TW200529309A - 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 a 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

200529309 V. Description of the invention α) [Technical field to which the invention belongs] The present invention relates to a selective etching method for 11 I-V semiconductors, and particularly relates to an aluminum arsenide having an aluminum content of not more than 30% Method for selectively etching a gallium arsenide layer [GaAs] on a gallium layer [AlGaAs] and a solution used therefor. ^ [Prior art] The III-V semiconductor device system can be widely used in pseudomorphic high electron mobility transistors (PHEMT), heterojunction bipolar transistor [heterojunctioon bipolar transistors, ΗβΤ], light emitting diodes (LEDs), and lasers (lasers) and other products, while the i nV semiconductor devices can still be improved in the process, especially in the selective etching process. 2. Provincial selective etching methods for 1 1 1 _ V group semiconductor devices can be divided into selective reactive ion etching (gas phase selective etching) and selective wet chemical etching (seUctive wet chemical etching). The ion bombardment (i on bombardment) generated in the phase selective ion etching method will still slightly affect the optoelectronic characteristics of III-V semiconductor devices, and even cause damage. In addition, Gas storage towers, gas delivery tubes, and ionization reaction 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 operation. When the selective wet chemical etching method is used to remove a 丨 丨 丨-v family half

200529309 V. Description of the invention (2) ----- When the gallium arsenide layer [GaAs] of the conductor device, it should be noted that the aluminum gallium arsenide layer [A1GaAs] under the gallium-enhanced layer cannot be removed. In comparison, the etching solution for removing the gallium arsenide layer on the aluminum gallium arsenide layer has a better etching option than the phosphoric acid / hydrogen peroxide etchant and the ammonia / hydrogen peroxide etchant. [Etching selectivity] and a flatter etching surface, but only when the aluminum content of the aluminum gallium arsenide layer is higher than 30% can the citric acid / hydrogen peroxide etchant have a selectivity ratio of 100 or more, but so high However, the content of aluminum oxide has changed the electrical characteristics of III-V semiconductor devices and affected the reliability of the devices. [Please refer to Y · Uenishi, H. Tanaka, and H. Ukita, 11 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, if the aluminum content is less than 23%, this problem can be avoided. However, if the aluminum content of the gallium layer of Shishenhua Ming is reduced, the citric acid / hydrogen peroxide balance will be found. The etching selectivity ratio of the etching solution will also be severely reduced. In addition, at the current level of etching, the use of citric acid / hydrogen peroxide etching solution with an aluminum content of less than 23% is required to achieve high selectivity. The engraving rate 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 AlxGa ^ _ xAs for AlGaAs / InGaAs / AlGaAs pseudomorphic high electron mobility transistor, n J. Appl. Phys., vol. 84, pp. 3933-3938, 1 998. Literature].

Page 8 200529309 V. Description of the invention (3) During selective etching, the gallium arsenide layer (cap layer) of the 111-V semiconductor device will be excessively laterally etched, resulting in increased source resistance [Source resistance] and reducing product characteristics, therefore, in 1994, J. Electrochem · Soc. 141, pp. 1082-1085, Mao published an article entitled "The applications of citric acid / hydrogen peroxide etching solutions in the processing of pseudomorphic MODFETs Literature, Mao tried to directly dilute the citric acid / hydrogen peroxide solution with deionized water [β I wa t er] to reduce the

The etch rate of the GaAs layer, but unfortunately, the etch selectivity of the GaAs layer over the AlGaAs layer will disappear, and it is impossible to achieve a highly selective GaAs layer etched on the AlGaAs layer. The exact chemical chemistry of the People ’s Republic of China on the gallium layer is between 1: 300 [the bulk layer is etched to the rate of engraving to the money, to the Kunhua I Lu Yu engraving the Shi Xiyuan [gate], arsenization Aluminium gallium layer national patent engraved controlled arsenide production ratio] engraving depth of silicon atoms makes the recording layer, sub-layer, can be determined arsenic

Public Tongue No. U7145 "Method of in-v compound semiconducting f =" reveals a method for selective etching of the gallium layer, which is based on the aluminum gallium arsenide layer and the arsenic-silicon atom layer, using ammonia: hydrogen peroxide: water = 2 mixed solution etches the gallium arsenide layer, and the silicon layer 'the ammonia / hydrogen peroxide / water mixture lL9 is suppressed and the depth direction is greatly reduced, and then the mixed solution of water and water is not excessively etched in the exposure Shi Shihua's aluminum boring fire is a well-established ^ inscription layer made of gate polarization ΪΓ water / hydrogen peroxide / water mixture does not have significant etching selectivity, 200529309

The silicon atomic layer between the aluminum gallium arsenide layer and the gallium arsenide layer is a necessary technical means to increase the etching and process steps. However, the aluminum gallium arsenide layer and the gallium arsenide layer under the source and drain electrodes are increased. The silicon atomic layer still exists between the layers, which affects the electrical functions of the III-V semiconductor device.

