Silicon light modulator and compensation doping method thereof

Abstract

The invention discloses a silicon light modulator which comprises a silicon substrate, an insulating oxide layer, a top-layer silicon waveguide modulation region and a top-layer covering oxide layer which are stacked in sequence, and the top-layer silicon waveguide modulation region sequentially comprises an n-type heavily doped region, an n-type main doped region, a p-type main doped region and a p-type heavily doped region in the first direction. The invention further discloses a compensation doping method of the silicon light modulator. The silicon light modulator has the advantages that compensation doping is carried out on the flat plate region in an oblique ion implantation mode, and the effects of improving the bandwidth and the modulation efficiency of the silicon light modulator can be achieved at the same time. And compared with a single bandwidth optimization scheme and a single efficiency optimization scheme of the silicon optical modulator, the extra insertion loss introduced by the method is not obviously increased.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic materials and devices, and in particular to a silicon optical modulator and a compensatory doping method thereof. Background Art

[0002] The global communications industry has entered a new period of development with great integration, great change and great transformation. The new generation of information technology represented by next-generation communication networks, cloud computing, the Internet of Things, smart grids and artificial intelligence is becoming an important driving force for the next round of domestic and even global economic development. In order to cope with the explosive growth of mobile data traffic, massive device connections, and the emergence of various new services and application scenarios in the future, modern optical communication networks are increasingly using silicon photonics technology. In the field of optical communications, silicon photonics solutions carry the industry's expectations due to their strong competitive advantages of high integration, low power consumption, small packaging and large-scale manufacturability. Silicon photonics solutions have always been considered an important pillar for the large-scale commercial use of optical technology.

[0003] Silicon optical modulator is one of the core devices for realizing silicon-based optoelectronic integration and its application. Its basic function is to realize the conversion of information from the electrical domain to the optical domain. However, due to the centrosymmetric structure of silicon materials, there is no Pockels effect, and the Kerr effect is also very weak. Therefore, most of the most successful silicon optical modulators demonstrated in recent years work through the plasma dispersion effect. The principle is to use the change of free carrier concentration to affect the refractive index of the material, thereby changing the optical properties of the material. Taking the carrier-depleted silicon-based electro-optical modulator as an example, the pn junction is formed by doping the ridge waveguide, and then the size of the depletion region is changed under an external reverse bias, thereby changing the carrier concentration and realizing the modulation of the refractive index.

[0004] Modulation efficiency and insertion loss are two important technical indicators for measuring silicon-based electro-optical modulators. In addition, as the communication bandwidth becomes larger and larger, higher requirements are placed on the bandwidth of silicon optical modulators. For carrier-depleted silicon optical modulators, the optimization method to increase the modulator bandwidth essentially requires increasing the doping concentration of the modulator slab area. The usual practice is to adjust the position of ion implantation in the slab area to make it closer to the waveguide ridge area, which will increase the bandwidth of the silicon optical modulator and introduce additional insertion loss to the modulator, but will not affect the modulation efficiency of the modulator. On the other hand, the improvement of the modulation efficiency of this type of silicon optical modulator requires increasing the ion doping concentration in the ridge area, but at the same time it will increase the insertion loss of the modulator and reduce the bandwidth of the modulator. Summary of the invention

[0005] The technical problem to be solved by the present invention is that in the known technology, the optimization of the bandwidth and modulation efficiency of the carrier depletion type silicon optical modulator is usually two contradictory directions. On the one hand, by adjusting the position of the ion implantation in the slab region to make it closer to the waveguide ridge region, the bandwidth of the silicon optical modulator increases, and at the same time, it will introduce additional insertion loss to the modulator, but it will basically not affect the modulation efficiency of the modulator. On the other hand, the improvement of the modulation efficiency of such silicon optical modulators requires increasing the ion doping concentration in the ridge region, but at the same time it will increase the insertion loss of the modulator and reduce the bandwidth of the modulator.

[0006] In order to solve the above technical problems, the first purpose of the present invention is to propose a silicon light modulator, and the specific technical solution adopted is as follows: A silicon optical modulator comprises a silicon substrate, an insulating oxide layer, a top silicon waveguide modulation region and a top covering oxide layer stacked in sequence, wherein the top silicon waveguide modulation region comprises an n-type heavily doped region, an n-type main doped region, a p-type main doped region and a p-type heavily doped region in sequence along a first direction.

