SEMICONDUCTOR DEVICE HAVING INCREASED IMMUNITY AGAINST ALPHA-PARTICLES AND EXTERNAL NOISE

Abstract: A semiconductor device includes a layer (3) doped with impurities, provided between a buried layer (2) and an epitaxial layer (4), and having a conductivity of the type opposite to that of said buried layer (2) and said epitaxial layer (4). A reversely biasing voltage is applied across the buried layer (2) and the doped layer (3). Side surfaces of the epitaxial layer (4) are surrounded by an insulator (7). This helps effectively to prevent any element (10...14) formed in the epitaxial layer (4) from being affected by α-particles and greatly improves the reliability of the semi­ conductor device.

Description: Background of the Invention The present invention relates to a semiconductor device, and more specifically to a semiconductor device having increased immunity against α-particles and external noise. In a conventional semiconductor device as disclosed, for example, in Japanese Patent Laid-Open No. 1556/1981 (which corresponds to DE-A- 3 022 565), a p-type substrate is provided with a buried layer which is doped with large amounts of n-type impurities, an epitaxial layer is grown thereon, and a transistor is formed in the epitaxial layer. With the thus formed transistor, however, as the α-particles infiltrate from the external side to generate electron and hole pairs in the p-type substrate, the electrons are absorbed by the epitaxial layer through the buried layer and the potential undergoes the change. Therefore, the memory cell using such a transistor leaves a problem with regard to that the data tends to be easily destroyed, and it has been urged to solve this problem. Summary of the Invention The object of the present invention is to provide a semiconductor device which is free from the above-mentioned problem inherent in the conventional art, which has increased immunity against external noise, and which is very little likely to develop soft error by α-particles. To achieve the above object according to the present invention, a doped layer of a first type of conductivity surrounded by an insulator is interposed between a buried layer of a second type of conductivity that is formed in the surface region of a semiconductor substrate of the first type of conductivity and an epitaxial layer of the second type of conductivity that is formed on said buried layer and that is surrounded by the insulator. This helps prevent the infiltration of electrons from the substrate into the epitaxial layer of the second type of conductivity which is the active region. In the conventional device, the electrons generated in the substrate of the first type of conductivity due to α-particles that have entered from the ceramic package into the substrate, enter into the epitaxial layer of the second type of conductivity which is the active region giving rise to the occurrence of a serious problem of so-called soft error. According to the present invention, however, the doped layer of the first type of conductivity exists between the epitaxial layer of the second type of conductivity and the buried layer of the second type of conductivity, and both the epitaxial layer and the doped layer are surrounded by the insulator. Therefore, the electrons are effectively prevented from flowing into the epitaxial layer from the substrate. Thus, a variety of memory devices can be formed in the epitaxial layer which is the active region, featuring very little probability of soft error by α-particles and very high reliability. Brief Description of the Drawings Figs. 1,2 and 3 are diagrams showing one example of steps for producing semiconductor devices of the present invention; and Figs. 4, 5 and 6 are section views showing different embodiments of the present invention. Description of the Preferred Embodiments Figs. 1, 2 and 3 are diagrams showing one example of steps for producing semiconductor devices of the present invention. As shown in Fig. 1, first, antimony is selectively doped by the known gas diffusion technology into a desired portion in the surface region of a p-type silicon substrate 1, to form an n-type buried layer 2 of a low resistivity. Further, boron is seletively doped by the ion implantation technology to form a p-type doped layer 3. Referring to Fig. 2, silicon is epitaxially grown by the well-known chemical vapor deposition method to form an n-type epitaxial layer 4, and a silicon dioxide film 5 and a silicon nitride film 6 are formed on the epitaxial layer 4. Then, a silicon dioxide region 7 is formed as shown in Fig. 3 by the well-known selective oxidation method. Here, side surfaces of the p-type doped layer 3 under the active region are surrounded by the silicon dioxide region 