DE3741567A1 - TRANSISTOR CLAMPED WITH SCHOTTKY BARRIER DIODE - Google Patents

Abstract

An insulating layer, which is formed on a collector active region, has a contact hole (11b) with a circumferential line (14) changing its direction in the manner of a curvature. A metal layer is produced in the contact hole (11b) by etching, so that the metal layer forms a Schottky junction with the collector active region. Since the circumference of the contact hole does not have any sharp corner section, there does not occur any over-etching, which causes a stray current. <IMAGE>

Description

The invention relates to a Schottky junction diode clamped transistor (Schottky Barrier Diode Clamped Transistor) and a method of manufacturing the same and it particularly concerns one with a Schottky junction diode clamped transistor that reduces the output stray current and a method of manufacturing the same.

Reference is made to the prior art. Fig. 1A is a plan view schematically showing the structure of a known Schottky junction transistor clamped structure described in the data manual (Mitsubishi Semiconductors 1985 Bipolar Digital IC ALSTTL "published by Mitsubishi Electric), and Fig. 1B is a sectional view along line AA of Fig. 1A, Fig. 2 shows an equivalent circuit of the transistor clamped with Schottky junction diode.

The transistor clamped with Schottky junction diode consists of an NPN transistor ( 1 ) and a Schottky junction diode ( 2 ). A collector active region of the NPN transistor ( 1 ) consists of an epitaxial layer ( 3 ) of the N-conduction type and a covered diffusion layer ( 5 ) of an N⁺-conduction type, which are in a boundary region between the epitaxial layer ( 3 ) of the N-conduction type and a semiconductor substrate ( 4 ) of a P-type is arranged, while the base region and the emitter-active region of the transistor are each formed by a diffusion layer ( 6 ) of a P-type and a diffusion layer ( 7 ) of an N⁺-type. The epitaxial layer ( 3 ) of the N-type is equipped with a diffusion layer ( 8 ) of an N⁺-type for electrode extraction. Metallic interconnection layers ( 9 a , 9 b , 9 c) are electrical via contact holes ( 11 a , 11 b , 11 c) , each formed in an insulating oxide layer ( 10 ), with the aforementioned collector, base and Emitter active areas connected. The contact hole ( 11 b) is formed over the surfaces of the N-type epitaxial layer ( 3 ) and the P-type diffusion layer ( 6 ), and a metal layer ( 12 ) made of platinum silicide or the like is in the contact hole ( 11 b) over the Surfaces are provided to form a Schottky junction between them and the N-type epitaxial layer ( 3 ). With regard to the manufacturing steps, metal layers, similar to the metal layer ( 12 ), are also provided in the contact holes ( 11 a , 11 c) .

If the NPN transistor ( 1 ) of the transistor clamped with a Schottky junction diode is in the ON state, the collector and base thereof are clamped by the Schottky junction diode ( 2 ), as a result of which an excessive base current flows to the collector. Since no excessive carrier is stored in the base, the NPN transistor ( 1 ) is not saturated and the storage time of the transistor clamped with a Schottky junction diode and thus the switch-off time can be reduced. However, if there is a leakage current (I _leak ) in the blocking characteristic of the Schottky junction diode ( 2 ), a leakage current (I _leak ) for the collector is caused to flow, ie an output leakage current (I) results as follows:

I = I _leak + I _c
= I _leak + h _FE · I _leak
= I _leak + (1 + h _FE )

where h _{FE represents} a current amplification factor of the NPN transistor ( 1 ). If h _FE ≈ 100, then I = 100 × I _leak , and thus the output _leakage current (I) cannot be neglected even if I _leak itself is small.

In general, such a stray current caused in a Schottky junction diode is generated by the manufacturing process thereof. Namely, a metal layer is etched over the entire surface including the surface of the oxide layer (10), leaving the metal layer (12) so takes place over-etching by isotropic etching in sharp corner portions of the contact hole (11 b) which, according to Fig. 1A square configuration , whereby said formed in a later step interconnect metal layer (9 b) is made of N-conductivity type in the overetched portions in direct contact with the epitaxial layer (3), to form an incomplete Schottky junction and induce scattering. Thus, most of the stray current (I _leak) in the Schottky barrier diode (2) is caused in the outer peripheral portion, especially in the sharp corner portions (13) of the contact hole (11 b). On the other hand, the PN junction is formed by diffusion, and thus an area of a P line type is necessarily in contact with an area of an N line type, so that the stray current is small. If it is assumed that the stray current of a PN area diode is 50 pA, that of a Schottky junction diode of the same size is approximately 800 pA.