[0007] The second purpose of the present invention is to propose a compensation doping method for silicon optical modulators, which uses the method of vertical implantation of III-V group element ions to perform main doping to construct PN junctions, and performs compensation doping on the flat plate area by oblique ion implantation, which can simultaneously achieve the effect of improving the bandwidth and modulation efficiency of the silicon optical modulator. Compared with the single bandwidth optimization scheme and the single efficiency optimization scheme of such silicon optical modulators, the additional insertion loss introduced by the method does not increase significantly.

[0008] The specific technical solutions adopted are as follows: A compensatory doping method for a silicon optical modulator comprises the following steps: S1, prepare a photoresist mask, then select the center position of the top silicon waveguide modulation area, and remove the photoresist on one side of the center position; S2, injecting group V element ions into the silicon material of the top silicon waveguide modulation region along the normal direction of the silicon substrate to form an n-type main doping region in the top silicon waveguide modulation region; S3, adjusting the injection concentration and injection energy of the group V element ions, and injecting the group V element ions obliquely from the side with the photoresist to the side without the photoresist into the top silicon waveguide modulation area, wherein the injection direction forms a first angle with the normal direction of the silicon substrate, and the first angle is greater than 0° and less than 80°; S4, re-prepare the photoresist mask to remove the photoresist on the other side of the center position of the top silicon waveguide modulation area; S5, injecting group III element ions into the silicon material of the top silicon waveguide modulation region along the normal direction of the silicon substrate to form a p-type main doping region in the top silicon waveguide modulation region; S6, adjusting the injection concentration and injection energy of the group III element ions, and injecting the group III element ions obliquely from the side with the photoresist to the side without the photoresist into the top silicon waveguide modulation area, wherein the injection direction forms a second angle with the normal direction of the silicon substrate, and the second angle is greater than 0° and less than 80°; S7, depositing a layer of silicon oxide as a mask on the top silicon waveguide, and etching a ridge waveguide structure with a flat plate area on both sides of the center of the modulator waveguide modulation area; S8, then depositing a thin shielding oxide layer on top, preparing a photoresist mask, adjusting the implantation concentration and implantation energy of the III group element ions, implanting the III group element ions into the silicon material of the top silicon waveguide modulation region along the normal direction of the silicon substrate, and forming a p-type heavily doped region in the top silicon waveguide modulation region; then, after re-preparing the photoresist mask, adjusting the implantation concentration and implantation energy of the V group element ions, implanting the V group element ions into the silicon material of the top silicon waveguide modulation region along the normal direction of the silicon substrate, and forming an n-type heavily doped region in the top silicon waveguide modulation region; S9, silicon wafer temperature rises, ion activation, annealing and cooling; S10, depositing a covering silicon oxide layer over the entire device.

[0009] In a further preferred embodiment of the technical solution of the present invention, in steps S2, S3 and S8, the group V element is phosphorus, and the implantation energy is 20-200 keV.

[0010] In a further preferred embodiment of the technical solution of the present invention, the ion implantation energy in step S3 is higher than the ion implantation energy in step S2. This is to implant the compensatory doping ions into the bottom area of ​​the top silicon layer as much as possible, so that the positions of the two side plates where the compensatory ions are implanted have a higher ion concentration, but the compensatory doping step will not significantly affect the ion concentration of the waveguide ridge region.

[0011] In a further preferred embodiment of the technical solution of the present invention, in steps S5, S6 and S8, the group III element is doped with boron or boron fluoride, and the injection energy is 10-220 keV.

[0012] As a further preference for the technical solution of the present invention, when the ion types injected in steps S5 and S6 are both boron or boron fluoride, the ion injection energy in step S6 is higher than the ion injection energy in step S5; when the ion types injected in steps S5 and S6 are different, there is no such limiting relationship.

[0013] In a further preferred embodiment of the technical solution of the present invention, the thickness of the photoresist mask is 1 um to 4 um. By controlling the thickness of the photoresist mask, the position of the compensation doping ions injected into the slab region and the degree of influence on the ion concentration in the waveguide ridge region are adjusted, thereby optimizing the performance of the silicon optical modulator of this solution.

[0014] In a further preferred embodiment of the technical solution of the present invention, the direction of the oblique ion injection is downward from the side with the photoresist to the side without the photoresist.

