JPH02231706A - Reduced projection exposure method - Google Patents

Abstract

PURPOSE:To improve the reliability and manufacturing yield of semiconductor devices by measuring the reflectivity for ultraviolet rays at the surface of the semiconductor device beforehand, and setting the amount of exposure in response to said reflectivity. CONSTITUTION:Before the exposure of a wafer, the reflectivity of the wafer is measured. When the reflectivity is R3, the optimum amount of exposure E3 at the reflectivity R3 is obtained. All the wafers in the objective lot are exposed with the amout of exposure E3. At this time, the most effective method is as follows: the relational straight line l1 between the reflectivity and the amount of exposure is inputted into a computer in a stepper beforehand; the optimum amount of exposure is automatically computed based on the result of the reflectivity measurement; and the exposure with the obtained optimum amount of exposure is performed automatically. Therefore, the time for exposure, development, size measurement and the like by using a test wafer can be omitted. Even if there is dispersion in reflectivity in the wafer, the pattern size can be formed constantly. In this way, the integrated circuit device whose reliability and manufacturing yield are improved can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reduction projection exposure method used in the manufacturing process of semiconductor volumetric circuits and the like. [Prior art] In recent years, high integration and miniaturization have been promoted in order to mass produce semiconductor integrated circuits at low cost and achieve high performance.
A high-density memory circuit device called . Super L
In order to form an SI circuit pattern on a semiconductor substrate,
It is necessary to form fine patterns accurately, and for this purpose a reduced projection exposure device, a so-called stepper, is used.
Figure 4 is a schematic diagram showing the basic configuration of a conventional stepper. A stage 107 movable in two directions, X and Y, is installed on a seismic stand 108. A wafer stand 106 is installed on the stage 107 on which a wafer 105 that requires exposure is placed. The ultraviolet light 100 generated from the light source 101 becomes a parallel beam of light at the condenser lens 102,
The semiconductor integrated circuit pattern passes through a reticle 103 formed to be enlarged n times larger than its actual size. The reticle image is reduced to 1/n, that is, to the actual size, by a reduction projection lens 104, and is imaged and exposed onto a wafer 105. By the way, the area that can be exposed at one time using the reduction projection lens 104 is usually about 52 to 152 mm2, and the wafer used for this is 100 to 200 wu.
Since it is about aφ, it is impossible to expose the entire wafer at once. Therefore, after exposing a certain area, the stage 107 is moved to expose another area, and the stage movement and exposure are repeated again to expose the entire wafer, but at this time, the amount of exposure at each area is constant. It is maintained. The workpiece and a resist for pattern transfer are coated on the wafer to be exposed, but when performing exposure, the optimum exposure to obtain the design dimensions is determined depending on the reflectance of the workpiece under the resist to the exposure light. The times are different. For example, when the workpiece is a metal such as aluminum, the reflectance is high and the resist is also exposed to reflected light, so the amount of exposure may be small. On the other hand, when the reflectance is low, such as silicon oxide or silicon nitride, the amount of exposure becomes large. For example, when exposing OFPR800 resist (manufactured by Tokyo Ohka Kogyo Co., Ltd.) coated on an aluminum film to a thickness of approximately 1.5 μm with mercury g-line having a wavelength (λ) = 436 nm, an isolated line with a design dimension of 1 μm The optimum exposure dose is about 100 mJ, but if the underlying layer is a silicon nitride film (15
00 human film thickness), it is approximately 150 mJ.

