Preparation method of roughened ITO film layer on surface of LED wafer

Abstract

The present invention provides a method for preparing a roughened ITO film layer on the surface of an LED wafer, comprising the steps of: (1) placing an ITO source 1 in a crucible, and placing an ITO source 2 on the upper surface of the ITO source 1 for use in evaporation; (2) placing the cleaned wafer to be evaporated into the evaporation chamber, and then heating and evacuating; adjusting the cooling water flow rate of the crucible to Q1, waiting for the coating temperature to reach T1, and after the vacuum degree reaches the set value, evaporating the bottom ITO film layer; (3) after completing the above step (2), turning off the heating, cooling the chamber temperature to T2, and adjusting the cooling water flow rate of the crucible to Q2, and then evaporating the roughened ITO film layer. The preparation method of the present invention directly evaporates a rough ITO film layer mainly through the control of the evaporation process to obtain an LED chip with a higher light extraction efficiency. The preparation method of the present invention has a lower cost and an ideal roughening effect, and is suitable for large-scale operation.

Description

Technical Field

[0001] The present invention relates to a method for preparing a roughened ITO film layer on the surface of an LED wafer, belonging to the technical field of semiconductor processing. Background Art

[0002] A light emitting diode (LED) is a semiconductor component that emits light when an electric current is applied, and has many advantages such as small size, environmental protection, long lifespan, energy saving, and high stability, and is widely used. At present, the brightness of LEDs is mainly improved through technical solutions such as roughening the epitaxial layer on the wafer surface, roughening the current spreading layer on the wafer surface, fabricating a reflective electrode, using a high-temperature etching sidewall process, fabricating a metal mirror, and performing stealth dicing. Among them, roughening the current spreading layer on the wafer surface is widely used because it causes no damage to the wafer surface, the current spreading layer is easy to operate, and the equipment cost is low. However, in the actual roughening of the current spreading layer, problems such as incomplete roughening, excessive roughening degree, additional processes added during the roughening process, and unstable roughening often occur, resulting in the failure to achieve the desired brightness improvement. For the current spreading layer, the most ideal state is to form the best ohmic contact while the surface layer can form a rough surface as much as possible to maximize the light extraction in the light emitting area. However, in actual fabrication, it is often difficult to achieve both. To form a good ohmic contact layer, the current spreading layer must have a smooth contact performance, but when the surface is smooth, the reflection will be high.

[0003] Chinese Patent Document CN104064638A discloses a method for roughening an LED transparent conductive layer and a vacuum device, and the method includes: growing an epitaxial layer on a substrate; evaporating a transparent conductive layer on the cleaned epitaxial wafer; evacuating the cavity where the transparent conductive layer is located; heating the cavity at a preset temperature within a preset time, and using the pressure difference between the cavity and a gas cylinder at a preset pressure to introduce the volatile substances of the transparent conductive layer etching solution into the cavity as a carrier gas with nitrogen at a preset carrier gas flow rate to etch the transparent conductive layer. Among them, the volatile substances of the conductive layer etching solution are stored in the gas cylinder, and by safely and controllably roughening the transparent conductive layer, the total reflection of light in the LED can be reduced, and the light extraction efficiency of the LED can be improved. In this invention patent, directly etching and roughening the ITO surface in the cavity is difficult to implement in practice. Generally, the cavity is made of stainless steel for high-temperature resistance reasons, and introducing corrosive substances is extremely likely to corrode the cavity wall, and there are risks in a high-vacuum environment.

[0004] Chinese patent document CN111354843A discloses a preparation method for roughening the ITO surface. The LED includes: an insulating substrate material, an N-type layer, a light-emitting layer, and a P-type layer; a semiconductor thin film and a metal layer are prepared on the P-type layer, and then the thin film layer is subjected to physical annealing treatment to obtain a three-dimensional hexagonal pyramid pattern, achieving the effect of roughening the surface. In this invention, the ITO particles form a specific pattern mainly through a high-temperature annealing process to achieve the roughening effect. However, when using an annealing temperature of 400 - 600 °C, there is uncertainty in verifying this method using different devices, and large-scale operation cannot be achieved. Moreover, the inventor of this invention patent does not give a specific and clear explanation for forming this pattern.

