Semiconductor device and etching mask used for fabricating the same

Abstract: A semiconductor device (Fig. 6) is provided with a device formation region (50) formed by etching using a reticle (52; Fig. 5) as an etching mask. The device formation region is shaped to have at least two curved portions having different radii (R₁, R₂) being encircled with an insulation layer (59), so that radiated light is not converged to a single point inside the device formation region by light reflection on the inner edge of the insulation layer. Unwanted etching away of portions of gate electrodes (56, 58) is thereby avoided.

Description: This invention relates to a semiconductor device, and, more particularly, to a shape of a device-formation region and a reticle, hereinafter referred to as an etching mask, used for fabricating the same. A known semiconductor device is positioned on a device-formation region of a semiconductor substrate, and is separated by a device separation region thereof. There are two methods for fabricating a device-formation region, that is, one is a selective (preferential) oxidation method, and the other is a trench separation method. According to the selective oxidation method, the device-formation region is formed by photoetching with an etching mask. A known etching mask is composed of a light transmission layer and a light shield region formed to be a rectangle on the light transmission layer. In fabrication of a known semiconductor device, a first resist pattern is formed on a silicon substrate by photoetching with using the etching mask. At this time, the first resist pattern is formed to be along a 27% uniform intensity line of light passing through the light transmission layer. Thus, the first resist pattern has two curved portions each having the same radius. Next, a field oxide layer is formed on the silicon substrate as an insulation layer for a device separation region, and a device-formation region is formed by etching with using the first resist pattern as an etching mask. At this time, the device-formation region is shaped to be like a concave mirror being encircled with an inner edge of the field oxide layer. Next, a polysilicon layer is formed on the whole process surface of the substrate, and a resist layer is formed on a surface of the polysilicon. After that, the resist layer is etched, so that a second resist pattern for gate electrodes is formed thereon. Finally, the polysilicon layer is etched with using the second resist pattern as an etching mask, so that the gate electrodes are formed on the device-formation region. According to the known semiconductor device, however, there is a disadvantage in that, when the device-formation region is formed, radiation light is converged to an inside of the device-formation region by light reflection on the inner edge of the field oxide layer, because the device-formation region is shaped to be like a concave mirror. Then, the reflected light is radiated to a side surface of the second resist pattern, so that the side surface which is an inaccurate portion is also etched. Therefore, depressions are formed at the second resist pattern, so that the gate electrodes are provided with depressions corresponding to the depressions of the second resist pattern. As a result, a reliability of the semiconductor device is lowered. European Patent Application EP-A-0 090 447 is an example of a description of the sequence of steps involved in the manufacture of a semiconductor device using masking layers. The invention in its various aspects is defined in the independent claims below, to which reference should now be made. Advantageous features are set forth in the appendant claims. The invention will now be described in more detail, by way of example, with reference to the drawings, in which: Figs. 1A to 1F are cross-sectional views showing a fabricating process of a known semiconductor device; Fig. 2 is a plan view showing a known etching mask used for fabricating the known semiconductor device; Fig. 3 is a plan view showing the known semiconductor device; Figs. 4A and 4B are cross-sectional views showing a fabricating process of a semiconductor device of a first preferred embodiment according to the invention; Fig. 5 is a plan view showing an etching mask used for the first preferred embodiment; Fig. 6 is a plan view showing the semiconductor device of the first preferred embodiment; and Fig. 7 is a plan view showing an etching mask used for a second preferred embodiment according to the invention. Before describing a semiconductor device according to the invention, the aforementioned known semiconductor device will be explained in conjunction with Figs. 1A to 1F, 2 and 3. The known semiconductor device is fabricated by the following process shown in Figs. 1A to 1F. First, a resist pattern 10 is formed on a silicon substrate 12 as shown in Fig. 1A by photoetching with using an etching mask 14. The etching mask 14 which is shown in Fig. 2 is provided with a light shield region 16 of chrome which is shaped to be rectangle on a light transmission area 18. The resist pattern 10 is shaped along a 27% uniform intensity line 20 of light passing through the light transmission area 18, and has two curved portions each having a radius "R" at both sides. The 27% uniform intensity line 20 becomes a border line of the patterning in a high resolution positive photoresist. Next, a field oxide layer 22 is formed on the silicon substrate 12, and a device-formation region 24 is formed thereon by a selective (preferential) oxidation method with using the resist pattern 10 as a mask as shown in Fig. 1B. At this time, the device-formation region 24 is shaped to be like a concave mirror being encircled with an inner edge of the field oxide layer 22. Then, a polysilicon layer 26 is formed on the whole process surface of the substrate as shown in Fig. 1C, and a resist layer 28 is formed on a surface of the polysilicon layer 26 as shown in Fig. 1D. After that, a resist pattern 30 for gate electrodes 32 and 34 is formed by photoetching as shown in Fig. 1E. In this process, radiation light is converged to an inside of the device-formation region 24 by light reflection on the inner edge of the field oxide layer 22, so that the reflected light is radiated to a side surface of the resist pattern 30. Therefore, the resist pattern 30 is etched at the side surface, so that depressions 36 and 38 are formed thereat. Finally, the polysilicon layer 26 is etched with using the resist pattern 30 as an etching mask, so that the gate electrodes 32 and 34 are formed on the device-formation region 24 as shown in Fig. 1F. In this process, the gate electrodes 32 and 34 are provided with depressions 40 and 42 as shown in Figs. 1F and 3. According to the known semiconductor device, however, there is a disadvantage in that a reliability thereof is lowered, because the gate electrodes 32 and 34 are provided with the depressions 40 and 42. Next, a semiconductor device of a first preferred embodiment will be explained in conjunction with Figs. 4A, 4B, 5 and 6. In the first preferred embodiment, an etching mask 52, as shown in Fig. 5, which is provided with a light shield region 53 of chrome in a part of a light transmission area 18 is used. The light shield region 53 is shaped to have two triangular notches 51a and 51b so that a uniform intensity line 55 has two curved portions having different radiuses "R 1 " and "R 2 ". According to the first preferred embodiment, a resist pattern 54 for gate electrodes 56 and 58 are formed to have no depression as shown in Fig. 4A and 6, because a device-formation region 50 which is encircled with a field oxide layer 59 is shaped to have two curved portions having different radiuses corresponding to the etching mask 52. Therefore, the gate electrodes 56 and 58 are shaped to have no depression as shown in Fig. 4B and Fig. 6. Fig. 7 shows an etching mask 60 of a second preferred embodiment according to the invention. The etching mask 60 is provided with a light shield region 62 of chrome in a part of a light transmission area 18. The light shield region 62 is shaped to have two rectangular notches 63a and 63b so that a uniform intensity line 64 has two curved portions having different radiuses "R 3 " and "R 4 " as shown in the figure. According to the second preferred embodiment, the same advantage as in the first preferred embodiment can be obtained. According to the first and second preferred embodiments, the etching masks 52 and 62 are provided with the two notches 51a and 52a, and 63a and 63b, however, the etching mask may be provided with more than three notches. Although the invention has been described with respect to specific embodiment for complete and an etching mask used for clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modification and an etching mask used for alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.

