KR100567346B1 - Etchant for wet etching AlGaAs epitaxial layer and method for manufacturing semiconductor device using the etchant - Google Patents

Abstract

An Al _x Ga _1-x As epi layer etchant and a method of manufacturing a semiconductor device using the same are disclosed. The etchant according to the present invention consists of a mixture of H ₃ PO ₄ , H ₂ O ₂ and CH ₃ OH. When the Al _x Ga _1-x As (0 ≦ _x ≦ 1) epitaxial layer is etched using the etchant according to the present invention, an isotropic etching characteristic is obtained to form a mesa having a side surface having a vertical profile, and a GaAs layer. The etching selectivity with the AlGaAs layer is close to 1, so that a smooth surface shape is obtained from the side of the mesa.

AlGaAs Epilayer, Wet Etch, Vertical Mesa, DBR

Description

Etching AlGaAs epitaxial layer and method for manufacturing semiconductor device using the etchant}

1 is a flowchart illustrating a method of manufacturing a semiconductor device in accordance with a preferred embodiment of the present invention.

2A through 2E are cross-sectional views illustrating a process sequence in order to show an example in which a manufacturing method according to a preferred embodiment of the present invention described in FIG. 1 is applied.

Figure 3 shows a schematic configuration of a water bath apparatus suitable for use as a wet etching apparatus in manufacturing a semiconductor device according to the present invention.

4 is a table for explaining the epilayer sample structure of the etching target used in the experimental example of the present invention.

5A to 5C are photographs showing side and top surfaces of mesas formed by a wet etching process using an etchant according to the present invention, respectively.

6A and 6B are side and top images of mesas formed by a wet etching process using an etchant according to the prior art.

Figure 7a is a photograph showing the surface roughness of the substrate when the mesa is formed by a dry etching method according to the prior art.

7B to 7F are photographs showing roughness of a substrate surface according to various temperatures of an etchant when mesas are formed by a method of manufacturing a semiconductor device according to the present invention, respectively.

<Description of the symbols for the main parts of the drawings>

100: substrate, 110: n-type DBR, 120: active layer, 130: p-type DBR, 140: mask pattern, 150: pure, 200: mesa, 300: wet etching device, 310: wafer sample, 320: magnetic spin bar, 322: thermometer, 324 carrier, 330 etchant, 332 container, 340 water.

The present invention relates to an etchant for etching an epi layer and a method of manufacturing a semiconductor device using the same, and in particular, an etchant for wet etching an AlGaAs epi layer, and an optical switch including forming a mesa using the same. A method of manufacturing a semiconductor device, such as a device or a laser unit device.

In the manufacture of devices such as heterojunction bipolar transistors (HEBTs), high electron mobility transistors (HEMTs), and semiconductor lasers, wet etching processes using chemical reactions have been used. However, most of the wet etching processes used up to now have selective etching characteristics, and are limitedly used only in processes in which mesas having vertical surfaces do not affect device characteristics.

Until now, a dry etching process was absolutely required to fabricate a device requiring vertical mesas. Details of vertical etching using dry etching processes are already known (eg, Mats Hagberg et al., J. Vac. Sci. Technol. B 12 (2), Mar / Apr 1994; and Jun-Youn Kim et al., J. Vac. Sci. Technol.B 19 (4), Jul / Aug 2001). As already described in the literature, the dry etching process requires a large maintenance cost to maintain expensive equipment and high vacuum degree, and also requires a long time to hold the vacuum to perform the etching process, resulting in a long overall process period. Lose.

In order to solve the problems in the dry etching process as described above, a method using a wet etching process has been studied. Wet etching, unlike dry etching, has properties such as isotropic etching, low aspect ratio, undercut, and the like.