[0015] In a further preferred embodiment of the technical solution of the present invention, in steps S2 and S5, the concentration range of the ion implantation in the main doping region is 1×10 12 Up to 1×10 14 ions / cm 2 In steps S3 and S6, the concentration range of ion implantation during oblique compensation doping is 1×10 13 Up to 1×10 15 ions / cm 2 In step S8, the concentration range of ion implantation in the heavily doped region is 1×10 15 Up to 1×10 17 ions / cm 2 .

[0016] In a further preferred embodiment of the technical solution of the present invention, in step S7, the waveguide is a ridge-doped waveguide, and the parameters determining the waveguide shape include but are not limited to the width of the waveguide ridge region, the height of the plates on both sides of the ridge region, and the distance between the waveguide center and the doping center position.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The silicon light modulator of the present invention performs compensation doping on the slab region by means of oblique ion implantation, thereby achieving the effects of improving the bandwidth and modulation efficiency of the silicon light modulator at the same time.

[0018] Compared with the single bandwidth optimization solution and the single efficiency optimization solution of this type of silicon optical modulator, the silicon optical modulator of the present invention does not introduce a significant increase in additional insertion loss.

[0019] The compensatory doping method of the silicon light modulator of the present invention can make the optimization direction of the silicon light modulator under this scheme tilt toward better bandwidth or better modulation efficiency by controlling the angle, energy and concentration of oblique injection, which can be flexibly selected according to design requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the cross-sectional structure and doping region distribution of the carrier depletion type silicon optical modulator prepared by the present invention; Figure 2 — Fig.15 is a schematic diagram of a process flow of a silicon optical modulator according to an embodiment of the present invention; Fig.16 It is a schematic diagram of the distribution of the implantation area and the shadow area formed in the silicon waveguide modulation area due to the blocking of the photoresist mask during the oblique implantation of ions; Fig.17is a comparison diagram of the optimization results of the silicon optical modulator for bandwidth in this embodiment; Fig.18 is a comparison chart of the modulation efficiency result obtained by simulating the silicon optical modulator in this embodiment and the modulation efficiency result of the single bandwidth optimization solution; Fig.19 is a comparison chart of the insertion loss results obtained by simulating the silicon optical modulator of this embodiment and the insertion loss results of the single bandwidth optimization solution and the single modulation efficiency optimization solution; Among them, 1 represents the top covering silicon oxide layer, 2 represents the top silicon waveguide modulation area, 3 represents the insulating oxide layer, 4 represents the silicon substrate, 5 represents the n-type heavily doped area, 6 represents the n-type main doped area, 7 represents the p-type main doped area, 8 represents the p-type heavily doped area, 9 represents the photoresist mask, 10 represents the silicon oxide mask, 11 represents the shielding silicon oxide layer, and 12 represents the metal electrode. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the following Figure 1-Figure 19 The present invention is further described in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other. Specific embodiments

[0022] The silicon-based electro-optic modulator involved in the embodiment of the present invention is a Mach-Zehnder modulator, and its cross-sectional structure is shown in FIG. Fig.15 , including a top-covering silicon oxide layer 1, a top silicon waveguide modulation region 2, an insulating oxide layer 3, a shielding silicon oxide layer 11, a metal electrode 12 and a silicon substrate 4. The implementation method of the compensation doping described in this embodiment includes the following steps: refer to Figure 2 Using the photoresist 9 as a mask, the film thickness is 1.7 μm, and the V group element phosphorus ions are implanted along the normal direction of the silicon substrate 4, with an implantation energy of 35 KeV and an ion implantation concentration of 8.5×10 12 ions / cm 2 , so that an n-type main doping region 6 is formed in the area not covered by the photoresist.

[0023] refer to Figure 3 and Figure 4 , the V group element phosphorus ions were injected twice in a mirror-image oblique manner, with the injection direction forming a first angle of 25° with the normal line of the silicon substrate 4, the injection energy was 150KeV, and the ion injection concentration was 1.3×10 14 ions / cm 2 , compensatory doping is performed in the area not covered by the photoresist, so that phosphorus ions can be implanted into the bottom area of ​​the top silicon.

[0024] refer to Figure 5 , re-prepare the photoresist mask with a film thickness of 2.2 μm, and implant the III-group boron fluoride ions along the direction perpendicular to the normal of the silicon substrate with an injection energy of 85 KeV and an ion implantation concentration of 1×10 13 ions / cm 2 , so that a p-type main doping region 7 is formed in the area not covered by the photoresist.

