METHOD FOR ARRANGEMENT OF A BURIED CAPACITOR, AND A BURIED CAPACITOR ARRANGED ACCORDING TO SAID METHOD

Abstract: The present invention relates to a method for arrangement of a buried capacitor on a substrate or the like, and a buried capacitor arranged according to the method. In order to diminish the resistive losses in a capacitor and to make it more efficient, in semiconductor circuits, instead of the polycrystalline layer, one or more bodies (14) of metal such as aluminium or tungsten may be used. This has been made possible using a new technique in which a trench filling consisting of conducting material is etched away without removal through etching of the insulating layer (13) in the trench. After the removal through etching of the trench filling, the trench is filled using the metal (14) as above, whereby the insulating layer (13) between the conducting material and the metal body will separate two conducting surfaces, thereby forming the buried capacitor.

Description: Method for arrangement of a buried capacitor, and a buried capacitor arranged according to said method. FIELD OF THE INVENTION The present invention concerns a method of arranging a buried capacitor on a substrate or the like, and a buried capacitor arranged according to said method. STATE OF THE ART In order to arrange for a capacitance function or a capacitor on a substrate in the manu- facture of integrated circuits, an insulating layer has been used between e.g. a layer of polycrystalline silicon and a layer of monocrystalline silicon, whereat a groove or the like insulates the capacitor formed from the surrounding region. In Figure 1 is shown a cross section of a construction of a capacitor according to the above, in which an insulating layer 1 is situated between a polycrystalline silicon layer 2B and a mono- crystalline silicon layer 3. A first metal conductor 4 is connected to a first metal plug 5, which is connected to a layer of polycrystalline silicon 2 A on the monocrystalline silicon layer 3. A second metal conductor 6 is connected to a second metal plug 7, which is connected to the polycrystalline silicon layer 2B. Between the polycrystalline silicon layer 2B and the underlying monocrystalline silicon layer 3 the insulating layer 1 is situated, whereat the region delimited by the polycrystalline silicon layer 2B, the insulating layer 1 and the underlying part of the monocrystalline silicon layer 3 constitutes the capacitor, per se, which is connectable via the metal conductors 4 and 6. Such a capacitor construction is easily manufactured using modern technique. In order to separate the capacitor construction from the other parts on the substrate, the substrate has been provided with grooves/trenches 8 having insulating wall material 9 filled with suitable filling. The polycrystalline layer in the capacitor, however, contributes to the resistive losses in the capacitor. The resistive losses make the capacitor less effective in decoupling of disturbances, generates more thermal noise, which may be a limiting factor in a radio construction. A filter construction in which a capacitor of the above described type is a part may cause high losses in the filter, e.g. make the filter less efficient. In e.g. US 5 013 680, US 5 466 628 and WO-A 90 11 619 arrangements of capacitor functions/capacitors on substrates are shown. DESCRIPTION OF THE INVENTION In semiconductor circuits, in order to reduce the resistive losses in a capacitor and to make it more efficient, one or more metal bodies such as bodies of aluminum or tungsten may be used, which metals show a lower resistivity than the polycrystalline layer. This has been made possible using a new technique, in which the trench filling is etched away without etching away the insulating layer in the trench. When the trench filling has been etched away the trench is filled with a metal according to above, whereat plug metal may be used as filling and a so-called buried capacitor is thereby obtained. The metal plug may be directly coupled to a metal conductor, which in conjunction with the low resistivity in the fill metal decreases the resistive losses in the capacitor and makes it more effective. Knowing that one buried capacitor may be arranged, several capacitors may be arranged together and interacting on the same substrate, whereat, in dependence of the pattern build-up of the capacitors and the degree of coupling of these, a capacitor function having a predetermined capacitance may be achieved. The invention will now be further described with reference to the attached drawings. LIST OF FIGURES Fig. 1 is a cross section of a known construction of a capacitor. Fig. 2 is a cross section of a capacitor according to the invention. Fig. 3a - c are cross sections of steps in the manufacture of the capacitor in Figure 2. Fig. 4a - h are cross sections of alternative steps in the manufacture of the capacitor in Figure 2. Fig. 5a and b are views from above of a composite capacitor according to the invention. Fig. 6a and b are views from above of an alternative composite capacitor according to the invention. Fig. 7a and b are views from above of a further embodiment of a composite capacitor according to the invention. PREFERRED EMBODIMENTS OF THE INVENTION In Figure 2, a cross section of the build-up of a capacitor 10 according to the invention is shown. In a layer 11 of monocrystalline silicon in a substrate and a component carrier, grooves 12 and/or holes have been etched, which have been provided with a layer 13 of insulating material. Depending on the build-up of the capacitor, one or more grooves/trenches or holes or a pattern of holes have been filled with metal 14, such as aluminum or tungsten, a so-called plug metal, which has been connected with an upper conductor metal 15 in order to constitute one side of the contact surface of the capacitor 10. The second surface of the capacitor constitutes a short metal plug 17 connected to a polycrystalline silicon layer 18 connected to the layer 11 comprising monocrystalline silicon, whereat the insulating layer 13, situated between the monocrystalline silicon layer 11 and the trench metal 14, separates two conducting surfaces, thus forming a buried capacitor. In Figures 3a - c, a method of manufacturing a buried capacitor is shown in cross- section. In a substrate comprising a upper insulating layer 19 and an underlying conducting layer 20 of polycrystalline silicon, one or more holes 21 or one or more grooves/trenches have been etched, see Figure 3a. The holes have thereafter been provided with an insulating layer 22 in order to insulate the filling placed in the holes, see Figure 3b. In Figure 3c is shown that the hole/trench has been filled with a suitable metal 23, which metal also may cover a part of the region above the insulating layer in order to form a first contact surface of the buried capacitor. The second contact surface may be formed according to Figure 2. In Figures 4a - h, an alternative method of manufacturing a buried capacitor is shown in cross-section. This method has the advantage of the high temperature processes being performed before the low temperature processes in the manufacture of buried capacitors. In a substrate comprising an upper insulating layer 19 and a lower conducting layer 20 of monocrystalline silicon, one or more holes 21 or grooves/trenches have been etched, see Figure 4a. The hole has thereafter been provided with an insulating layer 22 for insulation of a filling placed in the hole, see Figure 4b. In Figure 4c the hole in the substrate has been filled using an insulator suitable for the purpose, e.g. polycrystalline silicon 24. In Figure 4d an insulated trench cover 25 is shown placed in the hole in the insulating layer above the trench filling. Hereafter, other components in the circuit may be formed. In Figure 4e is shown that a further insulating layer 26 has been placed over the prior arranged insulating layer, as a step in a subsequent metallisation step. In Figure 4f is shown that a hole 27 or a trench has been etched down through the insulating layers 19, 26 and down into the trench filling for removal of the same, whereat the insulated hole remains. In Figure 4g is shown that the hole 27 or the trench has been filled with a metal plug 28, such as aluminum or tungsten, in order to achieve a buried insulated metal body in the substrate. In Figure 4h is shown that a conducting layer 29 has been added onto the upper insulating layer in contact with the metal plug for forming of a first buried capacitor contact surface, whereat the second contact surface may be formed as in Figure 2, whereby a buried capacitor exhibiting good performance characteristics has been achieved on the substrate. In Figures 5a and b, the build-up of a composite capacitor 30 is shown from above, consisting of several assembled and buried capacitors. The capacitor in Figure 5a is delimited outwardly by an insulated groove 31 in a layer 32 of monocrystalline silicon on a substrate. The first contact surface on the composite capacitor is a metal conductor 33 connected to the metal plugs 34 connected to a polycrystalline silicon layer 35 connected to a layer 32 of monocrystalline silicon on the substrate. The second contact surface on the composite capacitor is an upper layer 36 insulated against the environ-ment connected to the metal plugs/fillings 37 made of e.g. aluminum or tungsten in insulated holes in the monocrystalline silicon layer 32. In Figure 5b, insulated grooves 38 filled with suitable metal as aluminum and tungsten in contact with the upper con-ducting surface layer 36, insulated against the environment, have been arranged instead of several holes having metal plugs. Depending on the number of holes and/or the length of the grooves, the effective conducting surfaces, separated by insulation, can be varied and, thus, the capacitance of the capacitor can be varied. In Figure 6a, the build-up of an alternative composite capacitor is shown from above, which capacitor consists of several combined and buried capacitors. In this embodiment the first contact surface consists of two metallic conductors 33,39 connected to metal plugs 34,40, which are connected to a polycrystalline silicon layer 35,41 connected to the layer 32 of monocrystalline silicon on a substrate. The second contact surface essentially corresponds to the second contact surface described in Figure 5. Also in this build-up, insulated grooves 38 in the monocrystalline silicon layer 32 filled with suit-able metal may be used in order to form two separated conducting surfaces, as shown in Figure 6b. In Figures 7a and b, the build-up of a further embodiment is shown from above, in which a surrounding and closed outer contact surface constitutes the first contact surface, in which embodiment the contact surface is a circumventing metallic conductor 42 connected to metal plugs 34 connected to a circumventing polycrystalline silicon layer 43. The second contact surface essentially corresponds to the second contact surface described in Figure 5. In this capacitor also, build-up insulated grooves 38 in the monocrystalline silicon layer 32 filled with suitable metal may be used, as is shown in Figure 7b. The invention is naturally not limited to the above described embodiments and to the embodiments shown in the Figures, but may be modified within the scope of the attached claims.

