Abstract:
Explosive forces are used to fill interconnect material into trenches, via holes and other openings in semiconductor products. The interconnect material may be formed of metal. The metal may be heated prior to the force filling step. The explosive forces may be generated, for example, by igniting mixtures of gases such as hydrogen and oxygen, or liquids such as alcohol and hydrogen peroxide. To control or buffer the explosive force, a baffle may be interposed between the explosions and the products being processed. The baffle may be formed of a porous material to transmit waves to the semiconductor products while protecting the products from contaminants. Various operating parameters, including the flow rate of the fuel and the oxidizing materials, may be positively controlled. In another embodiment of the invention, a piston is used to transmit the explosive force. If desired, an annular space at the periphery of the piston may be maintained at atmospheric pressure to protect against wafer contamination. A compact apparatus for filling holes in semiconductor wafers is also disclosed.

Description:
This is a divisional of U.S. patent application Ser. No. 09/146,519, filed Sep. 3, 1998, the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the production of semiconductor products. More particularly, the invention relates to a method of filling trenches, holes and other surface discontinuities in semiconductor products. The invention also relates to an apparatus for forcing conductive metal into openings in semiconductor products. 
     2. Discussion of the Related Art 
     A method of filling metal into openings in semiconductor products is described in U.S. Pat. No. 5,527,561 (Dobson). According to the Dobson process, via holes are formed in a semiconductor wafer. An aluminum layer is formed over the holes by sputtering. The aluminum layer is deformed and caused to flow into the holes by high pressure and high temperature. The high pressure is applied by pressurized gas. 
     The Dobson process has several disadvantages. First, it may not always fill the via holes as desired. The process will not work unless the holes are completely covered over by aluminum. That is, the process will not work if openings in the aluminum layer permit equalization of the pressures inside and outside the holes. Openings in the aluminum layer may be formed during the sputtering process or during the application of high pressure and high temperature. 
     Another problem with the Dobson process is that it would be difficult to operate efficiently. It takes time to pressurize the gas in the Dobson process. The time it takes to handle the pressurized gas reduces the rate at which wafers can be processed. In addition, the mechanisms that would be used to create and maintain the high pressure are relatively large and complicated. 
     SUMMARY OF THE INVENTION 
     The disadvantages of the prior art are overcome to a great extent by the present invention. The invention uses explosive force to fill trenches, via holes and/or other openings or surface discontinuities. 
     The invention relates to a method of making a semiconductor product. The method includes the steps of providing a conductive layer on an insulating layer, and applying an explosive force to the conductive layer. The explosive force is used to efficiently and reliably drive the conductive material into openings defined in the insulating layer. 
     According to one aspect of the invention, the conductive material is a malleable metal material. The semiconductor product may be a semiconductor wafer in an intermediate stage of production. The metal material may form electrical interconnects in the wafer. 
     The explosive force may be provided by a variety of reactive materials and other instrumentalities. In one embodiment of the invention, the explosive force is generated by igniting a mixture of hydrogen and oxygen. In another embodiment of the invention, the reactive materials include alcohol and a suitable oxidizing agent. 
     To control or buffer the explosive force, a baffle may be interposed between the explosion and the wafer being processed. The baffle may be a solid structure. Alternatively, the wafer may be immersed in liquid or gas. In another embodiment of the invention, a piston is used to transmit and/or regulate the explosive force. 
     According to another aspect of the invention, the conductive material is softened by preheating, before the explosive force is applied to it. 
     The present invention also relates to an apparatus for processing semiconductor wafers. The apparatus includes a support member for supporting the wafers and a reaction chamber for containing explosive forces. In a preferred embodiment of the invention, the apparatus also includes a heater for preheating the wafers. In addition, an ignition device may be provided for initiating combustion reactions. 
     An advantage of the invention is that it may be practiced with compact equipment. The invention does not require bulky, complicated mechanical systems for producing and handling pressurized gas. 
     Another advantage of the invention is that explosive forces can be generated consistently and rapidly, resulting in faster sequential processing of semiconductor wafers. 
     Moreover, it has been found that explosive forces, characterized by high energy waves, are preferable to forces produced by gradually increasing gas pressure, in terms of reliably forming high quality electrical interconnects. 
     The present invention is particularly well suited for filling trenches and holes that have high height to width aspect ratios. 
     According to one aspect of the invention, a porous baffle may be used to protect semiconductor wafers from contaminants, such as contaminants created by sliding pistons. The baffle may be formed, for example, of sintered stainless steel. 
