Precursor vapor generation and delivery system with filters and filter monitoring system

A vapor delivery system for supplying vapor to a chamber in a plasma-enhanced chemical vapor deposition (PECVD) system includes a vapor supply that supplies vapor by vaporizing at least one liquid precursor in a carrier gas. A first path includes a first filter that filters the vapor flowing from the vapor supply to the chamber. At least one second path is parallel to the first path and includes a second filter that filters vapor flowing from the vapor supply to the chamber. A plurality of valves are configured to switch delivery of the vapor to the chamber between the first path and the second path.

FIELD

The present disclosure relates to vapor generation and delivery systems, and more particularly to vapor generation and delivery systems for chemical vapor deposition (CVD) systems.

BACKGROUND

Plasma-enhanced chemical vapor deposition (PECVD) is a type of plasma deposition that is used to deposit thin films from a gas state (i.e. vapor) to a solid state on a substrate such as a wafer. PECVD systems convert a liquid precursor into a vapor precursor, which is delivered to a chamber. PECVD systems may include a vaporizer that vaporizes the liquid precursor in a controlled manner to generate the vapor precursor.

SUMMARY

A vapor delivery system for supplying vapor to a chamber in a plasma-enhanced chemical vapor deposition (PECVD) system includes a vapor supply that supplies vapor by vaporizing at least one liquid precursor in a carrier gas. A first path includes a first filter that filters the vapor flowing from the vapor supply to the chamber. At least one second path is parallel to the first path and includes a second filter that filters vapor flowing from the vapor supply to the chamber. A plurality of valves are configured to switch delivery of the vapor to the chamber between the first path and the second path.

In other features, a vapor delivery system for supplying vapor to a chamber in a plasma-enhanced chemical vapor deposition (PECVD) system includes a vapor supply that supplies vapor by vaporizing at least one liquid precursor in a carrier gas. A diverter includes a first diverter valve that, when open, diverts the vapor away from the chamber, and a second diverter valve that, when open, diverts the vapor to the chamber. The carrier gas is supplied at a first time. Plasma is created in the chamber at a second time after the first time. The first diverter valve is open and the second diverter valve is closed at a third time, which is after the second time, when the at least one liquid precursor is supplied to divert the vapor away from the chamber. The first diverter valve is closed and the second diverter valve is open at a fourth time, after the third time, when the at least one liquid precursor is supplied to supply the vapor to the chamber.

DETAILED DESCRIPTION

A delivery system may be used to filter and controllably deliver vaporized precursor to a chamber in a plasma-enhanced chemical vapor deposition (PECVD) system. The delivery system may include a conduit, one or more valves and a filter to filter the vaporized precursor. Over time, the filter may become clogged and may not filter the vaporized precursor efficiently. It may be difficult to identify when the filter needs to be changed. In addition, changing the filter typically requires the PECVD system to be shut down. A precursor vapor generation and delivery system according to the present disclosure provides multiple paths for the flow of the vapor precursor. Accordingly, the flow of the vapor precursor can be changed from one or more paths to one or more other paths. For example, the precursor vapor generation and delivery system may switch the vapor precursor delivery path from a path with a clogged filter to a path with a clean filter and continue operation with little or no down time.

Referring now toFIG. 1, a precursor vapor generation and delivery system100is shown. The system100includes a heat exchanger102, a vaporizer104, two or more parallel vapor precursor delivery paths106(i.e. at least one redundant path) and a chamber108(as shown inFIG. 3). Each of the vapor precursor delivery paths106includes a filter110. The filter110may include a heating jacket for temperature control. Zero, one or more of the vapor precursor delivery paths106can be selected by a control module (described below inFIG. 3) using gate valves112. A diverter (not shown inFIG. 1) allows the vapor precursor to be diverted or supplied to the chamber108. Other valves (e.g. purge valves116and/or vacuum valves118) are used during a purge operation of the filters110. For example only, the purge operation may be used when changing from one type of precursor to another.

