KR100379886B1 - On-site generation system of ultra-purity buffered HF for semiconductor process - Google Patents

Abstract

The present invention relates to an on-site manufacturing process of ultrapure buffered hydrofluoric acid in a semiconductor manufacturing facility. Anhydrous ammonia is purified by the scrubber 17 into a high pH liquid and combined with high purity aqueous HF purified by a similar process. The production is monitored by density measurement to produce an acid whose pH and its buffer are precisely controlled.

Description

Ultra-high purity buffered HF on-site generation system for semiconductor process

The present invention relates to an apparatus and method for supplying ultra high purity buffered HF (buffered hydrofluoric acid) and / or ammonium fluoride (NH ₄ F) for semiconductor manufacturing.

Background: Contamination in IC Manufacturing

Contamination is of great importance in integrated circuit fabrication. In modern integrated circuit manufacturing, most of the processes are one kind or another kind of cleaning process; In this cleaning process, it is necessary to remove organic contamination, metal contamination, photoresist (or inorganic residue thereof), etching by-products, natural oxides, and the like.

In 1995, the cost of the new front end (integrated circuit wafer fabrication facility) typically exceeded $ 1 billion ($ 1,000,000,000), most of which was for particulate control, cleaning and contamination control measures.

One important source of contamination is impurities in process chemicals. Since cleaning is done frequently and is important every week, contamination due to cleaning chemistry is very undesirable.

The high purity levels required for semiconductor manufacturing are rare or unique among industrial processes. At such high purity levels, chemical treatment is inherently undesirable (though of course, it cannot be completely excluded). The exposure of ultrapure chemicals to air (particularly in the presence of workers) should be minimized. Such exposure poses the risk of introducing particulates and causing contamination. Due to the high risk of contaminants at the site of the original manufacturer or user, it is still not ideal to ship ultrapure chemicals in closed containers. In addition, there is a fear that undetected contamination may damage expensive bulk wafers.

Because many corrosive and / or toxic chemicals are commonly used in semiconductor processing, reagent supplies are usually away from the location of the operator of the front end. Building and managing pipes for ultra-pure gas and liquid is well known in the semiconductor industry, where most of the gas and liquid can be transported to any wafer manufacturing station from any location in the same building (or the same location).

Ammonia Tablets

The inventors of the present invention have developed a method for producing ultra-high purity ammonia in an on-site system installed at a semiconductor wafer production site, which extracts ammonia vapor from a liquid ammonia reservoir and finely filters the ammonia vapor. By passing through a filter, the filtered vapor is scrubbed with high pH purified water (preferably deionized water equilibrated by ammonia). This finding allows the conversion of commercial grade ammonia to high purity ammonia sufficient for high precision production without the need for conventional column distillation. The extraction of ammonia vapor from the feed reservoir itself serves as a group of distillations, such as alkali and alkaline earth metal oxides, carbonates and hydrides, transition metal halides and hydrides and high boiling hydrocarbons and halide carbons. Eliminates nonvolatile and high boiling impurities. Impurities that were previously thought to be removed only by distillation can be found in commercial grade ammonia, such as certain transition metal halides, group III metal hydrides and halides, certain group IV hydrides and halides, and halogens It has been found that reactive reactive volatile impurities can be removed by scrubbing to a high degree of accuracy. This is a surprising finding since cleaning techniques are commonly used to remove large scale impurities rather than fine scale.

Wet vs. dry process

One of the technological implementations that have long been used in semiconductor processing is the change (and attempted change) between dry and wet processes. In a dry process, only reactants in gas or plasma contact the wafer. In the wet process, various liquid reagents serve the purpose of etching silicon dioxide, removing natural oxide layers, removing organic or trace organic contaminants, removing metal or trace organic contaminants, etching silicon nitride, or silicon etching. To be used.

Plasma etching has many attractive capabilities, but is not suitable for cleaning. In short, there are no chemical reactions that can be used to remove some of the most undesirable impurities such as gold. Therefore, wet cleaning processes are essential for modern semiconductor processes and will continue to exist for some time.

Plasma etching is performed by photoresist in the appropriate position, and the high temperature process is not immediately followed. Instead, the resist is removed and then cleaning is required.

Materials to be removed by cleaning include photoresist residues (organic polymers), sodium, alkaline earth (eg calcium or magnesium), and heavy metals (eg gold). Since most of them do not form volatile halides, they cannot be removed by plasma etching. Therefore, there is a need for cleaning using wet chemical reactions.

