Method for reducing contact resistance of high-al component n-algan material and application

Abstract

This invention relates to the field of semiconductor optoelectronic device technology, specifically to a method and application for reducing the contact resistance of high-Al-content n-AlGaN materials in device manufacturing processes. The method involves surface atom adsorption and annealing of the n-AlGaN layer under a protective gas atmosphere; the atoms are Si and N atoms. This method significantly increases the carrier concentration on the material surface, thereby contributing to excellent ohmic contact performance and reducing the material's contact resistivity. It solves the problem of difficult ohmic contact preparation for high-Al-content n-AlGaN materials, especially the difficulty in forming ohmic contacts after etching. The method is simple and reproducible, effectively avoiding the complexity and instability of existing processes such as acid / alkali corrosion or high-temperature annealing. It ensures large-scale mass production and has no adverse effects on subsequent device fabrication, exhibiting good process compatibility.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor optoelectronic device technology, specifically relating to a method and application for reducing the contact resistance of high Al composition n-AlGaN materials in device manufacturing processes. Background Technology

[0002] In recent years, AlGaN-based deep ultraviolet (DUV) light-emitting devices, such as light-emitting diodes (LEDs), have attracted much attention due to their significant application prospects in water / air purification, sterilization, biochemical analysis, environmental monitoring, and secure communication. Meanwhile, due to their substantial advantages in high efficiency, environmental friendliness, energy saving, and portability, AlGaN-based DUV-LEDs are considered a promising deep ultraviolet light source to replace traditional gas mercury lamps.

[0003] Although significant progress has been made in the research of AlGaN-based DUV-LEDs, their electro-optical conversion efficiency (WPE) remains very low (typically below 5%), which greatly limits their commercial applications. Research indicates that reducing the operating voltage can decrease Joule heating, thereby improving the electro-optical conversion efficiency. Furthermore, from a device structure perspective, the ohmic contact resistance of n-AlGaN accounts for a large proportion of the total series resistance of the LED device; therefore, it is necessary to further reduce the ohmic contact resistance of n-AlGaN.

[0004] More importantly, n-AlGaN needs to be etched during device fabrication to form mesa structures. For n-GaN, plasma etching significantly improves its ohmic contact characteristics. The N vacancies generated during etching act as shallow donors, forming a heavily doped surface region, leading to increased electron concentration. Higher electron concentration enhances the tunneling effect at the contact interface, which helps reduce contact resistance. However, for n-AlGaN materials with high Al content, the etching process generates acceptor-like metal vacancies and deep-level center N vacancies. Both of these produce an electron compensation effect, reducing the surface carrier concentration, which further increases the difficulty of forming ohmic contacts.

[0005] Common methods for reducing material contact resistance include surface treatment, such as wet etching or plasma bombardment; or high-temperature annealing to eliminate surface damage. Wet etching and similar methods suffer from instability, low controllability, and poor effectiveness; plasma bombardment can cause secondary damage to the material surface to some extent; and high-temperature annealing is complex and requires sophisticated equipment, increasing process costs.

[0006] Currently, there is a lack of effective methods to reduce the contact resistance of high-Al content n-AlGaN materials, especially for high-Al content n-AlGaN with surface etching damage. Therefore, finding an effective method to recover from the etching damage of n-AlGaN is crucial for developing high-performance AlGaN-based optoelectronic devices. Summary of the Invention

[0007] A first aspect of the present invention is to provide a method for reducing the contact resistance of n-AlGaN materials with high Al content.

[0008] The method for reducing the contact resistance of high-Al content n-AlGaN material is as follows: under the action of a protective gas, the n-AlGaN layer is subjected to surface atomic adsorption and annealing treatment; the atoms are Si atoms and N atoms.

[0009] This invention provides that atomically shaped Si and N atoms are adsorbed on the surface of an n-AlGaN layer, and then annealing is performed to allow the Si and N atoms to diffuse into the n-AlGaN layer, thereby increasing the carrier concentration on the material surface, which helps to form excellent ohmic contact performance, reduces the contact resistivity of the material, and solves the problem of difficult preparation of ohmic contacts in high Al content n-AlGaN materials, especially the difficulty in forming ohmic contacts after etching.

[0010] The method is simple and easy to repeat, effectively avoiding the complex and unstable problems caused by acid and alkali corrosion or high-temperature annealing in existing processes. It can ensure large-scale mass production and will not have any adverse effects on subsequent device fabrication, thus having good process compatibility.

