Low vapor-pressure precursor dosage control

Abstract

A method and apparatus for controlling dosage of a low vapor-pressure reactant comprising a processing chamber (110) for processing substrates, an inert gas source system, a first inlet line (130) connecting the inert gas source system to the processing chamber (110), a precursor source vessel (150) for housing a low vapor-pressure precursor (160), a second inlet line (185) connecting the inert gas source system to a buffer volume (180) comprising a head space (155) of the source vessel (150), a third inlet line (170) connecting the source vessel (150) to the first inlet line (130) through the buffer volume (180) via a first pulsing valve (V1), wherein the apparatus (100) is configured to adjust pressure in the buffer volume (180) to a predetermined level during a purge phase of a process cycle.

Description

[0001] LOW VAPOR-PRESSURE PRECURSOR DOSAGE CONTROL

[0002] TECHNICAL FIELD

[0003] The present disclosure generally relates to precursor dosage control in a substrate processing apparatus. The disclosure relates particularly, though not exclusively, to regulating precursor dosage of low vapor-pressure precursor pulses.

[0004] BACKGROUND

[0005] This section illustrates useful background information without admission of any technique described herein representative of the state of the art.

[0006] Accurate precursor dosage control is important in substrate processing. Poor dosage control reduces processing quality and increases resource usage. Low vapor-pressure precursors provide additional challenges in obtaining and maintaining the desired pressure and dosage throughout successive reactant pulses. Therefore, improved means for accurate dosage control of low-vapor pressure precursors is desired.

[0007] SUMMARY

[0008] The appended claims define the scope of protection. Any examples and technical descriptions of apparatuses, products and / or methods in the description and / or drawings not covered by the claims are presented not as embodiments of the invention but as background art or examples useful for understanding the invention.

[0009] According to a first example aspect there is provided an apparatus comprising a processing chamber for processing substrates, an inert gas source system, a first inlet line connecting the inert gas source system to the processing chamber, a (precursor) source vessel for housing a low vapor-pressure precursor, a second inlet line connecting the inert gas source system to a buffer volume comprising a head space of the source vessel, a third inlet line connecting the source vessel to the first inlet line through the buffer volume and a first pulsing valve, wherein the apparatus is configured to adjust pressure in the buffer volume to a predetermined level during a purge phase of a process cycle.

[0010] Advantageously, controlling successive precursor pulses and pulse dosage may be improved.

[0011] In certain embodiments, the first pulsing valve is a multi-leg (multi-way) pulsing valve. In certain embodiments, the first pulsing valve is a three-leg (three-way) pulsing valve.

[0012] In certain embodiments, the apparatus comprises a third inlet line connecting the source vessel to the first inlet line through the buffer volume via the first pulsing valve.

[0013] In certain embodiments, the apparatus is configured to adjust pressure in the buffer volume to a predetermined level, when the leg of the first pulsing valve downstream of the buffer volume is closed, during a purge phase of a process cycle.

[0014] In certain embodiments, the first inlet line is configured to provide a first inert gas flow to the processing chamber. In certain embodiments, the second inlet line is configured to provide a second inert gas flow to the buffer volume. In certain embodiments, the first inlet line is configured to provide a first inert gas flow to the processing chamber and the second inlet line is configured to provide a second inert gas flow to the buffer volume.

[0015] In certain embodiments, the first pulsing valve has a first open-close timing cycle configured to control precursor dosage from the buffer volume to the first inlet line during the process cycle. Advantageously, precursor dosage to the processing chamber may be improved.

[0016] In certain embodiments, the apparatus comprises a second pulsing valve in the second inlet line. In certain embodiments, the second pulsing valve is configured to control second inert gas flow to the buffer volume. In certain embodiments, the second pulsing valve is configured to control a second inert gas flow to the buffer volume during purge to adjust the pressure in the buffer volume to a predetermined level during purge. In certain embodiments, the apparatus comprises a second pulsing valve, the second pulsing valve being configured to control a second inert gas flow to the buffer volume to enable the pressure in the buffer volume to be adjusted to a predetermined level during purge phase of a process cycle. Advantageously, pressure in the buffer volume may be accurately controlled. Further, variance in the precursor dosage of successive pulses may be minimized. In certain embodiments, the second pulsing valve has second open-close timing cycle coordinated with the first open-close timing cycle of the first pulsing valve. Advantageously, pressure and process control of the apparatus may be improved.

[0017] In certain embodiments, the second pulsing valve is configured to open during pulse of the first pulsing valve. In certain embodiments, the second pulsing valve remains open when entering the purge phase after a reactant pulse through the first pulsing valve until a predetermined pressure level in the buffer volume is achieved.

[0018] In certain embodiments, the apparatus is configured to enter idle phase in response to achieving the predetermined pressure level in the buffer volume during purge.

[0019] In certain embodiments, the apparatus comprises a first restriction between the first pulsing valve and the buffer volume. Advantageously, precursor flow and dosage control may be further improved.

[0020] In certain embodiments, the buffer volume comprises an additional gas reservoir volume configured to provide additional buffer volume. Advantageously, precursor dosage control may be improved.

[0021] In certain embodiments, the apparatus comprises more than one inert gas source.

[0022] In certain embodiments, the apparatus comprises first flow control means in the first inlet line upstream of the first pulsing valve for controlling the first inert gas flow. In certain embodiments, the first flow control means comprises a mass flow controller. In certain embodiments, the first flow control means comprises a pressure transducer.

[0023] In certain embodiments, the first inert gas flow is constant.

[0024] In certain embodiments, the apparatus comprises second flow control means in the second inlet line upstream of the second pulsing valve configured to control the second inert gas flow.

[0025] In certain embodiments, the second flow control means comprises a mass flow controller.

[0026] In certain embodiments, the second flow control means comprises a pressure transducer.

[0027] In certain embodiments, the second flow control means comprises a second restriction. In certain embodiments, the second flow control means comprises a pressure controller, wherein the pressure controller is configured to receive data from a pressure transducer located in the buffer volume to adjust the second inert gas flow to the second pulsing valve.

[0028] In certain embodiments, the apparatus comprises a check valve upstream of the second pulsing valve.

[0029] In certain embodiments, the apparatus comprises a control unit. In certain embodiments, the control unit is configured to control the apparatus. In certain embodiments, the control unit is configured to control the open-close timing cycles of the first and second pulsing valves. In certain embodiments, the control unit is configured to coordinate the open-close timing cycles of the first and second pulsing valves. In certain embodiments, the control unit is a computer-based system. In certain embodiments, the control unit comprises at least one processor. In certain embodiments, the control unit comprises at least one memory. In certain embodiments, the control unit comprises a user interface. In certain embodiments, the control unit is configured to operate as a valve controller.

[0030] In certain embodiments, the control unit is connected to the first pulsing valve. In certain embodiments, the control unit is configured to control the first pulsing valve.

