EP2769249A1

EP2769249A1 - Method for producing a refractive or diffractive optical device

Info

Publication number: EP2769249A1
Application number: EP12775238.4A
Authority: EP
Inventors: Michel Heitzmann
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2011-10-18
Filing date: 2012-10-17
Publication date: 2014-08-27
Also published as: US9529127B2; US20140285891A1; WO2013057152A1; FR2981460B1; FR2981460A1; JP2015504237A

Abstract

The present invention relates, in particular, to a method for producing a refractive or diffractive optical device, the method involving producing, in a first layer (10), at least one angled general profile (110) which is approximated by a stepped profile having a plurality of steps (100), wherein the production of the profile (110) includes the following steps: a step of forming buffer patterns (21) on the first layer (10), and at least one sequence of steps including: a step of forming masking patterns (40a, 50a, 60a), which is carried out such that each masking pattern (40a, 50a, 60a) has at least one edge (40b, 40c, 50b, 50c, 60b, 60c) located above a buffer pattern (21) and covers at least one area of the first layer (10) that is not masked by the buffer patterns (21), the step of forming the masking patterns (40a, 50a, 60a) further being carried out so as to define, for the fist layer (10), a plurality of free areas (20b, 30a) that are not masked by the masking patterns (40a, 50a, 60a) or by the buffer patterns (21); and a step of engraving the free areas (20b, 30a) in order to form grooves in the first layer (10), characterized in that producing the profile (110) also includes: a step of removing the masking patterns (40a, 50a, 60a), a step of removing the buffer patterns (21), thereby revealing walls (10a) previously covered by the buffer patterns (21), and then a step of isotropic engraving in order to excise the walls.

Description

"Method of producing a refractive or diffractive optical device"

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the production, by lithography and etching, of an inclined general profile. It receives for advantageous application a process for producing lithography and etching of an optical device in general and more particularly a method for producing a refractive or diffractive optical device.

STATE OF THE ART

Many areas of technology require the realization of inclined structures of millimetric, micrometric or even nanometric sizes. These inclined structures are in particular necessary for producing refractive or diffractive optical devices. In known manner, these devices exploit the phenomena of refraction or diffraction of light.

Small optical devices are often integrated into opto-electro-mechanical microsystems (MO EMs), such as optical switches, optical connectors or micro-mirror arrays. They can be integrated in many other applications such as light guides and, more generally, refractive or diffractive optics. These devices are based on a multitude of inclined profiles forming a general structure generally sawtooth or fish bones. The quality of the profile is important, in particular because it determines the performance of the optical device.

Usually, refractive or diffractive optical devices are obtained by engraving lines on the surface of a substrate such as a reflective mirror, for example made of glass or such as a silicon substrate. Etching can be done using a diamond or by using reactive plasma etching for finer structures.

In the latter case, two approaches are generally used.

A first known approach consists in placing a resin on a substrate to be etched and insolated so that it has the desired profile in sawtooth or fish bones after its development. The substrate is then etched using a method that etches the resin and the substrate at the same speed. The desired profile is transferred to the substrate. This approach is, for example, described in the publication entitled "Cost-effective mass manufacture of multilevel diffractive optical elements by use of a single optical exposure with a gray-scale mask on high-energy beam-sensitive glass", Daschner, Long, Stein, Wu and Lee, published in APPLIED OPTICS Vol.36 N ° 20, 10 July 1997.

For this first approach, a greyscale mask is used, which requires that a gray level be optimized for each pattern by possibly several iterations. This is a disadvantage especially if the number of components to be made is low and manufacturing times reduced.

A second approach is to approximate the desired inclined profile by a staircase profile. Steps of lithography and successive engravings are carried out to create trenches of varying depth and width so as to form the steps of the staircase. Given the low etching depth required, three lithography steps and three etching steps are generally sufficient to obtain a good approximation of the ideal profile. These lithography and etching steps are standard steps easily adaptable to each pattern.

The disadvantage of this approach lies in the alignment tolerances of a lithography step compared to the previous one. Indeed, a misalignment between two successive lithography steps generates unintended peaks or unwanted hollows and degrades the performance of the device. Figures 1, 2, 3, 4a and 5a illustrate the theoretical steps of a method according to this second approach in which the alignment is perfect.

As shown in FIG. 1, resin patterns 2a are formed on a substrate 1, these patterns 2a thus defining masked areas 3a. The substrate 1 is then etched (FIG. 2) at the level of the areas that are not masked by the resin 2a. The resin is then removed (Figure 3). As illustrated in FIG. 4, a new resin deposit is made so as to form patterns 2b on zones 4a not previously etched and on areas 5a previously etched. The width L ₂ of the patterns 2b formed second is half the width L of the patterns 2a formed first. The widths L and L ₂ are illustrated in FIGS. 2 and 5a respectively. A new step of etching the substrate is then performed at the level of the zones that are not masked by the patterns 2b. Trenches of different depths are thus obtained (see FIG. 5a). Then simply remove the resin patterns 2b to obtain a staircase profile.

In practice, it is relatively complicated to carry out the steps 4a and 5a described above. Indeed, these steps require very precisely position 2b patterns made second with respect to trenches already made.