As a result, the purity of chemicals in the plasma etching process is not so important because, after their fixing, the cleaning process is always followed before the high temperature process and before the dangerous contaminants are introduced by the high temperature process. This is because these contaminants can be removed from the surface by the process. However, the purity of liquid chemicals is even more important. This is because the collision speed at the semiconductor surface is usually one million times higher than the collision speed at the time of plasma etching, and the high temperature process immediately follows the liquid cleaning process.

However, the wet process has a significant defect called so-called ion contamination. Integrated circuit structures use only a few impurity species (boron, arsenic, phosphorus, and sometimes antimony) to form the desired p-type and n-type doped regions. However, many other types are electrically active impurities and are very undesirable contaminants. Many of these contaminants can have adverse effects such as increased junction leakage at concentrations well below 10 ¹³ cm ^-3 .

In addition, some of the undesirable undesirable contaminants may segregate and enter the silicon. That is, at the part where silicon is in contact with the aqueous solution, the equilibrium concentration of the contaminant is higher in the silicon than in the aqueous solution. In addition, some of the undesirable contaminants have a very high diffusion coefficient, so when these impurities are introduced into any part of the silicon wafer, these contaminants tend to diffuse throughout, including the junction where leakage occurs by these contaminants. There is this.

Therefore, for all aqueous solutions used in semiconductor wafers, it is desirable that the levels of total metal ions they have are extremely low. It is preferable that the density | concentration of all the metals couple | bonded is 300 ppt (one-tenth) or less, It is preferable that it is 10 ppt or less with respect to any one metal, and it is more preferable if it is below. In addition, contamination by both anions and cations should be controlled (some of the anions may have the opposite effect, such as reducing the mobile metal atoms or ions in the silicon lattice by complex metal ions).

Front end equipment typically includes an on-site purification system for producing high purity water (denoted as deionized water, ie "DI"). However, it is more difficult to obtain process chemicals of the required purity.

Innovative Systems and Methods for Manufacturing Semiconductors by On-Site Generation of Buffered HF and / or NH ₄ F

The present invention discloses an apparatus and method for on-site production of ultrapure chemicals in a semiconductor manufacturing facility, whereby the ultrapure chemicals can be transported directly to a point of use by pipes. have. Since the device disclosed herein is a very compact unit that can be installed in the same building (or adjacent building) as the front end, transport is avoided.

It has now been found that methods and apparatus similar to those used for the production of ultrapure aqueous ammonia can be used to prepare ultrapure hydrofluoric acid.

Anhydrous HF is usually prepared by adding sulfuric acid to fluorspar CaF2. Unfortunately, many fluorspars contain arsenic, which causes contamination to the resulting HF. Thus, arsenic contamination is a major problem for HF purification. One source (from China) contains a minimum of arsenic (As) and is the best raw material for ultra-high purity HF. HF prepared from this raw material can be purchased from Allied Chemical, USA. In conventional systems, other impurities are caused by the HF generation and delivery device. These impurities are due to the deterioration of the devices, which are designed for much less stringent uses than in the semiconductor industry. These contaminants must be removed to achieve good semiconductor performance.

<HF purification and vaporization>

The HF treatment process stream includes arsenic removal and evaporation processes in batch processes, fractional distillation tubes to remove most other impurities, ion purifier tubes to suppress contaminants not removed by the fractional distillation tubes, and HF or NH4F feeder (HFS or NH4FS) is included.

Arsenic is converted to +5 state by addition of an oxidant [KMnO ₄ or (NH ₄ ) ₂ S ₂ O ₈ ] and a cation source such as KHF ₂ to form salt K2AsF7 and preserved in the evaporator during distillation. This reaction is slow and will be a batch process because it must be completed and provided with sufficient time before distillation is performed. This process requires about 1 hour of contact time at nominal temperature. To complete the reaction in a continuous process, either high temperatures and pressures (not desirable for safety) or very large vessels and pipes are required. In this process, HF is introduced into a batch process evaporation vessel and treated by the oxidizer with stirring for a suitable reaction time.

HF then removes most of the metallic impurities by distillation by reflux in a fractionating distillation tube. Elements that show a significant decrease in this process

This includes.