[0005] Chinese patent document CN103904183A discloses a GaN-based LED chip with roughened ITO and its preparation method. This method deposits ITO on the surface of a GaN-based LED epitaxial wafer as a transparent conductive layer; then it is placed in a dilute hydrochloric acid solution for maskless wet etching; after cleaning with deionized water and baking; then a layer of tackifier is coated on the surface; then a positive or negative photoresist is coated, baked on a hot plate, and then ordinary ultraviolet exposure is carried out using a photomask with a micron-sized structure, and it is baked on the hot plate again; the substrate is developed in a developer; after cleaning with deionized water and then placed in an oven for baking; then it is placed in a dilute hydrochloric acid solution for masked wet etching; after removing the photoresist, high-temperature annealing is carried out. This method simultaneously prepares nano-scale and micron-scale roughened ITO structures, and due to the difference in their refractive indices, it has a relatively high light output power. However, the entire preparation process is cumbersome, with low efficiency and high cost.

[0006] Chinese patent document CN102214745A provides a manufacturing method for a gallium nitride-based semiconductor light-emitting device, including the following steps: (1) sequentially growing a GaN buffer layer, an undoped GaN layer, an N-GaN layer, a multi-quantum well layer, and a p-GaN layer on a semiconductor substrate; (2) evaporating an ITO layer on the p-GaN layer and controlling the electron beam evaporation conditions to form a roughened ITO layer. This method forms a roughened ITO layer by controlling the temperature or evaporation rate of ITO evaporation during the evaporation process of the ITO layer. However, this method mainly adjusts the ITO film-forming particles by controlling the chamber temperature, evaporation rate, and oxygen flow rate. The regulation of the size of the ITO film-forming particles by this method is limited, the degree of surface roughening is relatively light, and there are great limitations in improving the light extraction efficiency.

[0007] In view of this, it is necessary to study a process method that can not only form a good ohmic contact but also ensure that the surface of the transparent conductive layer is as rough as possible to improve the light extraction efficiency as much as possible. Summary of the Invention

[0008] In view of the deficiencies of the prior art, the present invention provides a method for preparing a roughened ITO film layer on the surface of an LED wafer. The preparation method of the present invention mainly controls the evaporation process to directly evaporate a rough ITO film layer, so as to obtain an LED chip with higher light extraction efficiency. At the same time, the preparation method of the present invention has low cost and ideal roughening, and is suitable for large-scale operation.

[0009] The technical solution of the present invention is as follows:

[0010] A method for preparing a roughened ITO film layer on the surface of an LED wafer, using the electron beam evaporation method, includes the following steps:

[0011] (1) ITO source preparation: Place the ITO source 1 in the crucible, and place the ITO source 2 on the upper surface of the ITO source 1 for evaporation use.

[0012] (2) Preparation of the bottom ITO film layer: Place the wafer to be evaporated after cleaning into the evaporation chamber, and then heat and evacuate; Adjust the cooling water flow rate of the crucible to Q1. When the coating temperature reaches T1 and the vacuum degree reaches the set value, evaporate the bottom ITO film layer.

[0013] (3) Preparation of the roughened ITO film layer: After step (2) is completed, turn off the heating, cool the chamber temperature to T2, and adjust the cooling water flow rate of the crucible to Q2, and then evaporate the roughened ITO film layer, that is, complete the preparation of the roughened ITO film layer on the surface of the LED wafer.

[0014] According to the present invention, in step (1), the crucible is a commonly used crucible for the electron beam evaporation method, including a vertical section and an inclined section.

[0015] Preferably according to the present invention, in step (1), the shape of the ITO source 1 is cylindrical, which is a commonly used shape of the ITO source in the art; the height of the ITO source 1 is less than or equal to the height of the vertical section of the crucible, and the ITO source 1 contacts the inner wall of the crucible.

[0016] Preferably according to the present invention, in step (1), the shape of the ITO source 2 is concave-shaped, and the opening of the concave shape faces the upper surface of the ITO source 1; the distance between the two sides of the concave shape and the inner wall of the vertical section of the crucible is 1-2 mm; the total amount of the ITO source at the bottom facing the opening of the concave shape is the same as the amount of ITO required for evaporating the bottom ITO film layer; the shape of the ITO source 2 in the present invention is not limited to the inverted concave shape, as long as it can achieve different contact effects, it is protected by the present invention.

[0017] According to the present invention, the amount of ITO of the ITO source 1 facing the opening of the concave shape can meet the amount of ITO required for evaporating the roughened ITO film layer.

[0018] According to the present invention, the purity of the ITO source in step (1) is above 4N grade.

[0019] Preferably according to the present invention, the cleaning method in step (2) is an existing technology in the art. For example, cleaning is performed using acetone and ethanol organic solvents, and then spin-drying is carried out using a spin dryer or drying is performed using hot nitrogen gas.

