TW201934474A - Methods for the purification of diborane - Google Patents

Abstract

A method for separating higher boranes from a mixture containing diborane, higher boranes and a balance gas is disclosed. The higher boranes are typically tetraborane, pentaborane and decaborane. In one embodiment, the diborane is separated using at least one cold trap. Alternatively, the higher boranes are separated by a liquid filtration unit before forming a gaseous diborane mixture. In another embodiment, the higher boranes are separated from the mixture by a distillation column.

Description

Method for purifying diborane

An important gas source for the p-type dopant boron in the diborane-based silicon and silicon-germanium semiconductor crystal layers is applied by an in-situ doping epitaxial process or a plasma / ion implantation process. Diborane is also used to make doped silicon dielectrics (borosilicate glass). Another application of diborane is as a reducing agent in tungsten atomic layer deposition (ALD).

However, at room temperature, diborane will slowly decompose into higher borane (BxHy, where x> 2 and y> 6) and hydrogen. Typical higher borane-based butorane B ₄ H ₁₀ , pentane B ₅ H ₉ and decorane B ₁₀ H _14. These can be achieved by GC-based methods (such as GC-MS and GC-DID) and FTIR Analysis technology for detection. Due to the instability of diborane (B ₂ H ₆ ), the content of higher borane can increase continuously if it is not controlled during transportation, storage and use in high pressure gas or gas mixture, specifically in cylinder products. The higher the diborane concentration in the gas mixture (eg 30%), the higher the cylinder pressure and the non-hydrogen equilibrium gases (eg argon and nitrogen), the worse the decomposition problem becomes. Higher boranes can be detrimental to semiconductor manufacturing processes. In-situ doping of leading edge PMOS FinFET transistors embedded in silicon-germanium (eSiGe) source and drain deposition, advanced borane molecules can be incorporated into the eSiGe layer and cause crystal defects.

Transporting a mixture of pure B ₂ H ₆ and diborane while constant cooling can be a solution to extend the shelf life of the product. However, it can be difficult to meet international transportation requirements and local storage requirements and conditions.

Producing B ₂ H ₆ at the point of use can be another solution to use the product before the higher borane impurity content increases. However, in current synthesis methods using boron halide and metal halide reactants, it is difficult or inefficient to produce high purity B ₂ H ₆ .

The industry still needs to purify diborane and its mixtures by removing advanced borane to provide local semiconductor customers with fresh and high-purity diborane products.

In the present invention, a purification method suitable for purifying diborane and its mixture gas locally or in situ is proposed. Thereby, the problem is minimized. Local purification of customer groups close to the same country or region. The purification location can be a regional ESG production plant or, if necessary, at the customer site or usually a diborane mixture supply system or subsystem.

The purification method of the present invention is disclosed in three different examples. The first is a cold trap for a gas phase diborane mixture. The second embodiment uses liquid filtration technology to promote liquid phase diborane and hydrogen separation and higher borane removal. The third embodiment uses low temperature distillation of gas / liquid phase.

Therefore, the three embodiments can be summarized as follows. The first embodiment is a method for removing higher borane impurities from a mixture containing higher borane, diborane, and an equilibrium gas (such as hydrogen), which comprises feeding the gas mixture to a cold trap by the method described herein, but Maintain the blending ratio of diborane to the equilibrium gas.

The second embodiment is a method for removing higher borane from a mixture containing higher borane, diborane, and equilibrium gas, which comprises feeding the mixture to a diborane liquefaction unit followed by a liquid filtration unit by the method described herein. The purified liquid diborane produced in the separation process can be used for subsequent blending with the equilibrium gas.

The third embodiment is a method for removing higher borane from a mixture containing higher borane, diborane, and equilibrium gas, which comprises feeding the mixture to a distillation column by the method described herein.

In a first embodiment, a method for removing higher borane from a mixture containing diborane, higher borane, and equilibrium gas is disclosed, which comprises the following steps: feeding the gas mixture to at least one cold trap, wherein the higher borane is solidified On the wall of the cold trap; recovering the diborane and equilibrium gas mixture without substantially liquefying diborane, thereby maintaining the ratio of diborane to the equilibrium gas; after recovering the diborane and equilibrium gas, the regeneration gas is fed into To the at least one cold trap, thereby regenerating the at least one cold trap; and discharging higher borane and regeneration gas as waste.

