Semiconductor Device for Integrated Injection Logic

This invention relates to a semiconductor device including bipolar transistors, and more particularly to a semiconductor device for integrated injection logic capable of reducing the power consumption and the signal propagation delay time.

In the case of forming bipolar transistors into an IC, it is necessary to completely isolate them from each other. This, however, makes the resulting IC construction complicated, which renders also complicated the manufacturing process of IC, and in addition causes an increase in power consumption. Conventionally, therefore, difficulties are encountered in constructing bipolar transistors into an LSI (Large Scale Integrated circuit) as compared with the formation of MOS transistors into an LSI. Recently, however, a fundamental structure of I.sup.2 L (Integrated Injection Logic) or MTL (merged Transistor Logic) has been exploited to render easier the formation of bipolar transistors into an LSI. According to this fundamental structure, through integrating ordinary planar bipolar transistors as upside-down operated transistors whose collector and emitter are constituted by the emitter and collector of those bipolar transistors, the isolation of the bipolar transistors from each other becomes unnecessary to cause not only an increase in the integrating density but also a decrease in the power consumption. The outline of the abovementioned fundamental structure will now be described by reference to FIGS. 1 and 2. Referring to FIG. 1, on an n.sup.+ substrate 1 connected to a ground terminal G an n layer 2 is formed, for example, by epitaxial growth method. In this n layer 2 a p layer 3 is formed by diffusion. Further, in this p layer 3, for example, two n.sup.+ layers 4a, 4b are formed by diffusion in a manner spaced from each other. Further, a p.sup.+ layer 5 is formed by diffusion in the n layer 2 in a manner adjacent the p layer 3. The p layer 3, n.sup.+ layers 4a, 4b, and p.sup.+ layer 5 are connected to an input terminal IN, output terminals OUT.sub.1, OUT.sub.2 and charge injection terminal +E, respectively. A semiconductor device shown in FIG. 1 can be represented by an equivalent circuit shown in FIG. 2, that is, a combined circuit of an npn transistor Q.sub.1 and a pnp transistor Q.sub.2. The npn transistor Q.sub.1 is a multi-collector type upside-down operated transistor wherein the collector is constituted by the n.sup. + layers 4a, 4b; the base by the p layer 3; and the emitter by the n layer 2. The pnp transistor whose emitter, base and collector use the p.sup.+ layer 5, n layer 2 and p layer 3, respectively. The pnp transistor Q.sub.2 is intended to inject carriers into the base of the npn transistor Q.sub.1 and is called"injector". The circuit of FIG. 2 is thus constructed such that the inverted signals OUT.sub.1, OUT.sub.2 of an input signal IN are obtained with a D.C. voltage of +E applied to the emitter of the transistor Q.sub.2. The fundamental structure shown in FIG. 1, the equivalent circuit shown in FIG. 2 and the operation of the inverter are described in Wiedmann, S, "Injection-Coupled Memory". IEEEJ. Solid State Circuits, Vol, SC-8, No. 5, Oct. 1973, p332 to 337.

FIG. 5 shows the relationship between the mean power consumption and mean propagation delay time of the above-mentioned I.sup.2 L. When consideration is given to a product of power consumption and delay time, the product with respect to the I.sup.2 L is relatively small as compared with that with respect to a TTL (Transistor-Transistor-Logic), and coincides with a 1 P. J. (1 Pico Joule) line as indicated by a solid line in FIG. 5. But the delay time is saturated at a point of about 10 nanosecond. As a result, even when the power consumption was increased, the delay time could not be shortened any further.

Accordingly, it is the object of the invention to provide a semiconductor device for integrated injection logic capable of reducing the signal propagation delay time and the power consumption.

A semiconductor device of the invention comprises a semiconductor substrate of a first conductivity type, a signal input region of a second conductivity type provided in the substrate, at least one signal output region of the first conductivity type formed in the signal input region, a charge injection region provided closely to the signal input region and forming a pn junction with the substrate and having a high impurity concentration, and electrodes provided for the substrate, signal input region, signal output region, and charge injection region, respectively, whereby to obtain an inverted output of an input signal by applying a forward bias voltage to the pn junction, said signal input region including a first region of the second conductivity type having a lower impurity concentration than the charge injection region, and a second region provided in at least part of the surface of the first region and having the same conductivity type as that of the first region and having a higher impurity concentration than the first region, said second region being adjoined to the signal output region and connected to the signal input electrode.

According to the invention, the signal propagation delay time can be remarkably decreased by causing a large reduction in lateral resistance of the signal input region. Simultaneously, the linear decreasing characteristic of the propagation delay time relative to the power consumption is improved to provide a semiconductor device wherein the delay time is not saturated up to sub-nanosecond.

