JP2006251598A - Manufacturing method of thin film structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method capable of forming a structure consisting of an optical multilayer film more precisely by using the lift-off method. <P>SOLUTION: The optical multilayer film 41G is formed over a mask layer 31 for the lift-off method formed on a substrate 21 and a crack 52 is introduced into a difference part 50 formed by the mask layer 31. By utilizing the crack 52, an etchant is introduced and, thereby, unnecessary parts on the optical multilayer film 41G as well as the mask layer 31 are reliably removed. According to the manufacturing method, the mask layer 31 can be thinned, the optical multilayer film provided with a prescribed optical performance up to the vicinity of the mask layer can be formed, and a color filter capable of expressing a bright and clear color image can be manufactured. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a thin film structure manufactured using lift-off.

  Many of optical components such as color filters of projector liquid crystal panels and sensors having various functions are provided with a thin film structure called a fine pattern or matrix composed of an optical multilayer film. In order to obtain an excellent optical function such as suppressing loss or heat generation due to absorption or performing sharp wavelength separation by the pattern of the optical multilayer film, it is necessary to form a highly accurate fine structure.

Methods for processing (manufacturing) a fine pattern with a thin film are roughly classified into three methods: a photo etching method, a mask method, and a lift-off (reverse etching) method. Among these, the photo-etching method is widely used for forming a fine pattern, and an example thereof is disclosed in Patent Document 1. However, the optical multilayer film is made of an oxide that is strong against etching such as SiO ₂ and Ta ₂ O _5, and it takes time to etch the multilayer film having a thickness of several μm, and the accuracy is high. Absent. Therefore, in terms of processing of the optical multilayer film, it is difficult to perform practical production by this method with the current technology.

  The mask method is the simplest manufacturing method, and it suffices to set a thin metal plate mask on an underlayer such as a substrate and form an optical multilayer film through the mask. However, there is a problem that the boundary of the pattern formed by the multilayer film becomes blurred due to the effect called “vignetting” due to the gap between the mask and the substrate and the thickness of the mask itself. Therefore, it is unsuitable for the use which manufactures a fine pattern with sufficient accuracy.

  The lift-off method is suitable for manufacturing a pattern made of a thin film having a thickness of several μm to several tens of μm. An example thereof is disclosed in Patent Document 2. In the lift-off method, first, an organic resist film serving as a mask layer or a sacrificial layer is formed on a substrate serving as a base layer alone or overlying a metal film that can be etched and removed. Next, a resist film corresponding to a portion where the optical multilayer film is to be formed is cut out by photolithography, thereby forming a mask pattern for the optical multilayer film. When the resist film is formed so as to overlap the base metal film, the resist film can be cut out so as to draw a desired pattern by etching the base metal film. An optical multilayer film is formed on the mask pattern (mask layer) made of this resist film. Then, by removing the mask layer, the part to be removed (the part unnecessary as the optical multilayer film) of the optical multilayer film can be peeled off together with the mask layer.

Even in the lift-off method, an etching solution is used in the step of removing the portion of the optical multilayer film to be removed together with the mask layer. Therefore, it is necessary to etch the optical multilayer film, and it does not change to spend time for that purpose. However, in the lift-off method, the optical multilayer film is interrupted on the mask layer due to the step with the mask layer, or the step-shaped portion at the boundary with the mask layer becomes thin, so that etching becomes easy.
JP-A-9-197392 Japanese National Patent Publication No. 8-508114

  In order to produce a sharper pattern by the lift-off method, it is necessary to make the mask layer thinner, reduce the shape change near the boundary with the mask layer, and form the boundary with the mask layer sharply. By forming the boundary with the mask layer sharply, for example, when forming a color filter for a multi-color image, the boundary between the adjacent optical multilayer films for different colors becomes clear, and each pixel is Expressed sharply.

