JP5884469B2 - Film thickness inspection method - Google Patents

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JP5884469B2
JP5884469B2 JP2011282488A JP2011282488A JP5884469B2 JP 5884469 B2 JP5884469 B2 JP 5884469B2 JP 2011282488 A JP2011282488 A JP 2011282488A JP 2011282488 A JP2011282488 A JP 2011282488A JP 5884469 B2 JP5884469 B2 JP 5884469B2
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知也 城森
知也 城森
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Description

本発明は、絶縁膜の膜厚を検査する膜厚検査方法に関するものである。   The present invention relates to a film thickness inspection method for inspecting the film thickness of an insulating film.

従来、例えば特許文献１に示されるように、シリコン基板と、このシリコン基板上に形成された絶縁膜及び導電パターンと、を備えるセンサデバイス構造体の検査方法が提案されている。この検査方法では、導電パターンとシリコン基板間の静電容量を測定し、この測定された静電容量値に基づいて絶縁膜の膜厚の良否を評価している。   Conventionally, as disclosed in Patent Document 1, for example, a sensor device structure inspection method including a silicon substrate, and an insulating film and a conductive pattern formed on the silicon substrate has been proposed. In this inspection method, the capacitance between the conductive pattern and the silicon substrate is measured, and the quality of the insulating film is evaluated based on the measured capacitance value.

特開２００７−３３２１２号公報JP 2007-33212 A

ところで、特許文献１に示される検査方法では、測定された静電容量値と、絶縁膜の膜厚を一定と仮定した場合に成立するコンデンサの静電容量値とが等しいという等式に基づいて、絶縁膜の膜厚を評価している。しかしながら、絶縁膜の膜厚は、実際には一定でなく、ばらつきがある。そのため、測定した静電容量値には、上記したばらつきの影響が含まれることになる。その値は、膜厚が一定であると仮定した場合のコンデンサの静電容量とは異なるため、上記した等式に基づいて膜厚を検査する方法では、膜厚の検査精度が十分ではなかった。   By the way, in the inspection method disclosed in Patent Document 1, based on the equation that the measured capacitance value is equal to the capacitance value of the capacitor established when the film thickness of the insulating film is assumed to be constant. The film thickness of the insulating film is evaluated. However, the thickness of the insulating film is not actually constant and varies. Therefore, the measured capacitance value includes the influence of the above-described variation. Since the value is different from the capacitance of the capacitor when the film thickness is assumed to be constant, the method for inspecting the film thickness based on the above equation does not have sufficient film thickness inspection accuracy. .

そこで、本発明は上記問題点に鑑み、絶縁膜の膜厚の検査精度が向上された膜厚検査方法を提供することを目的とする。   In view of the above problems, an object of the present invention is to provide a film thickness inspection method in which the inspection accuracy of the film thickness of an insulating film is improved.

上記した目的を達成するために、請求項１に記載の発明は、第１半導体層（１１）と第２半導体層（１２）と両層の間に挟まれた絶縁膜（１３）とを有する半導体基板（１０）を備え、第２半導体層（１２）と絶縁膜（１３）とを所定形状にエッチングすることで形成された、第１半導体層（１１）に対して可動な可動部（２３）と、絶縁膜（１３）を介して第１半導体層（１１）に固定された固定部（２２）と、可動部（２３）及び固定部（２２）を連結する梁（２４）とが第２半導体層（１２）に形成されたＭＥＭＳデバイス（１００）の絶縁膜（１３）の膜厚を検査する膜厚検査方法であって、梁（２４）は、第１半導体層（１１）と第２半導体層（１２）との積層方向に可撓性を有しており、可動部（２３）と第１半導体層（１１）との間に働く静電気力が徐々に高くなるように、可動部（２３）と第１半導体層（１１）とに検査電圧を印加することで、可動部（２３）を絶縁膜（１３）に近づける第１電圧印加工程と、該第１電圧印加工程時にて、可動部（２３）が絶縁膜（１３）に接触した際の接触電圧を計測する第１電圧計測工程と、該第１電圧計測工程後、可動部（２３）と第１半導体層（１１）との間に働く静電気力が徐々に低くなるように検査電圧を下げることで、可動部（２３）を絶縁膜（１３）から離反させる第２電圧印加工程と、該第２電圧印加工程時にて、可動部（２３）が絶縁膜（１３）から離反する際の離反電圧を計測する第２電圧計測工程と、該第２電圧計測工程後、検査電圧が印加されていない場合における可動部（２３）と絶縁膜（１３）との間の平均間隔をｄ０、可動部（２３）の下に位置する絶縁膜（１３）の最大厚さをｄ１、固定部（２２）の絶縁膜（１３）の厚さをｄ２、空気誘電率をε、絶縁膜（１３）の比誘電率をεｒ、可動部（２３）における絶縁膜（１３）及び第１半導体層（１１）との対向面積をＡ、梁（２４）における積層方向のバネ定数をｋ、接触電圧をＶ１、離反電圧をＶ２とすると、下記式