7. Then, a p-type doped layer 8 and an n-type doped layer 9 are provided so that a potential can be applied from the substrate surface to the p-type doped layer 3 and the n-type buried layer 2, respectively. Thereafter, any device such as bipolar transistor, diode, MOS transistor, capacitor or resistor is formed in the epitaxial layer 4 (active region) surrounded by the silicon dioxide region 7, thereby to form a semiconductor devise that is very little affected by the external noise or α-particles. Fig. 4 is a section view of a lateral pnp-type bipolar transistor which is obtained by forming a p-type doped layer 10 and an n-type doped layer 11 in the epitaxial layer 4. In Fig. 4, symbols 12, 13, 14, 17 and 18 denote aluminum electrodes formed by a conventional method. A reversely biasing voltage is applied across the p-type doped layer 3 and the n-type buried layer 2 via the electrodes 17, 18, and whereby a depletion layer is formed in the boundary between the p-type doped layer 3 and the n-type buried layer 2. Therefore, even if electrons are generated by α-particles that have infiltrated into the silicon substrate 1, the passage of electrons is blocked by the electric field in the depletion layer; i.e., the electrons are effectively prevented from infiltrating into the n-type epitaxial layer 4 which is the active region. As will be obvious from Fig. 4, furthermore, side surfaces of the n-type epitaxial layer 4 and the p-type layers 3 are surrounded by the silicon dioxide region 7. Therefore, electrons generated by the α-particles do not infiltrate into the epitaxial layer 4 through the side surfaces. Namely, electrons heading from the substrate 1 toward the bottom surface of the epitaxial layer 4 are blocked by the electric field in the depletion layer, and electrons heading from the sides toward the epitaxial layer 4 are blocked by the silicon dioxide region 7. Therefore, the bipolar transistor formed in the epitaxial layer 4 is very little affected by the α-particles, and the semiconductor device features a very high reliability. Fig. 5 illustrates another embodiment of the present invention in which a Schottky barrier diode is formed in the epitaxial layer 4. That is, a silicide layer (platinum silicide in this embodiment) 19 and an n-type doped layer 11 having a low resistivity are formed on the surface of the epitaxial layer 4, and then aluminum electrodes 15, 16 are formed. A Schottky contact is formed between the silicide layer 19 and the epitaxial layer 4, and an ohmic contact is formed between the n-type doped layer 11 and the aluminum electrode 16. Consequently, a Schottky barrier diode is formed in the epitaxial layer 4 with one aluminum electrode 15 as an anode and another aluminum electrode 16 as a cathode. Like the bipolar transistor of the above-mentioned embodiment, the Schottky barrier diode of this embodiment is very little affected by the α-particles and features a high reliability. Fig. 6 shows a further embodiment in which the invention is adapted to a semiconductor device such as bipolar transistor of the type wherein an electrode is taken out from a desired side surface of the semiconductor layer such as base via polycrystalline silicon having a low resistivity. As is obvious from Fig. 6, p-type doped regions 22 are provided by the sides of the p-type doped region 3 and the epitaxial layer 4, and polycrystalline silicon layer 21 of a low resistivity doped with boron is formed on the back side of the p-type doped regions 22 (on the side opposite to the epitaxial layer 4). A positive potential is applied to the aluminum electrode 18 and a negative potential is applied to the aluminum electrode 17. Then, the positive potential is applied to the n-type buried layer 2 via the n-type region 9 having a low resistivity and the negative potential is applied to the p-type doped layer 3 via the polycrystalline silicon layer 21 having a low resistivity and the p-type doped region 22. Like the aforementioned embodiments, therefore, a depletion layer is formed in the boundary between the p-type layer 3 and the n-type buried layer 2. The depletion layer effectively prevents the infiltration of electrons into the epitaxial layer 4 from the lower direction. Further, the infiltration of electrons into the epitaxial layer 4 from the side directions is blocked by the silicon dioxide regions 7, 20 that surround the side surfaces of the epitaxial layer 4 and the p-type layer 3. Therefore, the element (Schottky barrier diode in this embodiment) formed in the epitaxial layer 4 is far less affected by the α -particles than the conventional devices. This embodiment makes it possible to greatly reduce the area of the epitaxial layer 4 which is the active region (where