KR20050083051A - Qualified optical waveguide manufacturing method - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the formation of optical waveguides for optical passive devices used in optical communication. It is an object of the present invention to provide an optical waveguide device having a low propagation loss and optical damage, and a method of manufacturing the same.

According to the present invention, a lower layer clad is formed on a silicon or quartz substrate, and a silicon nitride film thinner than a wavelength used in optical communication is laminated. The nitride film serves as an end point detector and an external impurity blocking function in an etching condition. do. In addition, the silicon nitride film of the same thickness is formed even after the core layer is formed on the lower cladding to completely cover the core layer, which is an optical waveguide, with a nitride film.The optical waveguide layer is completely blocked from the outside, so the refractive index does not change under any conditions, so that the propagation loss And photodamage ensures the same reliability as the initial stage. In order to prevent the formation of voids at the branch of the optical waveguide, when the silica glass (BSG) containing boron (B) having good flowability is laminated after the optical waveguide is formed, the voids are formed. (Void) disappears, and the source can be sealed off from moisture and external impurities present in the voids.

As such, the optical waveguide was completely blocked from the outside to form an optical waveguide in which the light was confined in the waveguide, and the process design was made to remove impurities present in the pores by eliminating pores between core and clad.

Description

Reliability improved optical waveguide manufacturing method {QUALIFIED OPTICAL WAVEGUIDE MANUFACTURING METHOD}

The present invention describes a method of making an optical passive device using a silicon (Si) substrate or a quartz (Quartz) substrate, and relates to a method of manufacturing an optical waveguide so that reliability is improved rather than an existing optical waveguide. Since the optical waveguide formed on the existing silicon or quartz substrate forms a core layer immediately after laminating a thick clad layer, impurities of the clad layer are deposited outside the core by a high temperature process of 900 ° C. or higher after deposition. Out of diffusion, it was difficult to control the exact refractive index.

Furthermore, even after the upper clad layer is formed, a void occurs between the core portion and the upper clad at the optical waveguide branching point [FIG. 7], and external impurities or moisture are gathered in the void, and this impurity is generated. Are penetrating the core, causing a big problem in the reliability of the optical waveguide. Ion penetration or moisture penetration destroys the difference in refractive index between the core and the clad formed by the product design, resulting in increased light loss and impaired optical properties. The reason for such voids is that when the aspect ratio is larger than the width of the waveguide, the over clad material, which is a subsequent process, cannot fill the voids, and when the aspect ratio is low, it is difficult to fill the voids. Is not.

In addition, since the silicon nitride layer 23 does not exist under the core 31, the core is excessively etched so that CD (Critical Dimension) control of the core is very difficult, as shown in FIG. 4A. Compared with the high aspect ratio, it is almost impossible to fill voids by the over clad process.

In general, the reliability evaluation is conducted at 85 ° C / 90 ° C RH (humidity ratio) or higher. Usually, if the time is 100 hours or more, the refractive index of the core increases and the difference between the core and the cladding becomes larger. Coa is usually pentavalent Ge, P (Phosphorous) material is used to control the refractive index because it combines with the OH group by water to increase the refractive index.

The present invention blocks the penetration of external impurities by covering the optical waveguide layer much thinner than the optical wavelength by using a nitride film having a very high refractive index. The purpose is to use it as an end point detector when etching the core with this nitride film. After the formation of the optical waveguide core, a highly flowable oxide film (BSG: Boro Silica Glass, or BPSG: Boro Phospho Silica Glass) is deposited to perfect voids at the optical waveguide branch point (FIG. 7). This is to prevent impurity or moisture existing in the void by filling it.

In general, an optical waveguide formed on a Si substrate or a quartz substrate includes a lower clad 22 that guides light to a base layer as shown in FIG. 1, an optical waveguide layer (core) 31 through which light passes, and left and right upper layers. The upper cladding layer 61 has the same refractive index as the lower cladding. The configuration of the present invention is as follows.

As shown in FIG. 2, a lower clad 22 is formed on the silicon substrate 21, and a silicon nitride film 23 or an oxide nitride layer is laminated thereon. Nitride or Oxynitride is preferably laminated by PECVD (Plasma Enhanced Vapor Deposition) method, but better, LPCVD (Low Pressure CVD) method is more advantageous for thin film characteristics. The lower layer cladding process is performed in the same manner as the existing method, the thickness is also the same. On the other hand, since the thickness of nitride or oxynitride must block external impurities, it is preferable to adjust the thickness of the nitride or oxynitride to 5000 Å or less in order not to affect the light passing through the optical waveguide at about 100 이상 or more.

