MOS/BIPOLAR INTEGRATED CIRCUIT DEVICE AND MANUFACTURING METHOD THEREOF

Abstract: In a MOS/bipolar integrated circuit device using junction bipolar transistors (Q2) as active elements for directly controlling a large current, and metal oxide semiconductor field effect transistors or MOSFETs (Q1) as active elements for controlling the operation of the bipolar transistor (Q2), all of the MOSFETs (Q1) included in the circuit are simul­ taneously formed on a single-crystalline silicon substrate (10). The bipolar transistors (Q2) are stacked above the MOSFETs (Q1) through an SiO₂ film (26) having a drain contact hole (28), in a two-story manner. The bipolar transistors (Q2) have their base regions connected to the drains of the MOSFETs (Q1), respectively.

Description: MOS/bipolar integrated circuit device and manufacturing method thereof The present invention relates generally to an integrated semiconductor device and, more particularly, to a MOS/bipolar semiconductor device having different transistor elements, such as unipolar transistors including metal oxide semiconductor field effect transistors (MOSFETs) and bipolar transistors (e.g., junction transistors), on the same substrate, and to a manufacturing method thereof. Recently, it is known for those skilled in the art to form different types of transistor elements, such as MOS transistors and bipolar transistors, in a single integrated circuit, thereby achieving a desired technical objective. In order to form, for example, an integrated interface circuit for effectively controlling a considerably large current within such a single circuit, MOS transistors which have low power consumption and are suitable for high packing density are used as control signal sources, while bipolar transistors are used as elements for flowing high currents to be controlled. In such a case, an output control signal from the MOS transistor is supplied to the base of the bipolar transistor. In a conventional semiconductor integrated circuit device having a heterostructure of the different types of transistors described above, MOS and bipolar transistors are two-dimensionally formed on a major surface of the same semiconductor substrate. In this case, three problems are presented: (1) The area of the substrate surface on which the bipolar transistors are formed is larger than that of the MOS transistors, so that the bipolar transistors cannot achieve high packing density, thereby increasing the size of the substrate. (2) The manufacturing process of MOS transistors differs in principle from that of bipolar transistors, so that the manufacturing process becomes complicated when different types of transistors are formed on the same substrate (3) The thermal hysteresis in the epitaxial growth technique is prolonged, so that an impurity profile provided at the initial step of the manufacturing process causes redistribution, thereby degrading electrical characteristics of the element. In problem (3), when epitaxial growth is initiated in the bipolar element region of the substrate adjacent to the MOS element region, auto-doping and/or out-diffusion causes an impurity to diffuse from a prospective epitaxial buried layer into an undesirable portion of the MOS element region of the substrate. Therefore, the manufacturing process of the bipolar transistors adversely affects the MOS transistors. It is therefore an object of the present invention to provide a new and improved semiconductor device and a manufacturing method thereof wherein MOS transistors and bipolar transistors are formed on the same substrate in a high packing density and degradation of electrical characteristics can be prevented. According to the semiconductor device of the present invention, one of two types of transistors (i.e., a MOS or a bipolar transistor) included in an integrated circuit is formed directly on a substrate, with the other type being stacked above it. In this case, the bipolar transistors serve as active elements for directly controlling currents, and the MOS transistors serve as active elements for generating control signals to control the bipolar transistors. For example, MOS transistors are selected as the elements to be formed directly on the substrate. In this case, all the MOS transistors included in the integrated circuit are formed on the substrate at one time. The remaining type of transistors (i.e., bipolar transistors) are formed above the MOS transistors through an insulating layer which has contact holes therein. The present invention may be best understood with reference to the accompanying drawings, in which: Fig. 1A is a plan view partially showing the structure of a field insulation layer formed on the substrate when a MOS/bipolar IC device according to an embodiment of the present invention is manufactured; Fig. 1B is a sectional view partially showing the structure shown in Fig. 1A, taken along line 1B - IS thereof; Fig. 2A is a plan view partially showing the semiconductor device wherein a gate insulation film having a contact hole is formed; Fig. 2B is a sectional view partially showing the structure shown in Fig. 