JPH10242075A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a semiconductor device which prevents discoloration of a metal film for wiring connection of a semiconductor element. SOLUTION: An aluminum film is used in a pad aperture part of a power MOS(metal oxide semiconductor) FET(field effect transistor). A pad forming process contains an oxide film dry-etching process for eliminating a natural oxide film on the aluminum oxide film surface. A rear polishing process of a silicon substrate is performed before a rear metal depositing process for forming a drain electrode on the rear of the silicon substrate. A heat treatment process for performing heat treatment in a temperature range of 400-4500 deg.C is set between the pad forming process and the rear polishing process. Thereby a damage layer which is generated on the aluminum film surface in the oxide film dry-etching process is eliminated. When the silicon substrate is cleaned by using dilute hydrofluoric acid (HF) solution in the later pre-cleaning process, the aluminum film does not react with the dilute hydrofluoric acid solution, so that discoloration can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing a semiconductor device. The present invention relates to a method for manufacturing a semiconductor device having a film formed thereon.

[0002]

2. Description of the Related Art Conventionally, a semiconductor device in which many fine circuits are integratedly formed on a substrate using a lithography technique or the like has been manufactured.

In this type of semiconductor device manufacturing method, a conductive film, an insulating film, and the like are formed by CVD (Chemical Vapor Deposition).
Deposition) and the like, a mask forming step of forming a mask having a predetermined pattern using a photosensitive resist by using a photolithography technique or the like,
An etching step of selectively removing an underlayer using the mask; and selectively adding an impurity to a semiconductor layer at a predetermined position (eg, impurity diffusion or ion implantation) to form a P-type or N-type semiconductor region. An impurity addition step to be formed, a heat treatment (annealing) step of recovering crystal defects due to ion implantation by performing a heat treatment, a polishing step of polishing the substrate surface, or a cleaning step of cleaning and removing contaminants on the substrate surface. It was repeatedly used to form a semiconductor device having a multilayer structure.

For example, a vertical power MOS for high power
(Metal Oxide Semiconductor) In devices and the like, a drain electrode or the like is formed on the back side of a semiconductor substrate (hereinafter also referred to as a wafer), and an Al connecting to an external wiring is formed on the front side.
A pad opening made of a metal film such as (aluminum) is formed. In a manufacturing process of a power MOS device having such a structure, a metal film (Al) constituting a pad is deposited to a predetermined film thickness as shown in FIG. ), A passivation film such as PSG (Phospho-Silicate Glass) etc. is formed on the metal film, and a photoresist is applied thereon, and photolithography is performed in a pattern shape leaving portions other than the pad openings. A mask is formed by a technique (photolithography process), and dry etching is performed using the photoresist as a mask to selectively remove the passivation film and to perform an over-etch to remove a natural oxide film on the surface of the metal film (Al). Performed (oxide film dry etching process), and the photoresist on the passivation film is removed (resist removal process) . As a result, a pad opening made of a metal film (Al) for connection to an external wiring is formed, so that the above-described series of manufacturing steps is referred to as a pad forming step.

Further, in the manufacturing process of the power MOS device, the back surface of the wafer is polished before forming the drain electrode on the back surface side of the wafer (back surface polishing step), and a natural oxide film generated on the back surface of the wafer before the formation of the drain electrode is formed. Pre-cleaning was performed with a dilute HF (hydrofluoric acid) solution or the like (pre-cleaning step) to form a drain electrode on the back side of the wafer (back-side metal deposition step).

For a method of manufacturing such a semiconductor device (power MOS device), see, for example,
No. 6080 and the like.

[0007]

However, in such a conventional method for manufacturing a semiconductor device, a pre-cleaning step using a dilute HF (hydrofluoric acid) solution or the like before forming an electrode on the back surface of the wafer is performed. Then, the metal film (here, Al) in the pad opening on the wafer surface side is discolored, and when it is severe, the appearance abnormality such as blackening occurs. As described above, a semiconductor chip having a discolored metal film in the pad opening cannot be shipped as a product, and thus has a disadvantage of causing a great loss.

Therefore, according to the first aspect of the present invention, a heat treatment step for recovering damage caused on the surface of the metal film is added between the pad forming step and the polishing step, so that the solution cleaning is performed in the subsequent polishing step. It is an object of the present invention to provide a method of manufacturing a semiconductor device capable of preventing the surface of a wiring-connecting metal film from being discolored even if the process is performed.

According to a second aspect of the present invention, the metal film used in the method of manufacturing a semiconductor device according to the first aspect is aluminum, and the temperature range in the heat treatment step is 400 ° C. to 450 ° C.
It is an object of the present invention to provide a method of manufacturing a semiconductor device which can reliably recover damage caused on an aluminum surface by setting the temperature to ° C and prevent aluminum spikes from being generated on a substrate.