U.S. Patent No. 5,374,328, "METHOD OF FABRICATING GROUP III-V COMPOUND" discloses another method for selectively etching a gallium arsenide-containing in-v semiconductor by using aluminum arsenide with an aluminum content of less than 20%. Under the gallium layer, another thin aluminum gallium arsenide layer with a high aluminum content [A1> 25%] is additionally prepared as an etching stop layer, and the etching solution contains citric acid, citrate and hydrogen peroxide, and the pH value of the solution is controlled. Between 3 ~ 6, the etching rate can be reduced to less than 50 A / sec [It can be known from Figure 3 of the pre-patent of this patent ^, the control of the etching selectivity depends on the pH value of the etching solution and the solution contains 1, but Figure 4 and the detailed description of the previous case of the patent found that the aluminum content of the lower thin aluminum gallium arsenide layer has a more significant effect on the etching selectivity. When the aluminum content of the lower thin aluminum gallium arsenide layer is less than 30% At this time, the selectivity ratio of the upper aluminum low-aluminum gallium arsenide layer etched by the etching solution cannot exceed 丨 00 or more. [Summary of the Invention]

The main purpose of the present invention is to provide a selective etching method for ιη-ν semiconductors, in order to etch arsenic on an aluminum gallium arsenide layer with an aluminum content of less than 30% by a wet chemical etching technique. Aluminum oxide layer, the provided etching solution contains citric acid, hydrogen peroxide and water, wherein the volume percentage of hydrogen peroxide is higher than the volume percentage of citric acid and is between 0 · 2 ~ 0 · 3 times the volume percentage of water , The process of etching the gallium arsenide layer will reach

200529309 V. Description of the invention (5)-:-To the high etching selectivity ratio [high etching selectivity] which is higher than 100 than expected, it is not necessary to simply increase the aluminum content of the lower Al-GaN layer and the etching rate Can be controlled below 50A / sec for industrial use. The selective etching method for a III-V semiconductor according to the present invention includes the steps of: first providing a semiconductor substrate, the semiconductor substrate system including at least an aluminum gallium arsenide layer and a gallium arsenide layer, wherein the arsenide The aluminum content of the aluminum gallium layer is not more than 30%. Next, the gallium arsenide layer is wet-etched, and the solution used to etch the gallium arsenide layer contains citric acid, hydrogen peroxide and water. It is higher than the volume percentage of citric acid and it is between 0.2 and 0.3 times the volume percentage of water to achieve low etching, and the ratio [< 50 A / sec] to high etching selectivity ratio [ η 〇〇〕 Etch = shoulder gallium arsenide layer, in a specific embodiment, the etching solution of the screw = 驮 = volume percentage is not higher than the volume percentage of water 0.02 times, can be moved to the south A high etching selectivity ratio above 1000, in another specific embodiment, the volume percentage of citric acid in the ^ 4 solution is not higher than 0.001 times the volume ratio of water to 100 knives. High etch selectivity ratio above 2000. [Embodiment] With reference to the drawings, the present invention will be described by the following embodiments. For a first specific embodiment according to 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 Group V semiconductor devices, such as a gallium arsenide wafer. And contains at least a chemical link recording layer 11 and a gallium arsenide layer 2, wherein the aluminum gallium arsenide layer

