document 1).

The invention described in Patent Document 1 relates to impurities contained in the N ⁻ layer 2 as the depth in the N ⁻ layer from the junction surface between the anode electrode metal 4 and the N ⁻ layer 2 toward the N ⁺ substrate 3 increases. The N ^- layer 2 contains impurities so that the logarithm of the concentration increases linearly, and the depth (position) Xj from the guard ring surface 8 to the boundary surface 7 is increased.

  By adopting such a configuration, as shown in FIG. 4B, the logarithm of resistivity decreases linearly as the depth increases as compared with the conventional Schottky barrier diode with guard ring. It will have an inclined resistance profile.

Thus, N ^- conventional example are formed at a constant regardless of the depth of the layer than (see FIG. 3 (b)), N ^{- -} concentration of the impurity contained in the layer N depth layers The burden of the electric field in a deep region can be increased.

As a result, the electric field at the horizontal part of the PN junction, that is, the boundary surface between the guard ring and the N ⁻ layer can be strengthened, and the strong electric field can be distributed intensively in that part. Thereby, the concentration of the electric field at the corner portion 10 of the guard ring 1 can be reduced, that is, the avalanche can be performed at the bottom surface of the PN junction with an applied voltage that is lower in absolute value than the applied voltage avalancheed at the corner portion 10. .

  This allows a predetermined voltage (zener voltage) to avalanche in the horizontal part of the PN junction, increase the current by generating a large number of electron-hole pairs, and fix the applied voltage Can be added to the diode.

Further, the following configuration is known as another conventional example of a Schottky barrier diode with a guard ring. That is, in a Schottky diode, a low concentration and very shallow n ⁻ high resistance region is formed on the surface layer of the n drift layer, and the metal Schottky electrode forming a Schottky junction is in contact with the n ⁻ high resistance region. Compared to the conventional Schottky diode, the portion where the Schottky electrode contacts has a higher resistivity, so the leakage current is about ½, and the resistivity of the n drift layer is low. A configuration is known in which the forward voltage at the current is low (see Patent Document 2).

JP 2006-5168 A Japanese Patent Laid-Open No. 10-335679

In a Schottky barrier diode having a Zener diode function, the P layer forming the Zener portion has a resistivity-depth profile that is logarithmically inclined in a logarithmic manner, and the inclination is inclined in the depth direction from the surface side. It is formed shallower than the N ⁻ layer having a negative slope, and when it exceeds a predetermined reverse voltage (Zener voltage), it becomes an avalanche state at the bottom surface of the PN junction, and the electron-hole pair is Therefore, the current increases, the applied voltage is fixed, and power above the predetermined voltage is consumed as heat, so even if the Zener voltage is set below the surge voltage, the Zener voltage applied instantaneously Since the power consumed by the above surge voltage can be processed as heat, it does not break down.

  Conventional diodes easily cause irreversible breakdown when the reverse blocking voltage (in the above case, Zener voltage) is exceeded, so it is necessary to design the substrate specifications with a margin greater than the surge voltage. Therefore, it is necessary to increase the product of the resistivity-depth profile, which is the substrate specification, that is, the resistance. For this reason, the forward voltage drop increases, and consequently the forward blocking voltage and the forward blocking voltage increase. There was a conflicting relationship of losses.

  In general diodes, as described above, the reduction of forward loss and the improvement of reverse blocking voltage are in a contradictory relationship. However, when the diode with a Zener function is used on the same circuit, a normal diode is used. Since the Zener voltage (reverse blocking voltage) can be set lower than that, the substrate resistance can be lowered, and the forward loss can be reduced.

  However, the amount of power for processing the power of the voltage higher than the set Zener voltage of the diode with the Zener function as heat is limited by the rated surge reverse power. When a diode is used on the circuit, the thermal design must be such that the junction temperature of the diode is within the guaranteed temperature. However, if the rated surge reverse power is small, the junction temperature tends to rise, and the Zener The power to process is limited. The larger the rated surge reverse power, the lower the Zener voltage can be set. The Zener-equipped diode has room for improvement since the rated surge reverse power of the board specification is not controlled.

