WO2005080630A1

WO2005080630A1 - Semiconductor processing system and bubble trap

Info

Publication number: WO2005080630A1
Application number: PCT/IB2005/000169
Authority: WO
Inventors: Kohei Tarutani; Masao Kimura; Toshiyuki Nakagawa; Naoyuki Nakamoto
Original assignee: L'air Liquide
Priority date: 2004-01-26
Filing date: 2005-01-19
Publication date: 2005-09-01
Also published as: JP2005206911A; TW200529288A

Abstract

To provide a broadly applicable semiconductor processing system and bubble trap therefor that enable accurate control of the precursor liquid flow rate. A semiconductor processing system contains a liquid feed conduit (34) that feeds precursor liquid to a processing compartment (12) using transport by a pressurized gas. A vaporizer (22) and an MFC (24) are disposed in the liquid feed conduit (34). A bubble trap (26) is disposed in the liquid feed conduit (34) upstream from and in the vicinity of the MFC (24). The bubble trap (26) has a separator compartment (44) that separates, from the precursor liquid, bubbles of the pressurized gas originating from the pressurized gas and admixed in the precursor liquid. The bottom of the separator compartment (44) is provided with a liquid inlet (46) for introduction of the precursor liquid and a liquid outlet (48) for discharge of the precursor liquid. The top of the separator compartment (44) is provided with a gas outlet (52) that discharges the gas separated from the precursor liquid.

Description

Semiconductor processing system and bubble trap This invention relates to semiconductor processing systems and to a bubble trap that is disposed in a liquid feed conduit in the vicinity of and upstream from a mass flow controller in a semiconductor processing system. Here, semiconductor processing refers to the various

compris ng, e.g., nterconnec s, e ectro es t at connects to a semicon uctor device — substrate through the formation of, e.g.', semiconductor, dielectric, and conductor layers in desired patterns on the substrate. This substrate can be exemplified by semiconductor wafers and glass substrates for liquid crystal displays (LCD) and flat panel displays (FPD). Liquids are used in some cases during the process of fabricating semiconductor devices as precursors for semiconductor processing. It is typical in such cases for a pressurized gas, such as helium, to be fed into the precursor tank in order to transport the precursor liquid from the precursor tank to the point of use (POU). The precursor liquid is transported by the pressure of the pressurized gas from the precursor tank into the liquid feed conduit. Some of the pressurized gas may become dissolved in the precursor liquid at this point. Since the gas dissolved in the precursor liquid is an unnecessary component, it is removed by a degassing apparatus disposed in the liquid feed conduit. Figure 7 contains a schematic drawing that illustrates a prior-art precursor liquid feed section in a semiconductor processing system that uses liquid as a precursor in semiconductor processing. As shown in Figure 7, a liquid feed conduit 134 and a pressurization conduit 136 are connected to a precursor tank 132 in which precursor liquid is stored. The liquid feed conduit 134 feeds the precursor liquid from the precursor tank 132 and the pressurization conduit 136 feeds a pressurized gas, such as helium, into the precursor tank 132. A degassing apparatus 142 for removal of the gas in the precursor liquid is disposed in the liquid feed conduit 134. When the precursor liquid is highly toxic, the precursor tank 132 and degassing apparatus 142 are encompassed by a feed-side casing 138 that forms a local space. This local space within the feed-side casing 138 is connected through a detoxification section (not shown) to, for example, an exhaust duct (not shown) in the semiconductor fabrication plant, and is continuously exhausted. The degassing apparatus 142 comprises a dual-tube structure that is composed of an inner tube 144 and a gastight outer tube 146: the inner tube 144 comprises a fluororesin (for example, Teflon®) membrane capable of gas permeation while the outer tube 146 comprises a corrosion-resistant metal. The liquid precursor flows within the inner tube 144. A vacuum pump

152 is connected to the space 148 between the inner tube 144 and the outer tube 146. When the space 148 is depressurized by the vacuum pump 152, a large pressure difference is formed sandwiching the membrane that forms the inner tube 144. Due to this pressure difference, the gas in the precursor liquid flowing in the inner tube 144 is suctioned from the precursor liquid, traverses the membrane, and is discharged into the outer space 148, resulting in removal from the precursor liquid of the gas dissolved in the precursor liquid. In another structure used for degassing apparatuses, the precursor liquid flows, in contrast to the preceding, within the space 148 between the inner tube 144 and the outer tube

146 and the interior of the inner tube 144 is vacuum exhausted by the vacuum pump 152.