2A, taken along line 2B - 2B thereof; Fig. 3A is a plan view partially showing the semiconductor device wherein a patterned polycrystalline silicon layer and a source-drain region of the MOS transistor are further formed; ; Figs. 3B and 3C are sectional views showing the structure of Fig. 3A, taken along lines 3B - 3B and 3C - 3C, respectively; Fig. 4A is a plan view partially showing the semiconductor device wherein a polycrystalline silicon layer is further formed; Figs. 4B and 4C are sectional views showing the structure of Fig. 4A, taken along lines 4B - 4B and 4C - 4C, respectively; Fig. 5A is a plan view partially showing the semiconductor device wherein the polycrystalline silicon layer is converted by recrystallization to a single-crystalline silicon layer and the singlecrystalline silicon layer is then patterned to provide a prospective element formation region of bipolar transistors; ; Figs. 5B and 5C are sectional views showing the structure of Fig. 5A, taken along lines 5B - 5B and 5C - 5C, respectively; Fig. 6A is a plan view partially showing the semiconductor device wherein bipolar transistors are formed above the MOS transistors; Figs. 6B, 6C and 6D are sectional views showing the structure of Fig. 6A, taken along lines 6B - 6B, 6C - 6C, and 6D - 6D, respectively; Fig. 7 is a circuit diagram partially showing an equivalent circuit of the MOS/bipolar IC device shown in Fig. 6A; and Fig. 8 is a graph showing the measured electrical characteristics of the IC device shown in Fig. 6. In an integrated circuit (IC) device including unipolar transistors, such as metal oxide semiconductor field effect transistors (MOSFETs), and bipolar transistors, such as junction transistors, according to a preferred embodiment of the present invention, only MOS transistors are directly formed on a singlecrystalline semiconductor substrate, with bipolar transistors being formed above the MOS transistors through an insulating layer, in a two-storied structure. To clearly disclose the IC device having the unique structure according to the present invention, a description will be made with reference to the manufacturing steps of the device. An insulating layer or field insulation layer 12 having rectangular windows 14 is formed on an n-type single-crystalline semiconductor substrate 10 containing, e.g., phosphorus as an impurity, in a concentration of 1.5 x 1015 cam , as shown in Fig. 1A. The windows 14 correspond to element formation regions of MOS transistors such as enhancement-type MOS transistors. Fig. 1B illustrates a sectional view of the structure of Fig. 1A taken along the line 1B - 1B thereof. It should be noted that these drawings are not drawn to scale. Subsequently, the structure shown in Fig. 1 is exposed in a dry atmosphere at a predetermined temperature (i.e., at a high temperature of 9000C), to deposit a gate oxide film 16 thereon to a thickness of about 500 , as shown in Figs. 2A and 2B. A rectangular opening 18 corresponding to a contact hole of the drain region of. an MOS transistor is formed within each element formation region 14. P-type impurity ions such as boron ions are injected into the substrate 10 through the opening 18, at a dose of 4 x 1015 cm 2 and an ion acceleration voltage of 40 keV, thereby decreasing the resistance of the drain region of the substrate. Thereafter, a polycrystalline silicon film 20 having a thickness of, e.g., 3,000 A is deposited by a known reduced-CVD method to cover the entire surface of the structure shown in Figs. 2A and 2B. The polycrystalline silicon film 20 is patterned, as shown in Figs. 3A to 3C, thereby obtaining patterned films 20a and 20b. In this embodiment, the patterned polycrystalline silicon film 20a contacts the drain region of one MOS transistor formation region 14a through the contact hole 18 and also serves as the gate region of another MOS transistor to be formed in another MOS transistor formation region 14b. It should be noted that the self-alignment technique among silicon gate techniques is utilized to pattern the polycystalline silicon film 20. In this case, an etchant used for patterning the film 20 stops its etching action when the etchant reaches the gate oxide film 16 or the field insulation layer 12. Subsequently, a p-type impurity such as boron is injected under the same conditions as previously described, thereby forming two p-type high-impurity regions 22 and 24 in a surface layer of the substrate 10 within each of the MOS transistor formation regions 14. The respective high-impurity regions 22 and 24 correspond to the source and drain, respectively, of an MOS transistor. As a result, as clearly shown in Fig. 3C, a p-channel MOS transistor Q1 is prepared. It should be noted that boron ions are injected into the patterned polycrystalline films 20a and 20b as well as into the source and drain regions 22 and 24 within the substrate 10, in accordance with ion injection for forming the source and drain regions. Subsequently, an insulating film 26 such as a plasma CVD-SiO2 film is deposited to cover the entire surface of the structure shown in Fig. 4, to a thickness of, e.g., about 