  That is, depending on the application circuit in which the Schottky barrier diode is incorporated, an avalanche state occurs due to an unexpected surge voltage, and when the power exceeding the reverse blocking voltage is large, heat is generated and the junction temperature rises leading to destruction. . Therefore, it is necessary to improve the rated surge reverse power to improve the junction temperature and prevent the breakdown under the condition that the Zener voltage is set constant.

  In addition, the conventional diode controls the termination structure of the guard ring, and has a reverse blocking voltage close to the value obtained by solving the one-dimensional Poisson equation (approximately proportional to the ρt product) of the resistivity-depth profile of the substrate. However, in the diode with the Zener function, the reverse blocking voltage is close to the value obtained by solving the resistivity-depth profile from the deepest part of the P layer forming the Zener part by the one-dimensional Poisson equation. For this reason, when a substrate having the same ρt product is used, a diode with a Zener function has a lower reverse blocking voltage (Zener voltage) than a conventional diode.

  That is, the disadvantage of the diode with the Zener function is that the reverse blocking voltage is lower than that of the conventional diode with the same substrate specification (the same ρt product and the same forward loss). On the other hand, one of the features of the Zener-equipped diode described above is that the reverse blocking voltage can be set low when incorporated in a circuit.

  The improvement of the reverse blocking voltage and the reduction of the forward loss are in a contradictory relationship, and if the reverse blocking voltage is allowed to be low, the ρt product of the substrate specification can be set low, so the forward loss can be reduced. Features come out. Under the condition that the Zener voltage is constant, there is a problem that the features and drawbacks of the forward loss of the diode with the Zener function are offset. That is, there is room for improvement in reducing the forward loss while maintaining the Zener voltage in the diode with the Zener function.

  By the way, in the Schottky barrier diode having the Zener function described in Patent Document 1, the wafer specification (specifically, the resistivity in the depth direction of the substrate minus the depth) is set so as to obtain a desired reverse blocking voltage (Zener voltage). Profile) is designed. However, the Schottky barrier diode having the Zener function reduces forward loss due to the above reason compared with the conventional example (see FIG. 3) not having the Zener diode function designed to have the same reverse blocking voltage. This effect is offset by its features and disadvantages. That is, in a Schottky barrier diode having a Zener function, it is necessary to reduce the forward loss while keeping the Zener voltage constant.

Patent Document 2 discloses that a very shallow layer that is in contact with a Schottky electrode and forms a Schottky junction is a low-concentration n ⁻ high resistance region, so that a leakage current is reduced to about ½ and an n drift layer The forward voltage drop at the rated current is made low by reducing the resistivity of this.

In short, Patent Document 2 aims to reduce the leakage current when a reverse voltage is applied without increasing the value of the forward voltage drop. However, the P layer is not a Schottky barrier diode which is deeper than the depth of n ⁻ and the P layer forms a pn junction with the n ⁻ layer and has a Zener diode.

  Therefore, as described above, Patent Document 2 discloses a problem of securing a desired Zener voltage to be broken down and a solution thereof, which are necessary for a Schottky barrier diode having a Zener function so that the main body is not destroyed. Not. Further, since the avalanche state is generated by the surge voltage and causes destruction of the element, the problem that the rated surge reverse power needs to be improved and the means for solving the problem are not disclosed.

  The present invention presupposes improvement of forward characteristics (reduction of forward loss), and a desired breakdown voltage required for a Schottky barrier diode having a Zener function so that the main body is not destroyed. Ensuring (Zener voltage) is the main issue. It is another object of the present invention to increase the rated surge reverse power to increase resistance to surge voltage generated in an application circuit or the like and to prevent element breakdown.

A Schottky barrier diode comprising an anode electrode metal, a guard ring, an N ⁻ layer containing impurities, an N ⁺ substrate, and a cathode electrode metal, and having a Zener diode function by the guard ring and the N ⁻ layer. The N ⁻ layer is formed deeper than the guard ring with respect to the depth from the junction surface between the anode electrode metal and the N ⁻ layer toward the N ⁺ substrate side, and the junction surface between the anode electrode metal and the N ⁻ layer. the N ⁺ log of resistivity corresponding to the depth of the substrate toward the side of the a first region that is linearly reduced according to the depth increases, the second the depth is constant increases from and region, and a third area that sharply reduced in accordance with the depth increases, the N ^- are successively formed on the layer, from the log reduction of the resistivity of the first region, the Logarithmic reduction rate of the resistivity of the third area is large, the deepest portion of the first region, the guard ring and the N ^- providing a Schottky barrier diode, characterized in that in a position deeper than the junction surface of the layer .

