JPH02298027A - Etching of compound semiconductor - Google Patents

Abstract

PURPOSE:To be reproducible and practical, to make damage of a substrate extremely small after an etching operation and to form various processed shapes by a method wherein a refractive index and a film thickness of a material to be treated are measured by means of ellipsmetry during a dry etching operation. CONSTITUTION:A photoresist 3 (positive type) is formed on, e.g., ZnSe 1 on GaAs 2. A substrate 12 is placed on a sample holder 13; after that, an etching operation is executed by using pure chlorine (99.999%) as a reactive gas while an irradiation direction of an ion beam is set to a direction perpendicular to the substrate 12. A refractive index and a film thickness of an exposed part of the ZnSe 1 are measured continuously by means of ellipsometry during the etching operation. When a desired residual thickness is reached, microwaves are stopped. The refractive index is changed largely when the etching operation reaches an interface between the ZnSe 1 and the GaAs 2. Accordingly, the etching operation is stopped at the interface between the ZnSe 1 and the GaAs 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for etching a II-VI group compound semiconductor.

[Prior art] Zinc selenide (ZnSe), zinc sulfide (ZeS), etc.
Conventional microfabrication methods for II-VI 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 hydroxide (7+7% aqueous solution), hydrochloric acid, and a mixture of nitric acid and monohydrochloric acid. In order to obtain a suitable temperature,
Or used in compositions.

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

[Problems to be Solved by the Invention] However, the processing of n-vi group compound semiconductors by the above-mentioned conventional technology 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 that the etching speed will be faster (changed) between when the etching solution is prepared and when time has passed. be.

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 I[-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, Zn5eS
When ZnSxSe1-x is etched with an aqueous NaOH solution, the surface morphology is extremely deteriorated and it cannot be said to be suitable for precise etching. When hydrochloric acid is used, the etching rate is very slow and I[-V
This is not practical for manufacturing devices using Group I compound semiconductors.

On the other hand, in the ion etching technique using an inert gas such as Ar, it is necessary to increase the power of plasma discharge in order to increase the etching rate to a practical level, which causes great damage to the semiconductor substrate. Furthermore, although reactive ion etching using a reactive gas such as BCla can reduce damage to the substrate to some extent compared to ion etching, 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 II-VI group compound semiconductors using conventional methods is extremely difficult, and in particular, the reproducibility of the etching depth between batches is poor. This was a major obstacle in mass production technology. Therefore, the present invention is intended to solve the above-mentioned problems.The purpose of the present invention is to have reproducibility, practicality, minimize damage to the substrate after etching, and create various processed shapes. An object of the present invention is to provide a method for etching a ■-■ group compound semiconductor, which enables the etching of a ■-■ group compound semiconductor.

[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 If-VI includes a process of dry etching by irradiating the material with an ion beam having a uniform direction.
1. A method for etching compound semiconductors, characterized in that the refractive index and film thickness of the material to be processed are measured by ellipsometry during dry etching.

[Example] 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. 3 shows a schematic cross-sectional view of the structure of an etching apparatus according to an embodiment of the present invention. Since a gas containing highly reactive halogen elements is used as the etching gas, the sample preparation chamber 14 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 donner for generating a magnetic field and a C-shaped coil 9, and has a microwave-introducing quartz window at the connection part with the microwave waveguide 1°.

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. E
Ions generated in the CR plasma chamber 8 are accelerated by a Messinian extraction electrode section 11 and irradiated onto a sample 12 set in a sample holder 13. In addition, the etching chamber 7 is equipped with a port for incident light and a port for output light for ellipsometry, and the light is linearly polarized by a polarizer 22 from a light source 20 from the incident side, and then passed through a quarter-wave plate 23. The circularly polarized light that passes through it is incident. The incident light is reflected by the sample 12, becomes linearly polarized light, and enters the phototube 25 through the analyzer 24 from the output port. The rotation angles of the polarizer 22 and analyzer 24 and information on the phototube 25 are processed by a data analysis bag fii 26 to obtain the refractive index and film thickness of the sample.

FIG. 1 shows Zn5e on GaAs using the apparatus shown in FIG.
FIG. 3 is a cross-sectional view of one embodiment of the etching process.