6,000 . An opening 28 serving as another contact hole or drain contact hole is formed in a portion of the film 26 corresponding to the contact hole 18 of the MOS drain region. A second polycrystalline silicon film 30 having a thickness of 3,000 A is deposited to cover the entire surface of the film 26 having the drain contact hole 28. Therefore, the second polycrystalline silicon film 30 contacts the underlying first polycrystalline silicon film 20a through the drain contact hole 28. The polycrystalline silicon material on the drain region 24 of the MOS transistor Q1 at the position of the contact hole 18 has a total thickness of 6,000 , corresponding to the sum of the thicknesses of the first and second polycrystalline layers 20a and 30. The MOS drain region 24 is electrically connected to the second polycrystalline silicon film 30 through the two contact holes 18, 28 and the first polycrystalline silicon film 20a. Then, the second polycrystalline silicon film 30 is recrystallized by a rapid annealing technique, such as a laser beam annealing technique, so that the second polycrystalline silicon film 30 is converted to a single-crystalline silicon. In this embodiment, a CW-argon laser was used as an annealing beam source, the raster scan rate was 9.8 cm/sec, and the raster scan pitch was set at from 5 to 20 pm. The atmosphere temperature during annealing was kept at a temperature of 490 C, and the laser power was 7 to 15 W. When laser annealing was performed under these conditions, it was found that the second polycrystalline silicon film 30 was effectively recrystallized by using the film portion 30a at the drain contact hole 28 as a seed. In this embodiment, it was found that a suitable laser beam power was in the range between 7 W and 15 W. When the laser power exceeded this range, the second polycrystalline silicon film 30 was melted. However, when the laser power was below this range, the polycrystalline silicon film was not recrystallized. As a result, it was found that the polycrystalline silicon film 30 was sufficiently recrystallized in the laser power range between 7 W and 15 W. When the recrystallized film was observed by an electron diffraction test, Kikuchi lines were clearly observed. Furthermore, when the recrystallized film was observed by electron beam transmission, only a very small amount of polycrystalline silicon was observed. The polycrystalline silicon film 30 was substantially completely recrystallized to single-crystalline silicon. The recrystallized monocrystalline silicon film 30' is then patterned, as shown in Figs. 5A to 5C. Therefore, single-crystalline substrate layers 30'-1 and 30'-2 are prepared for forming bipolar transistors therein, respectively, above the MOS transistors. Subsequently, bipolar transistors are formed in the layers 30'-1 and 30'-2, respectively. For this purpose, arsenic is injected into each of the layers 30'-1 and 30'-2, using a known ion injection mask (not shown). As best illustrated in Fig. 6C, an npn bipolar transistor Q2 having a first n-conductivity type region (emitter region) 32, a p-conductivity type region 34 (base region) 34 and a second n-conductivity type region (collector region) 36 is formed in the layer 30'-1. A bipolar transistor is formed in the layer 30'-2, in the same manner as that formed in the layer 30'-1. The ion injection conditions for forming the pnp junction structure were given as follows: a dose of cm and cm 2 and an ion acceleration voltage of 30 keV at the bipolar transistor emitter region; a dose of cm loll cam¯2 and an ion acceleration voltage of 50 keV at the collector region; and a dose of 1 x l016 cm 2 and an ion acceleration voltage of 50 keV at a'portion adjoining a conductive layer (not shown) serving as the collector electrode. Thereafter, an insulating film 38 made of a CVD-SiO2 film is deposited to cover the entire surface of the structure. Contact holes 40a, 40b, 40c for the base, emitter and collector electrodes, respectively, are formed in the film 38. Wiring pattern layers (not shown) made of aluminum or platinum are deposited to cover the resultant structure and are patterned, thereby obtaining a desired configuration of circuit connections. Fig. 7 illustrates an equivalent circuit of a pair of a MOS and a bipolar transistor stacked in a two-storied structure in the semiconductor IC device manufactured as described above. The drain 24 of the underlying MOS transistor Q1 is connected to the collector region 36 of the overlying bipolar transistor Q2 and to a power supply terminal 42, through an equivalent resistor component R1 (including a junction resistance between the layer); and to the base region 34 of the bipolar transistor Q2, through another resistor component R2. A voltage VDD is supplied to the power supply terminal 42. In this embodiment, the resistance R1 between the power supply terminal 42 and the MOS drain 24 was measured to be 7.1 kQ, while the resistance R2 between the MOS drain 24 and the bipolar base 34 was measured to be 10 kn. Under such conditions, the ON resistance of the MOS transistor Q1 was 42.9 kn. When the DC