JP5258241B2 - Method for cleaning a UV irradiation chamber - Google Patents

Description

  The present invention relates generally to semiconductor processing by ultraviolet (UV) radiation and cleaning of a UV radiation chamber for semiconductor processing, and more particularly to the cleaning of a light transmissive window provided in a UV irradiation chamber.

The UV processing apparatus has been generally used for a long time to modify substances to be processed by ultraviolet rays and to produce substances using photochemical reactions. Reduction of interlayer capacitance is indispensable for high-speed device and low power consumption as a result of miniaturization of wiring design and multi-layer wiring structure due to the recent high integration of devices. Low-k (low dielectric constant film) material is used to reduce the interlayer capacitance, but the mechanical strength (EM: Elastic modulus) decreases with the reduction of the dielectric constant. It is difficult to withstand stress. As a method for improving the above problem, a method of improving the mechanical strength by curing a low-k material by UV irradiation can be considered (for example, Patent Document 1 (US Pat. No. 6,759,098), Patent Document 2). (U.S. Patent No. 6,296,909) The low-k material shrinks and cures by UV irradiation, and the mechanical strength EM can be improved by 50 to 200%.
U.S. Patent No. 6,759,098 U.S. Patent 6,296,909

  On the other hand, as another method associated with the recent high integration of devices, as a method of obtaining various thin films formed by thermal CVD or PECVD by a method that is not damaged by heat or plasma, light using a photochemical reaction has been conventionally used. CVD is being studied.

  However, when it is intended to irradiate the object to be processed or the reaction space with these light energies, 1) it is necessary to control the pressure of the reaction space and the atmospheric gas, 2) the UV lamp is contaminated with the generated gas, 3) It is necessary to partition the UV lamp from the reaction space for reasons such as safely exhausting the generated gas. As the partition plate, a light transmission window made of synthetic quartz that transmits light energy is usually used.

  However, UV light, which is high energy, is likely to cause a decrease in transmittance due to adhesion of the material of the transmission window and deposits attached to the window material, and in a curing process in which a large amount of outgas (decomposed gas that generates an irradiated film) is generated. There was a problem that the maintenance cycle (the number of treatments / time until the transmission window was cleaned or replaced) had to be very short.

Conventionally, a cleaning method in which ozone is generated by introducing O ₂ into the reaction space and irradiating UV, and deposits are removed with the generated ozone, is generally used in a curing process in which a large amount of outgas is generated. Since a long time is required for cleaning, a more efficient method is desired.

In an embodiment of the present invention, as a cleaning method, O ₂ is activated by remote plasma or an ozone generator and then introduced into the chamber for cleaning. In one embodiment, the activated oxygen is further accelerated by an UV lamp and cleaned. Furthermore, in some embodiments, this cleaning method and conventional O ₂ + UV ozone cleaning may be used in combination.

In another aspect of the present invention, as a cleaning method with further improved efficiency, a cleaning gas containing fluorine is used instead of O _{2 in} the above method or as an additive gas using a remote plasma, and then activated in the chamber. To introduce. In this case, in one embodiment, a material having a high transmittance that does not corrode the transmission window by fluorine is selected. As such a material, CaF ₂ , MgF ₂ , BaF ₂ , Al ₂ O ₃ coating on crystals such as CaF ₂ , MgF ₂ , BaF ₂ , Al ₂ O ₃ or synthetic quartz can be used.

  To summarize the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not all such objects and advantages necessarily have been achieved by the specific embodiments of the present invention. Thus, one of ordinary skill in the art would, for example, allow the present invention to achieve or optimize one group of advantages or advantages taught herein without having to achieve the other objects or advantages taught or suggested herein. It will be appreciated that it will be embodied or implemented.

  Other aspects, features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments.

  These and other features of the invention are described below with reference to the drawings of preferred embodiments. These drawings are intended to illustrate the invention and not to limit it. The drawings are too simplified for illustration purposes and are not proportional.

