Gas separation: apparatus – Solid sorbent apparatus – Plural diverse separating means
Reexamination Certificate
2000-01-24
2002-03-05
Spitzer, Robert H. (Department: 1724)
Gas separation: apparatus
Solid sorbent apparatus
Plural diverse separating means
C096S154000, C055S385200, C055S514000, C055S521000, C055S524000, C055SDIG005
Reexamination Certificate
active
06352578
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an air filter used in a high efficiency air cleaning apparatus, such as a clean room, a clean bench, a storage means (stocker), etc., for removing gaseous inorganic and/or organic impurities contained in the atmosphere in the high efficiency air cleaning apparatus. The invention also relates to a method for manufacturing the air filter and further relates to the high efficiency air cleaning apparatus, the device or the like provided with the filter manufactured according to the method.
BACKGROUND ATR
In these days, when semiconductors and LCD panels are manufactured, a high efficiency air cleaning apparatus is generally used. For instance, the production line for a semiconductor from a bare wafer to 1 megabyte DRAM chip, includes about 200 steps, and the production line to produce 9.4-inch TFT type LCD panel from solid glass includes about 80 steps. In these production lines, it is difficult to transfer wafers and glass substrates consecutively and continuously to next process. For instance, in the TFT-LCD production line, it is not rare to see half finished products, on which a predetermined circuit is already formed, forced to be kept inside of a carrier or a stocker, while being exposed to the inside atmosphere for several to several tens of hours until they are transferred to the next manufacturing step.
As stated above, when a semiconductor substrate or a LCD substrate is kept in an atmosphere of an ordinary clean room for a long time, gaseous impurities contained in the room would be deposited on the surface thereof. Recently, acid substances, basic substances, organic substances and various dopants are considered to exist in such clean room in a gaseous state and these substances give an ill influence to the performance of semiconductors or LCD panels when they are deposited on the silicon wafer surface used for semiconductor production, or on the glass substrate surface used for the LCD panel production.
According to an article titled “Forecast of Airborne Molecular Contamination Limits for the 0.25 Micron High Performance Logic Process” of Technology Transfer #95052812A-TR publicized by SEMATECH on May 31, 1995, these acid substances, basic substances, organic substances and dopants are called chemical contaminants and respectively defined as follows.
“acid substance”: a corrosive substance to react chemically like an electron acceptor. (hydrofluoric acid HF, sulfur oxides SOx, nitrogen oxides NOx, etc.).
“basic substance”: a corrosive substance to behave chemically like an electron donor. (ammonia NH
3
, amine, etc.).
“organic substance”: a substance having a boiling point higher than normal temperature under normal pressure, condensing on a cleaned surface. (siloxane, phthalate, HMDS, BHT, etc.).
“dopant”: chemical element to give ill influence to an electrical performance of the semiconductor device. (Boron B, phosphorus P).
Table 1 is a list of the allowable concentration (ppt) of the chemical contaminants required for 0.25 &mgr;process (after '98), which is disclosed in the article entitled “Forecast of Airborne Molecular Contamination Limits for the 0.25 Micron High Performance Logic Process” of Technology Transfer #95052812A-TR published by SEMATECH (U. S. A) on May 31, 1995. The value in percentage shown in the bottom of the allowable concentration (ppt) shows the reliability of each allowable concentration value. The table shows the allowable concentration of the chemical contaminants in clean space of four semiconductor production processes having serious chemical contamination problems. According to one example of the actual measurement of various contaminants contained in the atmosphere of the ordinary clean room not provided with any chemical protective measure against gaseous contaminants, it is reported that acid substances of about 100 ppt-1,000 ppt, basic substances of about 1,000 ppt-10,000 ppt, organic substances of about 1,000 ppt-10,000 ppt, and dopants of about 10 ppt-100 ppt, respectively are contained in such atmosphere.
TABLE 1
Max.
standby
Acidic
Basic
Organic
Process
hour
substance
substance
substance
Dopant
Pre-gate
4
13,000
13,000
1,000
0.1
oxidation
50%
50%
75%
90%
Salicida-
1
180
13,000
35,000
1,000
tion
50%
25%
75%
75%
Contact
24
5
13,000
2,000
100,000
formation
50%
25%
75%
75%
Photo-
2
10,000
1,000
100,000
10,000
litho-
75%
90%
50%
50%
graphy
When concentration of the chemical contaminants in the atmosphere of the ordinary clean room not provided with any chemical protective measure against gaseous contaminants, and the allowable concentration of the chemical contaminants in Table 1 are compared, it is found that severe controls are required for the processes stressed by underlines under the numerals of the allowable concentrations (ppt). That is to say, with regard to acid substances, they should be controlled to less than 180 ppt in the salicidation process, and less than 5 ppt in the contact formation process. As for basic substances, they should be controlled to less than 1 ppb, in the photolithographic process. With respect to the dopant, it should be controlled to less than 0.1 ppt for the pre-gate oxidation process. As to organic substances, they should be controlled to less than 1 ppb in the pre-gate oxidation process, and less than 2 ppb in the contact formation process.
Such impurities as gaseous acid substance, basic substance, organic substance, and dopant shown in Table 1, cause problems if contained in various high efficiency air cleaning apparatus for production of semiconductor substrate and glass substrate, such as clean room, cleanbench and clean chamber, various scale of high efficiency air cleaning apparatus such as stocker for keeping clean products, and local high efficiency air cleaning apparatus called mini environment.
Among them, dopant shows a chemical behavior resembling acid substance as water-soluble borate compound or phosphorous compound, and a filter having a capability to adsorb and remove gaseous acid substance can adsorb and remove the dopant. As apparent from Table 1, simultaneous removal of organic substance and dopant in the pre-gate oxidation process, and simultaneous removal of acid substance and organic substance are required respectively.
Though not mentioned in Table 1, gaseous contaminants generated in the photolithography process are HMDS (hexamethyl disilazane) and its decomposition product besides ammonia. HMDS is a lipophilic substance to coat on a wafer to improve affinity of a litho-film to a silicon wafer and very easy to adhere to a surface (wafer, lens, glass etc.). HMDS is hydrolyzed in a few days to gasify into ammonia and trimethyl silanol. When trimethyl silanol adheres to a lens or mirror thereby making the surface thereof blur, it causes an exposure trouble during the exposure process. KrF laser exposure (248 nm) is used in a device having 0.25 &mgr;m in line width, and the KrF laser exposure is considered to be still used in a gigabyte-capable device having 0.18 &mgr;m in line width which is expected to start mass production from the year of around 2000.
The clouding of lens by HMDS or trimethyl silanol gives a fatal effect. Both HMDS and trimethyl silanol are organic substances with no ionization and did not draw much attention at the time of 1997. In a photolithography process for manufacturing the gigabyte-capable device having 0.18 &mgr;m in line width, however, simultaneous removal of base and organic substance is necessary.
Of the four chemical contaminants, three kinds of contaminants, an acid substance, a basic substance, and dopant, are soluble and they are apt to give rise to ion-exchange reaction and neutralization reaction. As a means for removing these three kinds of chemical contaminants from the air in a clean space, there has been a method for removing them by dissolving into aqueous solution using a wet rinsing (scrubber rinsing) and a chemical adsorption method using so-called chemica
Okada Takao
Sakata Soichiro
Sato Katsumi
Takahashi Hideto
Patterson Belknap Webb & Tyler LLP
Spitzer Robert H.
Takasago Thermal Engineering Co., Ltd.
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