Figure 0005884469
Figure 0005884469
 に基づいて、平均間隔ｄ０、最大厚さｄ１を求めた後、ｄ２−ｄ０より、可動部（２３）の下に位置する絶縁膜（１３）の平均厚さｄ３を演算する演算工程と、を有することを特徴とする。 In order to achieve the above object, the invention described in claim 1 includes a first semiconductor layer (11), a second semiconductor layer (12), and an insulating film (13) sandwiched between both layers. A movable part (23), which includes a semiconductor substrate (10) and is movable with respect to the first semiconductor layer (11), which is formed by etching the second semiconductor layer (12) and the insulating film (13) into a predetermined shape. ), A fixed part (22) fixed to the first semiconductor layer (11) through the insulating film (13), and a beam (24) connecting the movable part (23) and the fixed part (22). 2 is a film thickness inspection method for inspecting the film thickness of the insulating film (13) of the MEMS device (100) formed on the semiconductor layer (12), wherein the beam (24) is connected to the first semiconductor layer (11) and the first semiconductor layer (12). 2 has flexibility in the stacking direction with the semiconductor layer (12), and the movable portion (23) and the first semiconductor layer (11). By applying an inspection voltage to the movable part (23) and the first semiconductor layer (11) so that the electrostatic force acting between the movable part (23) and the first semiconductor layer (11) gradually increases, the movable part (23) is brought closer to the insulating film (13). A first voltage applying step, a first voltage measuring step of measuring a contact voltage when the movable part (23) contacts the insulating film (13) at the time of the first voltage applying step, and the first voltage measuring step. Thereafter, the inspection voltage is lowered so that the electrostatic force acting between the movable part (23) and the first semiconductor layer (11) is gradually lowered, thereby moving the movable part (23) away from the insulating film (13). A second voltage applying step, a second voltage measuring step of measuring a separation voltage when the movable portion (23) is separated from the insulating film (13) in the second voltage applying step, and the second voltage measuring step. Thereafter, the movable part (23) and the insulating film (13) when no inspection voltage is applied. D 0 the average distance between the, d 1 the maximum thickness of the insulating film located below (13) of the movable portion (23), d 2 the thickness of the insulating film (13) of the fixed part (22), an air dielectric constant epsilon, the dielectric constant epsilon r of the insulating film (13), the opposing area between the insulating film (13) and the first semiconductor layer in the movable part (23) (11) a, in the beam (24) When the spring constant in the stacking direction is k, the contact voltage is V 1 , and the separation voltage is V 2 ,
Figure 0005884469
Figure 0005884469
 Then, after obtaining the average distance d 0 and the maximum thickness d 1 , the average thickness d 3 of the insulating film (13) located under the movable part (23) is calculated from d 2 -d 0. And an arithmetic step.

可動部（２３）の下に位置する絶縁膜（１３）、すなわち、エッチングされた絶縁膜（１３）の表面には突起があり、突起形成部分において、絶縁膜（１３）の厚さが最大となっている。これに対して、本発明では、絶縁膜（１３）の最大厚さｄ１を除いた、絶縁膜（１３）の平均厚さｄ３を求めている。これによれば、絶縁膜の表面に形成された突起（膜厚のばらつき）を含む静電容量と、絶縁膜の膜厚が一定とした場合の静電容量とが等しいという等式に基づいて、絶縁膜（１３）の膜厚ｄ３を検査する方法と比べて、膜厚ｄ３の検査精度が向上される。なお、上記した数１，２の成立する理由は、実施形態にて詳説する。 There are protrusions on the surface of the insulating film (13) located under the movable part (23), that is, the etched insulating film (13), and the thickness of the insulating film (13) is maximum at the protrusion forming portion. It has become. In contrast, in the present invention, excluding the maximum thickness d 1 of the insulating layer (13), and obtain the average thickness d 3 of the insulating film (13). According to this, based on the equation that the capacitance including protrusions (film thickness variation) formed on the surface of the insulating film is equal to the capacitance when the thickness of the insulating film is constant. , as compared to the method of inspecting the thickness d 3 of the insulating film (13), the inspection accuracy of the thickness d 3 is improved. The reason why the above formulas 1 and 2 are established will be described in detail in the embodiment.

請求項２に記載のように、第１電圧計測工程において、可動部（２３）の変位量に基づいて、接触電圧を計測する構成が良い。   As described in claim 2, in the first voltage measurement step, the contact voltage is preferably measured based on the displacement amount of the movable portion (23).

第１電圧印加工程にて、可動部（２３）と第１半導体層（１１）とに検査電圧が印加された際、可動部（２３）には、梁（２４）の復元力と静電気力とが互いに逆向きに生じる。当初、可動部（２３）は、上記した２つの力が釣り合った状態で、徐々に絶縁膜（１３）に近づく。しかしながら、静電気力が復元力を上回ると、可動部（２３）は瞬時に絶縁膜（１３）に接触して、停止する。したがって、可動部（２３）の変位における、急激な振る舞いの後に、停止した瞬間の検査電圧をモニタリングすれば、接触電圧を計測することができる。   When an inspection voltage is applied to the movable part (23) and the first semiconductor layer (11) in the first voltage application step, the restoring force and electrostatic force of the beam (24) are applied to the movable part (23). Occur in opposite directions. Initially, the movable part (23) gradually approaches the insulating film (13) in a state where the two forces described above are balanced. However, when the electrostatic force exceeds the restoring force, the movable portion (23) instantaneously contacts the insulating film (13) and stops. Therefore, the contact voltage can be measured by monitoring the inspection voltage at the moment of stopping after the sudden behavior in the displacement of the movable part (23).

請求項３に記載のように、第２電圧計測工程において、可動部（２３）の変位量に基づいて、離反電圧を計測する構成が良い。   According to a third aspect of the present invention, in the second voltage measurement step, it is preferable to measure the separation voltage based on the displacement amount of the movable part (23).

