TWI741924B - Methods for forming fresnel lens - Google Patents

Abstract

A method for forming Fresnel lens is provided in the present disclosure, including providing a substrate; patterning the substrate to form a plurality of concentric rings having jagged shape, wherein each of the concentric rings has a stepping structure, wherein a spike is formed between an upper step and a lower step of the stepping structure of at least one concentric ring; oxidizing the spike to form an oxide layer; and removing the oxide layer.

Description

The formation method of Fresnel lens

The present disclosure relates to a method for forming a Fresnel lens, and particularly relates to the improvement of the Fresnel lens manufacturing process and the Fresnel lens formed.

Generally speaking, a Fresnel lens can achieve the same optical effect as a traditional spherical lens through numerous concentric patterns (Fresnel zones) while saving the amount of material and reducing its thickness. It can be used in places where the image quality is not too demanding, such as car headlights, car taillights, traffic lights, spotlights, lighthouses, aircraft carriers, lens-view projectors, magnifiers, solar water heaters, etc.

Although the Fresnel lenses manufactured in the prior art can roughly meet their original intended use, they still do not fully meet the requirements in all aspects. For example, the sharp points produced during the manufacturing process cause the light diffraction efficiency to drop significantly. Therefore, the development of a further improvement in the optical diffraction efficiency and formation method of the Fresnel lens is still one of the current research topics in the industry.

The embodiment of the present invention provides a method for forming a Fresnel lens, including providing a substrate; patterning the substrate to form a plurality of zigzag-shaped concentric rings, each of which Each of the concentric rings has a stepped structure, and at least a point is provided between the upper and lower steps of the stepped structure of the concentric ring; the pointed end is oxidized to form an oxide layer; and the oxide layer is removed.

The embodiment of the present invention provides a Fresnel lens including a substrate, and the substrate includes a plurality of jagged concentric rings, wherein each concentric ring has a stepped structure, wherein at least the upper surface of the lower step of the stepped structure of the concentric ring and The junction of the side surfaces of the upper step has rounded corners.

In order to make the features of the present disclosure obvious and easy to understand, the following examples are specially cited, in conjunction with the accompanying drawings, and detailed descriptions are as follows. For other precautions, please refer to the technical field.

100: substrate

100A: Ladder structure

100C: rounded corners

100S: pointed

102: pad oxide layer

103: Etching process

104: oxide layer

200, 300, 400, 500: patterned mask

200Y, 300Y, 400Y: area

200N, 300N, 400N: area

1001, 1002, 1003, 1004, 1005, 1006, 1007, 1008: ladder

C: Concentric ring

C1, C2, C3, C4: concentric rings

H: Step height

H1, H2, H3: height

R1, R2, R3, R4: surrounding area

Rc: central area

W1, W2, W3, W4: width

W11, W12, W13, W21, W22, W23: width

W: width

T: thickness

Y1, Y2: ring

The embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. It should be noted that, according to standard practices in the industry, various features are not drawn to scale and are only used for illustration and illustration. In fact, it is possible to arbitrarily enlarge or reduce the size of the element to clearly show the characteristics of the embodiment of the present invention.

Figure 1 is a cross-sectional view of a Fresnel lens according to some embodiments of the present invention.

2A-2C are cross-sectional views of Fresnel lenses according to some embodiments of the present invention.

FIG. 3 is a top view of the topmost surface of the Fresnel lens corresponding to FIG. 2C according to some embodiments of the present invention.

4A-4B are diagrams illustrating a top view of a patterned mask used to form a Fresnel lens and a partial cross-sectional view of the Fresnel lens according to some embodiments of the present invention.

FIGS. 5A-5B illustrate a top view of a patterned mask used to form a Fresnel lens and a partial cross-sectional view of the Fresnel lens according to some embodiments of the present invention.

Figures 6A-6B illustrate the formation of Fresnel lenses according to some embodiments of the present invention. The top view of the patterned mask used and the partial cross-sectional view of the Fresnel lens.

Figures 7A-7C are partial cross-sectional views illustrating the formation of a Fresnel lens according to some embodiments of the present invention.

Fig. 8 is a partial cross-sectional view showing the formation of a Fresnel lens according to some embodiments of the present invention.

Figures 9A-9C are partial cross-sectional views illustrating the formation of a Fresnel lens according to some embodiments of the present invention.

Figure 10 is a partial cross-sectional view of a Fresnel lens according to some embodiments of the present invention.

