JPS63205908A - Plating method for semiconductor substrate - Google Patents

Abstract

PURPOSE:To enable high precision measuring of impurity diffusion depth, by soaking a wafer whose angle is polished into an acid or alkaline solution and next performing copper plating in a solution of copper sulfate under light radiation. CONSTITUTION:Mirror surfaces of two semiconductor substrates, which are mirror polished, are made to touch each other under a clean atmosphere which essentially contains no foreign matter, and heat treatment is performed to unify them. These substrates are copper-polished in a solution of copper sulfate under light radiation. After these substrates are soaked into an acid or alkaline solution at that time, they are copper-plated. Thereupon, an adhesion interface and a pn junction surface are concurrently and clearly detected. Hence, impurity diffusion depth can be measured with high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) This invention relates to a method of plating a semiconductor substrate made by a direct bonding method.

(Prior art) Generally, silicon sea urchins are bonded together without using adhesive.
In directly bonded bonded silicon wafers, measurement of the diffusion depth of impurities across the bonding interface (the distance between the bonding interface and the pn junction surface) is important in the semiconductor device manufacturing process.

Diffusion depth in conventional unbonded silicon wafers can be measured by resistive spreading, plating, etching, or the like. However, since a bonded silicon wafer has an adhesive interface, it is difficult to accurately measure the diffusion depth of impurities across the adhesive interface using the conventional measurement method described above. This is because it is not possible to simultaneously detect and evaluate the bonding interface and the pn junction surface of the bonded wafer.

Therefore, the present inventors devised a new copper plating method. This enables simultaneous and clear detection of the bonding interface and pn junction surface of the bonded silicon wafer, and accurate measurement of the diffusion depth.
It was easy to measure.

(The main problem to be solved by the invention) In the conventional measurement of the diffusion depth of impurities across the bonding interface of a directly bonded silicon wafer, the bonding interface and the pn junction surface must be detected simultaneously and clearly. This is difficult with conventional measurement methods.

The present invention provides a semiconductor substrate plating method for measuring the diffusion depth of directly bonded silicon wafers by simultaneously and clearly detecting the bonding interface and the pn junction surface and easily measuring the diffusion depth of impurities with high accuracy. This is what we provide.

[Structure of the invention]

(Means for Solving the Problems) In the measurement of the impurity depth across the bonding interface of directly bonded silicon wafers, the present invention involves immersing the angle-polished wafer in an acid or alkaline solution and then using sulfuric acid under light irradiation. This is a plating method for semiconductor substrates in which copper is plated in a copper solution.

(Function) In the present invention, when a bonded silicon wafer is copper-plated in a copper sulfate solution under light irradiation, the angle-polished bonded silicon wafer is immersed in acid and then copper-plated before being plated with copper.

In this wafer, the adhesive interface and the pn junction surface could be detected simultaneously and clearly, and the diffusion depth of impurities across the adhesive interface could be easily measured with high accuracy. Also, when a bonded silicon wafer was immersed in an alkaline solution and then plated with copper, results similar to those obtained with acid were obtained.

However, when bonded silicon wafers are similarly angle-polished and copper plated without immersing them in acid or alkaline solutions, both the bonding interface and the pn junction surface are unclear and cannot be detected, resulting in the depth of impurity diffusion across the bonding interface. It was not possible to measure the From this result, when measuring the diffusion depth of impurities across the adhesive interface of a bonded silicon wafer using the copper plating method, the method of immersing the bonded silicon wafer in an acid or alkaline solution and then plating with copper will reduce the diffusion depth. It has been found that the plating method requires only ftN and has high accuracy for measurement.

(Example) First example diameter: 76 mm, thickness: 0.40 mm, P-type surface orientation (10
0), N-type with the same diameter and thickness as a silicon wafer with a specific resistance of 0.003Ω・cIl (B-doped), and a surface orientation (100
), a silicon wafer with a specific resistance of 7 Ω·am (P-doped) was used.

Two wafers were degreased with trichlene and acelene, treated with a mixed acid of hydrogen peroxide and sulfuric acid, and treated with aqua regia.

