JP2005022921A - Synthetic quartz glass optical member, manufacturing method thereof, optical system, exposure equipment and surface heating furnace for synthetic quartz glass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a synthetic quartz glass optical member which can be used in combination with an optical member comprising a calcium fluoride crystal or one or more synthetic quartz glass whose characteristics are not suitable for annealing treatment to decrease distribution of birefringence value of the calcium fluoride crystal or one or more synthetic quartz glass whose characteristics are not suitable for annealing treatment. <P>SOLUTION: The manufacturing method comprises a surface heating step wherein the surface of a synthetic quartz glass block is heated to 500-1,100°C at a heating rate of ≥300°C/hr so that the surface temperature becomes higher than the temperature at the center and a subsequent cooling step wherein the surface of the synthetic quartz glass block is cooled at a cooling rate of ≥50°C/hr and <300°C/hr. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００９８】
【表２】

【００９９】
なお、屈折率均質性の測定はオイルオンプレート法を用い、合成石英ガラスブロックの９５％の面積において行った。
【０１００】
複屈折値はヘテロダイン干渉法を用い、３０°刻みに同心円状に外周から５ｍｍ内側の範囲まで測定した。
【０１０１】
屈折率・複屈折の測定は露光装置の光軸方向に使用する方向で行った。また、測定波長はヘリウムネオンレーザ発振波長である６３２．８ｎｍである。
【０１０２】
水素分子濃度はレーザラマン分光光度計を用いて測定した。波長４８８ｎｍのアルゴンイオンレーザ（出力 ４００ｍＷ）を部材に入射させ、入射光方向と直角方向に放射されるラマン散乱光のうち８００ｃｍ−１（石英ガラスの基本構造の振動に起因するピーク：参照光）と４１３５ｃｍ−１（水素分子の振動に起因するピーク）の強度を測定し、その強度比をとることにより水素分子濃度を算出した。
【０１０３】
この水素分子濃度の測定では、合成石英ガラスブロック内の厚さ方向・径方向について適当なピッチで水素分子濃度の測定を行うことによって、合成石英ガラスブロック内の水素分子濃度の分布を知ることが出来る。
【０１０４】
透過率については実施例及び比較例の合成石英ガラスブロックと同等の透過率を持ち、両面研磨されたφ６０×ｔ１０ｍｍの形状の試料片を合成石英ガラスブロックと同時に処理し、処理前後にＡｒＦエキシマレーザ発振波長である１９３．４ｎｍの透過率を測定した。なお試料片の透過率変化と合成石英ガラスブロックの透過率変化が等しいことはあらかじめ確認していた。
【０１０５】
実施例１では直径２９８ｍｍ、厚さ５７ｍｍの合成石英ガラスブロックを昇温速度３０００℃／時間で１０００℃まで昇温し、１５分保持した後９０℃／時間で降温した。熱処理中、合成石英ガラスブロックは図４に示すように出来るだけ炉壁や炉床から離して配置した（以後、このような配置を中空配置と呼ぶ）。
【０１０６】
このとき、表面加熱処理前後の複屈折変化量は最大で＋２ｎｍ／ｃｍで、＋複屈折分布を得た。この表面加熱処理前後の複屈折値の分布を図５に示した。図は中心側から周縁側までの分布であり、Ａが表面加熱前、Ｂが表面加熱後を示している。
【０１０７】
また、屈折率均質性変化領域は周縁部から３ｍｍで許容できる範囲内だった。更に、水素分子濃度、透過率の変化量も許容範囲内だった。
【０１０８】
実施例２では、直径２９８ｍｍ、厚さ５７ｍｍの合成石英ガラスブロックを中空配置し、実施例１と同様の昇温速度、保持温度で、保持時間を５分とし、１２０℃／時間で降温した。このとき、複屈折変化量は最大２ｎｍ／ｃｍで、＋複屈折分布を得た。
【０１０９】
実施例３は直径２５３ｍｍ、厚さ７６ｍｍの合成石英ガラスブロックを中空配置し、昇温速度３０００℃／時間で１０００℃まで昇温し、３０分保持した後９０℃／時間で降温した。このとき複屈折変化量は最大で＋２ｎｍ／ｃｍで、＋複屈折分布を得た。
【０１１０】
実施例４では直径２９８ｍｍ、厚さ４８ｍｍの合成石英ガラスブロックを中空配置し、昇温速度４００℃／時間で８００℃まで昇温し、３０分保持した後１０℃／時間で降温した。このとき複屈折変化量は最大で＋２ｎｍ／ｃｍで、＋複屈折分布を得た。なお、処理温度が低いため、屈折率変化領域は０ｍｍだった。
【０１１１】
実施例５では直径２８２ｍｍ、厚さ４９ｍｍの合成石英ガラスブロックを中空配置し、実施例１と同様の昇温速度、保持温度で、保持時間を１０分とし、１００℃／時間で降温した。このとき複屈折変化量は最大で２ｎｍ／ｃｍで、＋複屈折分布を得た。
【０１１２】
比較例１は直径２５５ｍｍ、厚さ４０ｍｍの合成石英ガラスブロックを中空配置し、実施例３に示した表面加熱処理において降温速度を５００℃／時間とした。複屈折変化は最大で−５ｎｍ／ｃｍで、所望の分布とは全く逆の−複屈折分布となった。
【０１１３】
比較例１の表面加熱処理前後の複屈折値の分布を図６に示した。図は中心側から周縁側までの分布であり、Ａが表面加熱前、Ｂが表面加熱後を示している。
【０１１４】
比較例２は直径２５５ｍｍ、厚さ４０ｍｍの合成石英ガラスブロックを中空配置し、実施例５に示した熱処理において、昇温速度を１０℃／時間とした。
【０１１５】
この熱処理による複屈折変化は観察されなかった。昇温に時間をかけたため、合成石英ガラスブロック内の温度分布が無くなり均熱となったために複屈折変化が生じなかったと考えられる。また昇温時間が長いため熱処理の全体時間が長くなり、均質性悪化領域も１０ｍｍとかなり大きかった。
【０１１６】
比較例３は直径２３７ｍｍ、厚さ３８ｍｍの合成石英ガラスブロックに対して実施例３とほぼ同じ条件の熱処理を施したが、中空配置ではなく、合成石英ガラスブロックを炉床の上に直接置いた。複屈折変化量は最大３ｎｍ／ｃｍと適切な値だったが、炉内雰囲気からの汚染による均質性の悪化が著しく、悪化領域は１０ｍｍとかなり大きかった。
【０１１７】
比較例４では直径２３７ｍｍ、厚さ３８ｍｍの合成石英ガラスブロックを炉床上に直接配置し、昇温速度２８００℃／時間で７００℃まで昇温し、６０分保持した後３００℃／時間で降温した。このとき複屈折変化は最大で−２ｎｍ／ｃｍで、＋複屈折分布を得ることが出来なかった。
【０１１８】
以上の実施例及び比較例から明らかな通り、実施例１〜５では、第２ステップの表面加熱処理において、３００℃／時間以上の急昇温を行うとともに、５０℃／時間以上３００℃／時間未満の降温速度で冷却したので、複屈折値が単調増加するとともに、比較例１〜４より大きな変化を有する分布を形成することができた。
【０１１９】
【発明の効果】
以上、詳述の通り、請求項１に記載の発明によれば、表面加熱工程において、合成石英ガラスブロックの表面を５００℃以上１１００℃以下の範囲の熱処理温度まで３００℃／時間以上の昇温速度で昇温して、表面を中心部より高い温度に加熱するので、光学部材の表面側の熱的な歪を大きくすることにより、周縁側の歪を大きくして、周縁側の複屈折値を中心側の複屈折値から大きく変化させることが可能である。また、冷却工程において、合成石英ガラスブロックの表面を５０℃／時間以上３００℃／時間未満の降温速度で冷却するので、その複屈折値の分布を維持して冷却し易い。そのため、周縁側の複屈折値が中心側の複屈折値より大きく変化した光学部材を容易に形成することが可能である。
【０１２０】
しかも、このようにして形成される複屈折値の分布がフッ化カルシウム結晶からなる光学部材とは逆の傾向を有する。従って、フッ化カルシウム結晶や、特性上アニール処理を施すことのできない１個乃至複数個の合成石英ガラスからなる光学部材とともに用いることにより、フッ化カルシウム結晶や、特性上アニール処理を施すことのできない１個乃至複数個の合成石英ガラスの比較的大きな複屈折値の分布を低減することが可能な合成石英ガラス光学部材を容易に製造することができる。
【０１２１】
また、請求項２に記載の製造方法によれば、冷却工程において合成石英ガラスブロックの表面を５０℃／時間以上２００℃／時間以下の降温速度で冷却するので、表面加熱工程で形成した複屈折値の分布をより維持し易くて合成石英ガラスブロックを冷却し易いとともに、冷却工程において、表面側が急冷されないため、表面加熱工程で形成された複屈折値の分布の傾向が変化し難い。そのため、周縁側と中心側とで複屈折値の差を大きくして、フッ化カルシウム結晶の複屈折値の分布とは逆の傾向を有する合成石英ガラスをより確実に製造し易い。
【０１２２】
また、請求項３に記載の合成石英ガラスの製造方法によれば、前記表面加熱工程前にインゴット又は合成石英ガラスブロックをアニール処理するので、合成石英ガラスの合成時の不均一な残留歪みを低減してから、表面加熱工程を行うことができる。そのため、表面加熱工程において、所望の複屈折値の分布を形成し易い。