In a second embodiment, a method for removing higher borane from a mixture containing diborane, higher borane, and equilibrium gas is disclosed, which includes the following steps: feeding the gas mixture to a cold trap liquid separator so that most of the Diborane and higher borane condensate; remove the equilibrium gas from the cold trap liquid separator; filter the liquid in the cold trap to remove the higher borane in the form of solid (ice) particles; recover and purify the second Borane liquid; feeding the recovered purified diborane liquid to a heat exchanger, wherein the purified liquid diborane forms a purified gaseous diborane; and selected from the group consisting of hydrogen, argon, and nitrogen The equilibrium gas is blended with the purified gas diborane, thereby forming a gaseous mixture having the purified gaseous diborane.

In another embodiment, a method for removing higher borane from a mixture containing diborane, higher borane, and equilibrium gas is disclosed, which comprises the following steps: feeding the mixture to a distillation column, wherein the purification is recovered from the top of the distillation column A gaseous mixture of diborane and hydrogen, and the liquid waste containing diborane and most of the higher-borane liquid wastes as waste is discarded from the bottom of the distillation column; the recovered gaseous mixture is fed to a cold trap, where the Purifying the liquid diborane; feeding the purified liquid diborane to a heat exchanger, thereby forming a gaseous diborane; and recovering the gaseous diborane from the heat exchanger to further blend with the equilibrium gas.

In the first embodiment, the diborane gas mixture will maintain the initial mixing ratio while limited removal of the higher borane. This method will be effective for low-concentration diborane mixtures (eg, 1% to 5% diborane in hydrogen). This method would be suitable, for example, at a customer site diborane mixture supply system or subsystem.

Advantages of the first embodiment include maintaining above the diborane condensation temperature, thereby maintaining the initial diborane mixing ratio with the equilibrium gas. Lower temperatures will be better when the higher borane is condensed, while still producing a higher borane impurity B ₄ H ₁₀ mixture of diborane up to ten parts per million of the gas mixture.

In a second embodiment, liquid phase diborane is produced. This mixture will have a higher higher borane concentration than that achieved in the first embodiment. This method can be used to produce a mixture with a selected equilibrium gas (such as hydrogen, argon or nitrogen) and can be produced on-site with respect to the end-user's premises.

The second embodiment provides advantages such as low temperature, and diborane is liquefied while the hydrogen gas remains in the gas phase. Purified diborane can be maintained for future mixing with an appropriate equilibrium gas or remixing with a pure hydrogen stream. Freezer temperature can be as low as -135 ° C. When using low-temperature gas as a coolant, a lower temperature can also be applied before diborane reaches its triple point of -164.9 ° C.

The third example uses cryogenic distillation to purify the diborane feed stream mixture. This example may depend on the desired results and operating conditions from either a higher purity diborane produced by the feed stream mixture or a slightly reduced purity diborane.

The third embodiment also provides the removal of higher borane with smaller diborane liquid flow. The recovered diborane liquid can be collected in a cold trap for future mixing with the selected equilibrium gas. B ₄ H ₁₀ pollutant levels of 10 theoretical levels can still be reached and still reach as low as 1 part per billion.

Both the second and third embodiments can use a full range of diborane mixtures and are not limited to lower diborane mixture ratios as used in the first embodiment. Although both embodiments can be used in a regional purification plant or a customer site, they are most efficient when used in a supplier's regional purification plant.

In all such embodiments, analytical equipment may be incorporated to measure the higher borane concentration of the purified gas stream. Analytical methods are commonly used for FTIR of higher borane and GC-based methods (such as GC-MS and GC-DID). The measurement for adjusting the mixing ratio can also be performed using a binary gas analyzer.

The higher borane can be selected from the group consisting of butane, pentane and decane.

For the method of the first embodiment, the diborane in the mixture will generally be less than 5% by mole or volume, and usually 1 or 2% and less by mole or volume. In the second and third embodiments, there is no limitation on the diborane concentration.