200529309 V. Description of the invention (6) The amount of inscription is not more than 30% 'In this embodiment, the aluminum content of the aluminum gallium arsenide layer is 20%, and the pseudo-type high-speed electron mobile transistor Cpseudomorphic High electron mobility transistor (PHEMT) II group IV semiconductor device is exemplified. The pHEMT semiconductor substrate 10 includes an AuGe / Ni / Au source [source] and a drain [drain] formed by evaporation, and then An ohmic contact electrode is formed after annealing at about 420 ° C. Next, a plurality of etching solutions are prepared in a conventional manner and a ratioing manner according to the present invention, and the gallium arsenide layer is wet-etched at a predetermined formation position of the gate electrode 2 for subsequent Ti / Pt / Au Gate production. When preparing each etching solution, first mix pure citric acid and DI water in a 1: 1 weight ratio to form a 50% citric acid solution, and then mix the appropriate volume ratio of hydrogen peroxide and deionized water. Then, perform wet chemical etching at various temperatures with etching solutions at different temperatures, and then wash the semiconductor substrate 10 with water, and then stop the etching. After that, use a scanning electron microscopy (SEM) to observe the etching object Negative surface, and can measure the etching depth and surface roughness after removing the photoresist layer = root mean square value 1 ^ 3 [1 ^ (^ 1116 & 113 (11181 ^].), Ming, read the second figure, and know The etching solution is prepared by diluting 50% citric acid with dihydrochloric acid]. The hydrogen peroxide solution is diluted at a fixed volume ratio of 3 ·· 1, and before the addition of deionized water, the ratio is 3: 1. The citrate / double emulsion etching solution can be used to obtain a ηη = ㈣ rate for the gallium arsenide layer 12 and an etch rate of 80 c for the material dysprosium layer 11. The gallium arsenide layer / ( A1 20%) 200529309 of AlGaAs layer

The etching selectivity is 1 · 3 7 5 and it is quite low and the etching rate is too high. As can be seen from the drawing, when the water amount [X] is increased, the ratio of 3: 1: X citric acid / hydrogen peroxide / water can be reduced. The solution engraving rate of the gallium arsenide layer 12 is below 10 / sec, but the remaining engraving rate of the gallium arsenide layer 11 does not decrease proportionally, resulting in the On the contrary, the etching rate is greater than the engraving rate of the deified chain layer 12, so that the selectivity of the last name is less than 1, and there is no characteristic of selective etching at all. ^ Please refer to Figure 3, fix the citric acid and water of the engraved 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 mixing of hydrogen peroxide. Dosage [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 ~ 0 · 3 times the volume percentage of water 〕 Will greatly reduce the remaining engraving rate [1 A / sec] of the gallium layer 11; however, the engraving rate of the gallium arsenide layer 12 is still 42.84 A / sec. The etch rate of the gallium layer 12 is divided by the etch rate of the Shishenhua aluminum gallium layer 11 to obtain a comparison chart of the etch selectivity of the gallium arsenide layer / shenhua shao layer. As shown in Figure 4, when the amount of hydrogen peroxide is between At 4 o'clock, the etching selectivity of the gallium arsenide layer / aluminum gallium arsenide layer is beyond the imagination. The local selectivity is as high as 10 2 ′, which achieves a very high etch selectivity and can control the #etch rate of the Shishen gallium layer 12 Below 50 A / sec, as shown in the illustration in Figure 4, using this ratio of solution to etch in 10 minutes After scanning the surface of the pHEMT 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 for the hydrogen peroxide

Page 13 200529309

Mixed with water, the amount [Υ] is divided into A, B ,. In the eight regions, the amount of hydrogen peroxide is between 0 and 5, and the remaining hydrogen peroxide is increased. The etching rate of the gallium arsenide layer 12 and the etching rate of the aluminum gallium arsenide layer are the same day. ^ The rate of the engraving of the Shishenhua I Lu Ga layer ii is slightly higher than the rate of the engraving of the Shishen Hua gallium layer 12, so the choice of Shishenhua gallium layer / Shishenhua Sha gallium layer The sexual system is about 0.85. In area B, the amount of hydrogen peroxide is between 15 and 40. The etching rate of the gallium arsenide layer 12 will exceed the etching rate of the aluminum gallium arsenide layer u, but there is no significant change between the two. However, in the area of c, when the use of hydrogen peroxide is larger than 40, the etching rate of the gallium arsenide layer 2 and the etching rate of the aluminum gallium arsenide layer 11 decrease sharply, and then return to a slow decrease. Within the range of hydrogen peroxide consumption where the etching rate is rapidly reduced, the decrease rate of the etching rate of the aluminum gallium arsenide layer 1 1 is significantly larger than the decrease rate of the etching rate of the gallium arsenide layer 12. The difference can produce a high etch selectivity greater than 100. According to previous literature studies, in the content of f etching solution, it can be understood that hydrogen peroxide system is used as oxidant and citric acid is used as reducing agent. Insoluble oxides formed on the surface of the aluminum gallium arsenide layer will inhibit the citric acid solution. In order to further analyze the reaction rate of the etching rate, the region A is regarded as a citric acid-rich region, the region B is regarded as a reaction equilibrium region, and the region c is regarded as a hydrogen peroxide-rich region.

