Internally heated porous filter for defect reduction with liquid or solid precursors

A heated filter assembly for heating gas supplied to a substrate processing system includes a housing defining a cavity, an inner surface and an outer surface. A filter element is arranged inside the cavity of the housing with an outer surface thereof in a spaced relationship relative to the inner surface of the housing. A heat transfer element is arranged inside of the filter element and includes an outer surface and an inner cavity. A plurality of projections is arranged on the outer surface of the heat transfer element in direct physical contact with an inner surface of the filter element. A plurality of portions is arranged on the outer surface of the heat transfer element, is spaced from the inner surface of the filter element and is located between the plurality of projections.

FIELD

The present disclosure relates to substrate processing systems, and more particularly to filters for filtering precursor delivered to substrate processing systems.

BACKGROUND

Substrate processing systems may be used to perform deposition and/or etching of film on a substrate such as a semiconductor wafer. Substrate processing systems typically include a processing chamber with a substrate support such as a pedestal, an electrostatic chuck, a plate, etc. A substrate such as a semiconductor wafer may be arranged on the substrate support. During chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes, a gas mixture including one or more precursors may be introduced into the processing chamber to deposit a film on the substrate. In some substrate processing systems, plasma may be used to activate chemical reactions. To obtain high quality film, it is important to deliver the precursor gas to the processing chamber at a desired temperature, a high uniformity, and with high purity. Gas mixtures are obtained by some combination of gases, vaporized liquids, and sublimed solids. Vaporized liquids, in particular, are almost always incompletely vaporized, and the resultant vapor contains liquid droplets of varying sizes. Unvaporized droplets cause wafer defects.

Heated filters may be used to heat and filter the precursor gas before delivery to the processing chamber. In addition, the heated filter can also prevent the unvaporized liquid droplets from entering the chamber due to pore size. Heated filters typically use one or more filter elements that are arranged inside a filter housing. An external heater jacket may be arranged around the filter housing to heat the filter element. When heating the filter element, heat travels through the filter housing to the center of the filter via convection or conduction. The mean heat conduction path for a typical heated filter is approximately 10″ through a 1/16″ porous wall, which also has a much lower thermal conductivity than its solid analogue. In addition, usually there is no direct conductive path from the filter element to the temperature monitoring and control system.

When using this heated filter arrangement, there is a large heating time lag due to the lack of direct contact between the heater and the temperature monitoring and control system. The time lag causes large temperature swings. Too much heat may cause thermal decomposition of precursors while too little heat may cause precursor condensation.

The filters are prone to clogging due to byproducts of decomposition clogging pores of the filter elements. The filters are also prone to clogging due to droplets diffusing through the filter element by capillary action and when the filter element cannot provide enough heat to vaporize the droplets. Other challenges include incomplete purging of atmospheric moisture due to poor and lagging thermal control, which increases clogging. Currently, the filter needs to be purged for 48 hours with inert gas prior to introducing precursor.

Additionally, it is difficult to maintain the required operating temperature as gases expand and cool down. When the gases cool down, heat is removed from the filter and the likelihood of precursor condensation increases. Furthermore, it is difficult to compensate for cold spots as droplets strike the filter element and remove heat.

SUMMARY

A heated filter assembly for heating gas supplied to a substrate processing system includes a housing defining a cavity, an inner surface and an outer surface. A filter element is configured to filter the gas and includes an inner surface and an outer surface. The filter element is arranged inside the cavity of the housing with the outer surface thereof in a spaced relationship relative to the inner surface of the housing. A heat transfer element is arranged inside of the filter element and includes an outer surface and an inner cavity. A plurality of projections is arranged on the outer surface of the heat transfer element in direct physical contact with the inner surface of the filter element. A plurality of portions is arranged on the outer surface of the heat transfer element, is spaced from the inner surface of the filter element and is located between the plurality of projections.

In other features, a heater is arranged in the inner cavity of the heat transfer element. The filter element comprises a porous metal filter. The plurality of projections of the heat transfer element includes axially elongated projections. The plurality of portions of the heat transfer element includes axially elongated scalloped portions.

In other features, an end cap is arranged adjacent to first ends of the housing and the filter element. The end cap is configured to maintain the spaced relationship between the housing and the filter element. The housing includes a gas inlet in fluid communication with a cylindrical space between the inner surface of the housing and the outer surface of the filter element. The end cap includes a gas outlet in fluid communication with the inner surface of the filter element.

In other features, the heat transfer element includes a body portion and a flanged portion extending from an end of the body portion. The heat transfer element and the housing abut the flanged portion of the heat transfer element. The housing and the filter element are made of a heat conducting material.

