JPH0687478B2 - Wiring layer inspection method - Google Patents

Description

The present invention relates to a method for inspecting a covering state of a wiring layer formed on a semiconductor substrate.

After the wiring layer is formed on the semiconductor substrate, the wavelength is measured from the back surface of the substrate for the purpose of promptly judging the quality of the covering state of the metal wiring layer and removing or reprocessing the defective substrate.
It is configured to irradiate light including infrared light of 1.3 to 6 μm, detect light transmitted through the substrate with an infrared detector, and inspect the covering state of the wiring layer by the transmitted light.

[Industrial application field]

The present invention relates to a method for inspecting a covering state of a wiring layer formed on a semiconductor substrate.

[Conventional technology]

FIG. 3 is a substrate cross-sectional view for explaining step coverage of contact holes.

In the figure, 1 is the Si substrate, 2 is the feed SiO ₂ layer, and 3 is the gate Si.
O ₂ layer, 4 is a gate poly-Si layer, 5 is a PSG interlayer insulating layer, 6 is a contact hole, and 7 is an A1 wiring layer.

FIG. 4 is a cross-sectional view of a substrate for explaining step coverage at a wiring intersection.

In the figure, 1 is a Si substrate, 7 is a lower A1 wiring layer, 8 is a PSG interlayer insulating layer, and 9 is an upper A1 wiring layer.

In the integrated circuit wafer process, as shown in FIG. 3, on the contact hole 6 for drawing out the electrode (A portion).
Alternatively, as shown in FIG. 4, the coating of the wiring layer becomes thin at a portion (B portion) where the two wirings 7 and 9 intersect with each other with the insulating layer interposed therebetween, which may cause a disconnection in a severe case.

As a method of improving such step coverage, a method of using phosphosilicate glass (PSG) for the interlayer insulating layer and reflowing it is used.

In this method, PSG is deposited on the substrate, and in the case of Fig. 3, when the contact hole window is opened and then heated to 1050 ° C or higher, the PSG flows and the steep steps of the contact hole are smoothed.

However, this method has a problem that the device is miniaturized and when the diameter of the contact hole becomes about 0.5 μm, the hole is blocked by the flow.

In addition, with the miniaturization, it is necessary to lower the process temperature.
It is no longer possible to heat above 050 ℃.

Furthermore, in the case of FIG. 4, since the lower layer wiring is A1, it is difficult to reflow the PSG to improve the step coverage of the upper layer wiring. This is because A1 reacts violently with PSG or SiO ₂ at about 500 ° C, causing damage to the lower layer wiring.

On the other hand, in order to lower the reflow temperature, SiO containing Pb
₂ or PSG with increased phosphorus concentration may be used,
These materials increase hygroscopicity and cause deterioration of integrated circuit characteristics.

Further, there is a method of making the step round by etching in order to improve the step coverage. However, its control is extremely unstable.

[Problems to be solved by the invention]

However, the various step coverage improvement methods described above are
It is extremely difficult to be perfect over all production lots.

Therefore, the present invention provides, immediately after depositing a metal wiring layer on a substrate,
The purpose is to detect a defective portion of the step coverage and perform the etching or deposition process again to correct the defective substrate, or to avoid a loss in which a subsequent process is performed on the defective substrate.

[Means for solving problems]

To solve the above problems, after forming the wiring layer on the semiconductor substrate,
Achieved by irradiating the back surface of the substrate with light containing infrared light having a wavelength of 1.3 to 6 μm, detecting the light transmitted through the substrate with an infrared detector, and inspecting the covering state of the wiring layer by the transmitted light. To be done.

[Action]

 FIG. 1 is a sectional view of a semiconductor substrate for explaining the present invention.

In the figure, 1 is the Si substrate, 2 is the field SiO ₂ layer, and 3 is the gate.
SiO ₂ layer, 4 is a gate poly Si layer, 5 is a PSG interlayer insulating layer, 6 is a contact hole, and 7 is an A1 wiring layer.

The present invention irradiates infrared light (IR) from the back surface of the Si substrate 1 after depositing the A1 wiring layer 7 on the entire front surface side of the substrate, and before patterning the wiring layer, so that leakage infrared light indicated by an arrow is emitted. This is to detect and determine the presence or absence of disconnection.

Here, if infrared light having a wavelength of 1.3 to 6 μm is used, Si, SiO ₂ , PSG, etc., transmit infrared light in this wavelength range well, and A1 does not transmit infrared light of any wavelength.