This fractional distillation tube performs a number of simple distillations in series. This can be realized by filling the distillation tube with a high surface area material together with the liquid flowing back, resulting in a complete equilibrium between the descending liquid and the rising vapor. Only a partial condenser is installed in the fractionation column to generate reflux, and purified gaseous HF is introduced into the HF ion purifier (HF IP). HF in this process is pure by standard criteria, except that carry over of arsenic treatment chemicals can occur, or quenching is required to remove these chemicals.

HF IP is used as an additional purity assurance measure before introducing HF gas into the feeder device. These elements are present in the treatment solution or introduced into the IP to absorb the sulfate delivered to the HF stream. For the following elements, a significant decrease in contamination of the HF gas stream occurred by the IP test.

Many of these elements are useful for the suppression of arsenic (As) contamination. Any carry-over in the fractionating distillation tube caused by the excess of these elements in the arsenic (As) treatment can be rectified in this process.

Note that batches of arsenic removal can be omitted if arsenic is sufficiently low in HF. In 1995, such raw materials were marketed by Allied Chemical, USA.

On-Site Preparation of Ultrapure Buffered HF and NH ₄ F

As mentioned above, hydrofluoric acid (HF) is a very important chemical treatment agent in semiconductor manufacturing processes, which is often used in buffered form to reduce the variation in pH when the acidic solution is charged by etching byproducts (HF Fluorosilic acid is produced by the reaction of with silicon, which strong acid changes the pH of the solution to change the etch rate). For this reason, it is well known to buffer acids, but the requirement for buffering in high purity chemicals presents another problem. This is because the buffer is also a source of contamination and must be pure enough to not degrade the device.

For buffered hydrofluoric acid (buffered HF), the buffer of acidic solution is provided by the ammonium component. According to an embodiment of the disclosed invention, buffered hydrofluoric acid can be prepared by bubbling ammonia and providing it in an acidic urine.

This process includes both buffered HF and ammonium fluoride, the only difference in the process being the molar ratio of NH ₃ and HF. The NH4F solution has a molar ratio of 1.00, while the HF is excess in the molar ratio in buffered HF.

The same equipment is used for both solutions, except setting the target value for concentration measurement to achieve the desired molar ratio.

The disclosed invention is described with reference to the drawings. The drawings show important embodiments of the invention and are incorporated herein by reference.

1 is an engineering flow diagram illustrating an embodiment of a ultrapure ammonia production unit.

2 is a block diagram of a semiconductor manufacturing line to which the generator of FIG. 4 may be coupled.

3A is a schematic diagram of a process flow in a production unit that introduces ultrapure ammonia into hydrofluoric acid to produce buffered HF.

3B1 through 3B3 show a detailed P & ID for the embodiment of the process flow of FIG. 3A.

4 illustrates an on-site HF purifier according to an embodiment of the disclosed subject matter.

A plurality of features relating to the invention of the present application will be described (by way of example and not by way of limitation) with reference to the preferred embodiment at this time.

<Purification of NH ₃ >

According to the invention, ammonia vapor is first extracted from the vapor space in the liquid ammonia feed reservoir. Steam extraction in this manner serves as a group of distillations, leaving any solid and high boiling impurities in the liquid state. The supply reservoir may be a conventional feed tank or other reservoir suitable for accommodating ammonia, which may be in the form of anhydride or in the form of an aqueous solution. The reservoir may be maintained at atmospheric pressure or, if necessary, at a pressure above atmospheric pressure to increase the flow of ammonia through the device. The reservoir is preferably thermally controlled so that the temperature is in the range of about 10 ° C. to about 50 ° C., preferably in the range of about 15 ° C. to about 35 ° C., more preferably in the range of about 20 ° C. to about 25 ° C. have.

Impurities removed by extraction of ammonia from the vapor phase include the Group I and Group II metals of the periodic table, as well as the aminated forms of these metals formed by contact with ammonia. The material to be removed includes not only oxides and carbonates of these metals, but also hydrides such as beryllium hydride and magnesium hydride, group III elements and their oxides, as well as ammonium adducts of hydrides and halides and transitions of these elements. Metal hydrides and halogenated carbons such as heavy hydrocarbons and pump oils.

Ammonia extracted from the reservoir is passed through a filtration unit to remove any solids entrained in the vapor. Microfiltration filters, ultrafiltration filters and membranes are commercially available and available. The grade and type of filter is selected as required. In the present preferred embodiment, a continuous 0.1 micron filter followed by a gross filter is used in front of the ion purifier, and no filtration occurs after the ion purifier.

