JP2708018B2 - Contact hole formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a contact hole, and more particularly, to a method for manufacturing a semiconductor device having a metal layer and an insulating layer covering the metal layer. The present invention relates to a method for forming a contact hole formed in a layer.

[0002]

2. Description of the Related Art A semiconductor integrated circuit device has a wiring formed of a metal layer for electrically connecting circuit elements such as transistors formed on a semiconductor substrate.

[0003] As the number of circuit elements integrated on a semiconductor substrate increases, the dimensions of the circuit elements and the distance between the circuit elements have been increasingly reduced. In order to connect such high-density circuit elements, semiconductor devices having a multilayer wiring structure have been developed.

FIG . 5 shows a part of a cross section of a semiconductor device having a two-layer wiring structure. The present semiconductor device is formed in a silicon substrate 30, a device isolation oxide film 31 formed in a predetermined region on the surface of the silicon substrate 30, and a region (device region) where the device isolation oxide film 31 is not formed in the silicon substrate 30. Was done
MOSFETs 36a and 36b and a first covering MOSFETs 36a and 36b
An insulating layer 32, a first metal layer 33 for electrically connecting the plurality of MOSFETs 36a and 36b to each other, a second insulating layer 34 covering the first metal layer 33, and a second insulating layer. It has a second metal layer 34 formed on the layer 34.

The MOSFETs 36a and 36b include an impurity diffusion layer (functioning as a source / drain) 38 formed in a predetermined portion of an element region of the silicon substrate 30, a gate oxide film 39 formed on the element region, and a gate oxide film 39. And a gate electrode 41 formed on the film 39.

[0006] The first and second insulating layers 32 and 34 are also called interlayer insulating films, and include gate electrodes 41, 36 of the MOSFETs 36a and 36b.
The first metal layer 33 and the second metal layer 35 are electrically separated from each other.

The first metal layer 33 and the second metal layer 35 are in contact with each other through a contact hole 40 formed in a predetermined portion of the second insulating layer 34 covering the first metal layer 33. doing.

A conventional method for forming a contact hole 40 in the second insulating layer 34 is as follows.

First, the second insulating layer 34 is formed of a first metal layer 33.
Is deposited on the silicon substrate 30 so as to cover the substrate. As a deposition method, a CVD method is used. A photoresist (not shown) functioning as an etching mask is deposited on the second insulating layer 34, and thereafter, a photoresist on a region (contact hole region) where the contact hole 40 is to be formed in the insulating layer 34 is formed. It is removed by a normal photolithography method. Thereafter, the contact hole region of the second insulating layer 34 is etched using an etching gas. At this time, the portion of the second insulating layer 34 that is covered with the photoresist is caused by the presence of the photoresist.
Since there is no contact with the etching gas, no etching is performed.

The etching step will be described in more detail. The etching gas used in the etching step is selected according to the material of the insulating layer 34 to be etched. For example, when the insulating layer 34 is made of silicon dioxide, a mixed gas containing CHF ₃ , C ₂ F ₆ , O _2, He, and the like is selected as the etching gas.

The etching is performed in an etching apparatus such as an RIE apparatus. When performing highly anisotropic etching, the etching gas introduced into the etching apparatus is:
It is ionized by the discharge between the electrodes in the etching apparatus, and becomes a plasma state.

FIG . 6 shows that the second insulating layer 34 is formed by etching .
1 schematically shows a state in which a contact hole 40 is formed.

Ions are accelerated toward the silicon substrate 30 from an etching gas in a plasma state which is at least partially ionized, and the photoresist on the silicon substrate 30 is exposed.
Ions are incident on 37 and the second insulating layer 34. The acceleration of the ions is caused by a sheath electric field formed in a portion near the surface of the silicon substrate 30 in the plasma.

The contact hole region of the second insulating layer 34 is
With the assistance of these ions, etching is performed efficiently. As etching progresses, contact hole 40
A polymer film containing carbon is deposited on the side wall of the photoresist 37. Due to the presence of this film (deposit 38), the etching of the second insulating layer 34 on the side wall of the contact hole 40 is prevented. Thus, the etching of the second insulating layer 34 proceeds in the direction perpendicular to the main surface of the silicon substrate 30, and the formation of the contact hole 40 having a high aspect ratio becomes possible. When the second insulating layer 34 is a TEOS layer, TE
Since the OS layer contains a large amount of carbon, a thick deposit 38 is formed.

