JP2008227082A - Optical element, exposure apparatus and manufacturing method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element in which the contamination of its surface is removed or prevented. <P>SOLUTION: This optical element is provided with a voltage source (105) for applying a bias voltage to the surface of the optical element, and an ammeter (107) for measuring an optical electron current generated in irradiating the surface of the optical element with a light. The optical element is configured so that the voltage of the voltage source is adjusted to change the optical electron current generated in irradiating the surface of the optical element with light. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical element for EUV (Extreme Ultraviolet) light, an exposure apparatus using the optical element, and a method of manufacturing a semiconductor device including a step of performing exposure transfer using the exposure apparatus. The present invention also relates to a substance specifying method for determining a component of a substance attached to the surface of an optical element for EUV light and a deterioration suppressing method for suppressing deterioration of the optical element for EUV light.

  In recent years, with the miniaturization of semiconductor integrated circuits, EUV (Extreme Ultraviolet) having a shorter wavelength (11 to 14 nm) is used instead of conventional ultraviolet rays in order to improve the resolution of an optical system limited by the diffraction limit of light. A projection lithography technique using light (extreme ultraviolet rays) has been developed (for example, Patent Document 1). This technique is recently called EUV lithography, and is expected as a technique capable of obtaining a resolution of 45 nm or less, which cannot be realized by conventional optical lithography using light having a wavelength of about 190 nm.

Since the refractive index of EUV light is close to 1 for most substances, a transmission-refractive optical element cannot be used as an optical element for EUV light. Therefore, as an optical element for EUV light, a multilayer film reflecting mirror in which a multilayer film is laminated on a substrate is used.
US Pat. No. 6,833,223

  When an optical element such as a multilayer film reflecting mirror is used for a long time in an exposure apparatus, particles adhere to the surface of the optical element, the surface of the optical element is oxidized, or a carbon film is generated on the surface of the optical element. Further, the substrate material of the optical element is deteriorated. When such a change occurs in the optical element, optical characteristics such as reflectance of the optical element deteriorate. When the optical characteristics of the optical element are deteriorated, the throughput of the exposure apparatus is reduced, the exposure stability is lowered, and exposure unevenness is caused.

  Accordingly, there is a need for an optical element that can suppress degradation, an exposure apparatus that uses the optical element, and a method for manufacturing a semiconductor device that includes a step of performing exposure transfer using the exposure apparatus. There is also a need for a substance identification method that determines the component of a substance that has adhered to the surface of an optical element, and a degradation suppression method that suppresses degradation of the optical element.

  An optical element according to a first aspect of the present invention includes a voltage source for applying a bias voltage to the surface of the optical element, and a photoelectron current generated when light is irradiated on the surface of the optical element. An ammeter. The optical element is configured to be capable of adjusting a voltage of the voltage source so as to change a photoelectron current generated when light is irradiated on the surface of the optical element.

  According to a second aspect of the present invention, a substance specifying method for determining a component of a substance attached to a surface of an optical element applies a bias voltage to the surface of the optical element while irradiating the optical element with light. The photoelectron current generated by the light applied to the optical element is measured while changing the bias voltage, and the relationship between the applied bias voltage value and the measured photoelectron current value is measured on the surface of the optical element. Including determining the components of the deposited material.

  The deterioration suppressing method for suppressing deterioration of an optical element according to the third aspect of the present invention applies a bias voltage to the surface of the optical element and irradiates the optical element while irradiating the optical element with light. Adjusting the bias voltage to suppress the photoelectron current generated by the light.

  According to the optical element of the present invention, the photoelectron current can be measured by an ammeter while changing the bias voltage applied to the surface of the optical element by the voltage source. According to the substance specifying method for determining the component of the substance attached to the surface of the optical element of the present invention, the component of the substance attached to the surface of the optical element is determined based on the relationship between the value of the applied bias voltage and the value of the measured photoelectron current. Can be determined. After the substance is identified by this method, the substance can be removed by implementing measures suitable for removing the substance. According to the deterioration suppressing method for suppressing deterioration of the optical element of the present invention, the bias voltage is applied to the surface of the optical element to suppress the emission of photoelectrons from the surface of the optical element, resulting in the emission of photoelectrons. Can be prevented.