[0031] In certain embodiments, the control unit is connected to the second pulsing valve. In certain embodiments, the control unit is configured to regulate the second pulsing valve based on a feedback loop, wherein a control algorithm is used to tune opening of the second pulsing valve during the open cycle of the second pulsing valve based on the detected pressure of the buffer volume. In certain embodiments, the control unit tunes (or is configured to tune) the magnitude of the opening of the second pulsing valve during open cycle of the second pulsing valve. In certain embodiments, the frequency of the opening of the second pulsing valve is tuned. In certain embodiments, the magnitude of the opening of the second pulsing valve is tuned. In certain embodiments, the magnitude and frequency of the opening of the second pulsing valve are tuned.

[0032] In certain embodiments, the second pulsing valve is closed in idle phase to prevent backflow from the source vessel, wherein in the idle phase the first pulsing valve allows the first inert gas flow to the processing chamber but precursor pulse is blocked, and the pressure in the buffer volume is at the predetermined level. In certain embodiments, in the idle phase, the first pulsing valve allows the constant inert gas flow to the processing chamber but precursor pulse is blocked, and the pressure in the buffer volume is at the predetermined level. In certain embodiments, the apparatus comprises shut-off valve(s) to isolate the source vessel from any gas flow during maintenance purge. In certain embodiments, the apparatus comprises a first shut-off valve upstream in immediate proximity of the source vessel. In certain embodiments, the apparatus comprises a second shut-off valve downstream in immediate proximity of the source vessel.

[0033] In certain embodiments, the apparatus comprises a by-pass valve configured to allow the second inert gas flow to by-pass the isolated source vessel during maintenance purge.

[0034] According to another example aspect there is provided an apparatus comprising a first pulsing valve configured to control precursor pulse dosage to a first inert gas flow in a first inlet line leading to a processing chamber, low vapor-pressure reactant (precursor) in a source vessel, wherefrom the reactant is allowed to evaporate to the buffer volume, wherein the buffer volume comprises the source vessel head space, the buffer volume being connected to the first inlet line through the first pulsing valve, a second inert gas flow to the buffer volume, and a second pulsing valve upstream of the source vessel configured to adjust the second inert gas flow to the source vessel such that the pressure in the buffer volume is adjusted to a predetermined pressure level during purge phase of a process cycle.

[0035] According to a second example aspect there is provided method for controlling dosage of a low vapor-pressure reactant comprising providing low vapor-pressure precursor from a source vessel to a buffer volume located upstream of a first pulsing valve, wherein the first pulsing valve controls precursor pulses to a processing chamber, providing an inert gas flow from an inert gas source system to the buffer volume, wherein the buffer volume comprises a head space of the precursor vessel, and adjusting the pressure in the buffer volume to a predetermined level during purge phase of a process cycle.

[0036] In certain embodiments, the method comprises providing a first inert gas flow to the processing chamber and a second inert gas flow to the buffer volume, wherein the precursor pulses through the first pulsing valve are provided to the first inert gas flow. In certain embodiments, the method comprises providing a first inert gas flow to the processing chamber via a first inlet line and a second inert gas flow to the buffer volume via a second inlet line. In certain embodiments, the method comprises providing, by the first pulsing valve, the precursor pulses to the first inlet line upstream of the processing chamber. In certain embodiments, the method comprises providing, by the first pulsing valve, the precursor pulses to the first inert gas flow in the first inlet line upstream of the processing chamber.

[0037] In certain embodiments, the first inert gas flow is constant. In certain embodiments, the first inert gas flow is constant during pulse and purge phases of the process cycle. In certain embodiments, the method comprises providing constant first inert gas flow during pulse and purge phases of the process cycle.

[0038] In certain embodiments, the method comprises controlling the (second) inert gas flow to the buffer volume by a second pulsing valve located upstream of the buffer volume.

[0039] In certain embodiments, the method comprises coordinating the open-close timing cycle of the second pulsing valve with the open-close timing cycle of the first pulsing valve. In certain embodiments, the method comprises opening the second pulsing valve during pulse phase of the process cycle. In certain embodiments, the method comprises keeping the second pulsing valve open during a purge phase of the process cycle until a predetermined pressure level in the buffer volume is achieved.

[0040] In certain embodiments, the method further comprises regulating the opening of the second pulsing valve during open cycle of the second pulsing valve based on a feedback loop based on the detected pressure in the buffer volume. In certain embodiments, the method comprises regulating the magnitude of the opening of the second pulsing valve during purge. In certain embodiments, the method comprises regulating the frequency of opening of the second pulsing valve during purge.

[0041] In certain embodiments the method further comprises after having closed the first pulsing valve to stop precursor pulse to the processing chamber and after the predetermined pressure in the buffer volume has been achieved, entering idle phase by closing the second pulsing valve to prevent precursor and / or inert gas backflow from the buffer volume.

[0042] In certain embodiments, the method further comprises, outside of a process cycle, performing maintenance purge by a) separating precursor source vessel from any gas flow by closing shut-off valve(s) and opening a by-pass valve, and b) opening both the first and the second pulsing valves to flush the gas lines with inert gas without the inert gas flow entering the source vessel.

[0043] According to another example aspect there is provided a method in an apparatus of certain example aspects for controlling precursor dosage to a processing chamber wherein a first pulsing valve is configured regulate precursor pulses to the processing chamber, and a second pulsing valve is configured to regulate pressure in a buffer volume upstream of the first pulsing valve by controlling an inert gas flow to the buffer volume, the method comprising coordinating the open-close timing cycle of the second pulsing valve with the open-close timing cycle of the first pulsing valve such that i) during a pulse phase, wherein the first pulsing valve is open to allow precursor pulse to the processing chamber, also opening the second pulsing valve; and ii) during purge phase, wherein the first pulsing valve is closed to prevent precursor pulse from entering the processing chamber, keeping the second pulsing valve open until a predetermined pressure level in the buffer volume is achieved.

[0044] Different non-binding example aspects and embodiments have been illustrated in the foregoing. The embodiments in the foregoing are used merely to explain selected aspects or steps that may be utilized in different implementations. Some embodiments may be presented only with reference to certain example aspects. It should be appreciated that corresponding embodiments may apply to other example aspects as well.

[0045] BRIEF DESCRIPTION OF THE FIGURES

[0046] Some example embodiments will be described with reference to the accompanying figures, in which:

[0047] Fig. 1a schematically shows an apparatus in a pulse configuration according to certain embodiments;

[0048] Fig. 1b schematically shows an apparatus in a purge configuration according to certain embodiments;

[0049] Fig. 1c schematically shows an apparatus in an idle configuration according to certain embodiments;

[0050] Fig. 1d schematically shows an apparatus in a maintenance purge configuration according to certain embodiments; Figs. 2-4 schematically show apparatuses in a pulse configuration according to certain other embodiments;

[0051] Fig. 5 schematically shows an apparatus comprising a control unit according to certain embodiments;

[0052] Fig. 6 shows a flow chart of a method for controlling pulse dosage according to certain embodiments; and

[0053] Fig. 7 shows a flow chart of another method for controlling pulse dosage according to certain embodiments.

