TWI229379B - Method and solution for selectively etching III-V semiconductor - Google Patents

Abstract

A method for selectively etching III-V semiconductor is disclosed to etch a GaAs layer on an AlGaAs layer of a semiconductor substrate with high selectivity. Firstly an etching solution is prepared, that comprises citric acid, hydrogen peroxide and water. Volume percent of the hydrogen peroxide is higher than volume percent of the citric acid, and is between 0.2-0.3 times the volume percent of the wafer. Therefore, there is a dominant progress to etch the GaAs layer with high etching selectivity over AlGaAs and lower etching rate.

Description

1229379 V. Description of the invention (1) [Technical field to which the invention belongs] The present invention relates to a method of selective etching of a III-V semiconductor, and particularly to a method in which the aluminum content does not exceed 30%. Method for selectively engraving the gallium layer [◦ aas] on the layer [A 1 G a A s] and its solution. '' [Prior art] III-V semiconductor devices are widely used in pseudomorphic high electron mobility transistors (PHEMT), hetero junction bipolar transistors, HBT], light emitting diodes (LED) and laser devices [laser], and i 丨 丨 -v semiconductor devices can still be improved in the manufacturing process, especially in selective Etching process. • The conventional selective etching methods of II-V semiconductor devices can be divided into selective reactive ion etching in the gas phase and selective wet chemical etching, in which The ion bombardment produced by the phase selective ion etching method will still slightly affect the optoelectronic characteristics of 111-V semiconductor devices, and even cause improper damage. In addition, gas phase selective ion etching equipment such as Gas storage towers, gas_pipes, and ionization chambers are all quite expensive. However, although the selective wet chemical etching method has the advantages of simplicity, low cost, and reduced product damage, there are still many problems to be overcome in actual process operations. When the selective wet chemical etching method is used to remove a 丨 i 丨—V family half

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The god of the conductor device is wrong r Γ »Λ, +., _ A Gallium is the GaAS daily inch. It should be noted that the arsenic button below the primary basal gallium layer cannot be removed. You s seconds Chen She 4 Shen Zai Ming ... * & Y Layer As], it has been determined at present that, = In addition to the comparison of the etched solution of the gallium sand layer on the chemical gallium layer, the etchant of the rolling water on the silk will be more than the phosphoric acid / hydrogen peroxide etchant and ammonia / dibutyl Emulsion etchants have better etch selectivity and flatter etched surface, but only when the aluminum content of the aluminum gallium arsenide layer is higher than 30% can the citric acid / hydrogen peroxide etchant be made.罝 There is an etching selectivity ratio of more than 100, but such a high content changes the electrical characteristics of III-V semiconductor devices and affects the reliability of the devices [please refer to Y. Uenishi, H. Tanaka, and H. Ukita ,

Characterization of AlGaAs microstructure

fabricated by AlGaAs / GaAs micromachining, " IEEE

Trans. Electron Devices, vol. 41, pp. 1778-1783, oct. 1 994, literature], for long-term stability considerations of components, if the aluminum content is less than 23%, this problem can be avoided, but if arsenic is reduced The aluminum content of the gallium layer will be found, and the etch selectivity ratio of the citric acid / hydrogen peroxide etchant will also be severely reduced. In addition, at the current level, the use of citric acid / hydrogen peroxide etchant at an aluminum content of less than 23 For high selectivity below%, for

The etching rate of the gallium gallium layer will be as high as 110 A / sec. [Please refer to E. a Moon, J. J. Lee, and Η. M. Yoo, " Selective wet etching of GaAs on k \ xGa {. XAs for

AlGaAs / InGaAs / AlGaAs pseudomorphic high electron mobility transistor, M.J. Appl. Phys., Vol. 84, pp. 3933-3938, 1 998. Literature], with this high etching rate will be selected

