CN110456451A - A kind of preparation method of area thick film silicon nitride - Google Patents

Abstract

The invention provides a method for preparing regional thick-film silicon nitride, comprising: sequentially forming a lower cladding layer and a sacrificial layer on a semiconductor substrate, and the height of the sacrificial layer is the same as the thickness of the preset waveguide device region; the upper surface of the lower cladding layer is The termination layer forms a plurality of core layer area grooves; depositing core layer materials in the plurality of core layer area grooves and on the sacrificial layer to form the first core layer, the thickness of which is less than the thickness of the preset waveguide device area; the upper surface of the sacrificial layer is used as the termination layer , remove the redundant first core layer; repeat the above steps until the thickness of the formed core layer reaches the thickness of the preset waveguide device area; remove the sacrificial layer from the upper surface of the lower cladding layer as the termination layer to form a plurality of core layer areas, and engrave them Etching to form a preset waveguide device structure; forming an upper cladding layer on the preset waveguide device structure and the lower cladding layer. This solution solves the problem of high stress caused by too thick film, which is beneficial to realize the high integration of chips, and at the same time solves the problem that direct trenching is not conducive to the preparation of highly integrated waveguide devices.

Description

A kind of preparation method of area thick film silicon nitride

technical field

The invention relates to the technical field of integrated optics, in particular to a preparation method of regional thick-film silicon nitride.

Background technique

At present, the silicon nitride film growth and preparation methods mainly include LPCVD (low pressure chemical vapor deposition) and PECVD (plasma chemical vapor deposition). Thick film deposition can be achieved by using PECVD, but there are many impurities in the film and the compactness is poor, so the waveguide prepared by it has high transmission loss. However, the silicon nitride film deposited by LPCVD has good quality and low waveguide loss, but there is a problem of high stress, especially when the film thickness is greater than 300 nanometers, it is difficult to achieve large-area growth, and a large number of cracks will appear in the film, which cannot realize high-performance devices. preparation. In the existing production process, a dry etching process is usually used to open a groove in the silicon dioxide cladding layer, and then fill the groove with silicon nitride to obtain a thick-film silicon nitride optical waveguide, but in the preparation of highly integrated nitrogen When siliconizing devices and chips, a lot of unequal width and high-density silicon dioxide grooves are required, which will cause unevenness of CMP and increase the difficulty of design and process. Problems such as poor straightness and high roughness.

Contents of the invention

In order to overcome the technical problems of high stress in silicon nitride deposited thick films in the prior art, as well as many process difficulties caused by trenching, a method for preparing regional thick film silicon nitride is provided to meet different design needs .

The invention provides a method for preparing a regional thick-film silicon nitride, comprising:

S1, sequentially forming a lower cladding layer and a sacrificial layer on the semiconductor substrate along the thickness direction of the semiconductor substrate, and the height of the sacrificial layer is the same as the thickness of the predetermined waveguide device region;

S2. The upper surface of the lower cladding layer is used as a termination layer, and the sacrificial layer is photolithographically etched to form a plurality of core region grooves in the sacrificial layer;

S3. Depositing core material in grooves in multiple core regions and on the sacrificial layer to form a first core layer, the thickness of the first core layer is smaller than the thickness of the preset waveguide device region;

S4, using the upper surface of the sacrificial layer as the termination layer, and removing the redundant first core layer by using a surface planarization process;

S5, repeating S3 and S4 until the thickness of the core layers formed in the grooves of the multiple core layer regions reaches the thickness of the preset waveguide device region;

S6. The upper surface of the lower cladding layer is used as a termination layer, and the sacrificial layer is removed to form a plurality of core layer regions;

S7. Etching a plurality of core layer regions respectively, forming a preset waveguide device structure in each core layer region;

S8, forming an upper cladding layer on the predetermined waveguide device structure and the lower cladding layer.

Further, the material of the lower cladding layer is a solid cladding material with a refractive index lower than 1.7 and higher than 1.

Further, the solid cladding material is silicon dioxide.

Further, the lower cladding layer is prepared by thermal oxidation and/or chemical vapor deposition.

Further, the sacrificial layer is formed by depositing amorphous silicon or polysilicon.

Further, the preset thickness of the waveguide device region is 350 nm to 1000 nm.

Further, the material of the core layer is any one of silicon nitride or silicon oxynitride.

Further, the thickness of the first core layer is 50 nm to 300 nm.

Further, when etching the multiple core layer regions, a dry etching process is used.