Pressure manometers120are used to monitor pressures in the vapor precursor delivery paths106. The control module (as shown inFIG. 3) monitors outputs of the pressure manometers120and generates a pressure differential. A filter clean/dirty status may be determined based on the pressure differential and one or more predetermined thresholds. As a result, the control module may be used to determine when the filter110in a particular path106needs to be changed. The control module may also use two or more different pressure differential thresholds depending upon the type of precursor that is being supplied.

By providing multiple paths, the flow of vapor precursor can be changed from one or more paths to one or more other paths very quickly if needed instead of shutting down the system100to change the filter. As a result, the precursor vapor generation and delivery system100may provide improved uptime. This is due in part to the ability of the precursor vapor generation and delivery system100to switch the vapor precursor delivery path from a path with a clogged filter to a path with a clean filter and subsequently continue operation. In addition, the paths from the vaporizer through the heat exchanger/filter to the chamber are heated by filter, conduit and/or valve heating units. More uniform heating reduces the incidence of particles in the system100.

Referring now toFIG. 2, multiple liquid precursors may be supplied to the vaporizer104. First and second liquid precursors are supplied via various conduits, pumps and valves to the vaporizer104. The liquid precursors enter the system100from a liquid precursor supply122. The first liquid precursor is supplied from the liquid precursor supply122to the vaporizer104via a flow controller/pump124-1and a conduit126-1. A flow meter128-1may be used to monitor the flow of the first liquid precursor. Similarly, the second liquid precursor is supplied from the liquid precursor supply122to the vaporizer104via a flow controller/pump124-2and a conduit126-2. A flow meter128-2may be used to monitor the flow of the second liquid precursor. A carrier gas is supplied the vaporizer104through a restrictor orifice130.

The conduit126-1may include a narrow portion at, for example,132-1. A diameter of the narrow portion132-1is smaller than a diameter of other portions of the conduit126-1. Consequently, pressure and velocity of the first liquid precursor flowing through the narrow portion132-1is increased. The increased pressure and velocity of the first liquid precursor reduces droplet size and intensifies the shearing effect of atomization. Similarly, the conduit126-2may include a narrow portion at, for example,132-2.

Referring now toFIG. 3, an exemplary implementation of the delivery system100is shown in further detail. The delivery system100inFIG. 3includes first and second paths140,142. When supplying vapor precursor via the first path140, valves V1and V3are open and the remaining valves V2and V4-V8are closed. Vapor precursor flows through the valve V1, filter F1and the valve V3to the chamber108. The first path140from vapor supply144to the108chamber is heated. A control module146actuates the valves V1-V8and monitors pressure manometers P1and P2to determine the pressure differential. A diverter valve (DV)148diverts flow from the paths140,142to either the chamber108or a vacuum pump150.

When the measured pressure differential exceeds a predetermined value, the control module146switches to the second path142. For example, the control module146may activate an indicator (e.g. on a display or other external user interface; not shown) to inform a user of the system100that the filter F1in the first path140is dirty. Accordingly, the user may interface with the system100(e.g. via the control module146or other inputs) to switch from the first path140to the second path142. Additionally, the control module146may be configured to automatically switch from the first path140to the second path142when the pressure differential exceeds the predetermined value.

When supplying vapor precursor via the second path142, the valves V2and V4are open and the remaining valves V1, V3, and V5-V8are closed. Vapor precursor flows through the valve V2, filter F2and the valve V4to the chamber108. The second path142from the vapor supply144to the chamber108is also heated. The control module146actuates the valves V1-V8and monitors the pressure manometers P1and P2to determine the pressure differential. When the measured pressure differential exceeds the predetermined value, the system100is switched back to the first path140.