[0011] The surface atom adsorption described in this invention is achieved using plasma-enhanced chemical vapor deposition. The specific process includes: introducing NH3 and SiH4 into the reaction apparatus under a protective gas atmosphere; decomposing NH3 and SiH4 using radio frequency plasma; and adsorbing the resulting Si and N atoms onto the surface of the n-AlGaN layer.

[0012] During the surface atom adsorption process, higher radio frequency (RF) power leads to higher decomposition efficiency of NH3 and SiH4, but excessively high power results in unnecessary energy consumption. Therefore, in this invention, the RF power is controlled between 50-200W, which can be adjusted according to the equipment and actual needs. According to an embodiment of this invention, based on a PECVD device, the RF power is 100W.

[0013] Regarding the introduction time of NH3 and SiH4, research results indicate that the introduction time should be minimized, especially when NH3 and SiH4 are introduced simultaneously, to prevent SiN from being exposed to the air. xThe large-scale generation and coverage of NH3 and SiH4 on the n-AlGaN surface reduces the contact area between the subsequent electrode and n-AlGaN, resulting in significant negative impacts. According to embodiments of the present invention, the introduction time of NH3 and SiH4 is 3-20 s, preferably 5-15 s.

[0014] In this invention, NH3 and SiH4 can be introduced simultaneously, sequentially, or alternately, depending on the specific needs.

[0015] When both are introduced simultaneously, the flow ratio of NH3 to SiH4 is 1-10. Studies have shown that when the flow ratio is around 15, dense SiNx is easily formed. Therefore, controlling the flow ratio within this range ensures good adsorption at the atomic surface.

[0016] If the flow is supplied sequentially or alternately, it is not limited by the flow ratio.

[0017] The present invention also found that during the surface atom adsorption process, the temperature of the n-AlGaN material should not be too high to avoid the formation of dense SiNx. Therefore, according to embodiments of the present invention, the temperature of the n-AlGaN material is controlled to not exceed 200°C.

[0018] By controlling the above conditions, we can improve the decomposition and adsorption efficiency while ensuring the atomic adsorption area, thus enhancing the adsorption effect.

[0019] The reaction apparatus described in this invention can be any commonly used equipment in the art, such as a PECVD apparatus. The protective gas can be N2.

[0020] The annealing conditions for n-AlGaN after surface treatment described in this invention are: temperature 500~900℃, preferably 750-850℃; treatment time 20~60s, preferably 25-40s. By controlling the annealing conditions, the diffusion degree of adsorbed atoms into the n-AlGaN layer is increased, thereby further increasing the carrier concentration on the material surface, which is more conducive to forming excellent ohmic contact performance and further reducing the contact resistivity of the material.

[0021] In the method described in this invention, the n-AlGaN layer can be an unetched high-Al content n-AlGaN material or a high-Al content n-AlGaN material with etching damage. Preferably, the etching depth is 250-350 nm.

[0022] The etching can be wet etching, dry ICP etching, or RIE etching; the specific etching thickness can be determined according to the actual needs of the device.

[0023] Studies have shown that the operating conditions of surface atomic adsorption and annealing are related to the etching degree of the n-AlGaN layer.

[0024] As one specific embodiment of the present invention, for an n-AlGaN layer with an etching depth of 250-350 nm, the operating conditions for surface atom adsorption in the method are as follows: the introduction time of NH3 and SiH4 is 5-15 s; the flow ratio of NH3 to SiH4 is 8-10; the power of the radio frequency is 80-110 W; the temperature of the n-AlGaN material is 140-160 °C; and the conditions for subsequent annealing are: temperature 750-850 °C, processing time 25-40 s. By optimizing the surface atom adsorption and annealing conditions, etching losses can be effectively repaired, while avoiding the formation of sheet-like SiN layers. x The formation of this structure results in excellent ohmic contact performance.

[0025] A second aspect of the present invention provides a method for preparing an n-AlGaN ohmic contact metal, comprising the steps of etching an n-AlGaN layer and performing a surface pretreatment thereon; the surface pretreatment is the method described above. By employing the above method, etching damage can be effectively repaired, thereby reducing the contact resistivity of the material.

[0026] As one specific embodiment of the present invention, the method for preparing the n-AlGaN ohmic contact metal includes:

[0027] (1) Epitaxial growth of an n-AlGaN layer on a substrate;

[0028] (2) Etching the surface of the n-AlGaN layer;

[0029] (3) Perform surface pretreatment on the etched n-AlGaN layer; the surface pretreatment includes surface atom adsorption and annealing.