characteristics of the bipolar transistor Q2 were measured, the results shown in Fig. 8 were obtained. A base-emitter voltage VBE is plotted along the axis of the abscissa, and a collector current density JC is plotted along the axis of the ordinate. A collector-emitter voltage VCE is preset to be 5.0 V. As is apparent from the graph in Fig. 8, thebipolar transistor has good electrical characteristics. When the lifetime of the electrons in the base was measured in accordance with these electrical characteristics, it was found to be 10 6 sec. This lifetime was substantially the same as that of a transistor formed on a conventional bulk substrate. The dynamic characteristics of the semiconductor IC device of the present invention may be described as follows. The power supply voltage VDD was -5 V, and a voltage which was -1.0 V higher than a threshold voltage was applied to the gate of the MOS transistor Q1, so that the MOS transistor Q1 was rendered conductive. Under such conditions, the potential (i.e., the drain potential) at a node 44 shown in Fig. 7 was measured by calculating the ratio of resistance R1 to the ON resistance of the MOS transistor Q1, and was found to be -4.29 V. Furthermore, the potential at the base was -4.3 V, since the resistance R2 was present between the MOS drain 24 and the bipolar base 34. In this case, the base current was not more than 10-6 A/cm , and the collector current JC was 10-4 JCA/cm2, under conditions wherein V BE = 0.7 V. However, when the MOS transistor was rendered nonconductive, the potential at the MOS drain was -4.9 V, the potential at the bipolar base was the same as that at the MOS drain, the base current was not more than 10 11 A/cm2, and the collector current was 10 A/cmê. Upon ON/OFF operation of the MOS transistor Q1, it was found that the collector current of ofthe bipolar transistor varied in the range between 10 4 A/cm2 and 10 11 A/cm2. In other words, it was found that good switching characteristics could be obtained. According to the embodiment of the present invention, the bipolar transistors Q2 were stereographically (in a two-storied structure) stacked above the MOS transistors Q1 formed on the substrate 10, through the insulating layer. Therefore, the packing density of the circuit with respect to the substrate 10 can be greatly increased. In the device of the present invention, it was confirmed by the present inventors that the element area of the substrate could be decreased by about 55%, as compared to that of the conventional twodimensional IC device having both MOS and bipolar transistors. Furthermore, according to the present invention, all of the MOS transistors can be simultaneously formed -on the substrate 10 in the first step. Thereafter, all of the bipolar transistors are simultaneously formed. Therefore, the manufacturing process of the present invention can be simplified as compared with that of the conventional IC device in which the MOS and bipolar transistors are formed on the same substrate in a mixed manner. The device of the present invention has better electrical characteristics of the transistor elements, due to the following reasons. First, the bipolar transistors are formed on the MOS transistors in a stacked manner through the insulating layer, so that adverse effects of the thermal hysteresis in the manufacturing process of the bipolar transistors (e.g., changes in impurity distribution in the active impurity regions) tend not to extend to the underlying MOS transistors due to the presence of the SiO2 layer having a small heat conduction. In the conventional device, since the bipolar transistors are adjacent to the MOS transistors, heat in the manufacturing process of the bipolar transistors is directly conducted to the MOS transistors through the substrate, thereby adversely affecting the MOS transistors. Secondly, rapid annealing, such as laser beam annealing, which does not substantially influence the underlying layer, may be used when the bipolar transistors are formed above the MOS transistors. Thirdly, since the bipolar transistors through which large currents flow are positioned above the MOS transistors, heat dissipation of the bipolar transistors can be improved. Although the present invention has been shown and described with respect to a particular embodiment, various changes and modifications, which are obvious to a person skilled in the art to which the invention pertains, are deemed to lie within the spirit and scope of the invention. For example, an electron beam may be used in place of a CW-argon laser beam in order to anneal and recrystallize the polycrystalline silicon film. The conditions for beam annealing are determined in such a way as to allow for the proper recrystallization of the polycrystalline silicon film and may be arbitrarily modified, as necessary. In the above embodiment, the p-channel enhancement-type transistor is used. However, the present invention may also be applied to an n-channel or depletion-type transistor. The substrate and thin film materials are not limited to silicon, but may be extended to any type of semiconductor.

