Silicon optical modulator and compensation doping method thereof

Abstract

The present invention discloses a silicon optical modulator, comprising 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. The present invention also discloses a compensation doping method for a silicon optical modulator. Advantageously, by compensating the doping of the flat plate region by oblique ion implantation, the effects of improving the bandwidth and modulation efficiency of the silicon optical modulator can be achieved simultaneously. Moreover, compared with the single bandwidth optimization scheme and the single efficiency optimization scheme of this type of silicon optical modulator, the additional insertion loss introduced by this method does not increase significantly.

Description

Technical Field

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

[0002] The global communications industry has entered a new era of significant convergence, transformation, and transformation. New-generation information technologies, represented by next-generation communication networks, cloud computing, the Internet of Things, smart grids, and artificial intelligence, as national strategic emerging industries, are becoming a key driver of the next round of domestic and global economic development. To cope with the explosive growth of mobile data traffic, the massive number of connected devices, and the emergence of new services and application scenarios, modern optical communication networks are increasingly utilizing silicon photonics technology. In the optical communications sector, silicon photonics solutions, with their strong competitive advantages of high integration, low power consumption, compact packaging, and large-scale manufacturability, hold high industry expectations. Silicon photonics solutions have long been considered a key pillar for the large-scale commercialization of optical technology.

[0003] Silicon optical modulators (SOMOs) are one of the most critical devices for silicon-based optoelectronic integration and its applications. Their fundamental function is to convert information from the electrical domain to the optical domain. However, due to the centrosymmetric structure of silicon, the Pockels effect is absent, and the Kerr effect is very weak. Therefore, most of the most successful SOMOs demonstrated in recent years operate through the plasma dispersion effect, which exploits the influence of changes in the free carrier concentration on the material's refractive index, thereby altering the material's optical properties. For example, a carrier-depleted SOMO is achieved by doping the ridge waveguide to form a pn junction. The depletion region is then modified under an applied reverse bias, thereby varying the carrier concentration and modulating the refractive index.

[0004] Modulation efficiency and insertion loss are two important technical indicators for measuring silicon-based electro-optical modulators. In addition, as communication bandwidth increases, higher requirements are placed on the bandwidth of silicon optical modulators. For carrier-depleted silicon optical modulators, the optimization method to improve the modulator bandwidth essentially requires increasing the doping concentration of the modulator slab region. The usual practice is to adjust the position of ion implantation in the slab region so that it is closer to the waveguide ridge region. This will increase the bandwidth of the silicon optical modulator and introduce additional insertion loss into the modulator, but will not affect the modulation efficiency of the modulator. On the other hand, improving the modulation efficiency of this type of silicon optical modulator requires increasing the ion doping concentration in the ridge region, but this will also increase the insertion loss of the modulator and reduce the modulator bandwidth. Summary of the Invention

[0005] The technical problem addressed by this invention is that, in conventional technologies, optimizing the bandwidth and modulation efficiency of carrier-depletion silicon optical modulators is often a conflicting proposition. On the one hand, adjusting the ion implantation position in the slab region closer to the waveguide ridge increases the bandwidth of the silicon optical modulator, while introducing additional insertion loss but substantially reducing the modulation efficiency. On the other hand, increasing the modulation efficiency of such silicon optical modulators requires increasing the ion doping concentration in the ridge region, which in turn increases insertion loss and reduces the modulator's bandwidth.

[0006] To solve the above technical problems, the first objective of the present invention is to propose a silicon optical modulator, and the specific technical solutions adopted are as follows:

[0007] 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.

[0008] A second objective of this invention is to propose a compensation doping method for silicon optical modulators. This method uses vertical implantation of III-V element ions to form the primary doping structure for the PN junction, and then uses oblique ion implantation to compensate for the doping in the slab region. This method can simultaneously improve both the bandwidth and modulation efficiency of the silicon optical modulator. Furthermore, compared with existing silicon optical modulator optimization schemes for single-bandwidth and single-efficiency optimization, this method introduces no significant increase in insertion loss.