The filtered steam is passed through a scrubber where the steam is washed with high-pH purified water (preferably deionized water). The high-pH water is preferably an aqueous ammonia solution and the concentration of the aqueous ammonia solution is raised until it is saturated by recycle through the scrubber. The scrubber can be easily operated as a conventional scrubber tube of a counter flow method. The operating temperature is not so critical, but the tube is preferably operated in a temperature range of about 10 ° C to about 50 ° C, more preferably in a temperature range of about 15 ° C to about 35 ° C. Similarly, although the operating pressure is not critical, it is preferred to operate at pressures on the order of about atmospheric pressure to about 30 psi or more above atmospheric pressure. Typically, the tube includes a conventional tube fill to provide a high degree of contact between the liquid and the gas, or preferably a mist eliminator.

In a preferred embodiment of the present invention, the tube realizes a fill volume of 0.84 cubic feet (24 L) with a fill height of about 3 feet (0.9 m) and an inner diameter of about 7 inches (18 cm), and is about 0.3 inches of water. Operating at a pressure drop (0.075 kPa) and a floodplain less than 10%, with a nominal about 2.5 gallons / minute (0.16 liters / second) or gallons / minute (0.32 liters / second) at 20% floodplain It has a gas inlet under the fill and a liquid inlet above the fill but below the defoamer. Preferred filling materials for the tubes described herein are those having a nominal size of 1/8 or less in diameter. The defogging part of the tube has similar or denser packings and is otherwise conventional in structure. The description and dimensions in this paragraph are to be understood as illustrative only and each parameter of the device may be changed.

Normal operation is initiated by first saturating deionized water with ammonia to form a solution used as starting detergent. While the scrubber is running, it periodically drains a small amount of liquid in the sump of the tube to remove accumulated impurities.

Impurities removed by the scrubber include reactive volatiles such as silane (SiH ₄ ) and arsine (AsH ₃ ); Halides and hydroxides of phosphorus, arsenic, antimony; Halides of common transition metals; And halides and hydroxides of Group III and Group IV metals.

The units described so far can be operated in a batch or continuous or semi-continuous manner, with continuous or semi-continuous operation being preferred. The volume throughput of the ammonia purification system is not a threshold and can vary significantly. However, in most of the operations in which the present invention is used, the flow rate of ammonia through the apparatus will be in the range of about 200 cc / h to several thousand l / h.

In some cases, the ammonia from the scrubber may be further purified before use depending on the particular type of manufacturing process in which the ammonia is purified. For example, when ammonia is used in chemical vapor deposition, it is preferable to include a dehydration unit and a distillation unit in the apparatus. Fractional distillation tubes can also be operated in a batch or continuous or semi-continuous manner. In a batch operation, a typical operating pressure can be 300 pounds per square inch (2.068 kPa) when the batch size is 100 pounds (45.4 kg). The distillation tube in this example is 8 inches (20 cm) in diameter, 72 inches (183 cm) in height, operates on a 30% floodplain, and has a vapor velocity of 0.00221 feet / second (0.00067 m / s). Theoretically, the plate is 1.5 inches (3.8 cm) tall with 48 plates. In this example, the boiler is about 18 inches (57.7 cm) in diameter, 27 inches (68.6 cm) in length, has a reflux rate of 0.5, and the recirculating coolant flows into 60 ° F (15.6 ° C.) at 90 °. It flows out at F (32.2 degreeC). Once again, this is just an example. Fractional distillation tubes can vary greatly in structure and operating parameters can be used.

Depending on the application, with or without a distillation process, purified ammonia can be used as purified gas or aqueous solution, in which case the purified ammonia is dissolved in purified water (preferably deionized water). The mixing ratio and the mixing means are the same as before.

A flow chart showing one embodiment of the ammonia purification unit according to the invention is shown in FIG. 1. Liquid ammonia is stored in the reservoir 11. Ammonia vapor 12 is extracted from the gas space in the reservoir, passes through a shutoff valve 13 and then passes through a filter 14. The filtered ammonia vapor 15 is sent to a cleaning distillation tube 17 including its filling section 18 and defogging pad 19 after its flow is controlled by a pressure regulator 16. When the ammonia vapor flows in the upward direction, the saturated ammonia water 20 flows in the downward direction, the liquid is circulated by the circulation pump 21, and the liquid level is controlled by the control sensor 22. Waste 23 is periodically discharged from the liquid remaining at the bottom of the scrubber. Deionized water 24 is supplied to scrubber 17 under a high pressure maintained by pump 25. The washed ammonia 26 is sent to one of three routes. These three routes are as follows:

1) A fractionation distillation tube 27 in which ammonia is further purified. Distilled ammonia 28 is sent to the point of use.

