JPH06101480B2 - Method for forming insulating layer of compound semiconductor - Google Patents

Description

The present invention relates to a method for forming an insulating layer of a compound semiconductor.

[Conventional technology]

Currently, ultra-high-speed gallium arsenide and LSI are being rapidly developed, and a higher performance single FET is expected as a basic element. As a method of forming the conductive layer, a method of selectively ion-implanting impurities such as silicon into semi-insulating gallium arsenide is currently common, but in order to improve the transconductance of the FET, which is a basic element, it is thinner, A high-concentration conductive layer is required, and studies have begun on a thin high-concentration conductive layer grown on a semi-insulating substrate by an epitaxial technique. At this time, element isolation technology between single elements becomes important, but with the miniaturization of elements, the demand for planarization becomes stronger, and from the viewpoint of controllability and reliability, the conventional element isolation technology by etching is replaced with ion. The importance of device isolation technology by implantation has been recognized. Further, this technology is very important not only for gallium arsenide LSIs but also for devices using heterojunctions of compound semiconductors and optoelectronic integrated circuits in which optical element groups and electronic element groups are integrated on the same substrate. .

Until now, many attempts have been made to insulate the conductive layer of gallium arsenide by ion implantation, and it has been reported that it is possible to insulate ions by ions such as protons, helium, oxygen, arsenic, and boron. Oxygen, arsenic,
It was limited to boron.

Focused ion beam technology is one of the technologies that are being rapidly researched recently as the next-generation ion implantation technology.
Studies on the formation of an insulating layer using this technique have also started.
By using a focused ion beam, fine ion implantation can be performed without a mask, so that various advantages such as simplification of a large process are brought about.

[Problems to be solved by the invention]

However, when this is viewed as an insulating layer forming technique, ion species, oxygen, arsenic, and boron for forming an insulating layer that is stable to the above-described high-temperature heat treatment are the ion source of the focused ion beam as described below. However, this is not always an appropriate ion source, and there has been a problem in practical use. In other words, in the formation of insulating layers using boron, Arimoto et al. (Japanese Journal of Applied Physics) 23
Vol. 1984, L165, pp. 165, developed an ion source capable of simultaneously obtaining silicon as an n-type dopant for gallium arsenide, beryllium as a p-type dopant, and boron for insulation. It has been reported that boron can be insulated by injecting submicron rays of boron. However, boron is a very reactive element and corrodes the emitter of the ion source, and as a result, the life of this ion source is only about 30 hours, which poses a practical problem. It was Although it is possible to improve this point by the conventional technique, special measures such as using carbon for the emitter of the ion source were required.

Regarding oxygen, it is necessary to use a field ionization type gas ion source that requires ultra-high vacuum for stable operation, but this type of ion source has just started to be developed with hydrogen and helium. The current situation is that there is no

Regarding arsenic, it has been reported that ions were obtained using a eutectic alloy ion source, but it was reported that only a small amount of current could be obtained due to the high vapor pressure of arsenic. There was a problem.

As described above, when looking at the focused ion beam technology as the insulating layer forming technology, it is possible to form an insulating layer that is stable even at high temperature heat treatment, and as a focused ion beam ion source, it is stable and easy for a long time. An ion source that can be used has not been obtained at present, and such an ion source has been desired.

Conventionally, the present invention provides a highly reliable ion source for a focused ion beam, which is stable and easy to use for a long time. It is based on the experimental fact that it was revealed for the first time that a stable insulating layer can be formed, but this experiment was conducted to observe the effect of a focused gallium ion beam on the activation of implanted impurities in gallium arsenide. It was carried out as an extension of the experiment of double injection of ions and focused gallium ions. As described above, in ion implantation for forming a conductive layer of a compound semiconductor, attempts to control the stoichiometric composition and, as a result, the activation rate by simultaneously implanting the constituent elements have not been carried out by ordinary non-implantation. There have already been many reported cases of focused ion implantation. A typical example is Inada et al. Radiation Effects (Vol. 48), 1980.
This is an example of improving the activation rate when selenium alone is ion-implanted by double-implantation of selenium and gallium, as shown on page 91 of the year. Ion Implantation In Semiconductor, edited by Chanau et al., Plenum Press, 149 pages. However, since the non-focused gallium ion is used in this report, the effect of the present invention has not been found in a remarkable form. Implant silicon ions at 250 keV at 3.0 × 10 ¹³ / cm ² and gallium ions at 250 keV 1.0 × 10 ¹⁵ / cm ² at 850 ° C.
In the sample annealed in the argon atmosphere with the silicon nitride film as the protective film for 15 minutes, carrier disappearance is certainly observed at a depth corresponding to the projected range of gallium ions, but it is deeper than that. On the side, an increase in the carrier was observed, and as a result, it was shown that the sheet carrier concentration did not change, but rather increased. Therefore, from this reported example, it is difficult to conceive of actively forming an insulating layer by gallium ion implantation as in the present invention.

An object of the present invention is to perform high temperature heat treatment by implanting gallium, which is one of the constituent elements of gallium arsenide, which is the most reliable ion source of a focused ion beam, into a conductive layer of a compound semiconductor gallium arsenide layer. Another object of the present invention is to provide a method for forming a stable insulating layer.

