METHOD OF MANUFACTURING A SEMICONDUCTOR DEVICE HAVING ISOLATION REGIONS

Abstract: A method of manufacturing a semiconductor device with clearly defined isolating regions between active regions whenever the problem of isolating oxide encroaching into the active regions is overcome, comprises the steps of forming a recess (63) in the upper surface of a silicon semiconductor substrate (62), forming an insulating film (64,65) covering the inner surface of the recess, forming a polycrystalline silicon film (68) on substantially the entire surface of the insulating film and oxidizing (71) the polycrystalline silicon film. In one embodiment the polycrystalline silicon film (68) is removed to expose the upper surface of the insulating film while leaving a portion (69) of the polycrystalline silicon film in the recess, the remaining portion of the polycrystalline silicon film is oxid­ ized to form an oxide film (71) thereof, and the insulating film (64,65) is etched off to expose the upper surface (86,87) of the substrate on the opposite sides of the recess. According to another embodiment, after removing the polycrystalline sili­ con film, except a portion thereof remaining in the recess, the resulting assembly is oxidized to form an oxide film of the remaining portion of the polycrystalline silicon film and an oxide film of the silicon substrate, and the oxide film of the silicon substrate is removed to expose portions of the upper surface thereof to form active regions.

Description: METHOD OF MANUFACTURING A SEMICONDUCTOR DEVICE BACKGROUND OF THE INVENTION This invention relates to a method of manufacturing semiconductor devices having miniaturized element isolation regions. PRIOR ART Recently, the degree of miniaturization of integrated circuits of semiconductor devices has become remarkably high, and this has depended much on advances in manufacturing techniques. Particularly, the selective oxidation method is one of the most important methods of manufactures for isolation between elements, and this method has been utilized frequently. The selective oxidation method is disclosed in Japanese Patent Publication No. 49916 (1972) as a LOCOS (Local Oxidation of Silicon) method. For example,Figs.1(a) through (d) show steps of manufacturing semiconductor device utilizing a prior art LOCOS method. Firstly, as shown in Fig. 1(a), a thin heat-grown oxide film 2 is formed on a silicon semiconductor substrate 3, and after which a nitride film 1 is formed by the CVD method on the surface of the oxide film 2. Then, as shown in Fig. l(b), an oxidation-resisting mask region 4 consisting of a nitride film 1' and an oxide film 2' is formed. Successively, as shown in Fig. l(c), the substrate is subjected to oxidation treatment to form a thick field oxide film region 5 for isolation of elements. Thereafter, an active region 6 is obtained by removing the mask region 4 as shown in Fig. 1(d). However, with the conventional LOCOS method, bird beak's regions are also produced below the end portions of the mask region 4 as shown in Fig. 1(c ! . Accordingly. dead spaces are produced by the bird beak's regions intruding into the oxidation-resisting mask region, whereby the width of the element isolation region is increased. As it is necessary to increase the dimension of the oxidation-resisting mask pattern by the dimension of the bird-beak's region intruding below the oxidation-resisting mask region, it becomes difficult to control the width of the element isolation region. Particularly, in the case where an active region for a MOS transistor element is to be formed, when the gate width is decreased above the designed value due to the intrusion of the bird beak's region, a narrow channel effect appears where the threshold value of the MOS transistor is increased. As a result, with the prior art LOCOS method, the bird beak's region made it difficult to realize an LSI having higher densities. SUMMARY OF THE INVENTION It is an object of the present invention to remove the conventional disadvantage described above, and to provide a method of manufacturing a semiconductor device capable of miniaturizing the element isolation region by preventing occurrence of bird beak's region. According to this invention, the method of manufacturing the semiconductor device comprises the steps of forming a recess on a semiconductor substrate, forming an insulating film having a form near to that of the recess on the recess, forming or depositing a polycrystalline silicon oxide film having substantially a flat surface on the entire surface of the insulating film, and oxidizing the polycrystalline silicon film leaving it only in the recess. In a further aspect this invention provides a method of manufacturing a semiconductor device wherein a film is formed on an upper surface of a silicon semiconductor device and subsequently removed to define an active semiconductor region characterised by the steps of forming a recess in the upper surface, forming an insulating film covering a surface of said recess, forming a polycrystalline film on said insulating film, and processing said polycrystalline film so that a separate portion of said