In other features, a secondary heat transfer element includes a heater that is attached to the outer surface of the housing. The heater of the secondary heat transfer element comprises a heater cartridge.

In other features, the housing, the filter element and the heat transfer element have generally cylindrical cross-sections. The heat transfer element includes a bore configured to receive a thermocouple.

In other features, the gas enters the gas inlet, passes through the filter element and is directed between the plurality of projections along the plurality of portions to the gas outlet.

In other features, the heater of the heat transfer element comprises a heater cartridge. A cylindrical space is defined between the outer surface of the filter element and the inner surface of the housing.

DETAILED DESCRIPTION

The heated filter according to the present disclosure is able to stay at a much more uniform and stable temperature during operation. As a result, the heater provides more uniform heating of precursor gas supplied to a substrate processing system and improved defect reduction. The heated filter provides dynamic monitoring and control of the temperature of the filter element as operating conditions change with very small time lag. The heated filter includes a heat transfer element that connects the thermal mass of the filter element directly to both the heater and a temperature monitoring and control system. As a result, the heat from the heater has a direct and very short path to the filter element (in some examples, less than 0.5″). In addition, there is no significant geometrical limitation on maximum heat flux. As a result, the filter element can provide enough heat to stay at the operating temperature while also providing enough heat to vaporize impinging droplets and prevent clogging.

More particularly, the heater arranged in the heat transfer element has a short and direct heating path to the filter element. Most traditional heaters rely on heater jackets arranged on the outside of the housing and therefore have a very long heating path (>10″). The heated filter according to the present disclosure can quickly heat the filter element while preventing temperature overshoot. The heated filter also shortens purging, maintenance, and replacement times from days to hours. In addition, the filter element can be maintained at the desired temperature regardless of convection to cold gases or liquid droplets. The heated filter also has the ability to precisely control the temperature of the filter element in real time to reduce or prevent precursor decomposition and condensation.

Referring now toFIG. 1, an example of a substrate processing system10is shown. While the substrate processing system10inFIG. 1relates to PECVD or PEALD systems, the heated filter may be used in other processes requiring heated precursor gas. The substrate processing system10includes a processing chamber12. Gas may be supplied to the processing chamber12using a gas distribution device14such as showerhead or other device. A substrate18such as a semiconductor wafer may be arranged on a substrate support16during processing. The substrate support16may include a pedestal, an electrostatic chuck, a mechanical chuck or other type of substrate support.

A gas delivery system20may include one or more vapor/liquid sources22-1,22-2, . . . , and22-N (collectively vapor/liquid sources22), where N is an integer greater than one. Valves24-1,24-2, . . . , and24-N (collectively valves24), mass flow controllers26-1,26-2, . . . , and26-N (collectively mass flow controllers26), or other flow control devices may be used to controllably supply precursor, reactive gases, inert gases, purge gases, and mixtures thereof to a manifold30, which supplies the gas mixture to the processing chamber12. A heated filter31may be arranged between the manifold and the processing chamber12. Alternately, one or more heated filters31may be arranged between the MFC26and the manifold30. In some examples, one or more of the vapor/liquid sources22may include a heated ampoule including liquid or solid precursor. Carrier gas is supplied to the heated ampoule by a valve. Another valve supplies a mixture of the carrier gas and the precursor that is sublimated or evaporated. A thermocouple32may be connected to a controller40and used to control a temperature of the heated filter31using a heater described further below.

The controller40may be used to monitor process parameters such as temperature, pressure etc. (using sensors41) and to control process timing. The controller40may be used to control process devices such as the gas delivery system20, a pedestal heater42, and/or a plasma generator46. The controller40may also be used to evacuate the processing chamber12using a valve50and pump52.

The plasma generator46generates the plasma in the processing chamber. The plasma generator46may be an inductive or capacitive-type plasma generator. In some examples, the plasma generator46may include an RF power supply60and a matching and distribution network64. Alternately, microwave power may be used to generate the plasma. While the plasma generator46is shown connected to the gas distribution device14with the pedestal grounded or floating, the plasma generator46can be connected to the substrate support16and the gas distribution device14can be grounded or floating. While plasma is generated between the showerhead and the pedestal inFIG. 1, remote plasma may be used.

Referring now toFIGS. 2 and 3, the heated filter31is shown in additional detail. The heated filter31includes an inlet110and an outlet114. The heated filter31may include an inlet adapter120including one or more inlet fittings124. The heated filter31further includes a housing130. In some examples, the housing130has a cylindrical shape. An end cap131is arranged at one end of the housing130and includes a bore133corresponding to the outlet114. The heated filter31further includes a filter element134connected at one end to the end cap131. A radially outer surface of the filter element134is spaced from a radially inner surface of the housing130define a space132therebetween. Precursor gas is delivered into the space132via the inlet110.