One or more of the filters F1, F2may be changed when the pressure differential indicates that one of the filters F1, F2is dirty. For example, one of the filters F1, F2may be changed when the system100is next shut down for maintenance or another purpose. Alternatively, a user may wait until both filters F1, F2are dirty before shutting down the system100to change the filters F1, F2. The system100may be arranged such that while supplying vapor precursor via the first path140, the filter F2in the second path142can be changed, and while supplying vapor precursor via the second path142, the filter F1in the first path140can be changed. Accordingly, shutting down the system100prior to changing one of the filters F1, F2would not be required.

As can be appreciated, additional paths can be provided. Furthermore, vapor precursor can be supplied by two or more of the parallel paths140,142at the same time to increase flow rates. Furthermore, while the pressure manometers P1, P2as shown inFIG. 3are arranged at junctions between the vapor supply144and the first and second paths140,142and between the first and second paths140,142and the chamber108, pairs of pressure manometers can be arranged in each140,142to separately monitor the pressure differential in each path140,142. This may be desirable when multiple paths are used at the same time. In other words, a system100with three paths may use one, two or three paths at a given time. When supplying the vapor precursor with two paths140,142, one of the two paths140,142may have a clogged filter F1or F2. The path with the clogged filter can be replaced by the remaining path with a clean filter. Monitoring pressure on each path140,142allows the control module146to differentiate between the two operating paths140,142in this case.

A purge operation may be performed. For example only, the purge operation may be performed when changing from one vapor precursor to another and/or when a mixture of precursors changes (such as when a concentration changes). Generally, a dirty filter will be purged when the control module146switches to another path with a clean filter because the dirty filter is clogged. When purging one of the filters F1, F2, the valves V1, V2, V3and V4are closed. To purge the filter F2, the valves V8and V6are opened to allow purge gas to flow into the valve V8, backwards through the filter F2, and through the valve V6. In some implementations, opening of the valves V8and V6is alternated to build up and release the purge gas so that enhanced purging of the filter may be performed. In other words, the valve V8may be opened while the valve V6is closed to allow the purge gas to reach the filter F2and build up pressure. The vacuum pump150builds up vacuum as well. Then, the valve V8is closed and the valve V6is opened. A similar approach may be used to purge the filter F1.

Referring now toFIG. 4, delivery of multiple liquid precursors to the vaporizer104is shown. WhileFIG. 2shows the delivery of two liquid precursors, the system100may supply any number N of liquid precursors from supplies200-1,200-2, . . . ,200-N (referred to collectively as supplies200). Each of the liquid precursors may be supplied via pumps202-1,202-2, . . . ,202-N (referred to collectively as pumps202) and valves206-1,206-2, . . . ,206-N (referred to collectively as valves206). Flow meters208-1,208-2, . . . ,208-N (referred to collectively as flow meters208) may also be used to allow metering of the valves206to be controlled more precisely.

Some vaporizers do not atomize high flow liquid precursors such as tetraethyl orthosilicate (TEOS) effectively, thereby limiting process capabilities and leading to poor particle performance. Poor vaporization of TEOS based liquid precursor may occur during process steps in which plasma is not turned on. For example, a wafer that has been exposed to carrier gases like oxygen when decorated with other films (like ashable hard mask (AHM)) does not contribute adders. However, a wafer exposed to oxygen and TEOS when decorated with other films may lead to a significant number of adders.

Referring now toFIG. 5, an exemplary vaporizer250according to the present disclosure is shown. The vaporizer250includes an atomizer252and a heat exchanger/filter256. For example only, the heat exchanger/filter256may be implemented by a Turbo Vaporizer as manufactured by MSP Corporation, though other suitable heat exchanger/filters may be used. A restrictor orifice258may be arranged at an inlet260of the atomizer252. A carrier gas flows through the restrictor orifice258and exits at a high linear velocity. For example only, the carrier gas may have a linear velocity that is greater than 300 meters/second, although other velocities may be used. One or more liquid precursor inlets262of the atomizer252receive liquid precursor via liquid flow controllers (LFCs)264and valves266.

