JPH0516660B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to the manufacturing of high-speed semiconductor devices, which includes a step of diffusing heavy metals as a lifetime killer to shorten the lifetime of carriers implanted into a silicon semiconductor substrate. It concerns an improvement in the method.

[Prior Art] In order to reduce the size and improve efficiency of so-called switching power supplies, high speed and high efficiency secondary side rectifying elements are required, and for the purpose of obtaining elements with low forward voltage drop and high speed recovery characteristics. , Schottky elements and high-speed rectifier elements are used, but improvements to the elements themselves continue to be made in pursuit of even higher speeds and higher efficiency. Improvements in such devices are generally made by growing an epitaxial layer with a required thickness on a highly impurity-concentrated silicon semiconductor substrate, and adding gold (Au) or platinum (as a lifetime rekiller) to shorten the carrier lifetime. Diffusion of heavy metals such as Pt) takes place.

[Problems to be solved by the invention] In the above case, due to the epitaxial substrate having a high impurity concentration and the shallow and high concentration diffusion layer, the active region that is the target of operation may be a defective part or an abnormality in the crystal. The problem is that precipitation of the heavy metals mentioned above is likely to occur at the points, and as a result, leakage current occurs as the heavy metal diffusion temperature rises, and devices with a large leakage current are treated as defective products that cannot be used, resulting in a decrease in yield. It was hot.

This invention was made in order to solve the problems of the conventional ones as described above, and its purpose is to provide a method for manufacturing high-speed semiconductor devices that can reduce leakage current of semiconductor devices and improve yield. It is something to do.

[Means for Solving the Problems] A method for manufacturing a high-speed semiconductor device according to the present invention includes: setting the temperature of the oxide film forming step, which is repeated multiple times during the manufacturing process of the high-speed semiconductor device, to 1100° C. or lower;
And the temperature drop from 1100℃ to 500 to 600℃ is 0.5~
A slow cooling step of 2°C/min, and after this step,
It is characterized by including a heat treatment step of holding at a temperature of 550 to 600° C. for at least one hour.

[Effect] By adding the heat treatment step before the heavy metal diffusion step, abnormal concentration of heavy metal impurities as a lifetime killer in a part of the semiconductor substrate during heavy metal diffusion and abnormal points in the crystal lattice that become the nucleus for separation and precipitation are created. Alternatively, generation of abnormal stress can be avoided.

[Example] FIG. 1 is a process diagram for explaining the manufacturing method of the present invention.

In Figure A, an N ⁺ type high concentration silicon substrate 1 on which an N type epitaxial layer 2 is grown is first prepared, and then, as shown in Figure B, the epitaxial substrate 3 is grown at a temperature of 1050°C. A silicon dioxide (SiO ₂ ) film 4 is formed on the epitaxial substrate 3 by heating in a moist oxygen atmosphere (Wet O ₂ ) for a predetermined time.

Next, after forming the SiO ₂ film 4, it is gradually cooled from 1050°C to 600°C at a rate of 0.5 to 2°C/min, and enters a heat treatment process that is a feature of the present invention.

That is, after slowly cooling the substrate 3 to 600°C,
Hold at 600°C for 1 hour or more, preferably about 30 hours.

Next, as shown in Figure C, a window 5 of a predetermined size is formed in the SiO ₂ film 4 using a normal photolithography technique to form a P ⁺ type anode layer 6.
Boron diffusion is performed in WetO ₂ at 1100 °C for a predetermined time.

The above board 3 is heated again from 1100℃ to 600℃ from 0.5 to
Cool slowly at a rate of 2°C/min and hold at 600°C for over 1 hour.
Heat treatment (annealing) is preferably performed for about 30 hours. Next, as shown in figure D, N ⁺⁺
A predetermined time at a temperature of 1100°C to form layer 7
Heat in WetO ₂ and then slowly cool from 1100°C to 600°C at a rate of 0.5-2°C/min. Then, as above, at 600℃ for 1 hour or more, preferably 30℃.
Hold for about an hour.

After the above annealing step, killer diffusion is performed for a predetermined period of time by a well-known method using heavy metals such as platinum (Pt) and gold (Au) to shorten the lifetime of the carrier.

This invention is based on the method described above before performing killer diffusion.
By performing heat treatment in the process after forming the SiO ₂ film, it is possible to avoid abnormal concentration of killer impurities during killer diffusion and the generation of abnormal points and abnormal stresses in the crystal lattice that can become nuclei for separation and precipitation. .

Next, FIG. 2 shows a graph comparing leakage current between an element manufactured by the present invention and an element manufactured by a conventional method. In the figure, the vertical axis shows the leakage current I _R
(mA), the horizontal axis shows the temperature Tc (°C), the solid line shows the device manufactured by the manufacturing method of this invention, the dotted line shows the device manufactured by the conventional manufacturing method, and the dashed line shows the leakage current. (Leak) Indicates standards.

As is clear from this graph, within the range up to the predetermined temperature tm, the leakage current of the device manufactured by the manufacturing method of the present invention is significantly lower than that of the device manufactured by the conventional method.

[Effects of the Invention] According to the present invention, heat treatment is performed under predetermined conditions after the oxide film formation step, which is repeated multiple times during the manufacturing process of high-speed semiconductor devices, as described above.
Abnormal concentration of killer impurities during killer diffusion, abnormal points in the crystal lattice that become nuclei for separation and precipitation, and generation of abnormal stress can be avoided, and as a result, high-speed semiconductor devices with low leakage current can be manufactured. Yield is improved.

[Brief explanation of drawings]

FIG. 1 is a process diagram for explaining the manufacturing method of the present invention, and FIG. 2 is a graph comparing the leakage currents of a device manufactured by the manufacturing method of the present invention and a device manufactured by a conventional method. In the figure, 1 is a silicon substrate, 2 is an epitaxial layer, and 4 is a silicon dioxide film.

Claims (1)

[Claims] 1. In a method for manufacturing a high-speed semiconductor device that includes a step of diffusing heavy metals as a lifetime killer to shorten the lifetime of a carrier injected into a silicon semiconductor substrate, oxidation that is repeated multiple times during the manufacturing process of the high-speed semiconductor device The temperature of the film forming process is set to 1100℃ or less, and the temperature is gradually lowered from 1100℃ to 550 to 600℃ by 0.5 to 2℃/min, and after this step, the temperature is continuously lowered to 550 to 600℃. 1. A method for manufacturing a high-speed semiconductor device, comprising a heat treatment step of holding at a temperature for at least one hour or more.