Claims: A semiconductor device, comprising: a semiconductor substrate (12); an insulation layer (59) formed on the semiconductor substrate (12) and comprising an inner edge encircling a device-formation region (50); and a device pattern (56,58) formed on the device-formation region; wherein the device-formation region at the substrate surface is shaped to have first and second end portions, each of the end portions having at least two adjacent corner regions bounded by curved portions with different radii of curvature so that photolithography light is not converged to a point inside the device-formation region by light reflection from the inner edge of the insulation layer. An etching mask (52) in combination with a semiconductor substrate (12) having a layer of positive photoresist thereon for fabricating a semiconductor device according to claim 1, the etching mask comprising: a light transmission area (18) through which light is transmitted; and a light shield region (16) formed on a part of the light transmission area (18); wherein the light shield region has a predetermined shape so that, when illuminated, a line of uniform light intensity passing through the light transmission area at the periphery of the light shield region is shaped to define a border line of a pattern in the photoresist which corresponds to the device-formation region and which has first and second end portions, each of the end portions having at least two adjacent corner regions bounded by two curved portions with different radii of curvature. An etching mask in combination with a semiconductor substrate for fabricating a semiconductor device, according to claim 2, wherein the predetermined shape is of a substantially rectangular shape having at least one notch at each of the first and second ends. An etching mask in combination with a semiconductor substrate for fabricating a semiconductor device, according to claim 3, wherein two triangular notches are positioned to be axially symmetrical with respect to the minor axis of the rectangular shape. An etching mask in combination with a semiconductor substrate for fabricating a semiconductor device, according to claim 3, wherein two rectangular notches are positioned to be point symmetrical about the centre of the rectangular shape. A method of fabricating a semiconductor device, comprising the steps of: providing an etching mask (52) and a semiconductor substrate (12) with a layer of resist thereon according to any one of claims 2 to 5; forming a pattern in the resist by illuminating the etching mask to define the device-formation region having a shape defined by the light transmission area (18); forming an insulation layer (59) on the semiconductor substrate, the insulation layer comprising an inner edge encircling the device-formation region; and forming a device pattern on the device-formation region by means of a photoetching process, in which light reflected at the inner edge of the insulation layer does not converge to the same place in the device-formation region.

Inventors: YAMANAKA KOJI, YAMANAKA, KOJI, YAMANAKA, KOJI, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1992
Main classification: H01L21
IPC codes: H01L21, G03F1