     According to another aspect of the invention, a piston with differential surface areas may be used to increase or decrease the intensity of waves applied to the surfaces of the wafers being processed. If desired, an annular space at the periphery of the piston may be maintained at atmospheric pressure to further protect the wafers from contaminants. 
     An advantage of the present invention is that it can be practiced with both gaseous and liquid fuels and oxidizing materials. According to one aspect of the invention, the oxidizer may be supplied to the reaction chamber under relatively high pressure. 
     These and other features and advantages of the invention will become apparent from the following detailed description of preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cross sectional view of a semiconductor wafer at an intermediate stage of production. 
     FIG. 2 is a partial cross sectional view of the wafer of FIG. 1 at another stage of production. 
     FIG. 3 is a partial cross sectional view of the wafer of FIG. 1 at yet another stage of production. 
     FIG. 4 is a cross sectional view of a wafer handling apparatus constructed in accordance with a preferred embodiment of the present invention. 
     FIG. 5 is a cross sectional view of another wafer handling device constructed in accordance with the present invention. 
     FIG. 6 is a cross sectional view of yet another wafer handling device constructed in accordance with the present invention. 
     FIG. 7 is a cross sectional view of yet another wafer handling device constructed in accordance with the present invention. 
     FIG. 8 is a cross sectional view of yet another wafer handling device constructed in accordance with the present invention. 
     FIG. 9 is a cross sectional view of yet another wafer handling device constructed in accordance with the present invention. 
     FIG. 10 is a cross sectional view of yet another wafer handling device constructed in accordance with the present invention. 
     FIG. 11 is a cross sectional view of yet another wafer handling device constructed in accordance with the present invention. 
     FIG. 12 is a cross sectional view of yet another wafer handling device constructed in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, where like reference numerals designate like elements, there is shown in FIG. 1 a semiconductor wafer  10  in an intermediate stage of production. The wafer  10  has a silicon substrate  12  and an insulating layer  14 . The substrate  12  has an active structure  16 . The insulating layer  14  has an opening  18  for providing access to the active structure  16 . The opening  18  may be a trench, a via hole, a contact well, or any other desired surface discontinuity. 
     For clarity of illustration, only one opening  18  is shown in the drawings. In practice, the insulating layer  14  may have numerous openings  18  of different shapes and sizes for providing access to a variety of active structures  16  and other devices. The openings  18  may be orthogonal to the insulating layer  14 , as shown in the drawings. The invention is also generally applicable, however, to openings that are inclined with respect to the insulating layer  14 . 
     In operation, a layer of conductive material  20  is deposited on the upper surface  22  of the insulating layer  14 . Then, an explosive force is used to move the conductive material  20  into the opening  18  (FIG.  2 ). Then, the wafer  10  may be subjected to further processing. For example, the conductive material  20  remaining on the insulating surface  22  may be removed, leaving just the interconnect metal  20  in the opening  18 . 
     The conductive material  20  may be deposited by sputtering, vapor deposition, or by another suitable technique. The deposition process creates ledges  24 ,  26  (FIG. 1) that extend over the side edges  28 ,  30  of the opening  18 . The ledges  24 ,  26  define a spacing  32 . If the deposition process is continued, the spacing  32  typically becomes closed over. That is, a bridge  34  (FIG. 3) may be formed over the opening  18 . The bridge  34  seals the interior of the opening  18  from the atmosphere. The present invention may be used to fill the opening  18  even when the bridge  34  is not fully formed. In particular, an explosive, high energy force may be used to move the ledges  24 ,  26  (FIG. 1) abruptly into the opening  18  even when the opening  18  is open to the atmosphere. 
     The present invention should not be limited to the deposition patterns illustrated in FIGS. 1 and 3. Different deposition techniques and different materials tend to cover openings in different ways. The deposition pattern may also be a function of the size and shape of the opening  18 , the temperature of the deposited material, and the surface characteristics of the insulating layer  14 . 
     The conductive material  20  is preferably malleable or deformable metal such as aluminum, gold, tungsten, platinum, copper, titanium, nickel, molybdenum, vanadium, and/or alloys thereof. Other materials, including plastic materials, may also be used to practice the invention. 
