JPS63216972A - Method for reflowing thin aluminum film - Google Patents

Abstract

PURPOSE:To maintain the thickness of a thin Al film of a fine pattern at the prescribed value or above and prevent imperfect contact, disconnection, etc., by subjecting a thin Al film formed on a semiconductor substrate with irregular surface to local heating in a vacuum tank by means of an electron beam. CONSTITUTION:The film thicknesses tB, tC of the side face and the bottom in a contact hole part tend to become thin as compared with the film thickness tA of a thin Al film adhering to the flat plane of a wafer. The above-mentioned wafer 6 is loaded on a heater 4 for preheating and placed in a vacuum tank 8, and then the inside of the vacuum tank 8 is held in a vacuum state and the thin Al film on the wafer 6 is grounded. Then, an electron beam 16 as a local heating source is emitted from a filament 12 by means of an electron gun 11, accelerated by an electrode plate 13, converged by an electron lens 15, and applied to the wafer 6 so as to heat this wafer 6. Local heating on the wafer 6 surface is successively shifted by means of an XY stage 2 so as to reflow the thin Al film. In this way, the thickness of the thin Al film can be maintained at the prescribed value or above.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to vapor deposition in the manufacture of semiconductor devices.

This invention relates to a method for improving step coverage defects in a thin aluminum film on a semiconductor substrate formed by sputtering or the like by post-processing using aluminum reflow.

[Conventional technology]

In the manufacturing process of semiconductor devices, especially semiconductor substrates (
In the wafer process for manufacturing wiring patterns between each element formed on a wafer (hereinafter referred to as a semiconductor substrate), contact windows for aluminum electrodes are opened, and aluminum is deposited on the wafer by ordinary sputtering or vapor deposition. A thin film is deposited on the entire surface. By forming a wiring pattern using the aluminum etching method, wiring between each element on the wafer is fabricated.

In recent years, as the degree of integration of semiconductor devices such as LSIs has improved, patterns formed on wafers have become smaller.

As a result, the width of the contact window of the aluminum electrode is narrowed, making it increasingly difficult to obtain sufficient step coverage of the aluminum thin film.

If the contact window width is 2 μ or more, the contact hole is sufficiently filled with aluminum and an aluminum electrode with few steps is formed. However, if the contact window width is 1 μ or less, the aluminum on the sides and bottom of the contact hole is There is a tendency for the thin film to become thinner than the flat surface other than the contact hole portion.

That is, as the pattern becomes finer and the depth of the contact hole portion becomes relatively deeper, a phenomenon occurs in which it becomes difficult to obtain good step coverage.

As a result, contact failures in fine contacts or disconnections in interconnects between elements occur.

Therefore, the functional reliability of the semiconductor device is significantly reduced. One way to solve this problem is to fill the contact hole with aluminum using a bias sputtering method, but the deposition rate is extremely low and there are many problems with mass production and controllability, and this is not a well-established technology. It's hard to say.

Even when using sputtering, which improves step coverage as the width of the contact window increases from 2μ to 1μ, the film thickness on the sides of the contact hole remains 1/2 of the film thickness on the flat surface of the wafer. It becomes difficult to maintain the value of 115 near 1μ.

In addition, when the contact hole becomes small, such as 1 μm or less, it becomes difficult to secure such a film thickness even by bias sputtering.

[Problems to be solved by the present invention]

The present invention solves the above-mentioned conventional drawbacks, and as circuit patterns become finer as the degree of integration of semiconductor circuits increases,
Even when the aluminum electrode contact window width is 1μ or less, the thickness of the aluminum thin film on the side and bottom parts of the contact window hole part is maintained at a certain level or more, thereby eliminating disconnections in the wiring between each element in the semiconductor device. This improves the functional reliability of the device.

[Means for solving problems]

In order to achieve the above object, in the aluminum thin film deposition method according to the present invention, the aluminum thin film deposited on the wafer surface by vapor deposition or sputtering is deposited as close to the aluminum surface as possible, and only on a very small part of the wafer. By repeatedly performing localized heating, the thin aluminum film on the entire surface of the wafer is reflowed, ensuring that the film thickness on the sides and bottom of the contact hole area exceeds a certain thickness over the entire surface of the wafer, thereby increasing the functional reliability of semiconductor devices. It is something that maintains the degree.