2) A dissolution unit 29 that combines ammonia with deionized water 30 to form an aqueous solution 31 that is sent to the point of use. In the case of a plant operation with a plurality of points of use, the aqueous solution can be collected in the tank sent, and ammonia is taken out of the tank and sent to each line to the destination of the points of use of the same plant.

3) a transport line 32 which carries gaseous ammonia to the point of use,

The second and third routes, which do not utilize fractional distillation tube 27, are suitable for producing ammonia with any metallic impurities of 100 ppt (parts per trillion) or less. However, it is preferable to include the fractionation distillation pipe 27 as a special use. An example is the use of ammonia in a furnace or chemical vapor deposition (CVD). For example, when ammonia is used in CVD, the fractionating distillation tube removes non-condensable materials that may interfere with CVD, such as oxygen and nitrogen. In addition, since the ammonia emitted from the scrubber 17 is saturated with water, it is possible to selectively include a dehydration unit between the scrubber 17 and the distillation tube 27 in the apparatus according to the characteristics and efficiency of the distillation tube.

In the above methods, the flow generated is gaseous ammonia or an aqueous solution, which is divided into two or more branch streams, each being sent to a different place of use, so that the purified ammonia from the purification unit is simultaneously applied to a plurality of places of use. Can be supplied.

<Purification of HF>

4 shows an on-site HF purifier according to an embodiment of the present invention disclosed.

HF purification is performed by first oxidizing arsenic to an oxidation state of ⁺⁵ , rectifying and removing As ⁺⁵ and metallic impurities. See US Pat. No. 4,929,435, which is incorporated herein by reference. As disclosed in the literature, various oxidants have been used for this purpose. See, for example, the following patents and patent applications cited herein by reference. US Patent No. 3,685,370; Canadian Patent No. 81-177347s; European Patent No. 351,107; Japanese Patent No. 61-151,002; Canadian Patent No. 74-101216; Canadian Patent No. 78-23343; US Patent No. 5,047,226; Soviet Patent No. 379,533; Canadian Patent No. 81-177348t; US Patent No. 4,954,330; US Patent No. 4,955,430; European Patent No. 276,542; US Patent No. 4,083,441; And Canadian Patent 98-P200672f.

Other publications have shown that fluorine (F ₂ ) acts and is now considered to be the preferred embodiment. F2 requires expensive piping work and safety devices, but is disclosed as feasible.

In a second preferred embodiment ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ), which is readily available in ultra high purity, is used.

Usually, an oxidizing agent in which a metal atom is not injected is preferable, and there are other H ₂ O ₂ and 0 ₃ .

The next preferred oxidizing agent is Caro acid (persulfuric acid, H ₂ SO ₅ : generates H ₂ O ₂ in solution). Another is ClO ₂ , but it has the serious disadvantage of being explosive. Others include HNO ₃ and Cl ₂ , but they inject the anions that must all be separated. (Reduction of nonmetallic anions is not as important as reduction of metal cations, but it is desirable to obtain anion levels of 1 ppb or less. Thus, the introduction of anions initially increases the load in the ion purification process.)

Allied Signal, co-working with the inventors, demonstrated the successful manufacture of ultra-pure HF using an initial As oxidation process at a plant in Geismar La. The inventors did not know all the steps of this process, but the allied's success in this regard further confirmed the feasibility of the disclosed invention.

KMnO ₄ is a representative oxidant and it is expected that if the disclosed ion purification and HF stripping process is continued after the supertablet, it is likely to be used in the supertablet. However, metal-free oxidants are preferred because this reagent imposes a substantial burden on the cation on the purifier.

In other embodiments, high purity 49% HF, which is essentially free of arsenic, may be used. These low arsenic materials are expected to be available from Allide in the third quarter of 1995, and are used in combination with on-site ion purification processes that do not contain arsenic oxidation reagents, resulting in ultrapure HF. Can be produced as

The HF treatment process includes an arsenic removal and evaporation process of the batch process, a rectifier tube to remove most other impurities, an ion purifier column to suppress contaminants not removed by the rectifier tube, and an HF feeder (HFS). do.