polycrystalline film is formed in and/or above said recess, oxidising said polycrystalline film and then processing the semiconductor device to remove said insulating film in regions other than said recess whilst leaving oxidised polycrystalline film in and/or above said recess. BRIEF DESCRIPTION OF THE INVENTION In the accompanying drawings: Figs. l(a) through (d) show steps of the prior art method for forming element isolation region, respectively; Figs. 2(a) through (h) show successive steps of manufacturing a semiconductor device having element isolation regions according to one embodiment of this invention, respectively; Figs.3(a) through (c) show successive steps of rnanu- facturing a semiconductor device according to the second embodiment of this invention, respectively. PREFERRED EMBODIMENTS An embodiment of the method of manufacturing semi conductor device according to this invention will now be described referring to the drawings. Figs. 2(a) through (h) show successive steps describing one embodiment. As shown in Fig. 2(a), an etching mask layer 61, such as a photo-resist, is formed on entire surface of a substrate 62, after w-hach the etching is removed selectively to expose desired surface of the silicon substrate. Successively, as shown in Fig. 2(b), a recess 63, having a depth of 0.5 to 2 ij, for example, is formed by means of a dry etching in a silicon substrate 62 using an etching mask layer 61 as a mask. Thereafter, as shown in Fig. 2(c), a thin heatgrown silicon oxide film 64, having a thickness of SOO to 2000 2, for ex.ample, is fcrnie# on entire surface of the silicon substrate 62. Then, as shown in Fig. 2(d), a thick insulation film 65, having 2 thickness of 0.5 to 2 u, for example, made of PSG or SiO2 is formed on the silicon oxide film 64 by reduced pressure CVD process. In this case, the recess 66 is formed to have a form substantially the same as that of the recess 63. Thereafter, as shown in Fig. 2(e), a thick polycrystalline silicon filin 68 or polycrystalline silicon film 68 containing phosphor having a thickness of 0.5 to 3 is deposited on the insulating film 65 using CVD method. Generally, the CVD polycrystalline silicon filt has a remarkably excellent characteristic in step coverage, so that the surface of the film 68 becomes substantially flat. Then, bv coating a polyimide resin layer, for example, (not shown) over the entire surface of the polycrystalline silicon film 68 with a thickness of about 1 to 2 u, making the surface perfectly flat. Next, as shown in Fig. 2(f), the polyimide resin and the polycrystalline silicon film 68 are removed by dry etching process at the same speed, until the surface of the insulating film 65 is exposed. whereby the polycrystalline silicon region 69 is left in the recess formed by the insulation film 65. Thereafter, as shown in Fig. 2(g), by heat-oxidizing the polycrystalline silicon region 69 in an oxygen atomosphere, the surface of the polycrystalline silicon region 69 is converted into a heat-grown. silicon oxide region 71. Then, as shown in Fig. 2(h), the entire surfaces of the CVD insulating film 65 and the silicon oxide region 71 are etched and removed by an etching solution of hydrofluoric acid type for example. By this means, since the etching speed of the heat-grown silicon is smaller than that of the CVD insulating material, the exposed CVD insu- lating film 65 is removed perfectly, and the surface of the silicon substrate iS exposed as show in Fig. 3(h), the active regions 86 and 87 are obtained. Accordingly, the element isolation regions formed by heat-grown silicon oxide films 64, 71, CVD insulating film 65 and polycrystalllne silicon region 69 can be formed. In the first embodiment described above, one example of the present invention is shown, but the effect or merit of this invention can fully be attained also by the following method. Thus, after obtainiriç t'ie foin shown in Pig. 2(fJ, using an etching solution of hydrofjuoric acid type whicr doesndt etch the polycrystalline silicon film 69, the exposed insulating layer 65 is etched off quickly as shown in Fig. 3(a). At this time, since the etching speed of the heat-oxidized film 64 is slower than that of the insulating film 65, the former remains as it is exposed. Then, whole of the semiconductor substrate is heat treated in an oxidizing atmosphere to obtain the oxidized region 105 of the polycrystalline silicon and the silicon oxide film 106. It will be evident that the effect of the invention will not be affected even when all of the polycrystalline silicon region 69 is converted into silicon oxide. Generally, the oxidation speed of a polycrystalline silicon containing phosphor is larger than that of the mono-crystalline silicon by 1.3 to 2 times, so that it is possible to make the thickness of the oxide film 105 to be sufficiently larger than that of the oxide film 106. Thereafter, as shown in Fig. 3(c), the oxide fil: 106 exposed on the silicon substrate 62 is etched off to obtain the element isolation region the same as that shown in Fig. 2. As described above, according to the method of this invention, the heat-grown silicon oxide film in the element isolation recess formed initailly in the silicon substrate is maintained throughout whole the process, so that the bird beak's region will not be produced. As the result, the element isolation region can be miniaturized, and it is not necessary to consider, with respect thereto, on adverse effect due to above-said bird beak's region. Accordingly, the method of manufacturing semiconductor device according to the present invention can sufficiently be applicable not only to the manufacture of a MOS type semiconductor device having an active region surrounded by extremely and accurately miniaturized element isol2- tics. region but also to the ,anufactu-e of a bipolar type cewiccr.ductor deuce h V' r.c an inductive isolation con struction