For example, in manufacturing a semiconductor device such as a semiconductor optical switch (SOS) device or a photonic quantum ring (PQR) laser unit device, a multilayer comprising a plurality of GaAs / AlGaAs epilayers is typically used. Forming a semiconductor layer of the structure, and then mesa etching it. In particular, in manufacturing a PQR laser unit device, a p-type distributed Bragg reflector (DBR) and an n-type DBR having a multi-layered GaAs / AlGaAs epilayer, interposed therebetween, and at least one quantum well In the fabrication of a photon-type laser diode including a GaAs active layer having a metal layer, a process of forming a vertical mesa having a vertical and smooth side by etching a semiconductor layer having a multi-layered structure composed of a GaAs / AlGaAs epi layer is performed to the active layer. .

Until now, it was not easy to wet-etch an epi layer having a multilayer structure of GaAs and AlGaAs to obtain a mesa having a vertical and smooth shape on its side. In addition, in the semiconductor layer of the multi-layered structure, since the etching ratio is different depending on the epi direction of each layer, it was also very difficult to form a mesa having a desired pattern shape.

To date, efforts have been made to obtain vertical mesas using wet etching processes (see, eg, J. Y. Lee et al., J. Vac. Sci. Technol. B 17 (6), Dec / 1999). However, in the technique published so far, when wet etching an epitaxial layer grown in a multilayer structure, a desired pattern shape cannot be obtained due to the difference in the etching rate depending on the epi direction, and after etching as the time for wet etching is prolonged, In the obtained pattern, surface roughness fell, and in the obtained mesa, there was no perpendicularity of mesa near the active layer area | region. As a result, in the case of forming mesa by wet etching, it was difficult to obtain a device having desired characteristics.

An object of the present invention is to solve the problems in the prior art, it is possible to form a vertical mesa by etching the epi-layer grown in a multi-layer structure using a wet etching process, the process cost is lower than the dry etching process It is to provide an Al _x Ga _1-x As epi layer etching solution.

Another object of the present invention is to provide a method for manufacturing a semiconductor device by etching the Al _x Ga _1-x As epitaxial layer using the etchant, to form a mesa having a desired pattern shape and a smooth vertical side.

In order to achieve the above object, the etchant according to the present invention for etching the Al _x Ga _1-x As (0≤x≤1) epilayer consists of a mixture of H ₃ PO ₄ , H ₂ O ₂ and CH ₃ OH. . Preferably, the mixed solution has a volume ratio of H ₃ PO ₄ : H ₂ O ₂ : CH ₃ OH = 3: 1: 1. Also preferably, the temperature of the mixed liquid is at least 40 ° C.

In order to achieve the above another object, in the method for manufacturing a semiconductor device according to the present invention, a structure including an Al _x Ga _1-x As (0 ≦ _x ≦ 1) epi layer is formed. A mask pattern is formed on the structure. Using the mask pattern as an etching mask, the Al _x Ga _1-x As epi layer is etched with a mixture of H ₃ PO ₄ , H ₂ O _2, and CH ₃ OH to form mesas.

Preferably, the etching of the Al _x Ga _1-x As epi layer is performed while stirring the mixed solution. The etching of the Al _x Ga _1-x As epitaxial layer may be performed using a water bath apparatus.

It is preferable that the said mask pattern consists of photoresists.

After etching the Al _x Ga _1-x As epi layer, the method may further include washing the mesa with de-ionized water. At this time, the washing may be performed for 1 to 5 minutes.

According to the present invention, an isotropic etching characteristic is obtained by wet etching an Al _x Ga _1-x As (0≤x≤1) epi layer using an etchant comprising a mixture of H ₃ PO ₄ , H ₂ O _2, and CH ₃ OH. It can be obtained to form a mesa having the side of the vertical profile, the etch selectivity of the GaAs layer and AlGaAs layer is close to 1 can be obtained smooth surface shape on the side of the mesa. Moreover, according to the shape of a mask pattern, a desired shape, for example, circular mesa can be formed. Therefore, according to the present invention, it is possible to form a large area array vertical mesa at a low process cost, unlike dry etching.

Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The etchant according to the present invention consists of a mixture of H ₃ PO ₄ , H ₂ O ₂ and CH ₃ OH.

Preferably, the mixed solution has a volume ratio of H ₃ PO ₄ : H ₂ O ₂ : CH ₃ OH = 3: 1: 1.