FIG. 1(a) is a cross-sectional view before etching, and 1 is a Z
n5e, 2 is GaAs, and 3 is a photoresist etching mask. A positive type photoresist 3 is used, and since the mask was manufactured by a normal photolithography process, the cross-sectional shape of the mask is tapered. After placing the substrate on the sample holder 13, pure chlorine (99,999%) was used as the reactive gas, and the gas pressure was 1.0×1.
Etching was performed at 0 day Pa, microwave input power 10 OW, extraction voltage 500 L, sample temperature 25° C., and ion beam irradiation direction perpendicular to the substrate. During etching, the refractive index and film thickness of the exposed portion of Zn5el are continuously measured by ellipsometry, and when the desired remaining thickness is reached, the microwave application is stopped. Furthermore, since the refractive index increases (changes) when etching reaches the interface between Zn5el and GaAs2, it is also easy to stop the etching at the interface between Zn5el and GaAs2.
Figure (b) is a sectional view after etching. ZnS e
The etching rate for photoresist (positive type) is approximately 200 A/min when the post bake condition is 120°C for 30 minutes.
/minute. Since the etching mask has a tapered shape and some etching occurs due to sputtering, the processed cross-sectional shape will be the shape shown in Figure 1 (b), and even if the ion beam is incident perpendicularly, it will not become a vertical cross-section. However, in terms of etching speed, there is no practical problem. Furthermore, the in-plane distribution of etching speed is 20 m
The surface morphology after processing was good within ±5% within the m×20 mm substrate. Furthermore, since the end point of etching was detected by ellipsometry, there was no over-etching compared to the case where the etching depth was controlled by the etching time, and etching could be performed extremely accurately and with good reproducibility.

FIG. 2 shows an example of vertical section processing of ZnSe on ZnSSe. First, as shown in Fig. 2(a), photoresist 3 (positive type) was spin-coded on Zn5el, and beta-coated at 200°C for 30 to 120 minutes.
Approximately 100 OA of Tf4.

It is formed on a photoresist using an electron beam evaporation method or the like.

Next, as shown in FIG. 2(b), a pattern of the photoresist 5 is formed by a normal photolithography process. Next, as shown in FIG. 2(C), the TI 4 is etched using the photoresist 5 as a mask. For wet etching, a buffered hydrofluoric acid solution is used, and for dry etching, reactive ion etching (RIE) using CFa gas is used. A slight dry etching is preferable. Next, as shown in FIG. 2(d), using T14 as a mask, the photoresist 3 is etched by RIE using oxygen plasma.

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, the etching will progress in the same direction, so it is not suitable in this case.T14 used as an etching mask for the photoresist 3 is Zn5e.
Before etching, remove with a buffered hydrofluoric acid solution or the like. Next, ZnSe is etched under the same conditions as in the embodiment shown in FIG. As a result, a vertical cross section as shown in FIG. 2(e) is formed. At this time, side etching hardly occurs. Therefore, although the process is somewhat complicated, the method shown in FIG. 2 can be said to be an effective means when it comes to anisotropic etching. Furthermore, by measuring the remaining Zn5e thickness by ellipsometry, Zn5e etching to a desired depth can be carried out with accuracy and reproducibility.

In this example, Zn5e was explained as an n-v'i group compound semiconductor, but znSxSe+-
It is also effective for other II-Vl group compound semiconductors such as x (0<x≦1). Furthermore, although the explanation was given using a photoresist as an etching mask, it is possible to use a material that has a good selectivity with respect to the material to be etched, for example, when Zn5e is used as the material to be etched, an insulator such as 510X or 5iNX, or 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 CC1zF, may also be used.
s:, etc. may also 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 ■-■ 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. Furthermore, damage to the semiconductor layer can be significantly reduced, especially compared to the conventional dry etching technique for -Vl group compound semiconductors. Furthermore, by controlling the shape of the ion beam and etching mask, it is possible to process tapered grooves, vertical cross sections, etc., making it possible to fabricate devices using I[-VI group compound semiconductors with high reproducibility, reliability, and It can be easily produced. Furthermore, the etching depth, which was conventionally controlled by the etching time based on the etching speed, can now be detected with extreme accuracy and reproducibility by observing the remaining thickness using ellipsometry, regardless of the etching speed. Batch-to-batch reproducibility in dry etching of II-VI group compound semiconductors is greatly improved, facilitating mass production of a variety of devices.

[Brief explanation of drawings]

FIGS. 1(a) and (+) are diagrams showing an example in which ZnSe on GaAs was etched by the method of the present invention using a photoresist as an etching mask. FIGS. 2(a) to 2(e) are diagrams showing an example in which vertical end face processing of Zn5e on ZnSSe was performed according to the present invention. FIG. 3 is a schematic diagram of an etching apparatus used in an embodiment of the present invention. l -・・Zn5e 2・・・GaAs 3...Photoresist 4...Ti 50・Photoresist 6---Zn5Se 7...Etching chamber 8...ECR plasma generation chamber 9...Electromagnet lO ... Microwave waveguide 11 ... Extraction electrode 12 ... Sample 13 ... Sample holder 14 ... Sample preparation chamber 15 ... Gas introduction section 16 ... Transport rod 17 ... Exhaust system 18...Exhaust system 19...Gate valve 20...Light source 21...Condenser lens 22...Polarizer 23...1/4 wavelength plate 24...Analyzer 25...Phototube 26... Data analysis equipment and above Applicant: Seiko Epson Co., Ltd. Representative Patent Attorney Kizobu Suzuki (and 1 other person)

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. 1. A method for etching a compound semiconductor, comprising measuring the refractive index and film thickness of the material to be processed by ellipsometry during dry etching.