International Quality Federation (IQF) is an all-volunteer organization of quality practitioners and subject matter experts that saw the need for standardization in the Six Sigma field. They have administered several hundred exams thus far, 80- 90% employer monitored and endorsed. Employers using the exam include Boeing, Visteon, and others.
Other organization offering similar Six Sigma certification services is American Society of Quality (ASQ). The comparison of IQF and ASQ certification schemes is given in the following link for your information.
Types of Certifications
International Quality Federation (IQF) USA offers third party certifications in the following three categories: DMAIC, Lean Six Sigma and DFSS. In each of these categories three levels of certifications are available: Green Belt, Black Belt and Master Black Belt.
View IQF Green Belt Certificate (Sample).