第２電圧印加工程にて、可動部（２３）と第１半導体層（１１）とに印加している検査電圧を徐々に弱めた結果、復元力が静電気力を上回ると、可動部（２３）は瞬時に絶縁膜（１３）から離反する。したがって、可動部（２３）の変位における、急激な振る舞いを示す瞬間の検査電圧をモニタリングすれば、離反電圧を計測することができる。   If the restoring force exceeds the electrostatic force as a result of gradually weakening the inspection voltage applied to the movable part (23) and the first semiconductor layer (11) in the second voltage application step, the movable part (23) Instantly leaves the insulating film (13). Accordingly, the separation voltage can be measured by monitoring the test voltage at the moment when the displacement of the movable part (23) shows an abrupt behavior.

請求項４に記載のように、ドップラー効果型レーザー干渉計によって、可動部（２３）の変位量を計測する構成を採用することができる。これによれば、非接触で可動部（２３）の変位量を計測することができる。   As described in claim 4, it is possible to employ a configuration in which the displacement of the movable portion (23) is measured by a Doppler effect type laser interferometer. According to this, the displacement amount of the movable part (23) can be measured without contact.

請求項５に記載のように、第１電圧計測工程において、可動部（２３）と第１半導体層（１１）との間に形成されるコンデンサの静電容量に基づいて、接触電圧を計測する構成が良い。   As described in claim 5, in the first voltage measurement step, the contact voltage is measured based on the capacitance of the capacitor formed between the movable part (23) and the first semiconductor layer (11). Good configuration.

第１電圧印加工程にて、可動部（２３）が、復元力と静電気力とが釣り合った状態で、徐々に絶縁膜（１３）に近づいている場合、可動部（２３）と第１半導体層（１１）との間に構成されるコンデンサの静電容量は、徐々に変化する。しかしながら、静電気力が復元力を上回り、可動部（２３）が絶縁膜（１３）に接触すると、コンデンサの静電容量が瞬時に上昇する。したがって、コンデンサの静電容量における、瞬時に上昇した瞬間の検査電圧をモニタリングすれば、接触電圧を計測することができる。   When the movable part (23) gradually approaches the insulating film (13) in a state where the restoring force and the electrostatic force are balanced in the first voltage application step, the movable part (23) and the first semiconductor layer The capacitance of the capacitor formed between (11) gradually changes. However, when the electrostatic force exceeds the restoring force and the movable part (23) contacts the insulating film (13), the capacitance of the capacitor increases instantaneously. Therefore, the contact voltage can be measured by monitoring the instantaneous inspection voltage in the capacitance of the capacitor.

請求項６に記載のように、第２電圧計測工程において、可動部（２３）と第１半導体層（１１）との間に形成されるコンデンサの静電容量に基づいて、離反電圧を計測する構成が良い。   According to a sixth aspect of the present invention, in the second voltage measurement step, the separation voltage is measured based on the capacitance of the capacitor formed between the movable part (23) and the first semiconductor layer (11). Good configuration.

第２電圧印加工程にて、復元力が静電気力を上回ると、可動部（２３）は瞬時に絶縁膜（１３）から離反し、コンデンサの静電容量が瞬時に下降する。したがって、コンデンサの静電容量における、瞬時に下降した瞬間の検査電圧をモニタリングすれば、離反電圧を計測することができる。   When the restoring force exceeds the electrostatic force in the second voltage application step, the movable part (23) is instantaneously separated from the insulating film (13), and the capacitance of the capacitor is instantaneously lowered. Therefore, the separation voltage can be measured by monitoring the inspection voltage at the moment when the capacitance of the capacitor decreases instantaneously.

請求項７に記載のように、ＭＥＭＳデバイス（１００）としては、加速度センサや角速度センサを採用することができる。   As described in claim 7, an acceleration sensor or an angular velocity sensor can be adopted as the MEMS device (100).

ＭＥＭＳデバイスの概略構成を示す断面図である。It is sectional drawing which shows schematic structure of a MEMS device. 電圧印加前の可動部を示す断面図である。It is sectional drawing which shows the movable part before a voltage application. 電圧印加による可動部の変位を示す断面図である。It is sectional drawing which shows the displacement of the movable part by voltage application. 可動部と絶縁膜との接触を示す断面図である。It is sectional drawing which shows the contact of a movable part and an insulating film. 検査電圧と可動部の変位を示すグラフ図である。It is a graph which shows a test voltage and the displacement of a movable part. 接触電圧と離反電圧それぞれの関係式の導出を説明するためのＭＥＭＳデバイスの簡略図であり、（ａ）は電圧印加前、（ｂ）は電圧印加時を示している。It is a simplification figure of a MEMS device for explaining derivation of a relational expression of each of contact voltage and separation voltage, (a) shows before voltage application and (b) shows the time of voltage application. 変位測定手段の変形例を示す断面図である。It is sectional drawing which shows the modification of a displacement measuring means.

以下、本発明の実施の形態を図に基づいて説明する。
（第１実施形態）
図１〜図６に基づいて、本実施形態に係る膜厚検査方法を説明する。なお、以下においては、互いに直交の関係にある方向をｘ方向及びｙ方向、これら２つの方向に直交する方向をｚ方向と示す。なお、ｚ方向が、特許請求の範囲に記載の積層方向に相当する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
A film thickness inspection method according to the present embodiment will be described with reference to FIGS. In the following, directions that are orthogonal to each other are referred to as an x direction and ay direction, and a direction orthogonal to these two directions is referred to as a z direction. The z direction corresponds to the stacking direction described in the claims.

