Abstract:
Apparatus and methods for manufacturing low-resistant substrate contacts in integrated circuits are disclosed. The contacts are low resistive conducting plugs and are located outside the areas of active components. The substrate is connected from the top portion in order to obtain a low resistance. Multiple metal plugs electrically interconnect the substrate of the integrated circuit with the top portion of the integrated circuit.

Description:
TECHNICAL FIELD 
     The present invention relates to devices, in particular substrate contacts and shielding devices, in a semiconductor component and methods of manufacturing these. Furthermore, the invention relates to a method of arranging substrate contacts. 
     BACKGROUND OF THE INVENTION AND PRIOR ART 
     In manufacturing silicon components being densely packed it is of great importance to avoid undesired coupling between different blocks of components located on the same silicon substrate. Such an undesired coupling or “cross-talk” between different blocks is most often more inconvenient in the manufacturing of analogue digital integrated circuits (IC) of a so called mixed-mode type. Cross-talk between different circuit blocks can either take place via capacitive coupling between the connection conductors or via substrate coupling. A number of different approaches for minimizing cross-talk, via the substrate, are described in literature, see for example K. Joardar; “A simple approach to modeling cross-talk in integrated circuits”, IEEE J. Solid State Circuits. vol. 29, 1994, pp. 1212. 
     It is characteristic of all described techniques that different types of isolation methods in combination with substrate contacts for suppressing cross-talk are used. In addition to having good isolation between the respective blocks it is also required that the subtract contact is made as low-resistant as possible in order to achieve the best possible result. 
     The drawback with the methods described in the paper mentioned above, is that the contact resistance between the metal and substrate becomes comparatively high, since doped silicon, a P-plug, is used as connection. Said diffusion of a P-type must also be made having a depth of several μm in order to secure contact between a high-doped substrate and metal. This requires a long drive-in diffusion time in combination with a high drive-in diffusion temperature which is not desirable in the manufacturing of modern components where a low temperature budget is aimed at. Last but not least, the P + -diffusion, i.e. the so called guard-ring, is space demanding, since lateral diffusion takes place simultaneously with the vertical diffusion. 
     SUMMARY 
     It is an object of the present invention to provide a low-resistant substrate contact for semiconductor components which overcomes the drawbacks arising when forming substrate contacts according to prior art. 
     It is further an object of the present invention to provide a method of locating and arranging these substrate contacts around a component or a block of components in order to obtain a good shielding between different components or blocks of components. 
     These and other objects are obtained using a substrate contact made of metal, extending deep down into the underlying semiconductor material, all the way down into the substrate. Furthermore, by means of locating several such metallic substrate contacts at close intervals around components or blocks of components effective shielding towards undesired coupling or cross-talk is achieved. 
     Thus, a semiconductor component is obtained in a usual manner by means of using different substructures at and/or on a surface of a substrate. There is an electrical connection in the shape of a plug of a material with good electrical conductivity between the substrate and the surface at and/or next to the semiconductor component. The material can be of another type than the substrate, which typically is semiconductive and can have different types of doping. The plug is preferably a metal plug and in any case extends from an inner part of the substrate to an area close to the surface next to or at the semiconductor component. Furthermore, the plug should extend deeper down into the substrate than into the PN-junctions introduced and/or existing in the substrate. Several such plugs are preferably arranged around the surface of the semiconductor component and can then serve as electrical shielding of the semiconductor component. Furthermore, the upper ends of the plugs are preferably electrically connected as by means of layers or paths of an electrically conducting material, which as above can be a material with good electrical conductivity, in particular a metal material. 
     In the manufacturing of the plugs, suitably shaped holes are first made and which then are filled with the electrically conducting material. 
     The filling is preferably provided at the same time as other contact holes for electrical contact with different electrodes in the semiconductor are filled. Holes can then be made having a diameter or largest across corner dimension, which essentially corresponds to the corresponding measures for the contact holes. In any event the diameters of the holes should be chosen so that they are completely filled in the process step for filling the contact holes. 
     Plugs of the above mentioned kind can also be arranged alongside a shielded electrical signal conductor in a semiconductor structure. The plugs must be arranged so close as to obtain a good lateral shielding of the electrical signal conductor. Shielding in a vertical direction can be achieved by means of suitable metal planes below and/or above the signal conductor, which can be manufactured at the same time as other metal planes in the semiconductor structure. The plugs are preferably in electrical connection with these metal planes. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention will now be described by way of non-limiting examples and with reference to the appended drawings, in which: 
     FIGS. 1 a-   1   c  show different steps carried out in the manufacturing of a substrate contact. 
     FIG. 2 is an overall view showing a number of substrate contacts arranged in order to shield a component. 
     FIG. 3 shows a shielded signal conductor. 
     FIG. 4 is an overall view of a number of components arranged on the same substrate. 