In addition, Nitride or Oxynitride prevents impurities inside the core from out-diffusion into the lower layer of the clad during the core process, and recognizes the end point of equipment when etching the core. end point detector).

3 is a process of forming a core layer on a silicon nitride film (Nitride) or an oxynitride (23), the method of laminating the core layer is the same as the existing one, but after forming the thin film 900 ℃ or more more preferably 30 ℃ It is preferable to perform high temperature heat treatment for more than one minute. The high temperature heat treatment removes hydrogen and OH￣ in the thin film and makes the thin film more dense, so that the film quality hardly changes after the film's reliability test (80 ℃, 90% humidity ratio, cycle and shocking test). have.

4A is a photo and etching process, but proceeds in the same manner as the conventional method, but since the silicon nitride layer (Nitride) 23 exists under the core layer 31 in the etching process, it is necessary to excessively etch the core unlike the existing method. There is no. This is because Nitride is the end point of the etching point, the Nitride material is recognized by the equipment at the time of etching, and when the Nitride material appears, the etching is stopped to make CD (critical dimension) control of the core layer 31 very easy. This can produce a more accurate core width than existing methods.

Figure 4b prevents excessive etching by the silicon nitride film (Nitride), which is the end point of etching, and if there is no Nitride, it must be excessively etched so that the voids at the core branch point are deeper than the core width. It will occur greatly.

FIG. 5 is a step of laminating a second nitride layer 51 or oxide nitride after a photographic and etching process. Through this process, the optical waveguide is safely surrounded by the nitride film. At this time, the nitride film 231 is preferably laminated to the same thickness as the nitride film 23 formed in the core lower layer. PECVD is also preferred, but more preferably, LPCVD is more advantageous.

6 is divided into two types of upper clad layers 61 and 62 and a final passivation layer 63. The upper cladding 1 (61), which is the first upper cladding, removes voids at the branching point of the optical waveguide and also has a low temperature (800 ° C) to fill the gap between the cores because the height of the core layer is several μm or more. It is preferable to use BSG (Boro Silica Glass: boron added silicon oxide film) or BPSG (Boro Phospho Silica Glass: boron and phosphorous added silicon oxide) material having good flow rate. The boron-doped silicon oxide film is composed of B2O3 and SiO2, and the higher the B2O3 composition ratio, the lower the refractive index and the better flowability. However, when the weight ratio is more than 10 Weight% (weight ratio), crystals are formed in the thin film. Can't get it. In addition, the silicon oxide film containing phosphorus (Phosphorous) is composed of P 2 O 5 and SiO 2, and the higher the composition ratio of P 2 O 5, the better the flowability but the larger the refractive index, as opposed to boron. Phosphorous also has a certain limiting capacity like boron, and if it exceeds 10 weight%, crystals form in the thin film, and thus the desired thin film cannot be obtained. Therefore, the BSG thin film or BPSG thin film which has a lower refractive index than the core and can fill the gap at the optical branch point [Fig. 7] is used in the layer above the optical waveguide core, but the B (boron) impurity is a regulator that lowers the refractive index. P (phosphorus) impurity is intended to be used as a regulator to increase the refractive index. When the thin film is BSG, the amount of B used is not more than 10 weight%, the most preferred amount is 3 to 5 weight% is most preferred. Also in the case of the BPSG thin film, the amount of two impurities of B or P does not exceed 10wt%, and the most preferable amount is most preferably 3 to 5wt%. The thickness of the thin film is suitably 5 µm to 1 µm, and the preferred thickness is less than 1 µm because the thickness is thinner than the light wavelength, so that the effect of the thickness can be almost neglected. If the voids (gaps and gaps) at the optical waveguide branch point can be sufficiently filled, the lower the thickness, the more preferable. After laminating the BSG or the BPSG, a stable thin film can be obtained by performing a high temperature treatment for 30 minutes or more between 850 ° C and 1000 ° C. In the subsequent cladding process 2 (62), a silicon oxide film (USG) having a uniform refractive index distribution and a lower refractive index than core is one of the most preferable materials. This material is preferably deposited by PECVD or APCVD (Atmospheric pressure CVD) and then treated at a high temperature of 900 ° C. or higher to obtain a stable film having a nearly constant refractive index distribution.

