JPH01259532A - Light irradiation plating and apparatus therefor - Google Patents

Abstract

PURPOSE:To eliminate undesirable temperature rise in a substrate due to light irradiation causing a plating current, by subjecting a semiconductor substrate to processes while irradiating the semiconductor substrate with the light having lower energy than the forbidden band gap of the semiconductor. CONSTITUTION:A semiconductor substrate with a p-n junction is electrically plated while being irradiated thereon with the light having lower energy than the forbidden band thereof. In order to irradiate such light having low energy, a thin piece of a semiconductor, which has the same forbidden band gap as that of the semiconductor to be processed, is used as a filter for eliminating the light having higher energy than the forbidden band gap of the semiconductor. As a result, the excessive energy supplied to the semiconductor substrate is largely reduced, so that the temperature rise in both the substrate and the plating bath can be reduced to small degrees.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a method and apparatus for electrolytic plating a semiconductor substrate having a pn junction, which avoids an unnecessary increase in substrate temperature due to light irradiation to generate a plating current. For this purpose, the light irradiating the semiconductor substrate is configured to be limited to light with energy lower than the forbidden band width of the semiconductor. Furthermore, in order to obtain low-energy light, a thin piece of the same semiconductor as the object to be processed is used as a filter.

[Industrial application field]

The present invention relates to a method and apparatus for electrolytically plating a semiconductor substrate having a pn junction therein, and more particularly to a process in which a semiconductor substrate is irradiated with light to generate a plating current.

When attempting to electrolytically plate a metal layer for the purpose of forming electrodes on a semiconductor substrate that has undergone impurity diffusion for element formation, the pn junction may be in the opposite direction and plating current may not flow. As a countermeasure for such cases, a method of irradiating the substrate with light is known.

Usually, this light is emitted from the back side of the substrate, which excites carriers within the semiconductor substrate.

Since the recombination current of carriers excited by light energy functions as a plating current, it is common to plate a desired metal layer on, for example, a Si substrate.

[Conventional technology]

Such treatments have been known for a long time, and light irradiation plating techniques are disclosed, for example, in Japanese Patent Publication No. 58-500920 and Japanese Patent Application Laid-open No. 58-2024. A common feature of known techniques including these is that the energy of the irradiation light is irradiated with high-energy light exceeding the forbidden band width of the object to be processed, thereby causing the semiconductor object to be processed to cross the forbidden band. This excites the carriers.

It is also known to use a jet type device that forcibly circulates a plating solution as a plating device.

[Problem to be solved by the invention]

In known light irradiation plating, high-energy light is irradiated using an incandescent light bulb or the like, so when electrons in the valence band are excited, they generate kinetic energy that exceeds the energy required to move up to the conduction band. It is often given as

Since it is sufficient for electrons to be excited into the conduction band to generate a plating current, any kinetic energy beyond that is released into the surroundings as thermal energy.

When such excitation occurs, not only does the efficiency of using light energy decrease, but a significant portion of the light energy absorbed by the semiconductor substrate is spent increasing the temperature of the substrate. As a result, the temperature in the vicinity of the plating surface increases, resulting in incomplete control of the plating solution temperature and failure to control the deposited film thickness.

The purpose of the present invention is to provide a light irradiation plating technology in which light energy is less consumed as heat energy, and to provide an electrolytic plating technology that causes almost no rise in temperature of the substrate and has high control accuracy of the deposited film thickness. It is to provide.

[Means to solve the problem]

In order to achieve the above object, in the light irradiation plating method of the present invention, a semiconductor substrate having a pn junction is subjected to electroplating while being irradiated with light having an energy lower than the forbidden band width of the semiconductor, and A semiconductor thin piece having the same forbidden band width as the semiconductor to be processed is used as a filter for removing light with higher energy than the forbidden band width of the semiconductor for irradiating low energy light.

[For production]

In the light irradiation electroplating of the present invention, unlike conventional light irradiation plating, light having an energy lower than the forbidden band width of the semiconductor substrate is used. The reason why such low-energy light generates a plating current and enables electroplating will be explained with reference to FIG. 1.

The energy band structure of the pn junction is shown in FIG. 1 [al]. Since the pn junction in the semiconductor substrate to which electroplating is applied is for forming elements, doped impurity levels exist in both the p-type region and the n-type region.