図１に示すように、ＭＥＭＳデバイス１００は、半導体基板１０と、半導体基板１０に形成された微細構造体２０と、を有する。半導体基板１０は、第１半導体層１１と第２半導体層１２との間に絶縁膜１３が挟まれて成るＳＯＩ基板であり、第１半導体層１１の主面１１ａは、ｘ方向とｙ方向とによって規定されるｘ−ｙ平面に沿っている。なお、半導体基板１０の厚さ、及び、構成材料は設計時に決定されるため、絶縁膜１３の厚さ、及び、誘電率などは既知となっている。   As shown in FIG. 1, the MEMS device 100 includes a semiconductor substrate 10 and a microstructure 20 formed on the semiconductor substrate 10. The semiconductor substrate 10 is an SOI substrate in which an insulating film 13 is sandwiched between a first semiconductor layer 11 and a second semiconductor layer 12, and a main surface 11a of the first semiconductor layer 11 has an x direction and a y direction. Along the xy plane defined by Since the thickness and constituent materials of the semiconductor substrate 10 are determined at the time of design, the thickness and dielectric constant of the insulating film 13 are known.

微細構造体２０は、周知の露光技術を用いて、第２半導体層１２と絶縁膜１３とを所定形状にエッチングすることで形成されたものである。微細構造体２０は、絶縁膜１３を介さずに、第１半導体層１１に対して第２半導体層１２が浮いた浮遊部２１と、絶縁膜１３を介して、第１半導体層１１に第２半導体層１２が固定された固定部２２と、を有する。浮遊部２１は、可動部２３と、該可動部２３と固定部２２とを連結する、ｚ方向に可撓性を有する梁２４と、を有する。これら可動部２３と梁２４の形状は、設計時に決定される。そのため、可動部２３における絶縁膜１３及び第１半導体層１１との対向面積と、梁２４のｚ方向のバネ定数などは既知となっている。   The fine structure 20 is formed by etching the second semiconductor layer 12 and the insulating film 13 into a predetermined shape using a known exposure technique. The microstructure 20 has a floating portion 21 in which the second semiconductor layer 12 floats with respect to the first semiconductor layer 11 without the insulating film 13 and the second semiconductor layer 11 on the first semiconductor layer 11 via the insulating film 13. And a fixing portion 22 to which the semiconductor layer 12 is fixed. The floating portion 21 includes a movable portion 23 and a beam 24 that connects the movable portion 23 and the fixed portion 22 and has flexibility in the z direction. The shapes of the movable part 23 and the beam 24 are determined at the time of design. For this reason, the area of the movable portion 23 facing the insulating film 13 and the first semiconductor layer 11 and the spring constant of the beam 24 in the z direction are known.

なお、上記した微細構造体２０を形成する際、第２半導体層１２の不要部位はウエットエッチングなどによって除去される。しかしながら、可動部２３の下にエッチング液が侵入し難いため、可動部２３の下に意図しない突起１３ａが生じ、その部位だけ局所的に厚みを増している。   Note that when forming the microstructure 20 described above, unnecessary portions of the second semiconductor layer 12 are removed by wet etching or the like. However, since it is difficult for the etching solution to enter under the movable portion 23, an unintended protrusion 13a is generated under the movable portion 23, and the thickness is locally increased only at that portion.

次に、図２〜図５に基づいて、絶縁膜１３の膜厚検査方法を説明する。図２に示すように、第１半導体層１１と第２半導体層１２とに検査電圧を印加する。こうすることで、第１半導体層１１と第２半導体層１２とに静電気力を発生させ、図３に示すように、可動部２３を絶縁膜１３側に引き寄せる。この可動部２３のｚ方向への変位は、可動部２３の変位によって生じるレーザーのドップラー効果によって測定される。本実施形態では、可動部２３の変位測定手段３０として、ドップラー効果型レーザー干渉計を用いている。   Next, a film thickness inspection method for the insulating film 13 will be described with reference to FIGS. As shown in FIG. 2, an inspection voltage is applied to the first semiconductor layer 11 and the second semiconductor layer 12. By doing so, electrostatic force is generated in the first semiconductor layer 11 and the second semiconductor layer 12, and the movable portion 23 is drawn toward the insulating film 13 as shown in FIG. The displacement of the movable part 23 in the z direction is measured by a laser Doppler effect caused by the displacement of the movable part 23. In this embodiment, a Doppler effect type laser interferometer is used as the displacement measuring means 30 of the movable part 23.

図５に示すように、可動部２３に働く静電気力が徐々に高くなるよう、検査電圧を徐々に高める。こうすることで、可動部２３は絶縁膜１３の方へと徐々に変位させる。この際、可動部２３には、梁２４の復元力と静電気力とが互いに逆向きに生じる。可動部２３は、これら２つの力が釣り合った状態で、徐々に絶縁膜１３に近づく。以上が、第１電圧印加工程である。   As shown in FIG. 5, the inspection voltage is gradually increased so that the electrostatic force acting on the movable portion 23 gradually increases. In this way, the movable part 23 is gradually displaced toward the insulating film 13. At this time, the restoring force and the electrostatic force of the beam 24 are generated in the movable portion 23 in opposite directions. The movable part 23 gradually approaches the insulating film 13 in a state where these two forces are balanced. The above is the first voltage application step.