【０１２３】
更に、請求項４に記載の製造方法によれば、表面温度が３００℃以下の合成石英ガラスブロックを予め５００℃以上１１００℃以下に加熱された加熱炉内に収容することにより合成石英ガラスブロックの表面を昇温するので、合成石英ガラスブロックの表面の温度を表面加熱温度より高い温度に加熱することを確実に防止して、急速に昇温することが可能であり、合成石英ガラスをより容易に製造することができる。
【０１２４】
更に、請求項５に記載の製造方法によれば、回転加熱しつつ形成された合成石英ガラスインゴットから得られた合成石英ガラスブロックが、回転対称の複屈折値の分布を有しているので、この合成石英ガラスブロックを、表面加熱工程及び冷却工程において、回転させながら加熱及び冷却すれば、合成石英ガラスブロックの表面を周方向に均一に昇温又は降温し易い。そのため、合成石英ガラスブロックの複屈折値の分布を回転対称に形成することが容易である。
【０１２５】
更に、請求項６に記載の製造方法によれば、光学部材を大気又は不活性ガス雰囲気下で表面加熱工程及び／又は冷却工程を行うので、合成石英ガラス光学部材の製造が容易である。
【０１２６】
また、請求講７に記載の製造方法によれば、表面加熱工程及び冷却工程を行うことにより、進相軸の方向が該合成石英ガラス部材の径方向に配向するものを正として測定される複屈折値が、中心側から周縁側に向けて単調増加する分布を形成するので、フッ化カルシウム結晶からなる光学部材ととともに用いることによって、その複屈折値の分布を解消し易い合成石英ガラス光学部材を確実に製造することができる。
【０１２７】
そして、請求項８に記載の光学部材によれば、進相軸が中心部から放射方向に配向するものを正として測定される複屈折値の分布が、中心部から周縁部全周に向けて単調増加する分布を有するので、フッ化カルシウム結晶からなる光学部材ととともに用いることによって、その複屈折値の分布を解消し易く、光学系全体の複屈折値の分布を低減することが可能な光学部材を提供することができる。
【０１２８】
また、請求項９に記載の光学系によれば、請求項８に記載の合成石英ガラス光学部材と、フッ化カルシウム結晶からなる光学部材とを、光路に直列に配置したので、フッ化カルシウム結晶からなる光学部材の複屈折値の分布を、合成石英ガラス光学部材の複屈折値の分布により抑制でき、より複屈折値の分布を抑えた光学系を提供することができる。
【０１２９】
更に、請求項１０に記載の露光装置によれば、より複屈折値の分布を抑えた光学系を照明光学系又は投影光学系に備えているので、複屈折値の分布が全体として小さく抑制されているため、より高精度に露光することが可能な露光装置を提供することができる。
【０１３０】
また、請求項１１又は１２に記載の表面加熱炉によれば、中空部を備えて合成石英ガラスブロックを載置する合成石英ガラス製のブロック載置台を有し、この中空部を通して合成石英ガラスブロックの底面が炉内の雰囲気に曝露されるので、合成石英ガラスブロックの底面に、熱処理炉の底面から直接熱が供給されることがなく、合成石英ガラスブロックの表面全体を均一に昇温させ易い。また、表面加熱時に底面から直接合成石英ガラスブロックに不純物が拡散されるのを防止することができる。そのため、不純物による品質の悪化を防止しつつ、光学部材の外表面全体を均一に表面加熱し易い表面加熱炉を提供することができる。
【０１３１】
更に、請求項１２に記載の表面加熱炉によれば、炉内の容積に対する合成石英ガラスブロックの体積の比率が０．０００５より大きく、且つ、０．１０より小さい範囲であって、合成石英ガラスブロックが、炉内の底面及び炉壁から２０ｍｍ以上離れて配置されるので、炉内の底面及び炉壁から直接不純物が合成石英ガラスブロックに拡散されることを防止しつつ、より表面側を急昇温させ易い表面加熱炉を提供することができる。
【図面の簡単な説明】
【図１】合成石英ガラス部材の熱処理温度に対する複屈折変化量及び屈折率均質性悪化領域をプロットしたグラフである。
【図２】この発明の実施の形態の露光装置の基本構成を示す図である。
【図３】フッ化カルシウム結晶からなる光学部材の複屈折値の分布及び合成石英ガラスからなる光学部材の複屈折値の分布並びに両光学部材を備えた光学系の複屈折値の分布を示す図である。
【図４】この発明の実施の形態の製造方法において用いる表面加熱炉の断面図である。
【図５】実施例１の合成石英ガラスブロックの表面加熱工程前後の複屈折値の分布を示す図である。
【図６】比較例１の合成石英ガラスブロックの表面加熱工程前後の複屈折値の分布を示す図である。
【符号の説明】
１０ 露光装置
１２ 照明光学系
１４ 投影光学系
３０ 表面加熱炉
３１ 合成石英ガラスブロック
４０ 合成石英筒体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a synthetic quartz glass optical member used for a lens material of an imaging optical system of an ultraviolet laser of 300 nm or less such as excimer laser lithography, an optical member, an optical system, an exposure apparatus, and heating of the synthetic quartz glass. Related to the furnace.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an exposure apparatus called an exposure apparatus is used in an optical lithography technique that exposes and transfers a fine pattern of an integrated circuit onto a wafer such as silicon. The light source of this exposure apparatus has been shortened from i-line (365 nm) to KrF (248 nm) and ArF (193 nm) excimer lasers with the recent high integration of LSI.
[0003]
In general, an optical glass used in an illumination optical system or projection optical system of an exposure apparatus that uses a light source having a wavelength longer than that of i-line has a significantly reduced light transmittance in a wavelength region shorter than that of i-line. In the wavelength region, most optical glass does not transmit light. Therefore, in an exposure apparatus using an excimer laser as a light source, only a fluoride crystal such as quartz glass or fluorite can be used. Quartz glass and fluorite are materials widely used in the optical system of ultraviolet rays and vacuum ultraviolet rays.
[0004]
When synthetic quartz glass is used in an optical system of an optical lithography apparatus, the quartz glass optical member is required to have very high quality in order to expose an integrated circuit pattern with a large area and high resolution. For example, when the refractive index distribution of the member is within a very large aperture having a diameter of 250 mm or more, 10 ^-6 It is required to be below the order. Further, reducing the amount of birefringence, that is, reducing the internal distortion of the optical member, has been regarded as important for the resolution of the optical system as well as improving the homogeneity of the refractive index distribution. . Further, since the total optical path length of the illumination optical system / projection optical system of the exposure apparatus using the excimer laser exceeds 1 m, the internal transmittance of the glass material used to avoid the loss of the light amount is 99.75% / cm. High transmittance is required.