Further, in step S8, a solid cladding material with a refractive index lower than 1.7 and higher than 1 is deposited on the upper cladding layer using a chemical vapor deposition process.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention forms a plurality of waveguide device regions by forming a plurality of core region grooves in the sacrificial layer, and then deposits the core layer material layer by layer to reach the thickness of the preset waveguide device region, which can solve the problem of using the prior art deposition method. The problem of high stress caused by too thick film; in addition, using the sacrificial layer as the isolation area, the multiple core layer regions formed are respectively etched, and a variety of preset waveguide device structures are formed in each core layer region, which is beneficial to Realize the high integration of the chip; in addition, the present invention also prepares the sacrificial layer by depositing, the thickness of the sacrificial layer is easy to adjust, and the thickness of the preset waveguide device area that is finally required is determined by controlling the thickness of the sacrificial layer, thereby realizing the preset waveguide The control of the thickness of the device structure meets different design needs, and is more convenient and flexible; the final waveguide device structure is formed by removing the sacrificial layer and etching the core layer region. Compared with the silicon nitride grown directly in the prior art, It can realize thicker film growth on a large wafer, and at the same time solve the problem that direct trenching is not conducive to the preparation of highly integrated waveguide devices.

Description of drawings

1 is a schematic flow chart of a method for preparing a regional thick-film silicon nitride according to an embodiment of the present invention;

Fig. 2 (1) to Fig. 2 (7) are schematic cross-sectional structural diagrams corresponding to the manufacturing process of a method for preparing a regional thick-film silicon nitride provided by an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

A method for preparing a regional thick-film silicon nitride in this embodiment, as shown in FIG. 1 , includes:

S1, sequentially forming a lower cladding layer and a sacrificial layer on the semiconductor substrate along the thickness direction of the semiconductor substrate, and the height of the sacrificial layer is the same as the thickness of the predetermined waveguide device region;

On the basis of the above solutions, further, the semiconductor substrate in this implementation manner is a silicon substrate, and in other implementation manners, the semiconductor substrate may also be a quartz substrate.

On the basis of the above solution, further, the lower cladding layer is formed by thermal oxidation and/or chemical vapor deposition process, and in other embodiments, the lower cladding layer can also be formed by physical vapor deposition process. The lower cladding material includes a solid cladding material with a refractive index lower than 1.7 and higher than 1, preferably silicon dioxide.

On the basis of the above solutions, further, the sacrificial layer is formed by depositing amorphous silicon or polysilicon.

On the basis of the above scheme, further, the thickness of the preset waveguide device area is the same as 350 nanometers to 1000 nanometers, and since the height of the sacrificial layer is the same as the thickness of the preset waveguide device region, the height of the sacrificial layer is 350 nanometers to 1000 nanometers .

S2. The upper surface of the lower cladding layer is used as a termination layer, and the sacrificial layer is photolithographically etched to form a plurality of core region grooves in the sacrificial layer;

S3. Depositing core material in grooves in multiple core regions and on the sacrificial layer to form a first core layer, the thickness of the first core layer is smaller than the thickness of the preset waveguide device region;

In some embodiments, by any of a variety of deposition techniques, including low pressure chemical vapor deposition (LPCVD), atmospheric pressure chemical vapor deposition (APCVD), plasma enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD) , sputtering and other suitable deposition techniques to form the first core layer.

On the basis of the above solution, further, the material of the core layer includes silicon nitride. In other embodiments, the material of the core layer may also be silicon oxynitride.

Further on the basis of the above solution, the thickness of the first core layer is 50 nm to 300 nm.

S4, using the upper surface of the sacrificial layer as the termination layer, and removing the redundant first core layer by using a surface planarization process;

On the basis of the above solution, further, the surface planarization process specifically adopts chemical mechanical polishing (CMP).

S5, repeating S3 and S4 until the thickness of the core layers formed in the grooves of the multiple core layer regions reaches the thickness of the preset waveguide device region;

Continue to deposit core layer materials in the grooves of multiple core layer areas and on the sacrificial layer to form a second core layer. The upper surface of the sacrificial layer is used as the termination layer, and the redundant second core layer is removed by surface planarization process, and the core layer area When the total thickness of the first core layer and the second core layer in the groove is less than or equal to the thickness of the preset waveguide device region, continue to repeat S3 and S4 until the thickness of the core layer formed in the groove in the core region reaches the preset waveguide device region up to the thickness;

S6. The upper surface of the lower cladding layer is used as a termination layer, and the sacrificial layer is removed to form a plurality of core layer regions;

S7. Etching a plurality of core layer regions respectively, forming a preset waveguide device structure in each core layer region;

On the basis of the above solution, further, when etching the multiple core layer regions, a dry etching process is adopted.

S8, forming an upper cladding layer on the predetermined waveguide device structure and the lower cladding layer.

On the basis of the above solution, further, the upper cladding layer in this step is formed by depositing a solid cladding material with a refractive index lower than 1.7 and higher than 1 by a chemical vapor deposition process.