  The invention will be further described with reference to specific embodiments, which are not intended to limit the invention.

  In one embodiment, the present invention provides a method for cleaning a UV irradiation chamber. The method includes (i) generating radical species of a cleaning gas outside the UV irradiation chamber after completing irradiation of the substrate with UV light transmitted through a light transmission window provided in the UV irradiation chamber; and ii) cleaning the light transmission window by introducing radical species into the UV irradiation chamber from the outside of the UV irradiation chamber.

  The UV irradiation process is disclosed in any suitable process, such as US Pat. No. 6,759,098 and US Pat. No. 6,296,909. It may be a process. This disclosure is fully incorporated herein by reference. Typically, this process involves a substrate (e.g., a semiconductor substrate) mounted on a susceptor provided in a UV irradiation chamber, and a light transmission provided between the UV light source and the susceptor in the UV chamber. Processing by irradiating the substrate with UV light through a window.

  In one embodiment, prior to the UV irradiation process, a film composed of Si, C, H, O, and optional N is formed on the substrate, for example, by PECVD, PEALD, PVD, or the like. In the above, the UV irradiation process is a film curing process. The UV irradiation process is not limited to the curing process. In one embodiment, the UV irradiation process is a photo-CVD process.

  This film is not limited, but is a low dielectric film. When the film formed on the substrate is cured in the UV irradiation chamber, a substantial amount of outgas is generated from the film as a result of the decomposition of the chemical structure in the UV irradiation chamber. This outgas consists of hydrocarbon species. The outgas accumulates on the surface of the inner wall of the UV irradiation chamber including the light transmission window. Accumulated outgas deposition prevents UV light from passing through the light transmission window, thereby reducing the efficiency of curing. Thus, in particular, the light transmissive window needs to be cleaned frequently.

  In one embodiment, cleaning gas radical species are generated outside the UV irradiation chamber by methods other than UV irradiation. Although the cleaning gas radical species can be generated by UV irradiation, it is difficult to obtain a considerable amount of radical species, although it depends on the wavelength of light and the intensity of light. For example, high pressure mercury lamps may generate ozone from oxygen on the order of several ppm to several tens of ppm. A Xe excimer laser may convert a few percent of oxygen to ozone. In one embodiment, radical species are generated in a remote plasma unit. If the cleaning gas is oxygen, an ozonizer or ozone generator may be used instead of the remote plasma unit. Externally excited species have higher energy than conventional UV irradiation and can clean the light transmission window more efficiently.

  In one embodiment, radical species are introduced from outside the UV irradiation chamber into the UV irradiation chamber, thereby cleaning the light transmission window. The cleaning gas may be oxygen gas. In one embodiment, the remote plasma unit converts as high as about 80% oxygen into ozone. However, the lifetime of ozone is short and some of the radicals are not maintained until they reach the UV irradiation chamber. Thus, in a preferred embodiment, radical species are further excited by irradiating the radical species with UV light through a light transmission window.

When a remote plasma unit (eg, ASTRON ™ manufactured by MKS) is used to excite oxygen gas, the cleaning process is controlled by controlling the pressure and flow within the UV irradiation chamber. In one embodiment, the pressure is 10 Toor or less (e.g., 1-7 Toor), the flow rate of oxygen gas is 0.1-10 slm (e.g., 0.3-1 slm), and an inert gas, e.g., Ar, He , Kr or Xe has a flow rate of 0.5 to 15 slm (for example, 1 to 5 slm; larger than the flow rate of oxygen gas), and a cleaning time of 5 to 1000 seconds (for example, 10 to 600 seconds, 50 to 50 seconds). 200 seconds). In the above, UV irradiation is preferably combined. In this case, UV light ^has an intensity of ^{1mW / cm 2 ~500mW / cm 2} ( ^{e.g., 100mW / cm 2 ~400mW / cm} 2), a wavelength of 100 to 1000 nm (e.g., 200 to 400 nm).