Degassing apparatuses of this type are disclosed, for example, in the following Patent

References 1-6. [Patent Reference 1] United States Patent Number 4,325,715

[Patent Reference 2]

United States Patent Number 4,986,837

[Patent Reference 3]

United States Patent Number 5,205,844 [Patent Reference 4]

United States Patent Number 5,425,803 [Patent Reference 5] United States Patent Number 5,772,736 [Patent Reference 6] United States Patent Number 6,474,077

During the course of their research the inventors found that problems with regard to general applicability and control of the precursor liquid flow rate, vide infra, occur in semiconductor processing systems that use a precursor liquid feed section according to the prior art as shown in Figure 7. The present invention was developed considering these problems with the prior art and takes as an object the introduction of a semiconductor processing system and bubble trap therefor that enable accurate control of the precursor liquid flow rate. Another object of this invention is to provide a very generally applicable semiconductor processing system and bubble trap therefor. A first aspect of the present invention is a system for delivering a precursor to a process compartment to process semiconductors or the like comprising : a precursor tank that holds a liquid precursor that is used in the semiconductor process; a vaporizer that produces process gas by vaporizing the liquid precursor; a liquid feed conduit that is connected to the precursor tank and that feeds the liquid precursor from the precursor tank to the vaporizer; a pressurization conduit that is connected to the precursor tank and that feeds pressurized gas from pressurized gas means into the precursor tank so as to push the liquid precursor out of the precursor tank and into the liquid feed conduit; a gas feed conduit that connects the vaporizer to the process compartment and that feeds the process gas from the vaporizer to the process compartment; a mass flow controller that is disposed in the liquid feed conduit upstream from the vaporizer; and a bubble trap that is disposed in the liquid feed conduit upstream from and in the vicinity of the mass flow controller; wherein the bubble trap has a separator compartment that separates, , bubbles of the pressurized gas from the liquid precursor which gas bubbles originate from the injection of the pressurized gas into the precursor tank and admixed in the liquid precursor wherein the separator compartment has a liquid inlet located at or near the bottom of said compartment at its bottom where the liquid precursor is introduced and a liquid outlet where the liquid precursor is discharged and has a gas outlet located at or near the top of said compartment where the gas separated from the liquid precursor is discharged. Preferably, the above system shall be used in a semiconductor processing method wherein the gaseous precursor is fed to a process compartment that holds a substrate on which a semiconductor process is executed. According to a second aspect of the present invention, the bubble trap is provided with an optical sensor that is disposed on the outside of the separator compartment and that optically detects the level of the precursor liquid; a valve that is connected to the gas outlet and that selectively opens the gas outlet; and a controller that opens and closes the valve based on the detection signal from the optical sensor. According to another aspect of the invention, there is provided an orifice that restricts the gas flow from the gas outlet and that is disposed between the gas outlet and the aforesaid valve. According to a further aspect of the invention, the optical sensor is provided with a first optical sensor and a second optical sensor, which are disposed at, respectively, the upper limit and the lower limit for the surface of the liquid precursor in the separator compartment. According still another of the invention, the bubble trap is provided with a window that is formed in the aforesaid housing and that enables optical surveillance of the liquid precursor level in the separator chamber from the outside, wherein the first and second optical sensors optically detect the liquid precursor level through this window. According to another aspect, the window referred to hereabove is provided with a first window and a second window that are disposed, respectively, in correspondence to the first and second optical sensors. The bubble trap may also be disposed in such a manner that the height of the liquid precursor level in the separator compartment forms the maximum height of the liquid precursor level from the precursor tank to the vaporizer. Preferable, the liquid feed conduit between the bubble trap and the mass flow controller has a length no greater than 50 cm. Optionally, the system according to the invention may be provided with a process-side casing that forms a local space that encloses the process compartment, vaporizer, mass flow controller, and bubble trap, wherein this local space within the process-side casing is exhausted by an exhaust system and wherein the precursor tank is disposed outside the process-side casing. The liquid precursor preferably used with the invention shall be a halogen compound or an a ine compound. The bubble trap that is disposed in a liquid feed conduit, e.g. in a semiconductor processing system, upstream from and in the vicinity of a mass flow controller, is provided with a housing that forms a separator compartment that separates, from the precursor liquid that will be fed to the mass flow