Page 8 1229379 V. Explanation of the invention (3) During selective etching, the gallium arsenide layer [cap 1 ayer] of the III-V semiconductor device will be excessively etched laterally [e X cessive 1 atera 1 etching], resulting in Increasing source resistance and reducing product characteristics'. Therefore, in 1949]. £ 16〇1; 1'〇 (: 116111.8〇〇: · 141 Volume 1082 ~ 1085 published a " "The applications of citric acid / hydrogen peroxide etching solutions in the processing of pseudomorphic MODFETs" document, Mao tried to directly dilute the citric acid / hydrogen peroxide etching solution with DI water to reduce the contact rate of the Shishenhua layer. However, unfortunately, the etching selectivity of the gallium arsenide layer over the aluminum gallium arsenide layer will disappear, and it is impossible to achieve the high selective etching of the gallium arsenide layer on the aluminum gallium arsenide layer.

The accuracy of the gallium recording layer 1: 300 sublayer is used as the etching speed until the arsenic is engraved with [gate Kunhua aluminum chemical etching layer extra [volume is Qian Xuan I] to the stone Xi rate The atomic layer can be formed on the gallium layer ^ ^ to control the depth of the gallium arsenide to make a ratio] to obtain the ammonia layer, and then layered, to determine the arsenization report No. 277 1 45 The "III-V compound semiconductor method" reveals a method for selectively etching the silicon layer, which is based on the aluminum gallium arsenide layer and the arsenic ten silicon atom layer. Ammonia: hydrogen peroxide: water = 2: mixed solution is used to etch the The gallium arsenide layer, and the silicon, the control layer 'the coupling of ammonia / hydrogen peroxide / water will be inhibited and the depth direction will be greatly reduced ^ The mixed solution of water / hydrogen peroxide / water will not excessively dump hydrogen with hydrogen I The gate electrode on the aluminum gallium arsenide layer exposed by the acid / ammonia / hydrogen peroxide / water mixture is that the ammonia / hydrogen peroxide / water mixture does not have significant etching selectivity on the gallium layer.

1229379 V. Description of the invention (4) The method between the Kunhua Shao gallium layer and the gallium arsenide layer, obtained bismuth M life, X 7 original thousand layers is a necessary technology for slave etching and process steps increased, However, the electrical properties of the silicon + screening π: ν material conductor device between the aluminum gallium arsenide layer and the gallium arsenide layer are at the source. To cut the atomic layer, U.S. Patent No. 5,374,328 "METHOD OF FUlUCATIMr =:; = _" reveals another method for selecting an iridium III-V + conductor, which is in a way that the aluminum content is less than 20%. Below the J layer, another thin thin film with a high content [Α1> 25%-] is additionally produced: the stop layer, and the engraving solution contains citric acid, osteoporosis and hydrogen peroxide, and the pH of the solution is controlled. The value is 36, and the etch rate is below 50 A / Sec. [It can be reduced from the third round of the previous case of the patent. The control of the etching selectivity depends on the pH value of the etching solution and the content of the solution. Figure 4 and the detailed description of the pre-patent case found that the aluminum content of the lower thin aluminum gallium arsenide layer has a more significant effect on the etch selectivity. When the aluminum content of the lower thin aluminum gallium arsenide layer is less than 30%, Using the etching solution Qian Tian to etch the selectivity ratio of the upper layer of low aluminum content aluminum gallium arsenide layer cannot exceed 丨 00 above 0 [Content of the invention]

The main purpose of the present invention is to provide a selective etching method for Η 丨 -V semiconductors, in order to use a wet chemical etching technique to selectively etch a semiconductor layer on an aluminum gallium arsenide layer with an aluminum content of less than 30%. The aluminum arsenide layer provides a solution containing citric acid, hydrogen peroxide, and water. The volume percentage of hydrogen peroxide is higher than the volume percentage of citric acid and is between 0.2 and 0. Between 3 times, the process of etching the gallium arsenide layer will reach