In one embodiment, the cleaning gas can be a gas containing fluorine in the molecule, such as NF ₃ , C ₂ F ₆ , and C ₃ F ₈ . The gas containing fluorine has high energy and can efficiently clean the light transmission window. On the other hand, however, the fluorine-containing gas can damage the light transmission window by corroding its surface. Usually, the light transmission window is made of synthetic glass (silicon oxide), and this synthetic glass is easily etched by a fluorine-containing gas. In a preferred embodiment, the light transmissive window may be composed of a material that is resistant to fluorine-containing gases. In one embodiment, light transmissive window _can be constituted by crystals of _{CaF 2, MgF 2, BaF 2} , or _Al 2 _{O 3.} In another embodiment, the light transmission window may be composed of synthetic quartz coated with CaF ₂ , MgF ₂ , BaF ₂ , or Al ₂ O ₃ . For example, CaF ₂ has a higher light transmission coefficient than SiO ₂ and is thus preferred.

UV irradiation can be further performed when a fluorine-containing gas is used as the cleaning gas, but in one embodiment does not need to be performed in a UV irradiation chamber. In one embodiment, the cleaning conditions are as follows. The pressure is 10 Toor or less (for example, 1 to 7 Toor), the flow rate of the fluorine-containing gas (for example, NF ₃ ) is 0.1 to 5 slm (for example, 0.5 to 1.5 slm), an inert gas, For example, the flow rate of Ar, He, Kr, or Xe is 1-15 slm (eg, 1-5 slm larger than the flow rate of the fluorine-containing gas), and the cleaning time is 5-1000 seconds (eg, 10-600 seconds, 50 to 200 seconds).

  In the above, oxygen gas and fluorine-containing gas may be used in combination as the cleaning gas.

  In one embodiment, the light transmissive window is used in a vacuum with a diameter of 110% to 150% (eg, 120% to 130%) of the diameter of the substrate (eg, 360 mm to 380 mm for a 300 mm diameter substrate). 10 mm to 30 mm (for example, about 20 mm). In one embodiment, the distance between the light transmission window and the substrate may be 5 mm to 30 mm (eg, 10 mm to 20 mm).

  In one embodiment, the present invention provides a method of processing a semiconductor by UV irradiation and cleaning a UV irradiation chamber for semiconductor processing. In this method, (i) a semiconductor substrate placed on a susceptor provided in a UV irradiation chamber is passed through a light transmission window provided between the UV light source and the susceptor in the UV irradiation chamber. (Ii) a space defined between the light transmission window and the susceptor from the outside of the UV irradiation chamber after the completion of the processing step. And a step of cleaning the light transmission window by introducing the light into the window. In the processing step, the UV light may have a wavelength of 100 nm to 500 nm (eg, 200 nm to 400 nm).

  The invention will now be described with reference to the drawings and preferred embodiments, which are not intended to limit the invention.

  In the present disclosure in which various conditions and / or structures are not particularly defined, those skilled in the art can easily determine such conditions and / or structures as a matter of ordinary practice in view of the present disclosure.

  FIG. 1 is a schematic view of a UV irradiation apparatus that can be used in an embodiment of the present invention. This apparatus is composed of a chamber capable of controlling the surroundings of atmospheric pressure from a vacuum and an ultraviolet light irradiation unit installed at the top of the chamber. That is, this apparatus includes a UV lamp 4, an irradiation window 2, a gas introduction port 3, a UV irradiation chamber 1, a heater table 8, an exhaust port 5 connected to a vacuum pump, and a load lock connected to the UV irradiation chamber. A chamber 7; In addition, if it is an apparatus which can implement UV irradiation, it will not be limited to this figure.