FIG. 1 is a sectional view of a prior art semiconductor device for integrated injection logic;

FIG. 2 is a circuit diagram showing an equivalent circuit of the semiconductor device shown in FIG. 1;

FIG. 3 is a sectional view of a semiconductor device according to an embodiment of the invention;

FIGS. 4A to 4D are views for explaining, respectively, the steps of manufacturing the device shown in FIG. 3;

FIG. 5 shows, by way of comparison, the relationships between the respective power consumptions and propagation delay times of the prior art device of FIG. 1 and the present device of FIG. 3;

FIG. 6 is a sectional view showing a first modification of the present device;

FIG. 7A is a plan view showing a second modification of the present device;

FIG. 7B is a sectional view on line 7B-7B of FIG. 7A;

FIG. 7C is a sectional view on line 7C-7C of FIG. 7A;

FIG. 8 is a sectional view showing a third modification of the present device;

FIG. 9 is a sectional view showing a fourth modification of the present device.

In FIG. 3, a substrate 11 of a first conductivity type is composed of an n.sup.+ layer 11a and n layer 11b, said n.sup.+ layer 11a being connected to a ground terminal G through a not shown electrode. A signal input region 13 of a second conductivity type (P) is provided in the n layer 11b. In this signal input region, signal output regions of the first conductivity type (n), for example, n.sup.+ regions 14a, 14b, are provided. The signal input region 13 is composed of a first region 13a and a second region 13b (p.sup.+) having the same conductivity type as that of the first region 13a (p) and a higher concentration than the same 13a (p), said second region 13b being directly adjoined to the respective outer peripheries of the signal output regions 14a, 14b and connected to a signal input electrode 1N. The signal output regions 14a, 14b are connected to signal output regions OUT.sub.1, OUT.sub.2, respectively. On the other hand, a charge injection region 15 composed of p and p.sup.+ layers of the second conductivity type is provided in the n layer 11b closely to the signal input region 13 and is connected to a charge injection electrode +E. The difference between the embodiment shown in FIG. 3 and the prior art semiconductor device shown in FIG. 1 resides in the respect that the signal input region 3 of FIG. 1 is constituted by a single p region whereas the signal input region 13 of FIG. 3 is constituted by the p region 13a and p.sup.+ region 13b. The equivalent circuit shown in FIG. 2 applies also to the device of FIG. 3.

An example of the manufacturing process of the device shown in FIG. 3 will now be explained by reference to FIGS. 4A to 4D. As shown in FIG. 4A, on an n.sup.+ substrate 11a having an impurity concentration of about 10.sup.18 /cm.sup.3 is first formed by a vapor phase growth method an n layer 11b having an impurity concentration of about 10.sup.14 /cm.sup.3 and a thickness of about 5.mu.. Next, as shown in FIG. 4B, a mask is formed on the n layer 11b by the use of a SiO.sub.2 mask 17 and thereafter p layers 13a, 15a having an impurity concentration of about 10.sup.16 /cm.sup.3 and a depth of about 3.mu. are formed by impurity diffusion. At this time, the p layers 13a and 15a have their surface impurity concentration of about 10.sup.17 /cm.sup.3. Next, as shown in FIG. 4C, high-concentration impurity diffusion is effected with the mask left as it stands to form on the p layers 13a, 15a p.sup.+ layers 13b, 15b having an impurity concentration of 10.sup.19 to 10.sup.20 /cm.sup.3 and a depth of about 1.mu.. Next, another mask (not shown) is formed by the use of, for example, a SiO.sub.2 film and thereafter, as shown in FIG. 4D, n.sup.+ layers 14a, 14b and 15b having an impurity concentration of about 10.sup.20 to 10.sup.21 /cm.sup.3 and a depth of about 2.mu. are formed in the p.sup.+ layer 13b and p layer 15a by impurity diffusion. Next, after forming a protective film, for example, a SiO.sub.2 film 18 on the entire surface of the resulting device, the film at those positions at which electrodes are to be provided is formed with bores by a known technique, respectively, and thereafter, for example, aluminum is deposited on the whole surface of the device and thereafter unnecessary portions of the deposited aluminum are removed to form electrodes IN, OUT.sub.1, OUT.sub.2 and +E.