Finally, the final passivation layer 63 is laminated with a thickness of 0.1 μm to 1 μm or less, which is also most preferably a nitride material. This material can also be laminated by PE-CVD, and most preferably by LPCVD. The reason is that the nitride film (Nitrid) laminated by LPCVD method rather than PE-CVD has less hydrogen content and can more effectively block hydrogen penetration into the lower layer.

In another embodiment, the light passing through the waveguide after the etching process of FIG. 4A is thinly coated with a material having a significantly lower refractive index than the core layer in order to cause total reflection from the clad layer (thickness: 100 μm to 1 μm, and the refractive index is 10 Material (lower than% core) is coated with a nitride film (Nitride) which is the best material with a high refractive index and a protective film as shown in FIG. When BSG (Boro Silica Glass) material having a lower refractive index than the core layer is laminated around the core and subjected to a high temperature process (above 900 ° C.), a hill-shaped core can be obtained, and a more effective optical waveguide can be obtained. 10

FIG. 8 is a BSG material 311 which is laminated with a BSG on the nitride 23 and then a core material 31 having a large refractive index, and then subjected to a photolithography process as shown in FIG. The process of laminating and then laminating Nitride is shown. Process techniques and methods use the same techniques and methods as in [Configuration of Invention]. However, the refractive index structure inside the core has a refractive index of 0.3% to 01% greater than that of the material of (31).

The core layer is covered with a nitride film or an oxynitride film in the same manner as above, and the voids at the branching point of the optical waveguide are removed by using a BSG or BPSG thin film having good flowability, thereby allowing the core layer to enter the core layer from the outside. Since impurity penetration can be blocked, the refractive index change can be reduced, thereby ensuring the reliability of the optical waveguide. In addition, Nitride can be applied as an end point detector for etching core layers, which are optical waveguides, to ensure more stable core width (CD) and more stable etching process. You can do it.

1 is a cross-sectional structural diagram of a typical optical waveguide

 21: silicon substrate

 (22): under clad: role of guiding light

 (31): core

 (61): over clad

Figure 2 lower layer clad and core protective film forming process

 (23): silicon nitride film (Nitride or Oxynitride)

[Figure 3] Core formation process

(31): core: optical waveguide through which light passes

[Fig 4a] Cross section after photo and etching process

(41): PR (Photo Resist)

4b is a cross-sectional view after a conventional etching process;

(42): part to be etched

Fig. 5 Core protective film forming process (nitride lamination)

(51): Nitride

[Figure 6] Upper clad and final protective film forming process

(61): upper cladding 1: good BSG material at low temperature

(62): upper cladding 2: USG (Undoped Silica Glass)

(63): final shield (nitride)

Figure 7 1x2 Y-Branch

(71): optical waveguide branch point

8 is a core process proceeds to 2 steps after the lower clad formation in another embodiment

(311): BSG (Boro Silica Glass)

9 is a cross-sectional view after a photo-etching process and a core forming process 1 according to another embodiment

Fig. 10 Core forming process of another embodiment 2

11 is a final cross-sectional view of another embodiment.

Claims (7)

 1 and 6, the thickness and temperature process of using the BSG or BPSG to fill the air gap at the branch of the optical waveguide sufficiently even at low temperature (800 ° C) as the upper cladding 1 (61) material. Optical passive device having a structure comprising a.  [2] and [4b] silicon nitride film or oxytride material to block out diffusion of impurities and moisture and external impurity penetration that control the refractive index of the lower clad layer on the lower clad layer. And a photo passive device which applies this material as an end point detector for an etching process. As shown in FIG. 5, after the core forming process (after the core layer is etched), a silicon nitride layer (Nitride) is used as a core protective layer to prevent external diffusion of impurities, which are the refractive index regulators of the core, and penetration of moisture and external impurities into the core (waveguide). And a passive optical device using Oxyntride and laminating it by PECVD or LPCVD method. In FIG. 6, an optical passive device constituting USG (Undoped Silica Glass) by using a method of PECVD or APCVD with a BSG or BPSG material having good flowability in a clad 1 layer and a second clad layer.  In Figure 6, in addition to the cladding 1 layer and the cladding 2 layer, a cladding layer forming process and structure composed of multiple layers to completely fill the voids of the optical waveguide branch point [Fig. 7].  6 is an optical passive device using Nitrid as the final protective film to block external impurity penetration into the clad layer. 7. After the process as shown in [Fig. 8], [9], [Fig. 10] and finally having the structure as shown in [Fig. 11], after forming the core, the total reflection condition in the optical waveguide using BSG or BPSG material is formed. Optical passive device having a satisfying process and structure.