JPS59168667A - Electrode material for semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a material enabled to form an electrode having low contact resistance without generating junction breakdown by a method wherein the material is constructed of silver powder, one kind or more of titanium and magnesium, one kind or more of silver phosphate, nickel phosphate and magnesium phosphate, an organic binder, and glass powder to be added in occasion demands. CONSTITUTION:Silver powder of 10g of 1mum or less of grain size, titanium powder (0.5-40pts.wt. to 100pts.wt. of silver powder) of 10mum or less of grain size performed with surface stabilization treatment, silver phosphate (5-40pts.wt. to 100pts.wt. of silver powder), and borosilicate lead glass frit of 1g are weighted. A viscous liquid obtained by dissolving 10pts.wt. of ethylcellulose of 10cps to 90pts.wt. of alpha-terpineol is added thereto to be kneaded, and a paste type electrode material of about 200 poise of viscosity is prepared. Screen process printing of the above-mentioned paste type electrode material is performed in a tandem type pattern shape on the N<+> type layer 2 of a P type silicon substrate 1 and in a solid pattern type on the P<+> type layer 3, they are dried at 150 deg.C, and after light receiving side electrodes 4 and back electrodes 5 are formed, calcination is performed at 600 deg.C in a nitrogen gas atmosphere containing 50ppm of oxygen to manufacture a solar cell, for example.

Description

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows an example of an electrode material suitable for manufacturing a semiconductor element having a relatively coarse pattern of electrodes, such as a solar cell in particular. In this structure, a light-receiving surface electrode 4° and a back-surface electrode 5 are formed on the light-receiving surface and back surface of a separate substrate on which a Le+/P/P+ junction is formed. Furthermore, an antireflection film or the like is generally provided.

An important issue in solar cells in recent years is to reduce manufacturing costs, and the light-receiving surface electrode 4. As for the method of forming the back electrode 5, low-cost plating methods and printing methods are being considered instead of the conventional empty deposition method. Among these, % [Printing method is widely considered because it is easy to automate and has low productivity.
colour. This printing method is a method in which a paste-like substance (hereinafter referred to as a paste) made by kneading metal powder, glass powder, etc. with an organic binder and an organic solvent is applied using a screen printing method, etc., and then fired. Silver powder is commonly used as gold powder.

A large number of such four-electrode pastes are commercially available for use in forming electrodes of solar cells, thick film circuit boards, and the like.

On the other hand, in the formation of electrodes for solar cells, etc., the electrodes are required to have high adhesive strength, low contact resistance to silicon, and no penetration to the diffusion layer (low leakage current).

However, the present inventors have discovered that various commercially available Ay systems, Ay1-pd
According to the results of studies on conductive pastes, the following problems occurred when any of the conductive pastes was applied by printing onto the bonding silicon wafer shown in the figure, dried, and fired. That is, Ay-based or Ay − for thick film circuit boards.
In the PtL-based conductive paste, a barrier was formed between the silicon wafer and the electrode, resulting in a high contact resistance, and when baked at a relatively high temperature, the bond was destroyed and leakage current increased.

Some Ag-based conductive pastes for solar cells do not form a barrier between the silicon wafer and the electrode, but they all have contact resistance, so understand the current-voltage characteristics of solar cells when irradiated with light. The fill factor was small, making it impossible to create highly efficient solar cells. Also, set the firing temperature to a relatively low temperature.
Although there was a tendency for the contact resistance to decrease, a problem arose in that the leakage current increased.

In this way, the above-mentioned conventional conductive paste does not cause bonding failure and the drawbacks seen in electrodes with low contact resistance can be overcome, making it very useful as an electrode thinning material for semiconductor devices such as solar cells. At least one metal selected from the family of magnesium, a small amount of metal selected from silver phosphate, nickel phosphate, and magnesium phosphate, a phosphorus compound of M, an organic solvent, and glass powder added as needed.

The present invention differs from conventional conductive pastes.