In the c region rich in hydrogen peroxide, the oxidant generates a sufficient concentration of the oxide layer as the remaining barrier layer, because the A1-0 bond is stronger than the (^ -〇 bond and the As -〇 bond and the oxide [AI 〇3] is extremely insoluble. It is an etching solution with a low citric acid concentration. Therefore, a small increase in hydrogen peroxide in the early stage of the C region results in a significant decrease in the etching rate of the aluminum gallium arsenide layer and a significant etching selectivity.

Page 14 200529309 V. Description of the invention (9) Area B indicates that there is an appropriate amount of citric acid which dissolves the oxide formed by hydrogen peroxide. When the oxidation and dissolution reactions in the etching solution are completely balanced, the gallium arsenide can be reached. The etch rate of layer 12 and the aluminum gallium arsenide layer is maximum

[55.5 A / sec and 52 A / sec, respectively]. In the citric acid-rich area A, the etching rate of the Kunhua Shao Gallium layer 11 is slightly higher than the etching rate of the GaAs layer 12. In the area A, the hydrogen peroxide concentration is quite low, which makes the lack of oxidants to protect Faceted by neodymium, and the citric acid concentration is relatively high enough to easily break the A0, Ga-0, As-0 bonds. In addition, aluminum is a metal that is extremely susceptible to oxidation. From a thermochemical point of view, the Λ (; τ.) Of alumina formation is larger than gallium oxide. [Please refer to Kubaschewski, CB Alcock, and PJ Spencer, Materials Thermochemistry, 6th ed: Pergamon, 1993, PP · 6 2 6 · Literature] 'Therefore, the oxidation rate of the aluminum gallium arsenide layer 11 is greater than the oxidation rate of the gallium oxide layer 2 at the same hydrogen peroxide ratio. The acid-rich A region can have a higher etching rate of the aluminum gallium arsenide layer. According to the second specific embodiment of the present invention, please refer to FIG. 5 to fix the etched citric acid and water. The volume ratio of 2:25 (the volume fraction of citric acid is about 0.008 times the volume percentage of water), and the mixed amount of hydrogen peroxide [X] is changed. The test shows that when the amount of hydrogen peroxide is between 6 1 ~ 65 o'clock [that is, the volume percentage of hydrogen peroxide is 244 to 0.26 times the volume percentage of water, not exceeding 0.2 to 3 times the volume percentage of water] 'The Kunhua boat gallium layer The etch rate of 11 will be greatly reduced to (K23 ~ 0 · 17 A / sec, but the etching rate of the GaAs layer 12 is between

Page 15 200529309 V. Description of the invention (10) 41 · 6 ~ 43 · 8 A / sec 'calculation shows that the best etch selectivity of the arsenide layer / arsenide layer is as follows: For 256 (when χ = 63), the coating layer / aluminum chloride is shown in Figure 6 '

250 volume ratio and select the hydrogen peroxide of one hundred eighty ^^ ,, 疋 隹 Z eight μ · β ί) 9 nq π v integral ratio is 0.2 ~ 0.3 times of the volume percentage of water [X = fn 1, eight PHFMT ^ Λ tein knife does not etch a gallium arsenide substrate and the FHL · M 1 semiconductor substrate 1 0, the surname Xuan 丨 丨, right, heir, and the company * etched to the %%, and the night / night to the The etching glaciality of Shishenhua's gallium substrate is linearly related to the 彳 π wind Μ d with the etching time, and when the etching solution is wet-chemically etched, the P Η Μ Μ semiconductor is etched; 1 nd ^ When the 1000-conductor storm plate is 10, in a period of etching time, the aluminum gallium arsenide and "its etching depth [approximately 300 liters, ϋ liters] have been etched, so the etching solution has a high degree of engraving. Selectivity. Please refer to Section 7®, using this solution to perform wet chemical chemistry on the EMT semiconductor substrate 10 at different engraving times. For the remaining semiconductor substrates, apply voltage to the source and drain. Due to the etching time of 10 seconds to 8 minutes, the etching rate in the AlGaAs layer 1 becomes quite slow. Therefore, the electrical μ can be controlled to a qualified percentage, making the money engraving operation quite simple, and there will be no problems of over-etching or under-etching. In addition, the illustration in FIG. 7 shows that the PEMT semiconductor substrate 10 is being etched. The subsequent surface was observed to be quite flat by SEM observation, and even after 50 minutes of etching time, the roughness was about 1.17 Α, which was used in the industry of the gate shape. The scope of the attached application patent shall prevail, and any changes and modifications made by those skilled in the art without departing from the spirit and scope of the present invention shall fall within the protection scope of the present invention. Page 16 200529309