A heat transfer element138is inserted into a cavity defined inside a radially inner surface of the filter element134. The heat transfer element138extends substantially the same length as the filter element134. In some examples, the heat transfer element138may be “T”-shaped. The heat transfer element138may have a cylindrical body and an end portion including a flange that extends radially outwardly. A radially outer surface of the heat transfer element138may include a plurality of elongated scalloped surfaces or portions142(as can be seen inFIG. 3) that define a space146between the filter element134and the heat transfer element138. Elongated raised portions148of the heat transfer element138(as can be seen inFIG. 2) extending axially between the plurality of scalloped portions142are in direct contact with the radially inner surface of the filter element134to provide heat transfer as will be described further below.

A first bore160extends in an axial direction at a radial center of the heat transfer element138to allow a heater162such as a cartridge heater to be inserted into the bore to heat the heat transfer element138. A connection164may be provided to control the heater162. A second bore165likewise extends in an axial direction spaced from the radial center of the heat transfer element138to allow the thermocouple32or temperature sensor to be inserted into the heat transfer element138to determine a temperature of the heat transfer element138.

An outer heat transfer element166may be connected to a radially outer surface of the housing130. A first bore168may be provided in the outer heat transfer element166to receive a heater169(with connector171) to heat the housing130. In some examples, the heater169is a cartridge heater. A thermocouple (not shown) may also be provided to determine a temperature of the heat transfer element166. An outlet adapter170including one or more outlet fittings174may be used to connect the heated filter31to the processing chamber of the substrate processing system.

During operation, precursor gas flows through the inlet110and into the space132. The precursor gas flows through the filter element134into the plurality of scalloped portions142. The precursor gas flows along the scalloped portions142to the outlet114. The temperature of the heated filter31is controlled in a uniform manner by heating the heat transfer element138using the heater162. The heat transfer element138is in direct contact with the filter element134via the raised portions148. More particularly, the raised portions148extend axially substantially the entire length of the filter element134to provide uniform heating of the filter element134. Likewise, the temperature of the housing130may be controlled in a uniform manner by the heater169.

Referring now toFIGS. 4-6, the heat transfer element138is shown in further detail. InFIGS. 4 and 5, the heat transfer element138may have a “T”-shaped cross-section with a cylindrical body portion200that extends substantially the same length as the filter element134and an end portion204. In some examples, the end portion204includes an inner cylindrical surface214(adjacent to the cylindrical body portion200) for receiving one end of the filter element134and a flanged portion216that projects radially outwardly from the cylindrical body portion200. InFIG. 6, the raised portions148are shown extending outwardly to a radially outer surface of the cylindrical body portion200at a plurality of locations (e.g.148-1,148-2, . . . ) to provide physical contact with the radially inner surface of the filter element134to provide heat transfer. In some examples, there are N scalloped portions142and N raised portions148in contact with the radially inner surface of the filter element134. In some examples, N is equal to 6, although N may be greater than 3, 4, 5, etc.

Referring now toFIGS. 7 and 8, additional details relating to the heat transfer element138are shown at opposite ends of the heated filter31, respectively. InFIG. 7, the scalloped portions142of the heat transfer element138terminate adjacent to the inner cylindrical surface214near an end of the filter element134. The inner cylindrical surface214locates and maintains a position of one end of the filter element134. In some examples, an outer diameter of the inner cylindrical surface214is substantially equal to an inner diameter of the filter element134. An end of the housing130may be welded or otherwise attached to the flanged portion216of the heat transfer element138.

InFIG. 8, the end cap131is shown to include a circular slot240on an inner surface thereof for receiving the opposite end of the filter element134. The circular slot240locates and maintains a position of the opposite end of the filter element134. The end cap131may be welded or otherwise attached to an opposite end of the housing130. An end portion242of the heat transfer element138is spaced from the end cap131to provide a cavity244adjacent to the outlet114. The precursor gas flowing in the space146flows to the cavity244and through the outlet114.

In some examples, the filter element134is a porous metal filter. In some examples, the housing130, the end cap131and/or the heat transfer element138are made of a heat conducting material such as metal. In some examples, the housing130and the end cap131are made of stainless steel and the heat transfer element138is made of aluminum, although other materials may be used.

The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.” It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure.

The controller may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces that are connected to a local area network (LAN), the Internet, a wide area network (WAN), or combinations thereof. The functionality of any given controller of the present disclosure may be distributed among multiple controllers that are connected via interface circuits. For example, multiple controllers may allow load balancing. In a further example, a server (also known as remote, or cloud) controller may accomplish some functionality on behalf of a client controller.