In the device shown in FIG. 3, the signal input region 13 is composed of the p layer 13a and the high-concentration p.sup.+ layer 13b provided on the p layer, and the signal input electrode IN is provided on the p.sup.+ layer 13b. Therefore, the lateral resistance of the signal input region 13 is largely reduced as compared with the conventional device. Accordingly, the time period, during which the input signal is to be propagated through the signal output region, is shortened. In other words, the signal propagation delay time is decreased to a great extent. For instance, FIG. 5 shows that as the power consumption is increased, the signal propagation delay time is proportionately reduced. As seen from FIG. 5, in the prior art case, the delay time indicates, as shown by solid lines, no more decay in the range of 10.sup.-7 to 10.sup.-8 seconds, whereas in the case of this invention the delay time is saturated, as denoted by dotted lines, in the range of 10.sup.-9 to 10.sup.-10 to obtain a device in which the delay time to be saturated is on the sub-nanosecond order. This saturation corresponds to that in the case of an ECL (Emitter Coupled Logic). Further, in the case of the prior art device, where a plurality of output regions are provided, there arises a problem that the points of time when the input signal reaches the output regions differ. According to the invention, however, the lateral resistance of the signal input region becomes extremely small and therefore there is no possibility that the said points of time are made substantially different. More in detail, according to the invention, since, in the upside-down operated transistor Q.sub.1, the resistance of its base becomes small, the resistance between the emitter and base also becomes small; and as the signal input region is composed of the p layer 13a and p.sup.+ layer 13b, the capacitance between the emitter and base becomes small.

In that first modification of the invention shown in FIG. 6, the thickness of the second region 13b of the signal input region 13 is made larger than that of the signal output regions 14a, 14b, and the underside surface of the signal output regions 14a, 14b is adjoined directly to the second region 13b. Though, in FIG. 6, the charge injection region 15a is wholly formed into a p.sup. + type region, it is completely equivalent to the injection region 15 of FIG. 3. The operation and effect of this modification are the same as those of the embodiment shown in FIG. 3.

In that second modification of the invention shown in FIGS. 7A, 7B and 7C, two p.sup.+ regions (second region of the input region) are so formed as to exist between three parallel p regions (first region of the input region). The signal output regions 14a, 14b are formed in the central exposed p region. Accordingly, the regions 14a, 14b have respective parts of their side faces adjoined directly to the second region (p.sup.+) and have their bottom surfaces adjoined directly to the first region (p). The operation and effect of this modification are the same as those of the embodiment shown in FIG. 3.

A third modification of the invention shown in FIG. 8 is a one prepared by further modifying the embodiment shown in FIG. 3. The second region 13b (p.sup.+) of the signal input region 13 surrounds the respective side faces of the signal output regions 14a, 14b and the thickness of this second region 13b is greater than that of the signal output regions 14a, 14b. The boundary between the underside of the first region 13a (p) of the signal input region 13 and the substrate 11 does not take a linear form, and a first boundary 20 opposed to the underside of the signal output regions 14a, 14b assumes a wavy shape so as to become nearer to the surface of the semiconductor device than a second boundary 21 opposed to the underside of the second region 13b (p.sup.+) enclosing the side faces of the signal output regions 14a, 14b. For this reason, according to this modification, the operation and effect of the embodiment shown in FIG. 3 can be much more improved.

FIG. 9 shows a further modification of the invention, and the difference between this modification and the modification shown in FIG. 8 lies in the respect that, in FIG. 9, the underside of the signal output regions 14a, 14b is adjoined directly to the second region 13b (p.sup.+) of the signal input region 13. Namely, the second region 13b (p.sup.+) of the signal input region 13 surrounds the side faces and the undersides of the signal output regions 14a, 14b, and the thickness of those portions of the second region 13b which surround the said side faces is greater than the sum of the thickness of a second-region portion adjoined directly to the underside of said output regions 14a, 14b and the thickness of the signal output regions 14a, 14b. The boundary between the underside of the first region 13a (p) of the signal input region 13 and the substrate 11 is not linear, and the first boundary 20 opposed to the underside of the signal output regions 14a, 14b takes a wavy form so as to become nearer to the surface of the semiconductor device than the second boundary 21 faced to the underside of the second region 13b (p.sup.+) surrounding the side faces of the signal output regions 14a, 14b. According to this modification, the operation and effect of the embodiment of FIG. 3 can be improved to a greater extent.

In the above-mentioned embodiment and modifications, the charge injection region 15 or 15a was so formed as to be made flush with the signal input region 13 and the signal output regions 14a, 14b. But this charge injection region 15 or 15a can be constructed so as to oppose the signal input region 13 in the depth direction of the substrate. Further, obviously, the injector transistor (FIG. 2-Q.sub.2) and the inverter transistor (FIG. 2-Q.sub.1) can of course be modified into an npn type and a pnp type, respectively.