The drag of the high velocity gas on the liquid precursor provides a mechanism for atomization. The high velocity carrier gas transfers momentum to the liquid precursor, which causes a shearing effect. The shearing effect breaks the surface tension of liquid precursor and creates droplets. For example only, the droplets may have a diameter of 1-5 microns, although other larger or smaller droplet sizes may be used.

A thermal break or insulator270may be provided between the atomizer252and the heat exchanger/filter256. The thermal break270decouples thermal characteristics of the heat exchanger/filter256and the atomizer252. The heat exchanger/filter256heats the droplets so that the droplets vaporize. The heat exchanger/filter256includes, for example only, a band heater272. The filter (not shown) of the heat exchanger/filter256may be arranged to receive and filter the output of the heat exchanger/filter256. The filter has one or more membranes through which the vapor precursor passes. The output of the filter may form a nozzle274. An additional heater (not shown) may be provided to heat the vaporized precursor at the outlet of the filter.

The heat exchanger/filter256may include a plurality of channels that heat and recirculate the droplets to form vapor precursor. Some of the channels may recirculate back near an inlet280of the heat exchanger/filter256. Other channels may be directed towards the filter. The fine droplets are converted into vapor before reaching the filter.

Referring now toFIG. 6, an exemplary diverter300according to the present disclosure is shown. The diverter300includes an inlet302, first and second valves304,306and first and second outlets308,310. The first valve304of the diverter300may supply vapor precursor to a path leading to the chamber108. A second valve306of the diverter300may supply vapor precursor to a diverter path leading to the vacuum pump150. As can be appreciated, the paths may be connected in the opposite manner.

The first and second valves304,306of the diverter300are preferably high conductance (low resistance) vapor valves having a low pressure drop and a fast response time. For example only, the first and second valves304,306preferably have a response time that is less than 100 ms. In some implementations, the first and second valves304,306have a composite flow coefficient that is greater than approximately 0.80. In some implementations, the first and second valves304,306have a composite flow coefficient that is greater than approximately 0.87. The first and second valves304,306may also be heated during operation. In some implementations, the valves304,306operate at temperatures up to 150° C. In other implementations, the valves304,306operate at temperatures up to 250° C. The first and second valves304,306of the diverter300may be diaphragm valves made of stainless steel, although other types of valves and materials may be used.

Referring now toFIGS. 7A and 7B, timing of non-diverting320and diverting330operation, respectively, are shown. For example only, the precursor may be TEOS and the carrier gas may be oxygen (O2) and helium (He). As can be appreciated, other precursors and carrier gases can be used. InFIG. 7A, the carrier gas is supplied at time1, the TEOS is supplied to the chamber at time3and the plasma (RF) is started at time4. Pressure increases accordingly at time2. At time4, the He supplied in the carrier gas is stopped and only the O2 is supplied as the carrier gas. Subsequently, the TEOS is turned off after a first period and then the plasma is turned off a second period after the first period. However, TEOS is not diverted during turn on or after the bulk deposition step. Therefore, the TEOS continues to reach the chamber108and additional unwanted deposition occurs.

InFIG. 7B, the carrier gas is supplied at time1, the plasma is started at time3and the TEOS is supplied but diverted by the diverter300at least until the TEOS has an opportunity to reach steady state. Pressure increases accordingly at time2. At time4, the He supplied in the carrier gas is stopped and only the O2 is supplied as the carrier gas. After reaching steady state at time4, the diverter300supplies the TEOS to the chamber108. After a first period, the TEOS is turned off to the chamber108using the diverter300. Then, after a second period after the first period, the plasma is turned off. As will be described further below, unwanted deposition is reduced.