[Means for solving problems]

The method for forming an insulating layer of a compound semiconductor according to the present invention is characterized in that focused gallium ions are injected into a compound semiconductor gallium arsenide layer, the injection region is used as an insulating layer, and the insulating layer is formed in an n-type conductive layer. There is.

[Action / Principle]

The present invention is based on a novel experimental fact found that a stable insulating layer is formed even after a high temperature heat treatment up to 850 ° C. by injecting a focused gallium ion beam into an n-type gallium arsenide conductive layer. It has been experimentally found that the dose of gallium required for conversion depends on the concentration of the n-type gallium arsenide conductive layer. For example, when the n-type gallium arsenide conductive layer is formed by ion implantation of silicon, the dose amount of gallium ions required for this insulation depends on the dose amount of silicon. As will be described later in detail in Examples, for a dose of silicon of 1 × 10 ¹³ / cm ² or less, a dose of silicon of about 1 × 10 ¹⁴ / cm ² and 1 × 10 ¹⁴ / cm ² is used. -3 × 10 ¹⁴ / cm ² and 1 × 10 ¹⁵ / cm ² gallium doses of about 3 × 10 ¹⁵ / cm ² are required to form the insulating layer. Is. When the conductive layer is formed by ion implantation as described above, the gallium ion may be implanted at a timing such as before or after the impurity ion implantation for forming the conductive layer, or before or after the annealing for activating the impurity ion. Although there is an opportunity, it was experimentally confirmed that a similar insulating layer was formed in any case. Even when the n-type conductive layer is formed by a crystal growth method such as a vapor phase epitaxy method or a molecular beam beam epitaxy method, by injecting a focused gallium ion beam, an insulating layer stable to high temperature heat treatment is formed. Also in this case, it was confirmed that the higher the concentration of the conductive layer, the larger the dose of gallium required for insulation.

The mechanism by which the insulating layer is formed by the ion implantation of gallium is considered to be residual damage that exists even after high temperature heat treatment, the formation of arsenic vacancies due to the presence of excess gallium, and the formation of deep impurity levels associated with these. As described in the conventional example, in the unfocused gallium ion beam, the insulating layer is not formed as efficiently as in the focused ion beam, and in the Raman scattering experiment, the dose of gallium forming the insulating layer causes the crystallinity to be high. Considering that the results are getting a little worse, it is expected that the cause of the residual damage is the main cause, but detailed elucidation of the mechanism remains in future research. There is.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

(Example 1) The resistance measurement of a double-implanted layer of gallium arsenide with silicon ions and focused gallium ions will be described with reference to Figs. In FIG. 1 (a), the double implantation of this experiment was performed by initially forming a focused ion beam of gallium narrowed to about 0.1 μm on a semi-insulating gallium arsenide substrate 1 with silicon dioxide (SiO ₂ ) 3. 3 × 10 ¹² / c by raster-scanning with an acceleration voltage of 100 keV on the hole measurement pattern
Implant dose ^{2 with} a dose of m ² to 1 × 10 ¹⁵ / cm 2
To form. After that, with an ordinary ion implanter, the silicon ion range is set to 2 × 10 ¹² , 1 × 10 ¹³ , 1 × 1 at an acceleration voltage of 30 keV so that the range is shorter than that of gallium.
0 ^14, 1 was injected at four different dose of × 10 ¹⁵ / cm ^2.
(FIG. 1 (b)). 4 is a gallium + silicon injection layer. After removing SiO ₂ , a new SiO ₂ protective film was deposited at 3000 Å and annealed in a hydrogen atmosphere at 850 ° C. for 15 minutes. Alloy of gold with germanium and nickel (Ni / AuGe)
After making ohmic contact at 6, titanium (Ti) and gold (Au) are vapor-deposited to form a pad 7 as shown in FIG. 1 (c), and a measurement sample is completed. FIG. 2 shows a characteristic diagram of the resistance value with respect to the gallium dose amount obtained by measuring the obtained sample. Second
The vertical axis of the figure shows the raw resistance value of the prepared sample. As is apparent from FIG. 2, it can be seen that as the dose amount of silicon increases, the dose amount of gallium required for high resistance increases. FIG. 3 is a graph showing the relationship between the dose of gallium and the dose of silicon for increasing the resistance, which is easier to understand. The white circles in the figure show the dose of gallium that transitions to high resistance, that is, the dose with the steepest gradient in the curve of FIG.

In this embodiment, the focused gallium ions are implanted first and then the silicon ions are implanted, but it was confirmed that similar results can be obtained even if the context is reversed.
Also, similar results were obtained when silicon was first implanted and then immediately annealed and activated, and then focused gallium ions were implanted and heat treatment was performed.