When a predetermined reverse blocking voltage is applied, the junction surface between the guard ring and the N ⁻ layer reaches a dielectric breakdown electric field, the applied voltage is fixed due to the avalanche phenomenon, and the guard ring has a Zener diode function. preferable.

  A resistivity profile indicating a change in logarithm of resistivity corresponding to the depth can obtain the same zener voltage as the zener voltage, and the logarithm of resistivity is obtained through the first region and the second region. For a resistivity gradient profile that decreases in a straight line, the logarithm of resistivity is low and the reduction rate is the same in the first region, and the logarithm of resistivity is low at a predetermined depth in the second region, It is preferable to have a configuration that increases from the depth.

In the Schottky barrier diode according to the present invention, the resistivity profile is in a state of decreasing, flattening, and steeply decreasing linearly in a logarithmic direction toward the direction in which the depth of the N ⁻ layer increases. The following effects are produced.
(1) By reducing the logarithm of the resistivity linearly from the surface of the N ⁻ layer by a predetermined depth, the forward characteristics can be improved (forward loss is reduced).

(2) Even if a reverse voltage is instantaneously applied to the diode by a surge voltage or the like, the voltage value is fixed by the value of the zener voltage because the zener function is provided, and the diode body is not broken.

(3) The rated surge reverse power can be increased by increasing the electric field strength in the transition region between the N ⁻ layer and the N ⁺ substrate when a predetermined reverse breakdown voltage is applied. Even when a voltage is generated, the resistance to device destruction is increased. In particular, when used in parallel, the Schottky barrier diode having the lowest Zener voltage is loaded with power due to the surge voltage. However, since the rated surge reverse power is high, it is difficult to break.

(4) Like the conventional Schottky barrier diode with a guard ring, it can be manufactured by using epitaxial growth by CVD method without using a special process, and the resistivity profile is linearly inclined in the depth direction. Since the difference in the logarithm of the resistivity at the starting point and the ending point of the reduced area is small, it is easy to adjust the impurity concentration for changing the resistivity in the manufacturing process, and the variation in manufacturing quality is reduced.

It is a figure explaining the structure of the Example of the Schottky barrier diode which concerns on this invention, (a) shows sectional drawing, (b) is a figure which shows the resistivity profile compared with prior invention. It is a figure explaining the electric field strength of the Example of the Schottky barrier diode concerning this invention compared with a prior invention, (a) is a figure which shows electric field strength distribution of a depth direction, (b) is depth. It is a figure explaining the electric field generation region of a direction. It is a figure explaining the structure of the Schottky barrier diode of a prior art example, (a) shows sectional drawing, (b) is a figure which shows a resistivity profile. It is a figure explaining the structure of the Schottky barrier diode of prior invention (invention of patent document 1), (a) shows sectional drawing, (b) is a figure which shows a resistivity profile.

  A mode for carrying out a Schottky barrier diode according to the present invention will be described below with reference to the drawings based on the embodiments. In particular, the present invention includes the improvement of the invention described in Patent Document 1 described above, and the features of the present invention will be described in comparison with the invention described in Patent Document 1 (hereinafter referred to as “preceding invention”).

  The Schottky barrier diode according to the present invention is a Schottky barrier diode having a guard ring and having a function of a Zener diode, as in the previous invention. FIG. 1A is a diagram showing a cross-sectional structure of an example of a Schottky barrier diode according to the present invention.

In FIG. 1A, 1 is a P layer constituting a guard ring, 2 is an N ⁻ epitaxial layer (hereinafter referred to as an N ⁻ layer), 3 is an N ⁺ substrate, 4 is an anode electrode metal, 5 is a cathode electrode metal, 6 Is an oxide film (SiO ₂ ). The anode electrode metal 4 is made of a metal whose main component is Mo.

  As shown in FIG. 1A, the cross-sectional structure of the Schottky barrier diode according to the present invention is substantially the same as that of the Schottky barrier diode of the prior invention (see FIG. 4A). Thus, it differs from the Schottky barrier diode of the prior invention. That is, the Schottky barrier diode according to the present invention is characterized by having a resistivity profile as shown in FIG.