[0005]
Further, in order to maintain a high transmittance during the operation of an exposure apparatus using an excimer laser, it is necessary to adjust the hydrogen molecule concentration, which is known as one of the ultraviolet resistance improving factors, to an appropriate value. Hydrogen molecules are incorporated into quartz glass during gas phase synthesis. Such a high-homogeneity, high-transmittance, UV-resistant large-diameter quartz glass is conventionally produced by a vapor phase synthesis method called the direct method.
[0006]
In this manufacturing method, oxygen gas and hydrogen gas are mixed and burned in a quartz glass burner, and high-purity silicon tetrachloride gas or organosilicon compound is diluted with a carrier gas as a raw material gas from the center of the burner. Quartz glass particles are generated by a hydrolysis reaction with water generated by combustion of the surrounding oxygen gas and hydrogen gas, or a combustion reaction with a flame, and the quartz glass particles are below the burner. In this method, a quartz glass ingot is obtained by depositing on a target made of an opaque quartz glass plate that is rotating, swinging and pulling down, and simultaneously melting and vitrifying by the combustion heat of the oxygen gas and hydrogen gas.
[0007]
Various stresses derived from the thermal history at the time of manufacture remain in the synthetic quartz glass member manufactured by the above-mentioned vapor phase synthesis method, and therefore it can be said that the refractive index and birefringence homogeneity inside the glass are good. Therefore, it is not suitable as an optical element for an exposure apparatus. In addition, since the quartz glass ingot is rapidly cooled by the atmosphere after the synthesis is completed, the structure determination temperature is high and the ultraviolet resistance is poor. Therefore, in order to release residual stress and improve homogeneity such as refractive index and birefringence value, and to adjust the structure determination temperature to an appropriate value and improve UV resistance, it is common to anneal after manufacturing Is.
[0008]
Although the synthetic quartz glass member thus annealed can improve the refractive index homogeneity and UV resistance to a satisfactory level, it is not easy to improve the birefringence performance. Therefore, when an exposure apparatus is configured by arranging a large number of optical members such as various lenses formed from such synthetic quartz glass, the birefringence of each optical member is integrated, and a large birefringence is formed in the entire exposure apparatus. .
[0009]
In order to reduce the distribution of the birefringence value, for example, in Patent Document 1 below, an exposure apparatus is configured by combining a plurality of optical members so that the birefringence value distributions in the transmission surface direction of the optical members cancel each other. It is known to suppress the distribution of birefringence values as a whole (see Patent Document 1 below).
[0010]
Here, the distribution of the birefringence value is reduced by annealing the block made of synthetic quartz glass to release the residual stress as much as possible and homogenize it. Furthermore, the distribution of birefringence values that cannot be sufficiently eliminated by annealing treatment is changed by heating some optical members again and quenching them at a cooling rate of 50 ° C./h or more, thereby birefringence of some optical members. The distribution of the values is formed in a tendency different from that of other optical members, and these are used in combination, thereby canceling the birefringence value and reducing the distribution of the entire optical system.
[0011]
[Patent Document 1]
International Publication No. 01/12566
[Problems to be solved by the invention]
However, in recent years, some exposure apparatuses using short-wavelength light such as KrF (248 nm) and ArF (193 nm) excimer lasers use an optical member made of calcium fluoride crystals. An optical member made of calcium fluoride crystals has a characteristic relatively large distribution of birefringence values. Moreover, since the calcium fluoride crystal is a crystal, this birefringence value distribution cannot be eliminated by annealing or subsequent heat treatment as in a synthetic quartz glass member.
[0012]
In addition, some synthetic molded glass members have a tendency similar to the distribution of birefringence of calcium fluoride crystals, depending on the production method, alone or in combination, and due to their characteristics, heat treatment such as annealing is performed. Sometimes it can not be applied. In an exposure apparatus provided with such an optical member made of a synthetic quartz glass member or the optical member made of the above-mentioned calcium fluoride crystal, a large distribution of birefringence values may occur in the entire apparatus.
[0013]
Therefore, in the present invention, a synthetic quartz glass optical member that easily controls the distribution of birefringence values of synthetic quartz glass by heat treatment and can easily reduce the distribution of birefringence values that tend to be similar to calcium fluoride crystals, and a method for manufacturing the same. It is an issue to provide.
[0014]
Another object is to provide an optical system and an exposure apparatus using the synthetic quartz glass optical member.
[0015]
Furthermore, another problem is to provide a surface heating furnace in which the synthetic quartz glass optical member can be easily manufactured.
[0016]
[Means for Solving the Problems]
The present inventors do not change the distribution of relatively large birefringence values of an optical member made of calcium fluoride crystal or an optical member made of some synthetic quartz glass. It has been found that the distribution of birefringence values can be integrated and canceled by combining optical members. However, since the distribution of the birefringence value of the optical member has a characteristic and relatively large change, a synthetic quartz glass having a distribution of birefringence value that has a change that is large enough to cancel this is required. In this case, it is necessary to control the value and distribution of the birefringence value of the synthetic quartz glass optical member rather than just having a small distribution.
[0017]
Therefore, the present inventors tried to control the birefringence by performing a new heat treatment on the synthetic quartz glass after annealing, and performing the heat treatment at various temperatures to change the refractive index and the birefringence before and after the treatment. investigated.
[0018]
As a result, the following was clarified.
[0019]
(1) The amount of change in the birefringence value increases as the processing temperature increases.
[0020]
(2) The amount of change in the birefringence value increases as the heating rate increases.
[0021]
(3) The higher the processing temperature and the longer the processing time, the worse the refractive index homogeneity and the reduction in hydrogen molecule concentration, that is, the deterioration in UV resistance.
[0022]
Among these, (1) and (2) indicate that the temperature distribution in the member to be processed determines the distribution of birefringence values. Therefore, by forming a temperature gradient such that (temperature at the center of the member) <(temperature around the member) by heat treatment in a short time and cooling so that this temperature distribution is maintained, the direction of the fast axis Can be obtained which has a distribution of positive birefringence values increasing in a quadratic curve when the one oriented in the radial direction of the synthetic quartz glass optical member is positive.
[0023]
The problem described in (3) occurs particularly at the outer periphery of the workpiece. For this reason, if heat treatment is performed in advance in a shape larger than the final part shape, that is, a shape with burrs in anticipation of deterioration of physical properties, quartz glass having a desired quality can be obtained. However, adding waste meat increases the volume of the object to be processed by about 1.5 times, and waste of the material becomes very large.
[0024]
Further, deterioration of physical properties can be avoided by lowering the treatment temperature, but such a low temperature heat treatment cannot provide a sufficient amount of change in birefringence value, preferably +2 nm / cm or more.
[0025]
In FIG. 1, the amount of change A of the birefringence value and the refractive index homogeneity deterioration region B are plotted against the heat treatment temperature. The processing time is 30 minutes at each temperature. It is clear that the amount of change in the birefringence value increases as the processing temperature increases, and at the same time, the refractive index homogeneity deterioration region increases, that is, the refractive index homogeneity deteriorates.
[0026]
Accordingly, the present invention solves the above-described problem by suppressing a region where the refractive index homogeneity is deteriorated while sufficiently changing the distribution of the birefringence value without adding a large sword. The manufacturing method described is a method of manufacturing an optical member by heat-treating a synthetic quartz glass block, and the surface of the synthetic quartz glass block is heated to a surface heating temperature in the range of 500 ° C. to 1100 ° C. to 300 ° C./hour. The surface heating step of heating at the above temperature rising rate and heating the surface to a temperature higher than the central portion, and the surface of the synthetic quartz glass block after the surface heating step is 50 ° C./hour or more and less than 300 ° C./hour And a cooling step of cooling at a temperature lowering rate.
