JPH02299230A - Etching process of semiconductor - Google Patents

Abstract

PURPOSE:To manufacture II-VI compound semiconductor with clean surface after etching process capable of taking various processing shapes in excellent reproducibility and serviceability with the least damage to a substrate after etching process by a method wherein a reactive gas is specified to be hydrogen halogenide such as HCl, HBr, etc. CONSTITUTION:Within the processing means of II-VI compound semiconductor, a reactive gas is to be a hydrogen halogenide such as HCl, HBr etc.; the gas pressure thereof is to be within the range of 5X10<-3>-1Pa; the microwave incident output is to be 1W-1kW; while the voltage leading-out ion beams from a discharge chamber to a processed material is to be within the range of 0V-1kV. Through these procedures, the title etching process in excellent reproducibility and controllability can be performed while notably reducing the damage to a semiconductor layer, furthermore, the processing of a taper groove, a vertical section, an oblique groove, etc., can be performed by controlling the shape of ion beams and an etching mask.

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)
Conventional microfabrication methods for II-VI group compound semiconductors made of these and mixed crystals include wet etching techniques and dry etching techniques using photoresist or an insulating film such as silicon dioxide as a mask. In wet etching technology, the etching solutions mainly used include sodium hydroxide aqueous solution, hydrochloric acid, and a mixture of nitric acid-hydrochloric acid-water. , at an appropriate temperature or composition.

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, or reactive ion beam etching in which pure chlorine gas is used as the reactive gas and etching is performed by microwave excitation/ECR plasma.

[Problems to be Solved by the Invention] However, the processing of II-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 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 1l-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, Zn5e, Z
When etching n5xSe+-x with an aqueous NaOH solution, the surface morphology deteriorates extremely, making it unsuitable for precise etching. When hydrochloric acid is used, the etching rate is very slow and is not practical for manufacturing devices using II-VI group 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 BCl3 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. The side etching is thick, which is a major drawback from the point of view of microfabrication.

Reactive ion beam etching using pure chlorine gas is
Compared to the above-mentioned etching methods, the damage caused to the semiconductor substrate can be considerably reduced, and the method is also good in terms of anisotropic etching, making it suitable for microfabrication. however,
When pure chlorine gas is used, chlorine is adsorbed onto the semiconductor substrate after etching, so that when the substrate is taken out into the atmosphere, the semiconductor surface immediately corrodes, making handling very difficult.

As described above, etching of the ■-■ group compound semiconductor by the conventional method is extremely difficult, and has been a major obstacle to the fabrication of devices using the ■-■ group compound semiconductor.

The present invention is intended to solve the above-mentioned problems, and aims to be reproducible, practical, cause extremely little damage to the substrate after etching, and allow the creation of various processed shapes. Moreover, it is an object of the present invention to provide a method for etching a II-VI group compound semiconductor in which the semiconductor surface is clean after etching.

[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 It-VI, which involves dry etching by irradiating the material with a uniformly oriented ion beam;
In the method for processing group compound semiconductors, the reactive gas is a hydrogen halide such as HCl or HBr, the gas pressure is in the range of 5 x 10-3 pa to 1 Pa, and the microwave incident power is 1 W or more and 1 kW or less. , the voltage for extracting the ion beam from the discharge chamber to the material to be processed is in the range of 0 V or more and 1 kV or less.

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

First, FIG. 8 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 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. 8 is an electron/cyclotron resonance (ECR) plasma chamber and a cylindrical donor for generating a magnetic field.