Claims: CLAIMS 1. A method of manufacturing a semiconductor device wherein a film (64) is formed on an upper surface of a silicon semiconductor device (62) and subsequently removed to define an active semiconductor region characterised by the steps of forming a recess (63) in the upper surface, forming an insulating film (64,65) covering a surface of said recess, forming a polycrystalline film (68) on said insulating film, and processing said polycrystalline film so that a separate portion (69) of said polycrystalline film is formed in and/or above said recess, oxidising (71) said polycrystalline film and then processing the semiconductor device to remove said insulating film (64,65) in regions other than said recess (63) whilst leaving oxidised polycrystalline film (71) in and/or above said recess (63). 2. A method of manufacturing a semiconductor device comprising the steps of: forming a recess (63) in an upper surface of a silicon semiconductor substrate (62); forming an insulating film (64,65) covering an inner surface of said recess and having a configuration substantially the same as that of said recess; forming a polycrystalline silicon film (68) on substantially the entire surface of said insulating film, said polycrystalline silicon film having a substantially flat surface; and oxidizing (71) said polycrystalline silicon film. 3. A method of manufacturing a semiconductor device comprising the steps of; forming a recess (63) in an upper surface of a semiconductor substrate (62); forming a first insulating film (64) on said surface of said semiconductor substrate, and on inner surfaces of said recess; forming a second insulating film (65) on said first insulating film; forming a relatively thick polycrystalline silicon film (68) on said second insulating film, removing said polycrystalline silicon film to expose said upper surface of said second insulating film while leaving a portion (64) of said polycrystalline silicon film in said recess; oxidizing said portion of said polycrystalline silicon film to form an oxidized film (71) thereof; and selectively etching off said first and second insulating films to expose portions (86,87) of the upper surface of said substrate on the opposite sides of said recess thereby forming a semiconductor device having an oxide film (71) covering said inner surface of said recess, an isolating region on said oxide film, a parasitic isolating region comprising said oxidized film of said polycrystalline silicon, and active regions constituted by said exposed portions (86,87) of the surface of said substrate. 4. The method according to claim 3 which further comprises the steps of applying a polyimide resin on the surface of said relatively thick poly-crystalline silicon film (68) to make flat said surface, and then etching a film of said polyimide resin and said polycrystalline silicon film with an etchant having the equal etching speed for said polyimide resin and said polycrystalline silicon film. 5. The method according to claim 3 wherein said second insulating film (65) is formed by CVD process. 6. The method according to claim 3 wherein said polycrystalline silicon film (69) contains phosphor and is deposited by reduced pressure CVD process. 7. A method of manufacturing a semiconductor device comprising steps of: forming a recess (63) in an upper surface (62) of a semiconductor substrate; forming a first insulating film (64) on said surface of said semiconductor substrate on inner surfaces of said recess; forming a second insulating film (65) on said first insulating film; forming a relatively thick polycrystalline silicon film (68) on said second insulating film; removing said polycrystalline silicon film to expose said upper surface of said second insulating surface (65) while leaving a portion of said polycrystalline silicon film (69) in said recess; oxidizing the resulting assembly to form an oxide film (105) of said remaining polycrystalline silicon film and an oxide film (106) of said silicon substrate; and removing said oxide film of said silicon substrate to expose portions (86,87) of the upper surface thereof to form active regions. 8. The method according to claim 7 wherein said polycrystalline silicon film (68) contains phosphor.

Inventors: YOSHIOKA, KENTARO OKI ELECTRIC INDUSTRY CO. LTD.
Applicants: OKI ELECTRIC INDUSTRY COMPANY, LIMITED
Application year: 1984
Main classification: H01L21
IPC codes: H01L21