[0010]

According to a first aspect of the present invention, there is provided a method of manufacturing a semiconductor device, wherein at least a wiring which is a part of a semiconductor element is formed on one surface of a substrate, and the semiconductor element is formed on the other surface of the substrate. In the method of manufacturing a semiconductor device in which the metal film for wiring connection is formed, after forming the metal film for wiring connection on the other surface of the substrate, the oxide film formed on the surface of the metal film is removed by dry etching. A pad forming step, a heat treatment step of recovering damage to the surface of the metal film, and a polishing step of polishing a wiring forming surface of the substrate and forming a solution before forming a wiring on one surface of the substrate, and sequentially performing a polishing step. Achieves the above object.

Here, the metal film for wiring connection refers to a metal film for connecting an external wiring and a semiconductor element such as a pad of a semiconductor element.

The pad forming step is a step of forming a pad opening or the like of a semiconductor element. Since a portion other than the pad opening is usually covered with a passivation film serving as a protective film, a pad forming step is performed when the pad opening is formed. After the passivation film is formed on the metal film corresponding to the above, the passivation film is selectively removed by dry etching (anisotropic etching) using a mask to expose and form the metal film under the passivation film. I do. When the passivation film is etched to expose the metal film, over-etching is performed to remove not only the passivation film but also the surface of the metal film. This is to ensure that the surface of the metal film is exposed and that a natural oxide film formed on the surface of the metal film is removed.

The polishing step is a step including a solution cleaning performed for the purpose of polishing the substrate surface before forming wiring on the substrate and removing a natural oxide film or the like generated on the wiring forming surface of the substrate surface. is there. This involves polishing and flattening the substrate surface to adjust it to a predetermined substrate thickness, and cleaning and removing the insulating film such as a natural oxide film generated on the substrate surface, thereby forming electrode wiring and the like formed on the substrate. Is to be surely electrically connected to the substrate.

The heat treatment step is a step of recovering the damage received on the metal film surface by the dry etching treatment in the pad forming step by performing a heat treatment (annealing). Here, the damage of the metal film surface refers to fine scratches or the like generated on the metal film surface when overetching by dry etching,
When solution cleaning with a hydrofluoric acid (HF) solution or the like is performed in this state, the surface of the metal film reacts with the cleaning solution to cause surface roughening, which causes discoloration of the metal film. The processing temperature in this heat treatment step is not constant, and the temperature required for repairing the damage varies depending on the type of the metal film used.

According to the above configuration, since the heat treatment step for recovering the damage on the surface of the metal film is performed between the pad forming step and the polishing step, even if the solution cleaning is performed in the subsequent polishing step, the surface of the metal film is removed. This removes the damage and does not react with the cleaning solution, thereby preventing discoloration of the metal film for wiring connection.

In this case, for example, as set forth in claim 2, the metal film is formed of aluminum, and the heat treatment step may be heat-treated in a temperature range of 400 ° C. to 450 ° C. .

Here, when aluminum is used for the metal film, there is no effect of recovering damage at a processing temperature as low as about 350 ° C., and a temperature of 400 ° C. or more is required. If the processing temperature exceeds 450 ° C., a spike phenomenon in which aluminum enters the substrate is likely to occur, so that it is necessary to perform the heat treatment under a certain range of temperature conditions that satisfy both of the above conditions.

According to the above structure, the metal film is made of aluminum, and the heat treatment is performed in the range of 400 ° C. to 450 ° C. in the heat treatment step between the pad forming step and the polishing step.
The discoloration can be prevented by recovering the damage on the surface of the aluminum film, and the spikes of the aluminum substrate can be prevented.

[0019]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. It should be noted that the embodiments described below are preferred embodiments of the present invention, and therefore, various technically preferable limitations are added. However, the scope of the present invention is not limited to the following description. The embodiments are not limited to these embodiments unless otherwise specified.

FIGS. 1 to 3 are cross-sectional views of a semiconductor device during each manufacturing step for explaining a method of manufacturing a semiconductor device according to the present invention. In this embodiment, a vertical power MOS FET (electric field) is used as a semiconductor device. Effect transistor: Field Ef
fect Transistor). FIG.
FIG. 4 is a diagram showing a process flow of a portion related to the present invention in a manufacturing process of a vertical power MOS FET.

FIGS. 1 to 3 are described in relation to FIG. 4. FIG. 1 is a cross-sectional view of the device after an oxide film dry etching step in the pad forming step in FIG.
FIG. 2 is a cross-sectional view of the device after the annealing (heat treatment) process in FIG. 4 has been completed, and FIG. 3 is a cross-sectional view of the device after the back metal deposition process in FIG. 4 has been completed.

