JPH02267936A - Etching of compound semiconductor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to etching of II-Vl group compound semiconductors [Prior Art] Zinc selenide (ZnSe), zinc sulfide (ZeS), etc.
Conventional microfabrication methods for If-Vl group compound semiconductors made of these mixed crystals include wet etching techniques and dry etching techniques using an insulating film such as photoresist or silicon dioxide as a mask. In wet etching technology, the etching solutions mainly used include aqueous sodium hydroxide solution, hydrochloric acid, and a mixture of nitric acid and monohydrochloric acid.
A suitable temperature or composition is used to obtain the desired etching rate.

On the other hand, dry etching technology uses parallel plate electrodes.
Ion etching with inert gas such as r, BCl3
Examples include reactive ion etching using a reactive gas such as.

[Problems to be Solved by the Invention] However, the processing of If-VI group compound semiconductors according to the prior art described above has the following problems.

A common problem with wet etching techniques is poor reproducibility.

A constant etching rate cannot be obtained unless the temperature, composition of the etching solution, etc. are controlled very strictly.

Furthermore, in the case of an etching solution containing volatile substances, the composition of the etching solution changes over time, so there is a problem in that the etching rate changes greatly between when the etching solution is prepared and when time has elapsed.

Furthermore, in the wet etching technique, etching proceeds in the same direction and side etching occurs, making it impossible to form a pattern according to the dimensions of the mask. Further, the shape of the processed cross section is also limited, and for example, it is difficult to form a vertical cross section or a deep groove with a large aspect ratio.

Wet etching of II-VI group compound semiconductors has more problems than other m-v group compound semiconductors. For example, when etching Zn5e with a hydrochloric acid-nitric acid-based etching solution, the etching solution soaks into the Zn5e, and it is difficult to completely remove it even with long-term water washing, resulting in a significant deterioration of film properties. . Also, Zn S e
, ZnSXS el-x, when etched with an NaOH aqueous solution, the surface morphology is extremely deteriorated and it cannot be said to be suitable for precise etching. When using hydrochloric acid, the etching speed is very slow;
This is not practical for manufacturing devices using II-VI group compound semiconductors.

On the other hand, ion etching using an inert gas such as Ar.

In the etching technology, it is necessary to increase the power of the plasma discharge in order to increase the etching speed to a practical level, which causes significant damage to the semiconductor substrate. Also, BCl3
Reactive ion etching using reactive gases such as
Compared to ion etching, damage to the substrate can be reduced to some extent, but it is not within an acceptable range. To simply reduce damage, the gas pressure can be increased even at low discharge power, but since the ion sheath width and the mean free path of ions and neutral particles are approximately the same, the ion beam loses directivity. Side etching becomes large, which is a major drawback from the point of view of microfabrication.

As described above, etching of n-VI group compound semiconductors using conventional methods is extremely difficult, and in particular, the reproducibility of etching depth between batches is poor. This was a major hindrance. SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned problems, and aims to be reproducible, practical, and cause extremely little damage to the substrate after etching.
An object of the present invention is to provide a method for etching a TI-VI group compound semiconductor, which allows the creation of various processed shapes.

[Means for Solving the Problems] The compound semiconductor etching method of the present invention includes the step of forming an etching mask, activating a reactive gas in a microwave excitation/ECR plasma chamber with a separate discharge chamber, and II-VI, which includes a process of dry etching by irradiating the material with a uniformly oriented ion beam;
The method for processing a group compound semiconductor includes the step of irradiating the surface of the II-VI compound semiconductor with a hydrogen ion beam before performing dry etching with the ion beam.

[Example 7] Hereinafter, an example in which a II-VI group compound semiconductor was etched by the method of the present invention will be shown.