The etchant according to the present invention is particularly effective for etching an Al _x Ga _1-x As (0 ≦ _x ≦ 1) epilayer having a multilayer structure. When etching the multi-layered Al _x Ga _1-x As (0≤x≤1) epilayer using the etchant according to the present invention, a bias of up to about 0.88 close to the anisotropic etching characteristic [1- (horizontal etching rate) Vertical mesa with vertical etch rate). It is also possible to form a desired shape, for example a circular mesa.

In forming a vertical mesa by etching an Al _x Ga _1-x As (0 ≦ _x ≦ 1) epilayer having a multilayer structure with an etchant according to the present invention, the surface roughness of the mesa is improved as the temperature of the etchant increases. It tends to be. Preferably, the wet etching step is performed while the temperature of the etchant is maintained at at least 40 ° C.

An active layer having a GaAs quantum well and a multi-layered Al _x Ga _1-x As (0 ≦ _x ≦ 1) epi layer formed to form a P-type and an N-type DBR formed therebetween, are suitably used. By using a mask pattern, for example, a photoresist pattern as an etching mask, by etching with the etchant according to the present invention, a circular mesa having a vertical cross section can be easily produced.

1 is a flowchart illustrating a method of manufacturing a semiconductor device in accordance with a preferred embodiment of the present invention. 2A through 2E are cross-sectional views illustrating a process sequence in order to show an example in which a manufacturing method according to a preferred embodiment of the present invention described in FIG. 1 is applied. 2A-2E, the size or thickness of the film or regions are exaggerated for clarity of specification. In addition, when a film is described as "on" another film or substrate, the film may be directly on top of the other film, and a third other film may be interposed therebetween. For example, in FIGS. 2A to 2E, a buffer layer, a space layer, a cap layer, etc. required for forming a semiconductor device may be further included. These should be understood as not shown for simplicity of the drawings.

1 and 2A to 2E, a basic process applied to the method of manufacturing a semiconductor device according to the present invention will be described.

In step 10 of FIG. 1, a structure including an Al _x Ga _1-x As (0 ≦ _x ≦ 1) epi layer is formed. The structure may be formed, for example, as shown in FIG. 2A. That is, the n-type DBR 110, the active layer 120 having a plurality of quantum wells, and the p-type DBR 130 are sequentially epitaxially grown on the substrate 100. The substrate 100 may be formed of a material such as GaAs, InP, or the like, and the active layer 120 may be formed of, for example, a GaAs layer. The n-type DBR 110 and the p-type DBR 130 are each composed of a plurality of layers of Al _x Ga _1-x As (0 ≦ _x ≦ 1) epi layers.

In step 20 of FIG. 1, a mask pattern 140 is formed over the structure as illustrated in FIG. 2A (see FIG. 2B). It is preferable to form a photoresist pattern as the mask pattern 140. The reason is that the photoresist is strong in acid, so it is hardly consumed during the etching process, and a pattern of a desired shape such as a circle or a rectangle can be easily formed by using an aligner device.

In step 30 of FIG. 1, using the mask pattern 140 as an etching mask, the Al _x Ga _1-x As epi layer is formed of an etchant including a mixture of H ₃ PO ₄ , H ₂ O _2, and CH ₃ OH. Wet etching forms the mesa 200. In this case, in order to perform reproducible wet etching, it is important to first create a stable etching atmosphere such as temperature and stirring speed.

As a mixed solution constituting the etching solution, one having a volume ratio of H ₃ PO ₄ : H ₂ O ₂ : CH ₃ OH = 3: 1: 1 is used.

3 is a view schematically illustrating a configuration of a water bath apparatus, which is a wet etching apparatus 300 suitable for use in the wet etching. In FIG. 3, reference numeral “310” denotes a wafer sample on which a structure to be etched is formed, “320” denotes a magnetic spin bar, “322” denotes a thermometer, and “324” denotes a carrier. "330" is an etchant and "340" is water. It is preferable to involve stirring using the magnetic spin bar 320 during wet etching using the wet etching apparatus 300. At this time, the stirring speed may vary depending on the size of the container 332 in which the etchant 330 is accommodated, but the etching speed of the etching solution depends on the diffusion rate of the etchant. In order to obtain the it is preferable to fix such that the stirring speed of the vortex does not occur in the surface of the etching solution. The temperature of the etchant 330 is preferably maintained at 40 ℃ or more. To this end, the temperature of the water 340 is maintained at 40 ℃ or more.