[0015]

However, in the above-described method for forming a contact hole, the first metal layer 33 is exposed after the surface of the first metal layer 33 is exposed through the contact hole 40 as the etching proceeds. Has a problem that the surface is sputtered by ions in the plasma. The metal or metal compound sputtered from the surface of the first metal layer 33 is implanted into the photoresist 37 near the contact hole 40 or the deposit 38 formed on the side wall of the contact hole 40. The surface of the photoresist 37 or the deposit 38 into which the metal or the metal compound is implanted,
To cure. Hardened photoresist 37 or deposit
38 is difficult to remove. Therefore, after the contact hole forming step, the photoresist 37 is removed using O ₂ plasma, or after the silicon substrate 30 is cleaned, the cured photoresist 37 or the deposit 38 is not removed.
Remains in the vicinity of the contact hole 40.

FIG . 4 shows the deposit 38 left near the contact hole 40. This figure is a perspective view drawn based on a scanning electron micrograph.

The contact hole 40 shown in FIG . 4 is a second insulating layer made of a TEOS layer covering the first wiring layer 33 made of A1.
This is a contact hole formed at 34. The etching of the second insulating layer 34 made of a TEOS layer was performed by a dry etching method using an etching gas in which CHF ₃ , O ₂ and He were mixed. The flow ratios of CHF ₂ , O ₂ and He are respectively
90 sccm, 10 sccm and 100 sccm.

An ordinary RIE (reactive ion etching) apparatus was used as the etching apparatus. The etching is performed by setting the thickness of the second insulating layer 34 to be etched to 1.
The etching was performed with sufficient time to etch the insulating layer having a thickness of 5 times. Such etching is called 50% over-etching.

As shown in FIG .
A hardened deposit 38 remains inside and around 40. Such deposits 38 form the second wiring layer 35 and the first wiring layer 33 to be formed through the contact holes 40.
Degrades the connection state. This causes a contact failure due to disconnection of the second wiring layer 35 or a short circuit between the second wiring layers 35, thereby lowering the manufacturing yield of the semiconductor device and deteriorating the reliability of the semiconductor device.

It is an object of the present invention to provide a method for forming a contact hole in which a deposit formed by an etching step for forming a contact hole is easily removed after the step.

Another object of the present invention is to provide a contact hole forming method capable of forming a contact hole in which a disconnection and a short circuit of a wiring hardly occur and a contact excellent in reliability is realized.

[0022]

SUMMARY OF THE INVENTION The present invention provides a semiconductor substrate,
A contact hole forming method for forming a contact hole reaching the metal layer in the insulating layer during a manufacturing process of a semiconductor device including the metal layer formed on the semiconductor substrate and the insulating layer covering the metal layer. A contact hole forming method by etching a predetermined portion of the insulating layer using an etching gas to which a gas containing a nitrogen atom is added. Is about 4.5% or more of the amount of the etching gas excluding the diluent gas.

Further, at least a part of the etching gas may be ionized, and the predetermined portion of the insulating layer may be etched using the ionized etching gas.

When the insulating layer is etched,
At least after the surface of the metal layer is exposed,
The ion energy of the ionized etching gas may be about 250 eV or less.

The ionization of the etching gas and the etching of the insulating layer may be performed in an apparatus selected from the group consisting of a high pressure narrow gap type RIE apparatus, a plasma etching apparatus, and an ECR etching apparatus.

When the insulating layer is etched,
Until the metal layer is exposed, using the insulating layer using an etching gas to which a gas containing a nitrogen atom is not added,
After the surface of the metal layer is exposed, an etching gas containing the gas containing a nitrogen atom may be used.