When performing this local heating, the entire wafer is
By preheating to around 00°C, aluminum glue flow can be made more effective, and by heating only the very surface of the aluminum thin film, the reaction layer between aluminum and bulk silicon can be made shallow, thus reducing the amount of reaction. As a result, cracks occurring in the semiconductor substrate can be suppressed.

In the present invention, by repeatedly heating the wafer locally, the entire surface of the wafer is reflowed with aluminum from the thickest part to the thinnest part, where it is difficult to deposit a thin aluminum film to a uniform thickness. However, if the entire area of the evaporator is rapidly heated, the heat dissipation of all the energy will not be sufficient and due to the difference in thermal expansion coefficients between aluminum and silicon due to temperature changes. Cracks occur on the substrate due to stress.

The present invention alleviates the stress caused by thermal expansion by applying heat locally to the very thin surface of the aluminum layer of the formed thin film, and by repeatedly applying heat to the entire surface of the wafer, thereby alleviating the stress caused by thermal expansion. It is appropriate that the size of the local heating part to suppress the occurrence of abnormal stress at the top is about φ30μ to φ1000μ.If this is the size, the stress due to the expansion of the aluminum body due to heating will be small on the left and right or bottom, and the It is thought that the stress is alleviated by the upward volume change. Also, due to local heating, the melting energy is 20 to 300W.
Therefore, although the total energy is small, the local temperature is high, and the contact area between the surrounding atmosphere and the high-temperature part is large, so heat can be dissipated smoothly. When localized heating is applied intermittently in a pulsed manner, heat is dissipated more smoothly.

On the other hand, heating the entire wafer at once is extremely dangerous and is often impractical; in addition, localized heating with an electron beam creates a high potential difference between the aluminum film and the semiconductor substrate with an insulating film sandwiched between them. , the higher the potential is charged, the higher the polarity becomes, so it is necessary to always connect the aluminum thin film and the semiconductor substrate to ground. As the miniaturization of semiconductor devices progresses, device elements are often damaged even by the slightest charge-up, and such a method is necessary as a countermeasure against static electricity during heat treatment.

In addition, local heating methods of the present invention include a method using an electron beam in a vacuum chamber, a method using arc discharge in an atmosphere mainly composed of an inert gas such as Ar or He, and a method using normal pressure or an inert gas such as Ar, He, or Xe. There is a method using induction heating under reduced pressure using an active gas as a 7 ohming gas.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing a cross-sectional shape of an aluminum thin film formed on a wafer by conventional vapor deposition or sputtering.

Thickness t of the aluminum thin film attached to the flat surface of the wafer
The film thickness tB at the side surface of the contact hole portion and the film thickness 1c at the bottom of the contact hole tend to be thinner than ^.

FIG. 2 is a diagram showing a cross-sectional shape of an aluminum thin film after aluminum reflow is applied to the aluminum shape of FIG. 1 according to the present invention. FIG. 3 is a diagram illustrating how aluminum flows into a contact hole portion and is embedded therein.

FIG. 4 is a diagram showing an embodiment of an aluminum reflow apparatus using electron beam heating according to the present invention.

Wafers 6 to be subjected to aluminum reflow are placed on a heater 4 to preheat to 350 to 400°C, and these are placed on an be. The XY stage 2 sequentially moves local heating on the surface of the wafer 6, so that local heating can be applied to the entire surface of the wafer 6.

Further, this XY stage 2 is placed on a support stand 1, and the entire system is fixed on a base plate 10.

These are housed in the vacuum chamber 8 and connected to a vacuum evacuation device (not shown) via an exhaust pipe 9, so that the inside of the vacuum chamber 8 is maintained in a vacuum state. The space between the vacuum chamber 8 and the base plate 10 is vacuum-sealed by an O-ring OR.

Further, the aluminum thin film on the wafer 6 is grounded by the wafer fixing fitting 5. An electron beam 16 as a local heating source is ejected from the filament 12 by an electron gun 11, accelerated by an electrode plate 13, focused by an electron lens 15, and hits the wafer 6, thereby heating the wafer 6.

14 is a cylinder surrounding the electrode plate 13.