  FIG. 1 is a diagram showing the relationship between the density of states of electrons and the energy level on the surface of an optical element. FIG. 1A is a diagram showing the relationship between the density of states of electrons and the energy level when no bias voltage is applied to the surface of the optical element. FIG. 1B is a diagram showing the relationship between the density of states of electrons and the energy level when a bias voltage (V) is applied to the surface of the optical element.

ここで、Ｅｂは表面物質のフェルミ準位から真空準位までのエネルギー（仕事関数）、Ｅｋは放出される光電子のエネルギー、ｅは電気素量である。 When EUV light having an energy of hv = 93 (electron volts) is applied while applying a bias voltage (V) to the surface of the optical element, the following relational expression is established.

Here, Eb is the energy (work function) from the Fermi level to the vacuum level of the surface material, Ek is the energy of the emitted photoelectron, and e is the elementary electric quantity.

  When the bias voltage V applied to the surface of the optical element is increased from zero, the energy Ek of the emitted photoelectrons decreases. In FIG. 1A, V = 0, and in FIG. 1B, Ek = 0.

とすると、図１から明らかなように、

が成立する。式（２）において、Ｅはエネルギーの固定値（常数）である。そこで、光学素子の表面に印加するバイアス電圧Ｖを変化させながら光電子電流Ｉを測定することによって、電子の状態密度関数

を求めることができる。具体的に以下の式（３）から、光電子電流Ｉの、バイアス電圧Ｖに対する微分値ｄＩ／ｄＶを求めることによって、電子の状態密度関数

を得ることができる。

ただし、電子の状態密度関数

は、ＥＵＶ光のエネルギー９３（電子ボルト）内に存在する伝導帯の状態密度となる。 The energy Ek of the emitted photoelectron can be measured as the photoelectron current I. Electron density of states function

Then, as is clear from FIG.

Is established. In the formula (2), E is a fixed value (constant number) of energy. Therefore, by measuring the photoelectron current I while changing the bias voltage V applied to the surface of the optical element, the electron density-of-state function

Can be requested. Specifically, by obtaining the differential value dI / dV of the photoelectron current I with respect to the bias voltage V from the following equation (3), the state density function of the electrons

Can be obtained.

However, the density of states function of electrons

Is the density of states of the conduction band existing in the energy 93 (electron volt) of EUV light.

  Here, photoelectrons generated by irradiation with EUV light have only a small energy, and the mean free path of electrons is as small as nanometers or less. Therefore, photoelectrons are only emitted from the surface of the optical element from a sub-nanometer depth, and the density of states of the electrons depends on the surface materials including those that are attached to the surface of the optical element or generated on the surface of the optical element. Value. Since the shape of the state density function of electrons varies depending on the elements such as oxides, carbon films, particles, and chemical bonding states, it can be distinguished by obtaining the state density function of electrons. Therefore, the substance on the surface of the optical element can be specified.

  FIG. 2 is a diagram illustrating an example of a change in the photoelectron current I with respect to a change in the bias voltage V. The substance on the surface of the optical element can also be specified from the shape of the photoelectron current I curve with respect to the bias voltage V without obtaining the differential value as described above.

  FIG. 3A is a diagram showing a configuration of the optical element 100 according to an embodiment of the present invention. The optical element 100 includes a substrate 101 and a multilayer film 103 formed thereon. A voltage source 105 and an ammeter 107 are connected in series between the surface of the multilayer film 103 and the ground point. Since the multilayer film 103 is a multilayer film in which silicon layers and molybdenum layers are alternately formed and is a conductor, an electric wire may be connected to the surface thereof. For example, a terminal may be provided in a metal housing outside the multilayer film (not shown in FIG. 3A), and a surface portion of the multilayer film may be extended on the terminal to connect an electric wire to the terminal surface. The voltage source 105 may be an electrometer that can be applied while adjusting a bias voltage value of about 100 (electron volts). The ammeter 107 only needs to be able to measure a nanoampere level current with a bias voltage applied.