Figures 4b, 5b on the one hand 4c, 5c on the other hand clearly illustrate the consequences of misalignment of the different lithography steps. These steps follow the steps described with reference to FIGS. 1 to 3.

As illustrated in FIG. 4b, if the resin patterns 2b have an offset d1 to the right with respect to their theoretical position illustrated in FIG. 4a, then a recess 5 is formed during the following etching. This hollow 5 appears clearly in Figure 5b and remains after removal of the resin patterns 2b.

As illustrated in FIG. 4c, if the resin patterns 2b have an offset d2 to the left with respect to their theoretical position illustrated in FIG. 4a, then a peak 6 is formed during the following etching. This peak 6 appears clearly in FIG. 5c and remains after removal of the resin patterns 2b.

This second approach thus induces a risk of creating spikes or parasitic hollows deriving from the superposition of the resin masks during the successive stages of lithography. The resulting profile therefore moves away from the desired profile which requires corrective steps or leads to a degradation of the performance of the device produced. The present invention aims to provide a solution to obtain an inclined profile while reducing the risk of peaks and troughs. SUMMARY OF THE INVENTION

The present invention relates to a method comprising producing, in a first layer, at least one inclined general profile approximated by a staircase profile having a plurality of steps; the embodiment of the profile comprising the following steps: a step of forming buffer patterns on the first layer so as to define on the first layer a buffer mask and at least one sequence of steps comprising:

a step of forming masking patterns, performed so that each masking pattern has at least one edge located above a buffer pattern and covers at least one area of the first layer not masked by the buffer patterns and performed so defining for the first layer a plurality of free zones, not masked by the masking patterns or by the buffer patterns;

a step of etching the free zones to form trenches in the first layer.

Preferably, the embodiment of the profile also comprises: a step of removing the masking patterns, a step of removing the buffer patterns revealing walls previously covered by the buffer patterns, then an etching step, preferably isotropic, to remove the walls.

Thus, the edge of a buffer pattern delimits at least one wall of a trench. Each masking pattern, on at least one of its edges, does not delimit one of the walls of the trench formed during the etching of the first layer. The etching patterns do not need to be perfectly aligned for at least one edge as long as this edge is located above the buffer pattern. The invention thus makes it possible to eliminate or at least reduce the consequences of misalignment of the masking patterns with respect to the other layers of the stack. This avoids the formation of undesirable hollows or bumps.

The advantages of the invention are all the more apparent since the method comprises a plurality of sequences each comprising the formation of masking patterns followed by etching of the first layer.

The buffer patterns thus serve as an absorbing buffer or eliminating the misalignment of the masking patterns. The present invention thus makes it possible to obtain more precise profiles while reducing the positioning constraints of the masking patterns.

Since the positioning constraints are reduced, the invention also makes it possible to reduce the cost of the necessary equipment and the cost of obtaining inclined profiles.

Optionally, the method of the invention may have at least any of the optional steps and features set forth below.

According to an advantageous embodiment, the method of producing the inclined general profile is implemented to produce a refractive or diffractive optical device.

Particularly advantageously, at least some of the masking patterns have two edges respectively located above a buffer pattern.

Thus, the two walls of the trenches are delimited by the edges of the buffer patterns. Therefore, regardless of their positioning and as their edges are located above a buffer pattern, the masking patterns do not define the walls of the trench. A defect in their alignment therefore has no consequence on the patterns formed in the first layer.

Advantageously, at the end of the etching step, the masking patterns are removed and the buffer patterns are left in place. This step of removing the previous masking patterns is performed at the end of the step of engraving each sequence.

Preferably, the method comprises at least two sequences.

Preferably, the method comprises at least one sequence in which at least one masking pattern covers at least one trench previously formed in the first layer.

Preferably, the method comprises at least one sequence in which at least one masking pattern covers at least one trench previously formed in the first layer and at least one free zone.

Preferably, the method comprises at least one sequence in which at least one masking pattern covers several trenches previously formed in the first layer, said trenches having different depths.

Preferably, the buffer patterns are arranged directly on the first layer. Alternatively, at least one intermediate layer is present between the buffer units and the first layer, this at least one intermediate layer can be etched during the etching steps to form trenches. Advantageously, during the masking step, at least one masking pattern covers at least one non-masked area by a buffer pattern, the number of areas not masked by a buffer pattern and covered by the same masking pattern being equal to 2 ⁿ where n is the number of etching steps previously performed in the first layer.

Preferably, the number of steps of the profile is equal to 2 ⁿ , where n is the number of etching steps previously performed to form trenches in the first layer.

Preferably, the method comprises several steps of trench etching, and wherein during each etching step a depth P is engraved such that P = p. 2 ⁿ where n is the number of etching steps previously performed to form trenches and where p is the depth etched during the first etching.

The method comprises a plurality of step sequences, the trench etching steps forming a plurality of the walls beneath the buffer patterns.

Advantageously, the self in a step of etching to form trenches is an anisotropic etching. The main direction of the anisotropic etching is substantially perpendicular to the plane of the first layer.

The method comprises, after the at least one sequence, a step of removing the masking patterns, and then a step of removing the buffer patterns.

Preferably, the method comprises: a step of removing the masking patterns, a step of removing the buffer patterns revealing walls previously covered by the buffer patterns, then an etching step to remove the walls.