  In the UV irradiation apparatus, an ultraviolet light emitter 4 that emits light continuously and in a pulsed manner, a heater 8 that is installed in parallel and opposed to the light emitter, and an irradiation window that is opposed in parallel between the ultraviolet light emitter 4 and the heater 8. Glass 2 is disposed. The irradiation window 2 is for realizing uniform UV irradiation, is for blocking the reactor from the atmosphere and transmitting UV. A plurality of ultraviolet light emitters 4 in the ultraviolet light irradiation unit are arranged in parallel, for example in a tube shape, and the positions of the light emitters are appropriately arranged for the purpose of uniform illuminance as shown in FIG. A reflection plate 9 is provided so as to appropriately reflect the ultraviolet light from the ultraviolet light emitter to the thin film (such as an umbrella above the UV lamp), and the angle of the reflection plate 9 can make the illuminance uniform. It can be adjusted.

  In addition, as shown in the schematic diagrams of FIGS. 2 (a) and 2 (b), in this apparatus, the inside of the chamber 1 that can control the surroundings of atmospheric pressure from a vacuum via a flange 11 provided with an irradiation window glass 2 is provided. The substrate processing section is separated from the ultraviolet light emitting section that houses the ultraviolet light emitting body 4 that emits light continuously and in pulses. A gas introduction port 3 is connected to the flange 11, and a plurality of gas discharge ports are provided at regular intervals in the circumferential direction so that the gas is uniformly discharged from the circumferential direction toward the inside. That is, gas is introduced through the flange 11, and a plurality of gas inlets are provided, and their arrangement is symmetrically arranged to create a uniform processing atmosphere. The ultraviolet light emitter 4 can be easily removed and replaced.

Further, as shown in the schematic diagram of FIG. 4, the pressure in the substrate processing unit is adjusted by a pressure control valve 21 provided in the exhaust port 5. The ultraviolet light emitting section is also a sealed space, but is provided with an intake port and a discharge port (not shown) for purge gas (which is always purged with the atmosphere or N ₂ or the like).

Although the example of the process of an ultraviolet light irradiation process is shown below, this invention is not limited to these aspects. First, a gas selected within chamber _{1 Ar, CO, CO 2,} C 2 H 4, CH 4, H 2, He, Kr, Ne, N 2, O 2, Xe, alcohol-based gas and an organic gas The pressure is set to an atmosphere of about 0.1 Toor to atmospheric pressure (including 1 Torr, 10 Toor, 50 Toor, 100 Toor, 1000 Toor, and a value between the above values), and about 0 degree to about 650 degree (10 ° C., 50 Through a gate valve on the heater 8 set at a temperature of 100 ° C., 100 ° C., 200 ° C., 300 ° C., 400 ° C., 500 ° C., 600 ° C., and preferably between 300 ° C. and 450 ° C. A semiconductor substrate, which is an object to be processed, loaded from the load lock chamber 7 is placed, and the wavelength is passed from the ultraviolet light emitter 4 through an appropriate distance (Gap) (1 cm to 100 cm). 100nm to about 400nm (150nm, 200nm, 250nm, 300nm, 350nm, and includes a value between the numerical value, preferably about 200 nm) from the output of about 1 mW / cm ² ultraviolet light of about 1000mW / cm ² (10mW / cm ² , 50 mW / cm ² , 100 mW / cm ² , 200 mW / cm ² , 500 mW / cm ² , 800 mW / cm ² , and values between the above values) in a continuous or pulsed manner from about 1 Hz to about 1000 Hz ( The thin film on the semiconductor substrate is irradiated with ultraviolet light at 10 Hz, 100 Hz, 200 Hz, 500 Hz, and a value between the above values. The irradiation time is about 1 second to about 20 minutes (including 5 seconds, 10 seconds, 20 seconds, 50 seconds, 100 seconds, 200 seconds, 500 seconds, 1000 seconds, and numerical values between the above values). The inside of the chamber 1 is exhausted from the exhaust port 5.

  This semiconductor manufacturing apparatus performs this series of processes in an automatic sequence, and gas introduction, ultraviolet light irradiation, irradiation stop, and gas stop steps can be performed as processing steps.

  When outgas is generated from the thin film on the semiconductor substrate by ultraviolet irradiation, it adheres to, for example, an irradiation window glass made of synthetic quartz and the inner wall of the chamber. Dirt accumulated on the irradiation window absorbs ultraviolet rays and reduces the curing efficiency. Also, the dirt accumulated on the inner wall of the chamber peels off and causes particles.