On the basis of the above embodiments, the material of the upper cladding layer is selected in the same way as the material of the lower cladding layer, and may be silicon dioxide. In some embodiments, other solid cladding materials with refractive indices below 1.7 and above 1 may also be used.

The technical solution of the application is described in detail below through examples.

S1, sequentially forming a lower cladding layer and a sacrificial layer on the semiconductor substrate along the thickness direction of the semiconductor substrate, and the height of the sacrificial layer is the same as the thickness of the predetermined waveguide device region;

As shown in FIG. 2 (1), those skilled in the art can deposit and form the lower cladding layer 201 by thermal oxidation and/or chemical vapor deposition process, wherein the material of the lower cladding layer 201 can be a material with a refractive index lower than 1.7 and higher than 1. Solid cladding material, the material used in the lower cladding layer 201 in this embodiment is preferably silicon dioxide; the sacrificial layer 202 adopts a deposition process, such as low pressure chemical vapor deposition (LPCVD), atmospheric pressure chemical vapor deposition (APCVD), plasma Enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), sputtering and other suitable deposition techniques to form. The material used for the sacrificial layer 202 is preferably amorphous silicon; the material used for the semiconductor substrate 200 may be a silicon substrate or a quartz substrate, and the material used for the semiconductor substrate 200 in this embodiment is preferably a silicon substrate.

Wherein, the predetermined thickness of the waveguide device region is 350 nanometers to 1000 nanometers. Specifically, the thickness of the preset waveguide device region can be set according to specific needs, preferably 400 nm to 900 nm, and most preferably 500 nm to 700 nm. For example, it can be any one of 350 nanometers, 400 nanometers, 500 nanometers, 700 nanometers, 900 nanometers or 1000 nanometers. In this embodiment, the thickness of the preset waveguide device region is preferably 400 nanometers. The thickness of the waveguide device area is assumed to be the same, so the height of the sacrificial layer 202 is 400 nanometers.

S2. The upper surface of the lower cladding layer is used as a termination layer, and the sacrificial layer is photolithographically etched to form a plurality of core region grooves in the sacrificial layer;

As shown in Figure 2 (2), the details of photolithography and etching of the sacrificial layer 202 are as follows: on the sacrificial layer 202, the process of coating photoresist, exposure, development, etching, and dry stripping is performed sequentially to form grooves in the core layer region 203. The etching method for forming the groove 203 in the core layer region may specifically be dry etching. A plurality of core region grooves 203 are formed in the sacrificial layer 202 .

S3. Depositing core material in grooves in multiple core regions and on the sacrificial layer to form a first core layer, the thickness of the first core layer is smaller than the thickness of the preset waveguide device region;

As shown in FIG. 2 (3), core material is deposited in multiple core area grooves 203 and on the sacrificial layer 202. The core material includes silicon nitride or silicon oxynitride. In this embodiment, silicon nitride is preferably used as Core layer material, a part of the core layer material is deposited in the core region groove 203, and a part is deposited on the sacrificial layer 202, and the low pressure chemical vapor deposition (LPCVD) process is used to fill the core layer region groove 203 with silicon nitride to form the first core Layer 204, wherein the first core layer 204 formed may have a thickness of 50 nm to 300 nm, preferably the first core layer 204 has a thickness of 80 to 200 nm, and most preferably the first core layer 204 has a thickness of 100 to 150 nm. In this embodiment The thickness of the first core layer 204 is 100 nanometers, which is 400 nanometers less than the thickness of the predetermined waveguide device region.

S4, using the upper surface of the sacrificial layer as the termination layer, and removing the redundant first core layer by using a surface planarization process;

As shown in FIG. 2 ( 4 ), the excess silicon nitride on the sacrificial layer 202 is removed through surface planarization process, such as forming the final first core layer 204 in the core region groove 203 . In this embodiment, the surface planarization process is specifically a chemical mechanical polishing method (CMP) for grinding.

S5, repeating S3 and S4 until the thickness of the core layers formed in the grooves of the multiple core layer regions reaches the thickness of the preset waveguide device region;

As shown in Figure 2 (5), silicon nitride is deposited in the groove 203 in the core layer area by low-pressure chemical vapor deposition (LPCVD) for many times, and excess silicon nitride is removed by chemical mechanical polishing (CMP) until finally The thickness of the core layer 205 reaches 400 nanometers of the predetermined waveguide device region.

S6. The upper surface of the lower cladding layer is used as a termination layer, and the sacrificial layer is removed to form a plurality of core layer regions;

As shown in FIG. 2 ( 6 ), the excess sacrificial layer 202 is removed by wet etching to form a plurality of core layer regions 206 .