FIG. 1B shows a resistivity profile, that is, the depth of the N ⁻ layer 2 from the junction surface (the surface of the N ⁻ layer 2) between the anode electrode metal 4 and the N ⁻ layer 2 toward the N ⁺ substrate 3 side. It is a figure which shows the state of the magnitude | size (high / low) of a resistivity over the length direction.

In particular, in FIG. 1B, in order to explain the characteristics of the Schottky barrier diode according to the present invention, the LL cross section of FIG. 1A of the Schottky barrier diode according to the present invention, that is, the resistance in the Schottky region. The rate profile is shown by a solid line in FIG. 1B, and the resistivity profile in the LL cross section of FIG. 4A of the prior-art Schottky barrier diode is shown by a dotted line in FIG. It shows. In FIG. 1B, the horizontal axis indicates the depth of the N ⁻ layer 2 and the vertical axis indicates the logarithm of resistivity (Ωcm).

N ^- resistivity of the layer 2, N ^- varies depending the concentration of impurities contained in the layer 2 (the content of impurities). That is, when the impurity concentration of the N ⁻ layer 2 is high (the impurity content is high), the resistivity is low (small), and when the impurity impurity concentration is low (the impurity content is low), the resistivity is high (large). Thus, N in the Schottky barrier diode according to the present invention ^- the resistivity profile of the layer 2, N ^- changing the impurity concentration of the layer 2 in the depth direction, be formed by changing the resistivity according to the depth direction it can.

Although not described in detail here in order to change the impurity concentration of the N ⁻ layer 2 in the depth direction, for example, in the step of forming the N ⁻ layer 2 by epitaxial growth using the CVD method, impurities are included. This is possible by continuously adjusting the gas concentration.

The Schottky barrier diode of the prior invention is shown in FIG. 1B in terms of the resistivity profile, the shallowest region t1 from the surface of the N ⁻ layer 2 to a predetermined depth and the deepest of the shallower region t1. A region on the deep side that continues from the position X1 of the portion to the junction position X2 between the N ⁻ layer 2 and the N ⁺ substrate 3 and t2.

With respect to the resistivity profile in the Schottky barrier diode of the prior invention, as shown in FIG. 1 (b), in the shallow region t1, the deep direction in the N ⁻ layer 2 from the surface (the depth of the N ⁻ layer 2 is The logarithm of the resistivity is decreased so as to be linearly inclined as it goes toward (increasing direction).

  In the deeper region t2, the resistivity decreases steeply from the deepest position X1 of the shallower region t1 toward the deeper direction. The reduction rate of the deeper region t2 is larger than the resistivity reduction rate of the shallower region t1 (which is the degree of resistivity reduction, which is shown as the slope of the straight line of the resistivity profile).

On the other hand, as shown in FIG. 1B, the Schottky barrier diode according to the present invention is composed of three regions as follows from the viewpoint of the resistivity profile.
(A) First region t1-1
Region (b) second region t1-2 from the surface of the first N ⁻ layer 2 to a predetermined depth position X1-1
A region (c) from the deepest portion position X1-1 of the first region t1-1 to a predetermined depth position X1 (the same depth position as the deepest portion position X1 of the shallower region t1 of the prior invention) 3 region t2
The region from the deepest position X1 of the second region t1-2 to the junction position X2 of the N ⁻ layer 2 and the N ⁺ substrate 3 and the region having the same depth as the deep region t2 of the prior invention

As shown in FIG. 1B, the first region t1-1 and the second region t1-2 of the Schottky barrier diode according to the present invention are viewed from the viewpoint of the depth from the surface of the N ⁻ layer 2. This corresponds to the region t1 on the shallow side of the Schottky barrier diode of the prior invention. From the viewpoint of the depth from the surface of the N ⁻ layer 2, the third region t2 of the Schottky barrier diode according to the present invention is the region t2 on the deep side of the Schottky barrier diode of the preceding invention as described above. It corresponds to.

Here, the deepest position X1-1 of the first region t1 is formed at a position deeper than the junction position Xj between the P layer and the N ⁻ layer 2.

With respect to the resistivity profile in the Schottky barrier diode according to the present invention, as shown in FIG. 1B, in the first region t1-1, the resistivity increases from the surface toward the deeper direction in the N ⁻ layer 2. It is inclined so that the logarithm decreases linearly.