Advantageously, the etching step for removing the walls is an isotropic etching. According to one embodiment, the isotropic etching is a delocalized plasma dry etching. According to another embodiment, the isotropic etching can be obtained in a deep silicon etching machine operating in isotropic mode. The isotropic etching of the silicon can also be obtained, without plasma, using the XeF2 gas. It is also possible to etch the walls with any liquid allowing isotropic etching on a layer of semiconductor or non-semiconductor material.

Advantageously, the thickness etched during the etching to remove the walls is greater than or equal to half the thickness of the widest wall. Particularly advantageously, the thickness etched during etching to remove the walls is approximately equal to twice the thickness of the widest wall. This reduces the roughness of the inclined profile approximated by the steps. Particularly advantageously, the width of the buffer patterns is greater than or equal to the equipment alignment tolerance interval for forming the masking patterns. Typically, the alignment tolerances of the equipment for forming the masking patterns are between -80 nm and + 80 nm and the pattern width is at least 160 nm.

Preferably, the buffer patterns have the same width.

Preferably, the trenches have the same width. Advantageously, the slope of the inclined general profile approximated by a staircase is constant. Alternatively, the trenches have different widths and the slope of the inclined general profile approximated by a staircase is variable.

According to a first embodiment, the first layer is a layer of semiconductor material. According to another embodiment, the first layer is a layer of at least partially reflective or mainly reflective material such as a metal. In this case, preferably, the device will operate mainly in diffraction. According to another embodiment, the first layer is a layer of at least partially transparent or mainly transparent material such as glass or quartz, for example. In this case, preferably, the device will function primarily in refraction.

Advantageously, the first layer forms a substrate. In general, the first layer may be formed of any anisotropically and isotropically etchable material.

Advantageously, the semiconductor material is silicon. Such a substrate has the particular advantage of being compatible with the MEMS MEMS devices or MOEMS optoelectromechanical microsystems developed elsewhere. Thus, the substrate or the layer in which the inclined profile is produced, is intended for producing MEMS or MOEMS.

Advantageously, the buffer units are made of silicon oxide. This material has the advantage of being able to withstand the etching of the first silicon layer and to be removed without damaging the latter. Advantageously, the silicon oxide buffer units are obtained from a silicon oxide layer. The thickness of the buffer layer and therefore that of the buffer units is between 100 nm and 2 micrometers. Preferably it is of the order of a few hundred nanometers and more precisely between 200 nm and 500 nm. It can be obtained by thermal oxidation of silicon or by deposition. Preferably, the buffer patterns are aluminum. This material has the advantage of being able to withstand the etching of the first quartz layer and to be removed without damaging the latter.

Advantageously, the masking patterns are made by photolithography from a buffer layer covering the first layer. For example, a resin mask may be deposited on the buffer layer, and then patterns may be formed in the resin layer prior to etching the buffer layer through the resin mask.

Advantageously, the method comprises, after the step of etching the walls, a step of metallizing the steps. This has the advantage of improving the reflectivity with respect to that of a silicon-type substrate. The efficiency of a diffractive device can thus be improved. The metal deposition may for example be achieved by known techniques of vacuum evaporation, sputtering or CVD or PECVD deposition.

Advantageously, several stair profiles are made in the same first layer. It is thus possible to obtain a "sawtooth" structure, in "fish bones".

According to another aspect, the invention relates to a system comprising at least one refractive or diffractive optical device obtained by a method according to any one of the preceding characteristics.

According to another aspect, the invention relates to a method of producing in a first layer at least one inclined general profile approximated by a staircase profile having a plurality of steps; the embodiment of the profile comprising the following steps: a step of forming buffer patterns on the first layer so as to define on the first layer a buffer mask and at least one sequence of steps comprising:

a masking pattern forming step performed such that each masking pattern has at least one edge located above a buffer pattern and overlaps at least one area of the first layer not masked by the stamp patterns and so defining for the first layer a plurality of free zones not masked by the masking patterns or by the buffer patterns;

a step of etching the free zones to form trenches.

Optionally and advantageously, the other steps and characteristics detailed with reference to the method of producing a refractive optical device or diffractive are perfectly applicable to the process of producing an inclined profile approximated by a staircase profile.

BRIEF DESCRIPTION OF THE FIGURES

Other features, objects and advantages of the present invention will appear on reading the detailed description which follows and with reference to the appended drawings, given by way of non-limiting examples and in which:

Figures 1 -3, 4a and 5a illustrate the main steps of a method of making trenches according to a known technique;

FIGS. 4b-5b illustrate steps of the production method according to the known technique and in which a misalignment occurs to the right,

FIGS. 4c-5c illustrate steps of the production method sliced according to the known technique and in which a misalignment occurs to the left,

FIGS. 6 to 17 illustrate the steps of a method according to an exemplary embodiment of the invention and making it possible to obtain an inclined profile approximated by a staircase profile as represented in FIG. 17. More precisely:

FIG. 6 illustrates a stack of layers comprising a buffer layer covering a first layer in which it is desired to produce an inclined profile approximated by a stepped profile;

FIG. 7 illustrates a step at the end of which the buffer layer is partially etched to form buffer patterns;

FIG. 8 illustrates a step of forming first masking patterns;

FIG. 9 illustrates a step where the first layer is etched through the masking patterns and the buffer patterns to form trenches;

FIG. 10 illustrates a second step of forming masking patterns;

- Figure 1 1 illustrates another step where the first layer is etched through the newly formed masking patterns and the buffer patterns to form or deepen trenches;

FIG. 12 illustrates a third step of forming masking patterns; FIG. 13 illustrates another step where the first layer is etched through the newly formed masking patterns and the buffer patterns to form or deepen trenches;

FIG. 14 illustrates a step of removing the masking patterns;

FIG. 15 illustrates a step of removing the buffer patterns;

FIG. 16 illustrates the first layer at the end of step 15 and illustrates the profile that will be obtained at the end of step 17; FIG. 17 illustrates a step of etching the remaining walls between the trenches and previously covered by the buffer patterns.