     Referring now to FIG. 4, a filling apparatus  40  constructed in accordance with the invention has a sealed reaction chamber  42 , a table  44  for supporting the wafer  10 , an inlet/outlet system  46  for supplying a combustible gas mixture, and an igniter  48  for igniting the gas mixture to initiate an explosion. The explosion generates an explosive force that propagates as waves throughout the reaction chamber  42 . The explosive force drives the ledges  24 ,  26  (FIG. 1) or the bridges  34  (FIG. 3) into the respective openings  18 . The openings  18  are not shown in FIG. 4 for the sake of clarity. 
     In the embodiment illustrated in FIG. 4, the combustible gas mixture includes hydrogen and oxygen in amounts that react completely with each other. If desired, a buffering agent may be added to the combustible mixture to promote a smooth but rapid expansion, and to promote clean burning of the combustible mixture. The combustible mixture preferably reacts chemically without producing residual soot or other byproducts that would damage the filling apparatus  40  or contaminate the wafer  10 . For example, the reaction byproducts may consist essentially of water vapor. The reaction byproducts may be removed from the reaction chamber  42  by the inlet/outlet system  46 . 
     The term “explosive force,” as used herein, is not limited to forces generated by combustion reaction explosions. The term is used herein generally to include any force characterized by high energy waves of the type produced by explosions. In a preferred embodiment of the invention, an explosive force generates a pressure equivalent to about seven hundred to eight hundred atmospheres on the exposed surfaces of the wafer  10 . The invention should not be limited to the preferred embodiments illustrated and described in detail herein. 
     A suitable transport mechanism (not illustrated) may be provided for rapidly moving wafers  10  into and out of the filling apparatus  40 . The wafers  10  may be cycled through the apparatus  40  one by one or in groups for batch processing. The movement of the wafers  10  may be synchronized with the ignition of the combustible gas mixture. A suitable programmable control device (not illustrated) may be connected to the transport mechanism, the inlet/outlet system  46  and the igniter  48  for high speed, synchronized operation. 
     The illustrated filling machine  40  has a baffle  50 . The baffle  50  is an optional piece of equipment. The filling machine  40  may be operated without the baffle  50 , if desired. 
     The baffle  50  may be used to regulate and/or smooth out the impact of the compression waves applied to the conductive material  20 . The baffle  50  provides flexibility for the operator in terms of the amounts and types of explosive materials that may be employed in the reaction chamber  42 . That is, the baffle  50  makes it possible to initiate high intensity explosions in the reaction chamber  42  without damaging the wafer  10 . It may be more economical to permit such high intensity explosions than to operate without the baffle  50 . 
     The illustrated baffle  50  is formed of a suitable solid material such as an elastomeric material or metal. The baffle  50  may be supported by the walls  52 ,  54  of the filling machine  40 . In the illustrated embodiment, the baffle  50  is a flexible diaphragm. Pressurized argon or another suitable inert gas may be located in the area  56  between the baffle  50  and the wafer  10 . 
     The table  44  may be provided with a heater for preheating the wafer  10  or for maintaining the temperature of the wafer  10 . The wafer  10  is preferably preheated to soften the metal material  20 . In a preferred embodiment of the invention, the wafer  10  is preheated to a temperature of about five hundred to six hundred degrees Fahrenheit. 
     A second filling machine  60  constructed in accordance with the invention is shown in FIG.  5 . The second filling machine  60  is essentially the same as the filling machine  40  shown in FIG. 4, except that the second filling machine  60  has a liquid baffle. The liquid baffle may be formed of de-ionized water  62  located in the bottom of the reaction chamber  42 . The wafer  10  may be completely immersed in the water  62 . The liquid baffle (or water blanket)  62  may be used to dampen, reduce and/or smooth out the impact of the explosive forces generated in the reaction chamber  42 . The liquid baffle  62  may also protect the wafer  10  by providing a physical barrier against contaminants. 
     If desired, the liquid baffle  62  may be replaced with a baffle formed of heavy gas. The term “heavy gas” means gas that is substantially more dense than the combustible gas mixture. The heavy gas would tend to collect at the bottom of the filling machine  60 , causing the combustible gas mixture to remain near the top of the reaction chamber  42  (in the vicinity of the igniter  48 ) prior to exploding. The gas baffle may be used to ensure that the combustible gas mixture is located near the igniter  48  during ignition. The gas baffle may also protect the wafer  10  by isolating the wafer  10  from reactive chemicals. 
     Referring now to FIG. 6, a third filling machine  70  may be constructed with a ram piston  72 . The edges  74 ,  76  of the piston  72  are slidably sealed to the walls  52 ,  54  of the filling apparatus  70 . The combustible gas mixture may be located in a reaction chamber  42  above the piston  72 . A compressible inert gas may be located below the piston  72 . The inert gas surrounds and protects the wafer  10 . The piston  72  helps prevent contamination of the wafer  10  and isolates the wafer  10  from reactive materials. 