[0025] refer to Figure 6 The III-group boron ions were injected obliquely from the photoresist side to the non-photoresist side. The injection direction formed a second angle of 20° with the normal line of the silicon substrate. The injection energy was 50 KeV and the ion injection concentration was 1.1×10 14 ions / cm 2 , compensatory doping is performed in the area not covered by the photoresist, so that boron ions are implanted into the bottom area of ​​the top silicon.

[0026] refer to Figure 7 , re-prepare the photoresist mask with a film thickness of 2.2 μm, and implant the III-group boron fluoride ions vertically along the substrate with an injection energy of 85 KeV and an ion implantation concentration of 1×10 13 ions / cm 2 , so that a p-type main doping region is formed in the area not covered by the photoresist.

[0027] refer to Figure 8 The III-group boron ions were injected obliquely from the photoresist side to the non-photoresist side. The injection direction formed a second angle of 20° with the substrate normal. The injection energy was 50 KeV and the ion injection concentration was 1.1×10 14 ions / cm 2 , compensatory doping is performed in the area not covered by the photoresist, so that boron ions are implanted into the bottom area of ​​the top silicon 2.

[0028] refer to Fig. 9 and Fig.11 , prepare a silicon oxide mask 10 to etch out the waveguide, and deposit a shielding silicon oxide layer 11 on top to prepare for heavy doping below. In this embodiment, the waveguide ridge width is 500nm, the waveguide ridge height is 220nm, and the thickness of the two side plates is 70nm.

[0029] refer to Fig.12 and Fig.13, using photoresist as a mask, vertically inject group V element ions, adjust the energy and concentration of ion injection, and form n+ heavily doped regions at corresponding locations. Since the injection concentration and energy are relatively large, the shielding silicon oxide can buffer the injected ions. Similarly, re-prepare the photoresist mask, vertically inject group III element ions, and form p+ heavily doped regions at corresponding locations.

[0030] refer to Fig.14 A top covering silicon oxide layer 1 is deposited on top to protect the device.

[0031] refer to Fig.15 , make the metal electrode 12, and the silicon-based Mach-Zehnder electro-optic modulator is completed.

[0032] The silicon light modulator in this embodiment can achieve both improvement in modulation efficiency and improvement in bandwidth by controlling the thickness of the photoresist mask and optimizing the oblique ion implantation angle, ion implantation concentration and implantation energy.

[0033] like Fig.16 As shown, the ion concentration of the flat plate area on both sides of the ridge region of the silicon light modulator is compensated by high-energy ion oblique injection, which increases the ion doping concentration of the flat plate area, reduces the resistance of the modulator, and increases the bandwidth of this type of silicon light modulator.

[0034] like Fig.18 As shown in the figure, when ions are injected obliquely, the ion concentration in the modulator ridge region does not increase significantly but only slightly due to the blocking of a certain thickness of photoresist, which improves the modulation efficiency of the modulator to a certain extent. At the same time, the increase in the modulator bandwidth brought about by the increase in the ion concentration in the slab region is sufficient to compensate for the decrease in bandwidth caused by the slight increase in the ion concentration in the ridge region, so that the bandwidth of the silicon optical modulator under this scheme is still increased as a whole. Fig.17 As shown, like Fig.19 As shown, compared with the modulator single bandwidth optimization scheme and the single modulation efficiency optimization scheme, the additional insertion loss introduced by the silicon optical modulator in this embodiment does not increase significantly; this is because the ion concentration in the modulator waveguide ridge region does not increase significantly due to the blocking of the photoresist mask during oblique ion implantation.

[0035] In this embodiment, the doped ion type, ion implantation concentration and energy, oblique doping angles, ie, the first angle and the second angle, etching height, photoresist thickness, etc. can be adjusted accordingly depending on the situation.

[0036] In this embodiment, by controlling the thickness of the photoresist mask and adjusting the angle, energy and concentration of the oblique ion implantation, the optimization direction of the silicon optical modulator under this scheme can be tilted toward better bandwidth or better modulation efficiency, and can be designed according to actual needs.

[0037] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A silicon optical modulator, characterized in that: The invention comprises a silicon substrate (4), an insulating oxide layer (3), a top silicon waveguide modulation region (2) and a top covering oxide layer (1) which are stacked in sequence, wherein the top silicon waveguide modulation region (2) comprises an n-type heavily doped region (5), an n-type main doped region (6), a p-type main doped region (7) and a p-type heavily doped region (8) in sequence along a first direction.

