Gas treatment method

A gas processing method is described. A workpiece is mounted on a platform in a chamber on which a silicon oxide film is formed on a surface of the workpiece; HF gas and a NH3 gas, as reaction gases, are discharged onto the workpiece on the platform from a plurality of gas discharge holes of a shower plate; and a treatment for causing a reaction between the reaction gases and the silicon oxide film on the surface of the workpiece is performed. Subsequently, the reaction product resulting from the treatment is heated and removed by decomposition, whereby etching is performed. The shower plate is divided into a plurality of regions in correspondence with the workpiece, and the gas discharge holes in one or more of the regions are blocked to control a distribution of at least one of the HF gas and the NH3 gas.

TECHNICAL FIELD

The present disclosure relates to a gas processing method of performing a chemical oxide removal process using a mixture gas of hydrogen fluoride (HF) gas and ammonia (NH3) gas.

BACKGROUND

In recent years, in the process of manufacturing semiconductor devices, a process called chemical oxide removal (COR) has been highlighted as an alternative method to dry etching or wet etching for realizing a fine etching process.

A process of etching a silicon oxide film using the COR technique has been known (for example, see Patent Documents 1 and 2). Specifically, in a chamber maintained in a vacuum state, a hydrogen fluoride (HF) gas and an ammonia (NH3) gas are adsorbed onto a silicon oxide film (SiO2film) on a surface of a semiconductor wafer during the COR process. The gases react with the silicon oxide film to generate ammonium fluorosilicate ((NH4)2SiF6; AFS). The ammonium fluorosilicate is heated and thereby evaporated in the subsequent step so that the silicon oxide film is etched.

PRIOR ART DOCUMENTS

Patent Documents

In Patent Document 2, the HF gas and the NH3gas are introduced into the chamber through a shower head installed above the semiconductor wafer. However, in some cases, etching uniformity may be deteriorated due to the non-uniformity of distribution of these gases. In addition, there are also instances where an etching distribution needs to be actively controlled. However, when the gases are introduced through the shower head, it is difficult to control the etching distribution.

Therefore, the present disclosure provides some embodiments of a gas processing method capable of controlling an etching distribution when a silicon oxide film is etched by HF and NH3gases.

SUMMARY

That is, according to one embodiment of the present disclosure, there is provided a gas processing method in which an object to be processed having a silicon oxide film formed on a surface thereof is mounted on a mounting table in a chamber, an HF gas and an NH3gas are discharged as reaction gases onto the object to be processed mounted on the mounting table through a plurality of gas discharge holes of a shower plate installed above the mounting table corresponding to the object to be processed mounted on the mounting table. A process of causing a reaction of the HF gas and the NH3gas with the silicon oxide film on the object to be processed is performed, and thereafter a reaction product generated by the reaction is heated and removed by decomposition, thereby performing an etching process, wherein the shower plate is divided into a plurality of regions according to the object to be processed, and the gas discharge holes of any one or more of the plurality of regions are blocked to control a distribution of the HF gas and/or the NH3gas.

In the present disclosure, the shower plate may be concentrically divided into an inside region and an outside region, and the gas discharge holes of any one of these regions may be blocked to control a distribution of the HF gas and/or the NH3gas.

In addition, the shower head may be configured such that the HF gas is discharged through a plurality of first gas discharge holes provided at the shower plate and the NH3gas is discharged through a plurality of second gas discharge holes provided at the shower plate. In this case, any one or both of the first gas discharge holes and the second gas discharge holes of the shower plate may be blocked.

In some embodiments, the reaction is conducted at an internal pressure of the chamber at 50 to 2000 mTorr. In addition, in some embodiments, a distance from a bottom surface of the shower plate to the surface of the object to be processed on the mounting table is in a range of 50 to 150 mm.

DETAILED DESCRIPTION

Hereinafter, various embodiments of the present disclosure will be described with reference to the drawings.