For a 100% diborane feed, according to supplier information, B ₄ H ₁₀ is typically present at about two hundred parts per million. The different feed mixtures will have B ₄ H ₁₀ concentrations which are diluted by the equilibrium gas Mohr fraction. However, thermal decomposition is a kinetic process that reacts with chains that form higher order and more stable hydrogenated borane polymers. Therefore, measurable higher boranes (such as butane, pentane and decane) are reaction intermediates. Therefore, the concentration may vary from case to case. The purification targets as embodied in the present invention in Examples 1, 2 and 3 are to achieve single-digit millionth, sub-millionth, and billionth-order higher borane contents, respectively.

The purified diborane will generally be in the form of a diborane gas mixture or a pure diborane liquid.

The end user can determine the diborane concentration and select an equilibrium gas based on the pure diborane liquid. Therefore, the equilibrium gas may be selected from the group of hydrogen, nitrogen, and argon.

The concentration of higher borane in purified diborane will range from 1 ppb to 0.1 ppm.

Cross-reference to related applications

This application claims priority from US Provisional Patent Application No. 62 / 622,199, filed on January 26, 2018.

Figure 1 is a graph showing vapor pressure versus temperature for diborane and various higher boranes. The curve applies only to liquid materials. It should be noted that B ₄ H ₁₀ is a solid / vapor phase below -120.8 ° C. B ₄ H ₁₀ is the key higher borane impurity because it is the most volatile of all higher boranes. When the diborane partial pressure exceeds the vapor pressure line, the diborane will be a vapor-liquid mixture. The hydrogen remains in the gas phase.

FIG. 2 is a graph of vapor pressure / liquid phase and vapor phase / solid phase vapor pressure curves of diborane and higher borane. Yaws handbook on vapor pressure curves. Extract the heat of evaporation and add the estimated heat of fusion of the solid. Therefore, the estimated solid sublimation vapor pressure is shown in FIG. 2.

FIG. 3 is a schematic diagram 10 of a purification process using a cold trap in the first embodiment of the present invention. A full-phase diborane mixture of higher borane, diborane, and equilibrium gas is fed by a feed line 12 and divided into two lines 14 and 16. The feed is usually a lower percentage of diborane, approximately 1 to 5% mixture. This allows lower temperatures to be used to more effectively remove higher borane from the mixture. The separate feed gases are fed to the polished cold trap beds A and B via valves V1 and V2 and lines 18 and 20, respectively.

A cold trap bed is usually a structured heat exchange component, such as a tube with a flowing coolant, which has a surface that maximizes heat exchange with a thermally conductive metal material. In the gas contact space surrounding the heat exchanger components, an adsorbent material (such as zeolite or metal-organic-framework) is added to increase the advanced borane removal capability of the cold trap bed. Lines 22 and 24 extending from the bottom of each bed A and B are controlled by valves V3 and V4 to allow the purified gas mixture to be recovered by means of line 26.

Preferably in a multi-bed system, one bed is in production mode and the other bed is in regeneration mode. In this embodiment, the hydrogen regeneration gas is fed to the line 28 and the flow rate is controlled by a valve V5 or V6. When one bed is in production mode, the corresponding valve V5 or V6 is closed, and the valve V6 or V5 to the other bed is opened to allow hydrogen to flow to it via lines 30 and 34 or 32 and 36, respectively. This regeneration will remove higher borane. When the other bed has reached the predetermined limit for higher borane, the bed in which the flow is reversed and is being produced is now regenerated and the previously regenerated bed begins to produce diborane. The advantage of this cycle is that continuous or semi-continuous operation can be achieved. The regeneration process can be performed at room temperature or elevated temperature.

To maintain the initial diborane mixing ratio, diborane must be kept in a gas phase by setting a lower temperature limit without condensing. Therefore, without substantially liquefying diborane, the initial diborane gas mixture ratio is maintained. Cooler temperatures are usually preferred to allow higher borane to condense. Due to this trade-off, higher borane concentrations can be as high as 10 ppm of the purified diborane mixture gas stream. As shown in Figure 4, the target bed (trap temperature) is an estimate of the maximum percentage of diborane in the mixture. Moreover, the amount (in parts per million) of B ₄ H ₁₀ is plotted against the well temperature on the right axis. Higher trap temperatures can result in both higher amounts of diborane and higher amounts of B ₄ H ₁₀ in the feed mixture. Therefore, at -110 ° C, a 5% diborane mixture will have an upper limit of 26 ppm of B ₄ H ₁₀ in the purified mixture. For a 2% diborane mixture, the trap temperature is -123 ° C, and the B ₄ H ₁₀ concentration can be as high as 4.4 ppm. In these examples, the total pressure is 6 bara.