Various embodiments or examples are provided below for implementing different elements of the provided semiconductor structure. If it is mentioned in the description that the first part is formed on the second part, it may include an embodiment in which the first and second parts are in direct contact, or may include additional parts formed between the first and second parts, so that the first An embodiment in which the second component is not in direct contact. In addition, the embodiments of the present invention may use repeated component symbols in many examples. These repetitions are only for the purpose of simplification and clarity, and do not represent a specific relationship between the various embodiments and/or configurations discussed.

Furthermore, related terms in space, such as "above", "below", "above...", "below..." and similar terms, in addition to the orientation shown in the diagram, also Contains the different orientations of the device in use or operation. When the device is turned to other orientations (rotated by 90 degrees or other orientations), the relative description of the space used here can also be interpreted according to the rotated orientation.

Here, the terms "about", "approximately" and "approximately" usually mean Within 20% of a given value or range, preferably within 10%, and more preferably within 5%, or within 3%, or within 2%, or within 1%, or 0.5 %within. It should be noted that the quantity provided in the manual is an approximate quantity, that is, without specifying "about", "approximately", "approximately", "about", "approximately" and "approximately" can still be implied. The meaning of "probably".

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs. It is understandable that these terms, such as those defined in commonly used dictionaries, should be interpreted as having meaning consistent with the relevant technology and the background or context of this disclosure, and should not be interpreted in an idealized or excessively formal way. Unless there is a special definition in the embodiment of the present disclosure.

Those skilled in the art will understand the term "substantially" in the specification, such as "substantially the same" or "substantially flat". In some embodiments, "substantially" may be removed. Where applicable, the term “substantially” may also include embodiments having “all”, “complete”, “all”, etc. Where applicable, the term "substantially" can also refer to 90% or higher, such as 95% or higher, and more specifically, 99% or higher, including 100%.

The Fresnel lens provided by the embodiment of the present invention can achieve a light diffraction efficiency close to 100% through a stepped structure. In addition, the spikes generated in the rounding process can further increase the light diffraction efficiency.

Please refer to Figure 1 first. Figure 1 is a cross-sectional view of an exemplary Fresnel lens according to some embodiments of the present invention. Compared with a spherical lens, the Fresnel lens removes the part that does not affect the refraction, and shifts the remaining curved part to the bottom of the lens, thereby saving material consumption and reducing the thickness of the lens.

As shown in Figure 1, the Fresnel lens divides the curved surface into a circle of concentric circles, and its edges are sharper, and the cross-section is jagged, and the center is a smoother curved surface. Here, the smooth curved surface is defined as the central area Rc, and as it moves away from the central area Rc, it is sequentially divided into surrounding areas R1, R2, R3, and R4. Here, the widths of the surrounding areas R1, R2, R3, and R4 become smaller and smaller as they move away from the central area Rc.

It should be noted that, for the sake of simplicity, only four surrounding areas R1, R2, R3, and R4 are illustrated in the figure. Those with ordinary knowledge in the field of the present invention can increase or decrease the surrounding areas according to actual needs.

Then, as shown in FIGS. 2A-2C, a stepped structure 100A can be formed on the substrate 100 to simulate the curved surface in Figure 1, and the more steps there are, the better the effect.

In Fig. 2A, the substrate 100 includes a plurality of concentric rings in a saw-tooth shape (in a cross-sectional view). Compared with the Fresnel lens in Fig. 1, the light refraction efficiency is 100% and the diffraction efficiency is close to zero. The embodiment in Fig. 2A has a stepped structure 100A including two steps in each surrounding area. Improve the diffraction efficiency.

Fig. 2B is similar to Fig. 2A, except that the step structure 100A includes four steps. Compared with the Fresnel lens in Fig. 1, the light refraction efficiency is 100% and the diffraction efficiency is close to zero. The embodiment in Fig. 2B has a step structure 100A including four steps in each surrounding area. Achieve a higher diffraction efficiency than that shown in Figure 2A.

FIG. 2C is also similar to FIG. 2A, except that the step structure 100A includes eight steps. Compared with the Fresnel lens in Fig. 1, the light refraction efficiency is 100% and the diffraction efficiency is close to zero. The embodiment in Fig. 2C has a stepped structure 100A including eight steps in each surrounding area. The diffraction efficiency is about 95%.

In other words, as the number of steps included in the stepped structure 100A increases, the light refraction efficiency of FIG. 1 can be approached closer.