[0027]

According to the present invention, the above structure allows the metal surface at the bottom of the contact hole to be hit with ions while nitriding. The nitrided metal surface has a lower sputtering rate for ions than when not nitrided, and the deposits formed on the resist sidewalls and the sidewalls of the interlayer insulating layer are hardly hardened. Therefore, these deposits are easily removed by O ₂ plasma or a cleaning step, and the reliability of the metal wiring in the contact hole can be greatly improved. Further, when the ion energy is reduced, the sputtering rate of the metal can be reduced, which helps to prevent the hardened deposit.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for forming a contact hole according to the present embodiment will be described with reference to FIG.

First, after the first insulating layer 2 was formed on the silicon substrate 1, the metal layer 3 was formed on the first insulating layer 2. After that, the second insulating layer 4 covers the first layer so as to cover the metal layer 3.
It was formed on the insulating layer 2. In this embodiment, the material of the metal layer 3 is an Al alloy containing 2% of Si. Other materials for the metal layer 3 include other alloys mainly composed of A1 and pure alloys.
A1, and a high melting point metal or the like can be used. The metal layer 3 was formed by depositing an A1 alloy over the entire surface of the wafer by sputtering and then patterning the alloy into a desired wiring shape by lithography. The material of the insulating layer 4 is TE
OS layer. The insulating layer 4 was formed by a CVD method using TEOS as a deposition gas.

In the following description, a silicon substrate 1
All objects such as the metal layer 3 and the insulating layers 2 and 4 formed on the silicon substrate 1 are collectively referred to as a wafer.

Next, a photoresist 7 functioning as a mask for etching for forming a contact hole.
Was formed on the insulating layer 4. The photoresist 7 was patterned into a predetermined pattern by exposure and development, and an etching mask having an opening defining a contact hole region of the insulating layer 2 was formed.

After the wafer was introduced into the RIE apparatus, an etching gas was introduced into the etching chamber of the apparatus. As an etching gas, an etching gas obtained by adding N ₂ to a mixed gas containing CHF ₃ , O ₂ and He was used. CH
The flow rates of F ₃ , O ₂ and He were 90 sccm, 10 sccm and 100 s, respectively.
ccm. In the present embodiment, the flow rate of N ₂ is 5 sccm. He is a diluent gas.

By applying an RF voltage between the electrodes in the RIE device, the etching gas in the device was discharged and a part of the etching gas was ionized. RF power is 30
It was set to 0W. The etching gas partially ionized by the discharge was in a plasma state. The etching gas in the plasma state came into contact with the wafer introduced into the RIE apparatus, and etched a portion of the insulating layer 4 on the wafer that was not covered with the photoresist 7 with high anisotropy.

The etching was performed under the condition of 50% over-etching. Therefore, even after the surface of the metal layer 3 was exposed at the bottom of the contact hole, the contact between the wafer and the etching gas in the plasma state was maintained for a while. More specifically, during this time, the interaction between the metal layer 3 and the plasma was performed via the contact hole. Since N ₂ is added to the etching gas used in this embodiment, the contact (interaction) causes the surface 3 a
Was nitrided. This nitriding occurs when a gas containing nitrogen atoms is added to the etching gas. Therefore, even if NH ₄ and NF ₃ are used instead of N ₂ as a gas containing nitrogen atoms, the surface 3 a of the metal layer 3 is nitrided.

The surface 3a of the nitrided metal layer 3 is hardly sputtered. Therefore, even if ions are bombarded from the etching gas in the plasma state on the surface 3a of the nitrided metal layer 3, the metal layer 3 is hardly sputtered. Therefore, for the deposit 8 on the side surface of the contact hole,
The implantation of the metal constituting the metal layer 3 or the compound of the metal was suppressed. For this reason, the deposit is hardly hardened and, as described later, is easily removed by washing after the etching step.

After the above etching step, a resist removing step using O ₂ plasma and a wafer cleaning were performed. Washing is performed for 5 minutes with nitric acid, and further for 10 minutes with pure water.
Made for a minute.

FIG . 2 shows the surface of the wafer after the above-mentioned cleaning. The photoresist 7 is removed by the resist removing step and the cleaning, and the second insulating layer 4 is exposed. The deposit 8 on the side surface of the contact hole hardly remains. The slightly remaining sediment 8, once again,
It was completely removed by repeating the above washing.