[0054] DETAILED DESCRIPTION

[0055] In the following description, like reference signs denote like elements or steps.

[0056] The present disclosure aims to improve dosage control of low vapor-pressure precursor pulses in a substrate processing apparatus 100. The substrate processing apparatus 100 is configured to exploit principles of vapor-deposition based techniques. In certain embodiments, the substrate processing apparatus 100 is configured as an Atomic Layer Deposition (ALD) apparatus.

[0057] In the context of this application, the term ALD comprises all applicable ALD based techniques and any equivalent or closely related technologies, such as, for example the following ALD sub-types: MLD (Molecular Layer Deposition) plasma-assisted ALD, for example PEALD (Plasma Enhanced Atomic Layer Deposition) and photon-enhanced Atomic Layer Deposition (known also as flash enhanced ALD).

[0058] ALD is a widely used technology for preparing thin films by depositing precursor coatings onto a substrate from a vapor phase. ALD is based on alternating self-saturating surface reactions on a substrate, wherein different reactants (precursors) provided as chemical compounds or elements in a nonreactive inert gaseous carrier are sequentially pulsed into a reaction space accommodating a substrate. Deposition of a reactant is followed by a purging the substrate by inert gas. Precursor pulse-purge cycles are repeated as many times as required for obtaining a film with a predetermined thickness.

[0059] The apparatus 100 can be further applied to other deposition technologies, such as Physical Vapor Deposition (PVD) and for Plasma-Enhanced Chemical Vapor Deposition (PECVD) processes, and to any other applicable technology of which Atomic Layer Etching (ALE) is mentioned as an example.

[0060] In Figs. 1a-5, a white (unshaded) triangle of a valve symbol depicts an open valve section (flow allowed to pass through the triangle and hence that specific leg of the valve), whereas a black triangle of a valve symbol depicts a closed valve section (no flow allowed to pass through the triangle and hence that specific leg of the valve).

[0061] Figs. 1 a-1d show an apparatus 100 according to certain embodiments in a pulse, purge, idle, and maintenance purge configuration, respectively.

[0062] The substrate processing apparatus 100 comprises a processing chamber 110. The processing chamber 110 is configured to accommodate a substrate or a plurality of substrates to be processed in the apparatus 100.

[0063] The substrate processing apparatus 100 comprises an exhaust conduit 115 downstream of the processing chamber 110. Gaseous substances in the processing chamber 110 are evacuated from the processing chamber 110 through the exhaust conduit 115. A pump 125 connected to the exhaust conduit 115 is used to actively remove the gaseous substances. In certain embodiments, the pump 125 is a vacuum pump.

[0064] The substrate processing apparatus 100 comprises an inert gas source system configured to provide inert gas. In certain embodiments, the inert gas source system comprises a first inert gas source 120a. In certain embodiments, the inert gas source system comprises a second inert gas source 120b. In certain embodiments, the inert gas source system comprises a plurality of inert gas sources.

[0065] In certain embodiments, as shown in Figs, 1 a-1 d, the inert gas source system comprises a first inert gas source 120a which is connected to the processing chamber 110 via a first inlet line 130. First inert gas flow is configured to flow along the first inlet line 130 from the first inert gas source 120a to the processing chamber 110. In other words, the first inlet line comprises the entire line from the inert gas source system, that is, the first inert gas source 120a in Figs. 1 a-1 d, to the processing chamber 110. In certain embodiments, the inert gas is N2 or Ar, He. The inert gas may be used, for instance, to purge the processing chamber 110 between precursor pulses and to separate subsequent precursor pulses from another. In certain embodiments, the inert gas source 120a is configured to provide first inert gas flow to the processing chamber 110. In certain embodiments, the inert gas flow is constant. In certain embodiments, the inert gas flow is constant through the first inlet line 130 from the inert gas source system to the processing chamber 110.

[0066] The substrate processing apparatus 100 comprises first flow control means 140 (marked with a dashed box in Figs. 1 a-1 d) in the first inlet line 130 downstream of the first inert gas source 120a. In certain embodiments, the first flow control means 140 comprise a mass flow controller 140a and a first pressure transducer 140b. The first flow control means 140 is configured to establish and ensure a stable first inert gas flow in the first inlet line 130 from the first inert gas source 120a to the processing chamber 110. In certain embodiments, the pressure of the first inert gas flow in the first inlet line 130 downstream of the flow control means 140 is 5 - 15 hPa at a first inert gas flow rate of 500 - 2000 seem.

[0067] The substrate processing apparatus 100 comprises a first pulsing valve V1 in the inlet line 130. The open-close cycle of the first pulsing valve V1 controls precursor pulse-purge cycles to the processing chamber 110. In certain embodiments, the first pulsing valve V1 is a pneumatic valve. In certain embodiments, the first pulsing valve V1 is a diaphragm valve. The first pulsing valve V1 is configured to provide low vapor-pressure reactant pulses from a reactant source to the inert gas flow in the first inlet line 130 upstream of the processing chamber 110 while allowing first inert gas flow in the first inlet line 130. In certain embodiments, the first inert gas flow is a constant flow. In certain embodiments, the first inert gas flow is maintained through pulse, purge, and idle phases of a substrate processing cycle.

[0068] In certain embodiments, the first pulsing valve V1 is a three-leg pulsing valve. A three-leg valve V1 enables providing precursor pulses from a precursor source vessel to the first inert gas flow in the first inlet line 130. In certain embodiments, the first pulsing valve V1 is a four- leg pulsing valve. A four-leg valve V1 enables providing precursor pulses from two separate precursor source vessels to the first inert gas flow in the first inlet line 130 and controlling the pulses by one multi-leg first pulsing valve V1 .

[0069] In certain examples, the apparatus 100 comprises more than one first pulsing valve V1. Therefore, a plurality of different precursors from different precursor source vessels may be connected to different parts of the first inlet line 130 through the plurality of first pulsing valves V1. In certain embodiments, the apparatus 100 comprises one, two, or three multileg first pulsing valves V1 . Alternatively, in certain embodiments, the apparatus comprises a plurality of inlet lines, similar to the first inlet line 130, each of which comprise a multi-leg pulsing valve V1 .

[0070] The first pulsing valve V1 has a predetermined open close timing cycle. Preferably, the first inert gas flow in the first inlet line 130 is allowed to proceed through the first pulsing valve V1 unhindered at all configurations. The first inert gas flow is preferably adjusted by the first flow control means 140. In certain embodiments, the first inert gas flow is constant.