In general, a semiconductor device is composed of single-crystal and poly-crystal Si except for wiring metal, and a film whose main component is SiO ₂ such as CVD-PSG, CVD-SiO ₂ , and thermally oxidized SiO ₂ .

On the other hand, the transmittance of Si changes greatly at wavelengths around 1.3 μm and increases above 1.3 μm, while the transmittance of SiO ₂ is 6 μm.
Greatly decreases when m or more.

An example of measuring the transmittance is as follows.

Wavelength (μm) 1 1.5 to 4 10 Transmittance Si 0.2 99 70 (%) SiO ₂ 90 90 3 PSG 90 90 3 A1 0.0 0.0 0.0 However, the film thickness is Si: 300, SiO ₂ : 70, PSG: 300, A1: μm.

From the above table, in the case of a semiconductor device with a Si thickness of 300 μm and a SiO ₂ thickness of at most 10 μm, 90% or more of infrared light with a wavelength of 1.5 to 4 μm is transmitted without a metal film, and 1 μm of A1 It can be seen that the transmittance becomes 0.0% with the film.

The above measurement results were measured in the wavelength range of 1.5 to 4 μm,
Due to the above-mentioned reason, there is an effect that is almost equal in the wavelength range of 1.3 to 6 μm.

〔Example〕

FIG. 2 is a block diagram of an apparatus for explaining an embodiment of the present invention.

In the figure, the infrared light emitted from the lamp house 11 is reflected by the mirror 12
It is reflected by and is incident on the back surface of the semiconductor substrate 13.

The light transmitted through the semiconductor substrate 13 is focused by the imaging lens 14 on the imaging surface.
An image is formed on 15 and detected by an infrared detector 16 placed on the image plane 15, amplified by an amplifier 17, and output.

Although not shown, a chopper may be placed between the substrate 13 and the imaging lens 14 to AC amplify the output of the infrared detector 16.

In this case, the entire surface of the substrate is reduced by the imaging lens 14 to form an image on the photosensitive plate of the infrared detector 16.

The infrared light emitted from the lamp house 11 may be monochromatic light having a specific wavelength within the wavelength range of 1.3 to 6 μm, or may be a plurality of monochromatic lights within this range. Furthermore, even if infrared, visible, or ultraviolet light other than the light within this range is included, these lights cannot pass through the metal film, so that there is no obstacle in carrying out the present invention.

As the lamp house 11, for example, a Tung-ten lamp filled with iodine (I) is used. The emission spectrum in this case is a continuous spectrum that rises at a wavelength of 0.2 μm or more, peaks near 1 μm, and gradually decreases as the wavelength increases.

As the infrared detector 16, a photovoltaic element using a HgCdTe-based compound semiconductor or a photoconductive element in which a Pb thin film is coated on a glass substrate is used.

Now, when one element of the infrared detector 16 is used, the output voltage of the amplifier 17 changes to analog according to the number of places where the coverage of the A1 film is bad or the degree of badness.

On the other hand, if a large number of elements of the infrared detector 16 are arranged in an array, an image of the substrate 13 can be obtained on the image plane 15,
The output of amplifier 17 can also be processed by computer to map which location on substrate 13 is poorly covered.

〔The invention's effect〕

As described in detail above, according to the present invention, it is possible to quickly determine the quality of the covering state of the metal wiring layer.

Therefore, by removing the defective substrate, it is possible to eliminate the loss due to the post-process, or by reprocessing the defective substrate, it can be changed to a non-defective substrate.

[Brief description of drawings]

1 is a sectional view of a semiconductor substrate for explaining the present invention, FIG. 2 is a configuration diagram of an apparatus for explaining an embodiment of the present invention, FIG. 3 is a sectional view of a substrate for explaining step coverage of a contact hole, FIG. 4 is a substrate cross-sectional view for explaining the step coverage at the wiring intersection. In the figure, 1 is a Si substrate, 2 is a field SiO ₂ layer, 3 is a gate SiO ₂ layer, 4 is a gate poly Si layer, 5 is a PSG interlayer insulating layer, 6 is a contact hole, 7 is an A1 wiring layer, and 11 is a lamp house. , 12 is a mirror, 13 is a semiconductor substrate, 14 is an imaging lens, 15 is an imaging plane, 16 is an infrared detector, and 17 is an amplifier.

Claims (1)

[Claims] 1. After forming a wiring layer on a semiconductor substrate, the back surface of the substrate is irradiated with light containing infrared light having a wavelength of 1.3 to 6 μm,
A method for inspecting a wiring layer, which comprises detecting light transmitted through the substrate with an infrared detector and inspecting the covering state of the wiring layer by the transmitted light.