As described above, by repeating the above-described cleaning, the residual deposit 8 having a low degree of hardening can be completely removed. However, it has been found that as the cleaning time or frequency increases, corrosion of the metal layer 3 is more likely to occur. Corrosion of the metal layer 3 causes a reduction in the manufacturing yield of the semiconductor device and a reduction in reliability.
Preferably, the deposit 8 is completely removed.

FIG . 3 shows a contact hole formed according to a second embodiment of the present invention using an etching gas in which the amount of N ₂ is further increased. These contact holes are formed by the same method as the above-described contact hole forming method except that the flow rate of N ₂ is 10 sccm. Wafer cleaning was performed after the resist removal step using O ₂ plasma.

The cleaning was performed with nitric acid for 5 minutes, and further with pure water for 10 minutes. By performing this cleaning only once, the deposit 8 was completely removed as shown in FIG .

According to the experiment, the amount of the gas containing nitrogen atoms was 4.5 times the amount of the etching gas excluding the diluent gas.
%, The deposit 8 was easily removed. If the amount of the gas containing nitrogen atoms is about 4.5% or less of the amount of the etching gas excluding the diluent gas, the metal layer 3
Since the surface 3a of the metal layer 3 is not sufficiently nitrided, the sputtering of the metal layer 3 cannot be sufficiently prevented. Therefore, the amount of the gas containing nitrogen atoms is preferably about 4.5% or more of the amount of the etching gas excluding the diluent gas.

Since a large amount of nitrogen molecules is contained in the atmosphere,
An etching gas to which nitrogen has not been added may inevitably contain a trace amount of nitrogen as an impurity. However, such an etching gas is not an etching gas to which a gas containing a nitrogen atom is added.
Even if such an etching gas is used, the surface 3a of the metal layer 3 is not nitrided to such an extent that the sputtering of the metal layer 3 can be suppressed.

As described above, according to the contact hole forming method of this embodiment, the surface 3
By nitriding a, the ratio (sputtering rate) at which the metal layer 3 is sputtered by ions decreases. Metal layer 3
Is further suppressed, the hardening of the deposit 8 is further suppressed. In order to reduce the sputtering rate, the RF power for discharge during etching is reduced, and the metal layer 3
The energy of the ions that collide with the surface may be reduced. This is because the sputtering rate strongly depends on the energy of the incident ions.

According to the experiment, when the energy of ions incident on the wafer from the etching gas in the plasma state was increased to about 250 eV or more by increasing the RF power, the amount of deposits remaining after the cleaning increased. Therefore, it is preferable to perform the etching under the condition that the ion energy is about 250 eV or less.

FIG . 7 shows an experimental result on the reliability of the contact chain. In FIG. 7 , the data group indicated by A is CHF ₃ (flow rate 90 sccm) and O ₂ (flow rate 10 sccm).
cm) represents the reliability of a contact chain connected via a contact hole formed using an etching gas containing (cm). On the other hand, the data group indicated by B is
Reliability of contact chains connected via contact holes formed by using an etching gas in which N ₂ (flow rate 10 sccm) is added to a mixed gas containing CHF ₃ (flow rate 90 sccm) and O ₂ (flow rate 10 sccm) Is shown. The material of the metal layer is A1 containing 2% of Si.

Each contact hole was formed by etching using a high pressure narrow gap type RIE apparatus. In addition, any etching is RF
The etching was performed under the conditions of a power of 350 W, an etching gas pressure of 150 Pa, and a 50% overetch. Cleaning after forming the contact holes is performed using nitric acid for each contact hole.
For 10 minutes and then for 10 minutes with pure water.

The diameter of the contact hole of the contact chain is 1.2 μm, and the number is 500 contact holes.
The experiment was performed under the conditions of a current of 28.8 mA and a temperature of 150 ° C.

From the data group shown in FIG . 7A , it can be seen that the average failure time of a contact chain having a contact hole formed using an etching gas to which N ₂ is not added is 0.3 years. On the other hand, from the data group indicated by B, it was found that the average failure time of the contact chain having the contact hole formed using the etching gas to which N ₂ was added was 1.8 years.

