Method for forming contact vias in integrated circuits

Abstract: Initially, a first protective layer (14) is formed on an insulating layer (12), and an opening (16) is created through the insulating layer (12) where a contact is to be made. A conductive layer (18,20) is deposited over the protective layer (14) and partially fills the opening (16), forming a conductive plug (20) in the opening (16). A second protective layer (22) is then formed over the conductive plug (20). Portions of the conductive layer (18) which were formed over the first protective layer (14) are removed. During removal of those portions of the conductive layer (18), the second protective layer (22) protects the conductive plug (20) from damage. The first and second protective layers (14,22) are then removed, leaving the conductive plug (20) in the opening (16) in the insulating layer (12). A conductive contact can now be made by depositing a second conductive layer (24) over the conductive plug (20).

Description: The present invention relates generally to integrated circuits, and more specifically to a method for forming contact vias in integrated circuits. As integrated circuit devices become more complex, greater numbers of interconnect levels are required to connect the various sections of the device. Generally contact vias are formed between interconnect levels to connect one level to another. When multiple layers of interconnect are used in this manner however, difficulties arise in forming upper interconnect levels and contact vias due to the uneven topographical features caused by the lower interconnect levels. Thus, the topography of interconnect layers affects the ease of manufacturing of the integrated circuit device. The uneven topographical features of multiple interconnect levels are caused by forming the various interconnect layers above each other, resulting in the creation of hills and valleys on the surface of the device. Those skilled in the art will recognize it is difficult to get upper interconnect layers to maintain constant cross-sections when crossing over uneven topography. This leads to portions of the interconnect lines having a higher current density, leading to electromigration problems and related device failure mechanisms. These step coverage problems can result in voids and other defects in the interconnect signal lines themselves, and in the contact vias formed between interconnect lines. Therefore, it would be desirable to provide a method for forming contact vias which are free of voids and other defects, and which result in a more planar topography. It is also desirable that such a method not significantly increase the complexity of the manufacturing process. It is therefore an object of the present invention to provide a method for forming contact vias in integrated circuits which are free of defects caused by step coverage problems. It is another object of the present invention to provide such a method which results in a more planar topography. It is another object of the present invention to provide such a method and structure which is compatible with standard process flows, and which add minimal additional complexity to the fabrication of a typical integrated circuit. European patent application publication No. 0239756 discloses a method of forming a conductive plug in an opening in an insulating layer such that the upper surface of such structure is substantially planar. The method involves depositing and exposing a photoresist layer over an oxide layer, depositing a conductive layer over the photoresist layer and forming a conductive plug in a contact opening formed, and forming a protective photoresist plug over the conductive plug formed in the contact opening to protect such conductive plug during subsequent removal of the remainder of the conductive layer. According to Claim 1 of the present invention there is provided a method for forming a contact structure in an integrated circuit, comprising the steps of depositing a barrier layer over a first oxide layer in the integrated circuit, depositing a second oxide layer over the barrier layer, depositing and patterning a photoresist layer to define an opening, forming the opening through the second oxide layer, barrier layer and first oxide layer where a contact is to be made, removing the photoresist layer, depositing a conductive layer over the second insulating layer wherein the conductive layer partially fills the opening forming a conductive plug, forming an oxide plug in the opening, removing a portion of the conductive layer wherein the second oxide layer is exposed, removing the second oxide layer wherein the barrier layer acts as an etch stop to protect the first oxide layer, removing the oxide plug and removing the barrier layer, wherein the conductive plug remains in the opening in the first oxide layer. A conductive contact can then be made by depositing a second conductive layer over the conductive plug. The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, and further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: Figures 1 - 6 are sectional views illustrating the method for forming a contact via in integrated circuits according to the present invention. The process steps and structures described below do not form a complete process flow for manufacturing integrated circuits. The present invention can be practiced in conjunction with integrated circuit fabrication techniques currently used in the art, and only so much of the commonly practiced process steps are included as are necessary for an understanding of the present invention. The figures representing cross-sections of portions of an integrated circuit during fabrication are not drawn to scale, but instead are drawn so as to illustrate the important features of the invention. Figures 1 - 6 illustrate a method which can be used to form a contact structure in an integrated circuit. Referring to Figure 1, a contact is to be formed on an underlying region 26 in an integrated circuit. The underlying region 26 can be either a semiconductor substrate or an interconnect signal line. A first insulating layer 28, typically made of oxide, is grown or deposited over the device. A barrier layer 30, typically made of silicon nitride, is deposited over the first insulating layer 28, followed by a second insulating layer 32. The second insulating layer 32 is typically made of oxide. A photoresist mask 34 is then deposited and patterned over the second insulating layer 32, and an opening 36 is formed through the second insulating layer 32, the barrier layer 30, and the first insulating layer 28 where a contact is to be made. Figure 2 illustrates the integrated circuit after the photoresist mask 34 is removed and a conductive layer 38 is deposited over the device. The conductive layer 38 covers the second insulating layer 32 and partially fills the opening 36, forming a conductive plug 40 in the opening 36. In this example of the preferred embodiment, the conductive layer 38 and conductive plug 40 are made of aluminum, but hey can be made of other conductive materials. The aluminum is preferably deposited by sputtering, so that it tends to deposit only on horizontal surfaces. This leaves little or no aluminum along the vertical sidewalls of the opening 36, so that the layer 38 and plug 40 are effectively detached. Referring to Figure 3, a dielectric layer 42 is deposited over the conductive layer 38 and extends into the opening 36. In this example of a preferred embodiment, the dielectric layer 42 is made of spin on glass, but it can also be made of other materials. The dielectric layer 42 is then etched down to approximately the point where the conductive layer 38 makes contact with the second insulating layer 32 (not shown). The etch back can be done, for example, by performing an isotropic etch. Figure 4 illustrates the integrated circuit after portions of the conductive layer 38 are removed, typically by performing an isotropic etch. The dielectric plug 44 protects the conductive plug 40 from damage during removal of potions of the conductive layer 38. The dielectric plug 44 and second insulating layer 32 are then removed, followed by removal of the barrier layer 30. Barrier layer 30 acts as an etch stop to protect the underlying insulating layer 28. Each of these removal steps can be done, for example, by performing an isotropic etch designed to remove each material. Following removal of the conductive plug 44, the second insulating layer 32 and the barrier layer 30, a contact structure as shown in Figure 5 is formed. The integrated circuit is now ready for further processing steps. A second conductive layer 24, such as a metal layer, could then be deposited over the device as shown in Figure 6 and patterned to define an interconnect signal line.