Conventionally, as a method for determining the optimum exposure amount, one wafer is extracted from a lot consisting of several to several dozen wafers, and the wafer is exposed by changing the exposure amount for each exposure shot. The method used is to measure the length of the pattern using a length measuring device after development, select an exposure dose that will form the pattern according to the designed dimensions, and then expose the remaining wafers to this exposure dose. This work is usually done for each loft. [Problems to be Solved by the Invention] The conventional reduced projection exposure method described above extracts one wafer from one lot, exposes and develops the wafer with varying exposure doses, and then changes the pattern size. Since the optimal exposure amount is determined by measurement, it takes a long time to determine the optimal exposure conditions, and the wafer used to set the conditions is wasted. In addition, if there are variations in reflectance between wafers in the loft or within a wafer, even when exposed with the same amount of light, which is thought to be optimal, the semiconductor may be defective due to underexposure or overexposure. This has the disadvantage of reducing device reliability and manufacturing yield. In contrast to the conventional reduction projection exposure method described above, the present invention involves determining in advance the relationship between the reflectance of each wafer to exposure light and the optimum exposure amount, and then determining the reflectance of the wafer when exposing the wafer. The difference is that the optimum exposure amount is determined from the above relationship without test exposure, and all wafers in the lot are exposed using that exposure amount. [Means for Solving the Problems] The reduction projection exposure method of the present invention sequentially applies reduction projection exposure to a pattern formed on a glass substrate using ultraviolet light onto a semiconductor substrate coated with a photosensitive organic film. In the reduction projection exposure method, the reflectance of the ultraviolet light on the surface of the semiconductor substrate is measured in advance, and the amount of exposure to the semiconductor substrate is set in accordance with the reflectance. [Example] Next, the present invention will be explained with reference to the drawings. FIG. 1 is a schematic diagram of a stepper for explaining an embodiment of the present invention. The basic configuration is almost the same as a conventional stepper, but the stepper used in this example has a reflectance measurement function for measuring the reflectance on the wafer surface. The reflectance measurement function consists of a light source 1, a half mirror 2, a lens system 3, and a detection system 4. The stage 107 is movable under the reduction projection lens 104 and the lens system 3. Since light of the same wavelength as the exposure light is used to measure reflectance, the resist is exposed when measuring reflectance. Therefore, when measuring the reflectance using light source 1, it is recommended to set the measurement area to a part of the wafer that will not be exposed using a stepper, or to decide the measurement area in advance and measure it before applying the resist. is necessary. Figure 2 shows the relationship between the reflectance of the wafer surface and the optimum exposure dose. The optimal exposure amount E1 for a wafer with a low reflectance R1 and the optimal exposure amount E2 for a wafer with a high reflectance R2 are determined in advance, and the relationship line e1 is determined. 2
When calculating l, it is better to use wafers with as many different reflectances as possible to obtain a highly accurate straight line. Furthermore, Figure 2 shows the results obtained when no resist is coated on the wafer. Straight lines are similarly determined when resist is applied.

First, as a first example, the reflectance of a wafer is measured prior to exposure. If the reflectance is R3, the optimum exposure amount E3 for the reflectance R3 is determined from FIG. 2, and all wafers in the target lot are exposed at the exposure amount E3. Second
The relationship straight line f between reflectance and exposure amount shown in the figure. If there is any problem with the computer inside the stepper. The most effective method is to automatically perform exposure using the determined optimum exposure amount by inputting the information in advance.

In this way, according to the first embodiment, since the optimum exposure amount is determined from the reflectance of the wafer, exposure defects are extremely rare. FIG. 3 is a top view of a wafer for explaining a second embodiment of the present invention.

When exposing the exposed areas A, B, C, . . . on the wafer 105 in this order, the exposed areas A, B, C, . . . are exposed before applying the resist.
・Measure the reflectance of ・in advance, and find the optimal exposure amount for each exposed area A, B, C, etc. according to the measured data. After coating the resist on the wafer 105, exposure is performed using the determined optimum exposure amount. As described above, according to the second embodiment, each exposure area on the wafer 105 can be exposed with the optimum exposure amount, so even if the reflectance of the workpiece deposited on the wafer is different, the exposure can be performed. The occurrence of defects is suppressed. [Effects of the Invention] As explained above, the present invention determines the reflectance of the wafer surface and determines the optimum exposure amount based on the reflectance. This has the effect of saving time and making it possible to form patterns with constant dimensions even if there are variations in reflectance within the wafer. Therefore, an integrated circuit device with improved reliability and manufacturing yield can be obtained. -, 106... Wafer stand, 107... Stage,
108... Earthquake prevention stand.

Claims (1)

[Claims] In a reduction projection exposure method in which a pattern formed on a glass substrate using ultraviolet light is sequentially subjected to reduction projection exposure onto a semiconductor substrate coated with a photosensitive organic film, the ultraviolet light on the surface of the semiconductor substrate is A reduction projection exposure method comprising measuring the reflectance of light and setting the amount of exposure to the semiconductor substrate according to the reflectance.