[0027]
In addition to the structure of claim 1, the manufacturing method according to claim 2 cools the surface of the synthetic quartz glass block at a cooling rate of 50 ° C./hour or more and 200 ° C./hour or less in the cooling step. It is characterized by doing.
[0028]
Furthermore, in the manufacturing method according to claim 3, before the surface heating step, the ingot or the synthetic quartz glass block is heated to an annealing temperature of 900 ° C. or more and held at the annealing temperature for a predetermined time, and then 500 ° C. An annealing step for cooling to the following temperature at a cooling rate of 10 ° C./hour or less is provided.
[0029]
Furthermore, in the manufacturing method according to claim 4, in addition to the configuration according to any one of claims 1 to 3, in the surface heating step, the synthetic quartz glass block having a surface temperature of 300 ° C. or less is preliminarily described. The surface of the synthetic quartz glass block is heated by being housed in a heating furnace heated to a surface heating temperature.
[0030]
Moreover, the manufacturing method of Claim 5 produces the said synthetic quartz glass block from the synthetic quartz glass ingot formed in addition to the structure as described in any one of Claims 1 thru | or 4, and rotating, In the surface heating step and the cooling step, heating and cooling are performed while rotating.
[0031]
Furthermore, in the manufacturing method according to claim 6, in addition to the structure according to any one of claims 1 to 5, the synthetic quartz glass block is added in at least one of the surface heating step and the cooling step. The treatment is performed in an atmosphere or an inert gas atmosphere.
[0032]
Further, in the manufacturing method according to claim 7, in addition to the configuration according to any one of claims 1 to 6, by performing the surface heating step and the cooling step, the direction of the fast axis is the synthesis. The birefringence value measured with the one oriented in the radial direction of the quartz glass member as positive forms a distribution that monotonously increases from the center side toward the peripheral side.
[0033]
The optical member according to claim 8 is a synthetic quartz glass optical member manufactured by the manufacturing method according to any one of claims 1 to 6, wherein the direction of the fast axis is the radial direction of the synthetic quartz glass member. The birefringence value measured with positive orientation is positively increasing from the center side toward the peripheral side.
[0034]
An optical system according to a ninth aspect is characterized in that the synthetic quartz glass optical member according to the eighth aspect and an optical member made of calcium fluoride crystal are arranged in series in the optical path.
[0035]
Furthermore, an exposure apparatus according to a tenth aspect is characterized in that the optical system according to the ninth aspect is provided in an illumination optical system or a projection optical system.
[0036]
In addition, the inventors, especially during the heat treatment, the homogeneity is particularly deteriorated at the portion in contact with the furnace wall and the bottom surface in the heat treatment furnace. Found that can be avoided.
[0037]
Therefore, the surface heating furnace according to claim 11 suitable for the manufacturing method according to claims 1 to 7 is a surface heating furnace that accommodates and heats a synthetic quartz glass block, and is provided with a hollow portion and synthesized. A synthetic quartz glass block mounting table for mounting the quartz glass block is provided, and the bottom surface of the synthetic quartz glass block mounted on the upper portion of the block mounting table is exposed to the atmosphere in the furnace through the hollow portion. It is characterized by that.
[0038]
Further, in the surface heating furnace according to claim 12, the ratio of the volume of the synthetic quartz glass block to the volume in the furnace is in a range larger than 0.0005 and smaller than 0.10, and the synthetic quartz glass The block is disposed at a distance of 20 mm or more from the bottom surface and the furnace wall in the furnace.
[0039]
In the present invention, the birefringence value is + (plus) when the fast axis direction and the radial direction of the optical member are parallel, and-(minus) when the direction is vertical. In addition, when the measured value of birefringence is small, the fast axis may not always be completely parallel or perpendicular to the radial direction of the member but may have an inclination. If the angle of the fast axis relative to is less than 45 degrees, it can be handled with +, and if it is greater than 45 degrees, it can be treated with-.
[0040]
Examples of the method for measuring the birefringence value include a phase modulation method and a rotation analyzer method. In phase modulation, the optical system includes a light source, a polarizer, a phase modulation element, a sample, and an analyzer. A He—Ne laser or a laser diode is used as the light source, and a photoelastic converter is used as the phase modulation element. The light from the light source is converted into linearly polarized light by the polarizer and enters the phase modulation element. The light beam from the phase modulation element projected onto the sample is modulated light whose polarization state continuously changes from linearly polarized light → circularly polarized light → linearly polarized light by the element. When measuring, rotate the sample around the light beam incident on the measurement point on the sample to find the output peak of the detector, and measure the amplitude at that time to determine the direction of the fast axis and the birefringence phase difference. Find the size. When a Zeeman laser is used as the light source, measurement can be performed without rotating the sample. In addition, phase shift method and optical heterodyne interferometry can also be used in the present invention.
[0041]
The rotating analyzer method has a device configuration in which a sample between a light source and a photodetector is sandwiched between a polarizer and a rotating analyzer, and the detector placed after the sample is rotated while rotating from the detector. The signal is measured, and the phase difference is obtained from the maximum value and the minimum value of the signal from the detector.
[0042]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0043]
FIG. 2 shows the basic structure of the exposure apparatus of this embodiment.
[0044]
The exposure apparatus 10 includes at least a light source 11 for supplying an excimer laser or the like as exposure light, an illumination optical system 12 for supplying the exposure light to the mask R, and a pattern image of the mask R on the substrate W to be exposed. A projection optical system 13 for projecting is included.
[0045]
The illumination optical system 12 includes an alignment optical system 14 for adjusting the relative position between the mask R and the substrate W to be exposed. The mask R is disposed on a mask stage 16 whose position is controlled by a mask exchange system 15. The substrate to be exposed W is disposed on the wafer stage 18 whose position is controlled by the stage control system 17. Further, the light source 11, the alignment optical system 14, the mask exchange system 15, and the stage control system 17 are controlled by the main control unit 19.
[0046]
In such an exposure apparatus 10, detailed illustration is omitted, but a large number of optical members are arranged in the illumination optical system 12 and / or the projection optical system 13. Some of these optical members are made of calcium fluoride crystals or one or more synthetic quartz glasses that cannot be annealed due to characteristics for various reasons. Even in the exposure apparatus 10 of this embodiment, an optical member made of calcium fluoride crystal or one or a plurality of synthetic quartz glasses that cannot be annealed due to characteristics is disposed. In other words, the illumination optical system 12 and / or the projection optical system 13 is composed of calcium fluoride crystals, one or more optical members made of synthetic quartz glass that cannot be annealed due to their characteristics, and optics made of synthetic quartz glass. This is an optical system in which members are arranged.
[0047]
Optical members made of calcium fluoride crystals are known to have negative birefringence inherent in the material on the [110] plane, and when a fluorite member is cut out from the [111] plane and processed into a lens shape The birefringence value decreases from the center toward the lens periphery, and has a relatively large negative birefringence distribution as shown by curve A in FIG.
[0048]
On the other hand, the synthetic quartz glass used for many optical members, in the synthesized state or the annealed state, the distribution of the signed birefringence values from the center side of the optical member due to the thermal history during synthesis, etc. There are various distributions such as those that are almost zero to the peripheral side, those that monotonously increase (+) or decrease (-) from the central side to the peripheral side, and those that have inflection points.
[0049]
When such synthetic quartz glass is directly formed on an optical member and used in combination with an optical member made of calcium fluoride crystal, it has a negative birefringence distribution with respect to the negative birefringence distribution of the optical member made of calcium fluoride crystal. A synthetic quartz glass optical member is combined, resulting in a larger negative birefringence, and the imaging performance of the exposure apparatus as a whole deteriorates.
[0050]
In addition, in the case of such an optical member made of synthetic quartz glass, it is usually used by performing an annealing treatment to reduce the distribution of birefringence values, but even if this is done, the birefringence of the calcium fluoride crystal The distribution of values is large and large negative birefringence remains, resulting in insufficient imaging performance as the entire exposure apparatus.