As can be appreciated, the timing of the first and second valves304,306of the diverter300can be adjusted to suit a particular application. For example, when transitioning from diverting the TEOS to supplying the TEOS in the chamber108, the second valve306of the diverter300(to the chamber108) can be opened a first predetermined overlap period before closing the first valve304of the diverter300(to the vacuum pump150). Likewise, when transitioning from supplying the TEOS in the chamber to diverting the TEOS, the first valve304of the diverter300(to the vacuum pump150) can be opened a second predetermined overlap period before closing the second valve306of the diverter300(to the chamber108).

Referring now toFIGS. 8A and 8B, adders on a conventional wafer360and on a wafer370processed according the present disclosure, respectively, are shown. In particular, Oxygen and TEOS exposed wafers after decorating with AHM film are shown for both standard system and the vapor delivery system described herein. While the standard system has approximately 800 adders at 0.085 um, the vapor delivery system according to the present disclosure has approximately 80 adders at 0.085 um. Thus, the vapor delivery system according to the present disclosure shows improved vaporization as compared to the standard system.

Referring now toFIG. 9, thickness is shown as a function of time for a conventional wafer380and a wafer390processed according to the present disclosure, respectively, after a bulk deposition step. Film interfaces are shaped by unwanted deposition that happens after bulk deposition is complete. This unwanted deposition happens during a step when the precursor liquid/vapor volume left in the system is at a lower concentration than in the bulk deposition step. This leads to films with different properties. Minimizing residue volume (liquid/vapor left to expel when liquid flow is turned off) has a direct impact on liquid-based PECVD processes.

In addition, flow “on” transient volume also affects wafer results. Flow “on” transient volume is defined as the volume of liquid that passes through a vaporizer prior to steady state flow. Without a diverter, the flow “on” transient volume causes marginal wafer to wafer uniformity and defects. Selectively diverting vapor downstream of the vaporizer minimizes residual unwanted deposition, smoothes operation at flow “on” and improves wafer-to-wafer uniformity.

FIGS. 10A and 10Bare charts illustrating adders for a conventional wafer400and a wafer410processed according to the present disclosure.FIGS. 10A and 10Bcompare in-film performance of ILDS and the vapor delivery system according to the present disclosure for 3500 A thick TEOS deposited using a first process where plasma is provided before TEOS delivery. While the standard system has approximately 20 adders @ 0.1 um, the vapor delivery system according to the present disclosure has less than 5 adders.

Referring now toFIG. 11, an exemplary CVD system is shown. The deposition of film is preferably implemented in a plasma enhanced chemical vapor deposition (PECVD) system. The PECVD system may take many different forms. The PECVD system includes one or more chambers or “reactors” (sometimes including multiple stations) that house one or more wafers and are suitable for wafer processing. Each chamber may house one or more wafers for processing. The one or more chambers maintain the wafer in a defined position or positions (with or without motion within that position, e.g. rotation, vibration, or other agitation). A wafer undergoing deposition may be transferred from one station to another within a reactor chamber during the process. Of course, the film deposition may occur entirely at a single station or any fraction of the film may be deposited at any number of stations.

While in process, each wafer is held in place by a pedestal, wafer chuck and/or other wafer holding apparatus. For certain operations, the apparatus may include a heater such as a heating plate to heat the wafer.

For example, a reactor500inFIG. 11includes a process chamber524, which encloses other components of the reactor and contains the plasma. The plasma may be generated by a capacitor type system including a showerhead514working in conjunction with a grounded heater block520. A high-frequency RF generator502, connected to a matching network506, and a low-frequency RF generator504are connected to the showerhead514. The power and frequency supplied by matching network506is sufficient to generate plasma from the process gas.

Within the reactor, a wafer pedestal518supports a substrate516. The pedestal518typically includes a chuck, a fork, or lift pins to hold and transfer the substrate during and between the deposition and/or plasma treatment reactions. The chuck may be an electrostatic chuck, a mechanical chuck or various other types of chuck.

The process gases are introduced via inlet512. Multiple source gas lines510are connected to manifold508. The gases may be premixed or not. Appropriate valving and mass flow control mechanisms are employed to ensure that the correct gases are delivered during the deposition and plasma treatment phases of the process.

