Tool Classifications at the LNF

This wiki page covers the LNF tool classification and related policies for materials and process flow. All LNF users are expected to familiarize themselves with the LNF tool classification and materials protocols to minimize the risks of contaminating equipment or cross-contaminating others’ samples.

Introduction

Working with chemicals, diverse sample materials, and processing systems involves cross-contamination risks. Contamination can significantly degrade device performance, even at low levels (e.g., parts per billion). At the LNF, we follow guidelines to minimize risks associated with micro- and nanofabrication while maintaining flexibility. The LNF tool classification reflects such guidelines put in place. As a shared facility, our equipment is highly versatile, accommodating a wide range of sample types and processes. The guidelines help to preserve the safety of users, staff, and equipment. Minimizing the risk of contaminating samples and equipment increases the chances of success.

LNF's materials rules consist of two parts. First, each tool has its own list of Approved Materials (i.e. materials restrictions) and Specific Tool Related Rules , including approved processes and sample preparation/cleaning requirements. These can be found on each tool's wiki page, and must be followed at all times. Second, each tool is classified into one of five Categories . For processes that use multiple tools, only certain Process Flow Paths are allowed in order to minimize tool and sample cross-contamination. If you wish to run a process or use materials that don't comply with these two rules, you must seek written permission from LNF staff before you proceed.

The following sections will describe in detail the materials rules in place at the LNF. When in doubt, contact the LNF staff via the Helpdesk system to ask questions or raise concerns.

Type of contaminants

Many of the materials present in our facility are incompatible with one another. Therefore, classifying contaminants is dependent on the type of technology we refer to. Historically, cleanrooms have been used for the fabrication of microchips; thereafter, silicon has been the reference everyone looks up to. In general, electronic devices can suffer significant performance degradation due to contaminants that affect terminal doping or gate performance. Beyond electronics, at the LNF, we care not only about silicon-based devices but also about a broad spectrum of materials. Our scientific community works on a wide range of topics, and we strive to support them all. Being aware of the state of our equipment is important to ensure good performance and fulfill our mission.

Organic (carbon) contamination

Organic contamination in cleanroom-processed devices involves trace amounts of volatile organic compounds and molecular contaminants that adhere to sample surfaces, leading to severe defects, reduced yields, and reliability issues. These contaminants, including airborne molecular contamination, plastics, and residues, cause hydrophobic surfaces, haze, and gate oxide degradation. Organic sources vary, but include photoresist coating and solvent residues. As a surface contamination, they can be effectively removed using a strong acid or oxygen plasma cleaning process.

Metal contamination

Metal contamination is a critical concern in semiconductor fabrication and other scientific research, where even trace amounts (often on the order of parts per billion) can degrade device performance, reduce manufacturing yields, and impair dielectric integrity. Key metallic contaminants include transition metals such as Fe, Ni, Cr, and Cu, as well as ions such as Na and Al, which originate from processing equipment, handling tools, chemicals, and water.

Particulate matter

These include many types of particles, such as dust, metal debris, and organic matter, such as skin flakes and fibers. They are a primary cause of defects and can originate from processing equipment or human handling.

About LNF systems and the material restrictions

When a sample is processed, there is a risk of picking up trace materials already in the tool, thereby altering the sample's content. Some contaminants may come from other users' samples or from the process system itself. At LNF, we strive to characterize our equipment to understand and minimize cross-contamination. To provide better service to our community, each of our systems has a set of rules in place.

Approved materials list

All materials contained in the sample to be processed must be explicitly approved for processing. A list of approved materials is published under each tool's LNF-wiki page. If you don’t see the materials you have approved on the tool you want to use, create a Helpdesk ticket to discuss your options with the LNF staff. We will try to accommodate all the requests as best as we can.

Specific tool-related rules

If an LNF tool lists your material as approved, you are still obligated to follow all the restrictions related to recipes and tool conditions. When in doubt, create a Helpdesk ticket to address your questions to the LNF staff.

LNF tool classification

The LNF tools are divided into five categories. Each tool has its own set of restrictions and approved materials. Users must refer to the corresponding tool's wiki page to review the latest version.

• Heavily-Restrictedː This category is reserved for a few tools with the most restrictions and the fewest allowed materials. Typically, only silicon-based and metal-free samples are allowed.

• Restrictedː This category has fewer restrictions compared to the Heavily-Restricted tools. It allows some other non-silicon-based materials and a few types of metals.

• Broadː This category has fewer restrictions compared to the Restricted tools. It allows a broad spectrum of materials.

• End-of-lineː This category allows many types of materials. However, samples processed in this category are not expected to be processed by other tools. Data show that tools in this category tend to contain high levels of metal contamination.

• Generalː This includes tools for patterning and metrology. These tools can be used freely within your process flow.

Supported process paths

The chronological order in which a sample is processed across different tools is important to minimize cross-contamination. It is expected that the cleanest tools are used earlier in the process flow whenever possible. This is described in the diagram below. Based on the diagram, it is expected that processes flow downward or sideways, and, when possible, avoid processing in higher-level tools. If a tool that is one level above the current integrated lowest level is needed, there is typically a supported path to achieve it, but it often requires additional decontamination steps. Users should read all the specific tool requirements in their corresponding LNF wiki page. If a tool that is two levels above the current integrated lowest level is needed, this is not supported, and inquiries should be addressed to staff to consider exceptions to this rule. Note that tools categorized as General refer to lithography and metrology tools that can be easily incorporated into any process.

Surface decontamination processes

Even though removing trace materials from the bulk of a sample is practically impossible, it is often possible to remove contamination from the surface. The surface decontamination process is sample and contamination-level-dependent but generally requires an acid cleaning followed by at least one RCA cleaning. If your sample is not compatible with these cleaning methods, please submit a Helpdesk ticket for assistance from LNF staff.

Below are some of the common decontamination processes we have established at the LNF.

RCA cleaning

RCA cleaning (Radio Corporation of America) was a method developed to remove both organic and ionic contaminants from wafer surfaces. More details about this process are described in RCA clean.

Fluorocarbons removal

Fluorocarbon residue from deep Si BOSCH process etching has proven to be challenging to remove and can be detrimental to LPCVD furnaces. Other fluorocarbon-based plasma etches may also pose similar risks. At the LNF, a methodical investigation was conducted to determine the most effective approach for decontaminating samples with fluorocarbon residues. The full protocol is described at Fluorocarbons Removal.

Particle and organic matter removal

In general, particles and organic residues are detrimental to device performance. Removing this can be challenging. More details about sample cleaning are described in Cleaning.

Post-dicing cleaning

Dicing samples creates a considerable number of particles. Also, our dicing tool processes a wide range of materials. All of this needs to be considered when samples move from the dicing tool to other LNF tools. The preparation and decontamination processes for pre- and post-dicing are described on the ADT dicing tool LNF wiki page.