[0071] During pulse phase of a process cycle (Fig. 1 a) of the apparatus 100, the first pulsing valve V1 is in pulse configuration. In pulse configuration, the first pulsing valve V1 is configured to allow a low vapor-pressure precursor pulse to the first inert gas flow in the first inlet line 130. That is, during pulse, a precursor pulse is allowed to the first inert gas flow and therefrom to the processing chamber 110. The process cycle comprises alternating pulse and purge phases until the surface process is complete. In certain embodiments, the process cycle also comprises an idle phase(s) in between the purge and pulse phases. In certain embodiments, maintenance purge is performed outside the process cycle.

[0072] During purge phase of a process cycle (Fig. 1 b) of the apparatus 100, i.e., before and after precursor pulses through the first pulsing valve V1 , the first pulsing valve V1 is in purge configuration. In purge configuration, the first pulsing valve V1 allows the first inert gas flow in the first inlet line 130, from an inert gas source system to the processing chamber 110, but prevents the low vapor-pressure precursor pulse to the first inlet line 130. That is, purge is the stage between subsequent precursor pulses, where only the first inert gas flow accesses the processing chamber 110 to flush the residues of a previous pulse from the chamber.

[0073] During idle phase (Fig. 1 c) of the apparatus 100, the apparatus is ready for another precursor pulse. The pressure in a buffer volume 180 upstream of the first pulsing valve V1 is at a predetermined level for the next pulse precursor pulse, i.e., pulse phase. Idle configuration of the first pulsing valve V1 is the same as the purge configuration.

[0074] During maintenance purge (Fig. 1 d) of the apparatus 100, the apparatus 100 is flushed clean with an inert gas apart from a source vessel 150. During maintenance purge the first pulsing valve V1 is in maintenance purge configuration. In maintenance purge configuration, the first pulsing valve V1 is kept fully open to allow inert gas flow through all of its openings. In certain embodiments, the pulse phase, purge phase and idle phase follow each other in cycles. Maintenance purge may be conducted to clean the gas lines, e.g., between separate processing runs. The configurations of the other members of the apparatus 100 at each of the said stages are described with respect to the discussion of those members below.

[0075] The substrate processing apparatus 100 comprises a source vessel 150. The source vessel 150 houses the low vapor-pressure precursor 160. The low-vapor-pressure precursor 160 may evaporate to a head space 155 of the source vessel 150. Evaporation of the low vaporpressure precursor is depicted with dashed arrows within the head space 155 in the Figs. 1-4. The low vapor-pressure precursor 160 may be, for example, tris(dimethylamino)cyclopentadienyl zirconium (ZyALD), tris(dimethylamido)cyclopentadienyl hafnium (HyALD), tetrakis(dimethylamido)titanium (TDMAT), hafnium tetrachloride (HfCI4), zirconium tetrachloride (ZrCI4), tetrakis(ethylmethylamino)hafnium (TemaHf), tetrakis(ethylmethylamino)zirconium

[0076] (TemaZr).

[0077] The source vessel 150 is connected to the multi-leg first pulsing valve V1 by a third inlet line 170. The evaporated low vapor-pressure precursor 160 proceeds from the head space 155 to the third inlet line 170. From the third inlet line 170 the first pulsing valve V1 is configured to control the flow of the low-vapor pressure precursor 160 to the first inlet line 130 and to the processing chamber 110.

[0078] The source vessel 150 is located downstream of the inert gas source system. The source vessel 150 is connected to the inert gas source system via a second inlet line 185. In certain embodiments, the inert gas source system is configured to provide, via the second inlet line 185, a preferably constant second inert gas flow to the head space 155 of the source vessel 150 which is part of the buffer volume 180. In certain embodiments, the inert gas source system comprises a second inert gas source 120b. In certain embodiments, the source vessel 150 is connected to the second inert gas source 120b as shown in Figs. 1a-1d. The inert gas may be, for example, N2 or Ar. Preferably, the inert gas of the second inert gas flow is the same as the inert gas of the first inert gas flow. In certain embodiments, the second inlet line 185 is connected to the same inert gas source system as the first inlet line 130. A second pulsing valve V2 is located in the second inlet line 185 between the inert gas source system and the source vessel 150. The head space 155 and the third inlet line 170 (and a short section of the second inlet line 185 downstream of a second pulsing valve V2) together form a buffer volume 180 (enclosed within a dashed polygon (depicted as a reversed L-shaped structure) in Fig. 1 a). The volume of the buffer volume in certain embodiments is at least 100 cm3.

[0079] In certain embodiment, the apparatus 100 is configured to adjust pressure in the buffer volume 180 to be in the range from 1 to 50 hPa. The pressure of the low vapor-pressure precursor 160 in the buffer volume 180 affects the precursor 160 pulse dosage through the first pulsing valve V1. In certain embodiments, the dosage of the low vapor-pressure precursor 160 in the precursor pulse through the first pulsing valve V1 is controlled by adjusting the pressure of the buffer volume 180.

[0080] In certain embodiments, the buffer volume 180 comprises an additional gas reservoir volume 175. In certain embodiments, the additional gas reservoir volume 175 is located in the third inlet line 170. The additional gas reservoir 175 increases the buffer volume 180. Bigger buffer volume 180 enables to better maintain pressure difference across the first pulsing valve V1 during precursor pulses.

[0081] The apparatus 100 comprises a first restriction R1 between the buffer volume 180 and the first pulsing valve V1 . The first restriction R1 establishes a flow restriction to control the low vapor-pressure precursor 160 flow from the buffer volume 180 to and through the first pulsing valve V1 during pulse stage. The precursor dosage is affected by the gas pressure in the buffer volume 180 and the restriction R1. Therefore, the restriction R1 partially determines the precursor pulse dosage. In certain embodiments, the first restriction R1 is configured to provide constant flow from the buffer volume 180 to the first pulsing valve V1 . Advantageously, pressure spiking during a precursor pulse and differences between subsequent precursor pulses may be minimized.

[0082] The precursor dosage in the pulse(s) through the first pulsing valve V1 is proportional to Ap * pi, where pi is the partial pressure of the precursor 160 in the buffer volume 180 and Ap is the pressure difference over the first restriction R1 . Ap can be modified by controlling the pressure in the vessel head space 155. In certain embodiments, as a response to pi decreasing over time, Ap is increased to compensate the change. Advantageously, the precursor 160 dosage in precursor pulse(s) may be kept constant, even though the pi in the buffer volume 180 does not stay constant. In certain embodiments, the second inert gas flow into the source vessel 150 increases pressure in the buffer volume 180 during purge phase to recover a preset pressure level. In certain embodiments, the second inert gas flow enables consistent low-vapor pressure precursor pulses through the first pulsing valve V1. In certain embodiments, the pressure loss in the buffer volume due to precursor pulses through the first pulsing valve V1 is compensated by the second inert gas flow. Advantageously, the pressure in the buffer volume and pulse dosage of the low-vapor pressure precursor may be controlled during and / or between successive precursor pulses by the second inert gas.