DETAILED DESCRIPTION OF THE INVENTION

The production of an inclined profile to form preferably an optical device will now be detailed with reference to FIGS. 6 to 17.

Beforehand, it is specified that in the context of the present invention the term "on" does not necessarily mean "in contact with". For example, the deposition of a layer on another layer does not necessarily mean that the two layers are directly in contact with each other but that means that one of the layers at least partially covers the other by being either directly in contact with it or being separated from it by a film, yet another layer or another element.

In the context of the present invention the term inclined profile means that the slope of the profile is inclined relative to the plane defined by the first layer. In the figures, this plane is transverse to the drawing and is parallel to the XY plane defined by the orthonormal coordinate system XYZ of Figure 6. The inclination is typically between 0 ° and 90 °.

As indicated above, the purpose of the following method is to make a profile 10 in steps that approximates an inclined general profile. The staircase comprises a plurality of steps 100. The profile 1 10 is illustrated in FIGS. 16 and 17. The inclined profile 1 and at least the steps 100 preferably have a micrometric / nanometric scale. In a first step, illustrated in FIG. 6, a buffer layer is deposited

20 on a first layer 10 in which it is desired to form the steps of the staircase. The first layer 10 is made of a material that can be etched isotropically and anisotropically. Advantageously, the first layer 10 serves as a substrate.

As illustrated in FIG. 7, patterns are formed in the buffer layer 20 so as to form a buffer mask 20c. These patterns are hereinafter referred to as buffer patterns 21. Thus, the buffer mask 20c defines for the first layer 10 areas masked by the buffer patterns 21 and free zones 20a not masked by the buffer patterns 21. Advantageously, the buffer patterns 21 are arranged so as to define an alternation of zones masked by the buffer patterns 21 and free zones 20a not masked by the buffer patterns 21. The buffer patterns 21 can be obtained by conventional lithography steps. In particular, it is possible to cover the resin buffer layer 20 and then to form patterns in the resin layer by nanometric printing using a mold comprising reliefs or by insolation of a selection of zones of the resin. it is a photosensitive resin. After a possible development of the resin, the buffer layer 20 is etched through the resin patterns, and then the latter are removed. The step of etching or selective etching of the buffer layer 20 is an anisotropic etching. It is advantageously performed by plasma etching. As illustrated in FIG. 8, a mask is made in a second layer. This mask has patterns designated masking patterns 40a.

Advantageously, these masking patterns 40a are made from a layer designated masking layer which has been applied to the stamping mask 20c.

The masking patterns 40a are preferably made of resin. They can thus be produced by a conventional method of nanoscale lithography or by photolithography, such as those mentioned above for the production of the buffer units 21.

The masking patterns 40a are made so as to cover certain free zones 20a not masked by the buffer patterns 21 and not to cover some other free zones 20a not masked by the buffer units 21. Thus, certain zones 20b of the first layer 10 are not covered by the buffer patterns 21 nor by the masking patterns 40a. These zones 20b appear in FIG.

By observing the stack of layers in section, according to a plane which comprises the X and Z axes, the zones 20a not covered by the buffer patterns 21 are, alternately, covered and not covered by the masking patterns 40a. Thus, except at the ends of the stack of layers, a zone 20b neither covered by a buffer pattern 21 nor covered by a masking pattern 40a is adjacent to two zones covered by a buffer pattern 21.

In a particularly advantageous manner, the masking patterns 40a have at least one edge (40b or 40c) which covers a buffer pattern 21.

It is specified that an edge is formed by a wall of a pattern which extends in a direction substantially perpendicular to the surface of the first layer 10, or in a direction substantially parallel to the Z axis of the reference of FIG. 6 When the pattern is a line, the edge forms, in a plane substantially parallel to that of the first layer 10, also a line. When the pattern is a ring, the edge forms, in a plane substantially parallel to that of the first layer, a circle of same center as the ring. In the illustrated figures, the edges appear in a section substantially transverse to the direction in which the pattern extends. Thus, in these figures, the patterns and trenches can be lines, a succession of segments aligned or not, circles and so on. The invention is not limited to the shapes defined by the patterns in a plane parallel to that of the first layer (XY plane).

The masking pattern 40a covers at least a portion of the stamp pattern 21 as well as an area of the first layer 10 not covered by the stamp pattern 21. Thus, regardless of the edge position (40b or 40c) of the masking pattern 40a on the buffer pattern 21 as this edge is located above the buffer pattern 21, then this edge (40b or 40c) will have no influence during an etching performed to form trenches in the first layer 10. This edge will not delimit any of the walls of the trenches.