     In operation, an explosion is initiated in the reaction chamber  42 . The explosion causes the piston  72  to move rapidly downward toward the wafer  10 . The rapid downward movement of the piston  72  causes a sudden compression of the inert gas, initiating a high energy wave that impacts the ledges  24 ,  26  (FIG. 1) and thereby force fills the conductive material  20  into the openings  18 . 
     The downward movement of the piston  72  may be stopped at a desired location by a suitable stop mechanism (not illustrated). In addition, the piston  72  may be biased upward by a compression spring (not illustrated). When the combustion products are withdrawn from the reaction chamber  42  through the inlet/outlet system  46 , the compression spring returns the piston  72  to the start position shown in FIG.  6 . 
     The inert gas in the lower chamber  78  (beneath the piston  72 ) may be precharged. For example, the lower chamber  78  may be pressurized to an initial pressure of about two thousand to three thousand pounds per square inch. The precharging may eliminate the need for the compression spring. In addition, pressurizing the gas in the lower chamber  78  may facilitate the rapid formation of intense compression waves. The pressure in the lower chamber  78  may be maintained by a suitable inlet/outlet mechanism  80 . 
     As shown in FIG. 7, a filling machine  82  may be provided with a baffle  84  for protecting the wafer  10 . The baffle  84  may be formed of porous filter media. The baffle  84  may be used to prevent contaminants from falling on the wafer  10 . The contaminants may be produced, for example, by frictional wear between the piston edges  74 ,  76  and the contacting walls  52 ,  54 . The high energy waves transmitted by the piston  72  are propagated through the pores in the porous baffle  84 . The porous baffle  84  may be formed, for example, of sintered stainless steel having pores that are about one-half micron or less in diameter. 
     FIG. 8 shows a fifth filling apparatus  90  constructed in accordance with the invention. The illustrated apparatus  90  has a differential piston  92  with first and second piston surfaces  94 ,  96 . The surface area of the first surface  94  is smaller than the surface area of the second surface  96 . The first surface  94  is slidably sealed within a fixed cylinder  98 . The differential piston  92  reduces the intensity of the explosive force applied to the wafer  10 . 
     The annular space  100  between the two platens  94 ,  96  may be maintained at atmospheric pressure. A vent  102  may provide fluid communication between the space  100  and the exterior of the device  90 . The vent  102  and the space  100  may be used to isolate the combustion chamber  42  from the lower chamber  78 . That is, the space  100  may be used to prevent combustion or reaction products from seeping into the lower chamber  78 . By maintaining the pressure in the lower chamber  78  above atmospheric pressure, contaminants located at the edge of the lower platen  96  are urged upwardly toward the annular space  100 . The piston travel distance  104  may be selected such that the vent  102  is never covered by the top platen  94 . The fifth filling apparatus  90  may be constructed either with or without the porous plate  84 . 
     Referring now to FIG. 9, a sixth filling apparatus constructed in accordance with the invention has a differential piston  192  with first and second piston surfaces  194 ,  196 . The first surface  194  has a greater diameter (and surface area) than the second surface  196 . The second surface  196  is slidably sealed within a fixed cylinder  198 . The space  100  between the platens  194 ,  196  may be maintained at atmospheric pressure as in the apparatus of FIG.  8 . The differential piston  192  (FIG. 9) increases the intensity of the explosive force supplied to the wafer  10 . 
     A seventh filling apparatus  210  is shown in FIG.  10 . The seventh filling apparatus  210  operates with liquid reactants. A liquid fuel is introduced into the reaction chamber  42  through a first input pipe  212 . The fuel may be, for example, alcohol. The fuel may be introduced at relatively low pressure. A liquid oxidizer (for example, hydrogen peroxide) flows into the reaction chamber  42  at a higher pressure through a second inlet  214 . The oxidizer is pressurized by a pressurizing system that includes first and second one-way valves  216 ,  218  and a high pressure reciprocating syringe type pump  220 . The pump  220  may have a reciprocating plunger  222  for applying pressure to the oxidizer. An exhaust valve  224  is provided for cyclically removing the reaction products from the reaction chamber  42 . The pump  220  may be used to control the pressure and feed rate of the oxidizer to thereby control the reaction rate in the reaction chamber  42 . 