FIG. 5 shows an example in which arc discharge is used as a local heating power source. An inert gas g such as He or Ar is introduced into the hood 18 through the inlet 20 to create an inert gas atmosphere around the wafer 6, and a high voltage is applied to the electrode 7 by the power source 17 to create an arc between the electrode 7 and the wafer 6. It generates electric discharge and locally heats it. This is done under normal pressure or reduced pressure.

In addition, if two or more electrodes are installed as discharge electrodes in close proximity and a high voltage is applied to these multiple electrodes at the same time to perform local heating, the aluminum between the electrodes in close proximity Thin film glue flow is extremely smooth.

As the material of the electrode 7, wear-resistant LaB6 is used.

This heating by arc discharge is performed intermittently in a pulsed manner.
The amount of heating is controlled by uty. Figure 3 shows the situation.

FIG. 6 shows an example in which induction heating by high frequency is used as a local heating source. Perform at normal pressure or reduced pressure,
At normal pressure, an atmosphere of an inert gas such as He or Ar is used, and at reduced pressure, these inert gases are used as the forming gas. A high frequency voltage is applied to the electrode 7 by a high frequency power supply 22 to locally heat the wafer 6.

The frequency of the high frequency varies depending on the thickness of the aluminum thin film on the substrate.
By increasing the heating frequency to about MHz to 40 MHz, only a very thin part of the surface of the aluminum thin film can be heated intensively due to the skin effect, so that only the surface of the aluminum thin film can be heated relatively easily. 21 is a valve for introducing inert gas.

[Brief explanation of the drawing]

FIG. 1 shows the cross-sectional shape of an aluminum thin film formed on a conventional wafer, and FIG. 2 shows the cross-sectional shape of the aluminum thin film after aluminum reflow according to the present invention. FIG. 3 shows an embodiment of the aluminum reflow apparatus according to the present invention, and shows an example in which an electron beam is used as a local heating method. The device uses arc discharge and high-frequency heating as local heating methods. Yomiuri Yokomachi Yogi → Mouth fever = 32 Lumi Riff C-Voice 1-
- Support stand 12 --- Filament 2 --- XY stage 13 - One electrode plate 3 =
=-1 Heat insulating material 14 --- Cylinder 4 □ Heater 15 -=-m-electron lens 5 --- Wafer fixing fitting 16 ---1 Electron beam 6 --- Wafer 17 ---
- Power supply 7 □ Electrode 18 □ - Hood 8 - Vacuum chamber 19 - m - Electrode holder 9 □ Exhaust pipe 20 - 1 Inlet port 10 - 1 Base plate 21 - m - Stop valve 11 - 1 Electron gun 22 - 1 High frequency power supply me58) +1 sword

Claims (1)

[Scope of Claims] 1) An aluminum reflow method characterized by locally heating an aluminum thin film formed on a semiconductor substrate with an uneven surface in a vacuum chamber using an electron beam. 2) An aluminum reflow method characterized in that the semiconductor substrate is locally heated by arc discharge under normal pressure or reduced pressure in an atmosphere mainly containing an inert gas such as Ar or He. 3) An aluminum reflow method according to claim 2, which is carried out by adding trace amounts of H_2 and N_2 to an inert gas and using LaB_6 as a discharge electrode. 4) An aluminum reflow method characterized by applying local induction heating to the semiconductor substrate under normal pressure or reduced pressure using an inert gas such as Ar, He, or Xe as a forming gas. 5) In the method using induction heating according to claim 4, since only the very surface of the aluminum thin film is heated, the heating frequency is 1 MHz to 40 MHz depending on the thickness of the aluminum thin film on the substrate in order to have a skin effect in the heated part. An aluminum reflow method characterized by the use of high frequency waves. 6) An aluminum reflow method according to claims 1, 2, and 4, characterized in that when performing aluminum reflow, a semiconductor substrate is preheated to effectively perform reflow. 7) When performing aluminum reflow according to claims 1, 2, and 4, the aluminum thin film on the semiconductor substrate is grounded to prevent charge-up of the aluminum thin film layer. Aluminum reflow method. 8) An aluminum reflow method according to claim 2, characterized in that heating is performed intermittently in a pulsed manner and the amount of heating is controlled depending on efficiency.