KR100429849B1 - Method for forming etch mask used in fabricating planar lightwave guide, especially preventing the damage of an epi layer like a mask pattern and a lightwave guide - Google Patents

Abstract

An etching mask forming method for use in optical waveguide fabrication is disclosed. The present invention forms an optical waveguide layer using a silica layer or the like on a substrate. Subsequently, a mask layer is formed on the optical waveguide layer, and a photoresist pattern exposing a predetermined region of the mask layer is formed on the mask layer. Subsequently, an inductively coupled plasma including a cathode, an inductively coupled plasma coil, and a chamber, to which a first radio frequency power is applied, is used as a mask layer exposing the photoresist pattern as an etch mask. The mask pattern is formed by patterning by an etching method using an inductively coupled plasma system. In this case, in the etching method using an inductively coupled plasma apparatus, when using a chromium layer as a mask pattern, chlorine gas (Cl ₂ ), oxygen gas (O ₂ ), or the like is used as a reaction gas. In addition, chlorine gas flow rate conditions of 10 sccm (Standard Cubic CentiMeter) to 50 sccm and oxygen gas flow rate conditions of 10 sccm to 50 sccm. In addition, it is carried out under a pressure condition of 3mTorr to 30mTorr maintained in the chamber, a first RF power condition of 10W to 100W applied to the cathode electrode, and a second RF power condition of 100W to 1500W applied to the inductively coupled plasma coil.

Description

Etch Mask Formation Method Used in Planar Waveguide Fabrication

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar lightwave guide fabrication method, and more particularly, to an etching mask forming method used for planar light waveguide fabrication.

An optical waveguide or a planar optical waveguide is a basic optical transmission element among various optical elements constituting an optical integrated circuit. When fabricating an optical waveguide, a process of patterning a material layer formed on a substrate, such as an optical waveguide layer, is required. In order to perform such a patterning process, for example, an etching process, a process of forming a mask pattern on the material layer is required. In this case, the mask pattern shields a part of the material layer and serves to protect a part of the material layer from the etching process, and thus is referred to as an etch mask. The process of forming such an etching mask affects the shape and precision of the mask pattern. Accordingly, the process of patterning the material layer to form a precise material layer pattern, for example, an optical waveguide formed by patterning the optical waveguide layer, is influenced by the process of forming the etching mask.

1 is a cross-sectional view for explaining an etching mask forming method by a lift-off method.

Specifically, in the above-described method of forming the etching mask, a lift for forming a photoresist pattern 40 on the substrate 10 and forming the mask layer 50 on the photoresist pattern 40. There is a way off. After the mask layer is formed in this manner, when the photoresist pattern 40 is lifted off, a mask pattern, that is, an etching mask is formed on the substrate 10. However, such a lift-off method may obtain a clean pattern when the thickness of the etching mask is very thin. However, as the thickness of the etching mask becomes thick, it is difficult to form the pattern.

FIG. 2 is a cross-sectional view illustrating an etching mask forming method by an etching method using a reactive ion etcher.

Specifically, after the mask layer 55 is formed on the substrate 10, the photoresist pattern 45 is formed on the mask layer 55. Thereafter, the mask layer 55 is etched using the photoresist pattern 45 as an etching mask. In this case, the mask layer is etched by a dry etching method using a reactive ion etchant (hereinafter, referred to as "RIE"). Alternatively, a wet etching method may be used as the etching method. In this way, the mask layer 55 is patterned to form a mask pattern.

However, in the etching method using the wet etching method, it is difficult to form an etching mask having a precise pattern by the isotropic etching characteristic by the wet etching. Moreover, problems due to the harmfulness of the etching solution used can be derived. In addition, the dry etching method using the RIE apparatus is required to increase in the etching speed. That is, when the RIE apparatus is used in the optical waveguide fabrication, the speed of etching the material layer and the mask layer shows a low speed, for example, a low etching speed of about 300 kW / min to 500 kW / min. Therefore, a limitation on the thickness of the mask pattern occurs by the etching process. That is, when forming a thicker mask pattern, a long time etching process is required, and a pattern failure due to an etching failure may occur. As described above, since difficulty in implementing a thicker mask pattern is derived, a limitation occurs in the thickness of the optical waveguide formed by using the mask pattern as an etching mask. Therefore, difficulty in controlling the thickness of the optical waveguide occurs.