By performing the etching process as described above, the mesa 200 having a bias close to the anisotropic etching characteristic can be obtained. In addition, according to the upper surface shape of the mask pattern 140, a desired shape, for example, a circular mesa is easily obtained.

In step 40 of FIG. 1, the mesa 200 formed product is washed with de-ionized water 150 (see FIG. 2D). The washing is carried out sufficiently for about 1 to 5 minutes, for example 3 minutes.

In step 50 of FIG. 1, the mask pattern 140 is removed. As a result, as shown in FIG. 2E, the upper surface of the mesa 200 having a vertical surface on the substrate 100 is exposed.

Next, specific experimental examples of forming a mesa by etching the epi structure according to the method of manufacturing a semiconductor device according to the present invention will be described.

Experimental Example

(1) Structure and experimental apparatus of the epi layer to be etched

In order to reproducibly wet-etch a structure consisting of an active layer having a GaAs quantum well and a p-type DBR composed of GaAs / AlGaAs and an n-type DBR composed of GaAs / AlGaAs whose refractive index is changed in accordance with the mole fraction of Al, first, temperature and stirring It is important to create a stable etching atmosphere such as speed.

4 is a table for explaining the structure of the epi layer sample of the etching target used in the present experimental example. In the etching of the epi structure of FIG. 4, the etching apparatus 300 as illustrated in FIG. 3 was used.

(2) Formation of Mask Pattern for Use as Etch Mask

The photoresist material was coated on the epitaxial layer of the clean object to be cleaned, thereby forming a photoresist pattern having a desired shape. Since the photoresist film is acid resistant and is not etched by the etchant during the etching process, it is suitable for use as an etching mask. In addition, the photoresist film may be easily patterned into various shapes such as a circle and a rectangle by using an aligner device. The mask pattern thus formed was hard baked in an oven maintained at 120 ° C. for 7 minutes. Finally, O ₂ plasma ashing was performed to remove the residue on the mask pattern to minimize the effect of defects.

Defects on the sample surface locally adversely affect the etching, resulting in poor uniformity of etching. The main factors affecting the etching are the thickness of the photoresist film and the hard baking time after the mask pattern formation. Preferably, the hard baking is done for about 7 minutes. Through the experiments, the present inventors found that when the hard baking time is set to less than 7 minutes, the etching liquid penetrates into the gap between the photoresist film and the epi layer due to the incomplete adhesion of the photoresist film, and the hardness of the photoresist film is reduced. ), It was confirmed that a case in which it could not endure the required etching time due to the shortage occurred. In addition, if the hard baking time is set too long, it is difficult to remove the PR after the end of etching. Of course, depending on the etching solution, it depends to some extent on the etching selectivity representing the ratio of the etching rate between the epitaxial layer and the photoresist film.

(3) etching using the etchant according to the present invention

The epilayer sample was etched using an etchant according to the invention having a volume ratio of H ₃ PO ₄ (purity 85%): H ₂ O ₂ (purity 30%): CH ₃ OH = 3: 1: 1. Here, in order to increase the etch rate of Al so that the etching selectivity between GaAs and AlGaAs is about 1, the ratio of phosphoric acid (H ₃ PO ₄ ) was set relatively higher than other components. Methanol (CH ₃ OH) was used as diluent. The reason for using methanol instead of water as a diluent is that the dielectric constant of methanol at room temperature (about 27) is less than the dielectric constant of water (about 81), so that the concentration of the etchant during the etching process is lowered by lowering the dissociation of H ₂ O ₂ . This is because it can be kept constant. However, the high volume ratio of H ₃ PO ₄ increases the viscosity of the etchant, which shows diffusion-limited etching characteristics in which the etching rate depends on the diffusion rate of the etchant. The epitaxial layer of the object to be etched covered by the mask pattern formed by the method as described in the above item (2) is H ₃ PO ₄ , H ₂ O ₂ and CH, which are etching liquids according to the present invention, in the wet etching apparatus 300 of FIG. Etched with a mixture of ₃ OH. At this time, the mixture was stirred at 140 rpm using the magnetic spin bar 320. In the stirring process using the magnetic spin bar 320, the rotational speed varies depending on the size of the vessel containing the etchant, but it is fixed to such an extent that the interface between the etchant and the atmosphere does not deviate from the level of approximately horizontal during stirring, thereby reproducible the experiment. Keep it. And, when the temperature of the water 340 to 21 ℃, 30 ± 0.5 ℃ and 40 ± 0.5 ℃, respectively, the etching characteristics according to the temperature was observed. After etching, after sufficiently washing in de-ionized water for about 3 minutes, the mask pattern used as an etching mask was completely removed.