検査電圧の上昇に伴って、可動部２３に生じる復元力と静電気力は徐々に高まる。そして、静電気力が復元力を上回ると、図４及び図５に示すように、可動部２３は瞬時に絶縁膜１３（突起１３ａ）に接触して、停止する。この瞬間の検査電圧が、特許請求の範囲に記載の接触電圧に相当する。この接触電圧を計測しておく。以上が、第１電圧計測工程である。   As the inspection voltage increases, the restoring force and electrostatic force generated in the movable portion 23 gradually increase. When the electrostatic force exceeds the restoring force, the movable portion 23 instantaneously contacts the insulating film 13 (projection 13a) and stops as shown in FIGS. This instantaneous inspection voltage corresponds to the contact voltage described in the claims. This contact voltage is measured in advance. The above is the first voltage measurement step.

第１電圧計測工程後、今度は、可動部２３に働く静電気力が徐々に低くなるよう、検査電圧を徐々に低める。以上が、第２電圧印加工程である。   After the first voltage measurement process, the inspection voltage is gradually lowered so that the electrostatic force acting on the movable portion 23 is gradually lowered. The above is the second voltage application step.

検査電圧の低下に伴って、可動部２３に生じる静電気力が徐々に低まる。復元力が静電気力を上回ると、図５に示すように、可動部２３は瞬時に絶縁膜１３（突起１３ａ）から離反する。この瞬間の検査電圧が、特許請求の範囲に記載の離反電圧に相当する。この離反電圧を計測しておく。以上が、第２電圧計測工程である。   As the inspection voltage decreases, the electrostatic force generated in the movable portion 23 gradually decreases. When the restoring force exceeds the electrostatic force, as shown in FIG. 5, the movable part 23 is instantaneously separated from the insulating film 13 (projection 13a). This instantaneous inspection voltage corresponds to the separation voltage described in the claims. This separation voltage is measured in advance. The above is the second voltage measurement step.

第２電圧計測工程後、計測した接触電圧Ｖ１、離反電圧Ｖ２、既知である、固定部２２を構成する絶縁膜１３の厚さｄ２、空気誘電率ε、絶縁膜１３の比誘電率εｒ、可動部２３における絶縁膜１３及び第１半導体層１１との対向面積Ａ、梁２４におけるｚ方向のバネ定数ｋ、及び、後述する演算式に基づいて、検査電圧が印加されていない場合における可動部２３と絶縁膜１３との間の平均間隔ｄ０、可動部２３の下に位置する絶縁膜１３の最大厚さ、すなわち、突起１３ａの主面１１ａからの長さｄ１を求める。その後、ｄ２−ｄ０より、可動部２３の下に位置する絶縁膜１３の平均厚さｄ３を演算する。以上が、演算工程である。 After the second voltage measurement step, the measured contact voltage V 1 , separation voltage V 2 , known thickness d 2 of the insulating film 13 constituting the fixed portion 22, air dielectric constant ε, and relative dielectric constant of the insulating film 13 When the inspection voltage is not applied based on ε r , the area A facing the insulating film 13 and the first semiconductor layer 11 in the movable portion 23, the spring constant k in the z direction in the beam 24, and an arithmetic expression described later. The average distance d 0 between the movable portion 23 and the insulating film 13 and the maximum thickness of the insulating film 13 located under the movable portion 23, that is, the length d 1 of the protrusion 13a from the main surface 11a are obtained. Thereafter, an average thickness d 3 of the insulating film 13 located under the movable portion 23 is calculated from d 2 -d 0 . The above is the calculation process.

上記した各工程を経ることで、可動部２３の下に位置する絶縁膜１３の平均厚さｄ３が求められる。これにより、可動部２３を構成する第１半導体層１１と、可動部２３の下に位置する第２半導体層１２との絶縁性が確保される程度に、絶縁膜１３の膜厚が確保されているか否かが判断される。また、図示しないが、可動部２３に形成された櫛歯電極間の隙間から、可動部２３と絶縁膜１３との間に異物が入り込んだとしても、可動部２３と異物との接触が抑制される程度に絶縁膜１３が除去されているか否かが判断される。 By going through the steps described above, the average thickness d 3 of the insulating film 13 located under the movable portion 23 is determined. Thereby, the film thickness of the insulating film 13 is ensured to such an extent that the insulation between the first semiconductor layer 11 constituting the movable part 23 and the second semiconductor layer 12 positioned below the movable part 23 is ensured. It is determined whether or not. Although not shown, even if a foreign object enters between the movable part 23 and the insulating film 13 from the gap between the comb electrodes formed on the movable part 23, the contact between the movable part 23 and the foreign object is suppressed. It is determined whether or not the insulating film 13 has been removed.

次に、電圧Ｖ１，Ｖ２と、平均間隔ｄ０、突起１３ａの長さｄ１の関係式の導出を図６に基づいて説明する。梁２４の機能としては、可動部２３を壁に連結し、ｚ方向にバネ定数ｋのバネ性を有することである。そのため、図６では、梁２４に相当する、ｚ方向のバネ定数がｋであるバネによって、可動部２３が壁に連結された絵になっている。図６（ｂ）に示すように、検査電圧Ｖの印加によって、可動部２３が絶縁膜１３へ変位し、可動部２３と絶縁膜１３の表面との間の距離がｘに変位したとする。この場合、可動部２３に生じる静電気力Ｆｅは、可動部２３と該可動部２３と対向する第１半導体層１１とによってコンデンサが構成されているので、下記式で表される。

Figure 0005884469
ただし、α＝（ｄ２−ｄ０）／εｒである。 Next, the derivation of the relational expression of the voltages V 1 and V 2 , the average interval d 0 , and the length d 1 of the protrusion 13a will be described with reference to FIG. The function of the beam 24 is to connect the movable portion 23 to the wall and to have a spring property with a spring constant k in the z direction. For this reason, in FIG. 6, the movable portion 23 is connected to the wall by a spring corresponding to the beam 24 and having a spring constant k in the z direction. As shown in FIG. 6B, it is assumed that the movable portion 23 is displaced to the insulating film 13 by applying the inspection voltage V, and the distance between the movable portion 23 and the surface of the insulating film 13 is displaced to x. In this case, the electrostatic force F e generated in the movable portion 23 is expressed by the following equation because the movable portion 23 and the first semiconductor layer 11 facing the movable portion 23 form a capacitor.
Figure 0005884469
 However, α = (d 2 −d 0 ) / ε r .

