JPH0339998B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new and improved method of manufacturing semiconductor electronic devices.

Traditionally, silicon single crystals grown using the Czyochralski method (CZ method) are contaminated with large amounts of oxygen impurities during the manufacturing process, and these oxygen impurities can cause crystal defects through thermal processes. Are known.

These defects mainly occur during the process of manufacturing devices, and if they occur on the wafer surface (the active region of the device), they can severely degrade device characteristics. Efforts have been made to reduce the oxygen impurity concentration as much as possible.

The present invention effectively utilizes the presence of oxygen impurities described above to contribute to improving the characteristics of devices. was introduced, and at this time the oxygen concentration was adjusted to 8.5×10 ¹⁷ to 10.5
This is a method for manufacturing semiconductor electronic devices in which a wafer obtained from a silicon single crystal with a density of ×10 ¹⁷ atoms/cubic centimeter is used as a starting material and an integrated circuit is formed on the surface of the wafer at a temperature of 900 to 1200°C.

To explain this, the present inventors conducted various studies on the oxygen concentration of single crystal silicon wafers for device substrates, and found that when the oxygen concentration is too low, even after heat treatment at 900 to 1200 degrees Celsius during device manufacturing, oxygen is removed. Precipitation does not occur much; on the other hand, when the oxygen concentration is too high, as mentioned above, oxygen precipitates on the wafer surface (device activation region), which causes defects and extremely deteriorates device characteristics. However, when the oxygen concentration of the silicon single crystal is defined as 8.5×10 ¹⁷ to 10.5×10 ¹⁷ atoms/cm3 according to the present invention as described above, the The present invention was completed after confirming that there were no defects on the wafer surface and, surprisingly, that the lifetime of the wafer surface could be improved.

For example, at approximately 800°C, the diffusion coefficient of oxygen atoms in the silicon single crystal becomes too small, but no oxygen precipitates inside the wafer, and as a result, the wafer's lifetime can only be improved. However, when a p-type silicon wafer with an oxygen concentration of 9.0×10 ¹⁷ atoms/cm3 and a volume resistivity of approximately 10 Ωcm was heat-treated at 800°C for 2 hours,
The lifetime, which was originally 200 microseconds, has decreased slightly. This decrease in lifetime is thought to be due to contamination during heat treatment. On the other hand, when the wafer was heat-treated at 1280°C, no oxygen was precipitated on the surface or inside the wafer. The reason for this is thought to be that in a high temperature region, the permissible solubility of silicon in oxygen increases, making it difficult for oxygen to precipitate within the wafer. From the above experiments and considerations, by heat-treating a wafer with an overall oxygen concentration of 8.5 x 10 ¹⁷ to 10.5 x 10 ¹⁷ atoms/cubic centimeter in the range of 900 to 1200°C, dissolved oxygen in the wafer can be removed from the surface of the wafer. They concluded that it is possible to improve the lifetime of the wafer surface on which integrated circuits are formed by precipitating inside the wafer and creating minute crystal defects.

Next, the present invention will be described in connection with forming a MOS type integrated circuit on a silicon wafer.

An example of the process for forming an N-channel MOS type integrated circuit limited to the formation of the gate oxygen film consists of the following 13 steps.

1st process Initial oxide film formation 1000℃ 2nd process Si ₃ N ₄ film growth 3rd process Photolithography 4th process Si ₃ N ₄ etching 5th process B ion implantation 6th process Photoresist removal 7th process Field oxidation 1000℃ 8th process SiO ₂ etch 9th process Si ₃ N ₄ film 10th process SiO ₂ etch 11th process Oxidation 1000℃ 12th process SiO ₂ etch 13th process Gate oxidation 950℃ As mentioned above, this is the heat treatment temperature in the integrated circuit forming process, and in the above example, around 1000° C. is selected as the heat treatment temperature.

During the above integrated circuit formation process, whether the oxygen contained in the wafer is precipitated or not due to heat treatment, and whether or not the oxygen contained in the wafer is precipitated or not is determined as a measure of the quality of the intended integrated circuit. Examples include electrical properties. Naturally, the withstand voltage of this oxide film is greatly influenced by the quality of crystal defect generation in the wafer surface layer, the formation of crystal defects inside the wafer, and the cleaning of the wafer surface due to its getter effect.