  However, when the mask layer is thinned, an optical multilayer film is uniformly formed including the mask layer. Therefore, since the optical multilayer film is continuously formed including the mask layer, it is difficult to remove the mask layer by etching. Further, since the step at the boundary portion with the mask layer is small and the change in shape is small, there is a problem that the boundary portion breaks into an indefinite shape and pattern accuracy deteriorates. Therefore, if a mask layer with a film thickness close to the optical multilayer film to be created (film thickness of 2 to 5 μm with a visible light filter) is not formed, a problem occurs in the peeling of the mask layer, or the boundary of the optical multilayer film The problem arises that the shape of the material becomes irregular. For this reason, theoretically, it should be possible to improve the accuracy of the thin film pattern made of the optical multilayer film by making the mask layer thin, but the accuracy of the thin film pattern will be deteriorated in consideration of actual work.

  Before the mask layer is thinned and the mask layer is lifted off, the optical multilayer film is etched into a predetermined shape by an electron beam or dry etching as in the photoetching method to form a shape along the mask layer, It is conceivable to form a passage (groove) for allowing the lift-off etchant (etching solution) to reach the mask layer. However, this method is the same as the photoetching method, and the advantages of the lift-off method are lost.

  Accordingly, an object of the present invention is to provide a method capable of manufacturing a thin film pattern (thin film structure) with high accuracy by a lift-off method using a thin mask layer.

  In the present invention, a step of forming a structural thin film that constitutes at least a part of the thin film structure overlaid on a lift-off mask layer formed on a base layer such as a substrate, and the formation along the mask layer Provided is a method for manufacturing a thin film structure, which has a crack introducing step for introducing a crack into a stepped portion of the structured thin film and a mask removing step for removing a mask layer by etching.

  Even if the mask layer is thin, a step portion is formed in the structural thin film along the mask layer in order to form the structural thin film over the mask layer. This stepped portion tends to concentrate stress compared to other flat and constant thickness regions of the structural thin film. In particular, when a structural thin film is formed on a thin mask layer, a structural thin film having a very stable thickness can be formed except for the boundary with the mask layer, so that a stress is applied to the step portion along the mask layer. Is easy to concentrate. In addition, the optical multilayer film is strong as described above, and easily breaks due to stress concentration. Therefore, after forming the structural thin film, it is possible to introduce a crack in the step portion by generating an appropriate stress in the structural thin film by an appropriate method. If the crack is introduced, the mask layer is peeled in a shape along the stepped portion, so that a highly accurate thin film pattern according to the mask layer can be manufactured. Further, since the mask layer is thin, there is no change in film thickness to the vicinity of the mask layer, and a thin film pattern having a sharp shape can be manufactured. Then, by introducing a crack, the etching layer for removing the etchant reaching the mask layer can be opened as it is or by performing a slight etching after the crack is introduced, so that the mask layer can be reliably peeled off. Even in this respect, a highly accurate thin film pattern can be manufactured.

  One method of concentrating stress on the stepped portion is temperature change. Therefore, in the crack introduction process, it is possible to introduce a crack by giving a rapid temperature change. By giving a temperature change, the structural thin film expands and contracts, and stress concentrates on the step portion. For this reason, a crack can be introduced into the stepped portion. It is also possible to use stress due to the difference in expansion coefficient between the underlayer and the structural thin film. Since the underlayer such as the substrate and the structural thin film are made of different materials, they have different linear expansion coefficients. Therefore, by giving a temperature change, particularly a sudden temperature change, the expansion amount varies with the difference in the linear expansion coefficient, and cracks are introduced by using this. For this reason, for example, when the linear expansion of the substrate is small and the linear expansion of the structural thin film is large, it is desirable to perform rapid cooling, and in the opposite case, it is desirable to perform heat treatment.