The positioning constraints of the masking pattern 40a can thus be relaxed.

It should be noted that it is preferable that the masking patterns 40a have their two edges 40b, 40c which cover a buffer pattern 21. This is illustrated in FIG. 8. Each of the two vertical edges 40b, 40c in the plane ZX is located above a buffer pattern 21. Each masking pattern 40a, except possibly those of the ends of the stack of layers therefore successively cover from one of their edge 40b: a buffer pattern 21, an area not masked by a buffer pattern 21 and another buffer pattern 21. As will be seen later in the other steps, the same masking pattern 40a, 50a or 60a can cover more than two buffer patterns 21 and several zones 20b of the first layer 10 uncovered a buffer pattern 21.

These are therefore the buffer patterns 21 which delimit the walls of the trenches which can be made by etching in the first layer 1 0. The masking patterns 40a have no influence on these walls. A misalignment of one or more masking patterns 40a, as long as the edges (40b, 40c) of this masking pattern 40a are arranged at the right of a buffer pattern 21, will have no influence on the positioning of the walls of the trenches. Such a misalignment will therefore not reveal a dip or peak. The invention thus makes it possible to reduce the alignment constraints and to considerably limit the risks of occurrence of hollows or peaks.

Particularly advantageously, the width of the buffer patterns 21 is greater than or equal to the alignment tolerances of the lithography equipment used to make the masking patterns (40a, 50a, 60a). In the context of the present invention, it is possible to use conventional lithography equipment, for example a ASM / 300 type equipment. The alignment tolerance of conventional lithography equipment is of the order of about +/- 75 nm (nanometers), a tolerance range of 150 nm. Buffer patterns 21 with a width of at least 150 nm will then be made. It is specified that the width of a pattern is its dimension taken in a direction substantially parallel to the surface of the first layer 10, or in a direction substantially parallel to the axis X of the reference of FIG. 6.

At the end of the first lithography step making it possible to create masking patterns 40a, the first layer 10, observed in section along the ZX plane and along the X axis direction, comprises several successions of zones, each succession comprising successively :

an area masked by a buffer pattern 21,

an area masked by a masking pattern 40a,

an area masked by a buffer pattern 21,

an unmasked zone 20b.

Preferably, all of the four preceding zones are repeated for the entire length of the first layer 10 along the X direction, except possibly at the ends.

At the end of the first lithography step, a first step of etching the first layer 10 is performed. The result of this step is illustrated in FIG. 9. The combination of the buffer patterns 21 and the masking patterns 40a forms an etching mask. for engraving the first layer 10 at the areas of this layer which are not covered by any pattern. Etching thus makes it possible to form trenches. The depth engraved p during this first step is typically between 200 nm and Ι μηη. It is preferably of the order of 400 nm. The depth is measured along the Z direction. This etching is anisotropic in principal direction along the Z axis.

A step of removing the masking patterns 40a is preferably carried out. The buffer patterns 21 are stored. A method of selective removal of the masking patterns 40a is therefore applied. This selective shrinkage is particularly simple when the masking patterns 40a are in resin and the buffer units 21 are made of silicon oxide, silicon nitride or metal.

As illustrated in FIG. 10, a second step of forming masking patterns 40a is carried out. Preferably, these new masking patterns 40a are made by lithography. These new masking patterns 50a are formed so that at least one of their edges 50b, 50c is located right of a buffer pattern 21. For the reasons mentioned above, it is preferable that the two edges 50b, 50c are each located vertically above a buffer pattern 21.

These new masking patterns 50a are also arranged so as to:

- cover: non-engraved areas and trenches formed in the previous step of etching and

- Do not cover: non-etched areas and trenches formed in the previous etching step.

At the end of this second lithography step making it possible to create new masking patterns 50a, the first layer 10, observed in section along the ZX plane and along the X axis direction, comprises several succession of zones, each succession comprising successively:

an area masked by a buffer pattern 21,

a trench masked by a masking pattern 50a and having been etched, this trench preferably having a depth p,

an area masked by a buffer pattern 21,

a trench masked by a masking pattern 50a and not having been etched,

an area masked by a buffer pattern 21,

an unmasked zone which has been etched, this trench preferably having a depth p,

an area masked by a buffer pattern 21,

- an unmasked area that has not been etched.

This succession of eight zones is repeated for the entire length of the first layer 10 along the X direction, except at the ends.

Preferably, a single marking pattern 50a is formed for a succession of zones as defined above. As illustrated in FIG. 11, a second etching of the first layer 10 is carried out through the mask formed by the combination of the buffer patterns 21 and the masking patterns 50a that have recently been formed.

The etching thus makes it possible to form trenches where there were no prior trenches and makes it possible to increase the depth of the trenches formed beforehand. The engraved depth during this etching is advantageously of the order of 2p, that is to say that it is twice the depth engraved during the previous etching step (illustrated in Figure 9). The first layer 10 thus has non-etched areas, trenches etched only once, the depth of which is p, trenches etched only once, the depth of which is 2p and trenches etched twice, the depth 3p (p + 2p ).