elements such as transistors and diodes are formed) compared with the above-mentioned other embodiment, and is very advantageous for increasing the degree of integration. Moreover, since the size of the p-type layer 3 can be reduced considerably, the capacity decreases relative to the n-type buried layer 2, and the element exhibits improved characteristics. According to the present invention, as obvious from the foregoing description, fault caused by the α-particles decreases greatly which is very effective to improve characteristics of the semiconductor device. For instance, if the present invention is adapted to a highly integrated memory LSI which employs very-high-speed bipolar transistors, there can be obtained a semiconductor device which develops very little soft error caused by α-particles and which is little affected by the external noise. A 1-kilobit bipolar memory prepared in accordance with the present invention exhibited a maximum collected charge of 4.8 x 10⁻¹³ C (about one-fifth that of the conventional charge), Q MC which is reduced to 1/3.5, and Q noise which is reduced to 1/5. Accordingly, the error bit rate becomes 10⁻⁵/sec (compared with the conventional rate of 10⁻¹/sec), and the immunity against the α-particles is improved by about ten thousand times compared with the existing memory cells. In the above embodiments, a bipolar transistor or a Schottky diode was formed in the n-type layer 4. According to the present invention, however, what can be formed in the n-type layer 4 is not necessarily limited to the bipolar transistor or the Schottky diode. For instance, there can be formed one or two or more elements such as MOS transistors, capacitors or resistors. It needs not be pointed out that there can be obtained a variety of memories or circuits by forming a plurality of such elements. Further, the thickness and impurity concentration of the doped layer 3 having the first type of conductivity are determined from the kind of the semiconductor device to be formed. Favorable effects can be obtained if the thickness is greater than about 0.4 µm and the impurity concentration is greater than about 1 x 10¹⁷ cm⁻³. In the above-mentioned embodiments, furthermore, side surfaces of both the n-type epitaxial layer 4 and the p-type layer 3 are surrounded by an insulator. The most desirable results are obtained if the two layers are surrounded by the insulator. Even when side surfaces of the n-type epitaxial layer 4 only are surrounded by the insulator without surrounding side surfaces of the p-type layer 3, the device still exhibits improved results compared with those of the conventional semiconductor devices.

Claims: A semiconductor device comprising: a buried layer (2) formed in the surface region of a semiconductor substrate (1) of a first type of conductivity and having a second type of conductivity opposite to the first type of conductivity; a doped layer (3) of the first type of conductivity and an epitaxial layer (4) of the second type of conductivity that are stacked on said buried layer (2); an insulator region (7) surrounding the side surfaces of at least said epitaxial layer (4); means (8, 9, 17, 18) through which a reversely biasing voltage across said buried layer (2) and said doped layer (3) is applied to form a depletion layer between the doped layer (3) and the burried layer (2); and at least one device (10...14) formed in said epitaxial layer (4). A semiconductor device according to claim 1, wherein said first type of conductivity is the p-type and said second type of conductivity is the n-type. A semiconductor device according to claim 1 or 2, wherein said insulator region (7) surrounds the side surfaces of said doped layer (3) and of said epitaxial layer (4). A semiconductor device according to any of claims 1 to 3, wherein said means for applying voltage to said doped layer (3) includes a region (22) of the first type of conductivity provided in contact with an end of said doped layer (3) and a polycrystalline silicon layer (21) having a low resistivity and being in contact with said region (22) of the first type of conductivity. A semiconductor device according to any of claims 1 to 4, wherein said device is a bipolar transistor, a diode, a memory element, a MOS transistor, a resistor and/or a capacitor. A semiconductor device according to claim 5, wherein said bipolar transistor (10...14) has the lateral pnp structure. A semiconductor device according to claim 5, wherein said diode is a Schottky barrier diode (11, 15, 16, 19).

Inventors: HOMMA, NORIYUKI, IKEDA, KIYOJI, KURE, TOKUO, NAKAMURA, TOHRU, NAKAZATO, KAZUO, SAGARA, KAZUHIKO
Applicants: HITACHI, LTD.
Application year: 1985
Main classification: H01L27
IPC codes: H01L21, H01L27, H01L29