  Thus, in this invention, since an etchant can be introduce | transduced from a crack, a mask layer can be peeled and removed reliably. For this reason, when the mask layer is as thin as about 1 μm, peeling of the mask layer was a problem, but with the manufacturing method of the present invention, the mask layer can be removed reliably and the structural thin film along the mask layer This structure (cracking) can also be stably obtained at a desired position. For this reason, a thin film structure (thin film pattern) having a sharper shape can be manufactured using the thin mask layer as described above.

  Moreover, in the manufacturing method of this invention, it is desirable to have further the pre-processing process which forms a dent or a groove | channel in the surface of a level | step-difference part before a crack introduction | transduction process. By forming a recess or groove in the stepped portion, cracks are likely to occur starting from the recess or groove. Therefore, cracks can be reliably introduced along the mask layer, and a highly accurate thin film pattern along the mask layer can be manufactured. Furthermore, in this manufacturing method, the dent or groove may be shallow because it only has to be the starting point of the crack. Therefore, long-time etching is not required unlike the photoetching method, the time required for etching is short, and the shape error due to etching is also small.

  In the pretreatment step, the dent or groove can be formed by mechanical excavation processing, mechanical cutting processing, electron beam etching processing, or electron beam drawing processing. It is sufficient to form a submicron recess or groove of a small size relative to the thickness of the structural thin film.

  With the manufacturing method of the present invention, a thin film pattern can be manufactured by a lift-off method using a thin mask layer without requiring a long time for etching. Therefore, the present invention is suitable for manufacturing a thin film structure having an optical multilayer film that is difficult to etch as a structural thin film.

  One form of a thin film structure using an optical multilayer film is a color filter.

  Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1A to 1D and FIGS. 2A to 2B show how a part of the structure of the color filter is manufactured by the method for manufacturing a thin film structure according to the present invention. In this example, a state is shown in which a band pass filter (green color filter) 10 that selectively transmits green light is manufactured on a substrate.

(Formation of mask layer)
As shown in FIG. 1A, a quartz glass substrate 21 having a refractive index of 1.46 is used as a base layer, an organic resist film is formed thereon, and a mask layer 31 is formed by patterning. A positive OFPR-800 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) is used as the resist film for forming the mask layer 31, and the thickness of the mask layer 31 is 1 μm, which is about 1/3 of the structure manufactured by lift-off. And the mask layer for lift-off is very thin. For the patterning, a technique such as cutting out a portion of the resist film to be formed by photolithography can be used. The lift-off mask layer 31 forms a pattern opposite to the pattern of the structure to be manufactured in the manufacturing method of this example, and a desired structure is formed on the substrate 21 by lifting off the mask layer 31. The body remains. In this example, in order to manufacture a color filter in which a color displayed in units of pixels is selected, the mask layer 31 is formed so that a thin film structure including an optical multilayer film is formed at a pixel pitch, for example, a pitch of 20 μm. Are patterned.

(Formation of structural layer)
Next, as illustrated in FIG. 1B, an optical multilayer film 41 </ b> G is formed on the substrate 21 so as to overlap the mask layer 31. The optical multilayer film 41G is used as a structural thin film, and a part of the optical multilayer film 41G is lifted off in a process described later, whereby a thin film structure 42G is formed. The optical multilayer film 41G (thin film structure 42G) of this example is an optical filter that selectively transmits green light. From the substrate 21 side, a layer of SiO ₂ (refractive index: 1.47) and Ta ₂ O ₅ (refraction index: 2.21) is formed by alternately laminating 38 layers. The design wavelength (λ) of the optical multilayer film 41G (structure 42G) of this example is 550 nm, and the total film thickness is 3.1 μm. FIG. 3 shows the layer structure of the optical multilayer film 41G (structure 42G). The thickness of each layer is shown in units of 0.25λ.