controller, gas bubbles admixed in the liquid precursor, wherein the separator compartment has at its bottom a liquid inlet where the liquid precursor is introduced and a liquid outlet where the liquid precursor is discharged and has at its top a gas outlet where the gas separated from the liquid precursor is discharged; a first window and a second window that are formed in the housing in such a manner that the level of the liquid precursor within the separator compartment can be subjected to optical surveillance from the outside; a first optical sensor and a second optical sensor, that are disposed on the outside of the separator compartment at different heights at a first position and a second position and that optically detect the level of the liquid precursor through the first and second windows, respectively; a valve that is connected to the gas outlet and that selectively opens the gas outlet; and a controller that opens and closes the valve based on the detection signals from the first and second optical sensors. Also, an orifice may be provided that restricts the gas flow from the gas outlet and that is disposed between the gas outlet and the aforesaid valve is provided for the bubble trap. Preferably, the CV value of the opening of the orifice at the bubble trap according to the twelfth aspect is 1 x 10^"5 to 1 x 10^"3. The bubble trap according to invention may also be provided with a housing substantially comprising material selected from the group consisting of stainless steel, nickel, nickel alloys, tantalum, tantalum alloys, niobium, niobium alloys, titanium, and titanium alloys, and the windows of this bubble trap substantially comprise material selected from the group consisting of heat-tempered glass, quartz, and sapphire. In addition, the embodiments of this invention explore a variety of executions of this invention, and various embodiments of this invention can be derived by suitable combination of the plural number of disclosed constituent elements. For example, when an embodiment of the invention has been derived in which some constituent elements have been omitted from the overall set of constituent elements presented for the embodiments, these omitted elements can be suitably fulfilled by conventional well-known technologies in the actual working of the derived inventive embodiment. Certain aspects of the present invention enable accurate control of the liquid precursor flow rate in a semiconductor processing system, while certain aspects of the present invention also endow a semiconductor processing system and bubble trap therefor with a very general applicability. During the course of developing the present invention, the inventors carried out research into the problems associated with prior-art precursor liquid feed sections as shown in Figure 7 and as a consequence obtained the knowledge provided below. Recent years have seen the use of many different types of liquids as precursors in semiconductor processing. For example, in the past Ti and TiN films were generally formed by physical vapor deposition (PVD), typically sputtering, but PVD has great difficulty providing the high coverage required by the increasing level of device miniaturization and integration seen in the last few years. The production of Ti and TiN films has therefore been carried out in recent years by chemical vapor deposition (CVD), which can be expected to provide better quality films. Gas containing TiCI₄ (titanium tetrachloride) is used as the process gas (along with a carrier gas and/or other reaction gases) when the formation of a Ti-type film by CVD is sought. However, since TiCI is a liquid at ambient temperature, it is stored as a precursor liquid in a precursor tank. This precursor liquid is transported out of the precursor tank and into and through a liquid feed conduit to a vaporizer by means of a pressurized gas, such as helium, that is introduced into the precursor tank. Contemporary CVD processes thus frequently employ highly toxic and/or highly corrosive metal halide or organometal precursor liquids. Typical examples here are the processes that produce the high-melting metal films and metal nitride films, such as the aforementioned Ti and TiN films, that are used as interconnect and barrier layers for the interconnect structures in semiconductor devices. The precursor liquid feed section illustrated in Figure 7 suffers from a limited applicability with respect to the diversification of precursor liquids for semiconductor processing. Thus, the membrane constituting the inner tube 144 of the degassing apparatus 142 may be quite susceptible to modification by the precursor liquid depending on the particular components in the membrane and the precursor liquid. For example, fluororesin membranes exhibit a low resistance to chlorine compound-type liquids such as TiCI and Si₂CI₆ (hexachlorodisilane or HCDS). The precursor liquid feed section illustrated in Figure 7 is also associated with another problem when degassing is inadequate: unstable control of the flow rate of the precursor liquid on the processing apparatus side. Thus, when dissolved gas remains in the precursor liquid, any reduction in pressure on the precursor liquid along the liquid feed conduit will result in the formation of bubbles in the precursor liquid. This formation of bubbles in the precursor liquid interferes with flow rate control by, for example, the mass flow controller (MFC), which causes flow of the precursor liquid to become unstable. It is therefore essential in the case of the precursor liquid feed section illustrated in Figure