[0051]
Furthermore, some optical members made of synthetic quartz glass cannot be annealed due to their characteristics, and the presence of one or more optical members made of such synthetic quartz glass makes it difficult to perform annealing. A negative birefringence distribution similar to that of an optical member made of calcium fluoride crystal may be obtained. Even in the case of an exposure apparatus using such an optical member, the imaging performance as a whole is similarly deteriorated.
[0052]
Therefore, in the exposure apparatus of this embodiment, the distribution of the birefringence value of at least a part of the optical member made of synthetic quartz glass is changed so as to monotonically increase from the center side toward the peripheral side, and this synthetic quartz glass optical By forming the optical system by arranging the members in series in the optical path, the birefringence value of the optical member made of calcium fluoride crystal or one or a plurality of synthetic quartz glasses that cannot be annealed due to characteristics is obtained. The distribution and the distribution of the birefringence value of the predetermined synthetic quartz glass optical member are integrated in the optical path, thereby reducing the distribution of the birefringence value of the exposure apparatus as a whole.
[0053]
That is, for example, if a synthetic quartz glass optical member having a birefringence distribution as shown by curve B in FIG. 3 is arranged, birefringence as shown by curve A of an optical member made of calcium fluoride crystal in the optical path. The distribution of the values and the distribution of the birefringence values of the synthetic quartz glass optical member are integrated, so that the entire optical system has a birefringence value distribution as shown by a curve C in FIG.
[0054]
In this embodiment, in order to manufacture a synthetic quartz glass optical member by changing the distribution of birefringence values so as to monotonically increase from the center side toward the peripheral side, from a previously prepared synthetic quartz glass ingot, A synthetic quartz glass block is formed, the surface of this block is rapidly heated, the distribution of birefringence values formed during synthesis is changed, the birefringence value distribution is maintained and cooled, and then It can manufacture by processing into an optical member.
[0055]
First, in this manufacturing method, synthetic quartz glass is synthesized in advance by a direct method or the like to produce an ingot. At that time, if the ingot is rotated and heated so that the temperature distribution is uniform in the circumferential direction, the birefringence distribution of the synthetic quartz glass block formed from the ingot can be formed rotationally symmetrically. .
[0056]
Then, a synthetic quartz glass block is formed from the obtained ingot so that the center of the ingot coincides with the center of the block.
[0057]
The synthetic quartz glass block may be an ingot itself or a lump of a size from which a plurality of target optical members can be taken out, preferably having the shape of the target optical member, or It is preferable to have a shape capable of obtaining a target optical member by performing a finishing process such as polishing.
[0058]
In this embodiment, the synthetic quartz glass block is heated to an annealing temperature of 900 ° C. or higher, held at this annealing temperature for a predetermined time, and then cooled to a temperature of 500 ° C. or lower at a temperature lowering rate of 10 ° C./hour or lower. I do. Thereby, the distortion of the synthetic quartz glass block can be homogenized. This annealing step can be performed in advance in an ingot state.
[0059]
Next, a surface heating process for rapidly increasing the temperature of the surface of the synthetic quartz glass block is performed.
[0060]
FIG. 4 shows a surface heating furnace used in this surface heating step.
[0061]
The surface heating furnace 30 is configured to accommodate a cylindrical synthetic quartz glass block 31, a furnace heater 34 capable of uniformly heating the furnace interior 32, and a hearth plate 36 that forms the bottom surface of the furnace 32. And. Two refractory bricks 38 as base members are placed in parallel on top of the hearth plate 36 with a gap 39 at an appropriate interval. Further, synthetic quartz glass is placed on the upper part of the two refractory bricks 38. A quartz glass cylinder 40 is disposed as a block mounting table having an outer peripheral shape substantially corresponding to the outer diameter of the block 31.
[0062]
The synthetic quartz glass block 31 is placed on the quartz glass cylinder 40 via a quartz glass chip 42. The quartz glass chip 42 supports the synthetic quartz glass block 31 at three points, thereby making the contact surface with the synthetic quartz glass block 31 as small as possible. The thickness of the quartz glass cylinder 40 is such that the quartz glass chip 42 can be stably disposed, and is desirably thin.
[0063]
In such a surface heating furnace 30, an interval 39 is provided between the two refractory bricks 38, and a hollow portion 40 a of the quartz glass cylinder 40 is continuous from the interval 39, whereby an air passage 44 is formed. The bottom surface 31 a of the synthetic quartz glass block 31 is exposed in the air passage 44. Therefore, the synthetic quartz glass block 31 can be in a hollow arrangement state in which substantially the entire periphery does not come into contact with the atmosphere in the furnace 32, so that heat is directly applied from the hearth plate 36 or the furnace wall 30 a of the surface heating furnace 30. Without being supplied, the entire surface of the synthetic quartz glass block can be heated uniformly.
[0064]
In such a surface heating furnace 30, since contaminants such as metallic sodium in the furnace deteriorate the refractive index homogeneity, the surface heating furnace 30 is baked before the surface heating process is performed on the synthetic quartz glass block 31. There is a need. At the time of surface heating work, wear gloves and a mask at a minimum. However, even if it does in this way, in-furnace contamination cannot be eliminated completely, it is important that the synthetic quartz glass block 31 and the in-furnace material of the surface heating furnace 30 are not contacted as much as possible.
[0065]
Therefore, in this surface heating furnace 30, the synthetic quartz glass block 31 is disposed 20 mm or more away from the hearth plate 36 and the furnace wall 30a in the furnace 32. Further, since three points are supported by the quartz glass chip 42, the contact between the synthetic quartz glass block 31 and the in-furnace material can be minimized, and impurities from the in-furnace material to the synthetic quartz glass block 31 can be reduced. Diffusion can be suppressed.
[0066]
In this embodiment, the surface heating process of the synthetic quartz glass block 31 is performed by such a surface heating furnace 30.
[0067]
In this surface heating step, first, the surface of the synthetic quartz glass block 31 is rapidly heated to a surface heating temperature in the range of 500 ° C. to 1100 ° C.
[0068]
Here, when the surface heating temperature is less than 500 ° C., the birefringence value hardly changes. When the surface heating temperature is higher than 1100 ° C., various physical properties of the synthetic quartz glass member such as the refractive index distribution deteriorates and the hydrogen molecule concentration decreases. It is easy to worsen.
[0069]
Further, the rate of temperature increase during this rapid temperature increase needs to be a rate of temperature increase of 300 ° C./hour or more, and preferably the temperature is increased to a surface heating temperature at a rate of temperature increase of 400 ° C./hour or more. Is preferred.
[0070]
During this rapid temperature increase, if heating is performed at a temperature increase rate of less than 300 ° C./hour, heat is easily transferred to the central portion of the synthetic quartz glass at the time of temperature increase, and the temperature difference between the outer surface and the central portion is reduced. Since the distribution of the birefringence value of the obtained synthetic quartz glass optical member becomes small, it is not preferable.
[0071]
Further, if the temperature is raised to the surface heating temperature at a temperature rising rate of 400 ° C./hour or more, the surface of the synthetic quartz glass block 31 can be surely rapidly heated rapidly, and the birefringence value on the peripheral side is changed to the birefringence value on the center side It is easy to change from.
[0072]
Furthermore, the temperature raising time can be shortened by preheating the synthetic quartz glass block 31 before the rapid temperature raising. In that case, the preheating temperature of the synthetic quartz glass block 31 is preferably less than 300 ° C. This is because if it is lower than 300 ° C., the concentration of hydrogen molecules contained in the synthetic quartz glass block 31 is difficult to decrease.
[0073]
When the surface heating furnace 30 as described above is used, the furnace 32 in the surface heating furnace 30 is heated to a surface heating temperature in advance, and the surface is rapidly increased by accommodating the synthetic quartz glass block 31 in the furnace 32. Can be warmed. In this way, it is possible to reliably prevent the temperature of the surface of the synthetic quartz glass block 31 from being heated to a temperature higher than the surface heating temperature, thereby rapidly increasing the temperature.