Next, a wafer with an oxygen concentration of 8.5 × 10 ¹⁷ ~ 10.5 × 10 ¹⁷ atoms/cm3 is
Explain how crystal defects occur on the surface and inside of silicon wafers due to heat treatment in the temperature range of 1200℃, and explain how heat treatment in the temperature range of 900 to 1200℃ is performed using wafers with the above oxygen concentration range. It will be explained that by employing this method in a part of the process, it is possible to form integrated circuits with high yield or high performance.

Figure 2 shows a silicon wafer with a high oxygen concentration, i.e. 12.5 x 10 ¹⁷ atoms/cm3.
This is an example of observing the defect distribution in the wafer cross section after heat treatment at 1000°C for 2 hours. In a wafer with such a high oxygen concentration, crystal defects are generated all the way to the surface, and if an integrated circuit is formed on the wafer surface under such conditions, the breakdown voltage characteristics of the gate oxide film mentioned above will clearly deteriorate in the MOS type. It is expected that In Figures 3 and 4, the oxygen concentration is 7.5.
x 10 ¹⁷ atoms/cubic centimeter, wafer that is 9.5 x 10 ¹⁷ atoms/cubic centimeter
This is an observation of defects on the wafer surface after heat treatment at 1100°C for 2 hours. In a wafer with a low oxygen concentration of 7.5×10 ¹⁷ atoms/cm3,
Although micro defects are formed on the wafer surface as in the case of the oxygen concentration of 12.5×10 ¹⁷ atoms/cm3, the nature of the defects is considered to be different. However, integrated circuits with good characteristics cannot be formed on a wafer surface that has defects. In the case of a bipolar type, a pn junction is formed near the wafer surface, but if there is any of the above defects, it is natural that abnormal diffusion will occur in that area and a normal pn junction will not be formed. Although no defects were observed on the surface of the wafer with an oxygen concentration of 9.5×10 ¹⁷ atoms/cm3, it is thought that oxygen was precipitated inside with a getter effect.

Figure 1 of the attached drawings plots the amount of oxygen loss after heating device substrate wafers made of single crystal silicon with various oxygen concentrations obtained by the CZ method to temperatures of 900 to 1100°C. 1st
The horizontal axis of the figure is the initial oxygen content of single crystal silicon,
Moreover, the vertical axis represents the amount of decrease in the contained oxygen after the above-mentioned thermal process.

As is clear from Figure 1, the oxygen concentration
Wafers with a size of less than 8.5×10 ¹⁷ atoms/cubic centimeter show almost no decrease in oxygen concentration through thermal processing, which means that no defects are generated, and no defect-based getter effect can be expected. On the other hand, when the oxygen concentration is 10.5×10 ¹⁷ atoms/cubic centimeter or more, most of the supersaturated oxygen is deposited on the wafer surface, and defects are generated throughout the wafer, resulting in extremely poor device characteristics. However, when the oxygen concentration of the device substrate is within the range of 17 to 21 ppma, no oxygen precipitation is observed and the desired getter effect can be obtained.

[Brief explanation of drawings]

Figure 1 is a graph showing the decrease in oxygen concentration due to thermal processing of single-crystal silicon wafers. Figure 2 is a cross-sectional view of a metal cross section of a silicon wafer with an oxygen concentration of 12.5 x 10 ¹⁷ atoms/cm3 heat treated at 1000°C for 2 hours. Micrograph of the structure. Figure 3 is a micrograph of the metal structure on the surface of a silicon wafer with an oxygen concentration of 7.5 x 10 ¹⁷ atoms/cubic centimeter heat-treated at 1000℃ for 2 hours, magnified 200x (a) and 400x (b) , Figure 4 shows a silicon wafer with an oxygen concentration of 9.5 x 10 ¹⁷ atoms/cm3.
A is a 200x and b is a 400x micrograph of the surface metal structure after heat treatment at 1000°C for 2 hours.

Claims (1)

[Claims] 1. A method for manufacturing a semiconductor electronic device, which comprises forming an integrated circuit on the surface of a semiconductor silicon wafer having an oxygen concentration of 8.5×10 ¹⁷ to 10.5×10 ¹⁷ atoms/cubic centimeter at a temperature of 900 to 1200°C. .