JPH0612775B2 - Method for manufacturing semiconductor device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, in particular, an improved method for forming an insulating layer and an electrode wiring on a semiconductor substrate.

[Technical background of the invention and its problems] Conventionally, in many semiconductor devices, a dark current (leakage current) has been one of the causes of deterioration of device characteristics. For example, in a memory device such as a dynamic RAM,
When dark current occurs, the amount of dark current generated increases and the signal holding time becomes shorter. Further, in a charge transfer device such as a CCD or BBD, the dynamic range is reduced by dark current, and in the case of a bipolar LSI device such as I ² L or ECL, the current amplification factor is reduced and the SN ratio is deteriorated.

One of the main sources of such dark current is various defects in the semiconductor substrate, and the other is a surface level. This surface level is generated at the interface between the semiconductor substrate or the electrically active region formed on this substrate and the insulating film laminated on these, and is caused by dumbling bonds or the like existing at this interface. It is known that

A conventional method of manufacturing a semiconductor device, including the steps of removing the two types of dark current sources, will be described below with reference to FIG. First, as shown in FIG. 2A, a field oxide film 32 for element isolation is formed on the main surface of a p-type semiconductor substrate 31. Then, the first layer gate electrode 34 is formed through the first gate oxide film 33.
And a second-layer gate electrode 36 to be a word line is formed via the second gate oxide film 35. Then, an n ⁺ type impurity region 37 to be a bit line is formed on the main surface of semiconductor substrate 31. Thus, an electrically active region such as a pn junction 38 is formed on the main surface of the semiconductor substrate 31.

Thereafter, as shown in FIG. 2B, a SiO ₂ film 39 is formed on the main surface of the semiconductor substrate 31. And this SiO ₂ film
The ring getter is performed from both the front surface of 39 and the back surface of the semiconductor substrate 31. By performing this ring getter process, a defect in the semiconductor substrate 31, which is one of the sources of dark current, is inactivated because the heavy metal is gettered. After that, an opening 40 for taking out the electrode is provided, and a vapor deposition film 41 of aluminum is formed.

Then, as shown in FIG. 2C, the unnecessary removed portion 42 of the vapor deposition film 41 of aluminum is etched, that is, patterned to form the electrode wiring 43. Next, heat treatment is performed in a non-oxidizing atmosphere such as hydrogen (H ₂ ) or nitrogen (N ₂ ). Due to the annealing effect in this heat treatment step, the semiconductor substrate 31 or the electrically active region (n ⁺ region 37,
The surface potential existing at the interface between the pn junction 38 and the like) and the insulator film (gate oxide films 33, 35 and SiO ₂ film 39) decreases to some extent.

After that, as shown in FIG. 2D, a passivation film 44 is formed using PSG or the like to complete the semiconductor device.

In such a manufacturing process, a defect in the semiconductor substrate 31, which is one of the sources of dark current, is almost completely inactivated by performing the above-mentioned ring getter process.

However, the surface level, which is another source of dark current, is not sufficiently reduced. That is, in such a heat treatment method, the semiconductor substrate 31 or the electrically active region (n ⁺ region 37, pn junction 38, etc.) formed in this semiconductor substrate is used.
And insulator film (gate oxide films 33 and 35 and SiO ₂ film 3
Since the surface level generated on the surface in contact with 9) is not sufficiently reduced, the dark current value generated in the manufactured semiconductor device cannot be sufficiently reduced.

[Object of the Invention] Therefore, an object of the present invention is to provide a method for manufacturing a semiconductor device in which the amount of dark current generated is significantly reduced by significantly reducing the surface states.

[Outline of the Invention] That is, in the method for manufacturing a semiconductor device according to the present invention, an insulating film containing hydrogen is formed on the main surface of a semiconductor substrate having an electrically active region via an insulating film. ,
Next, a metal film for electrode wiring is formed on this. Then, heat treatment is performed in a non-oxidizing atmosphere before patterning the metal film for forming electrode wiring, that is, in the state where the metal film is a perfect single film without holes. By this heat treatment, hydrogen is generated from the insulating film containing hydrogen, but this hydrogen does not leak into the atmosphere because it is blocked by the metal film, and the hydrogen fills under the metal film. Brings a very high annealing effect,
Dramatically reduce the surface level.

[Embodiment of the Invention] An embodiment of a method for manufacturing a semiconductor device according to the present invention will be described below with reference to the drawings. Here, dynamic RA
The manufacturing method of M will be described as an example, but this manufacturing method can be carried out when manufacturing all semiconductor devices regardless of whether they are of the MOS type or the pyvola type.

First, as shown in FIG. 1A, field oxide films 12 and 13 for element isolation are formed on the main surface of a p-type semiconductor substrate 11,
After that, a first-layer gate electrode 15 made of polycrystalline silicon is formed via the first gate oxide film 14. Then, the second gate layer electrode 17 is formed via the second gate oxide film 16. The second gate electrode 17 is separated from the first gate layer electrode 15 by an oxide film 18 continuing from the first and second gate oxide films 14 and 16. The first gate layer electrode 15 is separated by the oxide film 18. It partially overlaps with the electrode 15. The second gate layer electrode 16 is used as a word line and is made of polycrystalline silicon. Then, an n ⁺ impurity region 19 to be a bit line is formed on the main surface of the semiconductor substrate 11 between the field oxide film 13 and the second gate oxide film 16, and a pn junction is formed on the main surface of the semiconductor substrate 11. 20 such that electrically active regions are formed.

Then, as shown in FIG. 1B, a SiO ₂ film 21 is formed on the main surface of the semiconductor substrate 11 by the CVD method. Next, the ring getter is performed from both the front surface of the SiO ₂ film 21 and the back surface of the semiconductor substrate 11.