Claims: A method of forming a contact structure in an integrated circuit, comprising the steps of: depositing a barrier layer (30) over a first oxide layer (28) in the integrated circuit; depositing a second oxide layer (32) over the barrier layer (30); depositing and patterning a photoresist layer (34) to define an opening (36); forming the opening through the second oxide layer (32), the barrier layer (30), and the first oxide layer (28) where a contact is to be made; removing the photoresist layer (34); depositing a conductive layer (38) over the second insulating layer (32), wherein the conductive layer (38) partially fills the opening (36) forming a conductive plug (40); forming an oxide plug (44) in the opening (36); removing a portion of the conductive layer (38), wherein the second oxide layer (32) is exposed; removing the second oxide layer (32), wherein the barrier layer (30) acts as an etch stop to protect the first oxide layer (28); removing the oxide plug (44); and removing the barrier layer (30) wherein the conductive plug (40) remains in the opening (36) in the first oxide layer (28). The method of claim 1, wherein said step of forming the oxide plug (44) in the opening (36) in the first oxide layer (28) comprises the steps of: depositing an oxide layer (42) over the conductive layer (38) and extending into the opening (36); and removing a portion of the oxide layer (42), wherein the conductive layer (38) is exposed and a portion of the oxide layer (42) remains in the opening (36). The method of claim 2 wherein said oxide layer (42) comprises spin on glass. The method of claim 2 or claim 3 wherein said step of removing a portion of the oxide layer (42) comprises anisotropically etching the layer. The method of claim 2 or claim 3 wherein said step of removing a portion of the oxide layer (42) comprises isotropically etching the layer. The method of any one of claims 1 to 5 wherein said conductive layer (38) comprises aluminium. The method of any one of claims 1 to 6 wherein said step of removing the second oxide layer (32) comprises isotropically etching the layer. The method of any one of claims 1 to 7 wherein said step of removing the barrier layer (30) and oxide plug (44) comprises isotropically etching the barrier layer (30) and oxide plug (44) . The method of any one of claims 1 to 8 wherein said barrier layer comprises silicon nitride.

Inventors: BRYANT FRANK RANDOLPH, NGUYEN LOI NGOC, BRYANT, FRANK RANDOLPH, NGUYEN, LOI NGOC
Applicants: SGS THOMSON MICROELECTRONICS, SGS-THOMSON MICROELECTRONICS, INC.
Application year: 1992
Main classification: H01L21
IPC codes: H01L21