Patent Publication Number: US-2007099433-A1

Title: Gas dielectric structure formation using radiation

Description:
BACKGROUND OF THE INVENTION  
      1. Technical Field  
      The present invention relates generally to semiconductor interconnect structures, and more particularly, to methods of forming a gas dielectric structure for a semiconductor interconnect structure using radiation.  
      2. Related Art  
      In order to enhance semiconductor chip operational speed, semiconductor devices have been continuously scaled down in size. Unfortunately, as semiconductor device size is decreased, the capacitive coupling between conductors in a circuit tends to increase since the capacitive coupling is inversely proportional to the distance between the conductors. This coupling may ultimately limit the speed of the chip or otherwise inhibit proper chip operation if steps are not taken to reduce the capacitive coupling.  
      The capacitance between conductors is also dependent on the insulator, or dielectric, used to separate the conductors. Traditional semiconductor fabrication commonly employs silicon dioxide (SiO 2 ) as a dielectric, which has a dielectric constant (k) of approximately 3.9. One challenge facing further development is finding materials with a lower dielectric constant that can be used between the conductors. As the dielectric constant of such materials is decreased, the speed of performance of the chip is increased. Some new low-k dielectric materials that have been used to provide a lower dielectric constant between conductors include, for example, fluorinated glass and organic materials. Unfortunately, provision of newer low-k dielectric materials presents a number of new challenges, which increase process complexity and cost.  
      Implementation of organic materials to reduce the dielectric constant also reduces the overall back-end-of-line (BEOL) capacitance. Unfortunately, organic materials suffer from temperature limitations, shrinkage or swelling during manufacturing or chip operation, and poor structural integrity. Instead of using silicon dioxide (SiO 2 ), another approach is to implement gas, such as air, which is provided in the form of a gas dielectric structure in a semiconductor structure. Air has the lowest effective dielectric constant. Simple capacitance modeling of parallel wires shows that even a small air-gap near the wires results in a significant improvement in the overall dielectric constant (k) for a structure, e.g., a 10% air gap per edge will reduce the effective dielectric constant of a dielectric by approximately 15%. Current processing for implementing gas dielectric structures, however, is fairly complex and cannot be easily integrated. As a result, completely new integration schemes have been developed, which are more complex and more costly. For example, typical gas dielectric structure formation requires additional masking layers for reactive ion etching (RIE) processing steps relative to damascene wire formation.  
      In view of the foregoing, there is a need for an improved solution for forming a gas dielectric structure for a semiconductor interconnect structure.  
     SUMMARY OF THE INVENTION  
      Methods and resulting structure of forming a gas dielectric structure in an interconnect structure are disclosed. In one embodiment, the method includes providing the interconnect structure including at least one interconnect layer having a dielectric, at least one conductor and a first cap layer; and causing the dielectric to contract to form the gas dielectric structure by exposing the interconnect structure to radiation. The radiation can be electron beam radiation or ultraviolet (UV) radiation. In one embodiment, an interface-breaking enhancing film can be used to selectively locate the gas dielectric structures formed.  
      A first aspect of the invention is directed to a method of forming a gas dielectric structure in an interconnect structure, the method comprising the steps of: providing the interconnect structure including at least one interconnect layer having a dielectric, at least one conductor and a first cap layer; and causing the dielectric to contract to form the gas dielectric structure by exposing the interconnect structure to radiation.  
      A second aspect of the invention includes a method of forming a gas dielectric structure in an interconnect structure, the method comprising the steps of: providing the interconnect structure including an interlevel dielectric, at least one conductor and a first cap layer above the interlevel dielectric and a second cap layer below the interlevel dielectric; and causing the interlevel dielectric to contract from at least one of the first cap layer, the second cap layer and the at least one conductor to form the gas dielectric structure by exposing the interconnect structure to electron beam radiation.  
      A third aspect of the invention related to an interconnect structure comprising: a dielectric layer including at least one conductor positioned therein; at least one cap layer adjacent the dielectric layer; and at least one gas dielectric structure positioned within the dielectric layer, wherein the gas dielectric structure has a substantially arcuate shape extending from the at least one cap layer.  
      The foregoing and other features of the invention will be apparent from the following more particular description of embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein:  
       FIG. 1  shows an interconnect structure provided according to one embodiment of the invention.  
       FIG. 2  shows the interconnect structure of  FIG. 1  having a gas dielectric structure formed therein according to one embodiment of the invention.  
       FIG. 3  shows an alternative embodiment of one step of a method according to one embodiment of the invention  
    