Oxidant (KMnO ₄ or _{(NH 4) 2 S 2 O} 8) and held in the evaporator during the conversion of arsenic in the +5 state and distilled By K ₂ by the addition of a cation source such as AsF ₇ form a salt K ₂ AsF ₇ Let's do it. This reaction will be slow and a batch process will have to be allowed to complete before allowing distillation to take place. This process requires about 1 hour of contact time at nominal temperature. To obtain a complete reaction in a continuous process requires high temperature and high pressure (not desirable for safety) or very large vessel and pipe connections. In this process, HF is introduced into the evaporation vessel of the batch process and treated with oxidants with stirring for a suitable reaction time.

HF is then distilled by reflux in the rectifier tube, as a result of which most metallic impurities are removed. Remarkably decreasing elements in this process are as follows.

This fractional distillation tube performs a number of simple distillations in series. This can be realized by filling the distillation tube with a high surface area material together with the liquid flowing back, resulting in a complete equilibrium between the descending liquid and the rising vapor. Only a partial condenser is installed in the fractionation column to generate reflux, and purified gaseous HF is introduced into the HF ion purifier (HF IP). HF in this process is pure by standard criteria, except that carry over of arsenic treatment chemicals can occur, or quenching is required to remove these chemicals.

HF IP is used as an additional purity assurance measure before introducing HF gas into the feeder device. These elements are present in the treatment solution or introduced into the IP to absorb the sulfate delivered to the HF stream. For the following elements, a significant decrease in contamination of the HF gas stream occurred by the IP test.

Many of these elements are useful for the suppression of arsenic (As) contamination. Any carry-over in the fractionating distillation tubes caused by the excess of these elements in the arsenic (As) treatment can be rectified in this process.

The concentration control loop can be variously modified (such as using conductivity or the like instead of sonic speed) if necessary.

In another embodiment of the disclosed invention, arsenic reduced high purity hydrofluoric acid may be used in an onsite purifier as a bulk starting material. In this embodiment no oxidation process is required.

Generation of buffered HF

FIG. 3A shows an overview of the process flow in a generating unit where ultra-purity ammonia is introduced into hydrofluoric acid to produce buffered HF, and FIGS. 3B1 through 3B3 detail the P & ID diagram of an embodiment implementing the process flow of FIG. 3A. It is shown.

In a preferred embodiment of the present invention, the liquid volume of the ammonia purifier is 10 l and the maximum gas flow rate is about 10 standard l / min. The cleaning liquid is sufficiently purified continuously or increasing to sufficiently reverse at least once every 24 hours.

The concentration of the product (in both production processes) was measured using a sound velocity measurement instrument (manufactured by Mesa Labs) for concentration measurement, but may optionally be measured using conductivity, density, refractive index or IR spectroscopy.

In another embodiment of the disclosed invention, the on-site purifier may use arsenic reduced high purity hydrofluoric acid as a bulk starting material. In this embodiment no oxidation process is required.

To set up the process, the total concentration of HF and NH ₃ dissolved in water must be determined. For example, 40 wt% ammonia, fluoride solution in 1 kg contains 400 g of NH ₄ F and 600 g of ultrapure water. Since the molar ratio of HF and NH ₃ to pure NH ₄ F is 1: 1, 400 g of NH ₄ F contains 216 g of anhydrous HF and 184 g of anhydrous NH ₃ (molecular weight of NH4F = 237, molecular weight of HF = 20 , Molecular weight of NH ₃ = 17).

Upon completion of the HF production cycle, 216 g of HF is dissolved in 600 g of water or 26.5 wt%. On-board equipment is set to add HF to these concentrations. In addition, 49% HF can be diluted at this concentration.

After forming 26.5% HF solution, 189 g of NH 3 is added to form 40% NH ₄ F solution.

By adjusting the concentration measurement, different concentrations and molar ratios can be set by concentration measurement for different uses.