7 that the gas in the precursor liquid be removed to fairly low levels by the degassing apparatus 142. This makes it necessary, for example, to provide a large area of contact between the precursor liquid and the membrane forming the inner tube 144 of the degassing apparatus 142 or to provide the vacuum pump with a suitable exhaust capacity, which in turn creates the problems of a large size for the degassing apparatus 142 or high costs. Embodiments of the present invention, which was framed based on the aforementioned knowledge, are described hereinbelow with reference to the drawings. In the description that follows, constituent elements that have about the same structure and function have been assigned the same reference symbol and will not be described more than once unless necessary. Figure 1 contains a schematic drawing of a semiconductor processing system that comprises an embodiment of the present invention. This semiconductor processing system contains a semiconductor processing apparatus 10 that employs CVD to form TiN film on a substrate, such as a semiconductor wafer or a glass substrate for LCD or FPD applications. The operation of this semiconductor processing apparatus 10 is controlled by the controller CONT. The semiconductor processing apparatus 10 is provided with a processing compartment 12 that holds the substrate and executes semiconductor processing thereon. In order to accommodate strongly toxic process gases in the set of usable process gases, the processing compartment 12 is enclosed by a process-side casing 11 that forms a local space. This process-side casing 11 is disposed within a clean room 5 as generally employed in semiconductor processing facilities. The local space in the process-side casing 11 is connected by an exhaust conduit 11a through a detoxification section (not shown) to, for example, an exhaust duct (not shown) in the semiconductor fabrication plant, and is subjected to continuous exhaust. A mounting platform 14 (support member) that also functions as a lower electrode is disposed in the processing compartment 12 in order to mount the substrate. An upper electrode 16 that includes a shower head is disposed within the processing compartment 12 facing the mounting platform 14. A high-frequency (RF) field for converting the process gas into a plasma is formed in the processing compartment 12 by the application of RF power from an RF power source 15 between the two electrodes 14, 16. The lower region of the processing compartment 12 is connected to an exhaust system 18 for exhausting the interior thereof and establishing a vacuum therein. Gas feed systems 19, 30 for feeding process gases are connected to the processing compartment 12. The gas feed system 19 feeds, for example, N₂, H₂, or Ar to the processing compartment 12 and will not be described in detail because it has a gene ral structure as heretofore known in the art. The gas feed system 30, on the other hand, feeds TiCI₄ to the processing compartment 12 and its structure will be described in the following. The gases from the gas feed systems 19, 30 are fed into the processing compartment 12 through, for example, a shower head (upper electrode) 16. This shower head 16 can have a structure in which separate feed paths are provided for each reaction gas and these gases are first mixed in the processing compartment 12 (post-mixing type). The semiconductor processing apparatus 10 is styled in the embodiment under consideration as a plasma CVD tool that carries out film fabrication using a plasma. However, the semiconductor processing apparatus 10 may be, for example, a low-pressure (LP) CVD tool that carries out film fabrication without using a plasma. The gas feed system 30 is disposed outside of the clean room 5 and has a precursor tank