[0030] (4) The material obtained by surface pretreatment in step (3) is vapor-deposited with n-type electrode metal and then annealed to obtain n-AlGaN ohmic contact metal.

[0031] In step (1) above, the substrate can be sapphire or other substrates; the n-AlGaN layer can be any n-AlGaN material obtained by epitaxial structure.

[0032] In step (4) above, the n-type electrode metal is one or more of titanium, aluminum, nickel, gold, chromium, vanadium, etc., or an alloy thereof.

[0033] In step (4) above, the annealing conditions can be conventional annealing conditions in the art, such as a temperature of 600~1000℃ and an annealing time of 20~60s.

[0034] A third aspect of the present invention provides an n-AlGaN ohmic contact metal obtained by the above preparation method, which has a low contact resistivity, can effectively help the device reduce the operating voltage, reduce the generation of Joule heat, and greatly improve the stability and service life of the device.

[0035] A fourth aspect of the present invention provides a semiconductor optoelectronic device comprising the aforementioned n-AlGaN ohmic contact metal. The semiconductor optoelectronic device exhibits improved stability and lifespan.

[0036] Preferably, the semiconductor optoelectronic device is an AlGaN-based deep ultraviolet LED chip.

[0037] As one specific embodiment of the present invention, the method for fabricating the AlGaN-based deep ultraviolet LED chip includes the following steps:

[0038] (1) An AlN layer, an AlN / AlGaN stress modulation layer, an n-AlGaN layer, a multiple quantum well layer, an AlGaN electron blocking layer, a p-AlGaN layer and a p-GaN layer are epitaxially grown sequentially on the surface of the substrate;

[0039] (2) Remove part of the p-GaN layer, p-AlGaN layer, AlGaN electron blocking layer, multiple quantum well layer and part of the n-AlGaN layer to expose the surface of the n-AlGaN layer;

[0040] (3) Deep etching channels are fabricated on the chip, extending to the substrate surface, dividing the chip into individual units;

[0041] (4) Perform the above surface pretreatment on the material to obtain the surface-pretreated n-AlGaN layer;

[0042] (5) An n-type ohmic contact metal is prepared on the surface of the surface-pretreated n-AlGaN layer; the metal is one or more of titanium, aluminum, nickel or gold;

[0043] (6) A p-type ohmic contact metal is fabricated on the surface of the p-GaN layer and annealed; the metal is nickel and / or gold.

[0044] The beneficial effects achieved by this invention are as follows:

[0045] (1) The method for reducing contact resistance described in this invention is to provide atomically shaped Si and N atoms adsorbed on the n-AlGaN surface and diffuse into the n-AlGaN layer during annealing, so as to further increase the carrier concentration in the region near the material surface, thereby helping to form excellent ohmic contact performance and reduce the contact resistivity of the material.

[0046] (2) The present invention has a good effect on reducing contact resistance for both unetched high Al composition n-AlGaN materials and n-AlGaN materials with etching damage. In particular, for n-AlGaN materials etched by devices, it can provide Si and N atoms to actively occupy the acceptor-like metal vacancies and deep level center N vacancies generated by plasma etching, thereby effectively repairing etching damage, increasing the electron concentration of the n-AlGaN surface layer, reducing contact resistance, and thus helping the device reduce the operating voltage, reduce the generation of Joule heat, and greatly improve the stability and service life of the device.

[0047] (3) The method for reducing contact resistance described in this invention has the advantages of simple and easy-to-repeat process, which can effectively avoid the problems of complex and unstable processes caused by acid and alkali solution corrosion or high temperature annealing in existing processes, ensure large-scale mass production, and have no impact on subsequent device manufacturing, and has good process compatibility. Attached Figure Description

[0048] Figure 1 The diagram shows the cross-sectional flow chart of the sample preparation process in Example 1 and the pattern of the photomask used; where (a)-(d) are cross-sectional flow charts of each step in the preparation process, and (e) is the pattern of the photomask used for photolithography.

[0049] In the figure: 1 is the sapphire substrate, 2 is the AlN layer, 3 is the AlN / AlGaN stress modulation layer, 4 is the n-AlGaN layer, 5 is the etched n-AlGaN layer, 6 is the n-AlGaN layer after surface pretreatment, and 7 is the n-type ohmic contact metal.

[0050] Figure 2 The following is a test graph of the effect of Example 1, where (a) is the IV curve of Sample 1 and Sample 2, and (b) is the IV curve between each electrode of Sample 2.