  Comparing the resistivity profile in the first region t1-1 with the Schottky barrier diode according to the present invention and the Schottky barrier diode according to the prior invention, the Schottky barrier diode according to the present invention has a low resistivity and a resistance. The rate reduction rate is the same.

Regarding the resistivity profile in the Schottky barrier diode according to the present invention, in the second region, as shown in FIG. 1B, the resistivity at the deepest position X1-1 of the first region t-1 is as follows. It is a flat state that is constant and does not change over the depth direction of the N ⁻ layer 2.

  When comparing the resistivity profile in the second region with the resistivity profile of the Schottky barrier diode of the prior invention, the resistivity of the Schottky barrier diode of the prior invention is at the shallowest position X1-1 in the second region t1-2. Although it is lower, it is higher than the resistivity of the prior invention at the deepest position X1 in the second region t1-2. In short, in the second region t1-2, the flat resistivity profile of the Schottky barrier diode according to the present invention is formed so as to intersect the linearly sloped resistivity profile of the Schottky barrier diode of the prior invention. ing.

  And in 2nd area | region t1-2, the part between the resistivity profile of the prior invention and the resistivity profile of this invention of the shallow side (area | region of the depth until it cross | intersects from the shallowest point of t1-2) Is the area of the portion between the resistivity profile of the present invention and the resistivity profile of the prior invention on the deep side (region from the intersecting depth to the deepest). The difference (S2) between the two profile integral values is the same.

  This relationship means that both resistance values in the t1-2 region are the same. Therefore, the difference in total resistance between the prior invention and the present invention corresponds to the difference between the integral values of t1-1, S. By this resistance component value, the present invention can reduce the forward voltage drop than the prior invention. Thereby, the forward loss of the Schottky barrier diode can be reduced.

  Note that the fact that the portion S1 and the portion S2 shown in FIG. 1B are the same indicates that the resistance value (not the resistivity) of the t1-2 region is the same. The same resistance value indicates that the average value of the electric field value in the t1-2 region is the same. More specifically, since the reverse blocking voltage (breakdown voltage) is obtained when the electric field is integrated in the depth direction with respect to the t1-2 region, the average value of the electric field is the same and the depth is the same. The values are also the same, and the Zener voltage (reverse blocking voltage) is the same in the present invention and the prior invention.

By the way, the fact that the average value of the electric field is the same is an important point in the present invention. Even if the average value is the same, the electric field profile (see the electric field profile in FIG. 2A) is different between the prior invention and the present invention. Therefore, the value of the electric field at the position X1 of the transition region to the N ⁻ layer and the N ⁺ is clearly different between the two. In the present invention, since the electric field in this region is necessarily (intentionally) higher than that of the prior invention, a feature that the rated surge reverse power, which is the main effect of the present invention, becomes higher appears.

With respect to the resistivity profile in the Schottky barrier diode according to the present invention, as shown in FIG. 1B, in the third region t2, the position of the deepest portion X1 of the second region t1-2 to the N ⁺ substrate 3 The resistivity at the deepest position X1 of the second region t1-2 decreases sharply as it goes to.

  In the Schottky barrier diode according to the present invention, the resistivity reduction rate in the third region t2 is larger than the resistivity reduction rate in the first region t1-1, and the Schottky barrier diode of the prior invention is provided. Greater than the resistivity reduction rate in the deeper region (same as the third region of the present invention) t2.

Then, the resistivity of the deepest position (N ⁺ junction position with the substrate 3) X2 of the third region t2 of the Schottky barrier diode according to the present invention is the position of the deepest portion of the deeper region t2 of the prior invention. (Junction position with N ⁺ substrate 3) It is the same as the resistivity of X2.

The wafer specification, that is, the resistivity profile of the Schottky barrier diode according to the present invention is designed so as to ensure a desired breakdown voltage (zener voltage), and the above design is performed in the manufacturing process of the N ⁻ layer 2 utilizing epitaxial growth. The impurity concentration is adjusted so that the resistivity profile is obtained.

  When the back electromotive voltage becomes the designed breakdown voltage (zener voltage), breakdown occurs and it is possible to prevent damage to the Schottky barrier diode body.