Surrounded by the T-shaped coil 9, there is a microwave introducing quartz window at the connection part with the microwave waveguide lO. 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 GH2, when the magnetic field strength is, for example, 875 Gauss, and the electronic system absorbs the microwave energy resonantly. 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 360'' 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 Zn5e 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. Using HCI as the reactive gas, gas pressure 1.0XIO-'Fax, microwave input output ioow, extraction voltage s o o
v. Etching was performed at a sample temperature of 25° C. and an ion beam irradiation direction perpendicular to the substrate. Figure 1 (b
) is a sectional view after etching. The etching rate for Zn5e was about 900 A/min, while for photoresist (
The etching rate for the positive type is about 280 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 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. . When pure chlorine gas is used under the above conditions, the etching rate is 600 A/m 1 n, and when HCl gas is used, the etching rate is 1. It becomes five times. That is, for the same amount of etching, using HCl gas requires a lower plasma density and a lower accelerating voltage, which means that damage to the semiconductor substrate can be further reduced. FIGS. 2(a) and 2(b) compare the photoluminescence of the Zn5e substrate before etching and the Zn5e substrate after etching under the above conditions. (a) shows the photoluminescence before etching, and (b) shows the 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.

Furthermore, as a result of evaluating the contamination state of the surface of Zn5e after processing and ching using Auger electron spectroscopy, it was found that MCI was detected as a reactive gas.
The intensity of oxygen and chlorine was lower when using ct2 than when using ct2.

The reason for this is thought to be that oxygen and chlorine on the Zn5e surface are removed by the hydrogen radicals of the MCI gas plasma, and by using HCl gas, clean Zn
A 5e surface is obtained.

The in-plane distribution of etching rate was less than ±5% within a 20 mm x 2 Q mm substrate, and the surface morphology after processing was almost the same as before processing.

Practically effective etching conditions such as device fabrication are as follows.

First, regarding the gas pressure, qualitatively speaking, as shown in FIG. 5, the higher the gas pressure, the faster the cutting/notching speed. However, if the gas pressure becomes too high, discharge will not occur, and even if discharge occurs (over 1 Pa)
The ion sheath width and the mean free path of ions and neutrons are approximately the same, and the ion beam lacks directivity, making it unsuitable for microfabrication. Gas pressure is low (IXIO-3
pa), the etching speed is too slow and is not suitable for practical use. Table 1 shows the microwave incident power of 100 W.

The graph shows the change in the etching rate of Zn5e with respect to gas pressure when HCl gas is used as the etching gas at an extraction voltage of 500 mm. In addition, P in the table is the gas pressure (P a
), R is the etching rate (A/m1n), and S is the state of side etching.

As shown in FIG. 6, the higher the output power of the microwave, the more intense the excitation becomes, so the plasma density becomes higher and the etching rate becomes faster.

However, if the output is too high, the plasma temperature will rise, causing thermal deformation of the electrodes, and the substrate temperature will also rise due to radiant heat, making temperature control difficult. Good etching characteristics were obtained in the range of 1 W or more and 1 kW or less. Table 2
For this, the etching gas is HCl gas, and the gas pressure is lXl0.
Interest Pa.

The dependence of the ZnSe etching rate on the microwave input power when the extraction voltage is 400V is shown.

In the table, M is the incident power (W) of the microwave, and R is the etching rate (A/m1n).

Regarding the extraction voltage, as shown in FIG. 7, the higher the voltage, the higher the etching rate.

However, if the voltage is too high (1 kV or more), the physical sputtering will be strong, which will cause significant damage to the substrate crystal, which is undesirable.

When no extraction voltage is applied (0■), the board temperature is set to 20
If the temperature is raised to about 0°C, etching occurs due to radical species. In this case, etching proceeds in the same direction. Table 3
Table 2 shows the dependence of the etching rate on the extraction voltage when the etching gas is HC gas, the gas pressure is I x 10''Pa, and the microwave input power is 200W. , H is the extraction voltage (V), R is the etching rate (A/m1n),
D is the damaged state of the substrate.

FIG. 3 shows an example of processing a vertical cross section of Zn5e.

First, as shown in Fig. 3(a), photoresist 3 (positive type) was spin-footed on Zn5el and heated at 200°C.
Beta for 30 to 120 minutes with T14 at about 100 OA,
It is formed on a photoresist using an electron beam evaporation method or the like. Next, as shown in FIG. 3(b), a pattern of the photoresist 5 is formed by a normal photolithography process. Next, as shown in FIG. 3(C), Ti4 is etched 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 CFa gas.
In order to perform precise pattern transfer, dry etching with a small amount of side etching is preferable. Next, Figure 3 (
As shown in d), using Ti4 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. To produce an etching mask with a vertical cross-sectional shape without a taper, when using a normal parallel plate type dry etching device, the oxygen gas pressure is 5.
It is desirable that the pressure is about Pa.