Claims: Claims: 1. A semiconductor device using bipolar transistors (Q2) as first active elements for directly controlling currents, and unipolar transistors (Q1) as second active elements for supplying control signals to said bipolar transistors (02), said unipolar and bipolar transistors (Q1, Q2) having different operating modes and being formed on a single semiconductor substrate (10), characterized in that first transistors comprising one of said unipolar transistors (Q1) and said bipolar transistors (Q2) which are included in said integrated circuit are directly formed on said substrate (10), and that second transistors comprising the other of said unipolar and bipolar transistors (Q1, Q2) are stacked above said first transistors. 2. The device as recited in claim 1, characterized in that said unipolar transistors comprise metal oxide semiconductor field effect transistors (Q1), while said bipolar transistors comprise junction transistors (Q2) of a predetermined conductivity type. 3. The device as recited in claim 2, characterized in that said first transistors comprise said metal oxide semiconductor field effect transistors (Q1) each of which has source and drain regions formed in said substrate (10), and said second transistors comprise said junction bipolar transistors (Q2) having base regions, respectively. 4. The device as recited in claim 3, characterized by further comprising an electrical insulating layer (26) formed on said metal oxide semiconductor field effect transistors (Q1) as to be sandwiched between said metal oxide semiconductor field effect transistors (Q1) formed on said substrate (10) and said junction bipolar transistors (Q2), said insulating layer having at least one contact hole (28) in a portion thereof which corresponds to the drain region (24) of at least one of said metal oxide semiconductor field effect transistors (Q1). 5. The device as recited in claim 4, characterized in that the base region (34) of at least one junction bipolar transistor (Q2) positioned immediately above said at least one metal oxide semiconductor field effect transistor (Q1) is connected to the drain region (24) of said at least one field effect transistor (Q1) through the contact hole (28) of said insulating layer (26). 6. The device as recited in claim 5, characterized by further comprising single-crystalline semiconductor layer components (30'-1, 30'-2) in which said bipolar transistors (Q2) are respectively formed so as to have a# junction layer structure corresponding to the predetermined conductivity type, said single-crystalline semiconductor layer components (30'-1, 30'-2) being formed on said insulating layer (26) and above said field effect transistors (Q1), and being converted by recrystallization from a polycrystalline semiconductor material to a single-crystalline semiconductor material. 7. The device as recited in claim 6, characterized by further comprising a polycrystalline film (20a) formed between the drain region (24) of said at least one metal oxide semiconductor field effect transistor (Q1) formed on said substrate (10) and at least one layer component (30'-1) of said semiconductor layer components (30'-1, 30l-2), which contains therein said at least one junction bipolar transistor (Q2) having the base region (34) connected to the drain region (24) of said at least one metal oxide semiconductor field effect transistor (Q1), said polycrystalline film (20a) being injected with ions of a suitable impurity. 8. The device as recited in claim 7, characterized in that said polycrystalline silicon film (20a) extends under said insulating layer (26), thereby serving as a gate electrode of an adjacent metal oxide semiconductor field effect transistor (Q2). 