1229379… 丨 丨 丨 V. Description of the invention (5) If it exceeds the expected imagination, it is higher than J 〇 above '1 —selectlvity], it is not necessary to use the J selectivity ratio [― the content of the layer, and the narrative rate is not necessary. The system was used early in the lower-level Shishen Chemical Industry for industrial use. ^ Controlled below M A / ^ to select selective etching of 111-V semiconductors according to the present invention. The steps are as follows: firstly, half of the conductors are provided, and ^ plates are included, the semiconductor substrate is Sinochemical aluminum iridium layer and a gallium arsenide layer, in which the aluminum content of the vermiculite φ exo green exhibition does not exceed 30%. Next, the solution of the two gallium layer contains citric acid, The volume percentage of hydrogen peroxide and n Γ is higher than the volume percentage of citric acid by 0.2 times to 0.3 times the volume percentage, so as to achieve a low surname m [<5g A / sec] and high ㈣ selection Sex ratio [&gt; m] ground silver = Shishen 2 gallium layer 'Wherein in a specific embodiment, the volume percentage of the screw plate S of the solution at this moment is not higher than 0.2% of the volume percentage of water A high etch selectivity ratio higher than 100 can be obtained. In another specific embodiment, the volume percentage of citric acid in the etching solution is not more than 0.01 times the volume percentage of water, which can be higher than 20 High etching selectivity ratio above 0. [Embodiment] With reference to the drawings, the present invention will be described by the following embodiments. According to a first specific embodiment of the present invention, please refer to FIG. 1. First, a semiconductor substrate 10 is provided. The semiconductor substrate 10 is capable of providing various types of III-V semiconductor devices, such as a gallium arsenide wafer and includes at least There is a gallium layer 11 and a gallium arsenide layer. The aluminum gallium arsenide layer contains a. Page 11 1229379 V. Description of the invention (6) The amount of inscription is not more than 30%. In this embodiment, In the aluminum gallium arsenide layer, the I-containing amount is 20%. As an example, a group II semiconductor device of pseudomorphic high electron mobility transistor (PHEMT) is used. The pHEMT semiconductor The substrate 10 includes an Auge / ni / au source electrode [s 〇urce] and a drain electrode formed by vapor bonding, and then annealed about 4 2 0 to form an ohmic contact electrode. Next, a plurality of etching solutions are prepared in a conventional manner and a ratioing manner according to the present invention, and are predetermined at the gate.

A position wet chemical etching process is performed to form the gallium arsenide layer 2 for subsequent fabrication of the Ti / Pt / Au gate. At the beginning of preparing each etching solution, first mix pure citric acid and deionized water [DI water] into a 50% citric acid solution in a one-to-one weight ratio, and then mix the appropriate volume ratio of hydrogen peroxide and deionized water. Wet chemical etching at various temperatures with the same proportion of etching solution at normal temperature, and then washed the semiconductor substrate 10 with water to stop the etching. After that, the surface of the etched material was observed using a scanning electron microscopy (SEM). After removing the photoresist layer, the etch depth and surface roughness J RMS [root meari SQUare] can be measured.

Please refer to Fig. 2. The conventional etching solution is prepared by diluting 50% citric acid (hereinafter referred to as citric acid): hydrogen peroxide with a fixed volume ratio of 3: 丨 and directly diluting it with water. Deionization is not added. Before water, an etching rate of 3: 1 citric acid / hydrogen peroxide solution can be used to obtain an etch rate of the gallium arsenide layer, which is 2 A / sec, and that of the aluminum gallium arsenide layer, which is 8%. Human / 56 (: etch rate, its GaAs layer / (human 12%) GaAs layer