[0051] Figure 3 This is a cross-sectional view of the high-performance deep ultraviolet LED chip described in Example 2;

[0052] In the figure: 1 is the sapphire substrate, 2 is the AlN layer, 3 is the AlN / AlGaN stress modulation layer, 4 is the n-AlGaN layer, 5 is the multiple quantum well layer, 6 is the AlGaN electron blocking layer, 7 is the p-AlGaN layer, 8 is the p-GaN layer, 9 is the n-AlGaN layer after surface pretreatment, 10 is the n-type ohmic contact metal, and 11 is the p-type ohmic contact metal.

[0053] Figure 4 The IV curve is shown for the deep ultraviolet LED chip described in Example 2. Detailed Implementation

[0054] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0055] Example 1

[0056] This embodiment provides a method for reducing the ohmic contact resistance of high-Al-content n-AlGaN materials after etching, such as... Figure 1 As shown, it includes:

[0057] 1) An AlN layer 2, an AlN / AlGaN stress modulation layer 3, and an n-AlGaN layer 4 are epitaxially grown sequentially on a sapphire substrate 1;

[0058] The resulting n-AlGaN layer 4 has an Al composition of 55% and a carrier concentration of 2.5 × 10⁻⁶. 18 cm -3 .

[0059] 2) The n-AlGaN layer 4 was etched to a depth of 300 nm to obtain the etched n-AlGaN layer 5;

[0060] Etching can be performed using wet etching, dry ICP etching, or RIE etching.

[0061] 3) The sample was pretreated to obtain the pretreated n-AlGaN layer 6;

[0062] Surface pretreatment includes surface atomic adsorption and annealing.

[0063] Among them: the operating conditions for surface atomic adsorption are: processing time of 10s;

[0064] a. Simultaneously introduce NH3 and SiH4;

[0065] b. The insertion time is 10 seconds;

[0066] c. The flow ratio is 9;

[0067] d. RF power is 100W;

[0068] The temperature of the e,n-AlGaN layer is 150℃.

[0069] Annealing conditions: temperature 800℃, N2 atmosphere, annealing time 30s;

[0070] 4) Electrode fabrication and high-temperature alloying to form an n-type ohmic contact metal 7;

[0071] Electrode fabrication processes include: photolithography, development, metal evaporation, and lift-off; among which, photolithography uses a photomask pattern such as... Figure 1 As shown in (e), electrodes are used to implement the transmission line (TLM) electrode, with an electrode side length w of 200 μm and different spacing d.n The values ​​are 10, 15, 20, 25, 30, 35, and 40 μm, respectively.

[0072] Effect Test 1:

[0073] Comparative Example 1 (Sample 1) and Example 1 (Sample 2) were tested.

[0074] Comparative Example 1: The difference from Example 1 is that step (3) is omitted, that is, the n-AlGaN layer 5 obtained by etching in step (2) is directly used to form an electrode to form an ohmic contact.

[0075] The test results are as follows:

[0076] Measure the IV curves of every two adjacent electrodes in the sample, using the same voltage range of -2V to 2V, and measure their current values. Plot the obtained data as shown below. Figure 2 As shown:

[0077] in, Figure 2 (a) Comparison of the IV curves between the two electrodes from T1 to T2 for Sample 1 and Sample 2; Figure 2 It can be seen that Sample 1, without surface pretreatment after etching, does not have an ohmic contact and has a relatively high contact resistance. Sample 2, however, uses surface pretreatment, resulting in an ohmic contact where the contact resistance remains constant with changing current. This demonstrates that surface pretreatment can achieve ohmic contact in etched n-AlGaN materials, significantly reducing their contact resistivity.

[0078] Figure 2 (b) shows the IV curves between each pair of adjacent electrodes of sample 2. By fitting the data, the specific contact resistivity of sample 2 can be obtained as ρ. c =5.1×10 -5 (Ω·cm 2 ).

[0079] Furthermore, during the experiment, this invention also attempted to adjust the introduction time, flow rate ratio, temperature, and radio frequency power of NH3 and SiH4 during the atomic surface adsorption process. It was found that process parameters outside the aforementioned range were difficult to guarantee the atomic surface adsorption effect and easily led to the formation of SiN. x Excessive coverage reduces the effectiveness of the treatment and leads to an increase in specific contact resistivity.

