JPH04109623A - Semiconductor device with p-n junction - Google Patents

Abstract

PURPOSE:To obtain an excellent passivation film, which does not deteriorate the P-N junction of a semiconductor device, and a layer insulating film by forming a plasma silicon nitride film having film thickness allowing to hold positive charges having substantially the same density as negative charges induced in a silicon dioxide film onto a silicon dioxide film through a plasma vapor growth method and laminating two layer films. CONSTITUTION:The laminate of a silicon dioxide film 10 and a silicon nitride film 6 formed through a plasma vapor growth method are shaped onto a semiconductor substrate 1 with a P-N junction, and the film thickness of a silicon nitride film 6 is set to film thickness having positive charges having substantially the same density as negative charges induced in the silicon dioxide film 10. That is, the film thickness of the silicon nitride film 6 is set so as to have positive charges having substantially the same density as negative charges induced in the silicon dioxide film 10, and the two layer films are laminated, thus substantially bringing charges in the two layer films to zero. Accordingly, an excellent passivation film, which does not deteriorate a P-N junction, and a layer insulating film can be acquired.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor device having a pn junction in which deterioration of the pn junction is prevented by a padding film, an interlayer insulating film, or the like.

2. Description of the Related Art A semiconductor device is a device in which each circuit element, a passive element and an active element, is microfabricated on a single substrate in an inseparable manner.

FIG. 5 is a partial sectional view showing an example of the structure of this conventional semiconductor device. A thin film 2 of silicon dioxide (SiO2) is formed on a semiconductor substrate 1 by thermal oxidation or chemical vapor deposition. The thickness of this silicon dioxide film 2 is approximately 0.
．． It is 1 μm.

An opening 4 is provided in the silicon dioxide film 2 at a portion matching the p-type or n-type diffusion layer 3 formed on the surface of the semiconductor substrate 1 using phosphorography and etching techniques. A metal electrode 5 is patterned on the opening 4 . The metal electrode 5 is provided by patterning an aluminum (AJ) film formed to a thickness of about 1 μm by sputtering or vacuum evaporation using phosphorography and etching. On the entire surface of the silicon dioxide film 2 and the metal electrode 5, a silicon nitride thin film (hereinafter referred to as
A plasma silicon nitride film) 6 is coated thereon.

The thickness of plasma silicon nitride film 6 is between about 1 and 5 μm. This plasma silicon nitride film 6 acts as a passivation film that protects the semiconductor device from impurities, moisture, etc. entering from the outside world.

Conventionally, in addition to the silicon nitride film, silicon dioxide film (SiO2), silicate glass film (P205 +S 1o2), aluminum oxide film (Af□03), or polyimide film has been used as the Badge Vagelon film. However, due to the fact that silicon nitride film has the best moisture resistance, contamination resistance, and mechanical strength, and the development of plasma vapor phase epitaxy, which enables low-temperature formation at approximately 300°C,
Plasma silicon nitride films have come to be used as badge-base films in most semiconductor devices.

[Problems to be Solved by the Invention] However, in conventional semiconductor devices, a large amount of positive charges are induced in a plasma silicon nitride film used as a passivation film.

For example, the (100) plane of a p-type silicon single crystal substrate with a resistivity of 3ΩC1 is oxidized in water vapor at a temperature of 900°C to form a silicon dioxide film with a thickness of about too nm on the surface, and then plasma A plasma silicon nitride film is grown to a thickness of about 1 μm using a vapor phase growth method, and then a 1 μm thick film is grown on the plasma silicon nitride film using a sputtering technique.
An MIs (metal-insulator-semiconductor) capacitor was manufactured by forming an aluminum thin film and patterning only the aluminum thin film using lithography and etching techniques. Then, a high frequency voltage of I MHz is applied between the aluminum thin film electrode and the P-type silicon substrate to reduce the voltage -
The capacitance characteristics were measured. As a result, the charge density NFB in the insulator calculated from the obtained flat band voltage vFB and the insulator capacitance C is +5, ox 101012
a''. Since almost no charge is induced in the silicon dioxide film formed by the thermal oxidation method, all of this positive charge exists in the plasma silicon nitride film.

There are two types of positive charges that exist in the plasma silicon nitride film. One is silane (C3iH) and ammonia (NHZ) used as reaction gas in plasma vapor deposition method.
This is a case where hydrogen ions (H"") contained therein are taken into the plasma silicon nitride film, and the hydrogen ions in this case act as mobile charges. Another case is when the network of silicon and nitrogen atoms constituting the plasma silicon nitride film is partially separated, and the silicon or nitrogen atoms have dangling bonds. At this time, the dangling bond becomes a fixed charge with a positive charge.