[0009] The specific technical solutions adopted are as follows:

[0010] A compensating doping method for a silicon optical modulator comprises the following steps:

[0011] 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;

[0012] S2, implanting 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;

[0013] 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°;

[0014] S4, re-prepare the photoresist mask and remove the photoresist on the other side of the center position of the top silicon waveguide modulation area;

[0015] S5, implanting 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;

[0016] S6. Adjust the injection concentration and injection energy of the group III element ions, and inject the group III element ions obliquely from the photoresist side to the photoresist-free side into the top silicon waveguide modulation region, 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°;

[0017] S7. Deposit a layer of silicon oxide as a mask on top of the top silicon waveguide, and etch a ridge waveguide structure with a flat plate area on both sides of the center of the modulator waveguide modulation area;

[0018] S8. Then, a thin shielding oxide layer is deposited on top, a photoresist mask is prepared, the implantation concentration and implantation energy of the group III element ions are adjusted, and the group III element ions are implanted into the silicon material of the top silicon waveguide modulation region along the normal direction of the silicon substrate to form a p-type heavily doped region in the top silicon waveguide modulation region; then, after re-preparing the photoresist mask, the implantation concentration and implantation energy of the group V element ions are adjusted, and the group V element ions are implanted into the silicon material of the top silicon waveguide modulation region along the normal direction of the silicon substrate to form an n-type heavily doped region in the top silicon waveguide modulation region;

[0019] S9, silicon wafer temperature rises, ion activation, annealing and cooling;

[0020] S10, depositing a covering silicon oxide layer over the entire device.

[0021] 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 injection energy is 20-200 keV.

[0022] In a further preferred embodiment of the present invention, the ion implantation energy in step S3 is higher than that in step S2. This is to implant the compensating doping ions as far as possible into the bottom region of the top silicon layer, thereby achieving a higher ion concentration at the locations where the compensating ions are implanted on the two side plates. However, the compensating doping step does not significantly affect the ion concentration in the waveguide ridge region.

[0023] 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.

[0024] In a further preferred embodiment of the technical solution of the present invention, when the ion species 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 species injected in steps S5 and S6 are different, there is no such limiting relationship.

[0025] In a further preferred embodiment of the present invention, the thickness of the photoresist mask is 1 to 4 μm. By controlling the thickness of the photoresist mask, the position of the compensating dopant ions injected into the slab region and the degree of their influence on the ion concentration in the waveguide ridge region can be adjusted, thereby optimizing the performance of the silicon optical modulator of this embodiment.

[0026] 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.

[0027] 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 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 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 to 1×10 17 ions / cm 2 .

[0028] 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.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 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 both the bandwidth and the modulation efficiency of the silicon light modulator.

[0031] Compared with a single bandwidth optimization solution and a 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.

[0032] The compensation doping method of the silicon light modulator of the present invention can optimize the silicon light modulator in this scheme toward better bandwidth or better modulation efficiency by controlling the angle, energy, and concentration of the oblique injection, which can be flexibly selected according to design requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the cross-sectional structure and doping region distribution of the carrier-depleted silicon optical modulator prepared by the present invention;

[0034] Figure 2 — Figure 15 1 is a schematic diagram of the process flow of a silicon optical modulator according to an embodiment of the present invention;

[0035] Figure 16 This is a schematic diagram of the distribution of the implanted area and shadow area formed in the silicon waveguide modulation area due to the blocking of the photoresist mask during oblique ion implantation;

[0036] Figure 17 is a comparison chart of bandwidth optimization results of the silicon optical modulator in this embodiment;

[0037] Figure 18 2 is a diagram comparing the modulation efficiency results obtained by simulating the silicon optical modulator in this embodiment with the modulation efficiency results of the single-bandwidth optimization solution;

[0038] Figure 19 This is a comparison chart of the insertion loss results obtained by simulation of the silicon optical modulator of this embodiment with the insertion loss results of the single bandwidth optimization solution and the single modulation efficiency optimization solution;

[0039] 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, 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

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clear, the following Figures 1-19 The present invention is further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other. Specific embodiment 1:

[0042] The silicon-based electro-optical modulator involved in the embodiment of the present invention is a Mach-Zehnder modulator, and its cross-sectional structure is shown in FIG. Figure 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:

[0043] 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. The injection energy is 35 KeV and the ion implantation concentration is 8.5×10 12 ions / cm 2, so that an n-type main doping region is formed in the area not covered by the photoresist.

[0044] refer to Figure 3 and Figure 4 The V group element phosphorus ions were injected twice in a mirror-image oblique manner. The injection direction formed a first angle of 25° with the normal line of the silicon substrate 4. The injection energy was 150 KeV 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.

[0045] refer to Figure 5 , a new photoresist mask was prepared with a thickness of 2.2 μm, and boron fluoride ions of group III elements were implanted 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 is formed in the area not covered by the photoresist.

[0046] 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.

[0047] refer to Figure 7 , a new photoresist mask was prepared with a thickness of 2.2 μm, and boron fluoride ions of group III elements were implanted in the direction perpendicular to 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.

[0048] 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.

[0049] refer to Figure 9 and Figure 11A silicon oxide mask 10 is prepared to etch out the waveguide, and a shielding silicon oxide layer 11 is deposited 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.