In the following description, the gate oxide films 14 and 16, the oxide film 18 subsequent thereto, and the SiO ₂ film 21 will be referred to as a continuous, integral insulator film 22.

On this insulator film 22, as shown in FIG. 1C, an insulating film 23 containing hydrogen is formed. The hydrogen-containing insulating film 23 can be specifically formed of, for example, plasma silicon nitride. As is generally known, a silicon nitride (Si ₃ N ₄ ) film is usually produced from silane (SH ₄ ) and ammonia (NH ₃ ). There are two types of formation method, one is a thermal reaction (reaction temperature of about 700 ° C.) and the other is a plasma excitation reaction (reaction temperature of about 300 ° C.). Here, the plasma silicon nitride film formed by the latter reaction method is Are suitable.
In both reaction methods, the reaction products are silicon nitride (Si ₃ N ₄ ) and hydrogen (H ₂ ), whereas in the plasma excitation reaction, this hydrogen remains in the silicon nitride film. In the case of a thermal reaction, since the reaction is carried out at a high temperature, most of the generated hydrogen is vaporized into the reaction atmosphere and hardly remains in the silicon nitride film.

After forming such an insulating film 23 containing hydrogen,
As shown in FIG. 1 (D), an opening 24 for taking out the electrode is provided.

Then, as shown in FIG. 1 (E), a metal material such as aluminum is deposited on the insulating film 23 containing hydrogen,
A metal film 25 for forming electrode wiring is formed.

Then, in this state, as shown in FIG. 1 (F), nitrogen (N ₂ )
Heat treatment is performed in a non-oxidizing atmosphere such as. The temperature during this heat treatment is set to 400 to 500 ° C., for example. Further, as the non-oxidizing gas, hydrogen or a mixed gas of nitrogen and hydrogen can be used.

By this heat treatment, supersaturated hydrogen is generated from the insulating film 23 containing hydrogen. Generally, hydrogen does not easily pass through a metal film, but can easily diffuse into an oxide body such as SiO ₂ . In the case of FIG. 1 (F), since the metal film 25 is not patterned, the entire semiconductor substrate 11 having no removed portion 42 as shown in FIG. 2 (C) as a conventional example is formed. It is a film that completely covers. Therefore, the hydrogen generated during this heat treatment hardly diffuses into the atmosphere and diffuses into the insulator film 22 made of silicon oxide. The hydrogen is filled near the interface between the semiconductor film 11 having an electrically active region such as the n ⁺ region 37 and the pn junction 38 and the insulator film 22, and the dump ring bond existing at this interface is filled. To greatly reduce the surface level of this interface. Thus, by performing the heat treatment at the stage where the insulating film 23 containing hydrogen and the metal film 25 that completely covers the film are formed, it is possible to obtain a much higher annealing effect than in the past.

Thereafter, as shown in FIG. 1 (G), the metal film 25 is patterned to form an electrode wiring 26, and PSG or plasma silicon nitride is formed on the electrode wiring 26 as shown in FIG. 1 (H). Etc. are deposited to form a passivation film 27. After this, a semiconductor device is manufactured by further opening a pad portion (not shown) for wiring with an envelope (not shown).

The dark current value of the semiconductor device manufactured according to such a method is improved to 1/5 to 1/10 of that of the conventional semiconductor device, and the improvement of the annealing effect is recognized.

In addition to the aluminum, the metal film is an aluminum alloy (aluminum-silicon, aluminum-copper,
Aluminum-silicon-copper etc.) and refractory metals
(Molybdenum, tungsten, etc.) or metal silicide (molybdenum silicide, tungsten silicide, tantalum silicide, etc.).

Also, the temperature during heat treatment in a non-oxidizing atmosphere is 400
The temperature is not limited to ˜500 ° C., and may be further increased according to the material of the metal film used.

[Effects of the Invention] As described above, in the method for manufacturing a semiconductor device according to the present invention, an insulating film containing hydrogen is formed on the main surface of a semiconductor substrate having an electrically active region via an insulating film. Is formed and heat treatment is performed in a state of being covered with a metal film, the annealing effect is improved and the surface level is significantly reduced. As a result, it is possible to manufacture a semiconductor device in which the amount of dark current generated is significantly reduced.

[Brief description of drawings]

FIG. 1 is a process schematic cross-sectional view for explaining an embodiment of a semiconductor device manufacturing method according to the present invention, and FIG. 2 is a process schematic cross-sectional view for explaining a conventional semiconductor device manufacturing method. 11 …… Semiconductor substrate, 22 …… Insulator film, 23 …… Hydrogen-containing insulating film, 25 …… Metal film, 26 …… Electrode wiring.

Claims (5)

[Claims] 1. A step of selectively forming an electrically active region on a main surface of a semiconductor substrate; a step of forming an insulator film on the main surface of a semiconductor substrate having the electrically active region; A step of forming an insulating film containing hydrogen on the film, a step of forming a metal film on the insulating film containing hydrogen, and a step of performing heat treatment in a non-oxidizing atmosphere. A step of patterning the metal film to form an electrode wiring, the method for manufacturing a semiconductor device. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the insulating film containing hydrogen is a plasma silicon nitride film. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the metal film is formed of a material such as aluminum, an aluminum alloy, molybdenum, tungsten, or a metal silicide that does not melt by the heat treatment. 4. The method of manufacturing a semiconductor device according to claim 1, wherein the heat treatment is performed in a non-oxidizing gas atmosphere such as hydrogen or nitrogen or a mixed gas of hydrogen and nitrogen. 5. The temperature during the heat treatment is 400 ° C. to 500 ° C.
The method for manufacturing a semiconductor device according to claim 1, wherein the method is in ° C.