A cleanroom is a controlled environment where three things are controlled: contamination, temperature, and humidity. Temperature and humidity are controlled due to process sensitivities. Each metal layer and each insulating layer reacts differently to variations in temperature and humidity. Temperature is normally controlled to 68° ± 1.5°F while humidity is normally controlled to 45% ± 3%. The temperature and humidity are recorded by the particle counting system and are reported via the Facility Net monitoring system. Results may be seen on the computer near the cleanrrom exit.
The primary funciton of the cleanroom is to control particles harmful to the wafer and its devices. The classification of the cleanrrom is defined by either Federal Standard 208E or by the International Organization of Standardization Standard ISO 14644-1. (ISO 14644-1 is replacing Fed Std 208E) and involve the number of particles per unit volume of air greater than some given size (in microns). By Fed. Std. 208E, the unit of volume is one cubic foot of air, and the paricle sizes are the total number grater than 0.5 microns.
Typical paticle sizes for various common entities are given in Table 1.
| Item | Size (microns) | |
| Virus | 0.1 | |
| Tobacco Smoke | 0.3 | |
| bacteria | 1.0 | |
| Lung-damaging Dust | 5.0 | |
| Pollens | 30.0 | |
| Sea Fog | 1.0 - 50.0 | |
| Flour Mill Dust | 5.0 - 50.0 | |
| Visible to Naked Eye | >40.0 | |
| Human hair | 75.0 - 100.0 |
This cleanroom is classified as a level 10,000 cleanroom at 0.5 microns. This means that for each cubic foot of air in the lab, there are approximately 10,000 impurities which are larger then 0.5 microns.
Any contaminant may hinder processes or destroy devices. Sodium, which comes from sweat and skin cells can diffuse into the silicon at room temperature and create electron traps. Fibers from clothing or hair may interfere with photoresist applications. These particle must there be avoided. The major sources of particles and contaminants are: in the air circulated through the cleanroom; from people and the objects they carry into the cleanroom; from the chemicals and supplies that are brought into the cleanroom; and in the large quntity of water that is used to wash and rinse wafers during processing. We briefly discuss the cleanroom air in this section. More details may be found in such texts as those by Whyte1, and in the paper by Hendricks that provides the details for the Virginia Tech facility2. Elimination of contamination from people and objects brought into the laboratory is discussed in the laboratory protocol, and the elimination of particles and contaminants in our water supply is discussed in the section on de-ionized water.
The air entering the lab is cleaned through high-efficiency, particulate air (HEPA) filters and the lab itself is cleaned frequently to remove any particulate contamination. A schematic of the air flow in the cleanroom is shown in Figure 1.
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| Figure 1: Cleanroom air flow. |