[Schematic description] Figure 1: Cross-sectional view of the semiconductor substrate provided according to the family semiconductor selective method of the present invention; 〆 Figure 2 Figure 1 The etching rate of the semiconductor substrate with the conventional solution etched with water content Comparison diagram; Figure 3: Selectivity of III-v semiconductors according to the present invention-a comparison diagram of the etching rate as the hydrogen peroxide contains I in a specific embodiment; Figure 4: Selectivity of m-v semiconductors according to the present invention Etched in the first place: the specific embodiment with the change of hydrogen peroxide content; the remaining selectivity ratio of the remaining layer and the gallium layer is compared, the illustration shows the use of the PHEET substrate in the first embodiment Surface view of the selective ratio solution after etching for 10 minutes using a concealed electron microscope; Figure 5: Selective etching method for m-v group semiconductors according to the present invention 'follows in the second embodiment Comparison chart of etching rate and ratio of etching selectivity with changes in hydrogen peroxide content; Figure 6: Selective etching method of In-V group semiconductor according to the present invention 'in the second embodiment Comparison of etching depth over time with etching time; and FIG. 7 · Selective etching method of group II 丨 -v semiconductors according to the present invention ' Current comparison chart, the illustration of which has the highest selectivity ratio solution in the second embodiment after the PHEMT substrate is etched in 50 minutes 200529309

Claims (1)

200529309 [Scope of patent application] 1, 2: 11: Selective etching method of group semiconductors, including: Aluminum gallium diconducting hafnium substrate 'The semiconductor substrate includes at least-an aluminum iridium layer and a gallium arsenide layer; and a solution system for covering the gallium arsenide layer, for etching the gallium arsenide layer. Higher than hydrogen, hydrogen peroxide and water, the volume percentage of hydrogen peroxide n9n, the volume percentage of osmic acid and between υ · ζ times the volume percentage of water, to achieve highly selective etching of the gallium arsenide layer. As described in item 1 of the patent claim, the choice of group iii-v semiconductors I * is based on the method of engraving the last name ', wherein the etching selectivity ratio of the engraved solution to the gallium halide layer and the gallium layer of Shishenhua is higher. At 100. 3. The selective money engraving method for In-V semiconductors as described in item 1 of the scope of the patent application, wherein the etching selectivity ratios of the etching solution to the gallium arsenide layer and the gallium layer of Shishenhua are respectively high. At 200. 2. The selective leaving method of the I Π-V semiconductor as described in item 1 of the scope of patent application, wherein the aluminum content of the aluminum gallium arsenide layer does not exceed 30/0. 5. The selective money engraving method for a III-V semiconductor as described in item i of the scope of the patent application, wherein the volume percentage of citric acid in the etching solution is not greater than 0.02 times the volume percentage of water. 6. The selective remaining method of the 111-V group 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 0.01 times the volume percentage of water. 7. Selection of 1 1 1 —v semiconductor as described in item i of the scope of patent application 200529309 6. Scope of applying for patent. The method of etch, wherein the etching rate of the etching solution to the gallium arsenide layer does not exceed 50 A / sec. 8. A selective etching solution for group II I-V semiconductors, including citric acid, hydrogen peroxide, and water, wherein the volume percentage of hydrogen peroxide is higher than the volume percentage of citric acid and is between 0.2% and 2% by volume of water. 0.3 times' to achieve highly selective etching of a gallium arsenide layer. 9. The selective etching solution for a III-V semiconductor as described in item 8 of the scope of the patent application, wherein the etching selectivity ratios of the etching solution for the gallium arsenide layer and the reading stone Shenhua Sha gallium layer are respectively higher. At 丨 〇〇. μ 1 0. The selective etching solution of a π I -V group semiconductor as described in item 8 of the scope of patent application, wherein the etching selectivity ratios of the etching solution to the gallium arsenide layer and the deified gallium layer are respectively Above 200. 11. The selective #etching solution of the IΠ-ν semiconductor as described in item 8 of the scope of the patent application, wherein the volume percentage of citric acid in the etching solution is not higher than 0.02 times the volume percentage of water. 1 2. The selective etching solution for I π -V semiconductors 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 not higher than 0.001 times the volume percentage of water. . 13. The selective etching of the π and ν family semiconductors as described in item 8 of the scope of the patent application, wherein the remaining solution has an remaining rate of no more than 50 A / sec for the gallium layer of the Shishenhua. . ιΐϋ — Page 20