  FIG. 3B is a diagram showing a configuration of an optical element 150 according to another embodiment of the present invention. The voltage source 105 is installed between the surface of the multilayer film 103 and the ground point. A plate 109 for capturing photoelectrons emitted from the surface of the multilayer film 103 is installed, and an ammeter 107 is installed between the following 109 and the grounding point. In the present embodiment, the current is measured by capturing photoelectrons emitted from the surface of the multilayer film 103.

  FIG. 4 is a flowchart illustrating a material identification method for determining a component of a material attached to the surface of an optical element according to an embodiment of the present invention. In the present embodiment, the optical element 100 shown in FIG. 3A or the optical element 150 shown in FIG. 3B may be used.

  In step S4010 of FIG. 4, a bias voltage is applied to the film surface of the optical element.

  In step S4020 in FIG. 4, the bias voltage applied to the film surface of the optical element is changed, the photoelectron current is measured, and a photoelectron current curve with respect to the bias voltage is obtained.

  In step S4030 of FIG. 4, a differential value of the photoelectron current with respect to the bias voltage is obtained.

  In step S4040 in FIG. 4, the state density function of electrons on the surface of the optical element is estimated from the differential value of the photoelectron current with respect to the bias voltage, and the substance on the surface of the optical element is specified based on the result.

  If the substance on the surface of the optical element can be specified, the specified substance can be removed. For example, if the substance on the surface of the optical element is an oxide film, it can be removed by introducing a reducing gas such as hydrogen into the exposure apparatus. Further, if the substance on the surface of the optical element is dirt or a carbon film, it can be removed by introducing an oxidizing gas such as oxygen into the exposure apparatus.

  FIG. 5 is a flowchart showing a deterioration suppressing method for suppressing deterioration of an optical element according to an embodiment of the present invention. In the present embodiment, the optical element 100 shown in FIG. 3A or the optical element 150 shown in FIG. 3B may be used. As described below, the deterioration of the optical element is caused by contamination on the surface of the optical element or deterioration of the substrate material of the optical element. In the present specification and claims, the “dirt on the surface of the optical element” includes oxides, carbon films, particles, and the like on the surface of the optical element.

  In step S5010 of FIG. 5, a bias voltage is applied to the film surface of the optical element.

  In step S5020 of FIG. 5, the bias voltage applied to the film surface of the optical element is adjusted so as to suppress the photoelectron current. As shown in FIG. 2, when the bias voltage is set to a certain value or more, the photoelectron current is suppressed.

  The photoelectrons emitted when EUV light is irradiated onto the optical element collide with the organic matter adsorbed on the optical element surface or the organic matter present in the vacuum, generate active species, and form a carbon film on the optical element surface. Will be generated. In addition, the photoelectrons collide with the opposing optical elements in the exposure apparatus to cause problems of deteriorating the substrate material, generating electrical noise, particles, and the like.

Moreover, the oxidation of the optical element surface by EUV light irradiation is
M → M ⁺ + e-
Caused by electron emission (oxidation reaction) of metals. Therefore, by applying a bias voltage to flow electrons, the reverse reaction can be promoted and the oxidation reaction can be suppressed.

  In this way, by applying a bias voltage or a modulation bias voltage to the optical element so as to suppress the photoelectron current, the photoelectron emission from the surface of the photoelectron is suppressed, and the surface of the optical element or the substrate material of the optical element is suppressed. Deterioration can be suppressed.

  FIG. 6 is a diagram showing a configuration of an EUV exposure apparatus according to an embodiment of the present invention.

  The EUV exposure apparatus includes an EUV light source 31, an illumination optical system 33, and a projection optical system 301.

  The EUV light 32 emitted from the EUV light source 31 becomes a substantially parallel light beam via a concave reflecting mirror 34 that acts as a collimator mirror, and enters an optical integrator 35 including a pair of fly-eye mirrors 35a and 35b.

