Method of producing semiconductor integrated circuit device including bipolar transistor and insulated gate field effect transistor
This is a continuation of application Ser. No. 06/920,009 filed 10/17/86 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a semiconductor device in which a bipolar transistor and an insulated gate field effect transistor (hereinafter, &#34;MOS transistor&#34;) are formed on a single chip, and more particularly to a method of producing a semiconductor integrated circuit device including a bipolar transistor and an MOS transistor whose substrate region has a conductivity type opposite to that of a collector region of the bipolar transistor. 
     The integrated circuit including bipolar and MOS transistors is called a Bi-MOS IC and features the high speed operation of bipolar transistors and the high integration density of an MOS transistor. One type of Bi-MOS IC includes both P-channel and N-channel MOS transistors and is known as a Bi-CMOS IC. This device has the advantage of low power consumption in addition to high speed and high integration density. 
     In an integrated circuit device, regions of the same conductivity type are formed simultaneously in order to reduce manufacturing steps. In a case where the conductivity type of the substrate region of the MOS transistor is different from that of the collector region of the bipolar transistor, source and drain regions of that MOS transistor are formed simultaneously with an emitter region and a collector contact region of the bipolar transistor. The emitter region and the source and drain regions are formed with a shallow junction in order to enhance the integration density. As a result, the collector contact region is similarly made shallow. This causes an increase in the collector resistance of the bipolar transistor. The switching speed thereof is thus lowered. 
     It is possible to make the collector contact region deeper. However, several additional steps are required for this purpose and the total number of manufacturing steps is greatly increased to raise the manufacturing cost. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a method of producing a Bi-MOS IC or Bi-CMOS IC in which the collector resistance of the bipolar transistor is lowered without greatly increasing the number of manufacturing steps. 
     The present invention is favorably applied to Bi-MOS or Bi-CMOS IC, whose MOS transistor has a gate electrode of polycrystalline silicon. The polycrystalline silicon gate is usually formed by depositing a polycrystalline silicon layer over the entire surface and then doping the layer with impurities for the purpose of lowering the resistance thereof, followed by selectively etching the layer to leave the pattern of the gate electrode. According to the present invention, a collector contact hole is formed before the polycrystalline silicon layer is deposited. Therefore, the impurities doped into the polycrystalline silicon layer are diffused through the collector contact hole into a collector region to form a collector contact region. The diffusion for the collector contact region further proceeds when source and drain regions and an emitter region are formed. As a result, the depth and impurity concentration of the collector contact region can be made greater than that of the source, drain and emitter regions. 
     Thus, by adding only the one step of forming the collector contact hole, a semiconductor device can be produced whose bipolar transistor has a lowered collector resistance while maintaining shallow junctions at the source and drain regions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, advantages and features of the present invention will be made apparent from the following description taken in conjunction with the accompanying drawings, in which 
     FIGS. 1 to 8 are cross-sectional views showing one embodiment according to the present invention; and 
     FIGS. 9 to 16 are cross-sectional views showing another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a Bi-MOS IC or a Bi-CMOS IC in which the high speed of the bipolar transistor and a small size of each transistor are realized without greatly increasing the manufacturing cost a first embodiment will be described with reference to FIGS. 1 to 8. 
     Referring to FIG. 1, a P-type silicon substrate 21 having a resistivity of 10 Ω-cm is prepared, into which aresenic as an N-type impurity and boron as a P-type impurity are selectively diffused to form N +  -type buried regions 22 and 23 having a surface impurity concentration of 10 19  cm -3  and a P +  -type buried region 24 having a surface impurity concentration of 10 17  cm -3 , respectively. An N-type epitaxial layer 25 of 1 Ω-cm is deposited over the substrate 21 having the buried regions 22 to 24. Boron ions are selectively implanted into the epitaxial layer 25, followed by drive-in diffusion, to form a P-type well region 26 reaching the P +  -type buried region 24. The heat treatment for depositing the epitaxial layer 25 and that for the drive-in diffusion process allow the impurities in the buried regions 22 to 24 to diffuse upwardly into the epitaxial layer 25 as shown. Since the P-well region 26 is to be used as the substrate region of an N-channel MOS transistor, its impurity concentration takes a relatively low value, 10 15  cm -3 . The right-hand portion of the epitaxial layer 25 with respect to the P-well region 26 is to be employed as a substrate region of a P-channel MOS transistor and the left-hand portion thereof with respect to the region 26 is to be employed as a collector region of a bipolar transistor. 
