JPS6187866A - Method for vapor-depositing aluminum - Google Patents

Abstract

PURPOSE:To form a stable vapor-deposited Al film having a fine crystal structure by subjecting a body on which Al is vapor-deposited to sputtering treatment with ionized gaseous Ar and by plating ionized Al vapor. CONSTITUTION:A body on which Al is vapor-deposited such as a lead frame is placed in an atmosphere of gaseous Ar under <=1.0Torr pressure. The gaseous Ar is ionized, and the body is subjected to ion sputtering treatment for 3-20min by applying negative bias of >=0.1kV to the body. The surface of the body is cleaned by the treatment. Al is then vaporized and ionized under 10<-2>-10<-5>Torr pressure of gaseous Ar, and negative bias of 0.1-3kV is applied to the body to form a thin Al film by ion plating. By this method, a vapor- deposited Al film having superior resistance to heat, corrosion and expansion stripping is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for depositing aluminum on lead frames for semiconductor integrated circuits, and more specifically to a method for depositing aluminum on lead frames for semiconductor integrated circuits made of iron, copper alloy, or iron-nickel alloy. This article relates to an ion plating method for thin layer coating.

In the package of a conventional semiconductor integrated circuit device (hereinafter referred to as Ic for simplicity), as shown in the attached FIG. and are connected to external electrodes (not shown). Further, a metal or alloy film 5 is formed on the lead frame 1 by vapor deposition, electroplating, or roll cladding in order to facilitate the bonding between the lead frame 1 and the bonding wire 4.

Generally, most of the electroplated film 5 on the lead frame 1 is made of noble metals such as Au and Ag, which are extremely expensive. Furthermore, when aluminum is used as the bonding wire 4, a complex intermetallic compound is formed between Al and Ag-Al, resulting in the formation of an alloy layer, which causes embrittlement of the bonding portion, which becomes a major problem. was.

Therefore, a method of forming an aluminum film on the lead frame 1 using the roll clad method was considered, but there were limitations due to the directionality and accuracy of cladding the aluminum film, making it suitable for all lead frame shapes. I couldn't let it happen.

Under these circumstances, the vacuum evaporation method as shown in FIG.
We also propose a method of evacuating the crucible to about ~10-5 torr and vaporizing the aluminum stored in the crucible 8 with the electron beam 10 from the electron gun 9 (11) L, depositing aluminum on the lead frame 1 placed above the chamber. It was done.

However, it has become clear that the IcIJ-deframe in which the aluminum thin film is deposited by such a vapor deposition method has the following problems.

(i)! Adhesion of oil, foreign matter, etc. on the surface of the J-frame causes peeling of the aluminum thin film after coating and heat foaming.

(ii) In the vapor deposition method, aluminum atoms are formed in a columnar crystal shape on a bonded frame and become coarse, so that the interface of the columnar crystals is easily attacked by moisture. For example, an IC molded with a resin is subject to grain boundary erosion due to moisture in the resin, resulting in a decrease in the reliability of the IC.

Therefore, in order to improve these problems, an ion plating method (see FIG. 3) was proposed in which aluminum atoms are ionized and collided onto the substrate surface.

In the ion plating method, aluminum housed in a crucible 8 is evaporated by an electron beam from an electron gun 9, and the vaporized aluminum 11 is ionized (aluminum ions: 13) L with a high frequency excitation coil 12, while a lead frame Applying a negative bias 14 to 1,
It consists of forming an aluminum thin film on the frame 1.

- This method is said to be preferable for improving the adhesion between the lead frame and the aluminum thin film as well as the corrosion resistance of the thin film. However, in order to apply this method to IC lead frames, there are The reality is that the conditions for large-scale formation have not been sufficiently studied so far.

OBJECTS OF THE INVENTION An object of the present invention is to provide an optimal ion plating method for aluminum vapor deposition of IC lead frames.

Structure of the Invention In view of the current state of the conventional methods as described above, the present inventor particularly
As a result of various studies and studies to develop a vapor deposition method suitable for aluminum thin film coating on lead frames for commercial use, we first subjected the lead frame to be vapor-deposited to ion sputtering treatment under specified conditions, and then applied ion plating under the same specified conditions. It has been found that treatment is extremely effective in overcoming the various drawbacks of the conventional methods. The present invention is based on such new findings.

That is, in the vapor deposition method of the present invention, a lead frame as an object to be vapor deposited is maintained in an argon gas of less than 1,000 mA torr, and the argon gas is ionized, while a negative value of more than 0.1 V is applied to the lead frame. By applying a bias of 3
The lead frame was ion sputtered for ~20 minutes, then 10-2~10 while injecting argon gas.
The method is characterized in that aluminum is vaporized and ionized under -5 torrO, and a negative bias of 0.1 to 3 KV is applied to the lead frame to ion plate aluminum ions onto the lead frame.

