Hydrofluoroether as a heat-transfer fluid

Details Hydrofluoroether as a heat-transfer fluid Hydrofluoroether as a heat-transfer fluid

2000-09-14

2002-04-23

Atkinson, Christopher (Department: 3743)

Heat exchange

With retainer for removable article

Electrical component

C165S104330, C252S070000

Reexamination Certificate

active

06374907

ABSTRACT:

FIELD OF INVENTION
This invention relates to hydrofluoroether heat-transfer fluids. More particularly, this invention relates to 3-ethoxy-perfluoro(2-methylhexane) (n-C
3
F
7
CF(OC
2
H
5
)CF(CF
3
)
2
) as a heat-transfer fluid.
BACKGROUND
Presently various fluids are used for heat transfer. The suitability of the heat-transfer fluid depends upon the application process. For example, some electronic applications require a heat-transfer fluid which is inert, has a high dielectric strength, has low toxicity, good environmental properties, and good heat transfer properties over a wide temperature range. Other applications require precise temperature control and thus the heat-transfer fluid is required to be a single phase over the entire process temperature range and the heat-transfer fluid properties are required to be predictable, i.e., the composition remains relatively constant so that the viscosity, boiling point, etc. can be predicted so that a precise temperature can be maintained and so that the equipment can be appropriately designed.
In the semiconductor industry, there are numerous devices or processes which require a heat-transfer fluid having select properties. The heat-transfer fluid may be used to remove heat, add heat, or maintain a temperature.
Each of the semiconductor processes described below incorporates a device or a work-piece which has heat removed from it or has heat added to it. The heat transfer associated with either the heat removal or addition can take place over a wide temperature range. Thus, in each case a heat-transfer fluid is preferably used which has other attributes that make it “operator friendly”. In order for a heat-transfer fluid to be considered “operator friendly”, the heat-transfer fluid preferably exhibits low toxicity and low flammability.
For automated test equipment (ATE), equipment is used to test the performance of semiconductor dice. The dice are the individual “chips” that are cut from a wafer of semiconductor substrate. The dice come from the semiconductor foundry and must be checked to ensure they meet functionality requirements and processor speed requirements. The test is used to sort “known good dice” (KGD) from dice that do not meet the performance requirements. This testing is generally performed at temperatures ranging from about −80° C. to about 100° C.
In some cases the dice are tested one-by-one, and an individual die is held in a chuck. This chuck provides, as part of its design, provision for cooling the die. In other cases, several dice are held in the chuck and are tested either sequentially or in parallel. In this situation, the chuck provides cooling for several dice during the test procedure.
It may also be advantageous to test dice at elevated temperatures to determine their performance characteristics under conditions of elevated temperature. In this case, a coolant which has good heat-transfer properties well above room temperature is advantageous.
In some cases, the dice are tested at very low temperatures. For example, CMOS devices in particular operate more quickly at lower temperatures.
If a piece of ATE equipment employs CMOS devices “on board” as part of its permanent logic hardware, it may be advantageous to maintain the logic hardware at a low temperature.
Therefore, to provide maximum versatility to the ATE, a heat-transfer fluid preferably performs well at both low and high temperatures (i.e., preferably has good heat transfer properties over a wide temperature range), is inert (i.e., is non-flammable, low in toxicity, non-chemically reactive), has high dielectric strength, has a low environmental impact, and has predictable heat-transfer properties over the entire operating temperature range.
Etchers operate over temperatures ranging from about 70° C. to about 150° C. In this process, reactive plasma is used to anisotropically etch the features in a wafer. The wafers to be processed are kept at a constant temperature at each selected temperature. Therefore, the heat-transfer fluid preferably is a single phase over the entire temperature range. Additionally, the heat-transfer fluid preferably has predictable performance over the entire range so that the temperature can be precisely maintained.
Ashers operate over temperatures ranging from about 40° C. to about 150° C. This is a process that removes the photosensitive organic “mask”.
Steppers operate over temperatures ranging from about 40° C. to about 80° C. This is the process step in semiconductor manufacturing where the reticules needed for manufacturing are produced. Reticules are used to produce the patterns of light and shadow needed to expose the photosensitive mask. The film used in the steppers is typically maintained within a temperature window of +/−0.2° C. to maintain good performance of the finished reticule.
PECVD (plasma enhanced chemical vapor deposition) chambers operate over temperatures ranging from about 50° C. to about 150° C. In this process, films of silicon oxide, silicon nitride, and silicon carbide are grown on a wafer by the chemical reaction initiated in a reagent gas mixture containing silicon and either: 1) oxygen; 2) nitrogen; or 3) carbon. The chuck on which the wafer rests is kept at a uniform, constant temperature at each selected temperature.
Heat-transfer fluids which are presently used in these semiconductor applications include perfluorocarbons (PFCs), perfluoropolyethers (PFPEs), water/glycol mixtures, deionized water, silicone oils and hydrocarbon oils. However, each of these heat-transfer fluids has some disadvantage. PFCs and PFPEs are environmentally persistent, that is they exhibit atmospheric lifetime values of greater that 500 years, and up to 5,000 years. Water/glycol mixtures are temperature limited, that is, a typical low temperature limit of such mixtures is −40° C. At low temperatures water/glycol mixtures also exhibit relatively high viscosity. The high viscosity at low temperature yields high pumping power. Deionized water has a low temperature limit of 0° C. Deionized fluids (water or water glycol) are limited to a high temperature of 80° C. because this is the operating limit of commercially available deionizing beds. However, this high temperature limit may be significantly lower if high electrical resistivity is desired because deionized fluids become quite corrosive. Silicone oils and hydrocarbon oils are typically flammable.
Removing heat from electronic devices has become one of the most important obstacles to further improving processor performance. As these devices become more powerful, the amount of heat generated per unit time increases. Therefore, the means of heat transfer plays an important role in processor performance. The heat-transfer fluid preferably has good heat transfer performance, good electrical compatibility (even if used in “indirect contact” applications such as those employing cold plates), as well as low toxicity, low (or non-) flammability and low environmental impact. Good electrical compatibility requires the heat-transfer fluid candidate to exhibit high dielectric strength, high volume resistivity, and poor solvency for polar materials. Additionally, the heat-transfer fluid candidate must exhibit good mechanical compatibility, that is, it must not affect typical materials of construction in an adverse manner. In this application, heat-transfer fluid candidates are disqualified if their physical properties are not stable over time.
Materials currently used as heat-transfer fluids for cooling electronics or electrical equipment include PFCs, PFPEs, silicone oils, and hydrocarbon oils. Each of these heat-transfer fluids has some disadvantage. PFCs and PFPEs are environmentally persistent. Silicone oils and hydrocarbon oils are typically flammable.
Thermal shock testing is generally performed at temperatures ranging from about −150° C. to about 170° C. The rapid cycling of temperature in a part or device may be required to simulate the thermal changes brought on by, for instance, launching a missile. Thermal shock testing is required for

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