     FIG. 5 is a cross-section showing lateral shielding obtained by means of substrate contacts in combination with a vertically shielding upper metal layer. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In FIGS. 1 a-   1   c  different stages in the manufacturing of a substrate contact are shown. The FIGS. show the manufacturing of a substrate contact in a rudimentary NMOS-process flow. Another application area in which the manufacturing is of particular importance is in the manufacturing of bipolar components for radio purposes. Moreover, different variations of the method can be used in the manufacturing of CMOS-components and bipolar components. 
     FIG. 1 a  shows the active areas defined by for example LOCOS (LOCal Oxidation of Silicon) on a silicon substrate  101 , where the substrate also can be made of other semiconductor materials such as for example, germanium, gallium arsenide, silicon carbide, indium phosphide. On top of the silicon substrate an epitaxial layer of silicon  103  has been grown, which typically is 5-10 μm thick. The figure also shows the remaining layer of field oxide  102 . 
     Thereupon, see FIG. 1 b,  a thin gate oxide is thermally grown, and whereupon a coating of polysilicon  105 , which can be heavily doped with a doping of N-type, in order to form the gate, takes place. The gate is defined by means of lithography and dry etching. Implantation, with e.g. arsenic or phosphor, and drivein diffusion of the source-/drain areas  107 , is carried out in a self-aligned manner after etching of the gate. 
     Next, a passivation layer  109  and possibly a future hard mask  111  of preferably silicon nitride and/or oxide are deposited, whereupon a layer of photo resist  112  is applied on the wafer. The layer is then lithographically patterned in order to define the substrate contacts which might be located in the shape of a frame of discreet contacts around the whole or parts of the component. The latter is analogue with the so called P + -guard-ring described in the above cited paper. 
     The resist pattern having openings of about 1 μm is then by means of dry etching transferred to the hard mask and the oxide layers, in this case a combination of the deposited passivation layer and the thermally grown field oxide. The photo resist is removed from the wafer, followed by an anisotrophic silicon etch. The anisotrophic silicon etch is made so deep, typically several μm, so that it reaches down into the underlying high-doped P + -substrate. After completed etching possible etch remainings such as polymers and other impurities are removed by means of a combination of dry cleaning (plasma-strip) and wet chemical cleaning. The structure after these steps is shown in FIG. 1 b.    
     Photo resist is then again applied on the wafer which is then contact hole patterned and etched. The wafer is cleaned after the contact hole etching, whereby resist remains and other organic impurities are removed with the combination of dry cleaning (plasma strip) and wet chemical cleaning. After etching off the possible hard mask and common wet chemical cleaning, the process proceeds according to previously well-known technique. However, a substrate contact etching is accomplished, etched both through the oxide passivation and deep down into the silicon, approximately 5 μm or at least deeper than the deepest PN-junctions. In ordinary contact hole etching it is however a requirement that the etch is stopped at the silicon surface, and thus only goes through the passivation, in order for the component to work. 
     As is shown i FIG. 1 c  a thin layer, such as having a thickness of about 1000 A.U. of a contact metal  113  of for example titanium, platinum or cobalt for contacting is then deposited, for example by means of coherent sputtering, such as ionised metal plasma (IMP) or physical polymering, which later can be silicidized. In immediate connection, another thin metal layer  115 , for example having a thickness of about 500 A.U., is deposited by means of for example reactive sputtering or CVD-technique. This so called diffusion barrier which preferably is made of titanium nitride is deposited on the wafer, since it is then desired that the contact holes are conformally filled with a metal, preferably tungsten, by means of CVD-technique. In order to secure a good metallurgical connection with the silicon wafer, said contact metal can be brought to be alloyed with the silicon at an elevated temperature, whereby a silicide can be created in the contact area as indicated above. After depositing the contact metal and the barrier, the contact metal is hence silicidized by means of RTP (Rapid Thermal Processing), or alternatively by means of a traditional oven process. 
     After the contact formation e.g. tungsten is deposited by means of CVD-technique over the wafer. The CVD-coating is conformally executed, whereby both the contact holes  119  and the substrate contacts  117  will be overgrown (plugged), if the thickness of the deposited metal layer is of the same magnitude as the contact hole dimension. Ordinary metallisation and patterning of the same for connection of the different components to a circuit terminate the process. The result is shown in FIG. 1 c.    
     The metal plugs can also be located at locations not having a field oxide layer  102  as is shown by the metal plug  120 . 
     By using the method described above, a metallic, low-resistant connection with the substrate is obtained. Said metallic substrate contacts may also serve as a shielding cage, a screening cage, around respective component or block of components. Hereby a unique possibility for suppressing cross-talk is provided. 