Process gases exit chamber524via an outlet522. A vacuum pump526(e.g., a one or two stage mechanical dry pump and/or a turbomolecular pump) draws process gases out and maintains a suitably low pressure within the reactor by a close loop controlled flow restriction device, such as a throttle valve or a pendulum valve.

It is possible to index the wafers after every deposition and/or post-deposition plasma anneal treatment until all the required depositions and treatments are completed, or multiple depositions and treatments can be conducted at a single station before indexing the wafer.

Referring now toFIG. 12, a control module600for controlling the systems ofFIGS. 1,2and11is shown. The control module600may include a processor, memory and one or more interfaces. The control module600may be employed to control devices in the system based in part on sensed values. For example only, the control module600may control one or more of valves602, filter heaters604, pumps606, and other devices608based on the sensed values and other control parameters. The control module600receives the sensed values from, for example only, pressure manometers610, flow meters612, temperature sensors614, and/or other sensors616. The control module600may also be employed to control process conditions during precursor delivery and deposition of the film. The control module600will typically include one or more memory devices and one or more processors.

The control module600may control activities of the precursor delivery system and deposition apparatus. The control module600executes computer programs including sets of instructions for controlling process timing, delivery system temperature, pressure differentials across the filters, valve positions, mixture of gases, chamber pressure, chamber temperature, wafer temperature, RF power levels, wafer chuck or pedestal position, and other parameters of a particular process. The control module600may also monitor the pressure differential and automatically switch vapor precursor delivery from one or more paths to one or more other paths. Other computer programs stored on memory devices associated with the control module600may be employed in some embodiments.

Typically there will be a user interface associated with the control module600. The user interface may include a display618(e.g. a display screen and/or graphical software displays of the apparatus and/or process conditions), and user input devices620such as pointing devices, keyboards, touch screens, microphones, etc.

Computer programs for controlling delivery of precursor, deposition and other processes in a process sequence can be written in any conventional computer readable programming language: for example, assembly language, C, C++, Pascal, Fortran or others. Compiled object code or script is executed by the processor to perform the tasks identified in the program.

The control module parameters relate to process conditions such as, for example, filter pressure differentials, process gas composition and flow rates, temperature, pressure, plasma conditions such as RF power levels and the low frequency RF frequency, cooling gas pressure, and chamber wall temperature.

The system software may be designed or configured in many different ways. For example, various chamber component subroutines or control objects may be written to control operation of the chamber components necessary to carry out the inventive deposition processes. Examples of programs or sections of programs for this purpose include substrate positioning code, process gas control code, pressure control code, heater control code, and plasma control code.

A substrate positioning program may include program code for controlling chamber components that are used to load the substrate onto a pedestal or chuck and to control the spacing between the substrate and other parts of the chamber such as a gas inlet and/or target. A process gas control program may include code for controlling gas composition and flow rates and optionally for flowing gas into the chamber prior to deposition in order to stabilize the pressure in the chamber. A filter monitoring program includes code comparing the measured differential(s) to predetermined value(s) and/or code for switching paths. A pressure control program may include code for controlling the pressure in the chamber by regulating, e.g., a throttle valve in the exhaust system of the chamber. A heater control program may include code for controlling the current to heating units for heating components in the precursor delivery system, the substrate and/or other portions of the system. Alternatively, the heater control program may control delivery of a heat transfer gas such as helium to the wafer chuck.

Examples of sensors that may be monitored during deposition include, but are not limited to, mass flow control modules, pressure sensors such as the pressure manometers610, and thermocouples located in delivery system, the pedestal or chuck (e.g. the temperature sensors614). Appropriately programmed feedback and control algorithms may be used with data from these sensors to maintain desired process conditions. The foregoing describes implementation of embodiments of the invention in a single or multi-chamber semiconductor processing tool.