It contains at least one metal selected from titanium and magnesium, and at least one phosphorus compound selected from silver phosphate, phosphorous nickel, and magnesium phosphate. This is done by pressure printing a conductive paste containing these metals and a phosphorous compound onto a substrate such as silicon, and then firing it.

Joining? ＋”2 Relatively low temperature without the risk of causing damage (7)
This is due to the discovery that an electrode with extremely low adhesive resistance can be formed on a substrate even when fired at a temperature of 50°C.

It is believed that the reason why the electrode material of the present invention is capable of forming a very good electrode as described above compared to the conventional conductive base) is due to the following explanation. That is, when a conventional conductive paste is printed on, for example, a silicon substrate and fired, an insulating silicon oxide film is formed on the silicon surface due to oxygen contained in the firing atmosphere. In addition, when the conductive paste uses lead oxide-based low melting point glass, this silicon oxide film is also generated due to the reaction between lead oxide and silicon. Since a silicon oxide film is thus formed on the silicon surface, it is expected that the contact resistance between the fired electrode and the silicon becomes extremely high.

On the other hand, with the electrode material according to the present invention, a silicon oxide film is thought to be formed in the same way as described above, but the metals (titanium, magnesium) contained in the electrode material react with the silicon oxide film, reducing the silicon oxide and The formation of metal silicide compounds occurs, which lowers the contact resistance between the electrode and silicon, and furthermore, the addition of phosphate compounds (silver phosphate, nickel phosphate, magnesium phosphate) reduces the amount of silver in the paste. There is good contact between the powder and the silicide compound mentioned above.

It is expected that the contact resistance will be extremely low as a result.

The components of the electrode material of the present invention will be described in further detail below. The Ag powder, organic binder, and organic solvent among the constituent components may be the same as those used in conventional conductive pastes.

As the silver powder, those having a particle size of 1 μm or less are particularly preferably used, as the organic binder, cellulose compounds and polymethacrylate compounds are preferably used, and as the organic solvent, polyhydric alcohols are particularly preferably used.

The metals titanium and magnesium are preferably used in the form of N powder. However, since these metal powders have high activity, it is preferable to use ones that have been stabilized by a method such as forming a thin oxide film on the powder surface. titanium and magnesium.

One type may be used or two types may be used in combination. Furthermore, it is also possible to use these alloy powders or to coat the surface of the 4s powder with these metals. Further, phosphoric acid compounds such as silver phosphate, phosphorous nickel, and magnesium phosphate may be used alone or in combination of two or more.

Furthermore, the present invention does not necessarily require crows to be included. However, when combined with glass.

The adhesive strength of the formed electrode to the semiconductor element is improved. Furthermore, the compatibility of the electrode with respect to solder is also improved.

For this reason, especially when used for forming electrodes of solar cells, it is preferable to incorporate glass. The type of glass used here is not particularly limited. Further, by blending PD powder into the electrode material of the present invention, the resistance to solder of the formed electrode is further improved, and by blending PT powder, the adhesive strength of the 'a electrode is improved.

When the electrode material of the present invention is used particularly for forming electrodes of solar cells, the blending ratio of at least one metal selected from titanium and magnesium is 0.000 parts by weight per 100 parts by weight of silver powder.
It is preferable to set it as 5-40 vehicle volume parts. If the blending ratio is less than 0.5 parts by weight, the contact resistance of the formed electrode to silicon becomes even worse, and if the blending ratio exceeds 40 parts by weight, the conductor resistance of the formed electrode becomes even worse (21 parts by weight, and the efficiency of the solar cell decreases). For the same reason, the blending ratio of at least one phosphoric acid compound selected from silver phosphate, Tsunba nickel, and magnesium phosphorus should be 5 to 5 parts by volume of silver powder. The amount of 4ON is suitable.

[No”-a month 1 ko 1 (jiita 1) The present invention will be explained in more detail below with reference to Examples.