  In the present invention, in order to apply the maximum electric field to the PN junction position Xj, the deepest position X1-1 of the first region t1-1 is set below the PN junction position Xj. This makes it possible to maintain the Zener characteristics of the prior invention while using the resistivity profile of the present invention.

  When a set Zener voltage is applied to a Schottky barrier diode on a substrate having a resistivity profile that is a feature of the present invention, a breakdown electric field is reached at the position Xj of the PN junction, and an avalanche phenomenon occurs. When the avalanche phenomenon occurs, the carrier increases like an avalanche. When a voltage larger than the Zener voltage is applied, the current increases due to the above phenomenon, so that a phenomenon occurs in which the applied voltage is fixed at the Zener voltage.

  Originally, the electric power exceeding the applied voltage becomes an avalanche current generated in the PN junction at the depth of the position PN of the PN junction and is consumed as heat through the PN junction. This is a feature of the Zener of the present invention and the prior invention, and enables a Zener operation.

(Function)
In the Schottky barrier diode according to the present invention having the above-described configuration, when a forward voltage is applied between the anode electrode metal 4 and the cathode electrode metal 5 and the voltage is increased, a current flows in the forward direction at a predetermined forward voltage. The flow is turned on. In short, when a predetermined forward voltage is applied to the Schottky barrier diode, it is turned on.

  And when the reverse voltage of a Schottky barrier diode is applied, it will switch to an OFF state. The resistivity profile in the Schottky barrier diode according to the present invention is as shown in FIG. 1 (b) as compared with the prior invention. With such a resistivity profile, the forward loss is reduced, and the reverse Surge power tolerance (rated surge reverse power) is improved. These points will be described in more detail.

  In the resistivity profile of the Schottky barrier diode according to the present invention, the position X1-1 of the deepest part of the first region t1-1 is below the position Xj of the PN junction, and the resistivity gradient at this depth is , It is set in the same manner as the prior invention so as to break down at the bottom surface of the PN junction. As a result, at the desired breakdown voltage, the electric field reaches the breakdown electric field at the bottom surface of the PN junction, electron-hole pairs are generated by the avalanche phenomenon, and the current increases avalanche to fix the voltage. The function of the Zener diode is activated.

  In the first region t1-1 in FIG. 1B, the resistivity profile profile is set so that the resistivity of the present invention is lower than the resistivity of the prior invention. Therefore, the resistivity in the first region is lower than that in the prior invention, that is, the difference S in the integrated value of the resistivity of the present invention with respect to the prior invention in the first region t1-1. Forward loss is reduced.

By the way, the rated surge reverse power indicating the resistance against surge power is determined by the electric field strength applied to the boundary between the transition region (see FIG. 2B) 9 between the N ⁻ layer 2 and the N ⁺ substrate 3. FIG. 2A shows the distribution of the electric field intensity in the depth direction generated based on the resistivity profile shown in FIG. 1B, and the Schottky barrier diode according to the present invention with respect to the Schottky barrier diode according to the present invention. It is a figure shown in comparison.

2 (a), the Schottky barrier diode of the present invention and the prior invention, N ^- from the surface of the layer 2 P layer and the N ^- to a depth of bonding positions Xj layer 2, the logarithm of the resistivity at the same reduction rate The electric field strength (formally, the absolute value of the electric field strength) increases in the same state as it is reduced so as to incline linearly (see FIG. 1B). In FIG. 2, a region from the junction position Xj of the N ⁻ layer 2 to the deepest position X1 of the region t1 is denoted by t1−Xj.

Since the integrated value of the electric field strength in the depth direction corresponds to the applied voltage, the same breakdown electric field is applied to the Schottky barrier diode according to the present invention at the junction position Xj of the P layer and the N ⁻ layer 2 together with the prior invention. . In this state, if the integrated value of the electric field intensity-depth in the region t1-Xj in FIG. 2A is the same, the set Zener voltage is the same. That is, in the profile, for the range of the region t1-Xj, the area S3 in the shallow range and the area S4 in the deep range from the intersection of the prior invention and the present invention are as follows. The same is the condition for making the Zener voltages the same.