FIG. 1is a view showing a schematic configuration of a processing system for performing a gas processing method according to one embodiment of the present disclosure. A processing system1includes a loading/unloading unit2for loading and unloading semiconductor wafers W (which can also be simply referred to as wafers), two load lock chambers (L/Ls)3installed adjacent to the loading/unloading unit2, PHT (Post Heat Treatment) processing apparatuses (PHTs)4respectively installed adjacent to the load lock chambers3and configured to perform a PHT process on wafers W, and COR processing apparatuses (CORs)5respectively installed adjacent to the PHT processing apparatuses4and configured to perform a COR process on respective wafers W. The load lock chamber3, the PHT processing apparatus4and the COR processing apparatus5are arranged along a straight line in the aforementioned order.

The loading/unloading unit2includes a transfer chamber (L/M)12having a first wafer transfer mechanism11installed therein to transfer wafers W. The first wafer transfer mechanism11includes two transfer arms11aand11beach configured to support a wafer W in a generally horizontal position. A mounting table13is installed at a lateral side in the longitudinal direction of the transfer chamber12. The mounting table13is configured such that, for example, three carriers C, each of which can accommodate a plurality of arranged wafers W, may be connected to the mounting table13. In addition, an orienter14is installed adjacent to the transfer chamber12and configured to optically detect misalignment of a wafer W by rotating the wafer W and to perform alignment thereof.

In the loading/unloading unit2, wafers W are supported by the transfer arms11aand11b. The wafers W are transferred to desired positions by the first wafer transfer mechanism11, while being moved linearly in the horizontal plane or moved up and down in the vertical direction. Further, the wafers W are loaded and unloaded among the carriers C on the mounting table13, the orienter14, and the load lock chambers3by the transfer arms11aand11bbeing moved back and forth.

Each of the load lock chambers3is respectively connected to the transfer chamber12with a gate valve16interposed therebetween. Each load lock chamber3has a second wafer transfer mechanism17installed therein to transfer wafers W. The load lock chamber3is configured to be vacuum exhausted to a predetermined vacuum level.

The second wafer transfer mechanism17has an articulated arm structure and a pick configured to support a wafer W in a generally horizontal position. In the second wafer transfer mechanism17, the pick may be positioned inside the load lock chamber3when the articulated arm is contracted, the pick may contact the PHT processing apparatus4when the articulated arm is extended, and the pick may contact the COR processing apparatus5when the articulated arm is further extended. Accordingly, a wafer W may be transferred among the load lock chamber3, the PHT processing apparatus4, and the COR processing apparatus5.

As shown inFIG. 2, each of the PHT processing apparatuses4includes a chamber20configured to be vacuum exhausted, and a mounting table23on which a wafer W is mounted inside the chamber20. A heater24is embedded in the mounting table23. The wafer W, on which a COR process has been performed, is heated so as to perform a PHT process for evaporating (subliming) a reaction product generated by the COR process. The chamber20is provided with a transfer port20aon a side of the load lock chamber3to transfer a wafer W between the chamber20and the load lock chamber3. The transfer port20ais configured to be opened and closed by a gate valve22. In addition, the chamber20has a transfer port20bprovided on a side of the COR processing apparatus5to transfer a wafer W between the chamber20and the COR processing apparatus5. The transfer port20bis configured to be opened and closed by a gate valve54. Further, a gas supply mechanism26is provided including a gas supply line25configured to supply the chamber20with an inert gas, such as nitrogen gas (N2), and an exhaust mechanism28including an exhaust line27configured to exhaust the gas from the interior of the chamber20. The gas supply line25is connected to a nitrogen gas supply source30. The gas supply line25is also provided with a flow rate adjustment valve31capable of opening and closing the gas supply line25and adjusting the supply flow rate of the nitrogen gas. The exhaust line27of the exhaust mechanism28is provided with an opening/closing valve32and a vacuum pump33.