[0020] Preferably according to the present invention, in step (2), the flow rate Q1 of the crucible cooling water is 2 - 4 L / min, and more preferably 3 L / min.

[0021] Preferably according to the present invention, in step (2), the coating temperature T1 is 330 - 350 °C, and more preferably 340 °C; the set value of the vacuum degree is above 1.0E - 6 Torr.

[0022] Preferably according to the present invention, in step (2), the thickness of the bottom ITO film layer is 30 - 100 Å, and more preferably 50 Å.

[0023] Preferably according to the present invention, in step (2), oxygen needs to be introduced for evaporation during the evaporation of ITO. The purity of the oxygen used is greater than or equal to 99.999% to ensure the purity and use safety of oxygen; the oxygen flow rate is 3 - 20 sccm.

[0024] Preferably according to the present invention, in step (3), the cavity temperature T2 is 80 - 100 °C.

[0025] Preferably according to the present invention, in step (3), the flow rate Q2 of the crucible cooling water is 8 - 10 L / min, and more preferably 9 L / min.

[0026] Preferably according to the present invention, in step (3), the thickness of the roughened ITO film layer is above 600 Å; more preferably, the thickness of the roughened ITO film layer is 600 - 4000 Å.

[0027] Preferably according to the present invention, in step (3), oxygen needs to be introduced for evaporation during the evaporation of ITO. The purity of the oxygen used is greater than or equal to 99.999% to ensure the purity and use safety of oxygen; the oxygen flow rate is 3 - 20 sccm.

[0028] According to the present invention, after completing the above step (3), the P-side electrode is fabricated on the front side of the wafer. After the substrate is thinned, the N-side electrode is fabricated on the N side, and the N-side electrode and the ITO film layer are subjected to high-temperature alloying treatment. Then, the wafer is diced into individual die, thus completing the fabrication of the LED die with a roughened ITO film layer. Among them, the purity of the metal materials used for fabricating the P and N electrodes is above 5N grade. Conventional electrode structures can be used, and the preparation methods of the N-side electrode and the P-side electrode are conventional methods in the art. The temperature for the simultaneous high-temperature alloying treatment of the N-side electrode and the ITO is 340 - 380°C, and more preferably 360 - 370°C.

[0029] The technical features and beneficial effects of the present invention are as follows:

[0030] 1. In the present invention, two layers of ITO film layers are evaporated on the wafer surface. The bottom ITO film layer (i.e., the ohmic contact layer) is obtained by evaporation under high-temperature conditions, and during the evaporation process, the cooling effect of the crucible is minimized by controlling the flow rate of the crucible cooling water. Only a partial area of the ITO source 2 is indirectly in contact with the crucible wall through the ITO source 1, and the ITO source 2 is not directly in contact with the crucible. In this way, after the electron beam hits the ITO source 2, the ITO particles have higher kinetic energy and activation energy in a relatively high-temperature atmosphere, and the film-forming quality is denser, capable of forming the most ideal ohmic contact layer, that is, the bottom ITO film layer. The top ITO film layer (roughening layer) is obtained by evaporation at a relatively low temperature, and during the evaporation process, the temperature near the ITO source 1 is relatively low when the flow rate of the crucible cooling water is relatively large, and the ITO source 1 retains the largest contact area with the crucible wall. The ITO particles aggregate into relatively large particle clusters, forming a roughened surface on the wafer surface. Compared with the conventional method of controlling the surface roughness of the ITO film by generally controlling the cavity temperature below 300°C, the present invention mainly directly regulates the size of the ITO particles by regulating the temperature near the surface of the ITO source. The melting temperature near the surface of the ITO source generally needs to be above 1500°C. By directly regulating the temperature around the ITO source to form particles with controllable sizes, the roughening degree of the ITO film layer can be regulated to a greater extent.

[0031] 2. Different-shaped ITO sources are used in the present invention to deposit different ITO film layers. Among them, the ITO source 2 has a special concave shape. The advantage of using the ITO source 2 with a special concave shape is that it can ensure that while the bottom ITO film layer is formed, exactly the concave bottom part of the ITO source 2 can be used up. After the concave bottom part is used up, the electron beam hits the surface of the ITO source 1, and at this time, the deposition of the top ITO film layer just starts. The amount of ITO in the concave bottom part is specifically adjusted according to the thickness of the bottom ITO film layer to be deposited and the density of the ITO source, which is a conventional adjustment and will not be described additionally. Moreover, the design of this special ITO pattern can ensure that after the bottom part of the ITO source 2 is deposited, due to the support on both sides, the source will not tilt, ensuring the normal use of the subsequent ITO source 1. In the present invention, the design of using two different-shaped ITO sources and adjusting the flow rate of the cooling water on the side wall of the crucible makes the cooling effects of the two ITO sources different, so different ITO film layers are obtained.

