JPS59159530A - Photoprinting method and semiconductor substrate used for same method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for imprinting a mask onto a workpiece, particularly a semiconductor substrate for the manufacture of integrated circuits, in which a mask pattern is formed on the workpiece by illumination light directed through a projection lens. Prior to irradiating the previously marked workpiece imaged onto the photosensitive layer, the registration pattern of marks and the adjustment marks on the workpiece are imaged onto the photosensitive layer and corresponding adjustment marks are formed by the registration light reflected from the workpiece. and forces 1 aligned with each other by imaging towards each other in a matching pattern
, the actual mark where the adjustment mark creates a dark area in the matching light, j? It consists of the area around the mark that shines in the aligned light.

In the production of integrated circuits, it is necessary to print a mask with a seton on an ellipsoidal semiconductor substrate coated with a photosensitive layer. If the substrate already contains circuitry, the mask and substrate must be mutually aligned prior to the printing process to image the mask pattern in precisely defined areas.

No. An alignment pattern is provided on the mask for this alignment step, said alignment pattern being e.g. in transparent form;
C provided. @71 The adjustment mark d is, for example, a linear groove in the Sio2 layer of the semiconductor substrate. Corresponding adjustment ma-
The alignment and e-turns are imaged toward each other by alignment light reflected from the workpiece to obtain a single alignment reference.

Many visual manual alignment methods use polychromatic alignment light, such as alignment illumination. In such a case, the light source is an incandescent lamp or a Gysenon lamp, so that the wavelength of the matched light ranges from approximately 500 nm to infrared. However, matching methods using polychromatic light have a number of drawbacks. Due to the fact that the imaging efficiency of the matching lens is large, when using monochromatic light VC, most automatic matching methods require matching light with a relatively narrow spectrum (on the order of magnitude of a few nanometers). use.

One of these conventional systems uses a matched processing illumination source, typically a mercury vapor lamp. To#! 54771
A narrow 1/), X vector range of m or approximately 86 nm is used as the matching light.

Further problems arise in this regard. If the alignment process is carried out by a 4661 dedicated alignment light, this intensity will be extremely low b0, which means that the photosensitive layer on the semiconductor disk will be
This is due to its high absorption and photosensitivity at wavelengths shorter than 0 lumen. However, the photosensitive layer must not be pre-irradiated with aligned light.

This problem is solved by using a uniquely matched light source, or by changing the narrow spectrum to approximately the 547 range. The cost of a single matching light is separate from VC, and the constraints on the precise matching wavelength are 1.
This often has a disadvantageous effect, namely that due to interference phenomena, not only the actual mark but also its surroundings appear dark to the viewer, so that the mark is no longer visible or would simply represent an inappropriate contrast. The interference phenomenon described above is due to the fact that the semiconductor substrate used for the manufacture of integrated circuits is optically comparable to a reflective body of silicon coated with a reflective layer of silicon dioxide and a photocurable material. to cause. Despite this fact, the layer thickness is a multiple of the matched wavelength, and the light rays reflected by the first and second boundaries are annihilated by interference due to the large-b cohesive nature of the matched light.

It is therefore an object of the present invention to improve a method for printing masks, especially on semiconductor substrates, which provides high strength and high contrast, largely independent of the II order of the layers on the semiconductor substrate. signals are provided to the alignment mask and the semiconductor substrate to each other.

According to the invention, the above objects are achieved in that the optical thickness has at least two values within the immediate circumference of the mark.

This method states that if an interference condition causing annihilation exists for one area with a first value of optical thickness, then no reflection will occur for the other area with a different optical thickness. No light weakening occurs. If the optical thicknesses of the two regions do not differ from each other by values of i+, I(1) corresponding to multiples of half-wavelengths of the matched light, an exception will occur which must obviously be avoided. Dew. If the optical thickness around the mark changes in discrete steps, different values of the optical thickness differ from each other by an odd multiple of the wavelength of the matching light. From the point of view of manufacturing technology, it will generally be easy to obtain a continuous variation in the optical thickness of the partially reflective layer. In such cases, it should be considered that the difference in the optical thickness spread is sufficient as long as a suitable number of bright areas are provided beside the dark areas in the mark circumference.

The invention will now be described in detail with reference to embodiments and drawings.