[0080] Example 2

[0081] This embodiment provides a method for fabricating an AlGaN-based deep ultraviolet LED chip, including the following steps:

[0082] (1) Using an MOCVD apparatus, AlN layer 2, AlN / AlGaN stress modulation layer 3, n-AlGaN layer 4, multiple quantum well layer 5, AlGaN electron blocking layer 6, p-AlGaN layer 7 and p-GaN layer 8 are epitaxially grown sequentially on the surface of a clean sapphire substrate 1, as shown in the figure. Figure 3 As shown;

[0083] (2) By using photolithography and ICP etching techniques, the p-GaN layer, p-AlGaN layer, AlGaN electron blocking layer, multiple quantum well layer and part of the n-AlGaN layer in some areas are removed to expose the surface of the n-AlGaN layer;

[0084] (3) Deep etching channels are prepared for the chip by photolithography and ICP etching technology, extending to the sapphire surface, and the chip is divided into independent units;

[0085] (4) The sample is pretreated to obtain the n-AlGaN layer 9 after surface pretreatment; specifically, the atomic adsorption treatment time in PECVD is 10s, and the annealing treatment is 800℃, N2 atmosphere, 30s.

[0086] (5) An n-type ohmic contact metal 10 was prepared on the surface of the pretreated n-AlGaN layer 9 by peeling and then rapidly annealed in a N2 atmosphere at 800°C for 50s.

[0087] (6) A p-type ohmic contact metal 11 was fabricated on the surface of the p-GaN layer 8 by stripping and then rapidly annealed in an O2 atmosphere at 550°C for 300s.

[0088] Effect Test 2:

[0089] The IV characteristic curve of the chip obtained in Example 2 is as follows: Figure 4 As shown.

[0090] As shown in the figure, at 20mA, the operating voltage of this LED chip is only 6.3V, while the operating voltage of the chip without surface pretreatment technology is 8.5V.

[0091] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for reducing the contact resistance of high-Al-content n-AlGaN materials, characterized in that, The n-AlGaN layer was subjected to surface atomic adsorption and subsequent high-temperature annealing under a protective gas atmosphere. The atoms are Si atoms and N atoms; The surface atom adsorption includes: introducing NH3 and SiH4 into the reaction equipment under a protective gas atmosphere, decomposing NH3 and SiH4 by radio frequency plasma, and adsorbing the resulting Si and N atoms onto the surface of the n-AlGaN layer. The introduction time of NH3 and SiH4 is 3~20s; The temperature of the n-AlGaN material is not higher than 200℃; When NH3 and SiH4 are introduced simultaneously, the flow rate ratio of NH3 to SiH4 is 1-10.

2. The method for reducing the contact resistance of high Al content n-AlGaN materials according to claim 1, characterized in that, The power of the radio frequency is 50-200W.

3. The method for reducing the contact resistance of high Al content n-AlGaN materials according to any one of claims 1-2, characterized in that, The subsequent high-temperature annealing conditions are: temperature 500~900℃, processing time 20~60s.

4. The method for reducing the contact resistance of high Al content n-AlGaN materials according to any one of claims 1-2, characterized in that, The annealing conditions are: temperature 750-850℃, processing time 25-40s.

5. The method for reducing the contact resistance of high Al content n-AlGaN materials according to claim 3, characterized in that, The annealing conditions are: temperature 750-850℃, processing time 25-40s.

6. The method for reducing the contact resistance of high Al content n-AlGaN materials according to claim 1, characterized in that, For an n-AlGaN layer with an etching depth of 250-350 nm, the operating conditions for surface atom adsorption are as follows: the introduction time of NH3 and SiH4 is 5-15 s; the flow rate ratio of NH3 to SiH4 is 8-10; and the power of the radio frequency is 80-110 W. The surface atomic adsorption treatment of n-AlGaN material is carried out at a temperature of 140-160℃; the annealing conditions are: temperature 750-850℃, treatment time 25-40s.

7. A method for preparing an n-AlGaN ohmic contact metal, characterized in that, The method includes the steps of etching an n-AlGaN layer and performing a surface pretreatment on it; the surface pretreatment is the method described in any one of claims 1-6.

8. The ohmic contact metal of n-AlGaN obtained by the preparation method of claim 7.

9. A semiconductor optoelectronic device, characterized in that, The ohmic contact metal includes n-AlGaN as described in claim 8.

10. The semiconductor optoelectronic device according to claim 9, characterized in that, The semiconductor optoelectronic device is an AlGaN-based deep ultraviolet LED chip.

Images