[0032] 3. By regulating the shape of different ITO sources, the flow rate of the cooling water on the side wall of the crucible during evaporation, and the film thickness, the present invention realizes the roughening of the ITO film layer and improves the brightness of the LED. The method of the present invention is simple and easy to implement throughout the process. The roughening process of the ITO surface is achieved only through the evaporation method, avoiding the use of corrosive chemicals, and is suitable for the roughening manufacturing process of the transparent conductive film layer on the surface of all LED wafers, and is applicable to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic diagram of the crucible structure;

[0034] Figure 2 is a schematic diagram of the crucible with the ITO source;

[0035] Figure 3 is a microscope photo of the rough ITO surface after the evaporation in Example 1;

[0036] Among them, 001 is the crucible, 002 is the ITO source 1, and 003 is the ITO source 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The present invention will be further defined and described below in conjunction with the accompanying drawings of the specification and the embodiments, but not limited thereto.

[0038] Meanwhile, the experimental methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials, unless otherwise specified, can all be obtained from commercial channels.

[0039] The model of the electron beam evaporation platform used in the embodiments is FU-20PEB-ITO.

[0040] Example 1

[0041] A method for preparing a roughened ITO film layer on the surface of an LED wafer, comprising the following steps:

[0042] (1) ITO source preparation: Place the cylindrical ITO source 1 into the crucible (the schematic structural diagram of the crucible is as shown, including a vertical section and an inclined section). The height of the ITO source 1 is 2 mm lower than the height of the vertical section of the crucible, and the ITO source 1 contacts the inner wall of the crucible. Place the concave-shaped ITO source 2 above the ITO source 1. The opening of the concave shape faces the upper surface of the ITO source 1. The distance between the two sides of the concave shape and the inner wall of the vertical section of the crucible is 1 mm. The thickness of the bottom of the concave shape is 3 mm. The total amount of the ITO source at the bottom facing the opening of the concave shape is the same as the amount of ITO required for depositing the bottom ITO film layer. The width of each side of the concave shape is 3 mm. The amount of the ITO source 1 facing the opening of the concave shape is the same as the amount of ITO required for depositing the roughened ITO film layer, and it is ready for evaporation coating. The purity of the ITO source 1 and the ITO source 2 is 4N. The schematic diagram of the crucible equipped with the ITO source is as shown Figure 1 shown. Figure 2 as shown.

[0043] (2) Preparation of the bottom ITO film layer: Place the wafer to be evaporated coated, which has been cleaned, into the evaporation chamber, and then heat and evacuate. Adjust the cooling water flow rate of the crucible to 3 L / min. After the coating temperature reaches 340 °C and the vacuum degree reaches 1.0E-6 Torr, deposit the bottom ITO film layer under the condition that the oxygen flow rate is 5 sccm. The thickness of the bottom ITO film layer is 50 Å. The purity of oxygen is 99.999%.

[0044] (3) Preparation of the roughened ITO film layer: After step (2) is completed, turn off the heating, cool the chamber temperature to 100 °C, adjust the cooling water flow rate of the crucible to 9 L / min, and then deposit the roughened ITO film layer under the condition that the oxygen flow rate is 10 sccm. The thickness of the roughened ITO film layer is 600 Å. The purity of oxygen is 99.999%. The microscope photo of the ITO rough surface obtained after evaporation coating is as shown Figure 3 shown.

[0045] (4) Chip structure fabrication: After completing the above step (3), fabricate the P-side electrode on the front side of the wafer. After thinning the substrate, fabricate the N-side electrode on the N side, and perform high-temperature alloy treatment on the N-side electrode and the ITO film layer at a temperature of 365 °C for 7 min. Then cut the wafer into individual chips to obtain the LED chips with roughened ITO film layers. The purity of the metal materials used for fabricating the P and N electrodes is 5N grade.

[0046] Example 2

[0047] A method for preparing a roughened ITO film layer on the surface of an LED wafer is as described in Example 1, except that: in step (3), the flow rate of the crucible cooling water is adjusted to 8 L / min.

[0048] Example 3

[0049] A method for preparing a roughened ITO film layer on the surface of an LED wafer is as described in Example 1, except that: in step (3), the flow rate of the crucible cooling water is adjusted to 10 L / min.