[0074]
In this case, the ratio of the volume of the surface heating furnace 30, specifically, the volume of the space surrounded by the hearth plate 36 and the furnace wall 30 a in the furnace 32 and the volume of the synthetic quartz glass block 31 (synthetic quartz). The glass block volume) / (furnace volume) is preferably in the range of more than 0.0005 and less than 0.10, and particularly preferably in the range of 0.025 to 0.05.
[0075]
If this ratio is too small, even within a short time surface heat treatment, the inside of the synthetic quartz glass block 31 is heated uniformly, and the distribution of birefringence values tends to be small. On the other hand, if this ratio is too large, the distance between the furnace wall 30a and the hearth plate 36 and the synthetic quartz glass block 31 becomes too short, and impurities from the furnace wall 30a and the hearth plate 36 to the synthetic quartz glass block 31 are likely to diffuse. Become.
[0076]
Next, in this surface heating step, the surface of the synthetic quartz glass block 31 can be rapidly raised to the surface heating temperature and then held at that temperature. This is because it is easy to form a gentle gradient of the birefringence distribution.
[0077]
The operation of maintaining the surface heating temperature after the rapid temperature increase needs to be completed before at least the center reaches the surface heating temperature.
[0078]
More preferably, if the temperature at the center is, for example, less than 500 ° C., the change in the birefringence value on the center side can be reduced and the change in the birefringence value on the peripheral side can be easily increased. is there.
[0079]
Next, after the surface heating step, a cooling step is performed in which the surface of the synthetic quartz glass block 31 is cooled to a temperature of, for example, 500 ° C. or less at a temperature drop rate of 50 ° C./hour or more and less than 300 ° C./hour. This cooling step can be performed by adjusting the amount of heat of the in-furnace heater 34 in the surface heating furnace 30.
[0080]
In the cooling process, if the cooling is performed at a rate slower than 50 ° C./hour, the amount of heat transferred from the surface to the central portion increases, so the difference between the surface temperature formed by rapid temperature rise and the central portion temperature is small. As a result, the distortion becomes small and the distribution of birefringence values is easily homogenized, which is not preferable.
[0081]
On the other hand, when the cooling is performed at a temperature lowering rate higher than 300 ° C./hour, thermal strain opposite to the thermal strain formed by the rapid temperature increase after cooling tends to remain. As a result, it is difficult to obtain a distribution having a tendency opposite to that of the birefringence value of the optical member made of calcium fluoride crystal, which is not preferable.
[0082]
In particular, in this cooling step, it is preferable to cool the surface of the synthetic quartz glass block 31 at a temperature decreasing rate of 50 ° C./hour or more and 200 ° C./hour or less. With this cooling rate, a distribution having a tendency opposite to the distribution of the birefringence value of the optical member made of calcium fluoride crystal can be more reliably formed.
[0083]
The surface heating step and the cooling step can be performed in the atmosphere or an inert gas atmosphere.
[0084]
Moreover, in the case of the synthetic quartz glass block 31 formed from the ingot obtained by rotating and heating as in this embodiment, heating and cooling are performed while rotating in the surface heating step and the cooling step. Is preferred.
[0085]
In this way, since the synthetic quartz glass block has a rotationally symmetric birefringence distribution, the surface of the synthetic quartz glass block 31 is uniformly heated in the circumferential direction even in the surface heating step and the cooling step. By lowering the temperature, the distribution of birefringence values of the synthetic quartz glass block can be formed rotationally symmetrical.
[0086]
In this embodiment, after performing the surface heating step and the cooling step as described above, the synthetic quartz glass optical member is formed by performing processing such as grinding, polishing, and outer periphery processing called centering.
[0087]
And in the synthetic quartz glass optical member manufactured in this way, the birefringence value has a distribution that monotonously increases from the center side toward the peripheral side.
[0088]
If the synthetic quartz glass optical member is manufactured as described above, the surface temperature is rapidly raised in the surface heating step, so that the thermal strain on the surface side of the synthetic quartz glass optical member is increased to reduce the peripheral strain. The birefringence value on the peripheral side can be greatly changed from the birefringence value on the center side by increasing the value. Further, in the cooling process, the surface of the synthetic quartz glass block 31 is cooled at an appropriate temperature drop rate, so that the birefringence value distribution is maintained and cooling is easy. Therefore, it is possible to easily form a synthetic quartz glass optical member in which the birefringence value on the peripheral side has changed more than the birefringence value on the center side.
[0089]
Moreover, the distribution of birefringence values formed in this way tends to be opposite to that of optical members made of calcium fluoride crystals or one or more synthetic quartz glasses that cannot be annealed due to their characteristics. Therefore, it can be used together with calcium fluoride crystals and optical members made of one or more synthetic quartz glasses that cannot be annealed due to their characteristics. It is possible to reduce the distribution of relatively large birefringence values of one or more synthetic quartz glasses that cannot.
[0090]
Furthermore, since the surface is not rapidly cooled in the cooling step, the tendency of the distribution of the birefringence values formed in the surface heating step is difficult to change. Therefore, the difference in birefringence value between the peripheral side and the center side is large, and the distribution of birefringence values of calcium fluoride crystal or one or more synthetic quartz glasses that cannot be annealed due to their characteristics. Is easier to produce synthetic quartz glass having the opposite tendency more reliably.
[0091]
Further, in this embodiment, since the synthetic quartz glass block 31 is annealed before the surface heating process, the surface heating process can be performed after reducing non-uniform residual strain during the synthesis of the synthetic quartz glass. In the surface heating step, it is easy to form a desired birefringence value distribution.
[0092]
【Example】
Examples of the present invention will be described below.
[0093]
The synthetic quartz glass blocks of Examples 1 to 5 and Comparative Examples 1 to 4 were produced as follows.
[0094]
First, a quartz glass ingot was obtained by a vapor phase synthesis method and cut into a cylindrical synthetic quartz glass block having a size shown in Table 1 in which one or several quartz glass optical members can be cut out. The cut quartz glass block was annealed as a heat treatment in the first step. The annealing was performed by controlling the furnace temperature as follows. The temperature is raised to 1000 ° C. at 140 ° C./hour and held at 1000 ° C. for 10 hours. Thereafter, the temperature is lowered to 500 ° C. at 10 ° C./hour and allowed to cool. The atmosphere in the furnace during the treatment was air.
[0095]
Each synthetic quartz glass block after annealing was subjected to the surface heating treatment of the second step under the conditions shown in Table 1 using a surface heating furnace as shown in FIG.
[0096]
The refractive index homogeneity, birefringence, hydrogen molecule concentration, and transmittance of the synthetic quartz glass block thus obtained were measured before and after the surface heating treatment in the second step, and the amount of change was calculated. The results are shown in Table 2.
[0097]
[Table 1]

[0098]
[Table 2]

[0099]
The refractive index homogeneity was measured using an oil-on-plate method in an area of 95% of the synthetic quartz glass block.
[0100]
The birefringence value was measured using a heterodyne interferometry in a range of 5 mm from the outer periphery concentrically in increments of 30 °.
[0101]
The refractive index and birefringence were measured in the direction used in the optical axis direction of the exposure apparatus. The measurement wavelength is 632.8 nm which is a helium neon laser oscillation wavelength.
[0102]
The hydrogen molecule concentration was measured using a laser Raman spectrophotometer. Argon ion laser with a wavelength of 488 nm (output: 400 mW) is incident on the member, and 800 cm −1 of Raman scattered light emitted in a direction perpendicular to the incident light direction (peak: reference light due to vibration of the basic structure of quartz glass) And 4135 cm −1 (peak due to vibration of hydrogen molecules) were measured, and the hydrogen molecule concentration was calculated by taking the intensity ratio.
[0103]
In this hydrogen molecule concentration measurement, the hydrogen molecule concentration distribution in the synthetic quartz glass block can be known by measuring the hydrogen molecule concentration at an appropriate pitch in the thickness direction and radial direction in the synthetic quartz glass block. I can do it.
