JPH07120808B2 - Varactor diode manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a varactor diode.

[Conventional technology]

As shown in FIG. 2, the varactor diode is formed on the low resistivity substrate 9 by, for example, vapor phase epitaxy, an epitaxial layer 10 of the same conductivity type as the substrate and an epitaxial layer of the opposite conductivity type to the substrate.
11 are sequentially grown and a metal layer is formed on the epitaxial layer 11.
12 is formed by a vapor deposition method, and a mesa portion 13 is formed by a PR method and a chemical etching method to form a pn junction, and a change in the thickness of the depletion layer, that is, the junction capacitance due to the reverse voltage applied to this junction is changed. We are using. The higher the electron concentration of the epitaxial layer 10 which is the operating layer of the device, the smaller the resistance value in series with the pn junction, and the more the cause of the thermal noise of the device is reduced. It is rather inconvenient to maintain the reverse withstand voltage at the design value and cannot be increased unnecessarily. At present, the electron concentration of the epitaxial layer 10, which is the operating layer, is constant at 3 to 5 × 10 ¹⁵
cm in the range of ^{-3 2.5} to 3 as an epitaxial layer thickness. ⁵ mu
m is used.

Since the varactor diode uses the change in the junction capacitance due to reverse bias, the larger the change width of this capacitance, the larger the changing frequency width.For example, the characteristics of the tuner used in the microwave band made by using this element improves.

In order to increase the change width of the capacitance, the electron concentration of the epitaxial layer 10 may not be constant in the depth direction but may be decreased as the surface approaches the interface with the substrate.

If the gradient of the electron concentration is too large, the electron concentration at the interface between the operating layer 10 and the substrate 9 is reduced, and thus the series resistance is increased. Therefore, it is necessary to have a gentle gradient.

[Problems to be solved by the invention]

In order to obtain a gradient in the electron concentration distribution in this way, the epitaxial (operating) layer may be grown in vapor phase while gradually increasing the flow rate of the doping gas, but this control is difficult and there is a problem in reproducibility. If the P ⁺ layer is formed by growth, the concentration cannot be increased and the series resistance increases.

[Means for solving problems]

In view of this point, the present invention provides a method for manufacturing a varactor diode having an electron concentration distribution inclined with good reproducibility by simple control.

According to the method of the present invention, an N type epitaxial layer having a lower electron concentration than that of the N type gallium arsenide substrate is formed on the N type gallium arsenide low resistivity substrate. And activate the implanted silicon ions,
Further, P-type impurities are diffused from the surface of the epitaxial layer to form a pn junction, and the electron concentration is gradually decreased from the pn junction interface to the interface between the substrate and the epitaxial layer. It is characterized by having a distribution.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

2. on the low resistivity gallium arsenide substrate 1 having an electron concentration of 2~3 × 10 ¹⁸ cm ^-3, as shown in FIG. 1 (a) ~ (f) ⁵
To 3. ⁵ [mu] m layer 3-5 thick × 10 ¹⁵ cm ^-3 in to form an epitaxial layer 2 having an electron concentration of double charge ions of the silicon at 350 ^kev 10 ¹³ cm ^-2 implanted ion implanted layer 3 And cover this semiconductor substrate with a SiO ₂ film 4 800 ℃
Annealing is carried out for 20 minutes at the temperature, then the SiO ₂ film is chemically etched, vacuum sealed with a quartz tube, and Zn is diffused by a closed tube method at 620 ° C. for about 60 minutes to form a diffusion layer 5. Next, after forming the electrodes 6 and 7 by the vapor deposition method, PR
When the mesa portion 8 was formed by chemical etching by the method and the electron concentration distribution was measured by the CV measuring method, the result shown in FIG. 3 at 14 was obtained.

Further, 15 in FIG. 3 is 100 ^kev of silicon ion by the above method.
Shows the electron concentration distribution when 5 × 10 ¹² cm ^{-2 is} implanted. Reference numeral 14 in FIG. 3 shows that an epitaxial layer having a sloped distribution of electron concentration, which is optimum for a varactor diode, is obtained.

Next, the effect of the present invention will be described. First, as shown in FIG. ³ , the sample 16 having a constant electron concentration of ^{3 to} 5 × 10 ¹⁵ cm ^-3 on the low resistivity substrate and this method were carried out, and the concentration in the vicinity of the pn junction was approximately 4 to 5. The electron concentration decreases slowly as it gets deeper at 6 × 10 ¹⁶ cm ^-3. The concentration near the sample 14 and the pn junction is 0.9 to 1.0 × 10 ¹⁷ cm ^-3 , and the electron concentration decreases sharply as it gets deeper. Sample 15 was prepared and the reverse bias dependence of the junction capacitance was measured. The result is shown in FIG.

The sample 14 obtained by carrying out the present invention shows a gentle C-V curve with respect to the result 18 of the sample 15 as shown in 17 of FIG. 4, and the frequency-voltage linearity is good. The result 17 of the sample 14 has a larger capacitance change ratio and a wider frequency width than the result 19 of the sample 16.

Further, as can be seen from FIG. 3, the sample 14 has an effect that the electron concentration distribution is higher overall, the series resistance is small, and the cause of the thermal noise is reduced as compared with the samples 15 and 16.

Another advantage of the present invention is that when the double-charged ions of silicon are implanted, the epitaxial layer is partially covered with an appropriate mask, such as a photoresist or a dielectric mask, so that the CV curve can be easily and selectively applied to an arbitrary position. That is, it is possible to form a gradual varactor diode.

This is a great advantage when considering the gallium arsenide integrated circuit, which is currently being developed, together with the fact that it is difficult to selectively perform vapor phase growth by the conventional vapor phase growth method.

〔The invention's effect〕

As described above, according to the present invention, a diode having a tilted electron concentration distribution is manufactured with good controllability and reproducibility.

[Brief description of drawings]

1 (a) to 1 (f) are sectional views showing the manufacturing method of the present invention, FIG. 2 is a sectional view of a varactor diode according to a conventional method, FIG. 3 is an electron concentration distribution diagram, and FIG. It is a bias characteristic. 1,9 …… Gallium arsenide semiconductor substrate, 2,10 …… Epitaxial layer of the same conductivity type as the substrate, 3 …… Ion implantation layer, 4 …… Si
O ₂ , 5, 11 …… Diffusion layer of the opposite conductivity type to the substrate, 6, 12 …… Metal layer (front), 7 …… Metal layer (back), 8, 13 …… Mesa part, 14 ……
Electron concentration distribution according to the present invention, 15 ... Electron concentration distribution when silicon ions are implanted at 100 ^kev , 5 × 10 ¹² cm ^-2 by the same method as the present invention, 16 ... General varactor diode (without implantation) 17 …… Capacitance-reverse bias characteristics of sample 14, 18…
... Capacity-reverse bias characteristics of sample 15; 19-Capacity-reverse bias characteristics of sample 16.

Claims (1)

[Claims] 1. An N-type gallium arsenide low-resistivity substrate is formed with an N-type epitaxial layer having a lower electron concentration than that of the substrate, and silicon double charge ions are applied to the epitaxial layer at an energy of 350 kev. Implanting, activating the implanted silicon ions, diffusing impurities exhibiting P-type from the surface of the epitaxial layer to form a pn junction, and from this pn junction interface, the substrate and the epitaxial layer are formed. A method for manufacturing a varactor diode, which has an electron concentration distribution in which the electron concentration gradually decreases toward an interface.