That is, with respect to the Schottky barrier diode according to the present invention, both of the Schottky barrier diodes of the prior invention reach the same electric field, that is, the breakdown electric field at the junction position Xj of the P layer and the N ⁻ layer 2 at the time of breakdown. Since the integrated value in the depth direction corresponds to the applied voltage, if the integrated value of the electric field-depth, that is, the area surrounded by the profile in FIG. Will be.

The electric field strength is from the junction position Xj of the P layer and the N ⁻ layer 2 to the deepest position X1 of the second region t1-2. In the region, it is reduced to a curved line in the prior invention, and linearly reduced in the present invention. In order to have the same Zener voltage, there is a depth that always intersects in the middle as in the above condition. In the depth shallower than the intersecting depth, the electric field of the prior invention is higher than that of the present invention, and in the range deeper than the intersecting depth, the electric field of the present invention is necessarily higher than the prior invention.

  For this reason, the electric field strength at the depth of the transition region is always higher in the present invention than in the prior invention.

  Therefore, the Schottky barrier diode of the present invention can increase the rated non-repetitive surge reverse power relative to the Schottky barrier diode of the previous invention, improve the resistance to surge power, and reduce the surge current generated in the application circuit. Even if it flows through the Schottky barrier diode, the element is less likely to be destroyed.

  By the way, a plurality of Schottky barrier diodes do not have exactly the same quality of various characteristics such as a Zener voltage in manufacturing, and there are some variations depending on process capability as a practical problem. When multiple Schottky barrier diodes having the Zener diode function are used in parallel, surge reverse power is concentrated and loaded on the Schottky barrier diode with the lowest Zener voltage, and the Schottky barrier diode is easily destroyed. There's a problem.

However, the Schottky barrier diode of the present invention, at the position X1 of the deepest portion of the shallow side of the region t1 of said as second region value E ₂ of the electric field intensity prior invention in the position X1 of the deepest portion of t1-2 Since it is higher than the value of the electric field strength E ₁ (see FIG. 2 (a)), even if it is used in parallel, the reverse surge power of the diode connected in parallel to the diode having the lowest zener voltage is concentrated. However, it becomes difficult to be destroyed as the rated surge reverse power increases.

  The Schottky barrier diode of the present invention requires a special method for manufacturing a substrate by epitaxial growth using a CVD method, but can follow a conventional process for a wafer process and a package assembly process.

In this case, the resistivity profile that changes linearly and slopes changes the impurity concentration in the depth direction by adjusting the amount of impurity gas in the manufacturing process. It is difficult to manufacture to obtain a linear resistivity profile. In particular, if the difference in resistivity in the depth direction of the N ⁻ layer is large and the width in the depth direction is large, it is difficult to form a reduced (or increased) resistivity profile in a constant gradient line.

In FIG. 1 (b), the resistivity profile of the prior invention is inclined and changed linearly with the logarithm of resistivity, so that the difference between the upper limit and the lower limit is large in actual resistivity. In particular, when the range in the depth direction of the N ⁻ layer 2 where the resistivity changes is large, the difference between the upper limit and the lower limit of the resistivity becomes extremely large, and the resistivity may be out of the range where the resistivity can be controlled by the CVD process. For this reason, the range in which the Zener voltage can be set is limited.

However, the resistivity profile of the Schottky barrier diode of the present invention has a flat second region t1-2 in which the resistivity is constant, although there is a region that linearly slopes and changes with the logarithm of the resistivity. Therefore, in the first region t1-1, since the range in the depth direction of the N ⁻ layer 2 in which the resistivity is linearly inclined and reduced is narrower than that of the prior invention, the difference between the upper and lower resistivity Becomes smaller.

  Therefore, in the step of epitaxial growth by the CVD method, it becomes easier to adjust the gas amount for changing the impurity concentration, and in the first region t1-1, a profile having a reduced resistivity with a stable linear slope is obtained. It becomes possible.

(Test example)
The inventor has tested the characteristics of the Schottky barrier diode of the present invention as compared to the Schottky barrier diode of the prior invention. Table 1 below shows data obtained in the test.

  Each item in Table 1 will be described. The reverse blocking voltage (withstand voltage) is a design value that is a voltage (V) at which the Zener diode breaks down. “Slope” is the resistivity profile of the prior invention of FIG. 1B, and “Step” is the resistivity profile of the Schottky barrier diode of the present invention. The “barrier” is composed of an anode electrode metal 4 (barrier metal) mainly composed of Mo. “VZ” indicates the reverse voltage actually broken down. “IR” is a leakage current. “VF” is a forward voltage. PRSM is rated non-repetitive surge reverse power, and is an index of rated surge reverse power.