32 that holds liquid TiCI₄ (precursor liquid). A liquid feed conduit 34 and a pressurization conduit 36 are connected to the precursor tank 32: this liquid feed conduit 34 feeds precursor liquid from the precursor tank 32, while the pressurization conduit 36 feeds helium into the precursor tank 32 as pressurized gas. Since TiCI is highly toxic, the precursor tank 32 is enclosed by a feed- side casing 38 that forms a local space outside of the clean room 5. The local space in this feed-side casing 38 is connected by an exhaust conduit 38a through a detoxification section (not shown) to, for example, an exhaust duct (not shown) in the semiconductor fabrication plant, and is subjected to continuous exhaust. When the precursor used for semiconductor processing is a solid at ambient temperature and ambient pressure, it is converted into precursor liquid by heating or dissolution in solvent. In such cases, the precursor tank 32 is a sealed vessel that temporarily holds the precursor liquid obtained from the solid precursor and that is used for pressurized transport to the semiconductor processing apparatus 10. Thus, for the purposes of this Specification, "precursor liquid" refers to the state at the point of pressurized transport from the precursor tank 32 to the liquid feed conduit 34 and does not refer to the state of the precursor at ambient temperature and ambient pressure. Returning to Figure 1 , the liquid feed conduit 34 feeds liquid TiCI₄ (liquid precursor) to the vaporizer 22 for vaporization; this vaporizer 22 is disposed within the process-side casing 11 near the processing compartment 12. The liquid TiCI₄ is heated at the vaporizer 22 by a suitable heating medium and is thereby vaporized to produce TiCI₄ gas. The TiCI₄ gas produced by the vaporizer 22 is fed to the processing compartment 12 through the gas feed conduit 21 , during which it is mixed with a suitable gas (for example, carrier gas) from the gas feed system 19. A liquid mass flow controller (MFC) 24 for controlling the flow rate of the precursor liquid is provided in the liquid feed conduit 34 upstream from the vaporizer 22. A bubble trap 26 is provided in the liquid feed conduit 34 upstream from and in the vicinity of the liquid MFC 24. The bubble trap 26 is used to separate and remove, prior to feed of the precursor liquid to the MFC 24, He bubbles admixed into the precursor liquid and originating from the helium pressurized gas. The MFC 24 and bubble trap 26 are also disposed within the process-side casing 11 in the vicinity of the processing compartment 12 and vaporizer 22. The bubble trap 26 is disposed in such a manner that the height of the surface of the precursor liquid in its interior (in the separator compartment 44, infra) corresponds to the maximum height of the surface of the precursor liquid from the precursor tank 32 to the vaporizer 22. In addition, since the bubble trap 26 is provided in order to eliminate the deleterious influence of He bubbles in the precursor liquid on the MFC 24, the length of the liquid feed conduit 34 between the bubble trap 26 and the MFC 24 is desirably as short as possible. Viewed from this perspective, the length of the liquid feed conduit 34 between the bubble trap 26 and the MFC 24 is no greater than 50 cm and is desirably no greater than 15 cm. The bubble trap 26 is disposed substantially as a single unit with the MFC 24 in an even more preferred embodiment. When the bubble trap 26 and the MFC 24 are provided as separate units, the liquid feed conduit 34 preferably runs from the bubble trap 26 toward the MFC 24 in a substantially horizontal or downwardly inclined manner. Figure 2 is a drawing that contains an enlarged view of the bubble trap 26. The bubble trap 26 has a pressure-resistant housing 42 that is traversed by the precursor liquid being fed to the MFC 24 and that forms a separator compartment 44 for separation of the gas bubbles incorporated by the precursor liquid. The housing 42 is formed, for example, from corrosion- resistant material selected from the group consisting of stainless steel, nickel, nickel alloys, tantalum, tantalum alloys, niobium, niobium alloys, titanium, and titanium alloys. The bottom of the separator compartment 44 is provided with a liquid inlet 46 for introduction of the precursor liquid and a liquid outlet 48 for discharge of the precursor liquid. The liquid inlet 46 and liquid outlet 48 are connected, respectively, to the upstream side of the liquid feed conduit 34 and the downstream side of the liquid feed conduit 34. The top of the separator compartment 44 is also provided with a gas outlet 52 that discharges the gas separated from the precursor liquid into the head space. The gas outlet 52 is connected through a solenoid valve 54 to a detoxification section 56 in the exhaust system. An orifice 58 that restricts the flow of gas from the gas outlet is disposed between the gas outlet 52 and the solenoid valve 54. The orifice 58 is used to prevent a sudden release of gas from the gas outlet and outflow of the precursor liquid in the liquid feed conduit 34 from the separator compartment 44. The CV value of the orifice 58 is therefore determined as a function of the pressure in the liquid feed conduit 34. For the case of a supply system for a CVD precursor liquid such as TiCI₄ as in the embodiment under consideration, the CV value of the orifice 58 is 1 x 10^"5 to 1 x 10^"3 and desirably is 4 x 10^"5 to 5 x 10^"4. This CV value is the numerical value of the flow rate in US gallons per minute (gpm) when pure water at 60°F is made to flow while maintaining a pressure difference of 1 psi, wherein 1 psi = 6.8946 x 10³ Pa, 60°F = approximately 15.6°C, and 1 US gallon = 3.78543 liters. An upper window 62a and a lower window 62b are formed in a gastight manner in the housing 42 so as to enable external optical surveillance of the level RL of the precursor liquid in the separator compartment 44. These windows 62a, 62b are formed, for example, of a transparent and corrosion-resistant material selected from the group consisting of heat- tempered glass, quartz, and sapphire. An upper optical sensor 64a and a lower optical sensor 64b are disposed at different heights on the outside of the housing 42 and in correspondence to the windows 62a, 62b. These optical sensors 64a, 64b optically detect the level RL of the precursor liquid in the separator compartment 44 through the windows 62a, 62b. The upper optical sensor 64a and the lower optical sensor 64b correspond, respectively, to the upper and lower limits of the level RL of the precursor liquid. A single narrow window that runs vertically can be used in place of the upper and lower windows 62a, 62b. The windows 62a, 62b become unnecessary when the entire housing 42 is made of a corrosion-resistant and transparent material that affords the necessary pressure resistance. The detection signals generated by the optical sensors 64a, 64b are transmitted to the controller 66 for the bubble trap 26. This controller 66 opens and closes the solenoid valve 54 based on these detection signals. More specifically, when the lower optical sensor 64b detects the fact that the level RL has reached the lower limit, the controller 66 opens the solenoid valve 54 and gas within the separator compartment 44 is discharged. The controller 66 closes the solenoid valve 54 when the upper optical sensor 64a subsequently detects the fact that the level RL has reached the upper limit. The controller 66 can as necessary or desired exchange information with the controller CONT for the CVD tool 10. The following advantageous effects accrue when a semiconductor processing system as illustrated in Figure 1 contains a bubble trap as illustrated in Figure 2. First, the bubble trap 26 makes it possible to supply the MFC 24 with precursor liquid that has been freed of gas bubbles admixed therein. As a consequence, flow rate control by the MFC 24 is not subject to the deleterious influence of bubbles and flow rate control of the precursor liquid can therefore be carried out accurately. Second, the precursor liquid in the bubble trap 26 is in contact only with the inner surfaces of the windows 62a, 62b and the housing 42 composed of corrosion-resistant material. As a consequence, the bubble trap 26 can be used substantially without regard to the corrosiveness of the precursor liquid, which provides the system with a very general applicability. Third, since the optical sensors 64a, 64b are disposed on the outside of the housing 42, they are not subject to corrosion by the precursor liquid, and, even when they are temporarily nonfunctional, parts can be changed out without stopping the system.

