JPH0214749B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pattern inspection method for inspecting a reticle pattern by comparing the pattern printed on the surface of a semiconductor using a reticle with a reference pattern formed below. .

In the photo process used in the manufacture of semiconductor devices, a method known as contact baking, in which a photomask is brought into close contact with a photosensitive material layer such as a photoresist coated on the surface of a semiconductor wafer to transfer a pattern, has conventionally been common. In recent years, automatic processing technology using machines has advanced even in photo processing, and it has become possible to optically reduce an enlarged pattern called a reticle and print it directly onto a semiconductor wafer while sequentially shifting its position.

This is a method suitable for printing fine patterns.
In addition, since the process of creating a photomask of equal size is omitted and the photomask, which is a consumable item, is not required, the probability of defects occurring in the printed pattern is reduced, and further cost savings are achieved. However, new problems have arisen.

In this method of pattern transfer, the necessary reticle is selected from among several types of reticles prepared in the device and the pattern is printed onto multiple wafers, so there is no chance that the selected reticle may become contaminated with dust. If such a situation were to occur, a defective pattern would be printed onto every chip on every wafer.

This printing process is automatically processed in a printing device installed in a dust-proof room, so the probability of such an abnormality occurring on the reticle is low, but once printing is performed, all lots processed at the same time will be destroyed. Therefore, it is important to prevent this from happening, as it will cause enormous damage.

To do this, it is necessary to inspect the reticle during the printing process to ensure that there are no defects such as dust adhesion, so it is not sufficient to inspect the reticle in advance. No suitable solution to this problem has hitherto been known due to the time constraints of having to detect it while it is being performed.

The present invention provides a pattern inspection method that solves this problem, in which a reference pattern is formed on a semiconductor substrate by using a layer of a material whose surface has a different light reflectance from the light reflectance of the semiconductor substrate surface. A pattern to be comparatively inspected is transferred onto a photosensitive material layer coated on the substrate, and the pattern of the photosensitive material layer is determined to be different from the pattern formed by the material layer having a different surface reflectance. The present invention is characterized in that the presence or absence is detected according to a pattern signal obtained by photoelectric conversion, and the original pattern onto which the transfer has been performed is inspected.

Hereinafter, the present invention will be explained according to one embodiment.

Pattern inspection is essentially performed by comparing the pattern with a reference pattern to detect the presence or absence of differences, but in this example, this reference pattern is placed on a silicon (Si) wafer. Formed by a deposited silicon dioxide (SiO ₂ ) layer. This situation is illustrated in FIG.

First, a Si wafer 1 with a polished surface similar to that used in the manufacture of semiconductor devices is prepared, and a SiO ₂ layer 2 with a thickness of several hundred nm is deposited on the surface. A photoresist layer 3 is applied thereon, and a pattern is printed using a reticle to be inspected later or a reticle having an equivalent pattern, and then developed. obtained by this treatment. 1A shows a state in which a patterned photoresist layer 3 is formed on the SiO ₂ layer 2. As shown in FIG.

Next, using the photoresist layer 3 as a mask, the SiO ₂ 2 is patterned by plasma etching. Plasma etching is a directional etching method that causes almost no side etching, so the photoresist pattern is accurately transferred as a pattern of the SiO ₂ layer. This state is shown in FIG. 1b.

Plasma etching depends on its implementation conditions.
Since the etching rate for Si can be made sufficiently lower than the etching rate for SiO ₂ , etching can be stopped when SiO ₂ is etched away and the Si surface ₄ is exposed. In order to perform complete patterning, a slight overetch is added, so the Si
The substrate is also slightly etched. However, the Si surface exposed in this way is also flat, and its light reflectance is almost the same as that of a polished surface, so it does not affect the processing described later. During the above processing, the alignment reference mark is also transferred as a SiO ₂ pattern at the same time.

The SiO ₂ pattern obtained through this process is used as the reference pattern for inspection, but since this pattern must not have defects outside the tolerance range, it is carefully inspected by comparing it with the original drawing. will be inspected.

Since this reference pattern creation is a preliminary processing stage for the intended inspection, there is no particular time restriction and it may be repeated as many times as necessary until a good reference pattern is obtained.

In the method of the present invention, basically only one reference pattern is required to be formed on the Si wafer, but two or more can be used more widely. As for the creation of the reference pattern itself, the possibility of obtaining a good pattern is greater if multiple patterns are formed at the same time, so it is better to print several patterns onto one Si wafer and perform the above process. It's advantageous. If dust accidentally adheres to the reticle used at that time, the above-mentioned process must be repeated, but as mentioned above, the possibility of this happening is small. Furthermore, once one non-defective pattern is confirmed, all that is left to do is to compare it with this pattern, so this can be done using a known automatic pattern inspection method.

The first step of the present invention is to prepare a Si wafer having at least one good SiO ₂ pattern by the above-described process.

The next step is to check the state of the reticle in the actual photo process, and the reference wafer on which the reference pattern has been formed by the above process is added to the lot to be processed as the leading wafer. For example, when 24 wafers are made into one lot, this reference wafer is designated as No. 1, and the following wafers are designated as No. 2 to No. 25.

The reference wafer is similar to the following wafer:
A photoresist is applied to the surface and printed by projecting a reticle pattern, but the reference wafer is first developed and inspected. The other wafers, ie, No. 2 to No. 25, are sequentially subjected to the baking process in the same manner as in the prior art.