Both positive charges are generated due to thin film formation using plasma vapor phase epitaxy. In the plasma vapor deposition method using high-frequency discharge, the chemical bonds of the reaction gas are forcibly broken down under high-energy plasma conditions, and particles in a highly active chemical state (primarily radicals such as excited atoms and molecules) are group), and film growth occurs through reactions between activated particles. A substance formed by a reaction between excited radicals does not have a stoichiometric composition, contains many impurity atoms, has incomplete chemical bonds, and contains defects and dangling bonds. In this way, in a thin film forming method using a plasma reaction, it is impossible to avoid electric charges being induced in the film.

Positive charges existing in the passivation film have various adverse effects on the characteristics of semiconductor devices. For example, as shown in FIG. 6, an npn-type bipolar element having an n-type collector diffusion layer 7, a p-type base diffusion layer 8, and an n-type emitter diffusion layer 9 is formed using a badge vagelon film made of a plasma silicon nitride film. If it is not provided, there is no charge in the silicon dioxide film 2, so the pn junction does not deteriorate.

However, when a passivation film of plasma silicon nitride film 6 is formed on this bipolar element as shown in FIG. 7, an electric field is generated toward the diffusion layers 7 to 9 from the positive charges existing in the plasma silicon nitride film e. . As a result, the pn junction between the n-type emitter diffusion layer 9 and the p-type base diffusion layer 8 is bent toward the p-type base diffusion layer 8 near the surface of the semiconductor substrate 1. At the same time, the pn junction between the p-type base diffusion layer 8 and the n-type collector diffusion layer 7 is also
It bends in the direction of the p-type base diffusion layer 8 near the surface of the semiconductor substrate 1 . In such a state, the electric field becomes stronger near the part where each pn junction and the silicon dioxide film 2 contact each other than in other parts, making it easier for tunneling phenomena to occur, and the reverse current in the pn junction increases. do. This causes deterioration of the pn junction.

Furthermore, when obtaining a linear amplification effect using a normal npn type bipolar element, the pn junction formed by the base diffusion layer 8 and the collector diffusion layer 7 is reverse biased. In this case, an electric field is generated from the collector diffusion layer 7 toward the base diffusion layer 8, but this electric field is also generated inside the silicon dioxide wI:2 covering the surface of the semiconductor substrate 1 and the plasma silicon nitride film 6. Occur. A large amount of positive charges exist in the plasma silicon nitride film, and in particular hydrogen ions, which are mobile charges therein, move due to this electric field, enter the inside of the silicon dioxide film 2, and form a p-type base diffusion layer. It is gathered in the area directly above 8. When positively charged hydrogen ions are collected on the p-type base diffusion layer 8, in the region below the p-type base diffusion layer 8, p-type
The type is inverted to n-type, and the emitter diffusion layer 9 and collector diffusion layer 7 are short-circuited. As a result, characteristics as a bipolar element can no longer be obtained.

As described above, if the plasma silicon nitride film 6 containing a large amount of positive charge is used as a badge-base film, problems such as deterioration of the pn junction, leakage between elements, and short circuits will occur, and the characteristics and reliability of the semiconductor device will be significantly deteriorated. descend. this is,
The same applies not only to badge-base solar films but also to interlayer insulating films, for example.

The present invention has been made in view of such problems, and includes:
An object of the present invention is to provide a semiconductor device having a pn junction in which a high-quality passivation or interlayer insulating film can be formed without deteriorating the pn junction of the semiconductor device.

[Means for Solving the Problems] A semiconductor device having a pn junction according to the present invention has a stack of a silicon dioxide film and a silicon nitride film formed by plasma vapor deposition on a semiconductor substrate having a pn junction. The thickness of the silicon nitride film is set to have substantially the same density of positive charges as the negative charges induced in the silicon dioxide film.

[Function] In the present invention, the thickness of the silicon nitride film is set so that it has substantially the same density of positive charges as the negative charges induced in the silicon dioxide film, so this two-layer film is laminated. By doing so, the charge in the film can be reduced to substantially zero. Therefore, this laminate can constitute a high-quality passivation film and interlayer insulating film that do not deteriorate the pn junction.

[Embodiments] Next, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

FIG. 1 is a partial sectional view of a semiconductor device showing a first embodiment of the present invention. On the surface of the semiconductor substrate 1 on which the diffusion layer 3 is selectively formed, silicon dioxide M2 is formed by thermal oxidation or ordinary chemical vapor deposition. A contact hole is formed at a position aligned with 3. Then, by depositing a metal film by sputtering and patterning it, the metal electrode 5 is placed at a position aligned with the contact hole. The material of the metal electrode 5 is, for example, aluminum.

A thin silicon dioxide film 10 is formed on the silicon dioxide film 2 and the metal electrode 5 as a first passivation film. The silicon dioxide film 10 can be formed by a normal low pressure chemical vapor deposition method or an ordinary pressure chemical vapor deposition method. The thickness of the silicon dioxide film 10 is 0.1 μm
It is preferable that it is above. Silicon dioxide film 10. A plasma silicon nitride film 6 having a thickness of 0.25 .mu.m is formed thereon as a second packaged tan film by plasma vapor deposition.