If the pressure is too high, etching proceeds in the same direction, which is not suitable in this case. The Ti4 used as an etching mask for the photoresist 3 is removed with a buffered hydrofluoric acid solution or the like before etching the ZnS e 1.

Next, if Zn5e is etched with MCI gas plasma under the same conditions as in the example shown in FIG. 1, the result shown in FIG. 3(e) is
A duty cross section as shown in is formed.

Also, at this time, side etching hardly occurs.

Therefore, although the process is somewhat complicated, the method shown in FIG. 3 can be said to be an effective means when it comes to anisotropic etching.

FIG. 4 shows an example in which an ion beam is incident on the surface of a Zn5e substrate l 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, ZnS e was explained as an It-Vl group compound semiconductor, but ZnS x
It is also effective for other If-Vl group compound semiconductors such as Se-8 (0x≦1). Further, although HCI gas was used as the etching gas, similar results were obtained with other hydrogen halides such as HBr.

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

In the etching method for II-Vl group compound semiconductors using a reactive ion beam generated by microwave excitation and ECR plasma, hydrogen halides such as HCl and HBr are used as the etching gas, replacing the conventionally used pure chlorine gas. On the other hand, about 1. It is possible to obtain an etching rate five times higher, to perform etching at low plasma density and low accelerating voltage, and to almost eliminate damage to the semiconductor layer. Furthermore, contamination of the semiconductor surface after etching can be reduced, resulting in a clean semiconductor surface. Furthermore, by controlling the shape of the ion beam and etching mask, it is possible to process chi-shaped grooves, vertical cross sections, diagonal grooves, etc., making it possible to fabricate devices using U-Vl compound semiconductors with improved reproducibility and It can be manufactured reliably and easily.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are diagrams 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 by the method of the present invention, respectively. FIGS. 3(a) to 3(e) are views showing an example in which vertical end faces of Zn5e are processed according to the present invention. FIGS. 4(a) and 4(b) show that Zn
The figure which shows one Example which processed the diagonal groove of 5e. FIG. 5 is a diagram showing the relationship between etching speed and gas pressure. FIG. 6 is a diagram showing the relationship between etching speed and extraction voltage. FIG. 7 is a diagram showing the relationship between etching speed and microwave input power. FIG. 8 is a schematic diagram of an etching apparatus used in an embodiment of the present invention. 1...Zn5e substrate 2...Photoresist 3...Photoresist 4...TI 5...Photoresist 6...Sample preparation chamber 7...Etching chamber 8...ECR plasma generation chamber 9...Electromagnet 10...Microwave waveguide 11...Extraction electrode I2...Sample 13...Sample holder 14...Manipulator 15...Gas introduction part 16...Transportation rod 17... ...Exhaust system 18...Exhaust system 19...Gate valve and above Applicant Seiko Epson Co., Ltd. Representative Patent Attorney Kizobe Suzuki (and 1 other person) (e, T) (ku) 7r1-n-e, 8I-ya'-(eV)

Claims (4)

[Claims] (1) By forming an etching mask, activating the 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. A method for etching a compound semiconductor, wherein the reactive gas is a hydrogen halide such as HCl or HBr, in a method for processing a II-VI group compound semiconductor including a step of dry etching. (2) The pressure of the reactive gas is 5×10^-^3pa
2. The method of etching a compound semiconductor according to claim 1, wherein the etching pressure is within a range of from 1 Pa to 1 Pa. (3) The method for etching a compound semiconductor according to claim 1, wherein the incident microwave power is in a range of 1 W or more and 1 kW or less. (4) The method for etching a compound semiconductor according to claim 1, wherein the voltage for drawing the ion beam from the discharge chamber to the material to be processed is in the range of 0 V or more and 1 kV or less.