[0104]
The transmittance is the same as that of the synthetic quartz glass block of the example and the comparative example, and a sample piece of φ60 × t10 mm shape polished on both sides is processed simultaneously with the synthetic quartz glass block, and before and after the processing, an ArF excimer laser is processed. The transmittance at 193.4 nm, which is the oscillation wavelength, was measured. It was confirmed in advance that the transmittance change of the sample piece was equal to the transmittance change of the synthetic quartz glass block.
[0105]
In Example 1, a synthetic quartz glass block having a diameter of 298 mm and a thickness of 57 mm was heated to 1000 ° C. at a heating rate of 3000 ° C./hour, held for 15 minutes, and then cooled at 90 ° C./hour. During the heat treatment, the synthetic quartz glass block was placed as far away from the furnace wall and hearth as possible as shown in FIG. 4 (hereinafter, this kind of arrangement is called a hollow arrangement).
[0106]
At this time, the maximum birefringence change before and after the surface heat treatment was +2 nm / cm, and a + birefringence distribution was obtained. The distribution of birefringence values before and after the surface heat treatment is shown in FIG. The figure shows the distribution from the center side to the peripheral side, where A indicates before surface heating and B indicates after surface heating.
[0107]
Further, the refractive index homogeneity changing region was within an allowable range of 3 mm from the peripheral edge. Furthermore, the amount of change in the hydrogen molecule concentration and transmittance was also within acceptable ranges.
[0108]
In Example 2, a synthetic quartz glass block having a diameter of 298 mm and a thickness of 57 mm was arranged in a hollow space, and the temperature was lowered at 120 ° C./hour with a temperature rising rate and holding temperature similar to those in Example 1 and a holding time of 5 minutes. At this time, the maximum birefringence change amount was 2 nm / cm, and a + birefringence distribution was obtained.
[0109]
In Example 3, a synthetic quartz glass block having a diameter of 253 mm and a thickness of 76 mm was hollowly arranged, heated to 1000 ° C. at a temperature rising rate of 3000 ° C./hour, held for 30 minutes, and then cooled to 90 ° C./hour. At this time, the maximum change in birefringence was +2 nm / cm, and a + birefringence distribution was obtained.
[0110]
In Example 4, a synthetic quartz glass block having a diameter of 298 mm and a thickness of 48 mm was arranged in a hollow, heated to 800 ° C. at a heating rate of 400 ° C./hour, held for 30 minutes, and then cooled to 10 ° C./hour. At this time, the maximum change in birefringence was +2 nm / cm, and a + birefringence distribution was obtained. Since the processing temperature was low, the refractive index change region was 0 mm.
[0111]
In Example 5, a synthetic quartz glass block having a diameter of 282 mm and a thickness of 49 mm was disposed in a hollow manner, and the temperature was lowered at 100 ° C./hour with a temperature rising rate and holding temperature similar to those in Example 1 and a holding time of 10 minutes. At this time, the maximum change in birefringence was 2 nm / cm, and a + birefringence distribution was obtained.
[0112]
In Comparative Example 1, a synthetic quartz glass block having a diameter of 255 mm and a thickness of 40 mm was arranged in a hollow manner, and the temperature decreasing rate was 500 ° C./hour in the surface heating treatment shown in Example 3. The maximum change in birefringence was −5 nm / cm, which was a birefringence distribution completely opposite to the desired distribution.
[0113]
The distribution of birefringence values before and after the surface heat treatment of Comparative Example 1 is shown in FIG. The figure shows the distribution from the center side to the peripheral side, where A indicates before surface heating and B indicates after surface heating.
[0114]
In Comparative Example 2, a synthetic quartz glass block having a diameter of 255 mm and a thickness of 40 mm was arranged in a hollow manner, and in the heat treatment shown in Example 5, the rate of temperature increase was 10 ° C./hour.
[0115]
No change in birefringence due to this heat treatment was observed. Since it took time to raise the temperature, the temperature distribution in the synthetic quartz glass block disappeared and soaking was considered to have caused no birefringence change. In addition, since the temperature raising time is long, the entire heat treatment time is lengthened, and the homogeneity degradation region is as large as 10 mm.
[0116]
In Comparative Example 3, a synthetic quartz glass block having a diameter of 237 mm and a thickness of 38 mm was subjected to heat treatment under substantially the same conditions as in Example 3, but the synthetic quartz glass block was placed directly on the hearth, not in a hollow arrangement. . The amount of change in birefringence was an appropriate value of 3 nm / cm at the maximum, but the deterioration of homogeneity due to contamination from the furnace atmosphere was remarkable, and the deterioration area was as large as 10 mm.
[0117]
In Comparative Example 4, a synthetic quartz glass block having a diameter of 237 mm and a thickness of 38 mm was directly placed on the hearth, heated to 700 ° C. at a heating rate of 2800 ° C./hour, held for 60 minutes, and then cooled to 300 ° C./hour. . At this time, the maximum change in birefringence was −2 nm / cm, and a + birefringence distribution could not be obtained.
[0118]
As is clear from the above examples and comparative examples, in Examples 1 to 5, in the surface heating treatment of the second step, a rapid temperature increase of 300 ° C./hour or more is performed, and 50 ° C./hour or more and 300 ° C./hour is performed. Since cooling was performed at a temperature lowering rate of less than 1, the birefringence value monotonously increased, and a distribution having a greater change than Comparative Examples 1 to 4 could be formed.
[0119]
【The invention's effect】
As described above, according to the first aspect of the present invention, in the surface heating step, the temperature of the synthetic quartz glass block is increased by 300 ° C./hour or more to a heat treatment temperature in the range of 500 ° C. to 1100 ° C. Since the surface is heated to a higher temperature and heated to a temperature higher than the center portion, the thermal distortion on the surface side of the optical member is increased, the distortion on the peripheral side is increased, and the birefringence value on the peripheral side is increased. Can be largely changed from the birefringence value on the center side. Further, in the cooling step, the surface of the synthetic quartz glass block is cooled at a rate of temperature decrease of 50 ° C./hour or more and less than 300 ° C./hour, so that the birefringence value distribution is maintained and cooling is easy. Therefore, it is possible to easily form an optical member in which the birefringence value on the peripheral side has changed more than the birefringence value on the center side.
[0120]
In addition, the birefringence distribution thus formed has a tendency opposite to that of an optical member made of calcium fluoride crystals. Therefore, calcium fluoride crystals or annealing treatment cannot be performed due to the use of calcium fluoride crystals or one or a plurality of synthetic quartz glass optical members that cannot be annealed due to properties. A synthetic quartz glass optical member capable of reducing the distribution of relatively large birefringence values of one or more synthetic quartz glasses can be easily manufactured.
[0121]
Moreover, according to the manufacturing method of Claim 2, since the surface of the synthetic quartz glass block is cooled at a cooling rate of 50 ° C./hour or more and 200 ° C./hour or less in the cooling step, the birefringence formed in the surface heating step It is easy to maintain the distribution of values and to cool the synthetic quartz glass block, and the surface side is not rapidly cooled in the cooling process, so the tendency of the distribution of birefringence values formed in the surface heating process is difficult to change. Therefore, it is easier to reliably manufacture synthetic quartz glass having a tendency opposite to the distribution of the birefringence value of the calcium fluoride crystal by increasing the difference in birefringence value between the peripheral side and the center side.
[0122]
According to the method for producing synthetic quartz glass according to claim 3, since the ingot or the synthetic quartz glass block is annealed before the surface heating step, nonuniform residual strain during synthesis of the synthetic quartz glass is reduced. Then, a surface heating process can be performed. Therefore, it is easy to form a desired birefringence distribution in the surface heating step.
[0123]
Further, according to the manufacturing method of claim 4, the synthetic quartz glass block having a surface temperature of 300 ° C. or less is accommodated in a heating furnace heated in advance to 500 ° C. or more and 1100 ° C. or less. Since the temperature of the surface is raised, the temperature of the surface of the synthetic quartz glass block can be reliably prevented from being heated to a temperature higher than the surface heating temperature, and the temperature can be raised rapidly, making synthetic quartz glass easier. Can be manufactured.
