JP2013161919A

JP2013161919A - Exposure method

Info

Publication number: JP2013161919A
Application number: JP2012022101A
Authority: JP
Inventors: Takashi Sato; 隆佐藤
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 2012-02-03
Filing date: 2012-02-03
Publication date: 2013-08-19

Abstract

PROBLEM TO BE SOLVED: To provide an exposure method capable of correctly forming fine patterns.SOLUTION: An exposure method comprises: a step (S1) of performing first exposure with a photoresist formed on a substrate and a photomask having cyclic patterns spaced apart from each other by a first distance which is in accordance with a pitch of the patterns and a wavelength of exposure light, and then transferring the patterns on the photomask to a first position on the photoresist; and a step (S2) of performing second exposure with the photoresist and the photomask spaced apart from each other by a second distance which is in accordance with the pitch of the patterns and the wavelength of the exposure light but is different from the first distance, and then transferring the patterns on the photomask to a second position, on the photoresist, different from the first position.

Description

本発明の実施形態は、露光方法に関する。 Embodiments described herein relate generally to an exposure method.

半導体装置が微細化されるにつれて、微細なパターンを正確に形成することが難しくなってきている。 As semiconductor devices are miniaturized, it has become difficult to accurately form fine patterns.

このような問題に対し、ダブルパターニング等の露光方法が提案されている。しかしながら、ダブルパターニングでは、１回目の露光と２回目の露光との間で重ね合わせ誤差が生じるといった問題がある。 To solve such a problem, an exposure method such as double patterning has been proposed. However, the double patterning has a problem that an overlay error occurs between the first exposure and the second exposure.

また、基板上に形成されたフォトレジストと光学レンズとの間に液体を介在させた状態で露光が行われる液浸露光も提案されている。しかしながら、液浸露光では、液体の屈折率を光学レンズの屈折率以上にすることはできないため、微細化に限界がある。 In addition, immersion exposure has been proposed in which exposure is performed with a liquid interposed between a photoresist formed on a substrate and an optical lens. However, in the liquid immersion exposure, the refractive index of the liquid cannot be made higher than the refractive index of the optical lens, so there is a limit to miniaturization.

したがって、微細なパターンを正確に形成することが可能な新たな露光方法が望まれている。 Therefore, a new exposure method capable of accurately forming a fine pattern is desired.

特開２０１１−６１０３９号公報JP 2011-61039 A

微細なパターンを正確に形成することが可能な露光方法を提供する。 Provided is an exposure method capable of accurately forming a fine pattern.

実施形態に係る露光方法は、基板上に形成されたフォトレジストと周期的なパターンを有するフォトマスクとを前記パターンのピッチ及び露光光の波長に応じた第１の距離だけ離して第１の露光を行い、前記フォトマスクの前記パターンを前記フォトレジストの第１の位置に転写する工程と、前記フォトレジストと前記フォトマスクとを前記パターンのピッチ及び露光光の波長に応じた前記第１の距離とは異なる第２の距離だけ離して第２の露光を行い、前記フォトマスクの前記パターンを前記フォトレジストの前記第１の位置とは異なる第２の位置に転写する工程と、を備える。 In the exposure method according to the embodiment, a first exposure is performed by separating a photoresist formed on a substrate and a photomask having a periodic pattern by a first distance corresponding to the pitch of the pattern and the wavelength of exposure light. And transferring the pattern of the photomask to a first position of the photoresist; and the first distance according to the pitch of the pattern and the wavelength of exposure light between the photoresist and the photomask. Performing a second exposure separated by a second distance different from, and transferring the pattern of the photomask to a second position different from the first position of the photoresist.

タルボ効果の原理を模式的に示した説明図である。It is explanatory drawing which showed the principle of the Talbot effect typically. 実施形態に係る露光方法を示したフローチャートである。It is the flowchart which showed the exposure method which concerns on embodiment. 実施形態に係る露光方法の動作を示した説明図である。It is explanatory drawing which showed operation | movement of the exposure method which concerns on embodiment. 実施形態に係る露光方法の動作を示した説明図である。It is explanatory drawing which showed operation | movement of the exposure method which concerns on embodiment. 第１の露光におけるフォトレジスト表面の光強度分布を示した図である。It is the figure which showed the light intensity distribution of the photoresist surface in 1st exposure. 第２の露光におけるフォトレジスト表面の光強度分布を示した図である。It is the figure which showed the light intensity distribution of the photoresist surface in 2nd exposure. 第１の露光での光強度分布と第２の露光での光強度分布とを合成した図である。It is the figure which synthesize | combined the light intensity distribution in 1st exposure, and the light intensity distribution in 2nd exposure.