<Wafer cleaning>

Several cleaning stations in a conventional semiconductor manufacturing line are shown in FIG. The first unit in the cleaning line is a resist removal station 41 where the resist is removed by combining hydrogen peroxide 42 and sulfuric acid 43 to the semiconductor surface. The rinse station 44 is continued here, and deionized water is added here to rinse off the removal solution. Downstream of the rinsing station 44 is a washing station 45, where an aqueous ammonia solution and hydrogen peroxide are added. This solution is supplied from one of two ways. First, an aqueous ammonia solution 31 is mixed with hydrogen peroxide solution 46 and the resulting mixture 47 is fed to the washing station 45. Second, pure gaseous ammonia 32 is bubbled in a hydrogen peroxide solution 48 to produce a similar mixture 49, which is likewise fed to the washing station 45. Once cleaned with the ammonia / hydrogen peroxide mixture, the semiconductor is sent to a second rinse station 50, where deionized water is added to remove the cleaning solution. The next station is another cleaning station 54, where the aqueous solution of hydrochloric acid 55 and hydrogen peroxide 56 is mixed and applied again to the semiconductor surface. The last rinse station 57 is continued to this station, where deionized water is added to remove HCl and H ₂ O ₂ . In the deglaze station 59, diluted buffered HF is applied to the wafer (to remove the native oxide or other oxide). Diluted buffered hydrofluoric acid is fed directly from the generator 70 through a sealed pipe. As described above, anhydrous HF is stored in the reservoir 72 from which a gaseous HF stream is supplied to the generator 70 via an ion purifier 71. Preferably, gaseous ammonia is bubbled in the generator 70 to produce a buffer solution, and ultrapure deionized water is added to realize the desired dilution. It is then rinsed with ultrapure deionized water (station 60) and dried in station 58. The wafer or wafer batch 61 is supported on the wafer support 52 and carried by the robot 63 or other conventional sequential processing means from one workstation to the next. The transport means can be all fully automatic, partially automatic or fully non-automatic transport means.

The apparatus shown in FIG. 2 is only one example of a cleaning line for semiconductor manufacturing. In general, cleaning lines for high precision manufacturing can be drastically changed from those shown in FIG. 2 by removing or adding one or more units of the units shown, or replacing units not shown. However, the concept of making high purity ammonia in situ according to the invention can be applied to all such systems.

In workstations such as cleaning station 45 shown in FIG. 2, the use of ammonia and hydrogen peroxide as semiconductor cleaners is well known in the art. The ratio is changed, but in a nominal apparatus, deionized water, 29% by weight of ammonium hydroxide and 30% by weight of hydrogen peroxide are mixed in a volume ratio of 6: 1: 1. This detergent is used to remove organic residues and together with ultrasonic stirring at a frequency of about 1 MHz to remove particles in the range up to submicron size.

In one type of embodiment, by placing a purification (or purification and generation) device near the point of use of the ultrapure reagent in the production line, the distance between the purification unit and the production line is shortened. In addition, for plants with multiple points of use, ultrapure chemicals from the purification (purification and development) unit pass through an intermediate storage tank before reaching the point of use. And it can be supplied from the said storage tank by a separate outlet line at each use point. Thus, in either case, potential sources of contamination that normally arise when manufacturing and preparing a medicament without packaging or transporting, or excluding storage except in-line small reservoirs, i.e., for use outside the manufacturing facility. Ultrapure chemicals can be added directly to the semiconductor substrate without contact with the substrate. In this kind of embodiment, the distance between the point at which the ultrapure chemical exits the purification apparatus and the point at which the ultrapure chemical is used in the production line is generally several meters or less. If the purification apparatus is a plant-scale central system that is piped to two or more use stations, this distance may be longer and may be 2000 feet or more. The movement can be done through an ultra-pure transfer line made of a material that does not cause contamination. For most applications, polymers such as stainless steel or high density polyethylene or fluorinated polymers can be used well.

Since the purification unit is in close proximity to the manufacturing line, the water used in the unit can be purified according to semiconductor manufacturing standards. These standards are commonly used in the semiconductor industry and are well known among those skilled in the art or skilled in the practice and standards in this industry. Purification of water according to these standards includes ion exchange and reverse osmosis. Ion exchange methods typically include most or all of the following units; Chemical processors such as chlorine treatment to kill organisms; Sand filter for particle removal; Activated carbon filters for removing traces of chlorine and organic matter; Diatomaceous earth filter; Anion exchanger for removing strongly ionized acids; A hybrid grinding machine comprising all of the cation and anion exchange resin to remove additional ions; Sterilizers including chlorination or ultraviolet light; Filter through a filter of 0.45 microns or less. Reverse osmosis involves passing water under pressure through a selective permeable membrane through which many dissolved or suspended substances are not passed, instead of one or more units in the ion exchange process. Conventional standards for the purity of water produced from this process include resistivities of at least about 15 Mcm-cm (typically 18 Mcm-cm at 25 ° C), up to about 25 ppb of electrolyte, and about 150 / cm3 or less Fine particle content, particle size of 0.2 micron or less, microbial content of about 10 / cm 3 or less, and total organic carbon of 100 ppb or less.

