Effects of Borophosphosilicate Glass Dopant Concentrations on Isotropic Etch Profile
- PDF / 531,813 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 19 Downloads / 242 Views
Effects of Borophosphosilicate Glass Dopant Concentrations on Isotropic Etch Profile Chris Gibson
Bradley Williams
Stacey Evans
AMI Semiconductor, Inc., 2300 Buckskin Road, Pocatello, ID 83201
Abstract In the process of chemically etching contact openings, film characteristics of the Borophosphosilicate glass (BPSG) film strongly effect the formation of an ideal contact profile. Ideal contact profiles represent a wine glass shape to provide better metal step coverage into the contact opening in comparison to a vertical sidewall profile. The rounded shape of the wine glass is etched chemically (isotropic) allowing for etch in the vertical and horizontal direction. As the addition of dopants to the oxide film effect the etch rate, the profile of the isotropic etch will change which in turn effects the electrical device properties, down stream processes and device reliability. BPSG film characteristics are the area of investigation. Characteristics of concern are weight percent concentrations of boron and phosphorus, film density and dopant concentration profiles in relation to depth. To evaluate the entire contact formation module, chemical etch characteristics including etch rate in relation to film depth for thermal oxide films were also investigated. Experimentation in the form of a response surface design was used to model effects of previously discussed BPSG film characteristics. To achieve the desired and predictable wet etch rate of BPSG in a buffered oxide etch (BOE), calculated control limits were placed on the boron and phosphorus dopant concentrations. Results showed that dopant effects on the isotropic etch process exceeded the control capability of dopant concentrations in the deposition process. In relating process control capabilities to 6σ techniques, a Cpk above 1.5 is considered capable. To eliminate previously discussed defects created in the isotropic etch process, reject limits for dopant concentrations in a BPSG film deposition process would need to be set well within the typical 6σ giving a Cpk below 1.5
Introduction Problem Statement Failure mechanisms originating from contact isotropic etch relate to either one of two things, over-etch or under-etch. An over-etch scenario consists of the isotropic etch bowl being too large (too deep and too wide). With a large isotropic etch profile, a failure can take place in the photo process for metal 2. At metal 2 photo, depth-of-focus is increased with a large isotropic etch portion from contact etch. When the photo mask is printed in this condition, light reflects into a location that is not expected and in turn photoresist is removed in a location that should be patterned for a metal line.1 In an under-etch scenario, the isotropic etch portion is too small and will cause other potential failures. The first and most obvious failure would be incomplete contacts. In current processing setups this failure is most unlikely because of a large amount of over-etch in the anisotropic portion of the contact process. A second failure is decreased metal step
Data Loading...