The following experiments were carried out in order to investigate the advantageous effects of the bubble trap 26. Figure 3 contains a schematic drawing that illustrates the apparatus used in the experiments. As shown in Figure 3, a tank 72 holding liquid TiCI₄ was connected to a liquid feed conduit 74 and to a pressurization conduit 76 that supplied pressurized helium. The following were disposed in the liquid feed conduit 74 in the given sequence considered from the upstream side: a helium saturator 78, a bubble generator 80, a bubble trap 26, a liquid MFC 82, a bubble counter 83, a sampler 84, and a waste liquid tank 86. A helium concentration meter 88 was connected to the sampler 84. A bypass line 81 was connected in parallel to the bubble trap 26 to enable acquisition of data for comparative examples that did not employ the bubble trap 26. Using the apparatus illustrated in Figure 3, liquid TiCI₄ was fed at a flow rate of 0.42 cc/min from the tank 72 by supplying pressurized helium at a positive pressure of 0.3 MPa. The helium concentration in the liquid TiCI₄ was brought to the saturation concentration at the helium saturator 78 using a supplemental feed of helium. Bubbles of helium were intentionally generated in the liquid TiCI₄ by the bubble generator 80 again using a supplemental feed of helium. Comparative data were obtained under these conditions both using the bubble trap 26 . and without using the bubble trap 26 (use of the bypass line 81 ). Figure 4 contain graphs that show the output (representing the flow rate) of the liquid MFC 82: (a) refers to the absence of the bubble trap 26, while (b) refers to use of the bubble trap 26. As shown in Figure 4(a), the output of the liquid MFC 82 in the absence of the bubble trap 26 was centered on approximately 2.5 V with a large spike waveform of about ± 1.5 V and a small wave of about ± 0.05 V. In contrast to this, when the bubble trap 26 was used the output of the liquid MFC 82 was stabilized at about 2.5 V as shown in Figure 4(b). When the data is analyzed in detail, the average output of the liquid MFC 82 was 2.498 V in both Figures 4 (a) and (b), while the standard deviation was 0.230 V in Figure 4(a) and was 0.03 V in Figure 4(b). Thus, the stability was as much as 70-times higher with the bubble trap 26 than without the bubble trap 26. The standard deviation in Figure 4(b) satisfied the < 2% in the specifications of the liquid MFC 82. Figure 5 contains graphs that show the measurement results from the bubble counter 83, where (a) refers to the absence of the bubble trap 26 and (b) refers to the use of the bubble trap 26. The number of bubbles with a diameter > 0.1 mm is optically detected by the bubble counter 83. The bubble count on the y-axis in Figures 5(a) and (b) is reported in arbitrary units (AU). A large number of bubbles were observed in the liquid TiCI₄ when the bubble trap 26 was not used, as shown in Figure 5(a), and the bubble count also underwent substantial variation as a function of elapsed time. This variation is believed to have occurred because relatively small bubbles produced within the conduit were temporarily trapped within the conduit and were observed after some of the bubbles had combined. In contrast, when a bubble trap 26 was used, a very few bubbles were seen just in the initial stage of the measurement, as shown in Figure 5(b). Figure 6 contains graphs that show the measurement results from the helium concentration meter 88, where (a) refers to the absence of the bubble trap 26 and (b) refers to use of the bubble trap 26. The helium concentration on the y-axis in Figures 6(a) and (b) is reported in arbitrary units (AU). The helium concentration in the liquid TiCI₄ underwent a substantial timewise fluctuation when the bubble trap 26 was not used, as shown in Figure 6(a). It is thought that this fluctuation was due to whether or not helium bubbles were formed in the liquid TiCI . In contrast, the liquid TiCI had a stable helium concentration when the bubble trap 26 was used, as shown in Figure 6(b). This stable value is believed to be the saturation helium concentration in liquid TiCI₄ at a positive pressure of 0.3 MPa. Thus, the experimental data reported in Figures 4-6 confirmed that the bubble trap 26 could thoroughly separate and remove helium bubbles admixed in liquid TiCI₄ and also confirmed that this enabled accurate control of the precursor liquid flow rate by the MFC. The embodiments described above use TiCI₄ as the example of the precursor liquid, but the semiconductor processing system and bubble trap illustrated in Figures 1 and 2 can be broadly utilized over the entire universe of liquid precursors used in semiconductor processing, such as halogen compounds and amine compounds. The halogen compounds can be exemplified by tantalum (V) fluoride, titanium (IV) bromide, titanium (IV) chloride, zirconium (IV) bromide, zirconium (IV) chloride, aluminum bromide, boron chloride, chromium bromide, chromium chloride, chromium fluoride, gallium chloride, gallium bromide, niobium (V) fluoride, phosphorus trichloride, phosphorus tribromide, phosphorus oxychloride, phosphorus oxybromide, sulfur chloride, sulfur dichloride, antimony (III) bromide, antimony (III) chloride, antimony (V) chloride, silicon bromide, silicon chloride, hexachlorodisilane, tin (II) chloride, and tin (IV) chloride. The amine compounds can be exemplified by trimethylamine alane, dimethylethylamine alane, methylamine, ethylamine, dimethylamine, diethylamine, bisdimethylaminosilane, trisdimethylaminosilane, tetrakisdimethylaminosilane, trisilylamine, bis(tert-butylamino)silane, hexakisethylaminodisilane, tetraethoxytantalum dimethylamino ethoxide, tetrakisdiethylaminotitanium, tetrakisdimethylaminotitanium, tetrakisdimethylaminozirconium, and tetrakisdiethylaminozirconium. While various modifications and alterations within the technical sphere of the concept of this invention can be devised by the individual skilled in the art, it should be understood that these modifications and alterations also fall within the scope of this invention.