[0083] A first shut-off valve SV1 is located in the second inlet line 185 upstream in immediate proximity of the source vessel 150. A second shut-off valve SV2 is located in the third inlet line 170 downstream in immediate proximity to the source vessel. In certain embodiments, the shut-off valves SV1 , SV2 are manual valves. In certain embodiments, the shut-off valves SV1 , SV2 are closed during a maintenance purge to isolate the source vessel 150 from any gas flow.

[0084] In certain embodiments, the apparatus 100 comprises a by-bass line 195 equipped with a by-pass valve BV. In certain embodiments, the by-pass line 195 connects the second inlet line 185 to the third inlet line 170. In certain embodiments, the by-pass valve BV is a manual valve. In certain embodiments, the by-pass valve BV is closed during pulse, purge, and idle phases. In certain embodiments, the by-pass valve BV is opened for maintenance purge to allow the second inert gas flow from to flow from the second inlet line 185 along the by-pass line directly 195 to the third inlet line 170, thus by-passing the source vessel, to flush the gas lines with the inert gas.

[0085] The apparatus 100 comprises a second pulsing valve V2 in the second inlet 185 line upstream of the source vessel 150. In certain embodiments, the second pulsing valve V2 is a pneumatic valve. In certain embodiments, the second pulsing valve V2 is a diaphragm valve. The second pulsing valve V2 is configured to control the second inert gas flow from the second inert gas source 120b to the buffer volume 180. The second pulsing valve V2 has an open-close timing cycle coordinated with the open-close timing cycle of the multileg first pulsing valve V1. This is to regulate the pressure in the buffer volume 180 to a predetermined level for each reactant pulse of the multi-leg first pulsing valve V1 for controlling low vapor-pressure precursor dosage to the first inert gas flow. Advantageously, the pressure in the buffer volume may be actively controlled according to the open-close timing cycle of the first pulsing valve V1 . In certain embodiments, the second pulsing valve V2 is open during purge phase between two subsequent reactant pulses of the first pulsing valve V1. In certain embodiments, this is to increase the pressure in the buffer volume 180 to a predetermined level during purge before each precursor pulse, i . e. , opening of the first pulsing valve V1 . It is noted that during purge phase, continuous flow of the constant first inert gas flow through the first pulsing valve V1 is allowed while the low vapor-pressure reactant pulse to the inert gas flow is blocked.

[0086] In certain embodiments, the second pulsing valve V2 is open during a precursor pulse of the first pulsing valve V1 . In the pulse phase, the first pulsing valve V1 opens to allow low vapor pressure precursor pulse from the buffer volume 180 to the first inert gas flow in the first inlet line 130. In certain embodiments, the first pulsing valve V1 allows constant first inert gas flow through the first pulsing valve V1 during purge, pulse, and idle phase. In certain embodiments, the second pulsing valve V2 opens simultaneously with a precursor pulse of the first pulsing valve V1 to minimize pressure drop in the buffer volume 180 during a precursor pulse. Advantageously, maintenance of the pressure difference across the first pulsing valve (and restriction R1 ) may be improved.

[0087] In certain embodiments, the second pulsing valve V2 remains open when entering the purge phase, after being open during a low vapor-pressure reactant pulse through the multi-leg first pulsing valve V1 , until a predetermined pressure level in the buffer volume is achieved. In certain embodiments, this is to recover the pressure in the buffer volume to a predetermined level during purge before the subsequent precursor pulses(s). Advantageously, pressure drops in the buffer volume due to a precursor pulse may be compensated.

[0088] In certain embodiments, the pulsing valve V2 prevents backflow of the evaporated precursor and / or the second inert gas flow during idle phase. In the idle phase, the first pulsing valve is in purge configuration (i.e., precursor pulse blocked) and the pressure of the buffer volume 180 is at a predetermined level. That is, the apparatus 100 is ready for another precursor pulse through the first pulsing valve V1 . In certain embodiments, the pressure in the buffer volume 180 is passively maintained without a need for constant and active pumping of the second inert gas from the second inert gas source 120b the second pulsing valve V2 preventing the backflow. In certain embodiments, the second pulsing valve V2 is fully open during maintenance purge. In certain embodiments, this is to enable inert gas flow to proceed unhindered through the second pulsing valve V2 to flush the gas lines 185, 195, 170.

[0089] The apparatus 100 comprises second flow control means 190 in the second inlet line 185 downstream of the second inert gas source 120b. In certain embodiments, the second flow control means 190 comprise a pressure controller. In certain embodiments, the second flow control means 190 comprise a second restriction R2, as shown in Figs. 2 and 3. In certain embodiments, the second flow control means 190 receives pressure data from within the buffer volume 180 or the source vessel head space 155 and is configured to adjust the second inert gas flow to the second pulsing valve V2 accordingly. Preferably, the pressure and flow rate of the second inert gas flow to the second pulsing valve V2 is kept constant during substrate processing. In certain embodiments, the pressure in the buffer volume 180 is controlled by adjusting by the open-close timing cycle of the second pulsing valve V2.

[0090] In certain embodiments, the apparatus 100 optionally comprises a third pulsing valve V3 in the third inlet line 170. The third pulsing valve V3 is depicted here in connection to Fig. 1 a but it is applicable to other embodiments too. In certain embodiments, the third pulsing valve V3 is comprised by the precursor source vessel 150. The third pulsing valve V3 controls precursor flow from the headspace 155 along the third inlet line 170 towards the additional gas reservoir volume 175 in certain embodiments, and the first pulsing valve V1. Advantageously, pressure (dosage conditions) upstream of the first pulsing valve V1 may be further accurately controlled. In certain embodiments, the third pulsing valve V3 is a pneumatic valve.

[0091] Figs. 2-4 schematically show apparatuses 100 according to certain other embodiments in a pulse configuration. In addition to the teachings discussed below of embodiments according to Fig. 2-4, the embodiments according to Figs. 1 a-1d are also applicable here, and vice versa.

[0092] In embodiments according to Figs. 2-4, the buffer volume 180 of a substrate processing apparatus 100 comprises a head space 155 of the source vessel and the third inlet line 170 (and the short section of the second inlet line 185 downstream of the second pulsing valve V2). That is, in these embodiments, there is no additional gas reservoir volume 175 in the third inlet line 170 upstream of the first pulsing valve V1. In certain embodiments, the lack of additional gas reservoir volume enables more compact apparatus 100. Advantageously, the size of the apparatus and material use may be reduced.