1229379 V. Description of the invention (7) A — 'A &quot; · The etching selectivity is 1 · 3 7 5, which is quite low and the etching rate is too high. It can be seen from the figure j that when the amount of water [X] is increased, it can be reduced. 3: 1: X citric acid / hydrogen peroxide / water etching solution on the gallium arsenide layer 丨 2 etch rate to less than 〇A / sec, but the etching rate on the aluminum gallium arsenide layer 丨 丨 is not equal The reduction results in that the etching rate of the aluminum gallium arsenide layer 1 1 is higher than that of the gallium arsenide layer 12, so that the etching selectivity is less than 丨 and there is no characteristic of selective remaining.凊 Refer to Figure 3, fix the citric acid and water of the insect solution at a volume ratio of 3: 150 (that is, the volume percentage of citric acid is not higher than 0.02 times the volume percentage of water), and change the hydrogen peroxide. Mixed amount [γ], the test found that when the amount of hydrogen peroxide is 43 [that is, the volume percentage of hydrogen peroxide is 0.286 times the volume percentage of water, making it between 0, 2 and 0, 3 times the volume percentage of water. Time] will greatly reduce the remaining etch rate of the GaAs layer 11 [less than 1 A / sec], but the etch rate of the GaAs layer 2 will still be 42 · 84 A / sec. The etching rate of GaAs layer 12 is divided by the etching rate of Kunhua AlGa layer 11 to obtain the etching selectivity comparison chart of GaF layer / Shenhua Shao layer. As shown in Figure 4, when the hydrogen peroxide When the dosage is 4 3, the etching selectivity of the gallium arsenide layer / kunhua aluminum gallium layer is as high as 102 as expected, achieving a very high etch selectivity and controlling the contact rate to the kunhua gallium layer 12 at 50 Below A / sec, as shown in the illustration in Figure 4, using this ratio of solution to etch PHEM in 10 minutes After scanning the surface of the T substrate using a scanning electron microscope, it can be found that the etching surface is quite uniform, and the amount of hydrogen peroxide above or below the range cannot achieve such a high etching selectivity. Please refer to Figures 3 and 4 again.

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V. Description of the invention (8)

, 4 J The mixed amount of water [Y] is divided into areas A, B, and C and explained. .Af :, the amount of hydrogen peroxide is between 0 ~ 15. With the increase of the petrochemical time, the aluminum gallium arsenide renewed the rate of palladium etched to the lamella system with the gallium layer 12, "The chemical conversion rate is slightly higher than the fragmentation ^ ^. ΛΛ. a 1 〇 {The use of milk 1 is between I 5 and 4 0. The rate of ㈣ of layer 12 will be faster than that of the material layer. The surname Xuan of ==: 并 has not changed significantly. However, in the area C, when the initial rate is greater than 40, the rate of rhyme engraving of the deified gallium layer 12 decreases sharply, and then returns to slow and low: the range of hydrogen peroxide consumption β, which decreases sharply at the etching rate, The etch rate of the arsenic-gallium layer 12 is lower than n:,: ", and the selectivity is greater than that of the apotheosis. From previous literature studies, in terms of quantity, we understand that hydrogen peroxide system is used as the oxidant, and only the Sr series is used as the reducing agent ^ ± ^ The insoluble alumina generated on the surface of the aluminum gallium arsenide layer 11 will inhibit the etching of the citric acid solution Rate, in order to further analyze the reaction mechanism, the region A is regarded as a citric acid-rich region, the region B is regarded as a reaction equilibrium region, and the c region is regarded as a hydrogen peroxide-rich region. In the C region rich in hydrogen peroxide, the oxidant generates an oxide layer with a sufficient concentration as an etching barrier layer. Because the A1-0 bond is stronger than the -0 bond and the AS-0 bond, and the aluminum oxide [A 丨 2 03] is extremely insoluble. In the etching solution with a low citric acid concentration, a small increase in hydrogen peroxide in the early stage of the C region leads to a significant decrease in the etching rate of the aluminum gallium arsenide layer 1 and a significant etching selectivity. In the reaction equilibrium

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V. Description of the invention (9) B &quot; area, which means that there is an appropriate amount of citric acid to dissolve the oxide formed by hydrogen peroxide. When the oxidation and dissolution reactions in the etching solution are completely balanced, the gallium arsenide layer can be reached. 1 2 The etching rate of the AlGaAs layer is 55.5 A / sec and 52 A / sec, respectively. In the m = region, the etching rate of the gadolinium aluminum gallium arsenide layer 1 1 is slightly higher than the etching rate of the gallium arsenide layer 12. In the region a, the concentration of hydrogen peroxide is quite low, which makes the lack of an oxidant to protect the etched. The citric acid concentration is relatively high enough to easily break the A 1-0, Ga-〇, As-0 bonds. In addition, aluminum is a metal that is extremely easy to be rolled. From a thermochemical point of view, aGt is formed by oxidation. [Gibbs energy change] is greater than gallium oxide [please refer to 〇 · Kubaschewski, C. B. Alcock, and P. J. Spencer,