Thus, at the end of this second etching step of the first layer 10, the latter has, along the X direction, a repetition of three consecutive trenches whose depth is gradually reduced. Two of these trenches were etched during this second etching step and one was not etched during this step because protected by a masking pattern 50a resin. This last trench is adjacent to a non-engraved area.

Three trenches and one non-etched area are thus successively separated, each separated by a wall formed in the first layer. This succession is repeated along the X axis.

A removal step is preferably performed of the masking patterns 50a recently formed. The buffer patterns 21 are stored.

As illustrated in FIG. 12, a new step of forming masking patterns 60a is performed. Preferably, these new masking patterns 60a are made by lithography.

These new masking patterns 60a are formed so that at least one of their edges 60b, 60c is located in line with a buffer pattern 21. For the reasons mentioned above, it is preferable that the two edges 60b, 60c are each located vertically above a buffer pattern 21.

These new masking patterns 60a are also arranged so as to:

- cover: non-etched areas and trenches formed in the previous steps of etching and

At the end of this new lithography step making it possible to create new masking patterns 60a, the first layer 10, observed in section along the ZX plane, comprises several successions of zones. Each succession comprises a masking pattern 60a successively covering along the X axis:

an area masked by a buffer pattern 21,

a trench masked by a masking pattern 60a and having undergone two etching steps, this trench preferably having a depth of 3p,

an area masked by a buffer pattern 21, a trench masked by a masking pattern 60a and having undergone an etching step, this trench preferably having a depth 2p,

an area masked by a buffer pattern 21.

a trench masked by a masking pattern 60a and having undergone an etching step, this trench preferably having a depth of p,

an area masked by a buffer pattern 21,

a trench masked by a masking pattern 60a and not having been etched,

an area masked by a buffer pattern 21.

In addition, the succession of zones comprises, between two consecutive masking patterns 60a, four zones that are not masked by any pattern, these four unmasked zones being separated by three buffer patterns 21. These four unmasked areas being respectively:

a trench preferably having a depth of 3p,

a trench having preferably a depth 2p,

a trench preferably having a depth of p,

- an area that has not been etched.

As illustrated in FIG. 13, a third step of etching the first layer 10 is carried out through the mask formed by the combination of the buffer patterns 21 and the masking patterns 60a that have recently been formed.

The etching thus makes it possible to form trenches where there were no prior trenches and makes it possible to increase the depth of the trenches formed beforehand. The depth engraved during this etching is advantageously of the order of 4p, that is to say that it is twice the depth engraved during the previous etching step (illustrated in FIG. is four times larger than the depth engraved during the first etching step (shown in Figure 9). The first layer 10 thus has non-etched areas, trenches etched only once, the depth of which is p, trenches etched only once, the depth of which is 2p, trenches etched twice, the depth of which is 3p, trenches engraved only once, the depth of which is 4p, trenches engraved twice with a depth of 5p, trenches engraved twice with a depth of 6p and trenches engraved three times with a depth of 7p.

Thus, at the end of this third etching step of the first layer 10, the latter has, along the X direction, a repetition of: seven consecutive trenches whose depth is gradually reduced and a non-etched area. These seven trenches and this ungraved area are each separated by a wall formed in the first layer. This succession is repeated along the X axis.

As illustrated in FIG. 14, it is preferable to carry out a step of removing the masking patterns 60a that have recently been formed. The buffer patterns 21 are stored.

At the end of the last etching step of the first layer 10 to form trenches, the buffer units 21 are eliminated as illustrated in FIG.

This gives a structure with trenches of increasing or decreasing depth and separated from each other by walls 10a. These walls correspond to the zones of the first layer covered by the buffer patterns 21. The prior etchings being anisotropic, the etchings made in the first layer 10 have retained walls substantially vertically above the edges of the buffer units 21. It is therefore the buffer patterns 21 which delimit the walls of the trenches and walls 10a of trench separation.

As illustrated in FIGS. 16 and 17, the first layer 10 is etched so as to eliminate the trench separation walls 10a. The profile obtained is referenced 1 10 in these figures.

Preferably, this step of etching walls 10a is an isotropic etching step. According to one embodiment, the isotropic etching is a delocalized plasma dry etching also designated by its English term "remote plasma". The equipment used on the platform is for example an industrial machine of the equipment supplier Shibaura, consisting of a main frame, or basic module, Allegro supporting a CDE80 chamber. According to other alternatives, the isotropic etching can be obtained by a deep silicon etching machine operating in isotropic mode. For example, two industrial equipment from SPTS, intended for deep silicon etching, are used on the platform. Isotropic etching is achieved by operating only the source generator of the chamber. The isotropic etching of the silicon can also be obtained, without plasma, using the XeF2 gas. In this case, for example Xactix laboratory equipment may for example be installed on the platform. It is also possible to etch the walls 10a with any liquid allowing isotropic etching on a layer of semiconductor or non-semiconductor material.

This step of etching the walls 10a makes it possible to remove a thickness e2 from the material of the first layer 10 at least equal to half the width e1 of the walls 10a, or at least half the thickness e1 of the widest wall if they are not all the same width.

Advantageously, this engraved thickness is doubled, approximately equal to the width of a wall. In this case, the steps are smoothed and the wall of the slope becomes less rough and more straight.