  Thus, a substantial surface light source having a predetermined shape is formed in the vicinity of the reflective surface of the fly-eye mirror 35a, that is, in the vicinity of the exit surface of the optical integrator 35. The light from the substantial surface light source is deflected by the planar reflecting mirror 36 and then forms an elongated arc-shaped illumination area on the mask (reticle) M. Here, an aperture plate for forming an arcuate illumination region is not shown. The light reflected by the surface of the mask M is then reflected in turn by the multilayer reflectors M1, M2, M3, M4, M5, and M6 of the projection optical system 301 to form exposure light 1 on the surface of the mask M. An image of the pattern thus formed is formed on the wafer 2 (sensitive substrate) coated with the resist 3.

  Implementation of the present invention shown in FIG. 3A or FIG. 3B as an optical element such as a condensing reflecting mirror, a reflecting mirror 36 and reflecting mirrors M1, M2, M3, M4, M5, M6, etc., not shown in FIG. Optical elements according to the form can be used.

  In the EUV exposure apparatus according to the present embodiment, it is possible to identify and remove substances on the surface of the optical element and to suppress the emission of photoelectrons from the surface of the optical element. Therefore, since the optical characteristics of the optical element are maintained even when used for a long period of time, the EUV exposure apparatus according to the present embodiment uses the entire performance of the exposure apparatus such as throughput, exposure stability and uniform exposure performance for a long period of time. Is also maintained.

  Hereinafter, an example of an embodiment of a semiconductor device manufacturing method according to the present invention will be described.

  FIG. 7 is a flowchart showing an example of the embodiment of the semiconductor device manufacturing method of the present invention. The manufacturing process of this example includes the following processes.

(1) Wafer manufacturing process for manufacturing a wafer (or wafer preparation process for preparing a wafer)
(2) Mask manufacturing process for manufacturing a mask used for exposure (or mask preparation process for preparing a mask)
(3) Wafer processing step for performing necessary exposure processing on the wafer (4) Chip assembly step for cutting out chips formed on the wafer one by one and making them operable (5) Chip inspection step for inspecting the completed chips Each process further includes several sub-processes.

  Among these main processes, the main process that has a decisive influence on the performance of the semiconductor device is the wafer processing process. In this step, designed circuit patterns are sequentially stacked on a wafer to form a large number of chips that operate as memories and MPUs. This wafer processing step includes the following steps.

(1) A thin film forming process for forming a dielectric thin film to be an insulating layer, a wiring portion, or a metal thin film for forming an electrode portion (using CVD or sputtering)
(2) Oxidation step for oxidizing the thin film layer and wafer substrate (3) Lithography step for forming a resist pattern using a mask (reticle) to selectively process the thin film layer and wafer substrate (4) Resist Etching process (for example, using dry etching technology) that processes thin film layers and substrates according to patterns
(5) Ion / impurity implantation / diffusion process (6) Resist stripping process (7) Inspection process for inspecting processed wafers The wafer processing process is repeated as many times as necessary to produce semiconductor devices that operate as designed. To do.

  In the present embodiment, the EUV exposure apparatus according to the present invention including the optical element according to the present invention is used in the lithography process. Accordingly, a semiconductor device can be manufactured by performing a lithography process with high throughput, exposure stability, and uniform exposure.

  According to the optical element according to the embodiment of the present invention, the photoelectron current can be measured while changing the bias voltage applied to the surface of the optical element. As a result, it is possible to identify and remove substances on the surface of the optical element from the relationship between the bias voltage and the photoelectron current, or to adjust the bias voltage to suppress the photoelectron current and to suppress the photoelectrons emitted from the optical element surface. it can.

  According to the substance specifying method for determining the component of the substance attached to the surface of the optical element according to the embodiment of the present invention, the substance is attached to the surface of the optical element from the relationship between the applied bias voltage value and the measured photoelectron current value. It is possible to estimate the electron density of states function of a material and determine the components of the material. After the substance is identified by this method, the substance can be removed by implementing measures suitable for removing the substance.