     Referring to FIG. 2, silicon nitride films 27--1 to 27--4 to be used as oxidation-resist films are selectively deposited on the epitaxial layer 25 and the P-well region 26 via a thin silicon oxide film (not shown). The films 27--3 and 27--4 cover a base formation portion and a collector contact formation portion, respectively. Local oxidation of the exposed surface of the epitaxial layer is carried out while employing the nitride films 27 as a mask, so that thick silicon oxide films 28 as field insulators are formed with a thickness of about 6000 Å. 
     The silicon nitride films 27--1 to 27--4 and the silicon oxide films thereunder are thereafter removed, followed by gate oxidation. As shown in FIG. 3, gate oxide films 29--1 and 29--2 for P-channel and N-channel MOS transistors are thereby formed, and further the base formation portion and the collector contact formation portion are covered with oxide films 29--3 and 29--4, respectively. Boron ions as P-type impurities are implanted through the oxide film 29--3 into the base formation portion, followed by an annealing diffusion. As a result, a base region 30 is formed with a junction depth of 0.8 μm and a surface impurity concentration of about 10 16  cm -3 . 
     Thereafter, a collector contact hole is opened in the oxide film 29--4 in accordance with the present invention. For this purpose, as shown in FIG. 4, a photoresist film 31 is formed to cover the surface except for one at least one the oxide film 29--4, which is then exposed to a silicon oxide film etchant. As a result, a collector contact hole 32 is formed to expose a part of the collector contact formation portion. 
     After the photoresist film 31 is removed, a polycrystalline silicon layer 33 is deposited over the entire surface, as shown in FIG. 5. N-type impuries are diffused into the polycrystalline silicon layer 33 in order to lower the resistance thereof. It is favorable to employ phosphorus as the impurity, because phosphorus has a large diffusion coefficient. Phosphorus is diffused into the polycrystalline silicon layer 33 to such an extent that the impurity concentration thereof is saturated (10 21  cm -3 ). Phosphorus doped in the layer 33 goes through the contact hole 32 into the collector region of substrate, so that an N +  -type collector contact region 34 is formed with a high impurity concentration. The silicon oxide films 29--1 to 29--3 as well as the field oxide films 28 prevent phosphorus from reaching the P-well region 26, the base region 30 and the N-type substrate region. 
     Referring to FIG. 6, the resistance-lowered polycrystalline silicon layer 33 is selectively removed to form the gate electrode 41 of the P-channel MOS transistor, the gate electrode 40 of the N-channel MOS transistor and the collector electrode 42 of the bipolar transistor. If desired, part of the layer 33 may be utilized as wiring conductors for interconnecting gate electrodes to each other or to other transistors (not shown). A mask layer 35 having an opening 36 and made of aluminum is thereafter deposited, and N-type impurity ions are then implanted through the opening 36 of the mask layer 35. The implantation energy is 50 KeV and the dosage is 5×10 15  cm -2 . Arsenic having a small diffusion coefficient is preferably employed. Antimony may be used, if desired. An annealing treatment is carried out to activate the implanted arsenic ions. As a result, a source regions 37 and a drain region 38 of the N-channel MOS transistor and an emitter region 39 of the bipolar transistor are formed simultaneously with a junction depth of about 0.3 μm. During this annealing treatment, phosphorus in the collector contact region 34 is re-diffused into the collector region. In addition, the impurity in the buried layer 22 is also re-diffused into the collector region. The polycrystalline layers 40 and 42 are also doped with the implanted ions. 