  As a method for forming the optical multilayer film 41G, a known vacuum deposition method, sputtering, reactive sputtering method, ion plating, ion-assisted deposition, or the like can be employed. As one of the conditions for forming the optical multilayer film 41G, it is preferable to consider that the film is formed at a temperature that does not damage the mask layer 31 (relatively low temperature of about 150 ° C. or less). When the optical multilayer film 41G is formed on the substrate 21 so as to overlap the lift-off mask layer 31, the optical multilayer film 41G is formed on the upper surface of the optical multilayer film 41G along the boundary of the mask layer 31 as shown in FIG. A stepped portion 50 having a thickness (1 μm) of the mask layer 31 is formed.

(Pretreatment process (formation of stepped part))
As shown in FIG. 1C, a groove 51 slightly recessed by electron beam etching is formed along the stepped portion 50 on the upper surface of the optical multilayer film 41G. This pretreatment process is intended to make it easy for cracks to enter the stepped portion 50 in the crack introduction process described below, and it is not necessary to completely etch the optical multilayer film 41G. For this reason, the groove 51 may be formed at a depth that is a fraction of the thickness of the optical multilayer film 41G even if it is deep. The groove 51 can be manufactured not only by electron beam etching but also by a method such as dry etching using an appropriate etchant such as CHF ₃ or O ₂ . In any method, the groove 51 to be manufactured in this step may be shallow. Compared with the time for etching the optical multilayer film 41G until it reaches the base layer 21 or the lift-off mask layer 31 by a conventional photoetching method, The process is completed in a very short time.

(Crack introduction process)
As shown in FIG. 1D, a rapid temperature change is applied to introduce a crack 52 into the stepped portion 50 of the optical multilayer film 41G from the groove 51 (crack introduction step). By generating thermal strain in the optical multilayer film 41G, the stress is concentrated on the step portion 50 that is structurally the weakest, so that a crack 52 is generated. In particular, the optical multilayer film 41G is hard because of its composition, and the distortion due to thermal expansion is caused by the portion floating on the lift-off mask layer 31 or the stepped portion 50 at the boundary thereof, as compared with the portion in close contact with the substrate 21. concentrate. It is also possible to generate distortion by utilizing the difference in thermal expansion coefficient between the substrate 21 and the optical multilayer film (structural layer) 41G. In that case, when the linear expansion of the substrate 21 is small and the linear expansion of the optical multilayer film 41G is large, the substrate 21 is rapidly cooled, and vice versa.

  The crack 52 becomes a path for introducing the etchant for removal into the lift-off mask layer 31 or a part thereof, and forms an edge of the structure 42G made of the optical multilayer film (structure layer) 41G. Since the crack 52 is formed along the stepped portion 50 along the mask layer 31, the edge of the structure 42G remaining after being lifted off is along the mask layer 31, and the structure having a sharp edge and high accuracy. 42G is formed. Further, since the mask layer 31 is thin, there is little difference in the thickness of the boundary portion 43 between the mask layer 31 and the structure 42G, and it is difficult to be affected by the thickness of the mask layer 31 when forming the optical multilayer film 41G. An optical multilayer film 41G having a desired layer structure as shown in FIG. 3 can be manufactured up to the very vicinity of the layer 31. Therefore, the area that can be used as the color filter of the structure 42G becomes wider, and the shape of the edge of the structure 42G becomes sharper. Therefore, a color filter capable of displaying a bright and clear color image can be provided by the present invention.

(Etching process)
Further, as shown in FIG. 2A, the optical multilayer film 41G formed on the substrate 21 is etched along the pattern using an etchant 61 such as hydrofluoric acid to form a deep groove 53. . This step can be omitted when the crack 52 formed in the crack introduction step reaches the lift-off mask layer 31 and the crack 52 can be used as an etchant introduction path for removing the mask layer 31. .

  However, the degree of the crack 52 is not guaranteed, and this step is important for reliably removing the mask layer 31 and improving the yield. Further, since the crack 52 reaches the very vicinity of the mask layer 31 even when it does not reach the lift-off mask layer 31, a deep groove 53 as shown in FIG. The time to do is short.