[0093] In certain embodiments according to Fig. 2, the second flow control means 190 comprise a second restriction R2. In certain embodiments, the second flow control means 190 comprise only a second restriction R2. In certain embodiments, the restriction R2 comprises no moving parts. In certain embodiments, the second restriction R2 provides a flow restriction such that the second inert gas flow reaching the second pulsing valve V2 is constant. Thereby in certain embodiments, the open-close timing cycle of the second pulsing valve V2 regulates the second inert gas flow to the buffer volume 180. Advantageously, the second flow control means 190 may be kept simple and, for instance, need for maintenance may be reduced.

[0094] In certain embodiments, the second inert gas flow absolute pressure is identical to the absolute pressure of the first inert gas flow absolute pressure from the first inert gas source 120a.

[0095] In certain embodiments according to Fig. 3, the second inlet line 185 is connected directly to the third inlet line 170, which is the connected to the source volume 150 at one end and to the first pulsing valve V1 at another end. That is, different from the embodiments according to Figs. 1 -2, in certain embodiments, the second inert gas flow does not enter the buffer volume 180 through the source vessel head space 155. Regardless, in certain embodiments according to Fig. 3, the second inert gas flow increases the pressure in the buffer volume 180 (the buffer volume 180 comprising head space 155, the third inlet line 170 and the short section of the second inlet line 185 downstream of the second pulsing valve V2). Consequently, in certain embodiments, the apparatus 100 lacks also the by-pass line 195. Accordingly, in certain embodiments the source vessel 150 has only one shut-off valve SV. In certain embodiments, the by-pass valve BV may be used to separate the second inlet line 185 from the third inlet line 170. Advantageously, less gas lines and valves may be needed, thus, reducing, e.g., risks of leakages. Also, the source vessel 150 may be more easily detached from the gas lines.

[0096] In certain embodiments according to Fig. 3, the apparatus 100 comprises a check valve 310. The check valve 310 allows fluid flow only to one direction, i.e., second inert gas flow towards the source vessel 150. Therefore, in certain embodiments, the pressure downstream of the check valve 310 is easily maintained and the backflow of the second inert gas flow and / or the low vapor-pressure precursor is effectively prevented. In certain embodiments, the check valve 310 provides a backup in case the backflow prevention at the second pulsing valve V2 fails. Advantageously, the operational reliability of the substrate processing apparatus 100 may be improved.

[0097] In certain embodiments according to Fig. 4, the apparatus 100 comprises a valve controller 420. In certain embodiments, the apparatus comprises a second pressure transducer 410 configured to monitor the pressure of the buffer volume 180. In certain embodiments, the second pressure transducer 410 is located in the head space 155. In certain embodiments, the valve controller 420 controls the second pulsing valve V2 based on a pressure data received from the second pressure transducer 410. In certain embodiments, control unit 510 (see Fig. 5) operates as the valve controller 420. In certain embodiments, the valve controller 420 uses a feedback loop, wherein a control algorithm is used to tune opening (magnitude and / or frequency) of the second pulsing valve V2 during the open cycle of the second pulsing valve V2 based on the detected pressure of the buffer volume 180 or the head space 155. In certain embodiments, the valve controller 420 is configured to identify that a predetermined pressure in the buffer volume is achieved and to instruct closing of the second pulsing valve V2 accordingly, for instance, during a purge phase. In certain embodiments, the valve controller 420 is a general-purpose computing device, such as a personal computer. In certain embodiments, the valve controller 420 is configured to control also the second flow control means 190 and, thus, the flow rate and pressure of the second inert gas flow arriving to the second pulsing valve V2.

[0098] Fig. 5 schematically shows an apparatus comprising a control unit according to certain embodiments. In certain embodiments, the control unit is a computer-based system configured to control the apparatus 100. In certain embodiments, the control unit 510 autonomously (without requiring user input) operates the apparatus 100 during substrate processing. That is, the substrate processing is automatically controlled by the control unit 510. In certain embodiments, a user defines the process(es) and parameters to be monitored and carried out by the control unit.

[0099] In certain embodiments, control unit 510 controls the first pulsing valve V1. That is, in certain embodiments the control unit 510 opens and closes the first pulsing valve according to (predetermined) open-close timing cycle of the first pulsing valve V1 . Therefore, the control unit 510, by controlling the first pulsing valve V1 , controls the release and dosing of precursor pulses through the first pulsing valve from third inlet line 170 to the first inlet line 130. In certain embodiments, the control unit 510 controls the second pulsing valve V2. In certain embodiments, the control unit controls the open-close timing cycle of the second pulsing valve V2 according to the open-close timing cycle of the first pulsing valve V1. In certain embodiments, the control unit 510 opens the second pulsing valve V2 at the same time as the first pulsing valve V1. This way, in certain embodiments pressure decrease in buffer volume 180 is minimized during precursor pulse (pulse phase) through the first pulsing valve V1.

[0100] In certain embodiments, the control unit opens the second pulsing valve V2 during pulse (at the same time with the first pulsing valve V1 ) and keeps the second pulsing valve V2 open during purge (after closing the first pulsing valve V1 ) until the pressure in buffer volume 180 is adjusted to a predetermined level. This way, in certain embodiments, the control unit 510 ensures that the pressure in buffer volume 180 is adjusted to a predetermined level during purge before each precursor pulse. Advantageously, the control unit 510 ensures stable and accurate precursor dosage during pulse. In certain embodiments, the control unit 510 closes the second pulsing valve V2 during purge in response to having adjusted the predetermined pressure level in the buffer volume 180. That is, the control unit 510 sets the apparatus to idle phase by closing the second pulsing valve V2 in response to having adjusted the pressure in the buffer volume to a predetermined level. Advantageously, the predetermined pressure level in the buffer volume 180 can be passively maintained because the closed second pulsing valve V2 prevents gas backflow. Therefore, constant active provision of inert gas through the second pulsing valve V2 to the buffer volume 180 is not required.

[0101] In certain embodiments, the control unit 510 opens the second pulsing valve V2 only during purge (i.e. , when the first pulsing valve V1 is closed). In other words, in certain embodiments the second pulsing valve V2 is closed during pulse. This way, a predetermined pressure level in buffer volume 180 can be reached before each pulse and, thus, dosage of subsequent pulses accurately controlled.

[0102] In certain embodiments, the control unit 510 controls the third pulsing valve V3.

[0103] In certain embodiments, the control unit 510 receives data from the flow control means (140, 190) and / or the pressure transducers 140b, 410 and, as a response, controls the inert gas flow(s) of the apparatus 100 to provide constant flow(s). In certain embodiments, the control unit 510 is connected to the inert gas source system. In certain embodiments, the control unit 510 controls the inert gas flow(s) in the apparatus 100.

[0104] Fig. 6 shows a flow chart of a method for controlling pulse dosage according to certain embodiments. The method may be implemented for instance in any embodiments of the substrate processing apparatus 100 described above. Details regarding the apparatus, applicable to the method, have already been discussed hereinabove with reference to the embodiments shown in Figs. 1-5.