Continuing the previous example in which the buffer patterns 21 have a width of 150 nm, the walls 10a have a substantially width of 150 nm taken in the direction. The minimum depth to be engraved is therefore 75 nm. Advantageously it is 150 nm in order to smooth the roughness of the inclined profile.

Steps 100 forming a profile 1 10 are thus obtained in steps. With the sequence of the steps described above, the steps 100 are 8 in number.

This step of isotropic etching of the walls, associated with the preceding steps, makes it possible to reduce considerably the total number of steps. In addition, the isotropic etching step makes it possible to attack the wall laterally, which makes it possible to quickly consume thin and high walls as well as a small thickness in the bottom of the trenches, thus allowing a rapid elimination of the walls and smoothing. of the slope if the engraving is continued.

The invention is not limited to the number of steps or etching depths or patterns described in the previous example. These parameters will be adapted according to the inclined profile that one wishes to achieve.

Thus, in general, the number of steps 100 of the same profile 1 10 is equal to 2 ⁿ , where n is the number of etching steps previously performed to form trenches in the first layer. It is thus easy to determine the number of etching steps to be performed as a function of the number of steps to achieve to obtain the desired profile. Thus, at the end of step 17, three etching steps of the first layer 10 have been performed (see the steps illustrated in FIGS. 9, 11 and 13) and the number of steps is therefore 2 ⁿ = 8 .

Also generally, during a step of forming the masking patterns (40a, 50a or 60a), at least one masking pattern is produced which covers at least one non-masked area by a buffer pattern 21, the number of the zones not covered by a buffer pattern 21 and consecutive that the same masking pattern covers being equal to 2 ⁿ , where n is the number of etching steps previously performed in the first layer 10. Thus, as illustrated in FIG. masking 40a overlaps 2 ° = 1 unmasked area since no etching step of the first layer has been made prior to the embodiment of masking patterns 40a of Figure 8. As illustrated in Figure 10, each masking pattern 50a covers 2 ¹ = 2 unmasked areas since a single step of etching of the first layer (illustrated in FIG. 9) has been made prior to the production of the masking patterns of FIG. 10. As illustrated in FIG. 12, each masking pattern 60a covers 2 ² = 4 unmasked areas since only one etching step of the first layer (illustrated in Figure 1 1) was performed prior to the embodiment of the masking patterns 60a of Figure 12.

Likewise, at each step of forming the masking patterns, two consecutive masking patterns are separated so as to leave between them 2 ⁿ areas not covered by any buffering pattern 21 or masking pattern. Thus, 2 ⁿ areas not covered by buffer 21 and consecutive patterns are allowed to be etched, n still being the number of etching steps previously performed in the first layer 10.

In general, during each etching step of the first layer 10, a depth P is engraved such that P = p.2 ⁿ with:

n is the number of etching steps previously carried out in the first layer to form trenches and

- p is the depth of the first engraving.

Thus, the engraving illustrated in FIG. 9 is the first engraving and its depth is p. This depth verifies the law P = p.2 ° = p since no etching step of the first layer has been performed beforehand. The engraving illustrated in FIG. 1 1 is the second etching and its depth is P = p.2 ¹ = 2p since only an etching has been done beforehand in the first layer 10. The etching illustrated in FIG. 13 is the third etching and its depth is P = p.2 ² = 4p since two etchings have been carried out beforehand in the first layer 10. These two prior etchings correspond to the steps illustrated in FIGS. 9 and 11.

With the method according to the invention, steps 100 each having a height preferably of between 200 nm and 1 μm are obtained and typically of the order of 400 nm, the height being taken in the Z direction. The first etching or depth p is therefore preferably between 200nm and 1 μηι. In the illustrated example, the depth of the deepest trench before removal of walls 10a is 7p. It is therefore between 7 ^* 200nm and 7 ^* 1 μηη, ie between 1, 4μηΊ and 7μη "ΐ The width of a step 100, ie its dimension in the X direction is preferably between 200 nm and 1 μηη and typically order of 500 nm. On the same layer 10, several profiles 100 can thus be formed. The highest step of one of these other profiles appears on the left of Figures 16 and 17. It is thus possible to obtain sawtooth structures, fish bones. As indicated above, it is necessary that the first layer 10 is in an isotropically and anisotropically etchable material.

According to one embodiment, the first layer is made of a semiconductor material. Advantageously, the first layer is made of silicon thus allowing compatibility with other devices such as MEMSs or MOEMs. According to another embodiment, the first layer is a reflective or mainly reflective material layer such as a metal. In this case, preferably, the device will operate mainly in diffraction. According to another embodiment, the first layer is a layer of transparent or essentially transparent material such as glass or quartz, for example. In this case, preferably, the device will operate mainly in refraction.

The buffer layer 20 may be made of silicon oxide. The silicon oxide is advantageously obtained by thermal oxidation of silicon or by deposition. The buffer layer 20 has a thickness, measured along the Z axis, typically a few hundred nanometers.

According to one variant, the buffer layer 20 is made of silicon nitride, if the semiconductor material is silicon. It can also be aluminum if the semiconductor material is quartz. These materials can withstand the engravings described below and can be removed without damaging the first layer 10.

In order to improve its optical performance, optionally metallized profile 1 10 obtained. This has the advantage of improving the reflectivity compared to that of a less reflective substrate. The effectiveness of a device operating mainly by diffraction can thus be improved. The metal deposition may for example be achieved by known techniques of vacuum evaporation, sputtering or CVD or PECVD deposition.