A second embodiment of the present invention is shown schematically in FIG. 5. In this embodiment, filtration is used to help separate a mixture of diborane, higher borane, and equilibrium gas. In this schematic diagram 40, a feed 42 of 30% diborane in hydrogen is fed to the cold trap liquid separator C. The second feed 44 (optional) of ultra-high purity hydrogen can also be fed into the cold trap liquid separator C as a purge gas. The condensed liquid is fed to the filter unit C1 through the lower part of C, which can be a SS 315L sintered metal filter or a polytetrafluoroethylene (PTFE) membrane filter. These filters will remove the higher borane solid particles 48, producing a pure diborane liquid in D.

Pure diborane liquid is then fed 50 to heat exchanger E, where it is heated to form a purified gaseous diborane gas. Circulating hydrogen can be fed 52 from the cold trap liquid separator, or another option can be to feed fresh ultrahigh purity hydrogen or argon or nitrogen 54 to heat exchanger E, all mixed with pure gaseous diborane. This mixture can be fed into a gas mixing chamber F, which can deliver diborane of express purity via line 62 according to the desired concentration of the end user. Lines 56 and 58 are the continuations of the ultra-high purity balanced gas 54 and the circulating hydrogen line 52, respectively. For higher purity operations, for example, recycled hydrogen is discarded because it can contain impurities. Fresh ultra-high purity equilibrium gas systems are preferred, such as new UHP hydrogen for heat exchange and final mixing.

A purification simulation was performed that reused recycled hydrogen from the feed. At -135 ° C and 50 psig, the most critical higher borane B ₄ H ₁₀ is about 1 ppm or less. If a new ultra-high purity make-up gas is used for mixing, the impurity content should be at least 10 times lower than the estimated value of B ₄ H ₁₀ or about 0.1 ppm.

In this simulation, a borane mixture and hydrogen from a cooler were fed to a cold trap liquid separator. Hydrogen was removed from the top of the liquid separator and fed to the heater. The bottom liquid from the liquid separator is fed to a filtration unit where solid higher borane is removed from the bottom of the filtration unit. Hydrogen is also fed from the second cooler to the filter unit. Pure diborane liquid is fed from the filter unit to a heater to form a gas. Hydrogen, or fresh hydrogen feed and diborane can be fed as a gas to a gas mixer where diborane can be produced and delivered in a predetermined concentration.

Alternatively, a metal organic frame (MOF) can be used as the filter unit. MOF is used to selectively adsorb diborane molecules so that a wider operating temperature range can be achieved.

Figure 6 is a graph showing the B ₄ H ₁₀ solid vapor pressure as a function of latent heat of fusion and temperature. From this chart the cold trap performance can be estimated. For example, when recycling recycled hydrogen, at 50 psig, the performance of the freezer at -135 ° C will have a B ₄ H ₁₀ upper limit of about 1 ppm. In certain embodiments, a more pure mixture may require nitrogen instead of hydrogen.

FIG. 7 is a schematic diagram showing a third embodiment of the present invention. In this embodiment, a gas / liquid-phase low-temperature distillation method is used. By using a cryogenic distillation method, a well-defined higher temperature of the vapor / liquid phase can be used. Although distillation requires more complicated equipment, the separation of higher borane requires only about 10 theoretical plates to achieve a billion fraction content in the vapor phase of the product diborane and hydrogen mixture. Since the diborane concentration will be slightly reduced due to the removal of higher-level borane impurities, a new ultra-high-purity hydrogen stream is used to meet different dilution requirements.

The loss of diborane to liquid waste is about 1 to 10% of the amount of diborane in the feed, and is usually in the range of 2 to 5%. Suitable for ultra-high purity dilute diborane gas for customer on-site purification due to the ultra-high purity (ie, high borane content of higher borane) diborane gas mixture produced in the light product stream The feed of the mixture is the subsystem of the in situ blending system.

Alternatively, the liquefied ultra-high-purity diborane is collected in a cold trap while hydrogen is separated, and then it can be mixed with hydrogen, argon, or nitrogen to be collected as a diborane mixture.