The measurement conditions are as follows. With respect to the actual reverse blocking voltage (breakdown voltage) VZ, the measurement condition is @ IR = 1 mA (a leakage current of 1 mA flows). With respect to the leakage current IR, @RT VR = 80 V (a value when a reverse blocking voltage design value of 80 V is applied at room temperature) is set as a measurement condition. For the forward loss VF, the measurement condition is @RT IF = 180 A / cm ² (flowing 180 A per 1 cm ² at room temperature). Further, PRSM uses a pulse width of 100 μsec as a measurement condition.

  According to the test data of Table 1, the following is clear. In the Schottky barrier diode of the prior invention, a reverse voltage of 84.0 (V) is applied to break down the Zener diode. In the Schottky barrier diode of the present invention, the substrate specifications (resistivity-depth profile) It can be seen that the zener diode breaks down at 82.6 (V) despite the fact that the zener voltage is changed, and a zener voltage substantially equal to that of the preceding invention is secured.

  Further, the forward loss is 693.2 (mV) in the Schottky barrier diode of the prior invention, but it is 670.8 (mV) in the Schottky barrier diode of the present invention, and the difference between the two values is a significant difference. It can be seen that the forward loss is clearly reduced.

  Furthermore, in the Schottky barrier diode of the prior invention, the rated non-repetitive surge reverse power (PRSM) is 1.2 (W), but in the Schottky barrier diode of the present invention, the rated non-repetitive surge reverse power (PRSM) is 2 4 (W), which is twice that of the prior invention, indicating that the resistance to surge power is extremely high.

  As mentioned above, although the form for implementing the Schottky barrier diode which concerns on this invention was demonstrated based on the Example, this invention is not limited to such an Example, It was described in the claim It goes without saying that there are various embodiments within the scope of technical matters.

  Since the Schottky barrier diode according to the present invention has the above-described configuration, it can be applied to a high-frequency signal circuit, a power supply rectifier circuit, a reverse connection prevention circuit, and the like.

1 P layer 2 N constituting the guard ring ^- epitaxial layer 3 N ⁺ substrate 4 anode metal 5 cathode electrode metal 6 oxide film (SiO ₂ film)
7 Interface between P layer and N ⁻ layer (joint surface)
8 Guard ring surface 9 Transition region between N ⁻ layer and N ⁺ substrate 10 Corner portion of guard ring

Claims (3)

In a Schottky barrier diode comprising an anode electrode metal, a guard ring, an N ⁻ layer containing impurities, an N ⁺ substrate, and a cathode electrode metal, and having a Zener diode function by the guard ring and the N ⁻ layer,
The N ⁻ layer is formed deeper than the guard ring with respect to the depth from the junction surface between the anode electrode metal and the N ⁻ layer toward the N ⁺ substrate side.
A first region in which a logarithm of resistivity corresponding to a depth from the junction surface of the anode electrode metal and the N ⁻ layer toward the N ⁺ substrate side linearly decreases as the depth increases; A second region that is constant as the depth increases and a third region that decreases sharply as the depth increases are sequentially formed in the N ⁻ layer,
The logarithmic reduction rate of the resistivity of the third region is larger than the logarithm reduction of the resistivity of the first region,
The deepest portion of the first region is located at a position deeper than the junction surface between the guard ring and the N ⁻ layer. When a predetermined reverse blocking voltage is applied, the junction surface between the guard ring and the N ⁻ layer reaches a dielectric breakdown electric field, the applied voltage is fixed by an avalanche phenomenon, and the guard ring has a Zener diode function. The Schottky barrier diode according to claim 1. A resistivity profile indicating a change in logarithm of resistivity corresponding to the depth can obtain the same zener voltage as the zener voltage, and the logarithm of resistivity is obtained through the first region and the second region. For resistivity gradient profiles that decrease in a straight line,
In the first region, the logarithm of resistivity is low and the reduction rate is the same,
3. The Schottky barrier diode according to claim 2, wherein in the second region, the logarithm of resistivity is low at a predetermined depth and increases from a predetermined depth.

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