Thus, the Schottky junction diode of a known transistor clamped with Schottky junction diode has a non-negligible stray current which is increased by the current amplification factor in order to give a relatively large output stray current. There has been proposed a method to provide (11 b) a protective ring around the contact hole by the diffusion layer (6) is extended of the P-conductivity type to the stray current to increase, but the size of the array is increased by such a method.

The invention is therefore based on the object Schottky junction diode to create clamped transistor at which the output stray current can be reduced, without increasing the size of the arrangement, as well as a process for making the same.

This task is solved by a transistor clamped with Schottky junction diode, which is characterized by a semiconductor substrate, which is equipped with a base active area, a collector active area and an emitter active area; an insulating layer which has a first and a second and a third contact hole for interconnection with the base active area, the collector active area and the emitter active area, respectively, and a fourth contact hole for a Schottky junction with respect to the collector active area; metallic interconnect layers electrically connected to the base active region, the collector active region and the emitter active region via the first, the second and the third contact hole, respectively; and
a metallic layer for forming a Schottky junction with the collector active region via the fourth contact hole, the metal layer being electrically connected to the metallic interconnection layer with respect to the base active region; and the direction of a circumferential line of the fourth contact hole changes in a kind of curvature.

Other tasks, features, aspects and advantages the invention emerge in detail from the following  detailed description of the invention in connection with the drawings; show it

Fig. 1A and 1B, a plan view and a sectional view each schematically a known building, specify with Schottky barrier diode clamped transistor,

Fig. 2 is an equivalent circuit of the known, clamped with Schottky barrier diode transistor; and

Schematically each represent FIG. 3A and 3B is a plan view and a sectional view of the structure of a clip-on Schottky-barrier diode transistor according to the invention.

Reference is made to the preferred embodiment.

FIG. 3A is a plan view schematically illustrating the construction of a Schottky junction transistor clamped transistor according to an embodiment of the invention, and FIG. 3B is a sectional view taken along line BB in FIG. 3A. The equivalent circuit of the transistor clamped with Schottky junction diode according to the invention is similar to that of FIG. 2 and the transistor clamped with Schottky junction diode according to the invention is thus formed by an NPN transistor ( 1 ) and a Schottky junction diode ( 2 ), one with a Base of the NPN transistor ( 1 ) connected anode and a cathode connected to the same collector.

An N-type epitaxial layer ( 3 ) serving as a collector active region is formed on a P-type semiconductor substrate ( 4 ). A covered diffusion layer ( 5 ) of the N⁺-type high impurity concentration is formed in a boundary area between the epitaxial layer ( 3 ) of the N-type and the semiconductor substrate ( 4 ) and serves as a covered collector layer. Foreign atoms are selectively diffused into the N-type epitaxial layer ( 3 ) using a mask to obtain a P-type diffusion layer ( 6 ) that serves as a base active region. Subsequently, foreign atoms are selectively diffused in high concentration into the N-type epitaxial layer ( 3 ) and the P-type diffusion layer ( 6 ) using a mask to form an N⁺-type diffusion layer ( 7 ), which as a Emitter active area and a diffusion layer ( 8 ) of an N⁺ conduction type is used for electrode extraction.

An insulating oxide film ( 10 ) is produced over the entire surface and selectively etched through a mask to form contact holes ( 11 a , 11 b , 11 c) . The contact hole (11 b) is provided over the surfaces of the diffusion layer (6) of the P-conductivity type and the epitaxial layer (3) of the N-conductivity type. The contact hole ( 11 b) is a common contact hole which serves both as a contact hole for the base interconnection and as a contact hole for the Schottky transition. The contact hole (11 b) is formed such that its circumference has no sharp corner to the surface of the epitaxial layer (3) of the N-conductivity type, on which the Schottky junction is to be made, ie, it has according to FIG. 3A curved corner portions ( 14 ). In general, the direction of a circumferential line of a contact hole for a Schottky junction can change in the manner of a curvature in the present invention.