As described in the preceding, certain aspects of the present invention provide a semiconductor processing system and bubble trap therefor that enable the precursor liquid flow rate to be accurately controlled. In addition, certain aspects of the present invention provide a very widely applicable semiconductor processing system and bubble trap therefor.

Brief Description of the Drawings

- Figure 1 contains a schematic drawing of a semiconductor processing system according to an embodiment of the present invention;

- Figure 2 contains an enlarged view of the bubble trap used by the semiconductor processing system illustrated in Figure 1; - Figure 3 contains a schematic drawing of the apparatus used in experiments carried out in order to examine the effects of the bubble trap;

- Figure 4 contains graphs of the output of the liquid MFC in the apparatus in Figure 3, where (a) refers to the absence of the bubble trap and (b) refers to use of the bubble trap;

- Figure 5 contains graphs of the measurement results from the bubble counter in the apparatus in Figure 3, where (a) refers to the absence of the bubble trap and (b) refers to use of the bubble trap;

- Figure 6 contains graphs of the measurement results from the helium concentration meter in the apparatus in Figure 3, where (a) refers to the absence of the bubble trap and (b) refers to use of the bubble trap; - Figure 7 contains a schematic drawing that illustrates a prior-art precursor liquid feed section in a semiconductor processing system that uses a liquid as precursor for semiconductor processing.