FIG. 1 shows the necessary components of a projection copying apparatus for the manufacture of integrated circuits. This device essentially consists of an exposure device 1, a mask stand 4
, a projection objective lens 5, and a coordinate table 10. The mask 2 to be imaged is placed on the mask stand 4 within the object plane of the projection objective lens 5, and the semiconductor substrate 611-1:
It is arranged in the image plane on the six moving devices 9', 9'' and 9''.

The coordinate table 10 is masked 2 by a five-step iterative method.
A circuit is provided in a stepwise movement of the substrate 6 in a known manner to image a circuit number turn onto a predetermined area 7 in a continuous stepwise manner. In order that accurate alignment between the substrate 6 and the mask 2 to the projection device can be performed before each is imaged, alignment patterns 3 and adjustment marks 8 are placed in areas 7 on the substrate to avoid alignment errors caused by Ao. , the mask stage 4 is moved, for example in the coordinates of the object plane XY and ψ, and the substrate is moved along the optical axis of the system. In order to carry out a precise angular alignment of the substrate A in the image plane of the projection objective 5, six individually adjustable displacement devices 9', 9'' and 9' are provided.

Figure 1Q shows the equipment necessary for determining alignment error. The irradiation device 1 consists of two glasses 12' and 12'', between which a mask layer 13 is arranged.
placed above. The light beam projected from the illumination device 1 onto the registration mark 3, which is designed as a window with at least two parallel edges, is reflected by a semi-transparent mirror 15 arranged below the mask 2 and is reflected by the glass 12'. The combined adjustment mark 8 of the board B is passed through the mirror 14 arranged on the lower side.
oriented over the area. Top side of board and adjustment mark 8
The image 6' of the upper window A is back-projected by the projection objective 5 and projected by the mirror 14 onto the evaluation device 21 through the semi-transparent mirror 15.

In FIG. 2a, the superimposed layer structure of the semiconductor substrate 6 in the area of the adjustment mark 8 is shown. The semiconductor substrate 6 consists of a silicon body 17 with a 5io2 layer 18 disposed on its surface. A linear adjustment mark 8 is formed as a groove in the 5L02 layer. The semiconductor substrate is completely covered by a photosensitive layer 16 into which the circuit pattern of the mask is transferred. Since the optical properties of the photosensitive layer and the 5L02 layer 18 are similar,
The semiconductor substrate 6 is defined as a reflective body 17 covered by a partially reflective layer of thickness d. A strong and highly symmetrical adjustment signal can only be applied if the reflectivity of the combination layer of thickness d placed on the semiconductor substrate 6 and adjacent to the adjustment mark 8 is large enough, i.e. if the structural The λ limit can be obtained if the condition for λ is followed. This condition is d=)・5, where λ is a natural number, λ is the vacuum wavelength of the matched light, and the λ limit is is the refractive index of this layer. In other words, the intensity of the matched light reflected from the semiconductor substrate has a sufficient value only if the layer thickness d is an even multiple of the half wavelength of the matched light.

The matched light reflected from the semiconductor substrate is attenuated by substantially VC if the layer thickness d is within the range characterized by the following equation.

As can be easily seen from FIG. 3, the interference condition for weakening of the coherent light reflected from the semiconductor substrate is periodically repeated depending on the layer thickness. If the matched light reflected from the semiconductor is highly weakened, a signal J' (dashed line) will result instead of the ideal intensity shape J, as shown in FIG. 2c.

In order to eliminate this undesirable effect, the invention provides that such an area is always located within the circumference 19 of the actual mark 8 with an optical thickness that does not deviate from the optical thickness of the dark area by half a wavelength. Provide the following information.

As shown in FIG. 4α, the areas deviating from the optical thickness are arranged in a striped manner within a limited circumferential area of the adjustment mark 8. As shown in FIG.

If these stripes are arranged vertically offset from each other, as shown, their narrow edges will form adjustment marks 8, K, which appear dark in reflected light, as can be seen better in FIG. 4b. form. The cross-sectional view shown in Figure 4b shows why the individual stripes in Figure 4a are alternately bright and dark.

This is due to the fact that the reflective silicon plate 17 is not at a constant distance from the substantially planar surface of the photosensitive layer 16. A 5 tOz layer placed in the middle has a Jf of 18 V, which fluctuates [7] and does not charge the depressed area in the silicon plate 17. The difference Δd in the thickness of the semi-reflective layers on the left and right sides in FIG. This is also true for stripes that are continuous with each other in the direction of mark 8.