Materials Thermochemistry, 6th ed: Pergamon, 1993, pp. 6-2 6 · Literature], so the oxidation rate of the tritium gallium layer 11 is greater than the oxidation rate of the gallium oxide layer 12 at the same hydrogen peroxide ratio. The citric acid-rich A region can have a higher etching rate of the aluminum gallium arsenide layer 11. According to the second specific embodiment of the present invention, please refer to FIG. 5. The citric acid and water of the etching solution are fixed at a volume ratio of 2 ·· 250. [That is, the volume percentage of citric acid is about the volume percentage of water. 〇. 〇〇〇 times], and change the mixed amount of hydrogen peroxide [X], the test shows that when the amount of hydrogen peroxide is 6 ~ 65 [that is, the volume percentage of hydrogen peroxide is 0.244 ~ 0 · 26 of the volume percentage of water Times, not more than 0.2 to 0.3 times the volume percentage of water], the etch rate of the aluminum gallium halide layer 11 will be greatly reduced to 0 · 23 ~ 0 · 17 A / sec, but the arsenic The etch rate of the gallium layer 1 · 2 is between

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41 · 6 ~ 43.8 A / sec, the calculation shows that the optimal etching selectivity of the gallium arsenide layer / aluminum gallium arsenide layer is 256 [when χ = 63]. Refer to Fig. 6. Fix the citric acid and water in the etching solution at a volume ratio of 2: 250 and select the volume percentage of hydrogen peroxide to be 0.2 to 0.3 times the volume percentage of water (X = 63). The gallium substrate and the PEGMT semiconductor substrate, the etching depth of the etching solution on the gallium arsenide substrate is linearly proportional to the time, and the PEGMT semiconductor substrate is wet-etched with the etch solution. At this time, after a period of etching time, the etching depth [about 300A] cannot be increased in proportion because the aluminum gallium arsenide layer has been etched. Therefore, the etching solution has a relatively high degree of etching. Selective. Refer to FIG. 7. The pHEMT semiconductor substrate 10 is subjected to wet chemical etching with different etching times using the etching solution, and the semiconductor substrate is etched. The voltage is applied to the source and drain electrodes, and the etching is performed for 10 seconds to 8 minutes. Within time, the etching rate of the aluminum gallium arsenide layer 11 becomes quite slow. Therefore, the current can be controlled at a combined percentage, which makes the etching operation quite simple. The problem of insufficient etching is also shown in the illustration in Fig. 7. The surface of the PHEMT semiconductor substrate 10 after etching is quite flat through SEM observation. Even after 50 minutes of etching time, the roughness is about 1.17. A. The formation of Eli gate can be used in the industry. The scope of protection of the present invention shall be determined by the scope of the appended patent application. 'Anyone skilled in the art and any changes and modifications made without departing from the spirit and scope of the present invention shall fall within the protection scope of the present invention. .