    
     DETAILED DESCRIPTION  
      With reference to the accompanying drawings, various embodiments of methods of forming a gas dielectric structure in an interconnect structure will now be described.  FIG. 1  shows an illustrative interconnect structure  100  provided according to a first step. It should be recognized that interconnect structure  100  is only illustrative of various interconnect structures to which the invention can be applied. Interconnect structure  100  includes at least one interconnect layer  102  having an (interlevel) dielectric  104 , at least one conductor  106  and a first cap layer  108 . Dielectric  104  can be any now known or later developed high dielectric constant (HiK) organic dielectric material (no glass) such as hydrogenated silicon oxycarbide (SiCOH), SILK™ (from Dow Chemical), etc. Conductor(s)  106  can be any now known or later developed interconnect conductive material, e.g., copper (Cu), aluminum (Al), etc. Conductor(s)  106  can include lines  110 , vias  112  and/or combinations thereof. Cap layer  108  can be any conventional cap layer such as silicon nitride (Si 3 N 4 ) or silicon dioxide (SiO 2 ). The particular interconnect structure  100  also may include a second interconnect layer  120  including a second dielectric  124 , at least one conductor  126  ( FIG. 1 ) and a second cap layer  128 . Second interconnect layer  120  may include substantially similar materials as that of first interconnect layer  102 , or different materials.  
      Turning to  FIG. 2 , in a next step according to one embodiment of the invention, interconnect structure  100 , i.e., at least dielectric  104 , is exposed to radiation  130 , which causes dielectric  104  to cure. As shown, as curing occurs, radiation  130  causes dielectric  104  to contract to form a gas dielectric structure  132 A- 132 C. In one embodiment, radiation  130  can include electron beam radiation (preferred) or ultraviolet (UV) radiation. The electron beam radiation or UV radiation can be generated in any now known or later developed fashion, e.g., for e-beam, via a scanning electron microscope or similar electron beam generating structure.  
      In any event, the exposure must be sufficiently long enough and have energy (e.g., acceleration voltage for e-beam) sufficient to pierce cap layer  108  to interact with dielectric  104 . Where electron beam radiation is used, a dose of approximately 300 micro-Coulombs/cm 2  has been found advantageous. In one embodiment, this dose may be achieved using electron beam radiation of no less than approximately 2 KeV and no greater than approximately 10 KeV, for no less than approximately 1 minute and no greater than approximately 8 minutes. In addition, electron beam radiation preferably has an energy of no less than approximately 300 Pascal and no greater than 1 giga-Pascal. In one particular example, a silicon nitride (Si 3 N 4 ) cap layer having a thickness of approximately 3000 Å and a density of approximately 1.3 g/cm 3 , was exposed to electron beam radiation of approximately 3 KeV for approximately 2-3 minutes, which resulted in the above-described dose. The above-described parameters may vary, however, depending on the type of cap layer  108  used and its thickness.  
      Continuing with  FIG. 2 , gas dielectric structure  132 A-C can be formed in a number of different locations within dielectric  104 . Gas dielectric structures  132 A illustrate structures in which dielectric  104  contracts vertically from first cap layer  108 . Gas dielectric structures  132 B illustrate structures in which dielectric  104  contracts vertically from second (lower) cap layer  128 , even under line conductors  110 . Gas dielectric structures  132 C illustrate structures in which dielectric  104  contracts laterally from at least one of conductor(s)  106 . It should be recognized that gas dielectric structures  132 A-C can occur individually or in combinations. For example, dielectric  104  may contract at least vertically from first cap layer  108  alone, or it may contract at least vertically from second cap layer  128 , opposite first cap layer  108 .  
      Turning to  FIG. 3 , in one alternative embodiment, where breaking of an interface between dielectric  104  and the other materials, e.g., conductor  106  and/or cap layer  108 , using radiation is difficult, an interface-breaking enhancing film  140  may be selectively formed prior to formation of the other materials, i.e., as part of formation of interconnect structure  100 . Interface-breaking enhancing film  140  may also be selectively provided at location(s) at which a gas dielectric structure  132 A-C is desired, and omitted where a gas dielectric structure  132 A-C is not desired. In this fashion, the positioning of gas dielectric structures  132 A-C can be selectively optimized. Film  140  may include any material that reduces the energy required to break the interface between the particular materials, which fosters formation of gas dielectric structures  132 A-C by reducing the energy required.  
      The above-described methodology can be carried out after each cap layer is formed and at each level.  
      The resulting interconnect structure  200  ( FIG. 2 ) includes dielectric layer  104  including at least one conductor  106  positioned therein, at least one cap layer  108 ,  128  adjacent dielectric layer  104 ; and at least one gas dielectric structure  132 A-C positioned within dielectric layer  104 . In one embodiment, each gas dielectric structure  132 A-C has a substantially arcuate shape extending from the at least one cap layer  108 ,  128 . In addition, at least one gas dielectric structure  132 C has a substantially arcuate shape extending from at least one of conductor(s)  106 . It should also be recognized that gas dielectric structures  132 A-C may have different shapes in some circumstances. For example, gas dielectric structure  132 D is not arcuate.  
      While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.