Washed with water and dried. The wafers were bonded with their mirror surfaces in contact with each other in a clean atmosphere of class 1O or lower, and integrated by heat treatment at 1100° C. for 5 hours in an electric furnace in a nitrogen atmosphere. 5+om from this direct bonded silicon wafer
A pellet of X 10nv+ was cut out, fixed to a polishing jig at an angle of 5 degrees and 44 minutes, and mirror-polished so that the adhesive interface was exposed. While immersing the polished pellets in a saturated copper sulfate solution to which a small amount of boiling acid has been added for 15 seconds,
A copper plating film was deposited by illuminating it with an incandescent light bulb (100 W), washed with water, and then dried.

The adhesive interface of this pellet was examined under a microscope, but no adhesive interface could be detected and the pn junction surface was unclear.

However, similarly, mirror-polished pellets were soaked in hydrochloric acid for 3 seconds.
After immersion, the copper plating film was precipitated by immersing it in a copper sulfate saturated solution for 20 seconds and illuminating it with a lamp, followed by washing with water and drying.

When the adhesive interface of this pellet was examined using a microscope, both the adhesive interface and the pn junction surface could be clearly detected. The measured values of the impurity diffusion depth (distance between the adhesive interface and the pn junction surface) agreed with the calculated values with an accuracy of within 14.

Note that even when the polished pellets were immersed in boiling acid for 5 seconds and then copper plated, the same results as above were obtained for both the adhesion interface and the pn junction surface, and the measured values of the diffusion depth also matched. In addition, the same results were obtained when sulfuric acid, nitric acid, acetic acid, and ammonium fluoride were used.

Second example diameter 76av+, thickness 0.50mm, N type, surface orientation (
ioo).

P-type with the same diameter and thickness as a silicon wafer with a resistivity of 0.01Ω・am (P-doped), surface orientation (100), and resistivity 2
A silicon wafer of 8 Ω·cm (B doped) was used.

Two wafers were cleaned and dried in the same manner as in the first example, and then bonded and heat treated in the same manner to produce bonded silicon wafers. Polished pellets were made from this wafer in the same manner as in the first example. The pellets were immersed for 30 seconds in a saturated copper sulfate solution to which a small amount of boiling acid had been added.
The copper plating film is deposited by illuminating it with an incandescent light bulb, and after washing with water,
Dry.

The adhesive interface of the second pellet was examined using a microscope, but no adhesive interface could be detected and the pn junction surface was unclear. but,
Pellets prepared in the same manner were immersed in a 10% by weight sodium hydroxide solution for 5 seconds, and immersed in a saturated copper sulfate solution for 30 seconds in the same manner as above, while being illuminated with a lamp.
Deposit a copper plating film.

After washing with water, it was dried. When the adhesive interface of this pellet was examined using a microscope, both the adhesive interface and the pn junction surface could be clearly detected. The measured value of the impurity diffusion depth agreed with the calculated value with an accuracy of within 1 p.

In addition, even when the polished pellet was immersed in a 5% by weight potassium hydroxide solution for 20 seconds and then plated with copper, the same results as above were obtained for both the adhesive interface pn junction surface, and the measured value of the diffusion depth was also Agreed.

〔Effect of the invention〕

As described above, if the present invention is used, it is possible to easily and precisely measure the diffusion depth of impurities in a bonded silicon wafer, which was impossible with conventional methods.If applied to a semiconductor device manufacturing process using direct bonding technology, It will greatly contribute to the semiconductor industry in terms of device manufacturing technology and quality control.

Agent: Patent Attorney Noriyuki Chika Same Bamboo Flower Kikuo

Claims (1)

[Claims] Semiconductor substrates are manufactured using a direct bonding method in which the mirror surfaces of two mirror-polished semiconductor substrates are brought into contact with each other in a clean atmosphere that is substantially free of foreign matter, and then integrated through heat treatment.
A plating method for a semiconductor substrate, which is characterized in that when copper plating is performed in a copper sulfate solution under light irradiation, copper plating is performed after immersion in an acid or alkaline solution.