Cleaning is performed to remove these stains. For example, O ₂ is used for cleaning, and it is ozonized with ultraviolet rays to react with and remove dirt substances. Since the proportion of O ₂ that is ozonated by UV is quite low, in some embodiments of the present invention, O ₂ is radicalized by a remote plasma unit before being introduced into the chamber, and ozone is ozonized to increase the efficiency of ozone generation. . FIG. 3 shows a schematic diagram in which the remote plasma unit 31 is connected to the UV chamber 1. The cleaning gas is introduced into the remote plasma unit 31 and excited to be introduced into the UV chamber 1.

On the other hand, in the case of curing of a film that generates deposits that are not decomposed by ozone or a large amount of deposits, when ozone alone cannot be sufficiently cleaned, NF ₃ or the like may be used as a cleaning gas in some embodiments of the present invention. it can. Specifically, NF ₃ is introduced and decomposed into a remote plasma unit (see FIG. 3) to generate fluorine radicals, and then introduced into the chamber, and the irradiation window and the inner wall of the chamber are decomposed and removed with the fluorine radicals.

  Although this fluorine radical has the effect of decomposing and removing dirt in the reactor, it has the side effect of eroding the irradiation window surface made of synthetic quartz and lowering the ultraviolet transmittance.

FIG. 5 shows the results of measuring how much light of which wavelength the irradiation window glass (thickness 20 mm) passes using a spectrophotometer. The used glass is synthetic quartz (SiO ₂ ) and CaF ₂ glass. In FIG. 5, first, the UV transmittance (%) of the irradiated glass is measured, and then the substrate (300 mm) on which the low-k film (SiCOH system) is formed is carried into the UV chamber and cured under the following conditions. Carried out.
Pressure: 1-100 Toor, introduced gas: N ₂ , temperature: 300-450 ° C., distance between substrate and irradiation window: 0.1-10 cm, UV wavelength: 100-400 nm, output: 5-400 mW / cm ² , irradiation Time: 60-600 seconds.

  After UV curing of the low-k film under the above conditions, the UV transmittance (%) of the irradiated window glass was measured again.

Next, the inside of the UV chamber is cleaned. The cleaning conditions were as follows.
Remote plasma unit: ASTRON (trademark), cleaning gas: NF ₃ , pressure in chamber: 1-10 Toor, cleaning gas flow rate: 0.5-2 slm, Ar gas flow rate: 2-5 slm, cleaning time: 1 minute.
After cleaning, the UV transmittance (%) of the irradiated window glass was measured again.

As a result, as shown in FIG. 5, synthetic quartz (SiO ₂ ) transmits 90% or more of UV having a wavelength of 200 nm or more in the initial state, but after UV curing the low-k film, the wavelength of 300 nm or less is transmitted. It was confirmed that the light transmittance was reduced by about 1-2%. When the NF ₃ cleaning by the remote plasma unit was performed for 1 minute, the transmittance was significantly reduced, and a decrease of 10% was confirmed with 200 nm light. Moreover, the cloudiness and roughness of the glass surface were also confirmed visually.

On the other hand, as shown in FIG. 5, as a result of conducting an experiment similar to SiO ₂ using a glass window made of CaF ₂ , when the irradiation window is made of CaF ₂ having fluorine resistance, erosion by fluorine is prevented and radicals of NF ₃ It was found that the cleaning effect can be improved by cleaning. This time CaF ₂ was used considering fluorine resistance, but CaF ₂ itself has an advantage that the transmittance is higher than that of SiO _{2 as a} whole. Specifically, the transmittance decreases by 92% to 94% in the initial state and about 1% after the low-k film is cured, and after the NF ₃ cleaning by the remote plasma unit for 1 minute, the initial state is maintained. It was confirmed that the transmittance was recovered (the transmittance was higher than the initial state after cleaning, which is considered to be due to the removal of the measurement error or the dirt adhering to the initial state due to the cleaning). No white turbidity or roughness of the surface was observed visually. Thus, fluorine resistance of CaF ₂ glass was confirmed.