Then, on this two-layer stack of silicon dioxide film 10 and plasma silicon nitride film 6, two more sets of two-layer stack of silicon dioxide film 10 and plasma silicon nitride film 6 are formed in the same process. .

Next, the operation of the semiconductor device configured as described above will be explained.

First, the reason why two types of passivation films are formed on the semiconductor substrate 1, such as the silicon dioxide film 10 and the plasma silicon nitride film 6 described above, will be explained below.

FIG. 2 is a cross-sectional view of a MIS (metal-insulator-semiconductor) capacitor. This MIS capacitor has a surface crystal orientation of (100) and a resistivity of 3 Ωam on a p-type silicon single crystal substrate 15 having a thickness of 0.0 mm by low pressure chemical vapor deposition.
A 1 μm thick silicon dioxide film 10 is formed, and a plasma silicon nitride film 6 is formed on this silicon dioxide film 10 by plasma vapor deposition. The thickness of this plasma silicon nitride film 6 is 1 μm. The plasma vapor phase epitaxy apparatus used to form the plasma silicon nitride film 6 has parallel plate type electrodes, and the silicon substrate 15 is placed face down on the upper electrode, and the lower electrode has a frequency A high frequency voltage of 50KH2 is applied between the electrodes. A current of OA was applied so as to flow. Silane (StH+), ammonia (NH3), and nitrogen (N2) were passed between the electrodes as reactive gases to generate plasma particles and form a plasma silicon nitride film 6 on the silicon substrate IS. The film thickness of the plasma silicon nitride film 6 was controlled by changing the growth time. After forming an aluminum film with a thickness of 1 μm on the plasma silicon nitride film 6 by a sputtering method, an aluminum film having an area of 1.84×10−2 is formed by normal gluing and etching techniques.
The aluminum electrode 14 is formed by patterning to a thickness of cm2.

Then, the characteristics between the capacitance and voltage of this MIS capacitor were measured, and the obtained flat band voltage V FR
The charge density NFB in the insulator was calculated from the insulator capacitance C. FIG. 3 is a graph plotting this charge density NFB as a function of the film thickness T of the plasma silicon nitride film 6. In FIG. 3, the horizontal axis represents the film thickness T of the plasma silicon nitride film 6, and the vertical axis represents the charge density NFB contained in the plasma silicon nitride film 6 and the silicon dioxide film 10.

If NFB>O, positive charges are included in the film, and if Npa<O, negative charges are included in the film. NFB when the film thickness T of the plasma silicon nitride film is 0.25 μm or more
>0, indicating that positive charges are distributed in the film. The film thickness T is thicker (as the positive charge density becomes larger).

On the other hand, when the film thickness T is 0.25 μm or less, NFB<O, and negative charges are distributed.

This negative charge is formed as a result of negatively charged ions or radicals bombarding the surface of the silicon dioxide film 10 during the initial stage of growth of the plasma silicon nitride film 6, resulting in a charge-up of negative charges. , localized in the silicon dioxide 10 near the interface of the plasma silicon nitride film 6. When a plasma silicon nitride film 6 with positive charges such as hydrogen ions or dangling bonds is formed on the silicon dioxide film 10 which is negatively charged,
When the thickness of the plasma silicon nitride film is 0.25 μm or less, the positive charge density in the plasma silicon nitride film 6 is smaller than the negative charge density in the silicon dioxide film 10, and as a result, the total charge density NFB obtained from the MIS capacitor has a negative value. Conversely, when the thickness of the plasma silicon nitride film 6 is 0.25 μm or more, the positive charge density is greater than the negative charge density, and the total charge density NFB has a positive value.

When the film thickness of the plasma silicon nitride film 6 is 0.25 μm, the density of positive charges and negative charges becomes the same, and the amount of charge distributed throughout the insulating film appears to be above zero, making it ideal as a passivation film. state is realized.

Therefore, as in the semiconductor device shown in FIG. 1, if silicon dioxide l1ilO is formed as the first patchy basis film and a plasma silicon nitride film 6 with a thickness of 0.25 μm is formed as the second patchy basis film, the appearance is It is possible to form an ideal passivation film containing no upper charge.

However, when forming a plasma silicon nitride film as a passivation film for a normal semiconductor device and sealing it using a plastic package, etc., the film thickness is 0.25.
When μm, moisture resistance, alkali metal resistance, stain resistance,
Also, mechanical strength and the like are insufficient, and a film thickness of at least 1 μm is required.