Page 16 1229379 Brief description of the drawings Brief description of the drawings Figure 1: Sectional view of a semiconductor substrate provided by a selective etching method of a 111-V semiconductor according to the present invention; Figure 2: The semiconductor substrate is etched by conventional methods Comparison diagram of the etching rate of the solution as the water content changes; Figure 3: Comparison diagram of the etching rate as the hydrogen peroxide content changes in the first embodiment according to the selective etching method of the Group V semiconductor of the present invention Figure 4 ·· According to the selective etching method for a group v semiconductor according to the present invention, in the first specific embodiment, the engraving of the Kunhua gallium layer and the Kunhua Shao gallium layer with the change of the hydrogen peroxide content Selectivity ratio comparison chart, the illustration of which is a surface view of a PQETM substrate using the sweep electron microscope after etching with a solution with the highest selectivity ratio in the first specific implementation 7 minutes; Figure 5: According to the present invention The selective etching method for m-v semiconductors, in the second specific embodiment, a comparison chart of the etching rate and the ratio of the etching selectivity with the change of the hydrogen peroxide content; Fig. 6: Selective etching method of m-v semiconductors according to the present invention, 'Comparison of etching depth with etching time in the second embodiment; and Fig. 7: III according to the present invention- Selective etching method for ν semiconductors, 'In the second specific embodiment, a comparison diagram of the normal current with the etching time is shown in the second specific embodiment. Highest selectivity ratio solution

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Claims (1)

1229379 VI. Scope of Patent Application --- [Scope of Patent Application] 1. <Selective etching method of II type II semiconductors, including: Providing a semiconductor substrate, the semiconductor substrate is at least 3 aluminum gallium layer and one stone application Gallium layer; and Dagger 3 has an armor pack! = :! Gallium layer, and the solution used to etch the gallium layer includes a plate acid, hydrogen peroxide, and water, where the hydrogen peroxide is higher than the volume percentage of the selected acid and is between the volume percentage of water Between 0.2 and 0.3 times to achieve highly selective etching of the KunF layer. 2. The selective etching method of the mv group semiconductor as described in item 1 of the scope of the patent application, wherein the etching selectivity ratio of the etching solution to the gallium arsenide layer and the gallium layer of Shishenhuaming is higher than 100. . << ^ 3. The selective etching method for a III-V semiconductor as described in item 1 of the scope of the patent application, wherein the etching selectivity ratio of the etching solution to the gallium arsenide layer and the gallium layer of Shishenhuaming is higher At 200. A &quot; 4 The selective remaining method of the group I Π-V semiconductor as described in the first item of the patent application, wherein the aluminum content of the aluminum gallium arsenide layer is not more than 30%. The selective remaining method of the 111-ν semiconductor as described in item 1 of the scope of the patent application, wherein the volume percentage of citric acid in the etching solution is not more than 0.2 times the volume percentage of water. ′ The selective remaining method of the group I-V semiconductor as described in item 1 of the scope of the patent application, wherein the volume percentage of citric acid in the etching solution is not greater than 0.001 times the volume percentage of water. I. The choice of ν family semiconductor as described in item 丨 of the scope of patent application Page 19 1229379 6. The scope of the patent application etching method, wherein the etching solution does not exceed 50 A / sec for the system. Cut-off rate 8. A selective etching solution for III-V semiconductors, such as acid, hydrogen peroxide and water, where the volume of hydrogen peroxide is equal to the volume percentage of acid and is between the volume percentage of water. It is between two layers to achieve a highly selective etching of a gallium arsenide layer. 9. 仏 As described in item 8 of the scope of the patent application, the semiconductor group semiconductor etching = liquid, wherein the etching selectivity ratios of the gallium solution to the pair of gallium layer and the gallium layer of Shishenhua are respectively. Department is higher than 100. ', 10. The selective etching solution for a group ΙΠ-ν semiconductor as described in item 8 of the scope of the patent application, wherein the etching solution has a higher etching selectivity ratio for the gallium arsenide layer and the Kunhuaming gallium layer, respectively. At 2000. η 11. As described in item 8 of the scope of the patent application, the selective surname solution of a group V semiconductor, wherein the volume percentage of the citric acid of the etching solution is not higher than the volume percentage of water. 2 times. 12. The selective etching solution of the III-V semiconductor as described in item 8 of the scope of the patent application, wherein the volume percentage of the citric acid of the etching solution is 0.001 times higher than the volume percentage of water. 1 3. The selective etching solution for the I I I -V semiconductor as described in item 8 of the scope of the patent application, wherein the etching solution has an etching rate of no more than 50 A / sec for the gallium arsenide layer system. Page 20