Wherein, the process steps of the wet etching are as follows: the wet etching solution is determined according to the ratio of the amorphous silicon in the sacrificial layer 202 to the silicon dioxide in the lower cladding layer 201 . Specifically, a dilute tetramethylammonium hydroxide (TMAH) solution is used for wet etching. The etching rate of the selected wet etching solution to amorphous silicon is greater than that of silicon dioxide and silicon nitride, so that while removing the remaining sacrificial layer 202, no or only a small amount of core Layer 205.

S7. Etching a plurality of core layer regions respectively, forming a preset waveguide device structure in each core layer region;

As shown in FIG. 2 ( 6 ) and FIG. 2 ( 7 ), dry etching is performed on multiple core layer regions 206 to form multiple preset waveguide device structures 207 .

S8, forming an upper cladding layer on the predetermined waveguide device structure and the lower cladding layer.

As shown in Figure 2 (7), finally, a solid cladding material with a refractive index lower than 1.7 and higher than 1 is deposited on the formed preset waveguide device structure 207 to form an upper cladding layer. In this embodiment, silicon dioxide is specifically used , the upper cladding layer is formed by depositing silicon dioxide on the predetermined waveguide device structure 207, and together with the lower cladding layer 201 to form the cladding layer structure 208, the deposition process conditions of the upper cladding layer are the same as the deposition method of the lower cladding layer 201, here No longer.

The above is a preparation method of regional thick-film silicon nitride provided by the embodiment of the present application. This scheme proposes a novel region-dividing method, which solves the problem of high stress caused by too thick a film, and is beneficial to realize high integration of chips. It can realize thicker film growth on a large wafer, and at the same time solve the problem that direct trenching is not conducive to the preparation of highly integrated waveguide devices.

The above embodiments are only descriptions of preferred implementations of the present invention, and are not intended to limit the concept and scope of the present invention. Under the premise of not departing from the design concept of the present invention, various modifications and improvements made by ordinary persons in the art to the technical solution of the present invention shall fall within the scope of protection of the present invention, and the technical content claimed in the present invention has been fully described in the claims.

Claims (10)

1. a kind of preparation method of region thick film silicon nitride characterized by comprising

S1, along the thickness direction of the semiconductor substrate under-clad layer and sacrificial layer are sequentially formed on a semiconductor substrate, it is described sacrificial The height of domestic animal layer is identical as the thickness in default waveguide device region；

S2, using the upper surface of the under-clad layer as stop layer, photoetching and etch the sacrificial layer, formed in the sacrificial layer more A core region slot；

S3, deposition of core layer material in multiple core region slots and on the sacrificial layer, the first sandwich layer of formation, described first The thickness of sandwich layer is less than the thickness in the default waveguide device region；

S4, using the upper surface of the sacrificial layer as stop layer, extra first sandwich layer is removed using surface planarisation technique；

S5, S3, S4 are repeated until the thickness of the sandwich layer formed in multiple core region slots reaches the default waveguide device Until the thickness in region；

S6, using the upper surface of the under-clad layer as stop layer, remove the sacrificial layer, form multiple core regions；

S7, multiple core regions are performed etching respectively, forms default waveguide device structure in each core region；

S8, top covering is formed in the default waveguide device structure and the under-clad layer.

2. the preparation method of thick film silicon nitride in region according to claim 1, which is characterized in that the material of the under-clad layer Solid blanket material for refractive index lower than 1.7 and higher than 1.

3. the preparation method of thick film silicon nitride in region according to claim 2, which is characterized in that the solid blanket material For silica.

4. the preparation method of thick film silicon nitride in region according to claim 1, which is characterized in that the under-clad layer is using warm Oxidation and/or chemical vapor deposition process preparation.

5. the preparation method of thick film silicon nitride in region according to claim 1, which is characterized in that the sacrificial layer is by without fixed Shape silicon or polysilicon deposition are formed.

6. the preparation method of thick film silicon nitride in region according to claim 1, which is characterized in that the default waveguide device Region with a thickness of 350 nanometers to 1000 nanometers.

7. the preparation method of thick film silicon nitride in region according to claim 1, which is characterized in that the core material is nitrogen Any one in SiClx or silicon oxynitride.

8. the preparation method of thick film silicon nitride in region according to claim 1, which is characterized in that the thickness of first sandwich layer Degree is 50 nanometers to 300 nanometers.

9. the preparation method of thick film silicon nitride in region according to claim 1, which is characterized in that multiple sandwich layer areas When domain performs etching, using dry etch process.

10. the preparation method of thick film silicon nitride in region according to claim 1, which is characterized in that in the step S8, institute State solid blanket material of the top covering using chemical vapor deposition process deposition refractive index lower than 1.7 and higher than 1.