(Example 2) FIGS. 4 (a) to 4 (c) are schematic cross-sectional views showing a manufacturing process of a sample in which focused gallium ions are injected into an n-type epitaxial layer and resistance measurement is performed in the order of steps. Is.
In FIG. 4 (a), first, an epitaxial layer 5 having a thickness of 500Å and a carrier concentration of 3 × 10 ¹⁸ / cm ³ is grown on the semi-insulating gallium arsenide substrate 1. In FIG. 4 (b),
Approximately 3000 Å of SiO ₂ was pre-deposited on the ohmic alloy preparation part, and using this as a mask, gallium ions were raster-scanned at an acceleration voltage of 100 keV by a focused ion beam device,
× a sample was prepared with a dose of 10 ¹³ to 3 × 10 of ¹⁵ / cm ² range. Reference numeral 2 is a gallium injection layer, and 4 is a gallium + silicon injection layer. After removing SiO ₂ , a new 3000 Å SiO ₂
As a protective film and anneal in a hydrogen atmosphere at 850 ° C for 15 minutes to remove the conductive layer for about 30 minutes.
After performing a mesa etching of 00Å, an ohmic alloy Ni / AuGe6 was deposited and alloyed by the resistoff as shown in Fig. 4 (c), and Au / Ti7 was also formed as the electrode pad by the resistoff and the sample was formed. To complete. When this sample was measured, it was found that a high resistance layer could be obtained with a gallium dose of up to 3 × 10 ¹⁵ / cm ² . The concentration of the epitaxial layer 5 used here corresponds to the concentration obtained with a dose amount of up to 10 ¹⁵ / cm ² in the ion implantation of silicon performed in Example 1, and the dose amount of gallium for insulating the same. Also, it can be seen that Example 1 and Example 2 are about the same.

As described above, it was found that even in the case of the epitaxial layer, the insulating layer can be formed by implanting the focused gallium ions similarly to the ion implantation layer.

(Example 3) In Examples 1 and 2 described above, the gallium ion implantation was performed by the raster scan of the focused ion beam, but in this example, the gallium ion implantation was performed by the line scan of one focused ion beam.

5 (a) to 5 (c) are schematic cross-sectional views showing the manufacturing process of the sample for resistance measurement in the order of steps. In FIG. 5 (a), first, the semi-insulating gallium arsenide substrate 1 is provided with 30
An ion implantation layer 5 is formed by implanting silicon ions with a dose amount of 1 × 10 ¹³ / cm ² at an acceleration voltage of keV. As shown in Fig. 5 (b), SiO ₂ 3 was pre-applied to the ohmic alloy preparation part to about 3
000 Å was deposited, and gallium ions were used as a mark to perform one line scan at an accelerating voltage of 1000 keV by a focused ion beam device, and a sample with a dose amount in the range of 1 × 10 ¹³ to 1 × 10 ¹⁵ / cm ² was sampled. It was made. Reference numeral 2 is a gallium injection layer, and 4 is a gallium + silicon injection layer. After removal of the SiO _2,
Approximately 3000 Å SiO ₂ is newly deposited, and this is used as a protective film.
Anneal in hydrogen atmosphere at 0 ° C for 15 minutes, perform mesa etching of about 3000Å to separate the conductive layer,
As shown in FIG. 5 (c), after making ohmic contact with an ohmic alloy Ni / AuGe6, Au / Ti7 was vapor-deposited as an electrode pad to complete a sample. When this sample was measured, it was 1 ×
A high resistance was obtained with a gallium dose of 10 ¹⁴ / cm ² , and Example 1 was used.
We obtained almost the same result as. In addition, the line width of this insulating layer is about 0.4μ according to the evaluation of the sample that was obliquely polished and stainless-etched.
It was confirmed to be m, but the withstand voltage was as good as 30 V despite such a fine insulating layer.

〔The invention's effect〕

As described in detail above, according to the present invention, it is possible to insulate the gallium arsenide conductive layer by the longest-lived and highly reliable gallium ion as the ion source of the focused ion beam, and the fine insulating layer can be formed. It has an effect that it can be formed without a mask and the manufacturing process can be simplified and the controllability and reliability can be improved.

[Brief description of drawings]

1 (a) to 1 (c) are schematic cross-sectional views showing a sample manufacturing process in order of steps for explaining the first embodiment of the present invention, and FIG. 2 is a sample obtained in the first embodiment. FIG. 3 is a characteristic diagram showing the relationship between the resistance value obtained by resistance measurement and gallium dose amount. FIG. 3 is a characteristic diagram showing the gallium dose amount necessary for insulation with respect to the silicon dose amount. 4 (a) ~
FIG. 5C is a schematic cross-sectional view showing a sample manufacturing process for explaining the second embodiment in the order of steps, and FIGS. 5A to 5C are sample manufacturing processes for explaining the third embodiment. FIG. 3 is a schematic cross-sectional view showing in the order of steps. 1; semi-insulating gallium arsenide substrate, 2; gallium injection layer, 3; SiO ₂
Layer, 4; gallium + silicon injection layer, 5; silicon injection layer,
6; Ni / AuGe ohmic alloy layer, 7; Au / Ti pad.

Claims (1)

[Claims] 1. A compound semiconductor gallium arsenide layer is implanted with focused gallium ions, and the implanted region is used as an insulating layer.
A method for forming an insulating layer of a compound semiconductor, which comprises forming an insulating layer in an n-type conductive layer.