The vapor deposition method of the present invention will be explained in more detail.

According to the method of the invention, the lead frame on which aluminum is to be deposited is first subjected to a sputtering treatment with ionized argon gas. This sputtering treatment has the effect of cleaning the surface of the object to be vapor deposited, and is therefore an extremely important step in increasing the adhesion strength of the vapor deposition substance to the surface of the object to be vapor deposited in the subsequent vapor deposition process. That is, in this step, oil, foreign matter, etc. on the object to be deposited, which are found in the conventional method, are effectively removed.

In this sputtering process, the negative bias to be applied to the lead frame and the sputtering time are critical. The former is 0. IKV or more, preferably Ha0.1~
1.0KV] within range, 0.1KV1. : If it is not satisfied, sputtering effect cannot be expected. In addition, lK
Even if a bias exceeding V is applied, no significant effect can be expected, so it is not economically desirable. On the other hand, the sputtering time is within the range of 3 to 20 minutes, preferably 5 to 10 minutes, and if it is less than 3 minutes, it is difficult to obtain the above-mentioned cleaning effect on the surface to be deposited and, by extension, sufficient adhesion strength of the deposited material. This makes it impossible to solve problems such as peeling of the deposited film, and even if sputtering is performed for longer than the upper limit of 20 minutes, the above effects cannot be expected to be significantly improved, and from an economic point of view, It is also undesirable from a productivity standpoint.

In the first step, various known methods can be used to ionize argon, and particularly a high frequency excitation method or a direct current electric field method can be exemplified.

In this way, an aluminum thin film is then formed by ion plating on the surface of the lead frame which has been subjected to the ion sputtering treatment as the first step, the surface has been cleaned, and the adhesion strength to the vapor deposited substance has been improved. .

Here, the vaporization of aluminum is not particularly limited and can be carried out according to various conventionally known methods, and typical examples include an electron beam heating method, a high frequency heating method, a resistance heating method, and the like. Further, there is no restriction on the means for ionizing the vaporized aluminum atoms, and it can be carried out by, for example, a high frequency excitation method, a direct current electric field method, or the like.

Also in this ion plating process, the negative bias to be applied to the lead frame is critical in the method of the present invention, and is 0.1 to 3 KV, preferably 0.5 to 3 KV.
．． Must be within 0KV range.

When the bias is less than the lower limit of 0.1 V, the ionized aluminum particles have a strong tendency to form fine columnar crystals on the lead frame as in the conventional method, and when the bias exceeds the upper limit of 3 KV, the ionized aluminum particles tend to form fine columnar crystals on the lead frame. Even if it is applied, it does not make a significant difference in the fine crystallization effect and the equipment cost is relatively high, which is not preferable from an economical or industrial production point of view.

Furthermore, when backing a semiconductor chip after vapor deposition, in order to bond a bonding wire made of aluminum and a lead frame having an aluminum coating using an automatic bonder, the thickness of the aluminum vapor deposited thin film must be set to 0.5 to 8.
The inventor's experience has shown that it is advantageous to have a value of μ, preferably in the range of 0.8 to 5 μ. Therefore, especially for bonding bonding wires with an automatic bonder, the thickness of the aluminum coating is critical and must be within the above range.

The lead frame to which the vapor deposition method of the present invention is applied is made of iron, iron-nickel alloy, copper alloy, or the like. but,
It should be understood that the vapor deposition method of the present invention can of course be applied to materials other than the target IC lead frame, and that sufficient effects can be expected as well. Examples of applications other than lead frames include ceramics, inorganic materials, organic materials (plastics, etc.), and it has been found that aluminum thin films with excellent adhesion and corrosion resistance can be formed as well.

Effects of the Invention According to the vapor deposition method of the present invention, by first performing ion sputtering with ionized argon gas under predetermined conditions, and then ion plating with ionized aluminum gas in an argon atmosphere under predetermined conditions, It is possible to effectively avoid the conventional problems of peeling of the deposited film due to oil, foreign matter, etc. on the surface of the deposited object, formation of columnar crystals, and subsequent erosion due to moisture, etc.
A stable deposited film with a fine crystal structure can be formed.

To explain further, as will be demonstrated in the following examples, the aluminum thin film obtained by the vapor deposition method of the present invention is extremely excellent in heat resistance, corrosion resistance, and foam peeling resistance.

In addition, when the thickness of the deposited film is controlled within a predetermined range, very good results can be obtained in terms of bondability using an automatic bonder.

Suzuna man Hereinafter, the present invention will be explained in more detail according to examples.

However, these examples are merely for illustrative purposes;
There is no limit to the scope of the invention.