When etching using an RIE device, an increase in the etching speed may be realized by increasing the RF (Radio Frequency) power, increasing the concentration of plasma generated, and increasing the energy required for etching. Can be. However, increasing the RF power leads to an abnormal increase in DC bias voltage. Such an increase in the DC bias voltage may cause damage to the mask layer to be etched and the material layer under it, that is, the optical waveguide layer. In addition, it may cause damage to the surface of the optical waveguide and the substrate formed later. Such damage is a cause of deterioration of the characteristics of the optical device including the optical waveguide.

The technical problem to be achieved by the present invention is to prevent damage to the material layer, such as the mask pattern to be formed and the optical waveguide layer below, to form a more precise mask pattern, it is possible to further increase the etching rate of the mask layer The present invention provides a method of forming an etching mask used for manufacturing an optical waveguide.

FIG. 1 is a cross-sectional view for explaining an etching mask forming method used for manufacturing a planar optical waveguide by a lift off method.

FIG. 2 is a cross-sectional view for explaining an etching mask forming method used for fabricating a planar optical waveguide by an etching method using a reactive ion etching device.

3 to 7 are cross-sectional views illustrating an etching mask forming method used for fabricating a planar optical waveguide according to the present invention.

FIG. 8 is a view schematically illustrating an inductively coupled plasma apparatus used in an etching mask forming method used for fabricating a planar optical waveguide according to the present invention.

In order to achieve the above technical problem, the present invention forms a material layer on a substrate. In this case, a silica layer or the like is used as the material layer. Thereafter, a mask layer is formed on the material layer. In this case, a metal layer such as a chromium layer and a dielectric layer such as an amorphous silicon layer may be used as the mask layer. Next, a photoresist pattern exposing a predetermined region of the mask layer is formed on the mask layer. Subsequently, the mask pattern is formed by patterning the exposed mask layer using the photoresist pattern as an etching method using an inductively coupled plasma apparatus including a cathode electrode, an inductively coupled plasma coil, and a chamber to which a first RF power is applied. In this case, in the etching method using the inductively coupled plasma apparatus, when the mask pattern is used as the chromium layer, chlorine gas, oxygen gas, or the like is used as the reaction gas. In addition, the etching method using the inductively coupled plasma apparatus is performed under a chlorine gas flow rate condition of 10 sccm to 50 sccm and an oxygen gas flow rate condition of 10 sccm to 50 sccm. In addition, the dry etching method using the inductively coupled plasma apparatus includes a pressure condition of 3 mTorr to 30 mTorr maintained in the chamber, a first RF power condition of 10 W to 100 W applied to the cathode electrode, and 100 W applied to the inductively coupled plasma coil. To a second RF power condition of 1500 W or the like.

According to the present invention, it is possible to prevent damage to a material layer such as a mask pattern to be formed and an optical waveguide layer thereunder, and to realize a more precise mask pattern with anisotropic etching characteristics. In addition, since the etching rate of the mask layer can be further increased, efficient optical waveguide fabrication can be realized.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 to 7 are cross-sectional views illustrating an etching mask forming method used for fabricating an optical waveguide according to an embodiment of the present invention.

FIG. 8 is a diagram schematically illustrating an inductively coupled plasma apparatus used in an embodiment of the present invention.

3 illustrates a step of forming the optical waveguide layer 300 and the mask layer 500 on the substrate 100.

Specifically, the optical waveguide layer 300 is formed on the flat substrate 100 made of silicon (Si) or glass. In this case, a cladding layer 200 is first formed as a lower layer of the optical waveguide layer 300. In this case, the optical waveguide layer 300 is formed of a material having a larger refractive index than the cladding layer 200. For example, when forming a silica optical waveguide, a material layer whose main component is silicon oxide (SiO ₂ ), that is, an implementation layer is used as the optical waveguide layer 300. At this time, another element, such as germanium (Ge), is added to the silica layer to make the refractive index higher than that of the cladding layer. Hereinafter, in the present embodiment, a case of forming the silica optical waveguide is described by way of example, but the present invention is not limited only to the case of forming the silica optical waveguide.