This second pattern baking is performed according to the alignment standards formed on the SiO ₂ layer, so the developed pattern will have a pattern that exactly overlaps the previous SiO ₂ pattern, as shown in Figure 2. A pattern of photoresist will be formed. In reality, a shift equivalent to a positioning error occurs, but in order to facilitate understanding of the present invention, the explanation will be made assuming that there is no shift.

Since the reticle used in this step was set immediately before this printing process, there is a possibility that dust or the like may have adhered to it, unlike when the reference pattern was created. If this dust is of a light-shielding nature and the photoresist layer is positive type, resist 3', which should not originally exist, will remain on the Si surface as shown in FIG. Furthermore, depending on the material and shape of the dust, the resist may be removed in areas where light should not be irradiated due to reflection or refraction of light, and the surface 5 of the SiO ₂ layer may be exposed.

If there are multiple reticles with the same pattern and a reticle different from the one used to create the standard pattern is used for lot processing, there is a possibility that there is a defect in the reticle pattern, and in that case Also, the above-mentioned phenomenon of excess or shortage of photoresist occurs.

Such excess or deficiency of photoresist may not be caused by the reticle, such as dust adhering to the wafer surface or an accident during the development process, but it also indicates the possibility that the condition of the reticle is poor. If this is caused by a defect on the wafer side, the same defect will not occur in several printed patterns, so by examining the same position on other printed patterns, it will be immediately obvious whether or not it is a defect on the reticle side. do. It is because of this usage that it was stated earlier that it is more advantageous to prepare a plurality of reference patterns.

Although it is possible to detect excess or deficiency in the photoresist layer with the naked eye, automatic processing by a machine is desirable for accurate and rapid detection of complex patterns.
An example of this processing method will be described next.

In automatic pattern inspection processing, the target pattern is usually converted into an electrical signal.
In this embodiment as well, the surface of the reference wafer that has been patterned for the second time is photographed in a scanning manner using a video camera. When this video signal output is digitized, a pattern signal having four levels as shown in FIG. 4 is obtained.

These signal levels are determined by the reflectance of the surface of each layer, and the level of the Si surface with the highest reflectance is the level a in Figure 4, which is SiO ₂
Since the layer surface 5 has a low reflectance, the d level is close to 0. In the area where the photoresist layer 3' overlaps the Si surface, the reflectance decreases slightly to level b due to absorption by the photoresist, and when the photoresist layer 3 is deposited on the SiO ₂ layer, the photoresist layer It rises to level C due to reflection from the surface.

If the twice-baked pattern, that is, the SiO ₂ pattern, and the photoresist pattern exactly match, this pattern signal will contain only levels a and c, but if there is an excess or deficiency in the photoresist pattern, levels b or A level of d occurs. Therefore, by setting an appropriate slice level and monitoring the occurrence of the b level and d level, it is possible to easily discover mismatches between the two patterns.

The time required for such an inspection is about several tens of minutes, which is shorter than the baking process time for one lot of ware, so if a defective reticle is discovered, the baking process is immediately stopped and the photoresist is removed. , the process can be repeated by reapplying. In that case, of course, it is necessary to replace the reticle with another one or to perform a cleaning process.

As mentioned above, since the occurrence of defects in reticles is not a frequent phenomenon, such a monitoring method is sufficiently effective. In addition, in the pass/fail judgment by the above-mentioned automatic processing, the b level or d level caused by alignment error, or the b level or d level caused by defects within the tolerance range, is different from that in conventional comparative inspection. It is sufficient to absorb it through similar processing so that it will not be judged as defective. An effective processing method is for the final judgment of pass/fail to be made manually.

In this way, when the present invention is carried out automatically, the difference in surface reflectance of each material layer is utilized, so the material forming the reference pattern is polished.
It is necessary that the reflectance is sufficiently lower than that of the Si surface. In addition to SiO ₂ , polycrystalline Si can be cited as a material that satisfies this condition. In either case, the thickness is preferably about 400 nm in order to ensure pattern accuracy.

As explained above, according to the present invention, defects in the reticle can be found within the printing processing time of one lot, so it is possible to prevent an accident in which the same defect occurs in all chips.

[Brief explanation of drawings]

1 to 4 are diagrams explaining the present invention, in which 1 is a Si substrate, 2 is a SiO ₂ layer, 3 and 3' are photoresists, 4 is a Si substrate surface, and 5 is a SiO ₂ layer surface. .

Claims (1)

[Claims] 1. A reference pattern is formed by patterning a layer made of a second material having a light reflectance different from that of the first material on a substrate made of a first material; A photosensitive material is applied to the entire surface of the substrate including on the material layer to form a film, and a pattern to be compared and inspected corresponding to the reference pattern is optically transferred and chemically treated. Patterning the material film and irradiating light from above the photosensitive material film to obtain (a) reflected light intensity corresponding to the reflected light from the substrate surface, and (b) direct attachment of the photosensitive material film to the substrate surface. (c) a reflected light intensity corresponding to the reflected light from a portion where the photosensitive material layer is adhered to the surface of the second material layer; A pattern inspection method characterized in that the pattern to be comparatively inspected is inspected based on whether the distribution of reflected light intensity corresponding to the reflected light from the surface of the material layer of No. 2 is a distribution corresponding to the reference pattern. .