  As described above, according to an aspect of the present invention, the cleaning of the UV irradiation window is performed using a remote plasma cleaning or a fluorine-based cleaning gas having a high cleaning performance using a fluorine resistant irradiation window. By using it, the cleaning speed of the UV chamber can be greatly increased.

  As will be appreciated by those skilled in the art, numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the shapes of the present invention are illustrative only and are not intended to limit the scope of the present invention.

It is a schematic diagram which shows the UV irradiation apparatus which can be used by one Embodiment of this invention. FIG. 2A is a schematic view showing a UV irradiation chamber that can be used in an embodiment of the present invention, and FIG. 2B is a top view of the UV irradiation chamber shown in FIG. It is a schematic diagram which shows the UV irradiation chamber with which the remote plasma unit which can be used by one Embodiment of this invention was attached. It is a schematic diagram which shows the UV irradiation chamber which can be used by one Embodiment of this invention. It is a graph which shows the relationship between UV transmission coefficient (%) and a wavelength (nm) in several examples.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 UV radiation chamber 2 Irradiation window glass 3 Gas introduction port 4 UV lamp 5 Exhaust port 6 LL arm 7 Load lock chamber 8 Heater table 9 Reflecting plate 11 Flange 21 Pressure control valve 31 Remote plasma unit

Claims (12)

A method of cleaning a UV irradiation chamber,
Generating radical species of the cleaning gas outside the UV irradiation chamber after completing the irradiation of the substrate with the UV light transmitted through the light transmission window provided in the UV irradiation chamber;
Cleaning the light transmission window by introducing radical species into the UV irradiation chamber from outside the UV irradiation chamber;
Further comprising further exciting the radical species by irradiating the radical species with UV light through the light transmission window;
The cleaning gas is oxygen gas,
A method characterized by that.   The method according to claim 1, wherein the cleaning gas is used in combination with a gas containing fluorine in the molecule. Light transmissive _{window, CaF 2, MgF 2, BaF} 2, or method according to configured claim 2 Crystallization of _Al 2 _{O 3.} The method according to claim 2, wherein the light transmission window is composed of synthetic quartz coated with CaF ₂ , MgF ₂ , BaF ₂ , or Al ₂ O ₃ .   The method according to claim 1, wherein the generating step includes a step of generating radical species by a method other than UV irradiation.   The method of claim 1, wherein the generating step comprises generating radical species in the remote plasma unit. A method of cleaning a semiconductor processing UV irradiation chamber while performing semiconductor processing by UV irradiation,
By irradiating the semiconductor substrate mounted on the susceptor provided in the UV irradiation chamber with UV light through a light transmission window provided between the UV light source and the susceptor in the UV irradiation chamber. The process of processing;
After the completion of the treatment step, cleaning the light transmission window by introducing radical species of the cleaning gas from the outside of the UV irradiation chamber into the space defined between the light transmission window and the susceptor;
Further comprising the step of further exciting the radical species by irradiating the radical species with UV light through the light transmission window;
The method, wherein the cleaning gas is oxygen gas.   The method according to claim 7, wherein the UV light has a wavelength of 200 nm to 400 nm.   The method of claim 7, wherein in the processing step, a low dielectric film is formed on the substrate.   The method according to claim 7, wherein the cleaning gas is used in combination with a gas containing fluorine in a molecule. The method according to claim 10, wherein in the processing step, the substrate is irradiated through a light transmission window constituted by crystals of CaF ₂ , MgF ₂ , BaF ₂ , or Al ₂ O ₃ . In the step of processing, _{substrate, CaF 2, MgF 2, BaF} 2, or method according to claim 10 which is irradiated through the light transmission window constituted by coated synthetic quartz in _Al 2 _{O 3.}

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