[0105] The method comprises:

[0106] 610. Providing low vapor-pressure precursor 160 from a source vessel 150 to a buffer volume 180 upstream of a first pulsing valve V1 , wherein the first pulsing valve V1 controls precursor pulses from the buffer volume 180 to a processing chamber 110. The low vaporpressure precursor 160 constantly evaporates in a source vessel 150 to provide precursor 160 to the buffer volume 180. During purge and idle, evaporation of the precursor 160 accumulates precursor to the buffer volume for the next pulse. The buffer volume 180 aids in reducing pressure fluctuations during pulsing of the precursor 160 and maintaining the pressure difference across the first pulsing valve V1. In certain embodiments, during maintenance purge, the precursor source vessel 150 is separated from the rest of the apparatus 100 by closing shut-off valve(s) SV, SV1 , SV2 such that the evaporated precursor 160 does not exit the precursor source vessel 150 and any inert gas flow cannot enter the precursor source vessel.

[0107] 620. Providing inert gas flow to the buffer volume 180. In certain embodiments, the inert gas is N2 or Ar. However, other inert gases are possible too. In certain embodiments, the inert gas flow enables controlling the pressure in the buffer volume 180 more efficiently than based only on the evaporation kinetics of the low vapor-pressure precursor 160. In certain embodiments, inert gas is provided to the buffer volume 180 during pulse to decrease pressure drop in the buffer volume 180 during the pulse. In certain embodiments, inert gas is provided to the buffer volume between successive pulses to recover a predetermined pressure level in the buffer volume 180 during purge. In certain embodiments, inert gas is provided to the buffer volume 180 during both pulse and during pulse until a predetermined pressure level is reached. In certain embodiments, the apparatus 100 enters idle phase wherein providing the inert gas to the buffer volume 180 is stopped once a predetermined pressure level in the buffer volume 180 is reached during purge, i.e. the apparatus 100 is ready for the next pulse.

[0108] 630. Adjusting pressure in the buffer volume to a predetermined level during purge phase of a process cycle. In certain embodiments, the pressure conditions within the buffer volume 180 are controlled by controlling the inert gas flow to the buffer volume 180 during purge phase (when the first pulsing valve V1 is closed to prevent precursor pulses). Therefore, in certain embodiments, low vaporization kinetics (which effects the dosage) of the low vaporpressure precursor 160 are compensated by adjusting the pressure in the vessel head space 155 with the inert gas flow.

[0109] In certain embodiments, the second open-close timing cycle of the second pulsing valve V2 is coordinated with the first open-close timing cycle of the first pulsing valve V1 such that the pressure in the buffer volume 180 is adjusted to a predetermined level during purge for each successive pulse of the first pulsing valve. In certain embodiments, the pressure reduction during precursor pulses is further minimized by synchronizing opening of the second pulsing valve V2 with the first pulsing valve V1 during pulse phase. As a result, pressure fluctuations during substrate processing may be minimized and processing quality improved.

[0110] In certain embodiments, the second pulsing valve V2 follows the open-close timing cycle of the first pulsing valve V1 (i.e., open-close timing cycle of the second pulsing valve V2 is similar to the open-close timing cycle of the first pulsing valve V1 ). That is, in certain embodiments, the second pulsing valve V2 is open during pulse when the first pulsing valve V1 is open (and closed when the first pulsing valve V1 is closed). This way in certain embodiments, pressure drop in the buffer volume 180 during pulse is minimized.

[0111] In certain embodiments, the second pulsing valve V2 opens during pulse and remains open during purge until the pressure in the buffer volume 180 is adjusted to a predetermined level. This way, dosage and pressure profiles of successive pulses are accurately controlled. Advantageously, the pressure in the buffer volume 180 is adjusted to a predetermined level before each successive pulse through the first pulsing valve V1.

[0112] In certain embodiments, the second pulsing valve is closed during pulse (when the first pulsing valve V1 is open) and open during purge (when the first pulsing valve V1 is closed). That is, in certain embodiments, the open-close timing cycle of the second pulsing valve V2 is opposite to the open-close timing cycle of the first pulsing valve V1 . This way, in certain embodiments, the pressure in the buffer volume 180 is returned to a predetermined level during purge after the pressure has decreased during pulse. In certain embodiments, in response to achieving the predetermined pressure in the buffer volume 180 during, the second pulsing valve V2 is closed to prevent inert gas backflow and to maintain the pressure in the buffer volume 180 until the next pulse (idle phase).

[0113] In certain embodiments, both first pulsing valve V1 and second pulsing valve V2 are held fully open during the maintenance purge. This way, inert gas flow in the apparatus 100 is maximized.

[0114] Fig. 7 shows a flow chart of another method for controlling pulse dosage according to certain embodiments. Like the method of Fig. 6, the method may be implemented for instance in any embodiments of the substrate processing apparatus 100 described above. Also, the teachings and embodiments described above with respect to Figs. 1-5 are applicable herein, and vice versa.

[0115] Fig. 7 shows a method in an apparatus 100 hereinabove described for controlling low vaporpressure precursor 160 dosage to a processing chamber 110 wherein a multi-leg first pulsing valve V1 is configured regulate precursor 160 pulses to the processing chamber 110, and a second pulsing valve V2 is configured to regulate pressure in buffer volume 180 upstream of the first pulsing valve V1 by controlling an inert gas flow through a source vessel 150 to the buffer volume 180, the method comprising:

[0116] 710. Coordinating the open-close timing cycle of the second pulsing valve V2 with the openclose timing cycle of the first pulsing valve V1 such that:

[0117] 720. During a pulse phase, wherein the first pulsing valve V1 is open to allow a precursor pulse to the processing chamber 110, also opening the second pulsing valve V2 to provide inert gas flow to the buffer volume 180 minimize pressure drop in a buffer volume 180 during the pulse. Precursor pulse is followed by a purge phase. IN certain embodiments, the second pulsing valve V2 is opened and kept open at the same time as the first pulsing valve V1 , i.e., the pulsing valves have similar open-close timing cycles.

[0118] 730. During purge phase, wherein the first pulsing valve V1 is closed to prevent precursor pulse from entering the processing chamber 110, allowing inert gas flow through the second pulsing valve V2 until a predetermined pressure in the buffer volume is achieved. The second pulsing valve V2 is kept open or pulsed until the predetermined pressure is reached. Once the predetermined pressure is reached, the apparatus 100 is ready for a next pulse, or adapts an idle phase.

[0119] 740. Optionally, during idle phase, after having closed the first pulsing valve V1 to stop precursor pulse from entering the processing chamber 110 and after the predetermined pressure in the buffer volume has been achieved, entering idle phase by closing the second pulsing valve V2 to prevent precursor 160 and / or inert gas backflow from the buffer volume 180.