     The mask layer 35 is removed and as shown in FIG. 7, a new mask layer 43 made of aluminum is deposited to protect the N-channel MOS transistor, the emitter region 39 and the contact region 34. Boron ions are then implanted with an implantation energy of 50 KeV and a dosage of 5×10 15  cm -2 . The implanted boron ions are activated by an annealing treatment, so that a source region 44 and a drain region 45 of the P-channel MOS transistor and a base contact region 46 are formed simultaneously with a depth of about 0.4 μm. This annealing treatment again allows phosphorus to re-diffuse again into the collector region. The collector contact region 34 is thereby made deeper. The impurities in the buried region 22 are again re-diffused upwardly into the collector region. On the other hand, arsenic has a diffusion coefficient smaller than that of phosphorus, and therefore the re-diffusion of the emitter regions 39 and the source and drain regions 37 and 38 is suppressed to maintain their shallow junctions. 
     Thus, the collector contact region 34 formed during the step of lowering the resistance of the polycrystalline silicon layer 33 (see FIG. 5) is made deeper than the emitter region 39 and the source and drain regions 37 and 38, as shown in FIG. 7, since phosphorus contained in the region 34 is re-diffused into the collector region by the subsequent annealing treatments. The impurity in the buried region 22 is arsenic, but the impurity concentration thereof is very high. Therefore, the thickness of the buried region 22 is made large. As a result, the distance between the collector contact region 34 and the buried region 22 is made small. In this embodiment, the collector contact region 34 is finally formed with a depth of 1 μm, and the buried region 22 is re-diffused upwardly into the epitaxial layer 25 to a depth of 2 μm. The thickness of the epitaxial layer 25 is 4 μm. Accordingly, the distance between the regions 34 and 22 takes a value of 1 μm. The collector resistance of the bipolar transistor having an emitter region 39 of a 20 μm 2  area is about 105 Ω. 
     Referring to FIG. 8, the mask 43 is removed, and thereafter the polycrystalline silicon gates 40 and 41 and the polycrystalline silicon collector electrode 42 are covered with thin silicon oxide films. A protecting film 47 such as a silicon oxide film, a silicon nitride film or a phosphorus-silicate-glass (PSG) film is deposited over the entire surface. Electrode contact holes are opened in the film 47, and a metal such as aluminum is deposit to form the source electrode 50 and the drain electrode 51 of the N-channel MOS transistor, the source electrode 48 and the drain electrode 49 of the P-channel MOS transistor, and the emitter electrode 53, base electrode 54 and collector lead-out electrode 52 of the bipolar transistor. 
     As described above, adding only the simple step of forming the collector contact hole 32 before the deposition of the polycrystalline silicon layer 33 (see FIG. 4), there is produced a Bi-CMOS IC which includes a bipolar transistor having improved switching speed and P-channel and N-channel MOS transistors each having shallow source and drain regions. 
     With reference to FIG. 9 to FIG. 16, another embodiment of the present invention will be described. This embodiment includes improvements in further reducing the area of the bipolar transistor and enhancing isolation among the transistors. Therefore, the description will focus on these improvements, and the same constituents as in FIG. 1 to FIG. 8 are denoted by the same reference numerals. Moreover, the manufacturing steps shown in FIG. 9 to FIG. 16 correspond respectively to those shown in FIG. 1 to FIG. 8. 
     Referring to FIG. 9, boron ions are implanted in a large dosage into the epitaxial layer 25 to form a P +  -type isolation region 60, and thereafter the P-well region 26 is formed inside of the isolation region 60. Subsequently, phosphorus ions are implanted in a small dosage to form an N-type well region 61 having a desired impurity profile for use as a substrate region of a P-channel MOS transistor. 
     Local oxidation is carried out using silicon nitride films 27 as a mask to form field oxide film 28. In this embodiment, a silicon nitride film 25 covers the bipolar transistor formation section including base formation and collector contact formation portions, as shown in FIG. 10. 
     According to this embodiment, only the silicon nitride film 27--5 is removed and the remaining films 27--1 and 27--2 are left. Local oxidation is performed again under this condition to make a thick silicon oxide film covering the bipolar transistor formation section. The left silicon nitride films 27--1 and 27--2 are thereafter removed, followed by gate oxidation. As a result, as shown in FIG. 11, the P-well region 26 and the N-well region 61 are covered respectively with gate oxide films 29--2 and 29--1, whereas the bipolar transistor formation section is covered with a silicon oxide film 62 having a thickness larger than the gate oxide films 29. This structure may also be obtained by the following steps: The silicon nitride films 27--1, 27--2 and 27--5 are removed simultaneously and thermal oxidation is then carried out, followed by removing the oxidation films over the well regions 26 and 61 to then perform gate oxidation. 