In the method and apparatus of the present invention, it is possible to perform a high degree of control over the concentration of the product and the resulting flow rate by precisely monitoring and measuring using known instruments and measurements. A convenient means of performing this control is sound speed detection. Other methods will already be known to those skilled in the art. If necessary, it can be implemented by various modifications to the concentration control green (using conductivity or the like instead of sound speed).

<Modification and application example>

As will be appreciated by those skilled in the art, the concept of the invention described in this application can be modified and modified for a fairly wide range of uses, and the scope of the patented subject matter is thus limited by the teaching of any given embodiment. It doesn't work.

For example, the disclosed inventive techniques are not strictly limited to the manufacture of integrated circuits, but may also be applied to the manufacture of discrete semiconductor devices such as optoelectronic devices and power devices.

In other embodiments, the disclosed invention may be applied to other fabrication techniques to which integrated circuit fabrication methods such as thin film magnetic heads and active matrix liquid crystal displays are applied, but are primarily applied in fabrication of integrated circuits, and the disclosed techniques may be applied to other applications. It is secondary to apply.

In other embodiments, it is not necessary to use a scrubber to effect liquid vapor contact. That is, it is not so preferable because of the low efficiency of gas / liquid contact, but a bubbler may be used instead of the scrubber.

Optionally, other filtration or filtration processes can be combined with the disclosed purification apparatus.

Although not carried out in the preferred embodiment of the present invention, it should be noted that additives may be added to the purified water if necessary.

As mentioned above, the main embodiment is an on-site purification apparatus. Optionally, in alternative embodiments, the disclosed purification apparatus may be adapted to operate as part of a manufacturing unit for producing ultra high purity drugs for transportation. However, this alternative embodiment does not provide the benefits of the on-site purification described above. In this application, as stated above, there is an inherent risk in delivering ultra-high purity drugs, but the disclosed invention can be achieved by at least another technique for the desired customer (with accompanying delivery) of the packaged drug. It provides a way to achieve an initial purity higher than that at which it is. In other words, for this use, a drying process can be used after ion purification.

As mentioned above, the main embodiments relate to providing ultrapure water chemicals which are most important in semiconductor manufacturing. However, embodiments of the disclosed apparatus and method may be used to supply a purified gas stream (in many cases a dryer is used downstream of the refiner, but is useful in this case).

Note that in-line or pressure reservoirs may be included in the pipe connection that delivers ultrapure chemicals to the semiconductor front end. Thus, the expression "direct" pipe connection in the claims does not preclude the use of such a reservoir, but excludes exposure to an uncontrolled atmosphere.

Claims (5)

In an on-site subsystem, in a manufacturing facility for a semiconductor device, an ultra-high purity buffered ammonium fluoride or hydrofluoric acid is provided to a semiconductor manufacturing operation. A first evaporation source connected to receive the HF source and provide a flow of HF vapor; A second evaporation source connected to receive the ammonia liquid source and provide a flow of ammonia vapor; The flow of HF vapor is connected to a first ion purification unit that is in contact with the flow of HF vapor to provide recirculating high purity water containing high concentration HF, the first ion purification unit passing through purified HF gas. To; The stream of ammonia vapor is connected in contact with the stream of ammonia vapor to pass through a second ion purification unit that provides recirculating high purity water containing high concentration ammonium hydroxide, the second ion purification unit passing the purified ammonia gas. Pass through; The HF gas is received from the first ion purification unit, and the HF gas is coupled to combine with high purity acidic deionized water to produce ultrapure hydrofluoric acid, and also the top of the non-pure HF gas contaminated with light impurities A first generating unit for passing the stream; The flow of ultrapure hydrofluoric acid and the ammonia vapor are connected through a second generator to mix the ammonia vapor with the ultrapure hydrofluoric acid to produce a controlled concentration of ultrapure buffered hydrofluoric acid; An on-site subsystem, said pipe connection directing said aqueous solution to a point of use in a semiconductor device manufacturing facility. The on-site subsystem of claim 1, wherein the HF source consists of anhydrous HF. The on-site subsystem of claim 1, wherein the high purity water to be recycled contains no additives. The on-site subsystem of claim 1, wherein the HF source is essentially free of arsenic. The on-site subsystem of claim 1, wherein the HF source uses ultra-pure aqueous HF that does not contain arsenic.

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