Next, Figure 3 is a top view of the topmost surface of the Fresnel lens corresponding to Figure 2C (eight steps) according to some embodiments of the present invention. In Figure 3, the topmost surface of the surrounding regions R1, R2, R3, and R4 is a concentric ring C surrounding the topmost surface of the central region Rc. In addition, in Figure 3, the concentric ring C1 in the surrounding area R1 has a width W1, the concentric ring C2 in the surrounding area R2 has a width W2, and the concentric ring C3 in the surrounding area R3 has a width W3. The concentric ring C4 in R4 has a width W4. With the width W1>W2>W3>W4, the step width becomes smaller and smaller outward from the central region Rc, and the Fresnel lens close to the first figure can be obtained, thereby increasing the light diffraction efficiency.

Hereinafter, taking the Fresnel lens (eight steps) formed in Figure 2C as an example, the forming steps of the embodiment of the present invention will be described through Figures 4A-4B, 5A-5B, and 6A-6B. 4A, 5A, and 6A are top views of a patterned mask used to form a Fresnel lens according to some embodiments of the present invention. 4B, 5B, and 6B are partial cross-sectional views of Fresnel lenses according to some embodiments of the present invention. Specifically, by performing the patterning process with the patterned masks of 4A, 5A, and 6A, partial cross-sectional views of FIGS. 4B, 5B, and 6B can be obtained.

First, please refer to FIG. 4A. Here, only the central area Rc and the surrounding areas R1 and R2 are extracted as examples to simplify the illustration and highlight relevant features. In Figure 4A, the central area Rc is the area 200Y covered by the patterned mask 200, and the surrounding areas R1 and R2 have areas 200Y covered by the patterned mask 200 and areas not covered by the patterned mask 200. The area is 200N. Here, the patterned mask 200 exhibits an annular area covered 200Y, for example, having four rings in the peripheral region Y1 R _1, Y2 having four rings in the peripheral region R _2. In addition, each ring Y1 has the same width W11, and each ring Y2 has the same width W21.

FIG. 4B only extracts the cross-sectional views in the surrounding areas R1 and R2 as an example. First, the substrate 100 is provided, and the substrate 100 is patterned, as shown in FIG. 4B. In some embodiments, the substrate 100 may be a semiconductor substrate, such as a silicon substrate. In other embodiments, the substrate 100 may also be a composite substrate formed of glass, quartz, polymer, ceramic, or a combination of the foregoing.

In some embodiments, the step of patterning the substrate 100 includes: forming a patterned mask 200 on the substrate 100; etching the substrate 100 through an etching process; and removing the patterned mask 200 (not shown). Thereby, the substrate 100 including the step structure 100A having two steps can be formed.

The patterned mask 200 can be a photoresist material, and can be formed by a photolithography process. The aforementioned photolithography process includes photoresist coating, pre-exposure baking, mask exposure, development, and so on. In other embodiments, the patterned mask may be a hard mask layer, which includes oxide, oxynitride, or other suitable dielectric materials.

The etching process can be an anisotropic etching process, which includes various dry etching processes, such as reactive ion etching (RIE), neutral beam etch (NBE), inductively coupled plasma etching ( inductive coupled plasma etch), suitable etching process or a combination of the above, etc.

The step of removing the patterned mask includes performing a strip process, an ash process, a suitable removal process, or a combination of the above, and so on.

Here, the width W11 of the area 200N in the surrounding area R1 is larger than the width W21 of the area 200N in the surrounding area R2. Similarly, the width of the area 200Y in the surrounding area R1 is larger than the width of the area 200Y in the surrounding area R2. In addition, in Fig. 4B, the etched height of the substrate 100 is H1.

Next, following FIGS. 4A and 4B, after removing the patterned mask 200 of FIG. 4B, using the patterned mask 300 of FIG. 5A, a partial cross-sectional view as shown in FIG. 5B can be formed. Figure 5A is similar to Figure 4A, the central area Rc is the area 300Y covered by the patterned mask, and the surrounding areas R1 and R2 have areas 300Y covered by the patterned mask and not covered by the patterned mask. The area is 300N. Here, the patterned mask 300 exhibits an annular area covered 300Y, thus having two rings in the peripheral region Y1 R _1, Y2 and having two rings in the peripheral region R _2. In addition, each ring Y1 has the same width W12, and each ring Y2 has the same width W22. In addition, the widths of the rings Y1 and Y2 in Fig. 5A are twice the widths of the rings Y1 and Y2 in Fig. 4A.