     As an alternative to the above described embodiments, for example a uniformly doped, P − - or N − -silicon substrate may be used in the same manner as the P + /P − -epi-material described above. If such a uniformly low-doped material is used, an extra diffusion, i.e. doping, in the bottom of the substrate contacts should however be made in order to secure a low contact resistance. 
     The above described embodiment results in low-resistant metal contacts to the substrate which have a considerably better performance than the earlier substrate contacts obtained by means of diffusion. In certain cases also doped polysilicon may constitute and serve as the contact to the substrate. In the two latter cases a substantially higher resistance is however obtained. The method of making holes down into the inner of the substrate and then fill this with a conducting material, metal, polysilicon, etc. is easily implemented in existing CMOS and or bipolar flows. Only one additional mask step together with the following anisotrophic silicon etching are added. 
     The substrate contacts which typically are round 6 μm deep are simultaneously filled with the other standard contacts which are around 1 μm deep, the filling being made by means of for example CVD-tungsten. Also other metals, for example Al, Cu. etc. which are possible to deposit by means of CVD-technique should work in a similar manner. 
     The fact that the contact resistance between metal and substrate becomes relatively low, since metal is used as connection constitutes further advantages. Furthermore, an attained low temperature budget can be kept. Last but not least the method is much less space demanding than the traditional technique, since no lateral diffusion takes place. The method is furthermore elegant in the sense that the substrate contacts and the usual contacts are filled at the same time. Thus, the filling requires no extra process step. 
     Moreover, the deep metal contacts of the substrate can be located so closely, that the component or the components, blocks or modules of components, behave as if they were placed in a close screening cage providing a maximal electrical shielding. Thus, the method provides a unique possibility for electrical shielding at component level. 
     In FIG. 2, a semiconductor component which has been shielded according to this principle is shown. Thus, a component, or a block of components  201 , is shown on top of a substrate  203 . Around this component or this block of components a large number of holes have been made which extend deep down into the substrate  203  and these holes have subsequently been filled with metal in the above described manner in order to form metal plugs  205 . These metal plugs  205  are further connected to a conducting material  207 , which connects the upper parts of the metal plug  205 . The deep substrate contacts can furthermore easily be combined with traditional trench-isolation  209  in order to obtain maximal isolation in combination with good shielding, which is a requirement in the manufacturing of advanced integrated circuits for radio applications. 
     The obtained substrate contact can also be used in order to laterally shield an electrical signal conductor in a semiconductor structure. This is obtained by means of providing metal plugs manufactured in the above described manner next to, on both sides of, an electrical signal conductor. The electrical signal conductor can also preferably be shielded in the vertical direction in a conventional manner by means of metal planes. 
     In FIG. 3, a conductor  301  in a semiconductor structure shielded according to this principle is shown. The conductor  301  is here arranged between two metal planes  303  and  305 , respectively, one above and one below, shielding the conductor in a vertical direction. Furthermore, a number of holes have been made on both sides of the conductor, which reach down to the lower metal plane  305  and which are filled with a metal. The metal plugs  307  obtained in this manner shield the conductor in the lateral direction if they are placed close enough. The top ends of the metal plugs may also, like the material  207  shown in FIG. 2, be connected to an electrically conductive material, not shown. 
     Furthermore, FIG. 4 shows an overall view of two groups of semiconductor components  401  and  403 , arranged on a common substrate, shielded from each other and the environment by means of the above described substrate contact  405 . The substrate contacts  405  are in this embodiment arranged in triple rows around the component groups. The purpose of this is to obtain an even better shielding. Furthermore, signal conductors may in this embodiment be arranged between some of the rows of the substrate contacts  405 , whereby also the signal conductors become shielded in accordance with the above. The substrate contacts are further formed with an essentially quadratic cross-section and the spacing between the plugs in a row can, for example, be between 50 and 100% of the thickness of the plugs. 
     Finally, in FIG. 5 it is shown how cmponents and blocks of components can be shielded from each other by means of the above described substrate contacts in combination with a metal plane applied on top of the components. Thus, FIG. 5 shows a silicon substrate  501  on which a number of components have been arranged. The components are in this case shielded from each other laterally both by means of conventional trenches  503  filled with isolating polysilicon and also by means of metal substrate contacts  505  of tungsten made according to the above, going deep down into the substrate. 
     Furthermore, there is an additional metal layer  509  provided on top of the uppermost layer of passivation oxide  507 , which is connected to ground. The purpose of this metal layer is to provide a vertical shielding upwards of the components provided on the substrate. In this manner a screening cage for electrical shielding around the components is obtained. 
     The shielding layer of metal  509  does not need to be closed, it only needs to be arranged to cover such a large part of the top side of the components required to obtain a good vertical electrical upwards shielding. On the contrary it may be advantageous to provide perforations or holes  511  in the metal layer, which act in order to prevent or lower the risk for the metal to come loose.