Example 1 Silver powder 101 with a particle size of 1 μm or less, surface-stabilized titanium powder with a particle size of 10 μm or less (silver powder 10 [0.5 to 40 parts by weight), and phosphoric acid. Silver (silver powder 1 [5 to 40 parts by weight based on the JO nail part) and 1 g of Houkei 1 dredged glass frit were weighed. 10 for this
A viscous liquid prepared by dissolving 10 parts of cpz ethylulose in 90 parts of α-terpinemer is mixed in a light beam to form a paste with a viscosity of approximately 200 poise (grinding speed of 100/sec). Adjusted the polar material. As shown in the figure 71; 1, a silicon substrate for forming a junction for solar cells is formed on one side of a Pm silicon substrate 1 (specific resistance 1-5 ΩcnL, 6-inch diameter round wafer) by ion implantation to a depth of 0.2-0. 1 layer 2 of 4 μm (front and concave sheet resistance 50-70 Ω/hole) and aluminum on the other side with a thickness of 1 to 2 μm, heat spread and P
+Layer 3 was used. Next, the paste electrode material was screen printed on the P+ layer 2 of the silicon substrate 1 in a comb shape (turn shape) and on the P+ layer 6 in a solid pattern, and heated at 150°C.

After drying for 10 minutes, the light-receiving surface electrode 4. A back electrode 5 was formed. Next, this substrate was fired at 600° C. for 10 minutes in a nitrogen gas atmosphere containing 5 oppm of oxygen.

Current-voltage characteristics of the solar cell created in this way (1
-V%) and 1! contact resistance (RC) of the pole,
Leakage current at reverse bias (1V) 1 line factor (F, F
), open circuit voltage (p'oc), short circuit current (Isc)
I looked into it.

As shown in Table 1, the solar cell using the electrode material of the present invention containing titanium powder and silver phosphate has a higher performance compared to the case where the electrode material of the present invention containing titanium powder and silver phosphate is used as a comparative example. RC was significantly lower, F, F, and Ire were larger, and as a result, efficiency was also significantly improved. Furthermore, the leakage current was on the order of 10-.Ay/(2 m'' in all cases, and no problem was observed at all.

In this way, the electrode material Q of the present invention can be used at a relatively low temperature of 600°C.
Rc is sufficiently low even when firing
Despite being extremely thin at 4 μm, there was no increase in leakage current, and as a single-pole material, it was confirmed that the conductive paste had an extremely superior voltage compared to conventional conductive pastes.

Example 2 An example of the present invention will be described in which titanium and magnesium are blended as metals, and silver phosphate, nickel phosphate, and magnesium phosphate are blended as phosphoric acid compounds. Titanium and magnesium metal powder (with a thin oxide film on the surface 11114)
, phosphoric acid compounds (Tsuba silver, nickel phosphate, magnesium phosphate), and glass 7 lithium (lead borosilicate type).

A viscosity solution prepared by dissolving 10 parts by weight of ethyl cellulose in 90 parts by weight of α-terpineol was thoroughly kneaded to obtain a viscosity of about 20%.
Various paste-like electrode materials having different compositions with 0 voids (shear rate of 100/sec) were prepared.

This %L nanoparticle was screen-printed on the surface of a bond-forming silicon substrate similar to that in Example 1, and after drying at 150°C for 10 minutes, it was heated at 6°C for 1 hour in a gas atmosphere containing 10 ppm of enzyme.
Baked for 0 minutes. The properties of the solar mineral oil thus produced were investigated in the same manner as in Example 1, and the results are shown in Table 2 together with the inorganic components of the electrode material. Titanium, magnesium metals and phosphoric acid compounds (silver phosphate, nickel phosphate,
The electrode material of the present invention containing magnesium phosphate) is
Compared to the compositions of Comparative Examples 1 and 2, Rc is lower in both cases, and F', F, and Isc are larger, and as a result, the efficiency is significantly improved. Also, the leakage current is 10""4/
Cm'' order, and no problem was observed.It was thus confirmed that the electrode material of the present invention shown in Example 2 also provided extremely superior effects compared to conventional conductive pastes.