A metal layer made of platinum, for example, is formed over the entire inner and outer surface of the contact holes ( 11 a , 11 b , 11 c) and subjected to a heat treatment, whereby metal layers ( 12 ) made of platinum silicide within the contact holes ( 11 a , 11 b , 11 c) be formed. The metal layer sections in areas outside the contact holes ( 11 a , 11 b , 11 c) are removed by means of etching so that metal layers ( 12 ) only remain in the contact holes ( 11 a , 11 b , 11 c) . The extent of the contact hole (11 b) has arched corner sections (14) on the surface of the epitaxial layer (3) of the N-conductivity type for forming a Schottky junction, and thus no overetching is caused in the corner portions.

Subsequently, the metallic interconnection layers ( 9 a , 9 b , 9 c) are provided for electrical connection to the associated transistor active areas via the contact holes ( 11 a , 11 b , 11 c) in order to obtain the structure according to FIG. 3B. Since the metal layer is not over-etched (12) on the epitaxial layer (3) of the N-conductivity type, enters the metal interconnect layer (9 b) is not in direct contact with the epitaxial layer (3) of the N-conductivity type, an incomplete Schottky junction to form, which causes a stray current. If it is assumed that the stray current of a Schottky junction in the known arrangement is approximately 800 pA, it is reduced to approximately 100 pA in the embodiment according to the invention. The output leakage current of the transistor clamped with a Schottky junction diode according to the invention is thus very greatly reduced. Furthermore, since the direction of the circumferential line of the contact hole for the Schottky junction can only be changed in the type of curvature, the size of the device and therefore the size of the transistor is not increased and the masking can be easily performed similarly to the known device.

Although the invention has been described in detail and by means of the drawings was explained, this was only an example and not in a restrictive way and the basic idea and scope of the invention is limited only by that Claims set.

Claims (6)

1. A transistor clamped with Schottky junction diode, characterized by: a semiconductor substrate ( 4 ) which is equipped with a base active region ( 6 ), a collector active region ( 5 ) and an emitter active region ( 7 );
an insulating layer ( 10 ), which has a first, a second and a third contact hole ( 11 a , 11 b , 11 c) for interconnection with the base active area, the collector active area and the emitter active area, and a fourth contact hole ( 11 b) for a Schottky transition with respect to the collector active area ( 5 );
metallic interconnection layers ( 9 a , 9 b , 9 c) which are electrically connected to the base active region, the collector active region and the emitter active region, respectively via the first, the second and the third contact hole; and
a metallic layer (12) to form a Schottky junction with the collector-active area (5) via the fourth contact hole (11 b), wherein the metal layer (12) is electrically connected to the metallic interconnection layer with respect to the base active region (6) ; and
the direction of a circumferential line ( 14 ) of the fourth contact hole ( 11 b) changes in the manner of a curvature. 2. With Schottky junction diode clamped transistor according to claim 1, characterized in that the first and fourth contact holes are formed as a single common contact hole ( 11 b) . 3. Schottky junction diode clamped transistor according to claim 2, characterized in that the metal layer ( 12 ) for the Schottky junction is designed so that it is in contact with the upper surfaces of the base active region ( 6 ) and the collector active region stands in the common contact hole ( 11 b) and that the metallic interconnection layer ( 9 b) is formed on it with respect to the base active region. 4. Transistor clamped with Schottky junction diode  according to claim 1, characterized in that the base active area, the collector active area and the emitter active area as P-line type, N-line type and N-line type are. 5. A method for producing a transistor clamped with a Schottky junction diode, characterized by the following steps: producing a semiconductor substrate ( 4 );
Forming a base active region ( 6 ), a collector active region ( 5 ) and an emitter active region on the semiconductor substrate;
Forming an insulating layer ( 10 ) on the active areas, which has a first, a second and a third contact hole ( 11 a , 11 b , 11 c) with respect to the base active area, the collector active area and the emitter active area, and a fourth contact hole for a Schottky junction with respect to the collector active area, the first and fourth contact holes being formed as a common contact hole ( 11 b) and the direction of the circumferential line of the common contact hole changing in the manner of a curvature on the collector active area;
Forming a metal layer for making a Schottky junction with the collector-active region (5) at least in the common contact hole (11 b); and
Formation of metallic interconnection layers ( 9 a , 9 b , 9 c) , which are electrically connected to the base active region ( 6 ), the collector active region ( 5 ) and the emitter active region (in each case via the common, the second and the third contact hole) 7 ) are connected. 6. A method for producing a transistor clamped with Schottky junction diode according to claim 5, characterized in that the base active region ( 6 ), the collector active region ( 5 ) and the emitter active region ( 7 ) each as a P-line type, N -Line type and N-line type are formed.