Mesa etch shape according to the change of the temperature and the etching time during the etching of the epilayer sample is shown in FIGS. 5A to 5C, respectively. 5A to 5C, the photograph on the left is a shape seen from the side of the mesa, and the photograph on the right is a shape seen from the upper surface of the mesa.

More specifically, Figure 5a shows the mesa shape and surface roughness when etching for 10 minutes with the etchant according to the present invention maintained at a temperature of about 21 ℃. The total etch depth (H) measured from the top layer of mesa (layer number 18 in FIG. 4) is about 6.85 μm, exhibiting isotropic etching characteristics but forming vertical mesa up to about 1/3 (about 1 μm) of depth to quantum wells. It can be seen that. In addition, in FIG. 5A, despite the occurrence of undercut, the etch shape in the crystal orientation [1 0 0] direction maintains a circular shape that exactly matches the initial pattern. Since the volume ratio of H ₃ PO ₄ is high, residues may stick to the surface of the epi layer after etching. This phenomenon can be removed through the process of sufficiently washing with pure water while visually confirming the surface condition.

FIG. 5B is a result of the same process as in FIG. 5A except that the etching solution was deeply etched to H about 11 μm by performing an etching process for 15 minutes after increasing the temperature of the etching solution to 30 ° C., and vertical mesa was about 2 It can be confirmed that it was formed up to μm. The speckles seen on the mesa surface are those in which the photoresist material dissolved in acetone remains in the mesa upon removal of the photoresist mask pattern. In the etching process for mesa formation, in addition to the basic main etching process conditions, cleaning operations such as removing and rinsing a mask pattern have a great influence on the surface roughness of the mesa. Therefore, it is preferable to sufficiently set the washing time with pure water after the etching to about 3 minutes.

5C shows the results of the same conditions as in FIG. 5A except that the temperature of the etchant is 40 ° C. and is etched for 20 minutes. Epimesa shape formed on the GaAs substrate can be confirmed, and is still isotropic until H about 25㎛. However, considering the structure of the epilayer composed of p-type DBR-active region-n-type DBR, (horizontal etch rate) / (vertical etch rate) = (2.1 μm) / (8.68 μm) = about 0.24, A vertical plane close to anisotropic can be obtained. Moreover, considering only the etching depth up to about 3 mu m, (horizontal etch rate) / (vertical etch rate) = (0.39 mu m) / (3.21 mu m) = about 0.12. Considering that the (horizontal etch rate) / (vertical etch rate) obtained in most wet etching is about 1, superior mesa perpendicularity can be obtained compared to isotropic etching.

Control

Except that a mixture of H ₃ PO ₄ , H ₂ O ₂ and H ₂ O was used as an etchant, and an etchant having a volume ratio of H ₃ PO ₄ : H ₂ O ₂ : H ₂ O = 1: 1: 10 was used. , Mesa etching for 7 minutes under the same etching conditions as in the case of Figure 5b is shown in Figure 6a as a result, the upper surface shape of the mesa is shown in Figure 6b.