まず、実施形態の説明を行う前に、タルボ（Talbot）効果について説明する。 First, before describing the embodiment, the Talbot effect will be described.

フォトマスクに形成された周期的なパターンを干渉性の高い光源を用いて照明すると、光の進行方向に上記パターンのピッチ及び露光光の波長に応じた繰り返し周期で上記パターンの像が出現する。このような現象がタルボ（Talbot）効果である。 When a periodic pattern formed on the photomask is illuminated using a light source having high coherence, an image of the pattern appears in the light traveling direction at a repetition period corresponding to the pitch of the pattern and the wavelength of exposure light. Such a phenomenon is the Talbot effect.

図１は、タルボ効果の原理を模式的に示した説明図である。 FIG. 1 is an explanatory view schematically showing the principle of the Talbot effect.

周期的なパターン１１を有するフォトマスク１０の裏面側から照明光（図示せず）を照射する。このとき、０次光と１次光との干渉作用に基づき、照明光の進行方向において、パターン１１のピッチｐ及び照明光の波長に応じた周期Ｚ_T で、パターン１１に対応した像２１が出現する。すなわち、パターン１１に対応した光強度の高い位置２１が出現する。また、照明光の進行方向において互いに隣接する像２１の中間の位置２２では、光強度が低くなる。また、照明光の進行方向に垂直な方向（パターン１１が配列されている方向）において互いに隣接する光強度が低い位置２２の中間の位置２３では、光強度が高くなる。すなわち、照明光の進行方向において像（位置）２１からＺ_T ／２ずれ、且つパターン１１が配列されている方向において像（位置）２１からｐ／２ずれた位置に、パターン１１に対応した光強度が高い位置２３が出現する。したがって、位置２１と位置２３とで露光を行えば、ピッチｐの半分のピッチ（ｐ／２）で周期的なパターンの転写を行うことが可能である。 Illumination light (not shown) is irradiated from the back side of the photomask 10 having the periodic pattern 11. At this time, an image 21 corresponding to the pattern 11 is formed with a period Z _T according to the pitch p of the pattern 11 and the wavelength of the illumination light in the traveling direction of the illumination light based on the interference action between the zero-order light and the primary light. Appear. That is, a position 21 with high light intensity corresponding to the pattern 11 appears. In addition, the light intensity is low at an intermediate position 22 between the images 21 adjacent to each other in the traveling direction of the illumination light. In addition, the light intensity is high at a position 23 in the middle of the position 22 where the light intensity is adjacent to each other in the direction perpendicular to the traveling direction of the illumination light (the direction in which the pattern 11 is arranged). That is, the light corresponding to the pattern 11 at a position shifted by Z _T / 2 from the image (position) 21 in the traveling direction of the illumination light and shifted by p / 2 from the image (position) 21 in the direction in which the pattern 11 is arranged. A position 23 with high intensity appears. Therefore, if exposure is performed at the positions 21 and 23, it is possible to transfer a periodic pattern at a pitch (p / 2) that is half the pitch p.

なお、上記の周期Ｚ_T をタルボ周期と呼ぶことにする。すなわち、照明光の進行方向（フォトマスク１０の主面に垂直な方向）においてパターン１１に対応する像２１が一定の間隔で繰り返し出現する周期Ｚ_T を、タルボ周期と呼ぶことにする。 The period Z _T is referred to as a Talbot period. That is, the period Z _{T in} which the image 21 corresponding to the pattern 11 repeatedly appears at a constant interval in the traveling direction of the illumination light (the direction perpendicular to the main surface of the photomask 10) is called a Talbot period.

タルボ周期Ｚ_T を、２次の項まで近似して計算すると、
Ｚ_T ＝２ｐ²×ｎ／λ （式１）
となる。ただし、ｐはパターンのピッチ。λは照明光（露光光）の波長、ｎはフォトマスク１０を通過した照明光（露光光）が入射する物質の屈折率である。 When calculating the Talbot period Z _T by approximating to the second order term,
Z _T = 2p ² × n / λ (Formula 1)
It becomes. Where p is the pitch of the pattern. λ is the wavelength of the illumination light (exposure light), and n is the refractive index of the material on which the illumination light (exposure light) that has passed through the photomask 10 is incident.