9. A semiconductor integrated circuit device having a single-crystalline semiconductor substrate (10) having a surface portion, characterized in that said device comprises metal oxide semiconductor field effect transistors (Q1) which are directly formed on said substrate and include at least one pair of first and second field effect transistors (Q1) adjacent to each other, each of said field effect transistors having source and drain regions (22, 24) formed in the surface portion of said substrate (10), and a gate electrode; a conductive layer (20a) provided in such a way as to constitute the gate electrode of the first field effect transistor and to electrically connect the gate electrode of said first field effect-transistor (Q1) with a drain region (-24) of said second field effect transistor; a first insulating layer formed on said field effect transistors (Q1) and said conductive layer (20a) and having a contact hole (28) at a portion thereof corresponding to at least the drain region (24) of the second field effect transistor; singlecrystalline semiconductor layers (301-l, 30'-2) formed on said insulating layer (26) and above said field effect transistors (Q1), respectively, said semiconductor layers including a single-crystalline semiconductor layer (30#-l) which is formed above the second field effect transistor and is electrically connected to the drain region (24) of the second field effect transistor through the contact hole (28) of said insulating layer (26); and junction bipolar transistors (Q2) of a predetermined conductivity type respectively formed in said single-crystalline semiconductor layers (30'-1, 30'-2) so as to have base, emitter and collector regions (34, 32, 36), said bipolar transistors including a junction bipolar transistor (Q2) having a base region (34) connected to the drain region (24) of said second field effect transistor (Q1) through said conductive layer (20b) and the contact hole (28) of said insulating layer (26). 10. The device as recited in claim 9, characterized in that said conductive layer comprises a polycrystalline silicon layer into which ions of a suitable impurity are injected, and said first insulating layer comprises a silicon oxide layer. 11. The device as recited in claim 10, characterized by further comprising a second insulating layer (38) formed on said first insulating layer (26) and said single-crystalline semiconductor layer (30') having said bipolar transistors (Q2) formed therein, and having contact holes (40a, 40b, 40c) at portions thereof respectively corresponding to the base, emitter and collector regions (34, 32, 36) of said bipolar transistors (Q2). 12. A method for manufacturing a semiconductor device constituted by an integrated circuit including unipolar transistors, such as metal oxide semiconductor field effect transistors (Q1), and bipolar transistors, such as junction transistors (Q2) having a predetermined conductivity type, said unipolar and bipolar transistors being formed on a semiconductive substrate (10), characterized by comprising the steps of simultaneously forming, on said substrate (10), metal oxide semiconductor field effect transistors (Q1) which have drain regions (24) and which are included in said integrated circuit; depositing an electrical insulating layer (26) on said metal oxide semiconductor field effect transistors (Q1); forming contact holes (28) in portions of said insulating layer (26), which respectively correspond to the drain regions (24) of said metal oxide semiconductor field effect transistors (Q1); forming a single-crystalline silicon layer (30) to cover a resultant structure and patterning said single-crystalline silicon layer (30) to obtain single-crystalline silicon layer components (30'-1, 30'-2) respectively corresponding to said field effect transistors (Q1); and simultaneously forming junction bipolar transistors (Q2) in said single-crystalline silicon layer components (30'-1, 30'-2), respectively, said junction bipolar transistors (Q2) being included in said integrated circuit. 13. The method as recited in claim 12, characterized in that said single-crystalline silicon layer forming step comprises forming a polycrystalline silicon layer (30) to cover said resultant structure, and recrystallizing said polycrystalline silicon layer (30) in accordance with a beam annealing technique, thereby converting said polycrystalline silicon layer (30) to said single-crystalline silicon layer (30'). 14. The method as recited in claim 13, characterized in that said junction bipolar transistors forming step comprises injecting ions into said single-crystalline silicon layer components (30'-1, 30'-2) such that said junction bipolar transistors (Q2) respectively have base regions (34) connected to the drain regions (24) of said metal oxide semiconductor field effect transistors (Q1).

Inventors: DANG, RYO, ONGA, SHINJI
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1983
Main classification: H01L27
IPC codes: H01L27, H01L29, H01L21