First, FIG. 5 shows a schematic cross-sectional view of the construction of a machining/sawching apparatus according to an embodiment of the present invention. Since a gas containing a highly reactive halogen element is used as the etching gas, the sample preparation chamber 6 and the etching chamber 7 are separated by a gate valve 19, and the etching chamber 7 is always kept in a high vacuum state. ing. Reference numeral 8 denotes an electron/cyclotron resonance (ECR) plasma chamber, which is surrounded by a cylindrical donor for generating a magnetic field and a round-shaped coil 9, and has a microwave-introducing quartz window at the connection part with the microwave waveguide 10. Electrons ionized and generated by microwaves repeatedly collide with gas while performing cyclotron motion due to an axisymmetric magnetic field. This rotation period matches the microwave frequency, for example 2.45 GHz, when the magnetic field strength is, for example, 875 Gauss, and the electronic system resonantly absorbs the microwave energy. Therefore, discharge can be sustained even at low gas pressures, high plasma density can be obtained, and reactive gases can be used for a long time. Further, due to the high electrolytic distribution in the center, electrons and ions are focused at the center, so the sputtering effect of ions on the side walls of the plasma chamber is small, and highly clean plasma can be obtained. Ions generated in the ECR plasma chamber 8 are accelerated by a mesh-like extraction electrode section 11 and irradiated onto a sample 12. The sample holder 13 can be rotated by 360 degrees around the vertical direction by the manipulator 14, and the direction of the ion beam incident on the sample can be changed.

FIG. 1 is a cross-sectional view of an example of etching ZnSe using the apparatus shown in FIG.

FIG. 1(a) is a cross-sectional view before etching, and 1 is a Z
n5e, 2 is an etching mask. Etching mask 2 uses photoresist (positive type),
Because the mask was made using a normal photolithography process,
The cross-sectional shape of the mask is tapered. After the substrate was placed on the sample holder 13, and before etching, the surface of the substrate was cleaned with a hydrogen ion beam as follows. Using pure hydrogen (99,9999%), gas pressure 1.0xlO-'Pa, v microwave input and output, 6 input output 1
A hydrogen ion beam is irradiated perpendicularly to the substrate at a voltage of 400 V and a sample temperature of 25°C.

The hydrogen ion beam sputters residual impurities on the substrate surface, resulting in a clean substrate surface. After that, pure chlorine (99,999%) was used as the reactive gas, the gas pressure was 1.0XIO-'Pa, and the microwave incident power was 100.
Etching was carried out with the ion beam irradiation direction perpendicular to the substrate. FIG. 1(b) is a sectional view after etching. The etching rate of Zn5e is about 600 A/min, while the etching rate of photoresist (positive type) is about 200 A/min when the post-bake conditions are 120° C. for 30 minutes. Since the etching mask has a tapered shape and some etching occurs due to sputtering, the processed cross-sectional shape is
Although the shape shown in Figure (b) does not result in a vertical cross section even if the ion beam is perpendicularly incident, there is no practical problem in terms of etching rate. Furthermore, cleaning the hydrogen ion beam before etching improves the stabilization and reproducibility of the etching rate compared to when cleaning is not performed. Furthermore, the in-plane distribution of etching rate was less than ±5% within a 20 mm x 20 mm substrate, and the surface morphology after processing was almost the same as before processing. Figure 2(a),
(b) compares the photoluminescence of the Zn5e substrate before etching and the Zn5e substrate after etching under the above conditions. (a) is before etching.
(b) shows photoluminescence after etching. The relative intensity ratio between the band edge emission and the deep level emission remains unchanged at about 50 before and after etching, indicating that there is almost no damage to the semiconductor layer due to etching.

FIG. 3 shows an example of processing a vertical cross section of ZnSe. First, as shown in Figure 3(a), Zn5el
Photoresist 3 (positive type) is spin-coded on top, and it is cured at 200''C for 30 to 120 minutes, and TI4 is formed on the photoresist by electron beam evaporation or the like at about 100 OA.Next, as shown in FIG. As shown in (b), a photoresist 5 is formed by a normal photolithography process.
Pattern formation is performed. Next, as shown in FIG. 3(C), etching of T14 is performed using the photoresist 5 as a mask. As for the etching method, wet etching uses a buffered hydrofluoric acid solution, and dry etching uses reactive ion etching (RIE) using CF4 gas, but in order to perform precise pattern transfer, it is necessary to use a small amount of side etching. Dry etching is preferable. Next, as shown in FIG. 3(d), using T14 as a mask, the photoresist 3 is etched by RI using oxygen plasma.
Perform by E method. What must be noted at this time is the pressure of the oxygen gas. When an ordinary parallel plate type dry etching apparatus is used to fabricate an etching mask having a vertical cross-sectional shape without a taper, the oxygen gas pressure is preferably about 5 Pa.

If the pressure is too high, etching proceeds in the same direction, which is not suitable in this case. T14, which was used as an etching mask for photoresist 3, was removed with a buffered hydrofluoric acid solution or the like before etching ZnS e 1.Next, under the same conditions as in the example shown in FIG. Zn cleaning by beam cleaning and pure chlorine gas
If etching 5e is performed, a vertical cross section as shown in FIG. 3(e) will be formed. Also, at this time, side etching hardly occurs. Therefore, the process becomes somewhat complicated, but
Regarding anisotropic etching, the method shown in FIG. 3 can be said to be an effective means. Additionally, cleaning the substrate surface with a hydrogen ion beam was effective in suppressing side etching.

