JPH02213500A - Method for flattening surface of semiconductor substrate with high precision - Google Patents

Abstract

PURPOSE:To flatten the surface of a semiconductor substrate with high precision by opposing an acicular electrode to a fine projecting part on the substrate dipped in a soln., carrying out electropolishing and selectively dissolving the fine protrusion. CONSTITUTION:The Si substrate 1 specularly finished by ordinary mechanical polishing is dipped in an electrolyte 4 contg. 5% HF in a cell 3. The acicular electrode 2 is dipped in opposition to the substrate 1, and a power source 5 capable of adjusting the voltage and current is connected to the electrode 2 and the substrate 1. Meanwhile, the matching precision of the worked surface is inspected and the fine projecting part is detected by a flatness measuring instrument (not shown in the figure) using the conventional optical or electromagnetic methods such as the optical interference method and the impedance variation method. The tip of electrode 2 is then opposed to the fine projecting part. Electropolishing is carried out under such conditions, hence the fine projecting part is completely dissolved, and the surface of the substrate 1 is flattened with high precision. Since the worked surface is kept clean by this method, the semiconductor devices can be highly integrated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of processing a semiconductor substrate partially having minute ridges by removing the minute ridges and partially forming a flat surface with high precision.

BACKGROUND OF THE INVENTION Semiconductor substrates are manufactured from single crystal ingots through processing steps such as cutting, grinding, etching, and polishing.

And since high flatness is required for semiconductor substrates,
Usually, in the above-mentioned processing step, a mirror finish is performed by machining using a surface grinder, a lapping machine, or the like.

Although machining has the advantage of high processing speed, it forms a mechanically damaged area near the surface of the silicon substrate, and foreign matter and impurities tend to accumulate within the damaged area. Silicon substrates require a high level of cleanliness, and even if the workpiece is cleaned, it is difficult to completely remove these foreign substances and impurities.

However, mechanical polishing can be easily carried out in a batch process, and the level of flatness conventionally required can be achieved by mechanical polishing. Therefore, electrolytic polishing has not been used for mirror finishing of semiconductor substrates.

Recently, in connection with lithography technology for devices, it has become necessary for semiconductor substrates to have high flatness in partial regions. However, the flatness of the substrate surface finished by ordinary mechanochemical polishing often deviates from the required specifications in some areas. However, there is little guarantee that a substrate whose flatness is not accurate can be corrected even if it is polished again using normal polishing.

Problem to be Solved by the Invention: As described above, in a semiconductor substrate where high flatness is required in a partial region, it is possible to easily correct a substrate whose flatness accuracy partially deviates from the required specification. It is hoped that a reliable method will emerge.

The present invention provides a high-precision flat surface processing method for semiconductor substrates that satisfies the above requirements.

Means for Solving the Problems In order to achieve the above object, the high-precision flat surface processing method of the present invention involves electrochemically processing a semiconductor substrate that has been mirror-finished by ordinary mechanochemical polishing or electrolytic polishing. Microscopic pits are detected by optical or electromagnetic methods by immersing them in a liquid that reacts with High-precision planarization is performed by selectively dissolving the parts.

Electrolytic polishing is performed by placing a needle-like electrode facing the micro-protrusions of the semiconductor substrate immersed in the working solution, and by selectively dissolving the micro-protrusions present on the machined surface, high precision is achieved locally. It can be flattened and refinished with flatness that meets the required accuracy.

Furthermore, since the semiconductor substrate is electrolytically polished as an anode, impurities are removed from the processed surface of the semiconductor substrate, resulting in a clean surface.

Example Example 1 The details of this invention will be explained based on FIG.

A silicon substrate that has been mirror-finished by ordinary mechanical polishing (
1) as the electrolyte (4) and an electrolyte tank (3) containing 5% oxygen.
). Further, a needle electrode (2) is immersed opposite the silicon substrate (1). The tip of this needle-shaped electrode (2) is sharpened into a needle shape or protruded into a small spherical shape so that lines of electric force are concentrated at the position desired to be polished. And an electric current that can output adjustable voltage and current between the silicon substrate (1) and the needle electrode (2)! Connect (5).

Using a flatness measuring instrument (not shown) that uses an optical or electromagnetic method such as a normal optical interferometry method or an impedance variation method, the machining accuracy of the machined surface is checked and minute dents are detected. Then, the tip of the needle electrode (2) is adjusted to a close position facing the minute prong.

When electrolytic polishing is performed using this method, the polishing speed is adjusted by the liquid temperature and the amount of applied voltage. Therefore, the conditions for applying the electric field are determined by the shape of the microscopic portion.

Furthermore, if there are a plurality of microscopic pits on the surface to be machined, the needle-like electrodes are aligned using, for example, a computer-controlled X-Y stage, and electrolytic polishing is performed continuously.

When we performed electrolytic polishing under the following conditions, we were able to completely remove the microscopic ridges left after mirror polishing and create a highly accurate flat surface.

Silicon substrate: 5-inch diameter substrate with mirror finish by mechanical polishing Needle-shaped platinum electrode: Apply cathode Applied current and voltage conditions: 50 to 160 mA, 3 to 6 Electrolyte solution: 5% by weight HF Electrolyte temperature: 10 to 25° C. Example 2 A silicon substrate with a diameter of 6 inches was subjected to ordinary electrolytic polishing under the following conditions to give it a mirror finish.

Electrolyte: IHF:2)12sO4:5H
2O mixed electrolyte temperature: 20~80℃ plate-shaped platinum electrode: cathode applied current voltage conditions 280~200 mA4. 0.5～
6) In the same manner as in Example 1, minute ridges were selectively electrolytically polished on the silicon substrate mirror-finished by the electrolytic polishing described above to obtain a high-precision flat surface.

Effects of the Invention This invention makes it possible to finish a highly precise flat surface by selectively electrolytically polishing minute ridges using a needle-like electrode on a silicon substrate that has been mirror-finished by ordinary mechanochemical polishing or electrolytic polishing. In addition, since the processed surface can be kept clean, it can contribute to higher integration of semiconductor devices.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the basic configuration of an electrolytic polishing apparatus for carrying out the present invention. 1...Silicon substrate 2...Acicular electrode 3...Electrolyte solution tank 4...Electrolyte solution

Claims (1)

[Claims] 1. A semiconductor substrate that has been mirror-finished by ordinary mechanochemical polishing or electrolytic polishing is immersed in a liquid that electrochemically reacts with the semiconductor substrate, and minute protrusions are detected by an optical or electromagnetic method. A high-precision flat surface of a semiconductor substrate in which electrolytic polishing is performed with a needle-like electrode facing the micro-protrusions, selectively dissolving the micro-protrusions present on the processed surface and partially planarizing them with high precision. Processing method.