As shown inFIG. 3, each of the COR processing apparatuses5includes an airtight chamber40. Inside the chamber40, a mounting table42is provided to mount a wafer W thereon in a generally horizontal position. In addition, the COR processing apparatus5is provided with a gas supply mechanism43configured to supply an HF gas, an NH3gas, and the like into the chamber40, and an exhaust mechanism44configured to exhaust the interior of the chamber40.

The chamber40is configured with a chamber main body51and a lid52. The chamber main body51includes a generally cylindrical sidewall portion51aand a bottom portion51b. The chamber main body51has an opened upper portion, wherein the opening is covered by the lid52. A gap between the sidewall portion51aand the lid52is sealed by a seal member (not shown), thereby securing airtightness inside the chamber40.

The sidewall portion51ais provided with a transfer port53to load and unload a wafer W to and from the chamber20of the PHT processing apparatus4. The transfer port53is configured to be opened and closed by a gate valve54.

The lid52includes a lid member55defining an outside of the lid52, and a shower head56fitted inside the lid member55to face the mounting table42. The shower head56includes a main body57having a cylindrical sidewall57aand an upper wall57b, and a shower plate58installed at a bottom portion of the main body57. A space defined by the main body57and the shower plate58is provided with a plate59in parallel with the shower plate58. A first space60ais defined between the upper wall57bof the main body57and the plate59. A second space60bis defined between the plate59and the shower plate58.

A first gas supply pipe71of the gas supply mechanism43is inserted to the first space60a. A plurality of gas passages61leading to the first space60aextend from the plate59to the shower plate58. These gas passages61lead to a plurality of first gas discharge holes62formed at the shower plate58. In the meantime, a second gas supply pipe72of the gas supply mechanism43is inserted into the second space60b. A plurality of second gas discharge holes63formed at the shower plate58are connected to the second space60b.

In addition, the gas supplied from the first gas supply pipe71to the first space60ais discharged into the chamber40through the gas passages61and the first gas discharge holes62. Further, the gas supplied from the second gas supply pipe72to the second space60bis discharged through the second gas discharge holes63.

The mounting table42has a generally circular shape in a plan view and is fixed to the bottom portion51bof the chamber40. A temperature adjuster65configured to adjust a temperature of the mounting table42is installed inside the mounting table42. The temperature adjuster65has a tube line, for example, in which a temperature control medium (e.g., water or the like) circulates. Thus, heat exchange with the temperature control medium flowing in the tube line is performed to adjust a temperature of the mounting table42. Accordingly, a temperature control of a wafer W on the mounting table42is achieved.

The gas supply mechanism43includes the first gas supply pipe71and the second gas supply pipe72described above. In addition, the gas supply mechanism43includes an HF gas supply source73and an NH3gas supply source74connected to the first gas supply pipe71and the second gas supply pipe72, respectively. The first gas supply pipe71is connected to a third gas supply pipe75, and the second gas supply pipe72is connected to a fourth gas supply pipe76. The third gas supply pipe75and the fourth gas supply pipe76are connected to an Ar gas supply source77and an N2gas supply source78, respectively. The first to fourth gas supply pipes71,72,75and76are provided with flow rate controllers79configured to open and close the passages and control their flow rates. Each flow rate controller79includes, for example, an opening/closing valve and a mass flow controller.

In addition, the HF gas and the Ar gas pass through the first gas supply pipe71, the first space60aand the gas passages61and are discharged into the chamber40through the first gas discharge holes62. The NH3gas and the N2gas pass through the second gas supply pipe72and the second space60band are discharged into the chamber40through the second gas discharge holes63.