In Figure 5B, the patterned mask 300 in the region 300Y covers the two steps in Figure 4B, and the two steps in Figure 4B are exposed in the region 300N.

Figure 5B is also similar to and continues from Figure 4B. Using the patterned mask 300 in the area 300Y as an etching mask, the substrate 100 in Figure 4B is etched anisotropically along the two exposed steps. The two steps covered by the patterned mask 300 remain unetched, thus forming a substrate 100 including a step structure 100A having four steps.

Here, the width W12 of the area 300N in the surrounding area R1 in FIG. 5B is twice the width W11 of the area 200N in the surrounding area R1 in FIG. 4B. Similar to Figure 4B, in Figure 5B, the width W12 of the region 300N in the surrounding region R1 is greater than the width W22 of the region 300N in the surrounding region R2, and the width of the region 300Y in the surrounding region R1 is greater than that of the region 300Y in the surrounding region R2. The width is large. In addition, in Fig. 5B, the etched height of the substrate 100 is H2. In some embodiments, the height H2 in Figure 5B is twice the height H1 in Figure 4B to facilitate subsequent formation similar to Curved stepped structure 100A.

Next, following FIGS. 5A and 5B, after removing the patterned mask 300 in FIG. 5B, using the patterned mask 400 in FIG. 6A, a cross-sectional view as shown in FIG. 6B can be formed. Fig. 6A is similar to Fig. 5A, the central area Rc is the area 400Y covered by the patterned mask, and the surrounding areas R1 and R2 have the area 400Y covered by the patterned mask and not covered by the patterned mask. The area is 400N. Here, the patterned mask 400 exhibits an annular area covered 400Y, thus having a ring around Y1 region R _1, the ring having a peripheral region Y2 in R _2. In addition, the ring Y1 has a width W13, and the ring Y2 has a width W23. In addition, the widths of the rings Y1 and Y2 in Fig. 6A are twice the widths of the rings Y1 and Y2 in Fig. 5A.

In Figure 6B, the patterned mask 400 in the region 400Y covers the four steps in Figure 5B, and the region 400N exposes the four steps in Figure 5B.

Fig. 6B is similar to and continues from Fig. 5B. Using the patterned mask 400 in the area 400Y as an etching mask, the substrate 100 in Fig. 5B is etched anisotropically along the four exposed steps. The four steps covered by the patterned mask 400 remain unetched, thus forming a substrate 100 including a step structure 100A having eight steps.

Here, the width W13 of the area 400N in the surrounding area R1 in Fig. 6B is twice the width W12 of the area 300N in the surrounding area R1 in Fig. 5B, and is the same as in the surrounding area R1 in Fig. 4B The width of the area 200N is four times the width W11. Similar to Figure 5B, in Figure 6B, the width W13 of the region 400N in the surrounding region R1 is greater than the width W23 of the region 400N in the surrounding region R2, and the width of the region 400Y in the surrounding region R1 is greater than that of the region 400Y in the surrounding region R2. The width is large. In addition, in Fig. 6B, the etched height of the substrate 100 is H3. In some embodiments, Figure 6B The height H3 in Fig. 5B is twice the height H2 in Figure 5B, so as to facilitate the subsequent formation of a stepped structure 100A that is similar to a curved surface.

In addition, since the central area Rc in Figures 4B, 5B, and 6B is covered by the patterning masks 200, 300, and 400 in the step of patterning the substrate, the central area Rc is not affected by the patterning, but can be Maintain the same height before and after the step of patterning the substrate. In other words, the central area Rc can be maintained as the topmost surface of the substrate 100 and is substantially flat.

Through the process shown in Figures 4B, 5B, and 6B, a Fresnel lens with a stepped structure with eight steps can be obtained. However, in the step of patterning the substrate 100, the problem of sharp points is prone to occur, as shown in FIGS. 7A-7C. First, referring to FIG. 7A, the step of patterning the substrate 100 includes: forming a pad oxide layer 102; and forming a patterned mask 500 (including 200, 300, or 400).

In some embodiments, the pad oxide layer 102 can serve as a buffer layer between the substrate 100 and the patterned mask 500 (eg, photoresist), thereby increasing adhesion. If a defect occurs during the manufacturing process, the defect can also be removed together with the pad oxide layer 102 in a subsequent manufacturing process. In some embodiments, the pad oxide layer 102 can be formed by a thermal oxidation process.