Hereinafter, the method of manufacturing a semiconductor device according to the present invention will be described with reference to the drawings.

First, as shown in FIG. 1, a vertical power MOS FET 10 according to the present embodiment is manufactured through the same manufacturing process as in the prior art, and has P +, P-, N −, N + regions are formed, and a gate electrode 16 made of polysilicon is formed on the channel region via a gate oxide film 14, and a BPSG (Boron-doped) is formed on the gate electrode 16.
Phospho Silicate Glass) film 18 is formed to a predetermined thickness,
Further, an aluminum (Al) film 22, which is a metal film of the pad opening 20, is formed thereon by a CVD method or the like (pat deposition process). Note that this aluminum film 22 is connected to the source electrode side of the vertical power MOSFET 10.

Next, a passivation film PSG (Phospho Silicate Glass) is formed on the aluminum film 22.
A film 24 is formed on the entire surface, and a photoresist 26 is further applied on the PSG film 24, and a mask pattern is formed by photolithography (photolithography process).

When forming the pad opening 20, as shown in FIG. 1, plasma etching (dry etching) is performed using the photoresist 26 as an etching mask to remove the PSG film 24 and to remove the PSG film 24 therefrom. The surface of the aluminum film 22 is over-etched. As a result, the PSG film 24 is surely removed, and the natural oxide film formed on the surface of the aluminum film 22 is also removed, so that the pad opening 20 having good connectivity can be obtained. The conditions for the plasma etching in this embodiment are as follows.
Etching is performed using F ₄ , C ₂ F ₆ , CHF ₃ or the like at a gas pressure of 1.5 to 2.0 Torr.

As described above, when the aluminum film 22 is over-etched by dry etching, a damaged layer 28 is formed on the surface of the aluminum film 22 shown in FIG. According to the results of investigation and analysis by the present inventors, the damaged layer 28 is formed by a solution such as a dilute HF solution before forming a drain electrode (see the drain electrode 30 in FIG. 3) on the back surface of the silicon substrate 12 described later. When the cleaning is performed (pre-cleaning step), the damaged layer 28 on the surface of the aluminum film 22 reacts with the dilute HF solution as a cleaning solution to cause surface roughening, and the surface of the aluminum film 22 is discolored (in a severe case, black). ).

For this reason, the method of manufacturing a semiconductor device according to the present embodiment uses a pad forming process from a pad depositing process to a resist removing process shown in FIG.
The present embodiment is characterized in that a heat treatment (annealing) step for recovering the damaged layer 28 on the surface of the aluminum film 22 is added to the back side polishing step of polishing the back side of the substrate.
FIG. 2 shows a state after the heat treatment step.

In FIG. 2, the photoresist film 26 on the PSG film 24 is removed (resist removing step), and annealing is performed at a predetermined processing temperature. According to the experimental results of the present inventors, according to the experimental results of the present inventors, at a temperature of about 350 ° C., the damage layer 28
It was found that there was no effect of restoring and that a temperature of 400 ° C. or higher was required. Conversely, the processing temperature is set to 450 °
C or more, the aluminum film 22 becomes the silicon substrate 1
2, a spike phenomenon occurs. Therefore, it is necessary to determine a condition under which no spike occurs.

In order to determine these conditions, a plurality of samples having different processing temperatures and processing times are subjected to surface etching, and then subjected to a scanning electron microscope (SEM: Scan).
By using a ningElectron Microscope) to observe whether or not aluminum spikes are in the silicon substrate, the optimum parameters for the processing temperature are determined. This scanning electron microscope scans a focused electron beam on the surface of a sample (here, a silicon substrate), receives electrons emitted from each scanning point of the sample by a detector, and amplifies the electrons.
This can be observed by projecting this on a cathode ray tube or the like in synchronization with scanning on the sample. As a result of that observation,
The processing temperature in the heat treatment process is 400 ° C to 450 ° C
It was found that when the heat treatment time was 30 minutes to 60 minutes, the spikes of aluminum were suppressed while the damaged layer 28 was recovered. For example, among the plurality of samples, it has been confirmed that spikes of aluminum have not occurred in a sample heat-treated at a processing temperature of 420 ° C. for 45 minutes. 420 which is the heat treatment condition of
The heat treatment was performed at a processing temperature of ° C for about 30 minutes. Thus, the damaged layer 28 on the surface of the aluminum film 22 shown in FIG. 1 is removed (recovered) as shown in FIG. 2, and the spikes of aluminum can be reliably prevented from entering the silicon substrate. .