(Left below) Image A, IJ-like moon that makes it possible to form electrodes with low contact resistance without causing junction breakdown or increase in leakage current, even for semiconductor elements with shallow junctions, even during firing at a relatively low temperature. It is a department. Therefore, when the electrode material of the present invention is used to form electrodes of solar cells, it is possible to obtain solar cells with higher emergency pressure efficiency than when conventional conductive pastes are used.

In addition, the electrode coating material of the present invention can be applied by a printing method, and electrodes can be formed at low cost and with high productivity, making it very suitable for M applications from an industrial perspective. Furthermore, the electrode material of the present invention can also be used to form electrodes of light receiving elements other than solar cells and other semiconductor devices.

[Brief explanation of the drawing]

The figure is a cross-sectional view showing a typical configuration of a solar cell. 1...P-type silicon substrate 2...N-middle layer
3... Continuation of page 1 of P10 layer (Continuation of page 1) Author: Tokio Isogai, 292 Yoshida-cho, Totsuka-ku, Yokohama, Hitachi, Ltd., Production Technology Laboratory, C: Inventor: Tada Saito, 280 Higashi-Koigakubo-chome, Kokubunji City Hitachi, Ltd. Central Research Laboratory q3) Inventor Kunihiro Matsukuma 3-1-1 Saiwaimachi, Hitachi City Shares % formula % Amendment to procedures within Tachiharamachi Electronics Industry Co., Ltd. (spontaneous) Indication of the case 1988 Patent Application No. 42103 Name of the invention Person who corrects electrode materials for semiconductor devices / A song with llf'l Patent applicant name Do1'5μ I ceremony 111f) 't'-made f 乍 Agent Subject of person correction Contents of correction in the detailed description of the invention in the specification 1: "Contact resistance" on page 3, line 8 of the specification is corrected to "contact resistance." 2. "Contact resistance" on page 3, line 18 of the specification is corrected to "contact resistance." 3.Meiyo 1sho 1i84 Tei, “contact resistance” in the third line,
Corrected to "contact resistance". 46 In the 4th negative specification, from the 6th line to the 7th line, "contact resistance" is corrected to "contact resistance." 5. Details 1! [Contact resistance] on page 4, line 10,
Add 1 to “contact resistance”. 6. In the 5th negative line of the specification, 1. Adhesive resistance" is corrected to ``Contact resistance.'' 7. "Contact resistance" in the sixth negative line of the specification is changed to "contact resistance." 8. On page 6 of Specification 1, from line 12 to line 13, change "contact resistance" by one to "contact resistance." 9. Change "contact resistance" in line 17 on page 6 of the specification to "contact resistance." 10, Specification page 11, ratio 1 cell l in Table 1
Gaihiroike characteristic, Voc (V) 1fM17) l” 0
．． 58J + [0,54J J Koman J correct. 11, Specification 1i No. 14 Negative, solar cell characteristics of Comparative Example 2 in Table 2, Voc (V) grip [0,58J l'-0,
Press 55Ji. In the 15th and 4th lines of the 126 specification, "w: contact resistance" is corrected to "contact resistance."that's all

Claims (1)

[Claims] t) Silver powder, at least one metal selected from titanium and magnesium, silver phosphate, nickel phosphate, r)
1. An electrode material for a semiconductor device, comprising at least one phosphoric acid compound selected from magnesium phosphate, an organic binder, an organic solvent, and tunorasu powder added as necessary. λ The blending ratio of at least one metal selected from titanium and magnesium, or 100 parts by weight of silver powder r 0
．． The electrode material for a semiconductor device according to claim 1, characterized in that the content is 5 to 40 parts by weight. & A patent claim characterized in that the blending ratio of at least one phosphoric acid compound selected from silver phosphate, nickel phosphate, and magnesium phosphate is 1.5 to 40 parts by weight per 100 parts by weight of silver powder. The electrode material for a semiconductor device according to the first item.