In the schematic diagram 70 of FIG. 7, a feed of 30% diborane in hydrogen is fed 72 to a distillation column having approximately 10 stages. Liquid waste of higher borane is collected from bottom 74 of distillation column G and purified diborane and hydrogen mixture is collected from top 76 thereof. This purified diborane and hydrogen mixture is collected for end use or fed 78 to the cold liquid trap H, which produces a pure diborane liquid. Pure diborane liquid can be fed 80 to the heat exchanger and mixing unit I with or without ultra-high purity hydrogen, argon, or nitrogen 82 to produce a diborane gas mixture or pure diborane gas 84, As determined by the intended end user.

A purification simulation was performed that reused recycled hydrogen from the feed. At -90.4 ° C and 30 psig, the most critical higher borane B ₄ H ₁₀ is about one billionth of a billion in a pure vapor output gas stream. The liquid diborane can be collected from the liquid tank after being separated from the hydrogen equilibrium gas. In this simulation, the distillation column is in fluid communication with a unit for receiving advanced borane waste from the bottom of the column and directing a purified diborane and hydrogen mixture to a cold trap system, which combines hydrogen with pure diborane liquid Separate and recover gaseous hydrogen and liquid diborane.

Although the invention has been described with reference to specific embodiments thereof, it will be apparent that many other forms and modifications of the invention will be apparent to those skilled in the art. The accompanying patentable scope of the invention should generally be construed to cover all such obvious forms and modifications that fall within the true spirit and scope of the invention.

10‧‧‧ Schematic

12‧‧‧feed line

14‧‧‧line

16‧‧‧line

18‧‧‧line

20‧‧‧line

22‧‧‧line

24‧‧‧line

26‧‧‧line

28‧‧‧line

30‧‧‧line

32‧‧‧line

34‧‧‧line

36‧‧‧line

40‧‧‧ Schematic

42‧‧‧Feeding

44‧‧‧second feed

46‧‧‧line

48‧‧‧Advanced Borane Solid Particles

50‧‧‧Feed

52‧‧‧Circulating hydrogen line / feed

54‧‧‧Ultra-high purity balanced gas / feed

56‧‧‧line

58‧‧‧line

62‧‧‧line

70‧‧‧ Schematic

72‧‧‧Feed

74‧‧‧ bottom

76‧‧‧Top

78‧‧‧Feed

80‧‧‧Feed

82‧‧‧Ultra high purity hydrogen, argon or nitrogen

84‧‧‧Diborane gas mixture or pure diborane gas

A‧‧‧Polished cold trap bed / bed

B‧‧‧Polished cold trap bed / bed

C‧‧‧cold trap liquid separator / heat exchanger

C1‧‧‧filtration unit

D‧‧‧container

E‧‧‧Heat exchanger

F‧‧‧Gas mixing chamber

G‧‧‧ distillation tower

H‧‧‧ cold liquid trap

I‧‧‧Heat exchanger and mixing unit

V ₁ ‧‧‧ Valve

V ₂ ‧‧‧ Valve

V ₃ ‧‧‧ Valve

V ₄ ‧‧‧ Valve

V ₅ ‧‧‧ Valve

V ₆ ‧‧‧ Valve

Figure 1 is a graph showing the vapor pressure versus temperature of diborane and higher borane (B ₄ H ₁₀ , B ₅ H ₉ , B ₁₀ H ₁₄ ).

FIG. 2 is a graph showing estimated sublimation pressure curves of higher boranes B ₄ H ₁₀ and B ₅ H ₉ .

FIG. 3 is a schematic diagram of a polished cold trap bed for removing advanced borane in the first embodiment.

Figure 4 is a graph comparing the maximum percentage of diborane in the feed mixture to the well temperature in the first example.

5 is a schematic diagram of a purification system using filtration to remove higher borane from a diborane-containing mixture in a second embodiment.

Figure 6 is a graph of B ₄ H ₁₀ solid vapor pressure as a function of latent heat of fusion and temperature.

FIG. 7 is a schematic diagram of a gas / liquid-phase low-temperature distillation in a third embodiment according to the present invention.