また、可動部２３に生じる復元力Ｆｋは、下記式で表される。

Figure 0005884469
Further, the restoring force F k generated in the movable portion 23 is expressed by the following formula.
Figure 0005884469

第１電圧印加工程において、静電気力Ｆｅと復元力Ｆｋとが釣り合っている場合、数３、数４から、下記式が成立する。

Figure 0005884469
これを検査電圧Ｖについて求めると、下記式となる。
Figure 0005884469
 In the first voltage application step, when the electrostatic force F e and the restoring force F k are balanced, the following equation is established from Equations 3 and 4.
Figure 0005884469
 When this is obtained for the inspection voltage V, the following equation is obtained.
Figure 0005884469

上記したように、検査電圧が上昇して、静電気力が復元力を上回ると、可動部２３は絶縁膜１３（突起１３ａ）に接触して停止する。これは、数６で言うと、∂Ｖ／∂ｘ＝０を意味している。したがって、下記式が成立する。

Figure 0005884469
これを整理すると、下記式が成立する。
Figure 0005884469
 As described above, when the inspection voltage rises and the electrostatic force exceeds the restoring force, the movable portion 23 comes into contact with the insulating film 13 (projection 13a) and stops. In terms of Equation 6, this means ∂V / ∂x = 0. Therefore, the following formula is established.
Figure 0005884469
 If this is arranged, the following formula is established.
Figure 0005884469

以上により、数８をｘについて解き、それを数６に代入すると、接触電圧Ｖ１が下記式で表される。

Figure 0005884469
As described above, when Equation 8 is solved for x and substituted for Equation 6, the contact voltage V 1 is expressed by the following equation.
Figure 0005884469

また、離反する際のｘは、下記式を満たす。

Figure 0005884469
したがって、数１０を数６に代入すると、離反電圧Ｖ２が下記式で表される。
Figure 0005884469
 Moreover, x at the time of separating satisfies the following formula.
Figure 0005884469
 Therefore, Substituting Equation 10 into Equation 6, the separating voltage V 2 is represented by the following formula.
Figure 0005884469

数９、数１１は、ｄ０，ｄ１を変数とする関係式なので、これら２式より、ｄ０，ｄ１が求められる。なお、数９，１１は、特許請求の範囲に記載の数１，２に相当する。 Since Equations 9 and 11 are relational expressions using d 0 and d 1 as variables, d 0 and d 1 can be obtained from these two equations. The numbers 9 and 11 correspond to the numbers 1 and 2 described in the claims.

次に、本発明に係る膜厚検査方法の作用効果について説明する。上記したように、本検査方法では、意図せずして形成された突起１３ａを除いた、絶縁膜１３の平均厚さｄ３を求めている。これによれば、絶縁膜の表面に形成された突起（膜厚のばらつき）を含む静電容量と、絶縁膜の膜厚が一定とした場合の静電容量とが等しいという等式に基づいて、絶縁膜１３の膜厚を検査する方法と比べて、絶縁膜１３の膜厚の検査精度が向上される。 Next, the effect of the film thickness inspection method according to the present invention will be described. As described above, in this inspection method, except for the projections 13a formed unintentionally, seeking an average thickness d 3 of the insulating film 13. According to this, based on the equation that the capacitance including protrusions (film thickness variation) formed on the surface of the insulating film is equal to the capacitance when the thickness of the insulating film is constant. Compared with the method of inspecting the film thickness of the insulating film 13, the inspection accuracy of the film thickness of the insulating film 13 is improved.

ドップラー効果型レーザー干渉計によって、可動部２３の変位量を計測している。これによれば、非接触で可動部２３の変位量を計測することができる。   The displacement amount of the movable part 23 is measured by a Doppler effect type laser interferometer. According to this, the displacement amount of the movable part 23 can be measured without contact.

上記したように、第１電圧印加工程にて、当初、可動部２３は、静電気力と復元力とが釣り合った状態で、徐々に絶縁膜１３に近づく。しかしながら、静電気力が復元力を上回ると、可動部２３は瞬時に絶縁膜１３に接触して、停止する。この可動部２３の振る舞いをドップラー効果型レーザー干渉計によって観測し、可動部２３の変位における、急激な振る舞いの後に停止した瞬間の検査電圧をモニタリングすれば、接触電圧を計測することができる。   As described above, in the first voltage application step, initially, the movable portion 23 gradually approaches the insulating film 13 in a state where the electrostatic force and the restoring force are balanced. However, when the electrostatic force exceeds the restoring force, the movable portion 23 instantaneously contacts the insulating film 13 and stops. By observing the behavior of the movable portion 23 with a Doppler effect type laser interferometer and monitoring the inspection voltage at the moment when the displacement of the movable portion 23 stops after a sudden behavior, the contact voltage can be measured.