[0120] 750. Optionally, performing maintenance purge, by separating the source vessel from any gas flow by i) closing shut-off valves SV1 , SV2 and opening a by-pass valve BV, ii) opening both the first pulsing valve V1 and the second pulsing valve V2 to flush the gas lines with inert gas flow without the inert gas flow entering the source vessel 150.

[0121] Without limiting the scope and interpretation of the patent claims, certain technical effects of one or more of the example embodiments disclosed herein are listed in the following. A technical effect is improving substrate processing conditions. Further technical effect is reducing fluctuations in low vapor-pressure precursor pulses. Further technical effect is more accurate and reliable low vapor-pressure precursor dosing.

[0122] Various embodiments have been presented. It should be appreciated that in this document, words comprise, include, and contain are each used as open-ended expressions with no intended exclusivity.

[0123] The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments a full and informative description of the best mode presently contemplated by the inventors for carrying out the invention. It is however clear to a person skilled in the art that the invention is not restricted to details of the embodiments presented in the foregoing, but that it can be implemented in other embodiments using equivalent means or in different combinations of embodiments without deviating from the characteristics of the invention.

[0124] Furthermore, some of the features of the afore-disclosed example embodiments may be used to advantage without the corresponding use of other features. As such, the foregoing description shall be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.

Claims

CLAIMS1 . An apparatus (100) comprising: a processing chamber (110) for processing substrates; an inert gas source system; a first inlet line (130) connecting the inert gas source system to the processing chamber (110); a source vessel (150) for housing a low vapor-pressure precursor (160); a second inlet line (185) connecting the inert gas source system to a buffer volume (180) comprising a head space (155) of the source vessel (150); a third inlet line (170) connecting the source vessel (150) to the first inlet line (130) through the buffer volume (180) via a first pulsing valve (V1 ), wherein the apparatus (100) is configured to adjust pressure in the buffer volume (180) to a predetermined level during a purge phase of a process cycle.

2. The apparatus of claim 1 , wherein the first inlet line (130) is configured to provide a first inert gas flow to the processing chamber (110) and the second inlet line (185) is configured to provide a second inert gas flow to the buffer volume (180).

3. The apparatus (100) of any preceding claim, wherein the first pulsing valve (V1 ) has a first open-close timing cycle configured to control precursor dosage from the buffer volume (180) to the first inlet line (130) during the process cycle.

4. The apparatus (100) of any preceding claim comprising first flow control means (140) in the first inlet line (130) upstream of the first pulsing valve (V1 ) for controlling the first inert gas flow.

5. The apparatus (100) of claim 4, wherein the first inert gas flow is constant.

6. The apparatus (100) of any preceding claim, configured to enter idle phase in response to achieving the predetermined pressure level in the buffer volume (180) during purge phase.

7. The apparatus (100) of any preceding claim comprising a first restriction (R1 ) between the first pulsing valve (v1 ) and the buffer volume (180).

8. The apparatus (100) of any preceding claim, wherein the buffer volume (180) comprises an additional gas reservoir volume (175) configured to provide additional buffer volume.

9. The apparatus (100) of any preceding claim comprising more than one inert gas source (120a, 120b).

10. The apparatus (100) of any preceding claim, comprising a second pulsing valve (V2) in the second inlet line (185), the second pulsing valve (V2) being configured to control a second inert gas flow to the buffer volume (180) to enable the pressure in the buffer volume (180) to be adjusted to a predetermined level during purge phase of a process cycle.11 . The apparatus (100) of claim 10, wherein the second pulsing valve (V2) has a second open-close timing cycle coordinated with the first open-close timing cycle of the first pulsing valve (V1 ).

12. The apparatus (100) of claim 10 or 11 , wherein the second pulsing valve (V2) is configured to open during pulse of the first pulsing valve (V1 ).

13. The apparatus (100) of claim 12, wherein the second pulsing valve (V2) remains open when entering the purge phase after a reactant pulse through the first pulsing valve (V1 ) until a predetermined pressure level in the buffer volume (180) is achieved.

14. The apparatus (100) of any one of claims 10-13, comprising second flow control means (190) in the second inlet line (185) upstream of the second pulsing valve (V2) configured to control the second inert gas flow.

15. The apparatus (100) of claim 14, wherein the second flow control means (190) comprises a second restriction (R2).

16. The apparatus (100) of claim 14 or 15, wherein the second flow control means (190) comprises a pressure controller, wherein the pressure controller is configured to receive data from a pressure transducer (410) located in the buffer volume (180) to adjust the second inert gas flow to the second pulsing valve (V2).

17. The apparatus (100) of any one of claims 14-16, comprising a check valve (310) upstream of the second pulsing valve (V2).

18. The apparatus of any one of claims 14-17, wherein the second pulsing valve (V2) is closed in idle phase to prevent backflow from the source vessel (150), wherein in the idle phase the first pulsing valve (V1 ) allows the first inert gas flow to the processing chamber (110) but precursor pulse is blocked, and the pressure in the buffer volume (180) is at the predetermined level.

19. The apparatus (100) of any preceding claim comprising a control unit (510) configured to control the open-close timing cycles of the first and second pulsing valves (V1 , V2).

20. The apparatus (100) of claim 19, wherein the control unit (510) is configured to regulate the second pulsing valve (V2) based on a feedback loop, wherein a control algorithm is used to tune opening of the second pulsing valve (V2) during the open cycle of the second pulsing valve (V2) based on the detected pressure of the buffer volume (180).21 . A method for controlling dosage of a low vapor-pressure reactant (160) comprising: providing low vapor-pressure precursor (160) from a source vessel (150) to a buffer volume (180) located upstream of a first pulsing valve (V1 ), wherein the first pulsing valve (V1 ) controls precursor pulses to a processing chamber (110); providing an inert gas flow from an inert gas source system to the buffer volume (180), wherein the buffer volume (180) comprises a head space (155) of the precursor vessel (150); and adjusting the pressure in the buffer volume (180) to a predetermined level during purge phase of a process cycle.

22. The method of claim 21 , comprising providing a first inert gas flow to the processing chamber (110) and a second inert gas flow to the buffer volume (180), wherein the precursor pulses through the first pulsing valve (V1 ) are provided to the first inert gas flow.

23. The method of claim 22, wherein the first inert gas flow is constant during pulse and purge phases of the process cycle.

24. The method of claim 21 or 23 comprising controlling the second inert gas flow to the buffer volume (180) by a second pulsing valve (V1 ) located upstream of the buffer volume (180).

25. The method of claim 24 comprising coordinating the open-close timing cycle of the second pulsing valve (V2) with the open-close timing cycle of the first pulsing valve (V1 ).

26. The method of claim 25 further comprising, after having closed the first pulsing valve (V1 ) to stop precursor pulse to the processing chamber (110) and after the predetermined pressure in the buffer volume (180) has been achieved, entering idle phase by closing the second pulsing valve (V2) to prevent precursor and / or inert gas backflow from the buffer volume (180).

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