なお、パターンのピッチｐが波長λに近づくと、２次の項までの近似では誤差が大きくなる。このような場合、４次の項まで近似すると、
Ｚ_T ＝（２ｐ²×ｎ／λ）×（１／（１＋λ²／４ｐ²ｎ²））（式２）
となる。 As the pattern pitch p approaches the wavelength λ, the error increases in the approximation up to the second order term. In such a case, approximating to the fourth order term,
Z _T = (2p ² × n / λ) × (1 / (1 + λ ² / 4p ² n ² )) (Formula 2)
It becomes.

以下、上述した事項に基づいて実施形態の説明を行う。 Hereinafter, the embodiment will be described based on the above-described matters.

図２は、本実施形態の露光方法を示したフローチャートである。図３及び図４は、本実施形態の露光方法の動作を示した説明図である。 FIG. 2 is a flowchart showing the exposure method of this embodiment. 3 and 4 are explanatory views showing the operation of the exposure method of the present embodiment.

まず、第１の露光を行う（Ｓ１）。具体的には、図３に示すように、フォトレジスト３２が形成された半導体基板３１と、周期的なパターン（例えば、ラインアンドスペースパターン）４１を有するフォトマスク４０とを用意し、パターン４１のピッチｐ及び露光光５０の波長λに応じた第１の距離Ｌ１だけ離して、第１の露光を行う。すなわち、フォトレジスト３２とフォトマスク４０とを離間させ、フォトレジスト３２とフォトマスク４０との間に光学レンズを介在させないプロキシミティ露光を行う。第１の距離Ｌ１は、タルボ効果によってパターン４１の開口部の像の光強度が最大となるように選択する。この第１の露光により、フォトマスク４０に形成されたパターン４１がフォトレジスト３２の第１の位置６１に転写される。 First, first exposure is performed (S1). Specifically, as shown in FIG. 3, a semiconductor substrate 31 on which a photoresist 32 is formed and a photomask 40 having a periodic pattern (for example, a line and space pattern) 41 are prepared. The first exposure is performed by separating the first distance L1 according to the pitch p and the wavelength λ of the exposure light 50. That is, the proximity exposure is performed in which the photoresist 32 and the photomask 40 are separated from each other, and no optical lens is interposed between the photoresist 32 and the photomask 40. The first distance L1 is selected so that the light intensity of the image of the opening of the pattern 41 is maximized by the Talbot effect. By this first exposure, the pattern 41 formed on the photomask 40 is transferred to the first position 61 of the photoresist 32.

図５は、第１の露光におけるフォトレジスト３２の表面の光強度分布を示している。図５に示すように、第１の位置６１で光強度が高くなっている。 FIG. 5 shows the light intensity distribution on the surface of the photoresist 32 in the first exposure. As shown in FIG. 5, the light intensity is high at the first position 61.

次に、第２の露光を行う（Ｓ２）。具体的には、図４に示すように、フォトマスク４０のパターン４１のピッチｐ及び露光光５０の波長λに応じた第２の距離Ｌ２（第２の距離Ｌ２は第１の距離Ｌ１とは異なる）だけ離して、第２の露光を行う。すなわち、フォトレジスト３２とフォトマスク４０とを離間させ、フォトレジスト３２とフォトマスク４０との間に光学レンズを介在させないプロキシミティ露光を行う。第２の距離Ｌ２は、タルボ効果によってパターン４１の開口部の像の光強度が最大となるように選択する。この第２の露光により、フォトマスク４０に形成されたパターン４１がフォトレジスト３２の第２の位置６２に転写される。第２の位置６２は、第１の位置６１から水平方向にｐ／２だけずれている。 Next, second exposure is performed (S2). Specifically, as shown in FIG. 4, the second distance L2 corresponding to the pitch p of the pattern 41 of the photomask 40 and the wavelength λ of the exposure light 50 (the second distance L2 is the first distance L1). A second exposure is performed with a distance of (different). That is, the proximity exposure is performed in which the photoresist 32 and the photomask 40 are separated from each other, and no optical lens is interposed between the photoresist 32 and the photomask 40. The second distance L2 is selected so that the light intensity of the image of the opening of the pattern 41 is maximized due to the Talbot effect. By this second exposure, the pattern 41 formed on the photomask 40 is transferred to the second position 62 of the photoresist 32. The second position 62 is offset from the first position 61 by p / 2 in the horizontal direction.