(Mask removal process)
After the deep groove 53 that reaches the mask layer 31 completely is formed, it is immersed in an etchant 61 that removes the resist that constitutes the mask layer 31, and the portion of the optical multilayer film that overlaps the mask layer 31 is removed together with the mask layer 31. To do. As a result, as shown in FIG. 2B, a structure 42G that is part of the color filter is manufactured. FIG. 4 shows the transmission optical characteristics of green light of the color filter 10 obtained by this manufacturing method. As can be seen from this graph, an optical characteristic having a peak in the vicinity of 500 nm to 600 nm and selectively transmitting green can be obtained.

  As described above, in the manufacturing method of this example, by introducing cracks along the mask layer to be lifted off, the unnecessary optical multilayer film along with the mask layer is sharply removed along with the mask layer, and By using the crack, the etchant for removal reaches the mask layer. Therefore, even if the mask layer 31 is thinned, the mask layer 31 can be peeled off reliably, and a thin film structure 42G having a sharp shape along the mask layer 31 is obtained. By making the mask layer 31 thin, an optical multilayer film (structure) 42G having a desired performance can be formed up to the very vicinity of the mask layer 31. Therefore, in the color filter, the aperture ratio is improved, loss due to absorption or A color filter capable of suppressing heat generation and expressing a bright and clear color can be provided. Further, the edge of the structure 42G can be formed substantially perpendicular to the substrate 21, and the shape patterned by the mask layer 31 can be faithfully reproduced. Therefore, the shape of each pixel becomes sharp, and a color filter that can display a bright and clear image also in this respect can be provided.

  In the above manufacturing method, the mask layer 31 is formed alone on the substrate 21, but it is also possible to form the mask layer 31 on a metal film that can be etched and peeled instead of using the mask layer 31 alone. Street. The resist for forming the mask layer 31 is not limited to the above example, and may be a negative type, for example, SU-10A (Kayaku Microchem / Nippon Kayaku). It is also possible to use a metal such as aluminum.

  Furthermore, although the method for manufacturing a color filter portion that selectively transmits green light has been described above, a color filter portion that selectively transmits other colors can be manufactured by the same method. Further, the present invention is applicable not only to color filters but also to manufacturing MEMS using other optical elements or thin film structures.

It is a figure which shows the process in which a color filter (structure of an optical multilayer film) is manufactured with the manufacturing method of this invention. FIG. 2 is a diagram illustrating a process of manufacturing a color filter following FIG. 1. It is a figure which shows the layer structure of an optical multilayer film (structure). It is a graph which shows the optical characteristic of the optical multilayer film (structure) shown in FIG.

Explanation of symbols

10 Green color filter 21 Glass substrate, 31 Mask layer, 41G Optical multilayer film, 42G Structure 50 Step portion, 51 Groove (or recess), 52 Crack

Claims (6)

Forming a structural thin film overlying a lift-off mask layer formed on the underlayer, and forming a structural thin film constituting at least a part of the thin film structure;
A crack introduction step for introducing a crack into a step portion of the structural thin film formed along the mask layer;
And a mask removing step of removing the mask layer by etching.   2. The crack introduction step according to claim 1, wherein when the linear expansion coefficient of the foundation layer is smaller than the mask layer, rapid cooling is performed, and when the linear expansion coefficient of the foundation layer is larger than the mask layer, rapid cracking is performed. A method for producing a thin film structure, wherein the crack is introduced by heating.   3. The method of manufacturing a thin film structure according to claim 1, further comprising a pretreatment step of forming a recess or a groove on a surface of the stepped portion before the crack introduction step.   4. The method of manufacturing a thin film structure according to claim 3, wherein, in the pretreatment step, the dent or groove is formed by mechanical excavation processing, mechanical cutting processing, electron beam etching processing, or electron beam drawing processing. .   5. The method for manufacturing a thin film structure according to claim 1, wherein the thin film structure is an optical multilayer film.   6. The method for manufacturing a thin film structure according to claim 5, wherein the thin film structure is a color filter.

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