As described above, the contact chain having the contact hole formed by using the etching gas to which N ₂ was added exhibited high reliability.

In each of the above-described embodiments, the etching was performed by using the etching gas to which N ₂ was already added from the start of the etching of the second insulating layer 4. But,
In addition to such a method, etching is performed using a normal etching gas to which a gas containing a nitrogen atom is not added until the metal layer 3 is exposed, and then, after the surface of the metal layer 3 is exposed, Etching may be performed by adding a gas containing a nitrogen atom to the etching gas. This is because nitriding of the metal layer 3 becomes possible only after the surface 3a of the metal layer 3 is exposed at the bottom of the contact hole.

In any of the above-described embodiments, when etching the second insulating layer 4, it is not necessary to set the ion energy to about 250 eV or less from the start of the etching. The sputtering of the metal layer 3 occurs after the surface 3a of the metal layer 3 is exposed at the bottom of the contact hole. Therefore, the ion energy is about 25 until the surface 3a of the metal layer 3 is exposed at the bottom of the contact hole.
Even if it becomes 0 eV or more, after the surface 3a of the metal layer 3 is exposed at the bottom of the contact hole, the ion energy becomes about
If it is reduced to 250 eV or less, the hardening of the deposit 8 due to the sputtering of the metal layer 3 is suppressed.

In order to improve the throughput of the etching process while reducing the ion power to about 250 eV or less by reducing the RF power, a high-pressure narrow-gap RIE device, a plasma etching device, an ECR It is preferable to use an etching device. According to these devices, etching with a high etching rate is realized by ions having relatively low energy.

For example, high pressure narrow gap type RIE
According to the device, RF power 350W, ion energy 150eV
Under these conditions, an etching rate of 200 nm / min can be obtained.

[0054]

As described above, according to the present invention,
The deposit formed by the etching step for forming the contact hole is easily removed after the step. Further, a contact hole is formed in which a disconnection and a short circuit of the wiring hardly occur and a contact with excellent reliability is realized.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an etching step in a contact hole forming method of the present invention.

FIG. 2 is a perspective view showing a contact hole formed by a contact hole forming method according to a first embodiment of the present invention;

FIG. 3 is a perspective view showing a contact hole formed by a contact hole forming method according to a second embodiment of the present invention.

FIG. 4 is a perspective view showing a contact hole formed by a conventional contact hole forming method.

FIG. 5 is a sectional view showing a semiconductor device having a two-layer wiring structure;

FIG. 6 is a schematic view showing an etching process for forming a contact hole.

FIG. 7 is a characteristic diagram showing an experimental result on the reliability of a contact chain.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 1st insulating layer 3 Metal layer 4 2nd insulating layer 7 Fetoresist 8 Deposit

Claims (4)

(57) [Claims] 1. A semiconductor device comprising a semiconductor substrate, a metal layer formed on the semiconductor substrate, and an insulating layer covering the metal layer, the insulating layer is dry-etched on the surface of the metal layer. reach a contact hole forming process for forming a contact hole, a metal compound produced by the reaction of the etching gas in which the metal layer is used in the dry etching is formed on a sidewall of the contact hole, the metal layer Is pure Al, mainly composed of Al
Alloy or a high melting point metal, wherein a gas containing a nitrogen atom is added to the etching gas, and the amount of the gas containing a nitrogen atom is the amount of the etching gas excluding the diluent gas. A method for forming a contact hole, which is about 4.5% or more. 2. The gas containing a nitrogen atom includes N ₂ ,
2. The method according to claim 1, wherein NH ₄ or NF ₃ is used. 3. The contact hole forming method according to claim 1, wherein the ion energy of the ionized etching gas when the metal is exposed by performing the dry etching is about 250 eV or less. 4. When dry etching an insulating layer to form a contact hole reaching the surface of the metal layer, an etching gas to which a gas containing nitrogen atoms is not added until the metal layer is exposed, 2. The method according to claim 1, wherein an etching gas to which a gas containing a nitrogen atom is added after the metal layer is exposed is used.