Bi-layer etch stop process for defect reduction and via stress migration improvement

A method of forming a film stack in an integrated circuit, said method comprising depositing a layer of silicon carbide adjacent a first layer of dielectric material, depositing a layer of silicon nitride adjacent the layer of silicon carbide, and depositing a second layer of dielectric material adjacent the layer of silicon nitride.

BACKGROUND

An integrated circuit dielectric stack may comprise multiple layers of dielectric material. During fabrication of a dielectric stack, each of these layers of dielectric material is formed adjacent to another layer of material. Etch-stop layers generally are deposited between dielectric layers for use during etch-stop processes. However, the bonding and film properties of various etch-stop layers and dielectric materials can cause various problems. Specifically, defects that form as a result of poor adhesion strength between etch-stop layers and layers of dielectric material often delaminate (“peel off”) and spread throughout the dielectric stack, rendering useless a device comprising the dielectric stack.

“Via-stress migration” is another common problem attributable to the film properties of various etch-stop layers and layers of dielectric material and commonly occurs during extended operation of a device comprising the etch-stop layers and dielectric material. Via-stress migration may be induced by the stress of the films comprising the dielectric stack and electrically conductive metal lines (e.g., vias) encapsulated within the dielectric stack. The force exerted on metal lines by the stress mismatch between the dielectric stack and the metal lines gives rise to the accumulation of voids in the metal lines, thereby resulting in damaged metal lines. Damaged metal lines render the device useless.

BRIEF SUMMARY

The problems noted above are solved in large part by a method of forming a film stack in an integrated circuit, said method comprising a silicon carbide and silicon nitride bi-layer etch stop stack that reduces or eliminates via-stress migration and the production and/or delamination of defects. One exemplary embodiment may comprise depositing a layer of silicon carbide adjacent a first layer of dielectric material, depositing a layer of silicon nitride adjacent the layer of silicon carbide, and depositing a second layer of dielectric material adjacent the layer of silicon nitride.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to. . . . ” Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. Further, the term “adjacent” is generally meant to be interpreted as “abutting” and/or “immediately next to,” although in some embodiments, the term may be interpreted as “near” or “in close proximity to.” Thus, two adjacent items may abut one another or be separated by an intermediate item.

DETAILED DESCRIPTION

Described herein is a manufacturing process that reduces or eliminates via-stress migration and the formation of defects induced by delamination of dielectric films. FIG.1ashows a cross-sectional view of an integrated circuit dielectric stack100comprising, among various layers of metal, dielectric material and etch-stop layers, a film stack102. The film stack102preferably comprises a silicon carbide and silicon nitride bi-layer etch stop stack200sandwiched between an organo-silicate glass (“OSG”) layer104and a fluoro-silicate glass (“FSG”) layer106. As described below, the bi-layer etch-stop stack200reduces or eliminates the occurrence of via-stress migration and/or the formation of defects. As described herein, the silicon nitride layer204of the stack200may considerably reduce the occurrence and/or severity of via-stress migration. The silicon carbide layer202of the stack200substantially reduces the formation of the defects described above.

The adhesion strength between many etch-stop materials and OSG is generally poor, resulting in the formation of defects due to delamination. However, the adhesion strength between silicon carbide and OSG is considerably strong. Accordingly, the silicon carbide layer202is deposited adjacent the OSG layer104to prevent the formation of defects due to delamination. In general, the silicon carbide layer202may be relatively thin in comparison to the silicon nitride layer204and still achieve substantial adhesion strength with the OSG layer104. As previously explained, this adhesion strength prevents defect formation, even if the OSG layer104/etch-stop stack200is exposed to ambient conditions (e.g., ambient temperature, humidity) for a prolonged period of time. In a preferred embodiment, the silicon carbide layer202may range between approximately 100 angstroms and approximately 300 angstroms in thickness. In other embodiments, the silicon carbide layer202thickness is equal to or less than approximately 300 angstroms, although the scope of this disclosure also encompasses silicon carbide layers thicker than 300 angstroms. Furthermore, in some embodiments, the silicon carbide layer202may be pre-treated with an appropriate substance (e.g., helium, ammonia) to improve the adhesive properties of the silicon carbide layer202and to remove at least some unwanted substances from the silicon carbide layer202(e.g., passivation chemicals) prior to deposition.

Via-stress migration usually occurs due to the inability of electrically conductive metal lines to withstand forces induced by the surrounding dielectric material layers. Silicon nitride generally has lower stress levels than silicon carbide and thus is better able to preserve the functional integrity of the vias. Accordingly, the silicon nitride layer204is deposited adjacent, preferably abutting, the silicon carbide layer202to prevent via-stress migration upon deposition of the FSG layer106. The silicon nitride layer204may be considerably thicker than the silicon carbide layer202, such that the bi-layer etch stop stack200is of a thickness appropriate for an etching process. In a preferred embodiment, the thickness of the silicon nitride layer204may be between approximately 300 angstroms and approximately 900 angstroms. In other embodiments, the thickness of the silicon nitride layer204may be approximately 500 angstroms, although thicker or thinner silicon nitride layers also may be used.

An exemplary process of forming the film stack102ofFIG. 1ais shown inFIG. 1b. The process may be implemented by first depositing a silicon carbide material adjacent (e.g., abutting) a relatively low-dielectric constant (“low-k”) dielectric material, such as the OSG described above, or adjacent any suitable front-end material (block250). The low-k material and/or the front-end material may be less than approximately 15 kilo-angstroms and preferably range between approximately 1 kilo-angstrom and approximately 15 kilo-angstroms in thickness. If OSG is used, the OSG may be deposited adjacent the dielectric stack using a Novellus® Sequel Chamber, although OSG or other low-k dielectric material may be deposited using any suitable chamber. The silicon carbide material may be deposited using a suitable Applied Materials® chamber or any appropriate chamber.

A silicon nitride material then may be deposited adjacent (e.g., abutting) the silicon carbide material (block252), so that a silicon carbide and silicon nitride bi-layer etch stop stack is formed. The silicon nitride layer may be deposited using a Novellus® Sequel Chamber or any other suitable chamber. Finally, at block254, a high-density plasma fluoro-silicate glass, phospho-silicate glass or any other suitable type of oxide film (e.g., plasma-enhanced FSG or tetraethylorthosilicate) is deposited adjacent (e.g., abutting) the silicon carbide and silicon nitride bi-layer etch stop stack. In at least some embodiments, this oxide film may have a thickness less than approximately 20 kilo-angstroms and further, preferably between approximately 1 kilo-angstrom and approximately 20 kilo-angstroms. If FSG is used, the FSG may be deposited using a Novellus® Speed Chamber, although FSG or any other type of oxide film may be deposited using any suitable chamber and/or any suitable technique.