2. A compensatory doping method for a silicon light modulator, comprising compensatory doping of the silicon light modulator according to claim 1, characterized in that: The steps include: S1, preparing a photoresist mask, then selecting the center position of the top silicon waveguide modulation area (2), and removing the photoresist on one side of the center position; S2, injecting V group element ions into the silicon material of the top silicon waveguide modulation region (2) along the normal direction of the silicon substrate (4), so as to form an n-type main doping region (6) in the top silicon waveguide modulation region (2); S3, adjusting the injection concentration and injection energy of the group V element ions, injecting the group V element ions obliquely from the side with the photoresist to the side without the photoresist into the top silicon waveguide modulation area (2), wherein the injection direction forms a first angle with the normal direction of the silicon substrate (4), and the first angle is greater than 0° and less than 80°; S4, re-prepare the photoresist mask to remove the photoresist on the other side of the center position of the top silicon waveguide modulation area (2); S5, injecting group III element ions into the silicon material of the top silicon waveguide modulation region (2) along the normal direction of the silicon substrate (4), so as to form a p-type main doping region (7) in the top silicon waveguide modulation region (2); S6, adjusting the injection concentration and injection energy of the group III element ions, injecting the group III element ions obliquely from the side with the photoresist to the side without the photoresist into the top silicon waveguide modulation area (2), wherein the injection direction forms a second angle with the normal direction of the silicon substrate (4), and the second angle is greater than 0° and less than 80°; S7, depositing a layer of silicon oxide as a mask on the top silicon waveguide, and etching a ridge waveguide structure with a flat plate area on both sides of the center of the modulator waveguide modulation area; S8, then depositing a thin shielding oxide layer (11) on the top, preparing a photoresist mask, adjusting the implantation concentration and implantation energy of the group III element ions, and implanting the group III element ions into the silicon material of the top silicon waveguide modulation region (2) along the normal direction of the silicon substrate (4), thereby forming a p-type heavily doped region (8) in the top silicon waveguide modulation region (2); then, after re-preparing the photoresist mask, adjusting the implantation concentration and implantation energy of the group V element ions, and implanting the group V element ions into the silicon material of the top silicon waveguide modulation region (2) along the normal direction of the silicon substrate (4), thereby forming an n-type heavily doped region (5) in the top silicon waveguide modulation region (2); S9, silicon wafer temperature rises, ion activation, annealing and cooling; S10, depositing a covering silicon oxide layer (1) over the entire device.

3. The compensatory doping method for a silicon optical modulator according to claim 2, characterized in that: In steps S2, S3 and S8, the group V element is phosphorus, and the implantation energy is 20-200 keV.

4. The compensatory doping method for a silicon optical modulator according to claim 3, characterized in that: The ion implantation energy in step S3 is higher than that in step S2.

5. The compensatory doping method for a silicon optical modulator according to claim 2, characterized in that: In steps S5, S6 and S8, the group III element is doped with boron or boron fluoride, and the implantation energy is 10-220 keV.

6. The compensatory doping method for a silicon optical modulator according to claim 5, characterized in that: When the ion species implanted in steps S5 and S6 are both boron or boron fluoride, the ion implantation energy in step S6 is higher than the ion implantation energy in step S5; when the ion species implanted in steps S5 and S6 are different, there is no such limiting relationship.

7. The compensatory doping method for a silicon optical modulator according to claim 2, characterized in that: The thickness of the photoresist mask is 1um to 4um.

8. The compensatory doping method for a silicon optical modulator according to claim 2, characterized in that: The direction of the oblique ion injection is downward from the photoresist side to the non-photoresist side.

9. The compensatory doping method for a silicon optical modulator according to claim 2, characterized in that: In steps S2 and S5, the concentration range of ion implantation in the main doping region is 1×10 12 Up to 1×10 14 ions / cm 2 In steps S3 and S6, the concentration range of ion implantation during oblique compensation doping is 1×10 13 Up to 1×10 15 ions / cm 2 In step S8, the concentration range of ion implantation in the heavily doped region is 1×10 15 Up to 1×10 17 ions / cm 2 .

10. The compensatory doping method for a silicon optical modulator according to claim 2, characterized in that: In step S7, the waveguide is a ridge-doped waveguide, and the parameters determining the waveguide shape include but are not limited to the width of the waveguide ridge region, the height of the plates on both sides of the ridge region, and the distance between the waveguide center and the doping center position.

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