Thereafter, a mask layer 500 is formed on the optical waveguide layer 300. The material of the mask layer 500 may vary depending on the material of the material layer used as the optical waveguide layer 300. For example, a metal layer such as a chromium (Cr) layer, an oxide layer such as a polymer layer, a silicon oxide layer, or the like, a semiconductor layer such as a silicon nitride (Si ₃ N ₄ ) layer, or an amorphous silicon layer, etc. Dielectric layer or the like is used. In the case of forming the silica optical waveguide, the metal layer, the dielectric layer, and the like are used as the mask layer 500. Preferably, a chromium (Cr) layer is used.

When using the said chromium layer as the mask layer 500, it forms using a sputtering system. In this case, the thickness of the mask layer 500 is set in consideration of the thickness of the lower optical waveguide layer 300. For example, in the case of introducing the optical waveguide layer 300 having a thickness of about 8 μm, in order to etch with an etching selectivity of about 10: 1, it should have a thickness of about 8000 μs. Therefore, it forms in about 8000 mm thickness. However, the thickness of the mask layer 500 is differently formed according to the material, thickness of the optical waveguide layer 300 under the mask layer 500, and conditions for etching the optical waveguide layer 300. .

4 illustrates a step of forming the photoresist layer 400 on the mask layer 500.

For example, the photoresist layer 400 is formed on the mask layer 500 by using a positive photoresist material by spin coating. In this case, the thickness of the photoresist layer 400 is determined in consideration of the material, the thickness of the mask layer 500 and the etching conditions of the mask layer 500. That is, the thickness of the photoresist layer 400 is set so that approximately 8000 kPa, which is the thickness of the mask layer 500 described above, is sufficiently etched and removed. For example, it is formed in the thickness of about 1,4 micrometers.

FIG. 5 illustrates exposing the photoresist layer 400 using a photo mask 600.

In detail, the photomask 600 is introduced on the photoresist layer 400 to expose the photoresist layer 400. In this case, since the positive photoresist layer 400 is used in the present embodiment, the positive field photomask 600 is used. That is, a photomask 600 designed to irradiate light to a portion to be removed from the photoresist layer 400 is used. In this case, light having a different wavelength is used according to the type of photoresist material to be used. In the present embodiment, the photoresist layer 400 is exposed using UV (Ultra Violet) light.

6 illustrates forming a photoresist pattern 450.

Specifically, the exposed photoresist layer 400 is developed to form a photoresist pattern 450. In this case, the exposed portion of the photoresist layer 400 is removed in the developing step. Accordingly, the formed photoresist pattern 450 exposes a part of the surface of the mask layer 500.

7 illustrates forming a mask pattern 550.

Specifically, the substrate 100 on which the photoresist pattern 450 is formed is introduced into the cathode electrode 700 of the inductively coupled plasma (ICP) device shown schematically in FIG. 8. . The ICP device may include a chamber (not shown), a cathode electrode 700 to which the first RF power generated by the RF power generator 800 is applied, and an ICP coil to which the second RF power 950 is applied. And 900). The apparatus further includes an upper electrode 750 introduced opposite to the cathode electrode 700 and applied with a DC bias voltage. The overall configuration is similar to a conventional RIE apparatus, but is characterized by the introduction of the ICP coil 900.

The second RF power 950 is applied to the ICP coil 900 to deform the movement of electrons e ⁻ in the plasma formed by exciting the reaction gas. That is, by the ICP coil 900, the electrons in the plasma perform a spiral motion as well as a linear motion. Thus, the probability of collision between the electrons and atoms of the reactant gas or the electrons and ions in the plasma is increased. The effect of increasing the concentration of plasma generated thereby is expressed. Accordingly, the exposed portion of the mask layer 500 on the substrate 100 is etched at a higher speed by the higher concentration of plasma.