As can be seen in Figures 6a and 6b, due to the difference in the etching rate between the GaAs epi layer and the AlGaAs epi layer it can be seen that the GaAs layer as an active region is more etched to form a structure in which the region is recessed. The profile of the side is not vertical. Further, as shown in FIG. 6B, since the etching rate is different depending on the epi direction, it is difficult to obtain a circular shape that is the same as that of the mask pattern on the upper surface of the mesa. These results are typical results obtained by isotropic wet etching according to the prior art.

7A to 7F are AFM (Atomic Force Microscopy) photographs showing a change in roughness of a substrate surface according to visual conditions when the epi layer is etched by various etching processes.

More specifically, FIG. 7A illustrates a case where mesa etching is performed by a dry etching process using conventional chemically assisted ion beam etching (CAIBE). The surface roughness rms in FIG. 7A was 0.733 nm.

7B to 7F are substrates when the temperature of the etching solution is 20 ° C., 25 ° C., 30 ° C., 35 ° C., and 40 ° C. in performing mesa etching by the wet etching process using the etching solution according to the present invention. It shows the roughness of the surface. 7B to 7F, the surface roughness of the substrate is improved as the temperature of the etchant increases. The roughness on the side of the mesa obtained after etching cannot be directly confirmed by AFM analysis, but roughness is expected to be improved similarly to the substrate. This is because the etchant according to the present invention, that is, the etchant consisting of a mixture of H ₃ PO ₄ , H ₂ O ₂ and CH ₃ OH has an etching selectivity close to 1 for the GaAs layer and the AlGaAs layer. Respective surface roughnesses (rms) in FIGS. 7B-7F were 4.690 nm, 0.917 nm, 0.903 nm, 0.825 nm and 0.703 nm, respectively.

In the above results, the surface roughness decreases as the temperature of the etchant increases when mesa etching is performed using the etchant according to the present invention, but the temperature dependence is weakened at 25 ° C or higher. When the temperature of the etchant is 40 ℃ surface roughness shows a similar value to the dry etching process using the CAIBE of Figure 7a, compared to the photograph of Figure 7f compared to Figure 7a wet etching using the etchant according to the present invention It can be seen that the etching method has a more uniform surface.

The etchant according to the present invention consists of a mixture of H ₃ PO ₄ , H ₂ O ₂ and CH ₃ OH. When the Al _x Ga _1-x As (0≤x≤1) epitaxial layer is etched using the etchant according to the present invention, an isotropic etching characteristic is obtained to form a mesa having a side surface of a vertical profile, and a GaAs layer and AlGaAs The etch selectivity with the layer is close to 1 so that a smooth surface shape at the side of the mesa can be obtained. Moreover, according to the shape of a mask pattern, a desired shape, for example, circular mesa can be formed. Therefore, according to the present invention, it is possible to form a large area array vertical mesa at a low process cost, unlike dry etching.

In the above, the present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications and changes by those skilled in the art within the spirit and scope of the present invention. This is possible.

Claims (12)

delete delete delete Forming a structure comprising an Al _x Ga _1-x As (0 ≦ _x ≦ 1) epi layer, Forming a mask pattern on the structure; Using the mask pattern as an etching mask, etching the Al _x Ga _1-x As epi layer with a mixture of H ₃ PO ₄ , H ₂ O _2, and CH ₃ OH to form mesas; , Performed in a state in which said bath in the step of etching the Al _x Ga _1-x As epitaxial layer is the mixed solution accommodated in the container using a water bath apparatus in the water to maintain a temperature of at least 40 ℃, the Al _x Ga _{1- x The} method of manufacturing a semiconductor device, characterized in that the mixed solution is stirred in the vessel while etching the As epi layer. The method of claim 4, wherein The mixed solution has a volume ratio of H ₃ PO ₄ : H ₂ O ₂ : CH ₃ OH = 3: 1: 1. delete delete delete The method of claim 4, wherein And the mask pattern is made of a photoresist. The method of claim 4, wherein After etching the Al _x Ga _1-x As epitaxial layer, washing the mesa with de-ionized water. The method of claim 10, The washing is performed for 1 to 5 minutes, the manufacturing method of a semiconductor device. The method of claim 4, wherein And said mesa has a substantially circular top shape.

Images