If the undulating area of body 17 extends more or less continuously as shown in Figure 4C, the probability of finding an intermediate value of optical thickness is substantially the same for all values. In order to exclude the possibility of simultaneous nine-weakening within the entire circumference area 19, J
The width of the fluctuation of the wavelength is set to be at least equal to the wavelength of the matched light.

1-However, if the individual planar areas of the body are separated from each other by inclined areas, their optical influence is small and, according to the invention, the individual levels are within h of the wavelength of the matched light. 5 shows an application example of the vertical distance adjustment mark shown in FIG. 4 corresponding to an odd number multiple of the vertical distance. First of all, the silicon body 17 is oxidized by a chemical oxidation method.
, m and 3 Q nm is deposited. Silicon nitride (Sto
4) is precipitated on top of it by gas phase forces. A photosensitive layer 16 is deposited on the outside thereof. Once said layer 16 is exposed in area 21, it is removed therefrom and the portion of layer 20 underlying /* 20 is etched as shown in FIG. 5b.

The photocurable resin that is no longer needed is then removed, resulting in the condition shown in FIG. 5C. After the oxidation treatment in the furnace, the intermediate product shown in FIG. 5d is obtained. Oxide 1-1 located between layer 20 and layer 16
With a thickness of about 1:11 nrn, oxygen ingress is prevented in the area covered by silicon nitride during the oxidation process. This method is called local oxidation of silicon (Pocos). The bending of the silicon nitride layer at the edges of the oxidized area is a feature of this method, which is caused by the expansion of the silicon dioxide layer due to the inward diffusion of oxygen and the outward diffusion of silicon. It happens.

The product detailed by FIG. 4 etches layer 20 and
It is then covered again with a photocurable resin layer 16, so that the present invention is not limited to the form having the upper surface shown in FIG. 4α.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the known arrangement of the most important elements of a projection copying machine for the manufacture of integrated circuits; FIG. 1a is a diagram of the ray path for the alignment mark; FIG. 2b is the corresponding top view, FIG. 2C is the obtained alignment signal, and FIG. 6 is the optical depth of the partially reflective coating layer of the semiconductor substrate from the periphery of the mark. The intensity of the reflected light, Figure 4α is a top view of a particularly effective mar-shaped configuration, Figures 4h and 4C are the lines 1-I of Figure 4α.
Corresponding cross-sectional views taken along section 11-11, Figures 5a to 2D, illustrate the necessary steps in the corresponding manufacturing process. Symbols in the figure: 1... Irradiation device, 2... Mask, 6... Alignment mark, 6'... Image, 4
...Mask stand, 5...Objective lens, 6...
- Board, 7 - Scheduled area, 8... Adjustment mark, 9/, 9// 9M, - Movement device, 1
o--Coordinate table, 12', 12"...Glass, 16--Mask layer, 14...Mirror, 15
...-Mirror, 16--Photosensitive layer, 17--
Main body, 18-8tn2 layer, 19...periphery, 2()...layer, 21...evaluation device,
Indicates the area. Flg, 4a 7 II = 14

Claims (1)

Claims: 1. A method of printing a mask on a workpiece, in particular on a semiconductor substrate for the manufacture of integrated circuits, in which the pattern of the mask is formed by illumination light directed through a projection lens. The mask and the previously marked workpiece are imaged onto a layer of photocurable material covering the workpiece, and the alignment reflected from the workpiece prior to the alignment of the impressions with each other. A corresponding adjustment mark and an alignment pattern are imaged toward each other by light, said adjustment mark consisting of an actual mark that is dark in said alignment light and a mark circumference that shines in said alignment light, said alignment mark comprising at least one A printing method characterized in that it includes zones of optical thickness with two different values. 2. The method of claim 1, wherein the difference values of the optical thicknesses differ from each other by an odd multiple of the wavelength of the matching light. 3. A patent claim characterized in that the optical thickness of the mark periphery continuously changes, and the maximum and minimum values of the optical thickness differ from each other by at least the wavelength of the matching light. The method described in item 1. 4. comprising a silicon disc coated with silicon dioxide and a photocurable material, the varying optical thickness of the successive layer covering said silicon disc being due to differences in the local oxidation of silicon into the silicon dioxide ( A semiconductor substrate for carrying out the method according to any one of claims 1 to 6.