If the impurity concentration in the n-type region is high enough to be expressed as n° type, the impurity level is not a single line, but a donor band as shown in Figure 1Cb). It can be considered that the upper end of the band is so wide that it overlaps with the conduction band.

In a semiconductor having such a band structure, impurities are ionized by the energy Tnz given as thermal energy, but electrons in the valence band are excited to the donor band by light irradiation, and holes are generated in the valence band. The optical energy Tn provided in this case is smaller than the forbidden band width.

On the other hand, if the impurity concentration in the p-type region is not particularly high, it is appropriate to consider that the impurity level has a shape close to a line rather than a band, as shown in Figure 1 (C1). Even if there are almost no levels, the situation in which hole/electron pairs are generated can be considered in the same way; p-type impurities are ionized by the thermal energy Tpz, and furthermore, in the conduction band, external light causes ionization from the impurity level. Excited electrons are generated.The optical energy Tpl at this time is also smaller than the forbidden band width.

Returning to Figure 1 (al), since a voltage in the opposite direction is applied to the p-n junction, the holes in the n + 9i region valence band and the electrons in the p-type region conduction band move toward the junction. , where they recombine. Plating is performed by this recombination current.

That is, in the electrolytic plating of the present invention, plating is performed by a recombination current of hole/electron pairs excited by light irradiation, which is common to known light irradiation plating methods, but the excitation of hole/electron pairs is caused by impurities. Since it is carried out via levels, only lower optical energies are used and heat generation due to excess excitation energy can be avoided.

Furthermore, if a semiconductor wafer of the same type as the object to be processed is used as a filter to cut high-energy components of the irradiated light, light with energy exceeding the forbidden band width will be absorbed by the filter, resulting in excessive energy exposure. [Embodiment] FIG. 2 is a schematic cross-sectional view showing an embodiment of the present invention, and this drawing will be referred to hereinafter.

Inside the Si substrate 1, which is the object to be processed, there are a p- region 1 and an n''
Region 2 exists, and plating is performed on the surface of the n'' region.

The external electric field for passing the plating current is in the opposite direction to this p-n junction, so as mentioned above, low-energy light is irradiated to excite the carriers, but the excitation light is on the shorter wavelength side of the light from an incandescent bulb. is canted by the Si filter 5. Note that 3 is a SiOz film for limiting the plating surface.

A plating solution 7 is forcibly supplied to the plating GL region by a jet tank 8. Such jet plating is known, and the apparatus used in this example is also a known jet plating apparatus. The plating film 4 grows on the plating surface facing the anode 8, but at this time the plating current flowing in the Si substrate is generated under the conditions described above.

Next, the irradiation light, which is the main feature of the present invention, will be described.

The light source is an incandescent bulb, and depending on the SL filter 5,
Since half is canted, it is desirable that the light source is more powerful than usual. The Si wafer used as the filter is made of FZ with a low impurity concentration, preferably has a diameter of 5 inches if the object to be processed has a diameter of 4 inches, has a thickness of about 625 μm, and is used with mirror polishing on both sides. By using this filter, the semiconductor substrate has a wavelength of λ# 8000μ.
Only light with a wavelength longer than m will be irradiated.

〔Effect of the invention〕

According to the light irradiation plating of the present invention as described above, excess energy supplied to the semiconductor substrate is significantly reduced, so that the temperature rise of the substrate and the plating solution is small. As a result, there is no difference in liquid temperature between the plating liquid temperature measurement point and the plating progress area, and the control accuracy of the plating speed is significantly improved.

[Brief explanation of the drawing]

FIG. 1 is an energy band diagram explaining the present invention in detail, and FIG. 2 is a schematic cross-sectional view showing an embodiment. , 4 is the plating film, 5 is the St filter, 6 is the anode, 7 is the plating layer, and 8 is the jet tank. FIG. 2 is a schematic diagram showing an embodiment of the invention.

Claims (2)

[Claims] (1) In the process of performing electroplating on a semiconductor substrate having a pn junction by passing a current across the junction, the process is performed while irradiating the semiconductor substrate with light having an energy lower than the forbidden band width of the semiconductor. A light irradiation plating method characterized by: (2) The apparatus for performing light irradiation plating according to claim (1), wherein the filter that removes light having an energy higher than the forbidden band width of the semiconductor has the same forbidden band width as the semiconductor that is the object to be processed. A light irradiation plating device characterized by being made of a semiconductor with