JPS6146025A - Projection exposure - Google Patents

Abstract

PURPOSE:To prevent a required time for position-displacement confirming process from becoming long due to bleaching, by projecting light also on an alignment mark of the subsequent reduced projection position at each time reduced projection is done. CONSTITUTION:In an exposure process for position displacement confirming, a bright protuberance 30 which is correspondent with an alignment mark position of a neighbouring pattern to be exposed subsequently as shown in the figure and which has a sufficient size for exposing the alignment mark, is formed on a reticle 20'. Therefore, light is projected also on the position of the alignment mark for the subsequent reduced exposure process, through the bright protuberance 30 of the reticle 20' in the prior reduced projection exposure process, attaining a bleaching effect, so the true step section of the alignment mark can be recognized without requiring any bleaching time when the position alignment confirmation is done in the subsequent reduced projection exposure process.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a semiconductor device, and particularly to an improvement in a mask eyelet.

(Prior art) Pattern transfer technology in the manufacturing process of semiconductor devices is
It has become one of the important technologies. In particular, with the miniaturization and higher density of elements, there is an increasing demand for improved precision in pattern positioning (hereinafter referred to as alignment).

In order to meet this demand, reduction projection exposure apparatuses have been increasingly used in recent years. A reduction projection exposure apparatus repeatedly projects a reticle pattern onto a wafer in a reduced size and then moves the wafer step by step.・One of the advantages of reduction projection exposure equipment is that alignment can be performed every time reduction projection is performed, so the desired alignment accuracy can be obtained without being affected by wafer deformation, expansion and contraction, etc. . The process of performing alignment every time this reduction projection is performed is hereinafter referred to as die-by-die alignment.

In die-by-die alignment, various wavelengths of light are used to identify misalignment between the wafer pattern and the reticle pattern, but the wavelength that allows for the most accurate alignment is determined from the viewpoint of consistency of the optical system. , is the wavelength used for pattern transfer, that is, the wavelength to which the photoresist is sensitive.

(Problems to be Solved by the Invention) However, when the method is used to check the positional deviation of all patterns of photoresist at wavelengths sensitive to light, there are problems as described below.

Here, the mark on the wafer used as the alignment mark is shown in FIG. 3 (a) before coating the photoresist.
It is assumed that the cross section of the wafer is in the shape of a cross as shown in FIG.

The formation of a photoresist film on a wafer, which is carried out before exposure, usually involves dropping 7-photoresist onto the wafer and rotating the wafer. Since it flows due to force, the coverage of the 7-otoresist film on the step becomes asymmetrical, especially as it approaches the outer periphery of the wafer, as shown by the dotted line in FIG. 4(a). In other words, the cross section is shown in Figure 4 (bl
It will look like this. After this, 7.
When the photoresist is irradiated with light at the photosensitive wavelength, the alignment mark is formed as shown in Figure 4 (al).
The side surfaces m L and m R formed of the photoresist film 2 may be more clearly visible than the step tR.

Due to recognition errors in the positions of the alignment marks, alignment accuracy often decreases.

By the way, when irradiated with a photosensitive wavelength, the No. 7 photoresist exhibits a phenomenon generally called bleaching, in which the photoresist absorbs less light and becomes nearly transparent to this wavelength.

In order to reduce the recognition error of the position of the alignment mark mentioned above, this bleaching is used in the L-brush. In other words, if the photoresist photosensitive wavelength is irradiated for a certain period of time before the positional deviation confirmation process, the lines mI, , mB on the side faces of the dotted line in Figure 4 (al) become weaker.When the positional deviation confirmation process is started after that, the alignment mark This step is recognized as the side surface tL e tR of the original pattern, and the correct position is confirmed.

However, this method using bleaching also has the following drawbacks. In other words, in the case of die-by-die alignment, if this bleaching is performed for each reduction projection process, the time required for each image will be increased by (bleaching time) x (number of reduction projections for each image). This will hinder productivity.

An object of the present invention is to provide a method for checking positional deviation that does not require a long time in the positional deviation checking process even though bleaching is performed.

(Means for Solving the Problems) According to the present invention, by projecting light to the alignment mark (alignment mark) at the next reduction projection position for each reduction projection and performing bleaching, every reduction projection To obtain a method for confirming a pattern positional deviation in which the time required for a positional deviation confirmation step performed in the process is not increased due to bleaching.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

The alignment mark 10 for the positional deviation confirmation process is provided near one side of the reticle 20 as shown in Fig. Next, as shown in Figure 2 (al), in the exposure process to confirm positional deviation, the reticle 20'
Above, projections 30t of bright areas (areas that transmit light) are provided at nine locations where alignment marks were located in the previous reduction exposure process. The position and size of this protrusion $3° corresponds to the position of the 7 line mark of the pattern that will not be exposed later as shown in Figure 2 (bl), and this alignment mark 1 is large enough to be sufficiently exposed. It is also desirable to use a separate light source that can provide a higher illuminance than the actual light intensity for the light irradiated onto the bright portion projection 30 during exposure in order to enhance the bleaching effect. For this reason, in FIG. 2(b), the previous reduction projection exposure step 7' exposes the tickle la.
The light is irradiated through the entire bright part of the projection 30 of O' to the position of the 72 I/ment mark in the next reduction projection exposure step, and a bleaching effect is obtained. When checking the alignment, the true stepped portion of the 7-line mark can be recognized without requiring any particular bleaching time.

To give an example of improvement in processing time, if the pattern arrangement on the wafer is 8 x 8 and the bleaching time by the pattern transfer source is 2 seconds, the conventional method would be l') x
” - Hit p8X8X2=128 (seconds)% In the method using the present invention, the number of hits is 8X2=16 (seconds).
) The referee can shorten the required time by 1 minute 52 seconds.

(Effects of the Invention) As described above, by using the present invention, when performing die-by-die alignment, the exposure of the putter/position that is exposed first can be used as bleaching. The actual bleaching time required is only the first reduction projection exposure step of each row of the pattern array on the wafer, and alignment can be achieved with high precision.

[Brief explanation of the drawing]

Figure 2 (al) is a plan view showing the reticle on which alignment marks are formed, and Figure 2 (b) is a plan view showing how the reticle in Figure Tal is transferred onto the wafer. al is a plan view of the reticle aligned with the pattern in FIG. 1 (al), and FIG. Figure 3(a) is a plan view showing an example of the alignment mark, and Figure 3(a) is a plan view showing an example of the alignment mark. Fig. 4 (al is a plan view of the state in which 7 otoregis (f) is placed over the alignment mark, and the same figure (bl is a sectional view of position 2 in the same figure (al). 10... Alignment mark, 20.20'
...Reticle, 30...Protrusion in bright area, [...Protrusion on wafer, 2...
Photoresist. Sheep I Illustration 2

Claims (1)

[Claims] A projection exposure method characterized in that when projection exposure is performed on a wafer multiple times while aligning the same pattern, an alignment mark at the next projection exposure position is also exposed in the previous projection exposure step.