Therefore, on the plasma silicon nitride film θ used as the second passivation film, a second passivation film consisting of a combination of a silicon dioxide film 10 with a film thickness of 0.1 μm or more and a plasma silicon nitride film 6 with a film thickness of 0.25 μm is added. Stack several sets of layers to achieve the desired thickness. Note that the uppermost layer of the passivation film, which is in direct contact with the outside air, needs to be the plasma silicon nitride film 6, which has better moisture resistance.

In this way, it is possible to form a passivation film that does not deteriorate the pn junction due to the electric field created by the positive charges in the film and the moving charges, and has high reliability in terms of moisture resistance and mechanical strength.

Note that the present invention is not limited to passivation films, and a silicate glass (P2o5/5iO3) film formed by low pressure chemical vapor deposition or atmospheric pressure chemical vapor deposition may be used instead of the silicon dioxide film 10. It can also be applied to the formation of an interlayer insulating film in a multilayer electrode wiring structure.

FIG. 4 is a sectional view showing an embodiment in which the present invention is applied to an interlayer insulating film. A silicon dioxide film 2 and a metal electrode 5 are disposed on a semiconductor substrate 1, which are formed by a thermal oxidation method or a normal chemical vapor deposition method. An SOG film 11 is formed on the silicon dioxide film 2 and the metal electrode 5 by applying a silica film dissolved in a organic solvent by the SOG method (Spin On Glass).

After coating, this SOG film 11 is annealed at a temperature of approximately 350°C, whereby the organic solvent in the SOG film evaporates and silicon-oxygen bonds are generated, resulting in a thin film having a composition close to that of a silicon dioxide film. becomes. In a normal interlayer film forming process, the SOG film 11 is then etched back and the SOG film 11 is left only in the recesses between the electrodes, but in this embodiment, the SOG film 11 is not etched back and the SOG film 11 is left as it is.
Leave on the entire surface.

Next, by plasma vapor phase epitaxy on one SOG film,
A plasma silicon nitride film 6 having a thickness of 0.25 μm is formed. In this case as well, negatively charged ions or radicals are bombarded at the initial stage of plasma vapor phase growth and a negative charge-up occurs on the surface of the SOG film, resulting in a thickness of 0.25 mm.
It electrically neutralizes the positive charges in the μm plasma silicon nitride film θ, and the charges in the upper film appear to be zero. Thereafter, an SOG film 11 is formed on the plasma silicon nitride film θ with a film thickness of 0.
An interlayer insulating film having a desired thickness is formed by stacking several two-layer films in combination with a plasma silicon nitride film 6 of 25 μm. Thereafter, through holes 12 are formed using lithography and etching techniques, and then second layer electrodes 13 are patterned.

In this case, since the SOG film 11 having the function of flattening the step difference in the recessed portion is used in the interlayer insulating film, the unevenness on the surface of the interlayer insulating film is relatively small. For this reason,
It is possible to prevent the effective wiring length of the second layer electrode 13 from increasing and from disconnection. Second layer electrode 13
On top of this, several two-layer films consisting of a combination of an SOG film 11 and a plasma silicon nitride film 6 with a film thickness of 0.25 μm are stacked, and an electrode and an interlayer film are sequentially formed as a second interlayer film. . As a result, the pn junction is not deteriorated by the electric field created by the positive charges in the film and the moving charges, and a highly reliable interlayer insulating film can be formed.

[Effects of the Invention] As described above, the present invention provides a film having a thickness on a silicon dioxide film having substantially the same density of positive charges as the negative charges induced in the silicon dioxide film by plasma vapor deposition. By forming a plasma silicon nitride film with a plasma silicon nitride film and stacking these two films, it is possible to form a high-quality passivation film and interlayer insulating film that has zero charge in the film and does not deteriorate the pn junction of the semiconductor device. .

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention, FIG. 2 is a sectional view of a MIS capacitor, FIG. 3 is a graph showing the relationship between plasma silicon nitride film thickness and charge amount in the film, and FIG. 4 is a sectional view showing a second embodiment of the present invention, FIG. 5 is a sectional view showing a conventional semiconductor device, FIG. 6 is a sectional view of an npn bipolar element, and FIG. 1 is a cross-sectional view of an npn type bipolar element using a plasma silicon nitride film.

Claims (3)

[Claims] (1) A stacked body of a silicon dioxide film and a silicon nitride film formed by plasma vapor phase epitaxy is provided on a semiconductor substrate having a pn junction, and the silicon nitride film absorbs negative charges induced in the silicon dioxide film. 1. A semiconductor device having a pn junction, the thickness of which is set to have substantially the same density of positive charges. (2) The semiconductor device having a pn junction according to claim 1, wherein the stack of the silicon dioxide film and the silicon nitride film is a passivation film. (3) The semiconductor device having a pn junction according to claim 1, wherein the stack of the silicon dioxide film and the silicon nitride film is an interlayer insulating film.