Claims (29)

A method for separating higher borane from a mixture containing diborane and higher borane and an equilibrium gas, comprising the steps of feeding the mixture to at least one cold trap, wherein the higher borane is solidified in the at least one cold trap Recovering the diborane and equilibrium gas mixture without substantially liquefying the diborane; after the recovery of the diborane and the equilibrium gas, feeding the regeneration gas to the at least one cold trap, The at least one cold trap is thereby regenerated; and the higher borane and the regeneration gas are discharged as waste. The method of claim 1, wherein the at least one cold trap is two cold traps. The method of claim 1, wherein the regeneration gas system is hydrogen. The method of claim 1, wherein the concentration of the higher borane in the mixture is up to 50 parts per million in the feed and is 1 part per million or less in the purified product mixture. The method of claim 1, wherein the diborane is present in the mixture in an amount of 1% to 5%. The method of claim 1, wherein the concentration or mixing ratio of diborane remains unchanged. The method of claim 1, wherein the higher borane is selected from the group consisting of butane, pentane and decane. A method for separating higher borane from a mixture containing diborane, higher borane and equilibrium gas, comprising the following steps: feeding the gas mixture to a cold trap liquid separator so that the diborane and the higher boron Condensate; remove the equilibrium gas from the cold trap liquid separator; filter the condensed liquid in the cold trap liquid separator to remove the advanced borane in the form of solid particles; and recover from the cold trap liquid separator Purifying the diborane liquid; feeding the recovered purified diborane liquid to a heat exchanger, wherein the purified liquid diborane forms a purified gaseous diborane; and selected from the group consisting of hydrogen, argon, and nitrogen The equilibrium gas of the composed group is blended with the purified gaseous diborane, thereby forming a gaseous mixture having the purified gaseous diborane. The method of claim 8 wherein the recovered diborane is pure diborane from a diborane feed stream containing 1% to 100% diborane in the mixture. The method of claim 8, wherein the diborane is present in the mixture in an amount of about 30% by volume. The method of claim 8, wherein the hydrogen fed to the heat exchanger may be recirculated hydrogen from the cold trap liquid separator. The method of claim 8, wherein the hydrogen fed to the cold trap liquid separator is fresh ultra-high purity hydrogen. The method of claim 8 wherein the liquid mixture is advanced through a filter unit before being fed to the heat exchanger. The method of claim 8, wherein the filter unit includes a sintered metal filter or a polytetrafluoroethylene membrane filter. The method of claim 8, wherein the filtering unit is a metal organic frame. The method of claim 8 wherein the end user can determine the concentration of pure diborane recovered from the gas mixing chamber. The method of claim 8, further comprising generating liquid diborane. The method of claim 8 wherein the concentration of higher borane in the purified diborane is less than 0.1 ppm. The method of claim 18, wherein the concentration of higher borane is less than 1 ppm. A method for separating higher borane from a mixture containing diborane, higher borane and equilibrium gas, comprising the steps of feeding the mixture to a distillation column, wherein purified diborane is recovered from the top of the distillation column and A gaseous mixture of hydrogen, and the liquid waste containing diborane and most of these higher borane is discarded from the bottom of the distillation tower; the recovered gaseous mixture is fed to a cold trap, where a purified liquid diborane is formed; Feeding the purified liquid diborane to a heat exchanger, thereby forming a gaseous diborane; and recovering the gaseous diborane from the heat exchanger to further blend with the equilibrium gas. The method of claim 20, further comprising feeding to the heat exchanger a gas selected from the group consisting of hydrogen, argon, and nitrogen, wherein the gaseous diborane will interact with the gas selected from the group consisting of hydrogen, argon, and nitrogen. The group of gases is mixed. The method of claim 20, wherein the distillation column has about 5 to 50 stages. The method of claim 20, wherein the waste liquid comprises higher borane. The method of claim 20, wherein the recovered diborane is pure diborane from a diborane feed stream containing 1% to 100% diborane in the mixture. The method of claim 20, wherein the diborane is present in the mixture in an amount of about 30% by volume. The method of claim 20, wherein the purified diborane is in the form of a diborane gas mixture or a pure diborane liquid. The method of claim 20, wherein the end user can determine the diborane concentration and select an equilibrium gas based on the pure diborane liquid. The method of claim 27, wherein the equilibrium gas system is selected from the group consisting of hydrogen, nitrogen, and argon. The method of claim 20, wherein the concentration of the higher borane in the purified diborane is in the range of 1 ppb to 0.1 ppm.