Among the gases, the HF gas and the NH3gas are reaction gases. The HF gas and the NH3gas are not mixed until they are discharged from the shower head56but then mixed within the chamber40. The Ar gas and the N2gas are dilution gases. In addition, the chamber40is maintained at a predetermined pressure by introducing the HF gas and the NH3gas as reaction gases and the Ar gas and the N2gas as dilution gases into the chamber40at predetermined flow rates. At this time, the HF gas and the NH3gas react with a silicon oxide film formed on the wafer W, thereby generating ammonium fluorosilicate (AFS) as a reaction product.

As a dilution gas, the Ar gas or the N2gas may be used solely. Also, another inert gas may be used, or two or more kinds of Ar gas, N2gas and other inert gases may be used.

The exhaust mechanism44has an exhaust pipe82connected to an exhaust port81formed at the bottom portion5lb of the chamber40. In addition, the exhaust mechanism44has an automatic pressure control valve (APC)83configured to control an internal pressure of the chamber40and a vacuum pump84configured to exhaust the interior of the chamber40, which are installed at the exhaust pipe82.

For pressure gauges configured to measure the internal pressure of the chamber40, two capacitance manometers86aand86bare installed in the chamber40from the sidewall of the chamber40. The capacitance manometer86ais for high pressure measurement, and the capacitance manometer86bis for low pressure measurement.

The various kinds of components, such as the chamber40, the mounting table42and the like, which constitute the COR processing apparatus5, are made of Al. The Al material of the chamber40may be pure Al or one obtained by anodizing the inner surface thereof (the inner surface of the chamber main body51, the bottom surface of the shower head56, or the like). In the meantime, since the Al surface of the mounting table42is required to have high wear resistance, in some embodiments, the surface is anodized to form an oxide coating film (Al2O3) having high wear resistance at the surface.

As shown inFIG. 1, the processing system1includes a control unit90. The control unit90includes a controller having a microprocessor (computer) which controls the respective components of the processing system1. The controller is connected to a keyboard through which an operator performs a command input operation to manage the processing system1, a display which visually displays an operation status of the processing system1, and the like. The controller is connected to a memory part which stores a control program configured to implement various processes executed by the processing system1, such as the supply of the processing gas, the exhaust of the interior of the chamber40and the like in the COR processing apparatus5under the control of the controller; a control program configured to execute predetermined processes on respective components of the processing system1according to process conditions, i.e. a processing recipe; and/or various kinds of databases. The recipe is stored in a suitable memory medium of the memory part. Further, if needed, an arbitrary recipe may be called out from the memory part and may be executed by the controller. Thus, the desired processes of the processing system1are performed under the control of the controller.

Next, a gas processing method using such a processing system1will be described.

First, wafers W each having a silicon oxide film formed on a surface thereof are accommodated in a carrier C and then transferred to the processing system1. In the processing system1, in a state where the gate valve16at the atmospheric side is opened, one of the wafers W is transferred from the carrier C of the loading/unloading unit2to the load lock chamber3by any one of the transfer arms11aand11bof the first wafer transfer mechanism11. The wafer W is then delivered to the pick of the second wafer transfer mechanism17in the load lock chamber3.

Then, the gate valve16at the atmospheric side is closed to vacuum exhaust the interior of the load lock chamber3, and the gate valves22and54are opened. Then, the pick is extended to the COR processing apparatus5to mount the wafer W on the mounting table42.

Thereafter, the pick is returned to the load lock chamber3, and the gate valve54is closed to seal the interior of the chamber40. In such a state, a temperature of the wafer W on the mounting table42is adjusted to a predetermined target value (for example, 20 to 40 degrees C.) by the temperature adjuster65. The HF gas and the Ar gas are supplied to the shower head56from the gas supply mechanism43through the first gas supply pipe71and discharged into the chamber40from the first gas discharge holes62through the first space60aand the gas passages61. The NH3gas and the N2gas are supplied to the shower head56through the second gas supply pipe72and discharged into the chamber40from the second gas discharge holes63through the second space60b. In addition, any one of the Ar gas and the N2gas as dilution gases may be used.

