Integrated circuits may comprise layers of metal lines and dielectric layers dispose there between. Air gaps may be used as dielectrics between metal lines in order to reduce signal delay and hence improve performance.
Air gaps as dielectrics may pose problems when used in conjunction with unlanded vias. An unlanded via is partially coupled to the dielectric between metal lines instead of to a metal portion of the metal line. During fabrication, the cavity in which an unlanded via is to be formed may accidentally penetrate the dielectric portion and expose an air gap on a lower dielectric layer. The air gap may then be filled with metal during the via metallization step, causing a short in a circuit.
The several embodiments described herein are solely for the purpose of illustration. Embodiments may include any currently or hereafter-known versions of the elements described herein. Therefore, persons in the art will recognize from this description that other embodiments may be practiced with various modifications and alterations.
Referring now to
The dielectric ensemble 100 may comprise any number of layers. In the illustrated embodiment, the dielectric ensemble 100 comprises a first dielectric layer 101, a second dielectric layer 102, and a third dielectric layer 103. In some embodiments, the first dielectric layer 101 may exhibit a first porosity and, in some embodiments, the first porosity may be zero (e.g. non-porous). In some embodiments, the first porosity may be between zero and ten percent. The first layer 101 may comprise an inter layer dielectric such as, but not limited to carbon-doped oxide. The second dielectric layer 102 may exhibit a second porosity and, in some embodiments, the second porosity may be approximately 15 to 25 percent (e.g. 15 to 25% porous). In this example, the second layer is considered sacrificial. The second layer 102 may comprise porous carbon-doped oxide in some embodiments. The third dielectric layer 103 may exhibit a third porosity. The third dielectric layer 103 may be referred to as a screen layer and in some embodiments the third porosity may be approximately 5 to 20 percent. An adhesive layer (not shown) may be coupled to the third layer to aid in integrating the dielectric ensemble 100.
Now referring to
We now proceed to create the air gap 107 shown in
In some embodiments, the reaction may dissolve or strip all or part of the sacrificial second layer 102, resulting in one or more air gaps 107. The strip reaction byproducts may be extracted through the porous layer 103 leaving behind an air gap 107. In some embodiments, the one or more air gaps 107 may occupy 40 percent of the volume between the metal line 104 and 105. In some embodiments, the strip reaction byproducts may comprise a result of a reaction between the chemical and the second layer 102.
The utilization of the third layer 103 combined with design rules restricting the maximum space between two adjacent metal lines, preserves planarity of the substrate. In such case, no dielectric polish step is needed for the subsequent layer. A subsequent layer or ensemble may be applied directly on top of metal diffusion barrier layer.
The first dielectric ensemble may be coupled to the second dielectric ensemble using a metal diffusion barrier layer 411. After each dielectric ensemble has been subjected to a process such as process 500 of
The substrate 400 may comprise a first via 413 and a second via 414. The first via 413 may couple a first metal line 407 to a second metal line 412. The second via 414 may couple a third metal line 408 to a fourth metal line 415. In some embodiments, the second via 414 may be fully landed. As illustrated at 409 a portion of the first via 413 lands on the dielectric 403 and thus the first via 413 is an unhanded via. Since the third dielectric layer 403 may be only 10 to 15 percent porous, the third dielectric layer 403 may maintain substantial rigidity such that the unlanded via 413 may not fully penetrate the third dielectric layer 403 thereby preventing the filling of the air gap during the subsequent metallization steps which may cause electrical shorts in the circuit of substrate 400.
Each via 413/414 may lie in at least a portion of the fourth layer 104. In some embodiments, the first via 413 and/or the second via may lie in a portion of the third layer 403.
Next, at 503, a chemical is applied on the third layer to pass through (e.g. permeate) and dissolve a portion of the sacrificial second layer and the dissolved portion of the sacrificial layer is extracted through a plurality of pores in the third layer. The chemical is to attack the second layer but is not to substantially react with the first layer, the third layer, or the substrate metals. Therefore, in some embodiments, the chemical may pass through the third layer and not pass through the first layer. The dissolution of the second layer may leave or form one or more air gaps between the first layer and the third layer. According to some embodiments, the chemical comprises diluted hydrofluoric acid. Any suitable chemical may be used in conjunction with some embodiments.
At 504, a metal surface is passivated. This is a step known in the art where either a thin dielectric layer 411 or a selectively deposited metal cap may be utilized. Next, at 505, a via is fabricated at least partially disposed in a portion of the third layer to couple the first metal line to a second metal line where the via is unlanded and the via is prevented from penetrating into the second layer of the dielectric ensemble by the third layer.
At 506, a second dielectric ensemble may be deposited for a next level of metallization. The second dielectric ensemble may comprise a fourth dielectric layer exhibiting the first porosity, a fifth dielectric layer exhibiting the second porosity and a sixth dielectric layer exhibiting the third porosity. Next, at 507, dual damascene structures may be created in the second dielectric ensemble.
In some embodiments a via disposed in at least a portion of the third layer and the fourth layer may be fabricated and may couple the first metal line to a second metal line where the via is fully landed as illustrated by via 414. In some embodiments, a via disposed in at least a portion of the third layer and the fourth layer may be fabricated to couple the first metal line to a second metal line where the via is unlanded as illustrated by via 413. Via 413 may be prevented from penetrating into the second layer of the dielectric ensemble by the third layer 403. A chemical may be applied on the sixth layer to pass through and dissolve a portion of the fifth layer and a dissolved portion of the fifth layer may be extracted through a plurality of pores in the sixth layer.
Since dielectric assemblies may be stacked to attain multi-level metallization, the method of
Various modifications and changes may be made to the foregoing embodiments without departing from the broader spirit and scope set forth in the appended claims.