JPH0480879B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention involves implanting ions that can become N-type or P-type impurities into a compound semiconductor such as GaAs or InP, and then annealing the compound semiconductor at a high temperature to form an ion-implanted layer. It relates to a method of activation.

[Background technology]

When manufacturing transistors and integrated circuits by ion implantation using a compound semiconductor crystal substrate such as GaAs, an annealing process is essential for forming a conductive layer. Annealing generally involves heating a compound semiconductor substrate into which ions have been implanted at a high temperature for several tens of minutes in a resistance heating furnace. Since the heating temperature is higher than the temperature at which components with high vapor pressure contained in the substrate, such as As and P, begin to evaporate, there has been a problem that the substrate undergoes thermal decomposition. For this reason, there was a problem in that the electrical properties of the conductive layer formed on the substrate surface varied due to annealing, resulting in large variations.

To prevent this, annealing under the vapor pressure of components with high vapor pressure or a protective film to prevent evaporation, for example,
A method is used in which a SiO ₂ film or a Si ₃ N ₄ film is formed on the substrate surface and then annealed. However, in the former method, the problem remains that the gas containing components with high vapor pressure is toxic, making the process complicated to operate and processing, and resulting in extremely low productivity. On the other hand, in the latter case, since the properties of the protective film vary depending on the method and conditions for forming the protective film, there are problems such as low stability and reproducibility and cracking of the protective film during annealing.

In addition, the conventional annealing method involves high-temperature treatment for several tens of minutes in an electric furnace, which causes residual impurities in the substrate crystal.
It is known that Cr and Mn cause diffusion and high concentration near the surface, and interact with ion-implanted atoms. For this reason, the activation rate due to annealing becomes unstable, making it difficult to control the electrical characteristics of transistors and integrated circuits.
Furthermore, in conventional annealing methods, lateral diffusion is also known, in which implanted atoms diffuse several tenths of a micrometer in a direction parallel to the surface during annealing. This causes a change in the implanted region, for example, the effective gate length, which poses a serious problem in terms of device manufacturing, which requires microfabrication of 1 μm.

In contrast, an annealing method using an infrared lamp has been reported in recent years. FIG. 2 is an example. Due to its ability to rapidly heat the substrate, the annealing time is approximately two orders of magnitude shorter than that of conventional annealing methods, and lateral diffusion can be suppressed as well as the evaporation of As and P components, which have high vapor pressure, to a minimum. It is reported that it is possible. However, evaporation of As and P cannot be completely eliminated in principle. For example, 800℃
Mirror polishing was achieved even after heat treatment for 10 seconds.
Minute spots appear over the entire surface of the GaAs substrate, and so-called As omission is observed, and there still remains a problem with the evaporation of As and P.

[Disclosure of the invention]

The present invention eliminates the drawbacks of the conventional methods and provides an annealing method capable of preventing thermal decomposition of a compound semiconductor and at the same time suppressing lateral diffusion.

Hereinafter, the present invention will be explained based on Examples. FIG. 2 illustrates the configuration of an annealing method according to the present invention when a GaAs substrate is used as a compound semiconductor. Once evacuated, Si 3 with a thickness of 1000 Å is placed on both sides on a carbon graphite plate 13 with a thickness of several mm, which is held via a quartz jig 12 in the center of the quartz tube 11 filled with N _{2 gas.} A GaAs substrate 15 on which an N ₄ film 14 has been formed by plasma CVD is placed with the ion-implanted side facing up, and a GaAs substrate 1 on which a 1000 Å Si ₃ N ₄ film 14' is similarly formed on both sides is placed.
5′ and GaAs substrate 1 from outside of quartz tube 11.
5 is irradiated and heated from both sides using a lamp heater 16. The annealing temperature was measured by a thermocouple placed near the GaAs substrate 15, and the heating rate and annealing temperature were kept constant by PID control of the power applied to the lamp based on this measurement.
A sample annealed at 900°C for 10 seconds using the annealing method of the present invention showed a carrier concentration profile equivalent to a sample annealed at 800°C for 20 minutes in a conventional electric furnace.

In addition, by applying the lamp annealing method under the above conditions, when the pinch-off voltage is in the range of -0.5V to -1.2V,
When we fabricated a GaAs field effect transistor,
The results showed that the variation in pinch-off voltage of 6000 to 7000 FETs in a 17 mm x 17 mm area was 100 mV at 1 sigma. Incidentally, when annealing was performed without placing the substrate 15' on it, the pinch-off voltage was the same, only the variation was large at 200 to 150 mV at 1 sigma, and the reproducibility was deteriorated. From this, board 1
5' was confirmed to be effective in preventing thermal decomposition of both the GaAs substrate 15 and the Si ₃ N ₄ film 14.

One of the requirements constituting the present invention is to utilize not only infrared rays but also light with a shorter wavelength than infrared rays as the heat rays from the lamp. Since compound semiconductors have a high transmittance to light in the infrared region, the efficiency of heating the compound semiconductor substrate with infrared rays is extremely low. Therefore, the present invention aims to significantly improve heating efficiency by directly heating the substrate with light having a wavelength shorter than infrared rays and simultaneously heating the carbon graphite jig on which the substrate is mounted with infrared rays.

Yet another requirement is to form a protective film of an inorganic compound on at least the ion-implanted surface of the compound semiconductor substrate, and to place a substrate of the same structure on top of the protective film and anneal it. This makes it possible to completely prevent evaporation of components with high vapor pressure. Considering this purpose, the inorganic compound film is not limited to the Si ₃ N ₄ film in the example or the plasma CVD method, but also SiO ₂ film, Al ₂ O ₃ film, AlN film, etc.
It is also possible to form the film etc. by a well-known manufacturing method.

Furthermore, the atmosphere is not limited to the N ₂ gas used in the example, as the object of the present invention can be achieved if annealing is performed in an inert gas to avoid unnecessary chemical reactions at high temperatures on the compound semiconductor substrate. ,
It should be added that in addition to N ₂ , inert gases such as Ar and He, H ₂ gas, and mixed gases thereof can also be applied.

[Brief explanation of the drawing]

FIG. 1 shows an example of the structure of the annealing method according to the present invention, and FIG. 2 shows an example of the structure of the conventional annealing method. 11...Quartz tube, 12...Quartz jig, 13...
Carbon graphite plate, 14, 14'...Inorganic compound film, 15, 15'... Compound semiconductor substrate,
16...Lamp heater.

Claims (1)

[Claims] 1 Forming an inorganic compound film on at least the ion-implanted side surface of a compound semiconductor substrate into which ions that can be N-type or P-type are implanted, and forming an inorganic compound film on the ion-implanted surface of the substrate. A compound characterized in that the formed semiconductor substrates having the same structure are stacked so that the inorganic compound films of both substrates are in contact with each other, and the compound semiconductor is heated by irradiating the compound semiconductor with a lamp having a spectrum in the infrared rays and shorter wavelength ranges. Semiconductor annealing method.