[0124]
Furthermore, according to the manufacturing method of claim 5, since the synthetic quartz glass block obtained from the synthetic quartz glass ingot formed while rotating and heating has a rotationally symmetric birefringence distribution, If the synthetic quartz glass block is heated and cooled while rotating in the surface heating step and the cooling step, the surface of the synthetic quartz glass block can be easily heated or lowered uniformly in the circumferential direction. Therefore, it is easy to form a birefringence distribution of the synthetic quartz glass block in a rotationally symmetrical manner.
[0125]
Furthermore, according to the manufacturing method of the sixth aspect, since the surface heating step and / or the cooling step are performed in the atmosphere or in an inert gas atmosphere, the synthetic quartz glass optical member can be easily manufactured.
[0126]
Further, according to the manufacturing method described in claim 7, by performing the surface heating step and the cooling step, a compound in which the direction of the fast axis is oriented in the radial direction of the synthetic quartz glass member is measured as positive. Synthetic quartz glass optical member whose birefringence value distribution can be easily eliminated by using it together with an optical member made of calcium fluoride crystal because the refractive value forms a monotonically increasing distribution from the center side toward the peripheral side. Can be reliably manufactured.
[0127]
According to the optical member according to claim 8, the distribution of the birefringence values measured with the fast axis oriented in the radial direction from the center as positive is directed from the center toward the entire periphery. Since it has a monotonically increasing distribution, it can be used together with an optical member made of calcium fluoride crystal to easily eliminate the birefringence value distribution and to reduce the birefringence value distribution of the entire optical system. A member can be provided.
[0128]
Further, according to the optical system of the ninth aspect, since the synthetic quartz glass optical member according to the eighth aspect and the optical member made of calcium fluoride crystal are arranged in series in the optical path, the calcium fluoride crystal The birefringence value distribution of the optical member can be suppressed by the birefringence value distribution of the synthetic quartz glass optical member, and an optical system in which the birefringence value distribution is further suppressed can be provided.
[0129]
Furthermore, according to the exposure apparatus of the tenth aspect, since the illumination optical system or the projection optical system is provided with the optical system in which the birefringence value distribution is further suppressed, the birefringence value distribution is suppressed to be small as a whole. Therefore, an exposure apparatus that can perform exposure with higher accuracy can be provided.
[0130]
Moreover, according to the surface heating furnace of Claim 11 or 12, it has a synthetic quartz glass block mounting base which has a hollow part and mounts a synthetic quartz glass block, and a synthetic quartz glass block is passed through this hollow part. Since the bottom surface of the glass is exposed to the atmosphere in the furnace, heat is not directly supplied to the bottom surface of the synthetic quartz glass block from the bottom surface of the heat treatment furnace, and the entire surface of the synthetic quartz glass block is easily heated uniformly. . Further, it is possible to prevent impurities from diffusing directly from the bottom surface into the synthetic quartz glass block during surface heating. Therefore, it is possible to provide a surface heating furnace that can easily heat the entire outer surface of the optical member uniformly while preventing deterioration of quality due to impurities.
[0131]
Furthermore, according to the surface heating furnace of claim 12, the ratio of the volume of the synthetic quartz glass block to the volume in the furnace is in a range larger than 0.0005 and smaller than 0.10, and the synthetic quartz glass Since the block is arranged at a distance of 20 mm or more from the bottom surface and the furnace wall in the furnace, impurities are prevented from diffusing directly from the bottom surface and the furnace wall in the furnace to the synthetic quartz glass block, and the surface side is more abrupt. A surface heating furnace that can easily raise the temperature can be provided.
[Brief description of the drawings]
FIG. 1 is a graph plotting a birefringence change amount and a refractive index homogeneity deterioration region with respect to a heat treatment temperature of a synthetic quartz glass member.
FIG. 2 is a view showing the basic arrangement of an exposure apparatus according to an embodiment of the present invention.
FIG. 3 is a diagram showing a distribution of birefringence values of an optical member made of calcium fluoride crystal, a distribution of birefringence values of an optical member made of synthetic quartz glass, and a distribution of birefringence values of an optical system including both optical members. It is.
FIG. 4 is a cross-sectional view of a surface heating furnace used in the manufacturing method according to the embodiment of the present invention.
5 is a diagram showing the distribution of birefringence values before and after the surface heating step of the synthetic quartz glass block of Example 1. FIG.
6 is a graph showing the distribution of birefringence values before and after the surface heating step of the synthetic quartz glass block of Comparative Example 1. FIG.
[Explanation of symbols]
10 Exposure equipment
12 Illumination optics
14 Projection optical system
30 Surface heating furnace
31 Synthetic quartz glass block
40 Synthetic quartz cylinder

Claims (12)

A method of manufacturing an optical member by heat-treating a synthetic quartz glass block,
A surface heating step of heating the surface of the synthetic quartz glass block to a surface heating temperature in the range of 500 ° C. or higher and 1100 ° C. or lower at a temperature rising rate of 300 ° C./hour or higher, and heating the surface to a temperature higher than the central portion; ,
A method for producing a synthetic quartz glass optical member, comprising: a cooling step of cooling the surface of the synthetic quartz glass block at a temperature lowering rate of 50 ° C./hour or more and less than 300 ° C./hour after the surface heating step. 2. The method for producing a synthetic quartz glass optical member according to claim 1, wherein, in the cooling step, the surface of the synthetic quartz glass block is cooled at a temperature lowering rate of 50 ° C./hour or more and 200 ° C./hour or less. Prior to the surface heating step, the ingot or the synthetic quartz glass block is heated to an annealing temperature of 900 ° C. or more, held at the annealing temperature for a predetermined time, and then a temperature decrease rate of 10 ° C./hour or less to a temperature of 500 ° C. or less. The method for producing a synthetic quartz glass optical member according to claim 1, further comprising an annealing step of cooling at a step. The surface heating step is to heat up the surface of the synthetic quartz glass block by storing the synthetic quartz glass block having a surface temperature of 300 ° C. or less in a heating furnace previously heated to the surface heating temperature. The method for producing a synthetic quartz glass optical member according to any one of claims 1 to 3. The synthetic quartz glass block is produced from a synthetic quartz glass ingot formed while rotating and heated and cooled while rotating in the surface heating step and the cooling step. The manufacturing method of the synthetic quartz glass optical member as described in any one. The synthesis according to any one of claims 1 to 5, wherein the synthetic quartz glass block is treated in the atmosphere or an inert gas atmosphere in at least one of the surface heating step and the cooling step. A method for producing a quartz glass optical member. By performing the surface heating step and the cooling step, the birefringence value measured as positive when the direction of the fast axis is oriented in the radial direction of the synthetic quartz glass member is directed from the center side toward the peripheral side. The method for producing a synthetic quartz glass optical member according to claim 1, wherein a monotonically increasing distribution is formed. A synthetic quartz glass optical member manufactured by the manufacturing method according to claim 1,
Synthetic quartz characterized in that the birefringence value measured by assuming that the direction of the fast axis is positive in the radial direction of the synthetic quartz glass member has a distribution that monotonously increases from the center side toward the peripheral side. Glass optical member. An optical system comprising the synthetic quartz glass optical member according to claim 8 and an optical member made of calcium fluoride crystal arranged in series in an optical path. An exposure apparatus comprising the optical system according to claim 9 in an illumination optical system or a projection optical system. A surface heating furnace that houses and heats a synthetic quartz glass block,
It has a block mounting table made of synthetic quartz glass that has a hollow portion and mounts a synthetic quartz glass block,
A surface heating furnace characterized in that the bottom surface of the synthetic quartz glass block placed on the upper part of the block placing table is exposed to the atmosphere in the furnace through the hollow part. The ratio of the volume of the synthetic quartz glass block to the volume in the furnace is greater than 0.0005 and less than 0.10,
The surface heating furnace according to claim 11, wherein the synthetic quartz glass block is disposed at a distance of 20 mm or more from a bottom surface and a furnace wall in the furnace.

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