     A metering orifice  225  may be located in the inlet line  214  to control the feed rate of reactant flowing into the reaction chamber  42 . The metering orifice  225  may be operatively connected to a suitable programmable controller and/or transducers (described in more detail below). 
     Referring now to FIG. 11, there is shown an eighth filling apparatus  230  constructed in accordance with the present invention. The illustrated apparatus  230  has a high pressure injection chamber  232  located above the reaction chamber  42 . As in the embodiment described above, fuel (such as alcohol) flows into the reaction chamber  42  at relatively low pressure (for example, atmospheric pressure) through a first inlet  212 . The oxidizer flows through a first check valve  234 , a metering orifice  236 , and then through a second inlet  238  into the reaction chamber  42 . The injection chamber  232  has a second piston  240 . The second piston  240  is integrally connected to the main piston  72 , for example, by a sealed piston rod  244 . A cyclically operating exhaust valve  224  is provided as in the embodiment of FIG.  10 . 
     In operation, as an explosive reaction occurs in the reaction chamber  42 , the second piston  240  moves downward with the main piston  72 . The downward movement of the injection piston  240  creates high pressure in the injection chamber  232 . The high pressure causes the oxidizer to flow through the metering orifice  236  into the reaction chamber  42 . 
     The metering orifice  236  may be used to control the rate at which the reactants (the fuel and the oxidizer) are mixed. The rate at which the reactants are mixed may be the same as in the syringe pump embodiment of FIG.  10 . If desired, the pressure, temperature, and change of volume in the reaction chamber  42  may be controlled by a suitable programmable controller (not illustrated). Transducers (not illustrated) may be provided to measure the pressure, temperature and displacement of the lower surface  242  of the reaction chamber  42 . The controller may be programmed with a feedback system to control the operational parameters as desired. 
     FIG. 12 illustrates another filling apparatus  250  constructed in accordance with the invention. The filling apparatus  250  has a differential piston  192  like the one shown in FIG.  9 . The apparatus  250  is adapted to operate on liquid fuel. The liquid fuel is introduced into the reaction chamber  42  by a suitable inlet  212 . The inlet  212  may be connected to a suitable upstream source of fuel (not shown). The oxidizer, which may also be a liquid, is introduced through one-way valves  252 ,  254  that are connected together in series. In addition, a pressure accumulator  256  may be provided between the one-way valves  252 ,  254 . The lower chamber  258  of the accumulator  256  is in fluid communication with the space  78  beneath the differential piston  192 . 
     In operation, as an explosive reaction is initiated in the reaction chamber  42 , an operating pressure is applied to the upper chamber  260  of the accumulator  256  by the increasing pressure in the space  78  beneath the piston  192 . The operating pressure causes the oxidizer accumulated in the upper portion  260  of the accumulator  256  to flow through the second one-way valve  254  and into the reaction chamber  42 . 
     The oxidizer flows into the reaction chamber  42  because of the difference in pressure created by the differential piston  192 . If desired, the piston  192  may be replaced by a piston having equal surface area on both sides. In this alternative embodiment, a differential piston arrangement may be provided in the accumulator  256 , instead of the illustrated cylindrical piston  257 , to cause the reactant to flow into the reaction chamber  42 . 
     As in the previously described embodiments, suitable transducers and a feedback system may be provided for controlling the temperature, fuel and oxidizer flow rates, temperature and displacement of the piston  192  to achieve the desired pressure waves for processing the wafer  10 . If desired, the feedback system may be operatively connected to one or more metering orifices  259 ,  261 . The metering orifices  259 ,  261  may be used to control the feed rate of reactant into the reaction chamber  42 . 
     In each of the above-described embodiments, a suitable cooling apparatus or heat dissipation apparatus may be provided for the reaction chamber  42  and/or other parts of the system. Thus, for example, systems constructed in accordance with the invention may employ suitable fluid coolant and/or fins for dissipating heat. 
     An important advantage obtained with the present invention is that a large amount of energy may be obtained using a small amount of combustible materials, which may be gas or liquid. 
     For most wafer products, a single application of explosive force should be sufficient to produce high quality interconnects in the openings  18 . For other products, such as wafers that have non-orthogonal openings, or where indirect infusion of metal is required, it may be desirable to apply successive force waves to complete the filling operation. 
     The above descriptions and drawings are only illustrative of preferred embodiments which achieve the features and advantages of the present invention, and it is not intended that the present invention be limited thereto. Any modification of the present invention which comes within the spirit and scope of the following claims is considered part of the present invention.