Claims

1. A system for delivering a precursor to a process compartment to process semiconductors or the like comprising : a precursor tank that holds a liquid precursor that is used in the semiconductor process; a vaporizer that produces process gas by vaporizing the liquid precursor; a liquid feed conduit that is connected to the precursor tank and that feeds the liquid precursor from the precursor tank to the vaporizer; a pressurization conduit that is connected to the precursor tank and that feeds pressurized gas from pressurized gas means into the precursor tank so as to push the liquid precursor out of the precursor tank and into the liquid feed conduit; a gas feed conduit that connects the vaporizer to the process compartment and that feeds the process gas from the vaporizer to the process compartment; a mass flow controller that is disposed in the liquid feed conduit upstream from the vaporizer; and a bubble trap that is disposed in the liquid feed conduit upstream from and in the vicinity of the mass flow controller; wherein the bubble trap has a separator compartment that separates, , bubbles of the pressurized gas from the liquid precursor which gas bubbles originate from the injection of the pressurized gas into the precursor tank and admixed in the liquid precursor wherein the separator compartment has a liquid inlet located at or near the bottom of said compartment at its bottom where the liquid precursor is introduced and a liquid outlet where the liquid precursor is discharged and has a gas outlet located at or near the top of said compartment where the gas separated from the liquid precursor is discharged.

2. The system according to claim 1 , wherein the bubble trap is provided with an optical sensor that is disposed on the outside of the separator compartment and that optically detects the level of the liquid precursor and delivers a detection signal; a valve that is connected to the gas outlet and that selectively opens or closes the gas outlet; and a controller that opens or closes the valve, in response to the detection signal from the optical sensor.

3. The system according to claim 2, wherein an orifice that restricts the gas flow from the gas outlet is disposed between the gas outlet and the aforesaid valve.

4. The system according to claim 2 or 3, wherein the optical sensor is provided with a first optical sensor and a second optical sensor, which are disposed at, respectively, the upper limit and the lower limit for the surface of the liquid precursor in the separator compartment.

5. The system according to claim 4, wherein the bubble trap is provided with a window that is formed in the aforesaid housing and that enables optical surveillance of the precursor liquid level in the separator chamber from the outside, wherein the first and second optical sensors optically detect the liquid precursor level through this window.

6. The system according to claim 5, wherein the window is provided with a first window and a second window that are disposed, respectively, in correspondence to the first and second optical sensors.

7. The process according to any of claims 1 to 6, wherein the bubble trap is disposed in such a manner that the height of the liquid precursor level in the separator compartment corresponds to the maximum height of the precursor liquid level from the precursor tank to the vaporizer.

8. The system in accordance with any of claims 1 to 7, wherein the length of the liquid feed conduit between the bubble trap and the mass flow controller is no greater than 50 cm.

9. The system according to any of claims 1 to 8, comprising a process-side casing that forms a local space that encloses the process compartment, vaporizer, mass flow controller, and bubble trap, wherein this local space within the process-side casing is exhausted by an exhaust system and wherein the precursor tank is disposed outside the process-side casing.

10. The system according to any of claims 1 to 9, wherein the liquid precursor is a halogen compound or an amine compound.

11. A bubble trap system for a liquid feed conduit in a semiconductor processing system comprising : a housing that forms a separator compartment that separates, from the liquid precursor that will be fed to a mass flow controller, gas bubbles admixed in the precursor liquid, wherein the separator compartment has at its bottom a liquid inlet where the precursor liquid is introduced and a liquid outlet where the precursor liquid is discharged and has at its top a gas outlet where the gas separated from the precursor liquid is discharged; a first window and a second window that are formed in the housing in such a manner that the level of the precursor liquid within the separator compartment can be subjected to optical surveillance from the outside; a first optical sensor and a second optical sensor, that are disposed on the outside of the separator compartment at different heights at a first position and a second position and that optically detect the level of the precursor liquid through the first and second windows, respectively; a valve that is connected to the gas outlet and that selectively opens the gas outlet; and a controller that opens and closes the valve based on the detection signals from the first and second optical sensors.

12. The bubble trap according to claim 11, wherein an orifice that restricts the gas flow from the gas outlet is disposed between the gas outlet and the aforesaid valve.

13. The bubble trap according to claim 12, wherein the CV value of the opening of the orifice is 1 x 10^"5 to 1 x 10^"3.

14. The bubble trap according to any of claims 11 to 13, wherein the housing substantially comprises material selected from the group consisting of stainless steel, nickel, nickel alloys, tantalum, tantalum alloys, niobium, niobium alloys, titanium, and titanium alloys, and the windows substantially comprise material selected from the group consisting of heat-tempered glass, quartz, and sapphire.