42 alloy (Fe-42%Ni) with a thickness of 0.25mrn
Alternatively, a lead frame made of copper alloy (Olean 195, etc.) is first evacuated in a vacuum furnace and argon gas is injected into the lead frame under a pressure of 10-1 to 10-2 torr. Ion sputtering was performed by applying various negative biases within a range, while ionizing argon gas using a DC electric field method, and irradiating the lead frame surface with the ions for various times ranging from 3 to 20 minutes.

Next, after performing the ion sputtering treatment as described above, aluminum is immediately vaporized with an electron beam in an argon atmosphere of 10-3 to 10-'torr,
and ionization by excitation with high frequency (13,56 MHz; 100 W), while the lead frame was ionized with 0.1-3.
Various negative biases within the range of 0 KV were applied to deposit ionized aluminum gas onto the lead frame surface. The vapor deposition time was determined so that the thickness of each formed aluminum vapor-deposited thin film was a predetermined value within the range of 0.2 to 9.0 μm.

Separately, for comparison purposes, aluminum thin films were formed on the same lead frame according to a conventional vapor deposition method and a simple ion plating method, respectively.

Detailed manufacturing conditions are shown in the table below.

The aluminum vapor-deposited thin films thus formed under various conditions were then heated at 450°C for 10 minutes);
P conducted under the conditions of 120℃, 100% humidity, and 2 atmospheres.
The film was subjected to a bonding test using an automatic bonder ([:T) and an automatic bonder, and various physical properties were measured. For comparison, the results of a thin film obtained by a conventional method are also shown in the table below.

As is clear from the results below, it can be seen that samples c, D, and F, which fall within the range of the manufacturing conditions of the present invention, have sufficient characteristics. Short ion sputtering time A
B has poor removability, B, which is not subjected to ion plating, has problems in corrosion resistance, and E, in which the thickness of the deposited film is too thick (9μ), is insufficient in rebonding properties as expected, and On the other hand, the deposited film is too thin (
It can be seen that bonding properties are also poor for 0.2μ)G.

On the other hand, thin films formed by ordinary vapor deposition methods are unsatisfactory in both foaming releasability and corrosion resistance, but I, whose film thickness is within the range of the present invention, has good bonding properties.
- In the case of (2), which has a film thickness outside the range of the strength tree invention, the bonding properties are of course insufficient, and it is difficult to use it as an ICIJ-deframe as intended by the present invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the bonding state of a lead frame and a semiconductor chip in the backing of a semiconductor chip of a semiconductor integrated circuit, which is a particular object of the vapor deposition method of the present invention, and FIG. 2 and FIG. FIG. 3 is a diagram for explaining a vapor deposition method. (Main reference numbers) 1: Lead frame, 2: Semiconductor chip, 3: Electrode, 4: Bonding wire, 5: Plating layer (
6: Vacuum chamber, 7: Exhaust pipe, 8: Crucible, 9: Electron gun, 1O: Electron beam, 1
1: Al vapor, 12: High frequency excited Koinope 13 Nialuminum ion, 14: Bias patent applicant Sumitomo Electric Industries, Ltd. New Technology Development Corporation

Claims (9)

[Claims] (1) The object to be evaporated is maintained in an argon gas atmosphere of 1.0 torr or less, the argon gas is ionized, and a negative bias of 0.1 KV or more is applied to the object to be evaporated for 3 to 20 minutes. The surface of the object to be deposited is subjected to ion sputtering, and then 10^-^2~1 is applied while injecting argon gas.
Aluminum is vaporized and ionized under 0^-^5 torr, while applying a negative bias of 0.1 to 3 KV to the deposited body to ion plate aluminum on the deposited body. Characteristic aluminum vapor deposition method. (2) The method according to claim 1, wherein the object to be deposited is a lead frame for a semiconductor integrated circuit, and the aluminum deposited film has a thickness in the range of 0.5 to 8 μm. (3) The method according to claim 2, wherein the lead frame is made of copper alloy, iron-nickel alloy, or iron. (4) Negative bias during the ion sputtering is 0
．． 4. The method according to any one of claims 1 to 3, wherein the voltage is 1 to 1.0 KV. (5) The method according to any one of claims 1 to 4, wherein the ion sputtering time is within a range of 5 to 10 minutes. (6) The method according to any one of claims 1 to 5, wherein the ionization of the argon is performed by a high frequency excitation method or a direct current electric field method. (7) Negative bias during ion plating is 0
．． Claims 1 to 5 are within the range of 5 to 3.0 KV.
The method described in Section 6. (8) The method according to any one of claims 1 to 7, wherein the vaporization of aluminum during the ion plating is performed by electron beam heating, high frequency heating, or resistance heating. (9) The method according to any one of claims 1 to 8, wherein the ionization of aluminum during the ion plating is performed by a high frequency excitation method or a direct current electric field method.