Claims: Claims 1. Method for arrangement of a buried capacitor on a substrate or the like, characterized in at least one hole or one groove being etched in an electrically conducting material, the hole or the groove being supplied with an insulating layer, the insulated hole or groove being filled with a metal, e.g. aluminum or tungsten, whereat the insulating layer separates the two conducting materials in order to form a buried capacitor. 2. Buried capacitor for arrangement on a substrate or the like, characterized in that at least one metal body (14,28) of e.g. aluminum or tungsten, said at least one body provided with an insulating layer (13,22), is separately arranged in a hole and/or groove in a conducting material (11,20) constituting a first side of the buried capacitor, that the conducting material (11,20) surrounding the insulating layer (13,22) consti- tutes a second side of the capacitor, whereat the insulating layer (13,22) between the conducting material (11,20) and the metal body (14,28) separates the two conducting surfaces in order to form the buried capacitor. 3. Buried capacitor according to Claim 2, characterized in that a conductor (15,36) is connected to the metal body (14) or to the metal bodies (37,38) and constitutes a contact surface to the capacitor, and that a conductor (16) or several conductors (33,39,42) are connected to the conducting material (32) and constitutes a second contact surface to the capacitor. 4. Buried capacitor according to Claim 3, characterized in that the conductor connected to the conducting material (32) constitutes a composite conductor (43) arranged around one or more arranged composite metal bodies (37,38).

Inventors: JOENSSON JONAS, LARSSON TORBJOERN, JOENSSON, JONAS, LARSSON, TORBJOERN
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON
Application year: 1998
Main classification: H01G4
IPC codes: H01L21, H01L27, H01L29