Then, as shown in FIG. 3, the back surface of the silicon substrate 12 is polished to reduce the thickness of the substrate to 300 to 400.
After the thickness is set to μm (backside polishing step), the silicon substrate 12 is washed with a dilute hydrofluoric acid (HF) solution before the metal deposition serving as the drain electrode (prewashing step). This pre-cleaning step is usually
The cleaning is performed for about 10 to 30 seconds using a diluted hydrofluoric acid solution obtained by diluting a hydrogen fluoride (HF) solution at a ratio of 50 to 100: 1. This cleaning step allows the silicon substrate 1
It is possible to remove a natural oxide film or the like formed on the metal deposition surface on the back surface side of No. 2.

After the completion of the cleaning step, the silicon substrate 12
Ti (titanium) / Ni (nickel) / Ag (silver) or Ti / N
A metal film made of i / Au (gold) is formed.

As described above, in the conventional example, the aluminum film 22 of the pad opening 20 was discolored in the pre-cleaning step, but in the present embodiment, the aluminum film 22 is subjected to the heat treatment step performed before the pre-cleaning step. Since the damaged layer 28 on the surface of the film 22 is removed, the surface of the film 22 does not react with the diluted hydrofluoric acid solution to cause surface roughness, and discoloration of the pad opening 20 can be prevented.

According to the above embodiment, the processing temperature in the heat treatment step is set to 400 ° C. to 450 ° C., and the processing time is set in the range of 30 minutes to 60 minutes. At the same time, the occurrence of spikes on the silicon substrate of aluminum can be prevented, and the yield of products can be improved.

Although the invention made by the inventor has been specifically described based on the preferred embodiments, the invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the invention. It goes without saying that it is possible.

For example, in the above embodiment, an example of a power MOS device has been described. However, the present invention is not limited to this. Even in a semiconductor device other than a power MOS device, a metal film is dry-etched. If the semiconductor device has a process in which solution cleaning with an HF solution or the like is performed after that, there is a possibility that the surface of the metal film is discolored.

In the above embodiment, since aluminum (Al) is used for the metal film of the pad opening,
The optimal processing temperature in the heat treatment process is 400 ° C to 45 ° C.
The temperature was set to 0 ° C., and the processing time was set to 30 minutes to 60 minutes. However, these conditions are not universal, and differ depending on the metal film to be used. A heat treatment may be performed under conditions appropriate for the film to recover the damaged layer.

[0037]

According to the method of manufacturing a semiconductor device according to the first aspect of the present invention, a heat treatment step for recovering damage to the surface of the metal film is performed between the pad forming step and the polishing step. Even if solution cleaning is performed in the process, damage to the surface of the metal film is removed and the metal film does not react with the cleaning solution, and discoloration of the metal film for wiring connection can be prevented.

According to the method of manufacturing a semiconductor device of the present invention, the metal film is made of aluminum and the heat treatment step between the pad forming step and the polishing step is performed at a temperature of 400 ° C. to 450 ° C.
Since the heat treatment is performed in the range of ° C., damage to the surface of the aluminum film can be recovered to prevent discoloration, and spikes of aluminum to the substrate can be prevented.

[Brief description of the drawings]

FIG. 1 is an element cross-sectional view after an oxide film dry etching step in a pad forming step of a semiconductor device manufacturing method according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of an element after a heat treatment step in a method for manufacturing a semiconductor device according to an embodiment of the present invention;

FIG. 3 is a cross-sectional view of an element after a back metal deposition step in the method of manufacturing a semiconductor device according to one embodiment of the present invention;

FIG. 4 is a vertical power MOS related to a method of manufacturing a semiconductor device according to an embodiment of the present invention;
The figure which shows the part process flow of the manufacturing process of FET.

FIG. 5 is a view showing a part of a process flow of a conventional power MOS device manufacturing process.

[Explanation of symbols]

 Reference Signs List 10 vertical power MOS FET (semiconductor element) 12 silicon substrate (substrate) 22 aluminum film (metal film) 28 damage layer (damage) 30 drain electrode (wiring)

Claims (2)

[Claims] 1. A method of manufacturing a semiconductor device, comprising: forming at least a wiring which is a part of a semiconductor element on one surface of a substrate; and forming a metal film for wiring connection of the semiconductor element on the other surface of the substrate. After forming a metal film for wiring connection on the other surface of the substrate, a pad forming step of removing an oxide film formed on the surface of the metal film by dry etching, a heat treatment step of recovering damage to the surface of the metal film, A method of manufacturing a semiconductor device, comprising: a step of polishing a wiring-formed surface of a substrate to form a solution cleaning before forming a wiring on one surface of the substrate; 2. The method according to claim 1, wherein the metal film is made of aluminum.
The method according to claim 1, wherein the heat treatment is performed in a temperature range of 400 ° C. to 450 ° C. 3.