Next, the step of patterning the substrate 100 further includes etching the substrate 100 on which the patterned mask 500 is not formed by the etching process 103 to obtain the structure as shown in FIG. 7B. Since the formation of the patterned mask 500 may be difficult to be etched away due to unavoidable alignment offset or the large vertical thickness of the sidewall of the pad oxide layer 102, spikes may be generated at the connection of the upper and lower steps. 100S.

Next, the patterned mask 500 and the pad oxide layer 102 are removed, as shown in FIG. 7C. In this case, because the spike 100S between the upper and lower steps deviates from the predetermined shape of the step in FIG. 1, the light diffraction efficiency is reduced.

In some embodiments, the tip of the tip 100S may exhibit a flat angle or an acute angle, as shown in FIG. 7C.

Figure 8 further illustrates the distribution of the prongs 100S in the eight-step ladder structure.

In Figure 8, the substrate 100 in the surrounding area R1 has a stepped structure 100A, which includes eight steps, which are respectively called the first step 1001, the second step 1002, and the third step 1003 from the bottom surface to the top surface. , The fourth step 1004, the fifth step 1005, the sixth step 1006, the seventh step 1007, and the eighth step 1008. It can be seen that there is a pointed end 100S between the first step 1001 and the second step 1002, and there is also a pointed end 100S between the second step 1002 and the third step 1003... the sixth step 1006 and the seventh step 1007 There is also a pointed tip 100S in between.

In this embodiment, the stepped structure 100A has six prongs, which have not exactly the same height, but the number is not limited thereto. In some embodiments, the height of each step is H, taking the upper surface of the eighth step 1008 (or the top surface of the substrate 100) as a reference, and the distance between the tip and the upper surface of the eighth step 1008 is The ratio of height H is 0.5-4. That is to say, the highest point of the tip is not lower than the upper surface of the fifth step 1005. The reason may be that the lower step (such as the first step 1001, the second step 1002, etc.) has been in the previous process (such as 3B or Figure 4B) already has a pointed tip, it is more difficult to remove the sidewall of the pad oxide layer (not shown) during patterning, thus accumulating the height. The highest point of the tip will not be higher than the middle line of the seventh step 1007 and the eighth step 1008. The reason may be that the closer to the top surface, the easier it is to remove in the patterning process.

Continuing from FIGS. 7A-7C, FIGS. 9A-9C illustrate a partial cross-sectional view of forming a Fresnel lens according to some embodiments of the present invention. In detail, in order to solve the problem of the tip, a thermal oxidation process is used to oxidize the tip 100S, as shown in Figures 9A-9C. Fig. 9A is similar to Fig. 7C, in the stepped structure of the substrate 100, there is a tip 100S between the upper and lower steps. In some embodiments, the width W of the tip 100S is 1500-3000A.

Next, the top surface and side surfaces of the tip 100S and the stepped structure 100A are oxidized by a thermal oxidation process to form an oxide layer 104 on the substrate 100 (or the stepped structure 100A), as shown in FIG. 9B. The thermal oxidation process can include one or multiple oxidation processes with different thermal budgets. In some embodiments, the thermal oxidation process is performed for about 45-75 minutes in _{a humid oxygen (containing H 2} and O ₂ ) environment at a temperature of about 950-1150° C. and atmospheric pressure, which can save energy. The case completely oxidizes the tip.

In some embodiments, the side surface of the upper step, the upper surface of the lower step, and the right angle at the junction of the two react with oxygen through the thermal oxidation process, and the gas used in the thermal oxidation process will diffuse isotropically to The surface of the substrate reacts with the substrate, so right angles can be rounded into rounded corners.

In the comparative embodiment where the thermal oxidation process is not performed, the stepped structure is formed only by the etching process, and the final structure will not be rounded. In contrast, this case uses a thermal oxidation process to remove the sharp ends produced during the process, and rounded corners are formed on the structure.

In some embodiments, the ratio of the thickness T of the oxide layer 104 to the width W of the tip 100S is 1.5-2.5. If it is larger than this range, that is, the thickness T is too thick, too much energy and materials are lost, and the cost is increased. If it is less than this range, that is, the thickness T is too thin, the tip may not be completely oxidized and will not form a rounded corner between the subsequent upper and lower steps.