上記したように、第２電圧印加工程にて、可動部２３と第１半導体層１１とに印加している検査電圧を徐々に弱めた結果、復元力が静電気力を上回ると、可動部２３は瞬時に絶縁膜１３から離反する。この可動部２３の振る舞いをドップラー効果型レーザー干渉計によって観測し、可動部２３の変位における、急激な振る舞いを示す瞬間の検査電圧をモニタリングすれば、離反電圧を計測することができる。   As described above, when the restoring force exceeds the electrostatic force as a result of gradually weakening the inspection voltage applied to the movable portion 23 and the first semiconductor layer 11 in the second voltage application step, the movable portion 23 is Instantly leaves the insulating film 13. By observing the behavior of the movable portion 23 with a Doppler effect type laser interferometer and monitoring the test voltage at the moment when the displacement of the movable portion 23 shows an abrupt behavior, the separation voltage can be measured.

以上、本発明の好ましい実施形態について説明したが、本発明は上記した実施形態になんら制限されることなく、本発明の主旨を逸脱しない範囲において、種々変形して実施することが可能である。   The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

本実施形態では、可動部２３の変位測定手段３０として、ドップラー効果型レーザー干渉計を用いた例を示した。しかしながら、可動部２３の変位測定手段３０としては、上記例に限定されず、例えば、図７に示すように、静電容量計を採用することもできる。第１電圧印加工程にて、静電気力が復元力を上回り、可動部２３が絶縁膜１３に接触すると、可動部２３と対向する第１半導体層１１とによって構成されたコンデンサの静電容量が瞬時に上昇する。したがって、コンデンサの静電容量における、瞬時に上昇した瞬間の検査電圧をモニタリングすれば、接触電圧Ｖ１を計測することができる。また、第２電圧印加工程にて、復元力が静電気力を上回ると、可動部２３は瞬時に絶縁膜１３から離反し、コンデンサの静電容量が瞬時に下降する。したがって、コンデンサの静電容量における、瞬時に下降した瞬間の検査電圧をモニタリングすれば、離反電圧Ｖ２を計測することができる。図７は、変位測定手段の変形例を示す断面図である。 In the present embodiment, an example in which a Doppler effect type laser interferometer is used as the displacement measuring means 30 of the movable portion 23 is shown. However, the displacement measuring means 30 of the movable portion 23 is not limited to the above example, and for example, a capacitance meter can be adopted as shown in FIG. When the electrostatic force exceeds the restoring force in the first voltage application step and the movable part 23 comes into contact with the insulating film 13, the capacitance of the capacitor formed by the first semiconductor layer 11 facing the movable part 23 is instantaneous. To rise. Accordingly, in the electrostatic capacitance of the capacitor, if monitoring the test voltage at the moment of rise instantaneously, it is possible to measure the contact voltage V 1. Further, when the restoring force exceeds the electrostatic force in the second voltage application step, the movable portion 23 is instantaneously separated from the insulating film 13, and the capacitance of the capacitor is instantaneously lowered. Accordingly, in the electrostatic capacitance of the capacitor, if monitoring the test voltage at the moment of lowered instantaneously, you are possible to measure the separating voltage V 2. FIG. 7 is a cross-sectional view showing a modification of the displacement measuring means.

なお、本実施形態では、特に、ＭＥＭＳデバイス１００の用途を限定していなかったが、ＭＥＭＳデバイス１００としては、加速度センサや角速度センサを採用することができる。   In the present embodiment, the use of the MEMS device 100 is not particularly limited. However, as the MEMS device 100, an acceleration sensor or an angular velocity sensor can be employed.

１０・・・半導体基板
１１・・・第１半導体層
１２・・・第２半導体層
１３・・・絶縁膜
２３・・・可動部
２４・・・梁
３０・・・変位測定手段
１００・・・ＭＥＭＳデバイス DESCRIPTION OF SYMBOLS 10 ... Semiconductor substrate 11 ... 1st semiconductor layer 12 ... 2nd semiconductor layer 13 ... Insulating film 23 ... Movable part 24 ... Beam 30 ... Displacement measuring means 100 ... MEMS device

Claims (7)