[0050] refer to Figure 12 and Figure 13 Using a photoresist mask, group V ions are vertically implanted. The energy and concentration of the ion implantation are adjusted to form heavily n+ doped regions at the corresponding locations. Because the implantation concentration and energy are relatively high, the shielding silicon oxide acts as a buffer for the implanted ions. Similarly, a new photoresist mask is prepared, and group III ions are vertically implanted to form heavily p+ doped regions at the corresponding locations.

[0051] refer to Figure 14 A top covering silicon oxide layer 1 is deposited on top to protect the device.

[0052] refer to Figure 15 , make the metal electrode 12, and the silicon-based Mach-Zehnder electro-optic modulator is completed.

[0053] The silicon light modulator in this embodiment can achieve both improved modulation efficiency and bandwidth by controlling the thickness of the photoresist mask and optimizing the oblique ion implantation angle, ion implantation concentration, and implantation energy.

[0054] like Figure 16 As shown, the ion concentration of the flat plate area on both sides of the silicon light modulator ridge region 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.

[0055] like Figure 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 overall bandwidth of the silicon optical modulator under this scheme is still increased. Figure 17 As shown,

[0056] like Figure 19 As shown in the figure, 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 injection.

[0057] In this embodiment, the doping 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.

[0058] In this embodiment, by controlling the thickness of the photoresist mask and adjusting the angle, energy, and concentration of the oblique ion injection, 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.

[0059] It will be easily understood by those skilled in the art that the above description is merely 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 scope of protection of the present invention.

Claims

1. A compensation doping method for a silicon optical modulator, characterized in that: The steps include: S1, prepare a photoresist mask, then select the center position of the top silicon waveguide modulation area (2), and remove 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), thereby forming an n-type main doping region in the top silicon waveguide modulation region (2); 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 (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°; wherein the group V element ions are injected obliquely twice in a mirror image manner; S4, re-prepare the photoresist mask and remove the photoresist on the first 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), thereby forming a p-type main doping region 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, re-prepare the photoresist mask and remove the photoresist on the second side of the center position of the top silicon waveguide modulation area (2); S8, 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), thereby forming a p-type main doping region in the top silicon waveguide modulation region (2); S9, 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 (2), wherein the injection direction forms a third angle with the normal direction of the silicon substrate (4), and the third angle is greater than 0° and less than 80°; S10, depositing a layer of silicon oxide as a mask on top of 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; S11, then depositing a thin shielding oxide layer (11) on the top, preparing a photoresist mask, adjusting the injection concentration and injection energy of the group III element ions, and injecting 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 in the top silicon waveguide modulation region (2); then, after re-preparing the photoresist mask, adjusting the injection concentration and injection energy of the group V element ions, and injecting 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 in the top silicon waveguide modulation region (2); S12, silicon wafer temperature rises, ion activation, annealing and cooling; S13, depositing a covering silicon oxide layer (1) over the entire device; The silicon optical modulator comprises a silicon substrate (4), an insulating oxide layer (3), a top silicon waveguide modulation region (2) and a top covering oxide layer (1) stacked in sequence, wherein the top silicon waveguide modulation region (2) comprises a p-type heavily doped region, a p-type main doped region, an n-type main doped region, 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.

2. The compensation doping method for a silicon optical modulator according to claim 1, wherein: In steps S2, S3 and S11, the Group V element is phosphorus, and the implantation energy is 20-200 keV.

3. The compensation doping method for a silicon optical modulator according to claim 1, wherein: The ion implantation energy in step S3 is higher than that in step S2.

4. The compensation doping method for a silicon optical modulator according to claim 1, wherein: In steps S5, S6, S8, S9 and S11, the group III element is doped with boron or boron fluoride, and the implantation energy is 10-220 keV.

5. The compensation doping method for a silicon optical modulator according to claim 4, 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 limitation.

6. The compensation doping method for a silicon optical modulator according to claim 1, wherein: The thickness of the photoresist mask is 1um to 4um.

7. The compensation doping method for a silicon optical modulator according to claim 1, wherein: The direction of the oblique ion injection is downward from the photoresist side to the non-photoresist side.

8. The compensation doping method for a silicon optical modulator according to claim 1, wherein: In steps S2 and S5, the concentration range of ion implantation in the main doping region is 1×10 12 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 to 1×10 15 ions / cm 2 In step S11, the concentration range of ion implantation in the heavily doped region is 1×10 15 to 1×10 17 ions / cm 2 .

9. The compensation doping method for a silicon optical modulator according to claim 1, wherein: In step S10, the waveguide is a ridge-doped waveguide, and 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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