[0050] Comparative Example 1

[0051] A method for preparing a roughened ITO film layer on the surface of an LED wafer is as described in Example 1, except that: in step (3), the flow rate of the crucible cooling water is adjusted to 4 L / min.

[0052] Test Example 1

[0053] According to the methods described in Examples 1-3 and Comparative Example 1, gallium arsenide-based LED wafers with a size of 5.5 mil * 5.5 mil are prepared, and then the wafers are cut into individual die, and the brightness of each die is tested. The results are shown in Table 1.

[0054] Table 1 Brightness of the die prepared by the methods described in Examples 1-3 and Comparative Example 1

[0055] sample LOP1 luminance / mcd Example 1 225-245 Example 2 230-250 Example 3 240-260 Example 4 180-190

[0056] As can be seen from the above table, the brightness of the LED die with a rough ITO film layer prepared by the method of the present invention is significantly higher than that of the comparative example. Therefore, the method of the present invention can obtain an LED die with a higher light extraction efficiency, and the preparation method of the present invention has a lower cost, an ideal roughening effect, and is suitable for large-scale operation.

Claims

1. A method for preparing a roughened ITO film layer on the surface of an LED wafer, using the electron beam evaporation method, including the following steps: (1) ITO source preparation: Place the ITO source 1 into the crucible, and place the ITO source 2 on the upper surface of the ITO source 1 for use in evaporation; the ITO source 1 is cylindrical in shape, the height of the ITO source 1 is less than or equal to the height of the vertical section of the crucible, and the ITO source 1 is in contact with the inner wall of the crucible; the ITO source 2 is in the shape of a concave character, and the opening of the concave character is opposite to the upper surface of the ITO source 1; the distance between the two sides of the concave character and the inner wall of the vertical section of the crucible is 1-2 mm; the total amount of the ITO source at the bottom opposite to the opening of the concave character is the same as the amount of ITO required for evaporating the bottom ITO film layer; (2) Preparation of the bottom ITO film layer: Place the wafer to be evaporated after cleaning into the evaporation chamber, and then heat and evacuate; Adjust the cooling water flow rate of the crucible to Q1, and when the coating temperature reaches T1 and the vacuum degree reaches the set value, evaporate the bottom ITO film layer; the cooling water flow rate Q1 of the crucible is 2-4 L / min, and the coating temperature T1 is 330-350 °C; (3) Preparation of the roughened ITO film layer: After step (2) is completed, turn off the heating, cool the chamber temperature to T2, and after adjusting the cooling water flow rate of the crucible to Q2, evaporate the roughened ITO film layer, that is, complete the preparation of the roughened ITO film layer on the surface of the LED wafer; the T2 is 80-100 °C, and the cooling water flow rate Q2 of the crucible is 8-10 L / min.

2. The preparation method of the roughened ITO film layer on the surface of the LED wafer according to claim 1, characterized in that In step (2), the cooling water flow rate Q1 of the crucible is 3 L / min.

3. The preparation method of the roughened ITO film layer on the surface of the LED wafer according to claim 1, characterized in that, In step (2), the coating temperature T1 is 340 °C; the set value of the vacuum degree is above 1.0E-6 Torr.

4. The preparation method of the roughened ITO film layer on the surface of the LED wafer according to claim 1, characterized in that, The thickness of the bottom ITO film layer in step (2) is 30-100 Å.

5. The preparation method of the roughened ITO film layer on the surface of the LED wafer according to claim 1, wherein, The thickness of the bottom ITO film layer in step (2) is 50 Å.

6. The preparation method of the roughened ITO film layer on the surface of the LED wafer according to claim 1, characterized in that, When evaporating ITO in step (2), oxygen needs to be introduced for evaporation, and the oxygen flow rate is 3-20 sccm.

7. The preparation method of the roughened ITO film layer on the surface of the LED wafer according to claim 1, characterized in that, In step (3), the cooling water flow rate Q2 of the crucible is 9 L / min.

8. The preparation method of the roughened ITO film layer on the surface of the LED wafer according to claim 1, characterized in that, The thickness of the roughened ITO film layer in step (3) is above 600 Å.

9. The preparation method of the roughened ITO film layer on the surface of the LED wafer according to claim 1, characterized in that, The thickness of the roughened ITO film layer in step (3) is 600-4000 Å.

10. The preparation method of the roughened ITO film layer on the surface of the LED wafer according to claim 1, wherein, When evaporating ITO in step (3), oxygen needs to be introduced for evaporation, and the oxygen flow rate is 3-20 sccm.

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