第１半導体層（１１）と第２半導体層（１２）と両層の間に挟まれた絶縁膜（１３）とを有する半導体基板（１０）を備え、前記第２半導体層（１２）と前記絶縁膜（１３）とを所定形状にエッチングすることで形成された、第１半導体層（１１）に対して可動な可動部（２３）と、前記絶縁膜（１３）を介して前記第１半導体層（１１）に固定された固定部（２２）と、前記可動部（２３）及び前記固定部（２２）を連結する梁（２４）とが前記第２半導体層（１２）に形成されたＭＥＭＳデバイス（１００）の前記絶縁膜（１３）の膜厚を検査する膜厚検査方法であって、
前記梁（２４）は、前記第１半導体層（１１）と前記第２半導体層（１２）との積層方向に可撓性を有しており、
前記可動部（２３）と前記第１半導体層（１１）との間に働く静電気力が徐々に高くなるように、前記可動部（２３）と前記第１半導体層（１１）とに検査電圧を印加することで、前記可動部（２３）を前記絶縁膜（１３）に近づける第１電圧印加工程と、
該第１電圧印加工程時にて、前記可動部（２３）が前記絶縁膜（１３）に接触した際の接触電圧を計測する第１電圧計測工程と、
該第１電圧計測工程後、前記可動部（２３）と前記第１半導体層（１１）との間に働く静電気力が徐々に低くなるように前記検査電圧を下げることで、前記可動部（２３）を前記絶縁膜（１３）から離反させる第２電圧印加工程と、
該第２電圧印加工程時にて、前記可動部（２３）が前記絶縁膜（１３）から離反する際の離反電圧を計測する第２電圧計測工程と、
該第２電圧計測工程後、前記検査電圧が印加されていない場合における前記可動部（２３）と前記絶縁膜（１３）との間の平均間隔をｄ０、前記可動部（２３）の下に位置する絶縁膜（１３）の最大厚さをｄ１、前記固定部（２２）の絶縁膜（１３）の厚さをｄ２、空気誘電率をε、前記絶縁膜（１３）の比誘電率をεｒ、前記可動部（２３）における前記絶縁膜（１３）及び前記第１半導体層（１１）との対向面積をＡ、前記梁（２４）における積層方向のバネ定数をｋ、前記接触電圧をＶ１、前記離反電圧をＶ２とすると、下記式
Figure 0005884469
Figure 0005884469
 に基づいて、平均間隔ｄ０、最大厚さｄ１を求めた後、ｄ２−ｄ０より、前記可動部（２３）の下に位置する前記絶縁膜（１３）の平均厚さｄ３を演算する演算工程と、を有することを特徴とする膜厚検査方法。 A semiconductor substrate (10) having a first semiconductor layer (11), a second semiconductor layer (12), and an insulating film (13) sandwiched between the two layers, the second semiconductor layer (12) and the A movable part (23) movable with respect to the first semiconductor layer (11) formed by etching the insulating film (13) into a predetermined shape, and the first semiconductor via the insulating film (13) A MEMS in which a fixed part (22) fixed to a layer (11) and a beam (24) connecting the movable part (23) and the fixed part (22) are formed in the second semiconductor layer (12). A film thickness inspection method for inspecting the film thickness of the insulating film (13) of the device (100),
The beam (24) has flexibility in the stacking direction of the first semiconductor layer (11) and the second semiconductor layer (12),
An inspection voltage is applied to the movable part (23) and the first semiconductor layer (11) so that the electrostatic force acting between the movable part (23) and the first semiconductor layer (11) is gradually increased. A first voltage applying step of bringing the movable part (23) closer to the insulating film (13) by applying;
A first voltage measuring step of measuring a contact voltage when the movable part (23) contacts the insulating film (13) during the first voltage applying step;
After the first voltage measurement step, the test voltage is lowered so that the electrostatic force acting between the movable part (23) and the first semiconductor layer (11) gradually decreases, so that the movable part (23 ) From the insulating film (13), a second voltage application step,
A second voltage measuring step of measuring a separation voltage when the movable portion (23) separates from the insulating film (13) during the second voltage applying step;
After the second voltage measurement step, an average interval between the movable part (23) and the insulating film (13) when the inspection voltage is not applied is d 0 , below the movable part (23). The maximum thickness of the insulating film (13) positioned is d 1 , the thickness of the insulating film (13) of the fixed portion (22) is d 2 , the air dielectric constant is ε, and the relative dielectric constant of the insulating film (13). Ε r , A is a facing area of the movable part (23) facing the insulating film (13) and the first semiconductor layer (11), a spring constant in the stacking direction of the beam (24) is k, and the contact voltage is Is V 1 and the separation voltage is V 2 ,
Figure 0005884469
Figure 0005884469
 Then, after obtaining the average distance d 0 and the maximum thickness d 1 , the average thickness d 3 of the insulating film (13) positioned under the movable part (23) is calculated from d 2 -d 0. A film thickness inspection method comprising: a calculation step of calculating. 前記第１電圧計測工程において、前記可動部（２３）の変位量に基づいて、前記接触電圧を計測することを特徴とする請求項１に記載の膜厚検査方法。   The film thickness inspection method according to claim 1, wherein, in the first voltage measurement step, the contact voltage is measured based on a displacement amount of the movable portion (23). 前記第２電圧計測工程において、前記可動部（２３）の変位量に基づいて、前記離反電圧を計測することを特徴とする請求項１又は請求項２に記載の膜厚検査方法。   3. The film thickness inspection method according to claim 1, wherein, in the second voltage measurement step, the separation voltage is measured based on a displacement amount of the movable part (23). ドップラー効果型レーザー干渉計によって、前記可動部（２３）の変位量を計測することを特徴とする請求項２又は請求項３に記載の膜厚検査方法。   The film thickness inspection method according to claim 2 or 3, wherein a displacement amount of the movable part (23) is measured by a Doppler effect type laser interferometer. 前記第１電圧計測工程において、前記可動部（２３）と前記第１半導体層（１１）との間に形成されるコンデンサの静電容量に基づいて、前記接触電圧を計測することを特徴とする請求項１に記載の膜厚検査方法。   In the first voltage measurement step, the contact voltage is measured based on a capacitance of a capacitor formed between the movable part (23) and the first semiconductor layer (11). The film thickness inspection method according to claim 1. 前記第２電圧計測工程において、前記可動部（２３）と前記第１半導体層（１１）との間に形成されるコンデンサの静電容量に基づいて、前記離反電圧を計測することを特徴とする請求項５に記載の膜厚検査方法。   In the second voltage measurement step, the separation voltage is measured based on a capacitance of a capacitor formed between the movable part (23) and the first semiconductor layer (11). The film thickness inspection method according to claim 5. 前記ＭＥＭＳデバイス（１００）は、加速度センサ、若しくは、角速度センサであることを特徴とする請求項１〜６いずれか１項に記載の膜厚検査方法。 The film thickness inspection method according to claim 1, wherein the MEMS device is an acceleration sensor or an angular velocity sensor.
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