図６は、第２の露光におけるフォトレジスト３２の表面の光強度分布を示している。図６に示すように、第１の位置６１で光強度が低くなり、第２の位置６２で光強度が高くなっている。 FIG. 6 shows the light intensity distribution on the surface of the photoresist 32 in the second exposure. As shown in FIG. 6, the light intensity is low at the first position 61 and the light intensity is high at the second position 62.

図７は、第１の露光での光強度分布と第２の露光での光強度分布とを合成した図である。図７からわかるように、第１の露光及び第２の露光を行うことで、第１の位置６１及び第２の位置６２で光強度が高くなっている。したがって、フォトマスク４０のパターン４１のピッチｐの半分のピッチ（ｐ／２）で露光を行うことができる。 FIG. 7 is a diagram in which the light intensity distribution in the first exposure and the light intensity distribution in the second exposure are combined. As can be seen from FIG. 7, the light intensity is increased at the first position 61 and the second position 62 by performing the first exposure and the second exposure. Therefore, exposure can be performed at a pitch (p / 2) that is half the pitch p of the pattern 41 of the photomask 40.

上述した第１の距離Ｌ１と第２の距離Ｌ２との差Ｌ２−Ｌ１をＤとすると、
Ｄ＝（２ｍ−１）×Ｚ_T／２（式３）
と表される。ただし、Ｚ_T は上述したタルボ周期である。すなわち、Ｚ_T は、フォトマスクの主面に垂直な方向（露光光の進行方向）におけるパターン４１に基づく光強度の繰り返し周期である。また、ｍは正の整数である。 When the difference L2−L1 between the first distance L1 and the second distance L2 is D,
D = (2m−1) × Z _T / 2 (Formula 3)
It is expressed. Where Z _T is the Talbot period described above. That is, Z _T is a repetition period of light intensity based on the pattern 41 in a direction perpendicular to the main surface of the photomask (advancing direction of exposure light). M is a positive integer.

また、先に示した（式１）と上記（式３）とを用いると、
Ｄ＝（２ｍ−１）×ｎ×ｐ²／λ （式４）
と表される。 Moreover, when using (Equation 1) and (Equation 3) shown above,
D = (2m−1) × n × p ² / λ (Formula 4)
It is expressed.

以上のようにして第１及び第２の露光を行った後、現像を行う（Ｓ３）。その結果、パターン４１のピッチｐの半分のピッチ（ｐ／２）を有する周期パターンを形成することができる。 After performing the first and second exposures as described above, development is performed (S3). As a result, a periodic pattern having a pitch (p / 2) that is half the pitch p of the pattern 41 can be formed.

以上のように、本実施形態では、タルボ効果を利用して第１及び第２の露光を行うことにより、フォトマスクに形成されているパターンのピッチの半分のピッチで、フォトレジストにパターンを転写することができる。その結果、微細なパターンを正確に形成することが可能となる。また、プロキシミティ露光であるため、結像光学系が不要であり、収差のない露光を行うことが可能である。 As described above, in the present embodiment, by performing the first and second exposures using the Talbot effect, the pattern is transferred to the photoresist at a half pitch of the pattern formed on the photomask. can do. As a result, it is possible to accurately form a fine pattern. In addition, since it is proximity exposure, an imaging optical system is unnecessary, and exposure without aberration can be performed.