The present invention thus proposes a particularly reliable and simple method for obtaining an inclined profile having a plurality of steps of micrometric / nanometric size while avoiding the formation of hollows or peaks. It advantageously makes it possible to obtain quality refractive or diffractive optical devices improved. In addition, the positioning constraints being reduced, the invention makes it possible to reduce the cost of the necessary equipment and the cost of obtaining the profiles.

The present invention is not limited to the previously described embodiments but extends to any embodiment within its spirit. The invention is in particular not limited to steps that extend in a straight direction along the Y axis, nor to steps of constant height or thickness, nor to a given number of stages of engraving or of steps.

Claims

1. A method of producing, in a first layer (10), at least one inclined general profile (1 10) approximated by a stepped profile having a plurality of steps (100); performing the profile (1 10) comprising the steps of: a buffer pattern forming step (21) on the first layer (10) and at least one sequence of steps comprising:

a masking pattern forming step (40a, 50a, 60a) performed so that each masking pattern (40a, 50a, 60a) has at least one edge (40b, 40c, 50b, 50c, 60b, 60c) above a buffer pattern (21) and covers at least one area of the first layer (10) unmasked by the buffer patterns (21), the step of forming the masking patterns (40a, 50a, 60a) being further provided so as to define for the first layer (10) a plurality of free areas (20b, 30a) not masked by the masking patterns (40a, 50a, 60a) or by the buffer patterns (21);

a step of etching the free zones (20b, 30a) to form trenches in the first layer (10);

characterized in that the embodiment of the profile (1 10) also comprises: a step of removing the masking patterns (40a, 50a, 60a), a step of removing the buffer patterns (21) revealing walls (1 0a) previously covered by the buffer patterns (21), then an isotropic etching step to remove the walls.

2. Method according to the preceding claim, wherein at least some of the masking patterns (40a, 50a, 60a) have two edges (40b, 40c, 50b, 50c, 60b, 60c) located respectively above a buffer pattern ( 21).

3. Method according to any one of the preceding claims, wherein at the end of the etching step is removed masking patterns (40a, 50a, 60a) and is left in place the buffer units (21).

4. Method according to any one of the preceding claims comprising at least two sequences of steps each comprising a step of forming masking patterns (40a, 50a, 60a) and a step of etching the free zones (20b, 30a) for to form trenches.

5. Method according to any one of the preceding claims, comprising at least one sequence in which at least one masking pattern (50a, 60a) covers at least one trench previously formed in the first layer (10).

6. Method according to the preceding claim, comprising at least one sequence in which at least one masking pattern (50a, 60a) covers at least one trench previously formed in the first layer (10) and at least one free zone (20b, 30a). ).

7. Method according to any one of the two preceding claims, comprising at least one sequence in which at least one masking pattern (60a) covers several trenches previously formed in the first layer (10), said trenches having different depths.

A method according to any one of the preceding claims, wherein the width of the buffer patterns (21) is greater than or equal to the alignment tolerance range of the equipment for forming the masking patterns (40a, 50a, 60a). ).

9. A method according to any one of the preceding claims, wherein during the masking step, at least one masking pattern (40a, 50a, 60a) covers at least one unmasked area by a buffer pattern (21), the number of zones not masked by a buffer pattern (21) and covered by the same masking pattern (40a, 50a, 60a) being equal to 2 ⁿ , where n is the number of etching steps previously performed in the first layer ( 10).

The method according to any one of the preceding claims, wherein the number of steps (100) of the profile (1 10) is 2 ⁿ , where n is the number of etching steps previously performed to form trenches in the first layer (10).

1 1. Method according to any one of the preceding claims, comprising several steps of trench etching, and in which during each etching step a depth P is engraved such that P = p.2 ⁿ where n is the number of etching steps previously performed to form trenches and where p is the depth engraved during the first etching.

12. Method according to the preceding claim, wherein the depth p etched during the first etching is between 200nm and 1 μηη.

The method of any of the preceding claims, wherein the at least one etching step for trenching in the first layer (10) is anisotropic etching.

14. The method according to the preceding claim, wherein the isotropic etching is a delocalized plasma dry etching or a deep reactive ion etching or a chemical etching using an XeF2 gas.

15. A method according to any one of the preceding claims, wherein the thickness etched during etching to remove the walls (10a) is approximately equal to twice the thickness of the widest wall (10a).

The method of any of the preceding claims, wherein the first layer (10) is a layer of semiconductor material.

17. A method according to any one of claims 1 to 16, wherein the first layer (10) is a layer of at least mainly transparent material, wherein the inclined profile enters the embodiment of an optical device operating essentially in refraction. .

18. A method according to any one of claims 1 to 16, wherein the first layer (1 0) is a layer of material at least mainly reflective, wherein the inclined profile is part of the embodiment of an optical device operating essentially in diffraction.

The method of any one of the preceding claims, wherein the buffer units are aluminum.

20. Process according to any one of the preceding claims, comprising a step of metallizing the steps (100).

21. System comprising at least one refractive or diffractive optical device comprising at least one inclined general profile (1 10) obtained by a method according to any one of the preceding claims.