  According to the deterioration suppressing method for suppressing deterioration of an optical element according to an embodiment of the present invention, a bias voltage is applied to the surface of the optical element, and the bias voltage is set so as to suppress a photoelectron current generated by light irradiated on the optical element. Can be adjusted. As a result, emission of photoelectrons from the surface of the optical element can be suppressed, and contamination of the surface of the optical element and deterioration of the substrate material of the optical element due to the emission of photoelectrons can be suppressed.

It is a figure which shows the relationship between the density of states of an electron and the energy level of the surface of an optical element. It is a figure which shows an example of the change of the photoelectric current with respect to the change of a bias voltage. It is a figure which shows the structure of the optical element by one Embodiment of this invention. It is a figure which shows the structure of the optical element by other embodiment of this invention. 3 is a flowchart illustrating a material identification method for determining a component of a material attached to a surface of an optical element according to an embodiment of the present invention. It is a flowchart which shows the deterioration suppression method which suppresses deterioration of an optical element by one Embodiment of this invention. It is a figure which shows the structure of the EUV exposure apparatus by one Embodiment of this invention. It is a flowchart which shows an example of embodiment of the semiconductor device manufacturing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100,150 ... Optical element, 101 ... Board | substrate, 103 ... Multilayer film, 105 ... Voltage source, 107 ... Ammeter

Claims (16)

A voltage source for applying a bias voltage to the surface of the optical element;
An ammeter for measuring a photoelectron current generated when the surface of the optical element is irradiated with light, and
An optical element configured to be capable of adjusting a voltage of the voltage source so as to change a photoelectron current generated when light is irradiated on the surface of the optical element.   The optical element according to claim 1, wherein the ammeter measures a photoelectron current flowing from the surface of the optical element.   The optical element according to claim 2, wherein the voltage source and the ammeter are arranged in series between the surface and a grounding point.   The optical element according to claim 1, wherein the ammeter measures a current by capturing photoelectrons emitted from the surface of the optical element.   The optical element according to any one of claims 1 to 4, wherein the light is EUV light.   An exposure apparatus comprising at least one optical element according to any one of claims 1 to 5.   A method for manufacturing a semiconductor device, comprising the step of performing exposure transfer using the exposure apparatus according to claim 6. A substance identifying method for determining a component of a substance attached to the surface of an optical element, wherein the optical element is irradiated with light,
Applying a bias voltage to the surface of the optical element, measuring the photoelectron current generated by the light irradiated to the optical element while changing the applied bias voltage,
A substance specifying method comprising: determining a component of a substance attached to the surface of the optical element from a relationship between a value of the applied bias voltage and a value of a measured photoelectron current.   By obtaining a differential value of the measured photoelectron current value I with respect to the applied bias voltage value V, and obtaining an electronic state density of a conduction band of a substance attached to the surface of the optical element from the differential value, 9. The substance identification method according to claim 8, wherein a component of the substance attached to the surface is determined.   A voltage source for applying a bias voltage to the surface and an ammeter for measuring a photoelectron current generated by irradiating the surface with light are arranged in series between the surface and a grounding point. The substance identification method according to claim 8 or 9.   The substance specifying method according to claim 8, wherein the light is EUV light. A deterioration suppressing method for suppressing deterioration of an optical element, while irradiating light on the optical element,
Applying a bias voltage to the surface of the optical element;
A method for suppressing deterioration of an optical element, comprising adjusting the bias voltage so as to suppress a photoelectron current generated by light applied to the optical element.   A voltage source for applying a bias voltage to the surface and an ammeter for measuring a photoelectron current generated by irradiating the surface with light are arranged in series between the surface and a grounding point. The method for suppressing deterioration of an optical element according to claim 12.   The method for suppressing deterioration of an optical element according to claim 12 or 13, wherein the light is EUV light.   The method for suppressing deterioration of an optical element according to claim 12, wherein contamination of the surface of the optical element is suppressed by suppressing a photoelectron current generated by light irradiated on the optical element.   The method for suppressing deterioration of an optical element according to any one of claims 12 to 14, wherein deterioration of a substrate material of the optical element is suppressed by suppressing a photoelectron current generated by light irradiated on the optical element.

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