When etching the exposed mask layer 400 using the above-described ICP device, the etching step is performed using the following etching conditions. That is, the etching conditions are set in consideration of the material of the mask layer 400 to be etched and the etching conditions of the photoresist pattern 450. For example, in the case of using the mask layer 400 formed of a chromium layer, chlorine gas (Cl ₂ ) and oxygen gas (O ₂ ) are used as the reaction gas for forming the plasma. In addition, the reaction gas is supplied to the chamber under a chlorine gas flow rate condition of approximately 10 sccm (Standard Cubic CentiMeter) to 50 sccm and an oxygen gas flow rate condition of 10 sccm to 50 sccm. At this time, the chamber is maintained at a pressure of approximately 3mTorr to 30mTorr. In addition, the first RF power applied to the cathode electrode 700 is about 10W to about 100W, and the second RF power 950 applied to the ICP coil 900 is about 100W to about 1500W.

By using such an etching condition, an exposed portion of the mask layer 500 formed on the substrate 100 applied to the ICP device is etched using the photoresist pattern 450 as an etching mask. As such, the exposed portion of the mask layer 500 is removed to form the mask pattern 550. At this time, the etching method using the ICP device, it is possible to implement an increase in the etching speed compared to the etching method using a conventional RIE device. Accordingly, the mask pattern 550 having a thicker thickness can be formed as compared to the conventional method, for example, the lift-off method. Accordingly, the optical waveguide layer 300 having a thicker thickness can be introduced. That is, the thickness limit of the optical waveguide layer 300 may be further increased by limiting the thickness of the mask pattern 550 consumed when etching the optical waveguide layer 300. Therefore, it is possible to implement easier height adjustment in the optical waveguide formed by etching the optical waveguide layer 300 later. Therefore, it is possible to implement an easier optical waveguide.

In addition, since the etching rate of the higher mask layer 500 can be realized, a thicker mask pattern 550 can be easily implemented without applying a high first RF power to the cathode electrode 700. Therefore, the occurrence of an abnormal increase in the DC bias voltage to the upper electrode 750 due to the application of high RF power as in the etching method using a conventional RIE device is prevented. Accordingly, invasion of the optical waveguide layer 300 and the mask pattern 550 formed by the etching process may be prevented. In addition, the etching method using the ICP device may implement anisotropic etching as a kind of dry etching method. Therefore, the mask pattern 550 having a more precise size and shape can be implemented.

As mentioned above, although this invention was demonstrated in detail through the specific Example, this invention is not limited to this, It is clear that the deformation | transformation and improvement are possible by the person of ordinary skill in the art within the technical idea of this invention.

According to the present invention described above, a mask pattern having a thick thickness, that is, an etching mask may be implemented at a faster etching speed. Therefore, more effectively, it is possible to introduce an optical waveguide layer having a thicker thickness, it is possible to more easily implement the height control of the optical waveguide to be formed later. This makes it easier to manufacture the optical waveguide. In addition, the anisotropic etching can be implemented to implement an etching mask of a more precise size and shape. Therefore, in the manufacture of the optical waveguide, it is possible to realize an improvement in productivity.

Claims (8)

Forming an optical waveguide layer on the substrate; Forming a mask layer on the optical waveguide layer; Forming a photoresist pattern exposing the mask layer on the mask layer; And The exposed mask layer using the photoresist pattern as a mask Forming a mask pattern by patterning by an etching method using an inductively coupled plasma apparatus including a cathode electrode, an inductively coupled plasma coil, and a chamber to which the first RF power is applied, to form an etch mask for manufacturing an optical waveguide Forming method. The method of claim 1, wherein the optical waveguide layer is a silica layer. The method of claim 1, wherein the mask layer is any one selected from the group consisting of a metal layer and a dielectric layer. The method of claim 3, wherein the metal layer is a chromium layer. The method of claim 3, wherein the dielectric layer is an amorphous silicon layer. The method of claim 1, wherein the etching method using the inductively coupled plasma device An etching mask forming method used for fabricating an optical waveguide, wherein chlorine gas and oxygen gas are used as reaction gases. The method of claim 6, wherein the reaction gas And an chlorine gas flow rate condition of 10 to 50 sccm and an oxygen gas flow rate condition of 10 sccm to 50 sccm. The dry etching method of claim 1, wherein the dry etching method uses the inductively coupled plasma apparatus. 3mTorr to 30mTorr pressure conditions maintained in the chamber, the first RF power conditions of 10W to 100W applied to the cathode electrode and the second RF power conditions of 100W to 1500W applied to the inductively coupled plasma coil An etching mask forming method used to fabricate waveguides.

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