Accordingly, the HF gas and the NH3gas are not mixed in the shower head56and are discharged into the chamber40. The COR process is performed on the wafer W by these gases.

That is, the silicon oxide film on the surface of the wafer W chemically reacts with molecules of the hydrogen fluoride gas and molecules of the ammonia gas, such that ammonium fluorosilicate (AFS), water, and the like are generated as reaction products to be maintained on the surface of the wafer W.

After such a process is completed, the gate valves22and54are opened. The processed wafer W on the mounting table42is taken by the pick of the second wafer transfer mechanism17and is mounted on the mounting table23in the chamber20of the PHT processing apparatus4. Then, the pick is returned back into the load lock chamber3, and the gate valves22and54are closed. While the N2gas is introduced into the chamber20, the wafer W on the mounting table23is then heated by the heater24. Accordingly, the reaction products generated by the COR process are heated, evaporated and removed.

In this way, since the PHT process is performed after the COR process, the silicon oxide film can be removed from the surface of the wafer W in a dry atmosphere. Thus, no water mark or the like is generated. Further, etching can be performed under non-plasma conditions, and so the process causes little damage. In addition, since the COR process stops the etching after a predetermined time elapses, an end point management thereof is unnecessary because no reaction progresses even if over-etching is preset.

However, in the COR process, if the HF gas and the NH3gas are introduced into the chamber40simply through the shower head56, a distribution of these gases may not be uniform. Thus, etching uniformity may be deteriorated in some cases. In addition, there are also instances where an etching distribution needs to be actively controlled. However, there was no means for adjusting a gas distribution in such a case.

Therefore, in this present embodiment, the shower plate58of the shower head56is divided into a plurality of regions corresponding to the wafer W. In addition, a distribution of the HF gas and the NH3gas is controlled by blocking the gas discharge holes62and63of any one or more of the plurality of regions.

For example, as shown inFIG. 4, the shower plate58is concentrically divided into an inside region58aand an outside region58b, and the distribution of the HF gas and the NH3gas is controlled by blocking the gas discharge holes62and63of any one of the regions.

Since the COR process is performed under non-plasma conditions, when the HF gas and the NH3gas are diffused in the chamber40, the movement of gas molecules is smaller than that under plasma conditions. Thus, a gas distribution in which a position of the gas discharge holes of the shower plate58is reflected can be formed. That is, the gas discharge holes can be partially blocked to decrease a gas concentration in a wafer region corresponding to the blocked region, thereby enabling a gas distribution at the wafer surface to be adjusted. Accordingly, an in-plane etching amount distribution of the wafer can be finely adjusted.

For example, when the gas discharge holes62and63of the inside region58aofFIG. 4are blocked, the gases are discharged only from the gas discharge holes62and63of the outside region58bas shown inFIG. 5A. Thus, a gas distribution of the surface of the wafer W immediately below the shower plate58is typically as shown inFIG. 6A. Contrarily, when the gas discharge holes62and63of the outside region58bare blocked, the gases are discharged only from the gas discharge holes62and63of the inside region58aas shown inFIG. 5B. Thus, a gas distribution of the surface of the wafer W immediately below the shower plate58is typically as shown inFIG. 6B. Therefore, as the gas discharge holes corresponding to a partial region of the shower plate58as described above are blocked, it is possible to adjust an in-plane gas distribution of the wafer. In addition, an in-plane etching amount distribution of the silicon oxide film on the wafer can be finely adjusted.

In this way, since the in-plane etching amount distribution of the wafer can be adjusted, in-plane etching uniformity can be improved. In addition, an etching amount distribution can also be controlled to a desired level.

A means for blocking the gas discharge holes need not be limited to any one means. For example, plugs may be inserted into the respective gas discharge holes62and63, the inside region58aor the outside region58bmay be covered together, or the like. In addition, the gas discharge holes62and63may be opened or closed by an actuator.