なお、上述した実施形態において、フォトレジスト３２とフォトマスク４０との間には、空気（屈折率ｎ＝１）を介在させてもよいが、所望の液体を介在させてもよい。一般に、上述したような周期パターン（ピッチｐ）では、１次光が発生する条件は、
ｐ＞λ／ｎ（式５）
となる。したがって、屈折率ｎが大きいほど、ピッチｐを小さくすることができる。フォトレジスト３２とフォトマスク４０との間に屈折率ｎの大きい液体を介在させることで、ピッチｐを小さくすることが可能である。すなわち、第１の露光及び第２の露光ともに、フォトレジストとフォトマスクとの間に所望の液体を介在させた状態で行うことで、ピッチの小さいパターンを形成することが可能である。 In the above-described embodiment, air (refractive index n = 1) may be interposed between the photoresist 32 and the photomask 40, but a desired liquid may be interposed. Generally, in the periodic pattern (pitch p) as described above, the condition for generating primary light is:
p> λ / n (Formula 5)
It becomes. Therefore, the pitch p can be reduced as the refractive index n increases. By interposing a liquid having a high refractive index n between the photoresist 32 and the photomask 40, the pitch p can be reduced. That is, a pattern with a small pitch can be formed by performing both the first exposure and the second exposure in a state where a desired liquid is interposed between the photoresist and the photomask.

また、フォトレジストとフォトマスクとの間に光学レンズを介在させないプロキシミティ露光であるため、液体の屈折率を光学レンズの屈折率よりも小さくするといった制約がなく、屈折率の大きな液体を使用することが可能である。そのため、非常に小さなピッチのパターンを形成することが可能である。 In addition, since the proximity exposure does not include an optical lens between the photoresist and the photomask, there is no restriction that the refractive index of the liquid is smaller than the refractive index of the optical lens, and a liquid having a large refractive index is used. It is possible. Therefore, it is possible to form a pattern with a very small pitch.

本発明のいくつかの実施形態を説明したが、これらの実施形態は、例として提示したものであり、発明の範囲を限定することは意図していない。これら新規な実施形態は、その他の様々な形態で実施されることが可能であり、発明の要旨を逸脱しない範囲で、種々の省略、置き換え、変更を行うことができる。これら実施形態やその変形は、発明の範囲や要旨に含まれるとともに、特許請求の範囲に記載された発明とその均等の範囲に含まれる。 Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

１０…フォトマスク１１…パターン
２１…光強度の高い位置２２…光強度の低い位置
２３…光強度の高い位置
３１…半導体基板３２…フォトレジスト
４０…フォトマスク４１…パターン
５０…露光光６１…第１の位置６２…第２の位置 DESCRIPTION OF SYMBOLS 10 ... Photomask 11 ... Pattern 21 ... High light intensity position 22 ... Low light intensity position 23 ... High light intensity position 31 ... Semiconductor substrate 32 ... Photoresist 40 ... Photomask 41 ... Pattern 50 ... Exposure light 61 ... First 1 position 62 ... 2nd position

Claims

A first exposure is performed by separating a photoresist formed on a substrate and a photomask having a periodic pattern by a first distance according to a pitch of the pattern and a wavelength of exposure light, and the photomask Transferring a pattern to a first position of the photoresist;
Second exposure is performed by separating the photoresist and the photomask by a second distance different from the first distance according to the pitch of the pattern and the wavelength of exposure light, and the pattern of the photomask is removed. Transferring to a second position different from the first position of the photoresist;
With
The difference D between the first distance and the second distance is such that the light intensity repetition period based on the pattern in the direction perpendicular to the main surface of the photomask is Z, and m is a positive integer.
D = (2m−1) × Z / 2
And
The exposure method, wherein the first exposure and the second exposure are performed with a liquid interposed between the photoresist and the photomask.

A first exposure is performed by separating a photoresist formed on a substrate and a photomask having a periodic pattern by a first distance according to a pitch of the pattern and a wavelength of exposure light, and the photomask Transferring a pattern to a first position of the photoresist;
Second exposure is performed by separating the photoresist and the photomask by a second distance different from the first distance according to the pitch of the pattern and the wavelength of exposure light, and the pattern of the photomask is removed. Transferring to a second position different from the first position of the photoresist;
An exposure method comprising:

The difference D between the first distance and the second distance is such that the light intensity repetition period based on the pattern in the direction perpendicular to the main surface of the photomask is Z, and m is a positive integer.
D = (2m−1) × Z / 2
The exposure method according to claim 2, wherein:

The difference D between the first distance and the second distance is that the pitch is p, the wavelength of the exposure light is λ, and the refractive index of the material interposed between the photoresist and the photomask is n, m is a positive integer,
D = (2m−1) × n × p ² / λ
The exposure method according to claim 2, wherein:

The exposure method according to claim 2, wherein the first exposure and the second exposure are performed in a state where a liquid is interposed between the photoresist and the photomask.