FIG. 4 shows an example in which an ion beam is incident on the surface of the znSe substrate 1 from an oblique direction to perform etching. FIG. 4(a) is a cross-sectional view of the substrate before etching, and FIG. 4(b) is a cross-sectional view of the substrate of FIG. 4(a) after etching is performed by making an ion beam incident on the substrate in the direction indicated by the arrow. Etching progresses preferentially in the direction of incidence of the ion beam, and grooves are formed in diagonal directions.

In this example, Zn5e was explained as the If-VI group compound semiconductor, but ZnS.

It is also effective for other n-vr group compound semiconductors such as 5et-x (0<x≦1). Furthermore, although the explanation was given using a photoresist as an etching mask, it is also possible to use a photoresist that has a good selectivity with respect to the material to be etched, such as Zn5e.
When etched material is S I Ox, S i
Insulators such as Nx, Mo.

It is also effective for metals such as N1. Furthermore, although pure chlorine gas is used as the etching gas, gases containing halogen elements, such as BCl3 or CC12F, may also be used.
2, etc. may be used.

[Effects of the Invention] As described above, according to the present invention, the following effects can be obtained.

As an etching method for n-vr group compound semiconductors, by using a reactive ion beam using microwave excitation and ECR plasma, conventional wet etching technology,
Alternatively, etching can be performed with much better reproducibility and controllability than dry etching techniques such as ion etching and reactive ion etching. In addition, damage to the semiconductor layer can be significantly reduced, especially compared to conventional dry etching techniques for compound semiconductors of the ■-■ group. Furthermore, by controlling the shape of the ion beam and etching mask, it is possible to process tapered grooves, vertical cross sections, diagonal grooves, etc., making it possible to fabricate devices using ■-■ group compound semiconductors with high reproducibility and reliability. It can be produced well and easily.

Furthermore, by cleaning the substrate surface with a hydrogen ion beam before etching, oxygen on the substrate surface can be removed.
Impurities such as carbon are removed by sputtering. As a result, it is possible to stabilize the etching rate and improve batch-to-batch reproducibility in dry etching of II-VI group compound semiconductors, to suppress side etching during vertical section processing, and to improve the etching efficiency of different II-VI group compound semiconductors. Fast etching becomes possible, making it possible to manufacture a variety of devices.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are process sectional views showing an example in which Zn5e was etched using a photoresist as an etching mask by the method of the present invention. FIGS. 2(a) and 2(b) are diagrams showing the photoluminescence of the Zn5e layer before and after etching according to an embodiment of the method of the present invention, respectively. FIGS. 3(a) to 3(e) are process cross-sectional views showing an example in which vertical end face processing of Zn5e was performed according to the present invention. FIGS. 4(a) and 4(b) show that Zn
FIG. 5 is a process sectional view showing an example in which a diagonal groove of No. 5e is processed. FIG. 5 is a schematic explanatory diagram of the configuration of an etching apparatus used in an embodiment of the present invention.・Zn5e substrate・Photoresist・Photoresist・TI ・Photoresist・Sample r$ preparation room・・Etching room・ECR plasma generation chamber・・Electromagnet・Microwave waveguide・Extraction electrode・Sample・・Sample holder・・Manipulator・・Gas introduction part 204 ON e'-me gap (b) ・・Transport rod・・Exhaust system・・Exhaust system・Gate valve Above Applicant Seiko Epson Corporation Attorney Kizo Tsuchi Suzuki (and 1 other person) ) 7 Otoshi) Rui Ichi (Color V) (Ku) 7 Ton Engineer's Ax Rugi (tY> (Ton No. 2b (A) Kaya φ Akira

Claims (1)

[Claims] Dry etching is performed by forming an etching mask, activating reactive gas in a microwave excitation/ECR plasma chamber with a separate discharge chamber, and irradiating the material to be treated with an ion beam with a uniform direction. including the process of performing
Etching of a compound semiconductor characterized by comprising a step of irradiating the surface of the II-VI compound semiconductor with a hydrogen ion beam before performing dry etching with the ion beam, in the processing method of the II-VI group compound semiconductor. Method.