In order to control a gas distribution, in some embodiments, the chamber may have a high internal pressure, for example, 50 mTorr (6.7 Pa) or more. Further, in terms of the reaction, the internal pressure may be 2000 mTorr (266 Pa) or less.

Further, if a distance from the bottom surface of the shower plate58to the surface of the wafer W is too large, it is difficult to effectively adjust a distribution of the HF gas and the NH3gas due to diffusion of the gases. Thus, in some embodiments, the distance from the bottom surface of the shower plate58to the surface of the wafer W is 150 mm or less. In addition, since some degree of gas diffusion is needed in order to conduct the reaction of the HF gas and NH3gas with the silicon oxide film on the wafer surface uniformly, in some embodiments, the distance may be 50 mm or more.

Ranges of other conditions of the COR process may be as follows:

Processing Temperature: 10 to 80 degrees C., more specifically, 40 degrees or less

Flow Rate of HF Gas: 20 to 1000 sccm (mL/min)

Flow Rate of NH3Gas: 20 to 1000 sccm (mL/min)

Total Flow Rate of Ar gas and N2gas: 2000 sccm (mL/min) or less

Ranges of conditions of the PHT process are as follows:

Flow Rate of N2Gas: 500 to 8000 sccm (mL/min)

As described above, according to this embodiment, the shower plate is divided into a plurality of regions corresponding to the object to be processed, and the gas discharge holes of any one or more of the plurality of regions is blocked to control a distribution of at least one of the HF gas and the NH3gas. Thus, it is possible to finely control an in-plane etching amount distribution of the silicon oxide film on the object to be processed. For this reason, in-plane etching uniformity can be improved. In addition, an etching amount distribution can also be controlled to a desired level.

EXPERIMENTAL EXAMPLES

Next, experimental examples actually performed will be described.

Using the COR apparatus having the configuration shown inFIG. 3, COR processes were performed for the cases where the gas discharge holes of the inside region of the shower plate were blocked as shown inFIG. 5A(Inside Blockage), where the gas discharge holes of the outside region of the shower plate were blocked as shown inFIG. 5B(Outside Blockage), and where the gas discharge holes were not blocked (Standard). Then, AFS as a reaction product was removed by heat processing at the PHT processing apparatus. In addition, the distance between the bottom surface of the shower plate and the wafer surface, the COR process conditions, and the PHT process conditions were set to the above-described ranges.

FIG. 7is a view showing etching amount distributions in the diameter direction of a wafer in “Inside Blockage,” “Outside Blockage,” and “Standard” of Experimental Examples. As shown inFIG. 7, it was confirmed that the etching amount in the inside region could be adjusted to be small in “Inside Blockage” as compared to “Standard” and the etching amount in the outside region could be adjusted to be small in “Onside Blockage” as compared to “Standard.”

The present disclosure is not limited to the above-described embodiments and can be variously modified. For example, above describes that the shower plate is concentrically divided into the inside region and the outside region corresponding to a wafer, and a distribution of the HF gas and the NH3gas is controlled by blocking the gas discharge holes of any one of the regions. However, the number of regions may be three or more, and the divided shape of the regions is not limited to the concentric shape. That is, any type of configuration may be possible so long as the shower plate is divided into a plurality of regions corresponding to a wafer and the gas discharge holes of any one or more of the plurality of regions are blocked.

Further, the above embodiment describes a post mix type, in which the HF gas and the NH3gas are discharged from separate sets of gas discharge holes used as the shower head. Thus, both the sets of gas discharge holes in a predetermined region are blocked. However, only discharge holes corresponding to any one of the gases may be blocked. In addition, common gas discharge holes may be provided, and the HF gas and the NH3gas may be supplied at different timings.

In addition, although it has been described that the semiconductor wafer is used as the object to be processed, the object to be processed is not limited to the semiconductor wafer if it has an oxide film formed thereon.

EXPLANATION OF REFERENCE NUMERALS