Then, the oxide layer 104 is removed, and a fillet 100C can be formed at the junction of the upper surface of the lower step and the side surface of the upper step, as shown in FIG. 9C. In some embodiments, the radius of curvature of the rounded corner 100C is 0.3-0.6 μm. It should be noted that in the above heat Under the oxidation process, the boundary between the side surface of the lower step and the upper surface of the upper step still maintains substantially a right angle (or an obtuse angle close to a right angle) without forming rounded corners.

In some embodiments, the removal of the oxide layer 104 may include any acid or gas with high etching selectivity to the oxide layer 104 and the substrate 100 (such as a silicon substrate), such as a silicon dioxide etchant (buffered oxide etch, BOE), The oxide layer 104 is removed, but the invention is not limited to this.

Fig. 10 is a partial cross-sectional view of forming a Fresnel lens according to some embodiments of the present invention. Specifically, Fig. 10 is similar to Fig. 9C, which further depicts the distribution of rounded corners 100C in the surrounding area R1.

In some embodiments, after oxidizing and removing the tip 100S in the Fresnel lens of FIG. 8, the Fresnel lens as shown in FIG. 10 can be obtained. Due to the formation of the oxide layer 104, the right angle at the junction of the side surface of the upper step and the upper surface of the lower step is rounded into a rounded corner. Therefore, in Figure 10, there are rounded corners 100C between the upper and lower steps. That is, in the step structure 100A having eight steps, there are seven rounded corners. In addition, since the formed oxide layer 104 has substantially the same thickness T, the seven rounded corners formed in FIG. 10 have substantially the same radius of curvature.

Compared with the Fresnel lens that is molded and cut, the step structure formed by the patterning process in the embodiment of the present case can produce a small size (for example, 1.6×1.6mm) Fresnel lens, which can be applied to miniaturized Fresnel lenses. In the installation.

In summary, the method for forming Fresnel lens provided by the embodiments of the present invention can solve the problem of sharp tips during the manufacturing process, so that the stepped structure of the Fresnel lens manufactured is closer to the theory, and the light diffraction can be improved. efficient.

Several embodiments are summarized above so that those with ordinary knowledge in the technical field of the present invention can better understand the viewpoints of the embodiments of the present invention. In the technology of the present invention Those with ordinary knowledge in the technical field should understand that they can design or modify other manufacturing processes and structures based on the embodiments of the present invention to achieve the same purpose and/or advantages as the embodiments described herein. Those with ordinary knowledge in the technical field of the present invention should also understand that such equivalent manufacturing processes and structures do not depart from the spirit and scope of the present invention, and they can do so without departing from the spirit and scope of the present invention. Make all kinds of changes, substitutions and replacements.

100: substrate

100A: Ladder structure

100S: pointed

1001, 1002, 1003, 1004, 1005, 1006, 1007, 1008: ladder

R1: surrounding area

H: Step height

Claims (8)

A method for forming a Fresnel lens includes: providing a substrate; patterning the substrate to form a plurality of zigzag-shaped concentric rings, each concentric ring has a stepped structure, wherein at least one of the concentric rings There is a spike between the upper and lower steps of the step structure; the spike is oxidized to form an oxide layer; and the oxide layer is removed. The method for forming a Fresnel lens according to claim 1, wherein the step of forming the oxide layer further includes oxidizing the upper surface and the side surface of the stepped structure. Such as the method for forming a Fresnel lens of claim 1, wherein after removing the oxide layer, it further includes forming a rounded corner at the junction of the upper surface of the lower step and the side surface of an upper step. Such as the method for forming a Fresnel lens of claim 1, wherein the ratio of the thickness of the oxide layer to the width of the tip is 1.5-2.5. The method for forming a Fresnel lens according to claim 1, wherein the step of patterning the substrate includes a first patterning step performed by a first patterning mask and a second patterning mask in sequence In the second patterning step performed, the distance between the first patterned masks is smaller than the distance between the second patterned masks. Such as the method for forming a Fresnel lens of claim 1, wherein the concentric rings surround a central area, and the height of the central area is unchanged before and after the step of patterning the substrate. Such as the method of forming a Fresnel lens in claim 1, wherein the step Each step in the structure has a step height, and the ratio of the distance from the top surface of the substrate to the tip to the step height is 0.5-4. The method for forming a Fresnel lens according to claim 1, wherein before patterning the substrate, it further comprises forming a pad oxide layer on the substrate; and after patterning the substrate, it further comprises removing the pad oxide layer .

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