     Since the silicon oxide film 62 is thick, the selective boron ion implantation forms a base region 30 shallower than that of the first embodiment. 
     Referring to FIG. 12, a photoresist film 31 having two openings is formed and the oxide film 62 is then etched away selectively by using the photoresist film 31 as a mask. As a result, a collector contact hole 32 and an emitter contact hole 63 are opened in the film 62 to expose respective portions of the collector region and the base region 30. 
     After the photoresist film 31 is removed, a polycrystalline silicon film 33 is deposited over the entire surface, as shown in FIG. 13. Phosphorus is diffused into the polycrystalline silicon film 33. At this time, a portion of the silicon layer 33 filling the emitter contact hole 63 is covered with a mask layer 64 made of silicon oxide, for example. Therefore, phosphorus forms a collector contact region 34 by passing through the contact hole 32, but it cannot pass through the hole 63. 
     Referring to FIG. 14, the polycrystalline silicon layer 33 is selectively removed. A gate electrode 40 of the N-channel MOS transistor, a gate electrode 41 of the P-channel MOS transistor, and a collector contact electrode 42 of the bipolar transistor are thereby formed, and further a polycrystalline silicon layer 65 for the emitter electrode is formed. Since the layer 65 is not doped with phosphorus, the resistance thereof is extremely high. The polycrystalline silicon electrodes 40 to 42 and the layer 65 are oxidized to form thin silicon oxide films thereover. A mask layer 35 made of aluminum is thereafter deposited for the subsequent selective arsenic ion implantation. The mask layer 35 has an opening 36 for the N-channel MOS transistor as well as an opening 66 for the layer 65. The arsenic ion implantation is carried out, followed by the annealing treatment. An N-type source region 37 and drain region 38 are thereby formed, and the resistance of the layer 65 is lowered. Arsenic is diffused through the emitter contact hole 63 into the base region 30. As a result, an emitter region 39 and an emitter electrode 65&#39; are formed. 
     Referring to FIG. 15, a new mask layer 43 is deposited in place of the mask 35, and boron ions are then implanted, followed by the annealing treatment. As a result, P-type source region 44 and drain region 45 and a P-type base contact region 46 are formed. 
     After the mask 43 is removed, a protective PSG film 47 is deposited over the entire surface, as shown in FIG. 16. Contact holes are opened in the PSG film 47 to form aluminum electrodes 49 to 51 and 54. 
     According to this embodiment, the collector contact hole 32 is formed before the deposition of the polycrystalline silicon layer 33, and therefore the collector resistance of the bipolar transistor is lowered as mentioned hereinbefore. Moreover, the base region 30 is formed with a shallow junction and the field oxide film 28 between the base region 30 and the collector contact region 34 (see FIG. 2) is not required, so that the bipolar transistor is formed with a reduced size. The integration density is thus further increased. 
     Since the oxide film 62 is thicker than the gate oxide films 29, the arsenic ions implanted for the shallow source and drain regions 37 and 38 and the emitter 39 may not reach the base region 30 in spite of the opening 66. Therefore, an emitter contact hole 63 is formed simultaneously with the collector contact hole 32, and arsenic is diffused through the layer 65 and emitter contact hole 63 into the base region 30. 
     Although each described embodiment of the present invention is a Bi-CMOS IC, the present invention is applicable to a Bi-MOS IC including a bipolar transistor and a P-channel or N-channel MOS transistor. An insulative substrate may be employed in place of the silicon substrate. In the above embodiments, the polycrystalline silicon film 33 is doped with phosphorus before patterning it to form the collector electrode 42 and the gate electrodes 40 and 41 (see FIGS. 5 and 6 and FIGS. 13 and 14). However, the polycrystalline silicon film 33 can be patterned first and thereafter phosphorus doped into the patterned the polycrystalline silicon layers to form the collector contact region, the collector electrode and the gate electrodes. An impurity doped polycrystalline silicon film may be used in place of non-doped polycrystalline silicon film 33.